Research ArticleUse of Ethylenediaminetetraacetic Acid asa Scavenger for Chromium from lsquolsquoWet Bluersquorsquo Leather WasteThermodynamic and Kinetics Parameters
Joseacute E Resende1 Mateus A Gonccedilalves1 Luiz C A Oliveira2
Elaine F F da Cunha1 and Teodorico C Ramalho13
1Departamento de Quımica Universidade Federal de Lavras Caixa Postal 3037 37200-000 Lavras MG Brazil2Departamento de Quımica ICEx UFMG Campus-Pampulha 31270-901 Belo Horizonte MG Brazil3Biomedical Research Center University Hradec Kralove Hradec Kralove Czech Republic
Correspondence should be addressed to Teodorico C Ramalho teodqiuflabr
Received 3 July 2014 Revised 2 September 2014 Accepted 4 September 2014 Published 11 December 2014
Academic Editor Davut Avci
Copyright copy 2014 Jose E Resende et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
One serious consequence of the current consumer society is the transformation of the environment into a waste receptacle arisingfrom human activities Because of the potential toxic effects of chromium solid waste containing this metal there are grounds forserious concern for the tanning and leather processing industry The application of tannery waste as organic fertilizer has led toextensive contamination by chromium in agricultural areas and may cause the accumulation of this metal in soils and plants Thiswork evaluated the extraction of Cr+3 andCr+6 contained in solid waste from the leather industry through density functional theory(DFT) calculationsTheGibbs free energy calculations reveal that the chelator ethylenediaminetetraacetic acid (EDTA) formsmorestable complexes withmetal ions of chromium comparedwith the structures of the complexes [Cr(NTA)(H
2O)2] and [Cr-collagen]
the latter used to simulate the protein bound chrome leather
1 Introduction
Chromium compounds are used in various industrial pro-cesses such as the manufacture of dyes paints leather tan-ning and plating [1] Although most of the waste from theseprocesses contains Cr+3 which is much less toxic than Cr+6there is the concern expressed about the possible mutagenicand carcinogenic risks of Cr+6 formed as a result of Cr+3chemical oxidation [2] Presence of light heat pH above 5and reaction with the oxidized fat are some of the situationsthat cause the oxidation of Cr+3 to Cr+6 [3] since in basicsolutions the oxidation by oxidants such as peroxide occursmore easily [4] However the use of chromium in someindustry sectors includingmainly the leather industry due tolack of new processes that can compete with those based onCr chemistry is unlikely to be abandoned in terms of bothcosts and the quality of the final product [1]
In tanneries the animal skin goes through processingsteps preparing it for the tanning process The ldquowet bluerdquo
leather as the chrome tanned leather is called has a chromi-um content of 20 gsdotLminus1 and its function is to act as a bridgelinking the protein groups of leather providing greaterend product mechanical and chemical stability [5] Surveysconducted have shown that approximately 600000 tons ofsolid waste is produced each year worldwide by the leatherindustry and about 40ndash50 of all leather obtained is lost inshavings [6] These shavings are small pieces of leather in avariety of forms mainly composed of collagen complexedwith chromium [7] However all the methods available forreuse of the tanned leather residue require drastic treatmentschemical or thermochemical processes causing the completehydrolysis of leather and adding little value to the final mate-rial [8]
In recent years a viable alternative to recycle these wastesis gaining prominence as an excellent solution to the problem[8] It is the transformation of the waste (splinters flapsand sanding dust) into nitrogen-rich fertilizer The methodconsists of the complete dissolution of the solid removing
Hindawi Publishing CorporationJournal of ChemistryVolume 2014 Article ID 754526 8 pageshttpdxdoiorg1011552014754526
2 Journal of Chemistry
N
O
HO
N
OH
OH
HO
O
O
O
(a)
N
HO
HO
OH
O
O
O
(b)
Figure 1 Structure of the EDTA (a) and NTA (b)
the precipitate as Cr hydroxide and use of the proteinremaining in the organic liquid as fertilizer [8] A crucial stepin the realization of the method is the use of sequesteringagents which may complex the chromium from the organicmatter of the leather consisting mainly of collagen
Among the most important classic reagents containingmany industrial applications which can be used to removetoxic metal ions from contaminated water and soil stand outethylenediaminetetraacetic acid (EDTA) [9ndash12] and nitrilo-triacetic acid (NTA) [13ndash15] (Figure 1) These ligands in theform of alkali metal salt contain the respective polyacetateanion forming very stable complexes withmost metallic ionsThe evidenced importance of these ligands as chelating agentssupports the need for an exploration of their propertiesGiven these concepts theoretical studies concomitant withthe experimental addressing the understanding of the phe-nomenon involving a metal complexation by organic ligandsare always needed However due to the variety of possi-ble geometries and different oxidation states of the metaltheoretical calculations for metal complexes are generallycomplicated [16]The ab initio calculations (Hatree-Fock) [17]used to describe the complexes formed between metals andorganic ligands are limited by the complexity of the systembeing studied On the other hand the method of the densityfunctional theory (DFT) has been increasingly used to studyinteractions between biomolecules and metals [18 19] Thisapproach is interesting because it includes the effect of elec-tron correlation and enables the calculation for larger systems[20 21] Thus the objective of this work is to use molecularmodeling methods and DFT calculations to evaluate thethermodynamics of formation of Cr+3 and Cr+6 complexesformed by EDTA and NTA ligands relating them to therespective structures of Cr-collagen complex used to simulatethe interaction between the protein leather and chromeIn addition experimental kinetics studies were carried outin order to obtain the kinetics parameters for the studiedcomplexes
2 Computational Methods
Initially the structures of ligands and complexes were mod-eled using the PC Spartan Pro program [22] The modelswere submitted to optimization by the semiempirical andDFT methods PM3 [23] and BP866-31G for the atoms C
Figure 2 Structure of collagenThe red color represents the oxygenatom blue nitrogen gray carbon and white hydrogen
H O and N and LANL2DZ for the metal To simulate theinteraction between the target protein and chromium ionsthe three-dimensional structure of collagen was obtainedfrom Protein Data Bank (PDB) (httpwwwrcsborgpdb)(code 1A3I) Figure 2
This protein has been used as amodel structure for studiesof collagen [24] the most abundant protein in mammals andresponsible for the complexation of chromium in the leather[25] Because of the size of this protein there was a possibilityof complexation with two or even three chromium atomsHowever this work focuses on the complexation reactionfor a Cr-ligand ratio of 1 1 Thus the protein structurewas adjusted by cutting the edges altering the size of thestructure to an approximate radius of 17 A To investigatethe thermodynamic properties of the complexation betweenchromium (Cr+3 and Cr+6) and the ligands EDTA NTA andcollagen electronic structure calculations were performedon another level For this all structures were exported tothe GAUSSIAN 09 [26] program where the vibrational fre-quency calculations were performed using the method ofDensity Functional Theory (DFT) [12 27] combined withfunctional exchange-correlation (XC) BP86 [28]mdashexpressionBecke for exchange andPerdew for correlationmdashand the basisset 6-31G [29] for the atoms C H O and N and LANL2DZ[30 31] for the chromium atomThe latter by including pseu-dopotential is indicated for atoms that are from the fourthperiod of the periodic table
The complexation of a metal ion with a chelating agentusually occurs in aqueous medium In order to simulate
Journal of Chemistry 3
Crn+(aq) + Lig(aq) ΔG(aq)
a b c
Crn+ + Lig(gas) (gas) ΔG(g)(gas)[Cr(Lig) ]
(aq)[Cr(Lig) ]
Figure 3 Thermodynamic cycle
this situation we have employed a thermodynamics cycle(Figure 3) Since the theoretical calculations were performedfor the gaseous state and the interest is in obtaining the freeenergy of reaction in solution a new series of calculationswere performed in GAUSSIAN 09 to evaluate the solvationenergy of the species involved The solvent effects have beentaken into account with the Polarazible continuum model(PCM) developed by Shimizu et al [32] To get the Gibbsfree energy of complexation reaction solution (Δ119866
(aq)) shownin Table 1 calculations were made using the thermodynamiccycle below [12 18] and the following
Δ119866
(aq) = Δ119866(119892) + [119888 minus (119886 + 119887)] (1)
where 119886 = Δ119866solv(Cr119899+) 119887 = Δ119866solv(Lig) and 119888 = Δ119866solv
([Cr(Lig)])To justify the difference in stability between the com-
plexes analysis of natural bond orbitals (NBO) [33] wasperformed with the BP86 functional and the basis functions6-31G (C H O N) and SDD [34] (Cr) Furthermore QTAIMcalculations were carried out by using the program AIM11[35]
21 Experimental To evaluate the kinetics of complexationof trivalent chromiumwith EDTA [36] the following reagentswere used Merck PA chromium salt (Cr(NO
3)3sdot9H2O) and
EDTA (disodium) Furthermore we used thermostatic bath(Tecnal TE-210) and an UV-Vis spectrophotometer (Shi-madzu UV-160 1PC) For the Cr-EDTA complex formation(2) Cr3+ and EDTA solutions were prepared at concentra-tions of 1000 and 7158 ppm respectively so that the stoi-chiometry of the reaction 1 1 was obeyed
Cr3+(aq) + EDTA
4minus
(aq) 997888rarr [Cr (EDTA)](aq)(violet color)
(2)
5mL of each solution was placed in contact in severalcontainers with in order to measure the absorbance of thesolution at different reaction times The temperature wascontrolled by a thermostatic bath using temperatures of 2540 50 60 and 70∘C After removing the sample from ther-mostatic bath it was placed in an ice bath to stop the reactionand the solution was read in a UV-Vis spectrophotometer
3 Results and Discussion
31 EDTA and NTA Complex with the Cr Ion The EDTA lig-and is hexadentate and the atoms responsible for coordinat-ing with the chrome are four oxygen atoms of the carboxylicgroups and two nitrogen atoms of the amine groups In orderto develop different isomers of Cr-EDTA complex relative
Table 1 Variation of the Gibbs free energy for complexationreaction in kcalsdotmolminus1
Complex Charge on the Cr atom Δ119866(aq) ΔΔ119866(aq)
positions between the two nitrogen atoms in the structureswere considered However for structures that are initiallydifferent in the disposition of the atoms in the coordinationsphere after optimization and minimization of energy itwas found that all converged into a common structure witha more stable rearrangement (Figure 4(a)) Regarding theNTA coordination occurs between three carboxyl groupsand the nitrogen and thus a tetradentate ligand In this caseas the objective was to investigate complexes with octahedralgeometry since they tend to be more stable for developmentof the structures two water molecules were used as ligandthus completing the valence six of the chromium As withEDTA after optimization of the structure all converged intoa single (Figure 4(b))
32 Free Energy Calculations After optimization all calcula-tions of frequency (in the gaseous state and implicit solvent)were performed in GAUSSIAN 09 program as mentioned inthe methodology section Thus it was possible to obtain theGibbs free energy total for each species as per
119866tot = sum119864119879119866
+ 119864corr(119866) + 119864ZPE (3)
where 119866tot = Gibbs free energy of the total sum119864119879119866
= sum ofelectronic thermal and free Gibbs energy 119864corr(119866) = Gibbsfree energy correction and 119864ZPE = zero-point energy correc-tion
From the total free energy values (119864tot) of the species (rea-ctants and products) it was possible to perform the calcula-tion of the thermodynamic cycle and find the change in freeenergy for each complexation reaction in solution (Δ119866
(aq))and the corresponding relative free energy change (ΔΔ119866
(aq))as shown in Table 2
According to the results shown in Table 3 the stabilityorder for the complexes is as follows [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] This means that thecomplexation reaction between chromium and EDTA ismore favorable to occur in relation to the complexes[Cr(NTA)(H
2O)2] and Cr-collagen for both oxidation states
of the chromium It may also be noticed that for the same lig-and the complex formed with Cr+6 is more stable when com-pared to the corresponding complex with Cr+3 This is due tothe fact that there is a correlation between the complexationcapacity and size of the metal ion because the metal-ligandaffinity proves to be the inverse of the ionic radius [37] Thus
4 Journal of Chemistry
(a) (b)
Figure 4 Optimized structures of the complexes [Cr(EDTA)] (a) and [Cr(NTA)(H2O)2] (b) The green color represents the chrome atom
red oxygen blue nitrogen and gray carbon
Table 2 Relative Gibbs free energy values for the complexationreaction in solution (ΔΔ119866(aq))
Table 3 QTAIM parameters obtained by the main interatomicinteractions in the isomer (B) of the Cr-EDTA complex the Cr-NTA(H2O)2 and Cr-collagen complex in au
the results are consistent with the difference in size betweenthe ions 076 [38] and 044 A [39] for Cr+3 and Cr+6 respec-tively In addition molecular orbital and electronic structure
Table 4 Higher energies of nonbonding interactions betweenNBOs in the coordination sphere for complexes of Cr+6 kcalsdotmolminus1
calculations can be used to more deeply investigate themolecular basis for rationalizing the complexation reaction
33 Natural Bond Orbitals Analysis (NBO) The NBO anal-ysis provides information about the electronic structure of acomplex For example the interaction between the occupiedand vacant orbitals represents the deviation of the moleculesfrom the Lewis structure and the respective energies can beused as ameasure of structure stability [18 40] Table 4 showsthe most energetic interactions involving the transfer ofelectrons between orbitals (donorrarr acceptor) and energiesin the coordination sphere of the structures formed withCr+6 through which it is possible to justify the differencein stability between the respective complexes As can beseen the interactionsmentioned in relation to [Cr+6(EDTA)]complex are relatively much higher than the correspondentsin the structures of the [Cr(NTA)(H
2O)2] and [Cr(collagen)]
complexes These results indicate a greater stability for theCr-EDTA complex being in accordance with the Gibbs freeenergy variation obtained from the thermodynamic cycleIn order to investigate the electronic and steric effects thatmodulate the complexation reaction with chromium ions wehave performed NBO and AIM calculations
34 Quantum Theory of Atoms in Molecules (QTAIM) Thetopological analysis of the electron density can provide valu-able information about the properties of the system underconsideration The properties of electron density measure-ments in the so-called Bond Critical Point (BCP) such as the
Journal of Chemistry 5
CrO1
O2
O3
O4
C5
(a)
Cr
O1O2
O3
O4
O5
O6
(b)
H
HCr
O1
O2
O3
O4
11N
50150
260
25C
22C
12C
14C
16C
19C
23H
13H
21H
18H
4H
3H
7H
6H
(c)
Figure 5 Structures of the isomer ldquoBrdquo of the Cr-EDTA complex (a) Cr-collagen complex (b) and Cr-NTA complex (c)
electronic density at BCP (120588) the Laplacian of the electrondensity (nabla2120588) the potential energy (Vc) kinetic energy (Gc)and the total electron energy (Hc) are useful for detect-ing and characterizing the chemical bonds such as cova-lent bonds metal-ligand interactions hydrogen bonds andother weak noncovalent intramolecular interactions [41] Forexample for bonds predominantly covalent 120588 is generallygt020 nabla2120588 lt 0 and Hc lt 0 while for the bond of an electro-static nature (ionic) 120588 is generally lower (sim10minus2 for hydrogenbonding and sim10minus3 for Van der Waals interaction) withnabla
2120588 gt 0 and Hc relatively higher [13 42] Table 3 shows
the properties of BCPs for the most relevant interactionsthat occur among the atoms in the Cr+6 complexes shownin Figure 5 As with the data in Table 4 it can be seenthat the interactions established between chromium and theoxygen atom are electrostatic in nature with ionic bondingcharacteristics wherein the core supports the entire loadconcentration (nabla2120588 gt 0 and relatively high Hc) in contrast
for example with the values of the covalent bond O1ndashC5TheQTAIM analysis did not reveal relevant intramolecular inter-action such as hydrogen bonding for example However thetopological analysis revealed a greater electron density in thecoordination sphere region for Cr-EDTA complex than withthe complexes collagen-Cr and Cr-(NTA)(H
2O)2 Moreover
the electron density (120588) values in the coordination sphere ofBCPs for these two complexes were much lower indicatingthat electrostatic interactions are less
35 Formation Kinetics of Cr-EDTA Complex
351 Experimental Since our theoretical findings point outEDTA as the best ligand used for the complexation reactionwith chromium at both oxidation states Cr+3 and Cr+6 wehave performed the experimental part focused on EDTAcomplex The formation of the Cr-EDTA complex in relationto time can be evidenced by the gradual formation of its
6 Journal of Chemistry
18
16
14
12
10
08
06
04
02
00
400 450 500 550 600 650 700 750 800
Abso
rban
ce
Wavelength (nm)
180min
60min
15min10min
5min
1min
Figure 6 UV-Vis spectra of the Cr-EDTA complex at 70∘C
18
16
14
12
10
08
06
04
02
00
Abso
rban
ce
0 5000 10000 15000 20000 25000 30000
Time (s)
50∘C
70∘C
60∘C
40∘C
25∘C
(a)
Time (s)
50∘C70
∘C
60∘C
40∘C
25∘C
0 50 100 150 200 250 300 350 400 450 500 550 600
00
minus05
minus10
minus15
minus20
minus25
ln A
bs
k = 000389 sminus1
k = 000356 sminus1
k = 000144 sminus1
k = 000077 sminus1
k = 000020 sminus1
(b)
Figure 7The formation kinetics of the Cr-EDTA complex at different temperatures (a) and the linearization of the equation speed (ln [Abs]= 119896119905) with the respective constants (b)
absorption band in the visible region at 546 nm (Figure 6)The spectra show that at 70∘C the formation of the complexcan be studied with extreme speed only 5min of reactionis necessary The formation kinetics of Cr-EDTA complexwas studied at 546 nm at various temperatures as shownin Figure 7(a) It can be observed that increasing the tem-perature increases the rate of complex formation observingthe increase in absorbance for the same time In additionconsidering an approximately linear curve in short timesone can determine the rate constants for complex formationby linearizing the velocity equation ln [Abs] = 119896119905 shownin Figure 7(b) Using the Arrhenius equation [43] (4) andwith the data obtained in this experiment it was possible to
determine the activation energy required for the formationof the complex (119864
119886= 59 kJsdotmolminus1)
ln119870 = ln119860 minus119864at119877
119879
minus1
(4)
36 Effect of pH Complexation reactions involvingmetals byligands of aminopolycarboxylic acids are very dependent onpH such that according to the acidity of the reaction med-ium there will be a greater or lesser prevalence of a species ofligand at equilibrium At very low pH the nonionized speciesof the ligand predominates so that for the reaction to occurthemetal ionsmust be able to remove the ionizable hydrogens
Journal of Chemistry 7
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
the precipitate as Cr hydroxide and use of the proteinremaining in the organic liquid as fertilizer [8] A crucial stepin the realization of the method is the use of sequesteringagents which may complex the chromium from the organicmatter of the leather consisting mainly of collagen
Among the most important classic reagents containingmany industrial applications which can be used to removetoxic metal ions from contaminated water and soil stand outethylenediaminetetraacetic acid (EDTA) [9ndash12] and nitrilo-triacetic acid (NTA) [13ndash15] (Figure 1) These ligands in theform of alkali metal salt contain the respective polyacetateanion forming very stable complexes withmost metallic ionsThe evidenced importance of these ligands as chelating agentssupports the need for an exploration of their propertiesGiven these concepts theoretical studies concomitant withthe experimental addressing the understanding of the phe-nomenon involving a metal complexation by organic ligandsare always needed However due to the variety of possi-ble geometries and different oxidation states of the metaltheoretical calculations for metal complexes are generallycomplicated [16]The ab initio calculations (Hatree-Fock) [17]used to describe the complexes formed between metals andorganic ligands are limited by the complexity of the systembeing studied On the other hand the method of the densityfunctional theory (DFT) has been increasingly used to studyinteractions between biomolecules and metals [18 19] Thisapproach is interesting because it includes the effect of elec-tron correlation and enables the calculation for larger systems[20 21] Thus the objective of this work is to use molecularmodeling methods and DFT calculations to evaluate thethermodynamics of formation of Cr+3 and Cr+6 complexesformed by EDTA and NTA ligands relating them to therespective structures of Cr-collagen complex used to simulatethe interaction between the protein leather and chromeIn addition experimental kinetics studies were carried outin order to obtain the kinetics parameters for the studiedcomplexes
2 Computational Methods
Initially the structures of ligands and complexes were mod-eled using the PC Spartan Pro program [22] The modelswere submitted to optimization by the semiempirical andDFT methods PM3 [23] and BP866-31G for the atoms C
Figure 2 Structure of collagenThe red color represents the oxygenatom blue nitrogen gray carbon and white hydrogen
H O and N and LANL2DZ for the metal To simulate theinteraction between the target protein and chromium ionsthe three-dimensional structure of collagen was obtainedfrom Protein Data Bank (PDB) (httpwwwrcsborgpdb)(code 1A3I) Figure 2
This protein has been used as amodel structure for studiesof collagen [24] the most abundant protein in mammals andresponsible for the complexation of chromium in the leather[25] Because of the size of this protein there was a possibilityof complexation with two or even three chromium atomsHowever this work focuses on the complexation reactionfor a Cr-ligand ratio of 1 1 Thus the protein structurewas adjusted by cutting the edges altering the size of thestructure to an approximate radius of 17 A To investigatethe thermodynamic properties of the complexation betweenchromium (Cr+3 and Cr+6) and the ligands EDTA NTA andcollagen electronic structure calculations were performedon another level For this all structures were exported tothe GAUSSIAN 09 [26] program where the vibrational fre-quency calculations were performed using the method ofDensity Functional Theory (DFT) [12 27] combined withfunctional exchange-correlation (XC) BP86 [28]mdashexpressionBecke for exchange andPerdew for correlationmdashand the basisset 6-31G [29] for the atoms C H O and N and LANL2DZ[30 31] for the chromium atomThe latter by including pseu-dopotential is indicated for atoms that are from the fourthperiod of the periodic table
The complexation of a metal ion with a chelating agentusually occurs in aqueous medium In order to simulate
Journal of Chemistry 3
Crn+(aq) + Lig(aq) ΔG(aq)
a b c
Crn+ + Lig(gas) (gas) ΔG(g)(gas)[Cr(Lig) ]
(aq)[Cr(Lig) ]
Figure 3 Thermodynamic cycle
this situation we have employed a thermodynamics cycle(Figure 3) Since the theoretical calculations were performedfor the gaseous state and the interest is in obtaining the freeenergy of reaction in solution a new series of calculationswere performed in GAUSSIAN 09 to evaluate the solvationenergy of the species involved The solvent effects have beentaken into account with the Polarazible continuum model(PCM) developed by Shimizu et al [32] To get the Gibbsfree energy of complexation reaction solution (Δ119866
(aq)) shownin Table 1 calculations were made using the thermodynamiccycle below [12 18] and the following
Δ119866
(aq) = Δ119866(119892) + [119888 minus (119886 + 119887)] (1)
where 119886 = Δ119866solv(Cr119899+) 119887 = Δ119866solv(Lig) and 119888 = Δ119866solv
([Cr(Lig)])To justify the difference in stability between the com-
plexes analysis of natural bond orbitals (NBO) [33] wasperformed with the BP86 functional and the basis functions6-31G (C H O N) and SDD [34] (Cr) Furthermore QTAIMcalculations were carried out by using the program AIM11[35]
21 Experimental To evaluate the kinetics of complexationof trivalent chromiumwith EDTA [36] the following reagentswere used Merck PA chromium salt (Cr(NO
3)3sdot9H2O) and
EDTA (disodium) Furthermore we used thermostatic bath(Tecnal TE-210) and an UV-Vis spectrophotometer (Shi-madzu UV-160 1PC) For the Cr-EDTA complex formation(2) Cr3+ and EDTA solutions were prepared at concentra-tions of 1000 and 7158 ppm respectively so that the stoi-chiometry of the reaction 1 1 was obeyed
Cr3+(aq) + EDTA
4minus
(aq) 997888rarr [Cr (EDTA)](aq)(violet color)
(2)
5mL of each solution was placed in contact in severalcontainers with in order to measure the absorbance of thesolution at different reaction times The temperature wascontrolled by a thermostatic bath using temperatures of 2540 50 60 and 70∘C After removing the sample from ther-mostatic bath it was placed in an ice bath to stop the reactionand the solution was read in a UV-Vis spectrophotometer
3 Results and Discussion
31 EDTA and NTA Complex with the Cr Ion The EDTA lig-and is hexadentate and the atoms responsible for coordinat-ing with the chrome are four oxygen atoms of the carboxylicgroups and two nitrogen atoms of the amine groups In orderto develop different isomers of Cr-EDTA complex relative
Table 1 Variation of the Gibbs free energy for complexationreaction in kcalsdotmolminus1
Complex Charge on the Cr atom Δ119866(aq) ΔΔ119866(aq)
positions between the two nitrogen atoms in the structureswere considered However for structures that are initiallydifferent in the disposition of the atoms in the coordinationsphere after optimization and minimization of energy itwas found that all converged into a common structure witha more stable rearrangement (Figure 4(a)) Regarding theNTA coordination occurs between three carboxyl groupsand the nitrogen and thus a tetradentate ligand In this caseas the objective was to investigate complexes with octahedralgeometry since they tend to be more stable for developmentof the structures two water molecules were used as ligandthus completing the valence six of the chromium As withEDTA after optimization of the structure all converged intoa single (Figure 4(b))
32 Free Energy Calculations After optimization all calcula-tions of frequency (in the gaseous state and implicit solvent)were performed in GAUSSIAN 09 program as mentioned inthe methodology section Thus it was possible to obtain theGibbs free energy total for each species as per
119866tot = sum119864119879119866
+ 119864corr(119866) + 119864ZPE (3)
where 119866tot = Gibbs free energy of the total sum119864119879119866
= sum ofelectronic thermal and free Gibbs energy 119864corr(119866) = Gibbsfree energy correction and 119864ZPE = zero-point energy correc-tion
From the total free energy values (119864tot) of the species (rea-ctants and products) it was possible to perform the calcula-tion of the thermodynamic cycle and find the change in freeenergy for each complexation reaction in solution (Δ119866
(aq))and the corresponding relative free energy change (ΔΔ119866
(aq))as shown in Table 2
According to the results shown in Table 3 the stabilityorder for the complexes is as follows [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] This means that thecomplexation reaction between chromium and EDTA ismore favorable to occur in relation to the complexes[Cr(NTA)(H
2O)2] and Cr-collagen for both oxidation states
of the chromium It may also be noticed that for the same lig-and the complex formed with Cr+6 is more stable when com-pared to the corresponding complex with Cr+3 This is due tothe fact that there is a correlation between the complexationcapacity and size of the metal ion because the metal-ligandaffinity proves to be the inverse of the ionic radius [37] Thus
4 Journal of Chemistry
(a) (b)
Figure 4 Optimized structures of the complexes [Cr(EDTA)] (a) and [Cr(NTA)(H2O)2] (b) The green color represents the chrome atom
red oxygen blue nitrogen and gray carbon
Table 2 Relative Gibbs free energy values for the complexationreaction in solution (ΔΔ119866(aq))
Table 3 QTAIM parameters obtained by the main interatomicinteractions in the isomer (B) of the Cr-EDTA complex the Cr-NTA(H2O)2 and Cr-collagen complex in au
the results are consistent with the difference in size betweenthe ions 076 [38] and 044 A [39] for Cr+3 and Cr+6 respec-tively In addition molecular orbital and electronic structure
Table 4 Higher energies of nonbonding interactions betweenNBOs in the coordination sphere for complexes of Cr+6 kcalsdotmolminus1
calculations can be used to more deeply investigate themolecular basis for rationalizing the complexation reaction
33 Natural Bond Orbitals Analysis (NBO) The NBO anal-ysis provides information about the electronic structure of acomplex For example the interaction between the occupiedand vacant orbitals represents the deviation of the moleculesfrom the Lewis structure and the respective energies can beused as ameasure of structure stability [18 40] Table 4 showsthe most energetic interactions involving the transfer ofelectrons between orbitals (donorrarr acceptor) and energiesin the coordination sphere of the structures formed withCr+6 through which it is possible to justify the differencein stability between the respective complexes As can beseen the interactionsmentioned in relation to [Cr+6(EDTA)]complex are relatively much higher than the correspondentsin the structures of the [Cr(NTA)(H
2O)2] and [Cr(collagen)]
complexes These results indicate a greater stability for theCr-EDTA complex being in accordance with the Gibbs freeenergy variation obtained from the thermodynamic cycleIn order to investigate the electronic and steric effects thatmodulate the complexation reaction with chromium ions wehave performed NBO and AIM calculations
34 Quantum Theory of Atoms in Molecules (QTAIM) Thetopological analysis of the electron density can provide valu-able information about the properties of the system underconsideration The properties of electron density measure-ments in the so-called Bond Critical Point (BCP) such as the
Journal of Chemistry 5
CrO1
O2
O3
O4
C5
(a)
Cr
O1O2
O3
O4
O5
O6
(b)
H
HCr
O1
O2
O3
O4
11N
50150
260
25C
22C
12C
14C
16C
19C
23H
13H
21H
18H
4H
3H
7H
6H
(c)
Figure 5 Structures of the isomer ldquoBrdquo of the Cr-EDTA complex (a) Cr-collagen complex (b) and Cr-NTA complex (c)
electronic density at BCP (120588) the Laplacian of the electrondensity (nabla2120588) the potential energy (Vc) kinetic energy (Gc)and the total electron energy (Hc) are useful for detect-ing and characterizing the chemical bonds such as cova-lent bonds metal-ligand interactions hydrogen bonds andother weak noncovalent intramolecular interactions [41] Forexample for bonds predominantly covalent 120588 is generallygt020 nabla2120588 lt 0 and Hc lt 0 while for the bond of an electro-static nature (ionic) 120588 is generally lower (sim10minus2 for hydrogenbonding and sim10minus3 for Van der Waals interaction) withnabla
2120588 gt 0 and Hc relatively higher [13 42] Table 3 shows
the properties of BCPs for the most relevant interactionsthat occur among the atoms in the Cr+6 complexes shownin Figure 5 As with the data in Table 4 it can be seenthat the interactions established between chromium and theoxygen atom are electrostatic in nature with ionic bondingcharacteristics wherein the core supports the entire loadconcentration (nabla2120588 gt 0 and relatively high Hc) in contrast
for example with the values of the covalent bond O1ndashC5TheQTAIM analysis did not reveal relevant intramolecular inter-action such as hydrogen bonding for example However thetopological analysis revealed a greater electron density in thecoordination sphere region for Cr-EDTA complex than withthe complexes collagen-Cr and Cr-(NTA)(H
2O)2 Moreover
the electron density (120588) values in the coordination sphere ofBCPs for these two complexes were much lower indicatingthat electrostatic interactions are less
35 Formation Kinetics of Cr-EDTA Complex
351 Experimental Since our theoretical findings point outEDTA as the best ligand used for the complexation reactionwith chromium at both oxidation states Cr+3 and Cr+6 wehave performed the experimental part focused on EDTAcomplex The formation of the Cr-EDTA complex in relationto time can be evidenced by the gradual formation of its
6 Journal of Chemistry
18
16
14
12
10
08
06
04
02
00
400 450 500 550 600 650 700 750 800
Abso
rban
ce
Wavelength (nm)
180min
60min
15min10min
5min
1min
Figure 6 UV-Vis spectra of the Cr-EDTA complex at 70∘C
18
16
14
12
10
08
06
04
02
00
Abso
rban
ce
0 5000 10000 15000 20000 25000 30000
Time (s)
50∘C
70∘C
60∘C
40∘C
25∘C
(a)
Time (s)
50∘C70
∘C
60∘C
40∘C
25∘C
0 50 100 150 200 250 300 350 400 450 500 550 600
00
minus05
minus10
minus15
minus20
minus25
ln A
bs
k = 000389 sminus1
k = 000356 sminus1
k = 000144 sminus1
k = 000077 sminus1
k = 000020 sminus1
(b)
Figure 7The formation kinetics of the Cr-EDTA complex at different temperatures (a) and the linearization of the equation speed (ln [Abs]= 119896119905) with the respective constants (b)
absorption band in the visible region at 546 nm (Figure 6)The spectra show that at 70∘C the formation of the complexcan be studied with extreme speed only 5min of reactionis necessary The formation kinetics of Cr-EDTA complexwas studied at 546 nm at various temperatures as shownin Figure 7(a) It can be observed that increasing the tem-perature increases the rate of complex formation observingthe increase in absorbance for the same time In additionconsidering an approximately linear curve in short timesone can determine the rate constants for complex formationby linearizing the velocity equation ln [Abs] = 119896119905 shownin Figure 7(b) Using the Arrhenius equation [43] (4) andwith the data obtained in this experiment it was possible to
determine the activation energy required for the formationof the complex (119864
119886= 59 kJsdotmolminus1)
ln119870 = ln119860 minus119864at119877
119879
minus1
(4)
36 Effect of pH Complexation reactions involvingmetals byligands of aminopolycarboxylic acids are very dependent onpH such that according to the acidity of the reaction med-ium there will be a greater or lesser prevalence of a species ofligand at equilibrium At very low pH the nonionized speciesof the ligand predominates so that for the reaction to occurthemetal ionsmust be able to remove the ionizable hydrogens
Journal of Chemistry 7
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
this situation we have employed a thermodynamics cycle(Figure 3) Since the theoretical calculations were performedfor the gaseous state and the interest is in obtaining the freeenergy of reaction in solution a new series of calculationswere performed in GAUSSIAN 09 to evaluate the solvationenergy of the species involved The solvent effects have beentaken into account with the Polarazible continuum model(PCM) developed by Shimizu et al [32] To get the Gibbsfree energy of complexation reaction solution (Δ119866
(aq)) shownin Table 1 calculations were made using the thermodynamiccycle below [12 18] and the following
Δ119866
(aq) = Δ119866(119892) + [119888 minus (119886 + 119887)] (1)
where 119886 = Δ119866solv(Cr119899+) 119887 = Δ119866solv(Lig) and 119888 = Δ119866solv
([Cr(Lig)])To justify the difference in stability between the com-
plexes analysis of natural bond orbitals (NBO) [33] wasperformed with the BP86 functional and the basis functions6-31G (C H O N) and SDD [34] (Cr) Furthermore QTAIMcalculations were carried out by using the program AIM11[35]
21 Experimental To evaluate the kinetics of complexationof trivalent chromiumwith EDTA [36] the following reagentswere used Merck PA chromium salt (Cr(NO
3)3sdot9H2O) and
EDTA (disodium) Furthermore we used thermostatic bath(Tecnal TE-210) and an UV-Vis spectrophotometer (Shi-madzu UV-160 1PC) For the Cr-EDTA complex formation(2) Cr3+ and EDTA solutions were prepared at concentra-tions of 1000 and 7158 ppm respectively so that the stoi-chiometry of the reaction 1 1 was obeyed
Cr3+(aq) + EDTA
4minus
(aq) 997888rarr [Cr (EDTA)](aq)(violet color)
(2)
5mL of each solution was placed in contact in severalcontainers with in order to measure the absorbance of thesolution at different reaction times The temperature wascontrolled by a thermostatic bath using temperatures of 2540 50 60 and 70∘C After removing the sample from ther-mostatic bath it was placed in an ice bath to stop the reactionand the solution was read in a UV-Vis spectrophotometer
3 Results and Discussion
31 EDTA and NTA Complex with the Cr Ion The EDTA lig-and is hexadentate and the atoms responsible for coordinat-ing with the chrome are four oxygen atoms of the carboxylicgroups and two nitrogen atoms of the amine groups In orderto develop different isomers of Cr-EDTA complex relative
Table 1 Variation of the Gibbs free energy for complexationreaction in kcalsdotmolminus1
Complex Charge on the Cr atom Δ119866(aq) ΔΔ119866(aq)
positions between the two nitrogen atoms in the structureswere considered However for structures that are initiallydifferent in the disposition of the atoms in the coordinationsphere after optimization and minimization of energy itwas found that all converged into a common structure witha more stable rearrangement (Figure 4(a)) Regarding theNTA coordination occurs between three carboxyl groupsand the nitrogen and thus a tetradentate ligand In this caseas the objective was to investigate complexes with octahedralgeometry since they tend to be more stable for developmentof the structures two water molecules were used as ligandthus completing the valence six of the chromium As withEDTA after optimization of the structure all converged intoa single (Figure 4(b))
32 Free Energy Calculations After optimization all calcula-tions of frequency (in the gaseous state and implicit solvent)were performed in GAUSSIAN 09 program as mentioned inthe methodology section Thus it was possible to obtain theGibbs free energy total for each species as per
119866tot = sum119864119879119866
+ 119864corr(119866) + 119864ZPE (3)
where 119866tot = Gibbs free energy of the total sum119864119879119866
= sum ofelectronic thermal and free Gibbs energy 119864corr(119866) = Gibbsfree energy correction and 119864ZPE = zero-point energy correc-tion
From the total free energy values (119864tot) of the species (rea-ctants and products) it was possible to perform the calcula-tion of the thermodynamic cycle and find the change in freeenergy for each complexation reaction in solution (Δ119866
(aq))and the corresponding relative free energy change (ΔΔ119866
(aq))as shown in Table 2
According to the results shown in Table 3 the stabilityorder for the complexes is as follows [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] This means that thecomplexation reaction between chromium and EDTA ismore favorable to occur in relation to the complexes[Cr(NTA)(H
2O)2] and Cr-collagen for both oxidation states
of the chromium It may also be noticed that for the same lig-and the complex formed with Cr+6 is more stable when com-pared to the corresponding complex with Cr+3 This is due tothe fact that there is a correlation between the complexationcapacity and size of the metal ion because the metal-ligandaffinity proves to be the inverse of the ionic radius [37] Thus
4 Journal of Chemistry
(a) (b)
Figure 4 Optimized structures of the complexes [Cr(EDTA)] (a) and [Cr(NTA)(H2O)2] (b) The green color represents the chrome atom
red oxygen blue nitrogen and gray carbon
Table 2 Relative Gibbs free energy values for the complexationreaction in solution (ΔΔ119866(aq))
Table 3 QTAIM parameters obtained by the main interatomicinteractions in the isomer (B) of the Cr-EDTA complex the Cr-NTA(H2O)2 and Cr-collagen complex in au
the results are consistent with the difference in size betweenthe ions 076 [38] and 044 A [39] for Cr+3 and Cr+6 respec-tively In addition molecular orbital and electronic structure
Table 4 Higher energies of nonbonding interactions betweenNBOs in the coordination sphere for complexes of Cr+6 kcalsdotmolminus1
calculations can be used to more deeply investigate themolecular basis for rationalizing the complexation reaction
33 Natural Bond Orbitals Analysis (NBO) The NBO anal-ysis provides information about the electronic structure of acomplex For example the interaction between the occupiedand vacant orbitals represents the deviation of the moleculesfrom the Lewis structure and the respective energies can beused as ameasure of structure stability [18 40] Table 4 showsthe most energetic interactions involving the transfer ofelectrons between orbitals (donorrarr acceptor) and energiesin the coordination sphere of the structures formed withCr+6 through which it is possible to justify the differencein stability between the respective complexes As can beseen the interactionsmentioned in relation to [Cr+6(EDTA)]complex are relatively much higher than the correspondentsin the structures of the [Cr(NTA)(H
2O)2] and [Cr(collagen)]
complexes These results indicate a greater stability for theCr-EDTA complex being in accordance with the Gibbs freeenergy variation obtained from the thermodynamic cycleIn order to investigate the electronic and steric effects thatmodulate the complexation reaction with chromium ions wehave performed NBO and AIM calculations
34 Quantum Theory of Atoms in Molecules (QTAIM) Thetopological analysis of the electron density can provide valu-able information about the properties of the system underconsideration The properties of electron density measure-ments in the so-called Bond Critical Point (BCP) such as the
Journal of Chemistry 5
CrO1
O2
O3
O4
C5
(a)
Cr
O1O2
O3
O4
O5
O6
(b)
H
HCr
O1
O2
O3
O4
11N
50150
260
25C
22C
12C
14C
16C
19C
23H
13H
21H
18H
4H
3H
7H
6H
(c)
Figure 5 Structures of the isomer ldquoBrdquo of the Cr-EDTA complex (a) Cr-collagen complex (b) and Cr-NTA complex (c)
electronic density at BCP (120588) the Laplacian of the electrondensity (nabla2120588) the potential energy (Vc) kinetic energy (Gc)and the total electron energy (Hc) are useful for detect-ing and characterizing the chemical bonds such as cova-lent bonds metal-ligand interactions hydrogen bonds andother weak noncovalent intramolecular interactions [41] Forexample for bonds predominantly covalent 120588 is generallygt020 nabla2120588 lt 0 and Hc lt 0 while for the bond of an electro-static nature (ionic) 120588 is generally lower (sim10minus2 for hydrogenbonding and sim10minus3 for Van der Waals interaction) withnabla
2120588 gt 0 and Hc relatively higher [13 42] Table 3 shows
the properties of BCPs for the most relevant interactionsthat occur among the atoms in the Cr+6 complexes shownin Figure 5 As with the data in Table 4 it can be seenthat the interactions established between chromium and theoxygen atom are electrostatic in nature with ionic bondingcharacteristics wherein the core supports the entire loadconcentration (nabla2120588 gt 0 and relatively high Hc) in contrast
for example with the values of the covalent bond O1ndashC5TheQTAIM analysis did not reveal relevant intramolecular inter-action such as hydrogen bonding for example However thetopological analysis revealed a greater electron density in thecoordination sphere region for Cr-EDTA complex than withthe complexes collagen-Cr and Cr-(NTA)(H
2O)2 Moreover
the electron density (120588) values in the coordination sphere ofBCPs for these two complexes were much lower indicatingthat electrostatic interactions are less
35 Formation Kinetics of Cr-EDTA Complex
351 Experimental Since our theoretical findings point outEDTA as the best ligand used for the complexation reactionwith chromium at both oxidation states Cr+3 and Cr+6 wehave performed the experimental part focused on EDTAcomplex The formation of the Cr-EDTA complex in relationto time can be evidenced by the gradual formation of its
6 Journal of Chemistry
18
16
14
12
10
08
06
04
02
00
400 450 500 550 600 650 700 750 800
Abso
rban
ce
Wavelength (nm)
180min
60min
15min10min
5min
1min
Figure 6 UV-Vis spectra of the Cr-EDTA complex at 70∘C
18
16
14
12
10
08
06
04
02
00
Abso
rban
ce
0 5000 10000 15000 20000 25000 30000
Time (s)
50∘C
70∘C
60∘C
40∘C
25∘C
(a)
Time (s)
50∘C70
∘C
60∘C
40∘C
25∘C
0 50 100 150 200 250 300 350 400 450 500 550 600
00
minus05
minus10
minus15
minus20
minus25
ln A
bs
k = 000389 sminus1
k = 000356 sminus1
k = 000144 sminus1
k = 000077 sminus1
k = 000020 sminus1
(b)
Figure 7The formation kinetics of the Cr-EDTA complex at different temperatures (a) and the linearization of the equation speed (ln [Abs]= 119896119905) with the respective constants (b)
absorption band in the visible region at 546 nm (Figure 6)The spectra show that at 70∘C the formation of the complexcan be studied with extreme speed only 5min of reactionis necessary The formation kinetics of Cr-EDTA complexwas studied at 546 nm at various temperatures as shownin Figure 7(a) It can be observed that increasing the tem-perature increases the rate of complex formation observingthe increase in absorbance for the same time In additionconsidering an approximately linear curve in short timesone can determine the rate constants for complex formationby linearizing the velocity equation ln [Abs] = 119896119905 shownin Figure 7(b) Using the Arrhenius equation [43] (4) andwith the data obtained in this experiment it was possible to
determine the activation energy required for the formationof the complex (119864
119886= 59 kJsdotmolminus1)
ln119870 = ln119860 minus119864at119877
119879
minus1
(4)
36 Effect of pH Complexation reactions involvingmetals byligands of aminopolycarboxylic acids are very dependent onpH such that according to the acidity of the reaction med-ium there will be a greater or lesser prevalence of a species ofligand at equilibrium At very low pH the nonionized speciesof the ligand predominates so that for the reaction to occurthemetal ionsmust be able to remove the ionizable hydrogens
Journal of Chemistry 7
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
Table 3 QTAIM parameters obtained by the main interatomicinteractions in the isomer (B) of the Cr-EDTA complex the Cr-NTA(H2O)2 and Cr-collagen complex in au
the results are consistent with the difference in size betweenthe ions 076 [38] and 044 A [39] for Cr+3 and Cr+6 respec-tively In addition molecular orbital and electronic structure
Table 4 Higher energies of nonbonding interactions betweenNBOs in the coordination sphere for complexes of Cr+6 kcalsdotmolminus1
calculations can be used to more deeply investigate themolecular basis for rationalizing the complexation reaction
33 Natural Bond Orbitals Analysis (NBO) The NBO anal-ysis provides information about the electronic structure of acomplex For example the interaction between the occupiedand vacant orbitals represents the deviation of the moleculesfrom the Lewis structure and the respective energies can beused as ameasure of structure stability [18 40] Table 4 showsthe most energetic interactions involving the transfer ofelectrons between orbitals (donorrarr acceptor) and energiesin the coordination sphere of the structures formed withCr+6 through which it is possible to justify the differencein stability between the respective complexes As can beseen the interactionsmentioned in relation to [Cr+6(EDTA)]complex are relatively much higher than the correspondentsin the structures of the [Cr(NTA)(H
2O)2] and [Cr(collagen)]
complexes These results indicate a greater stability for theCr-EDTA complex being in accordance with the Gibbs freeenergy variation obtained from the thermodynamic cycleIn order to investigate the electronic and steric effects thatmodulate the complexation reaction with chromium ions wehave performed NBO and AIM calculations
34 Quantum Theory of Atoms in Molecules (QTAIM) Thetopological analysis of the electron density can provide valu-able information about the properties of the system underconsideration The properties of electron density measure-ments in the so-called Bond Critical Point (BCP) such as the
Journal of Chemistry 5
CrO1
O2
O3
O4
C5
(a)
Cr
O1O2
O3
O4
O5
O6
(b)
H
HCr
O1
O2
O3
O4
11N
50150
260
25C
22C
12C
14C
16C
19C
23H
13H
21H
18H
4H
3H
7H
6H
(c)
Figure 5 Structures of the isomer ldquoBrdquo of the Cr-EDTA complex (a) Cr-collagen complex (b) and Cr-NTA complex (c)
electronic density at BCP (120588) the Laplacian of the electrondensity (nabla2120588) the potential energy (Vc) kinetic energy (Gc)and the total electron energy (Hc) are useful for detect-ing and characterizing the chemical bonds such as cova-lent bonds metal-ligand interactions hydrogen bonds andother weak noncovalent intramolecular interactions [41] Forexample for bonds predominantly covalent 120588 is generallygt020 nabla2120588 lt 0 and Hc lt 0 while for the bond of an electro-static nature (ionic) 120588 is generally lower (sim10minus2 for hydrogenbonding and sim10minus3 for Van der Waals interaction) withnabla
2120588 gt 0 and Hc relatively higher [13 42] Table 3 shows
the properties of BCPs for the most relevant interactionsthat occur among the atoms in the Cr+6 complexes shownin Figure 5 As with the data in Table 4 it can be seenthat the interactions established between chromium and theoxygen atom are electrostatic in nature with ionic bondingcharacteristics wherein the core supports the entire loadconcentration (nabla2120588 gt 0 and relatively high Hc) in contrast
for example with the values of the covalent bond O1ndashC5TheQTAIM analysis did not reveal relevant intramolecular inter-action such as hydrogen bonding for example However thetopological analysis revealed a greater electron density in thecoordination sphere region for Cr-EDTA complex than withthe complexes collagen-Cr and Cr-(NTA)(H
2O)2 Moreover
the electron density (120588) values in the coordination sphere ofBCPs for these two complexes were much lower indicatingthat electrostatic interactions are less
35 Formation Kinetics of Cr-EDTA Complex
351 Experimental Since our theoretical findings point outEDTA as the best ligand used for the complexation reactionwith chromium at both oxidation states Cr+3 and Cr+6 wehave performed the experimental part focused on EDTAcomplex The formation of the Cr-EDTA complex in relationto time can be evidenced by the gradual formation of its
6 Journal of Chemistry
18
16
14
12
10
08
06
04
02
00
400 450 500 550 600 650 700 750 800
Abso
rban
ce
Wavelength (nm)
180min
60min
15min10min
5min
1min
Figure 6 UV-Vis spectra of the Cr-EDTA complex at 70∘C
18
16
14
12
10
08
06
04
02
00
Abso
rban
ce
0 5000 10000 15000 20000 25000 30000
Time (s)
50∘C
70∘C
60∘C
40∘C
25∘C
(a)
Time (s)
50∘C70
∘C
60∘C
40∘C
25∘C
0 50 100 150 200 250 300 350 400 450 500 550 600
00
minus05
minus10
minus15
minus20
minus25
ln A
bs
k = 000389 sminus1
k = 000356 sminus1
k = 000144 sminus1
k = 000077 sminus1
k = 000020 sminus1
(b)
Figure 7The formation kinetics of the Cr-EDTA complex at different temperatures (a) and the linearization of the equation speed (ln [Abs]= 119896119905) with the respective constants (b)
absorption band in the visible region at 546 nm (Figure 6)The spectra show that at 70∘C the formation of the complexcan be studied with extreme speed only 5min of reactionis necessary The formation kinetics of Cr-EDTA complexwas studied at 546 nm at various temperatures as shownin Figure 7(a) It can be observed that increasing the tem-perature increases the rate of complex formation observingthe increase in absorbance for the same time In additionconsidering an approximately linear curve in short timesone can determine the rate constants for complex formationby linearizing the velocity equation ln [Abs] = 119896119905 shownin Figure 7(b) Using the Arrhenius equation [43] (4) andwith the data obtained in this experiment it was possible to
determine the activation energy required for the formationof the complex (119864
119886= 59 kJsdotmolminus1)
ln119870 = ln119860 minus119864at119877
119879
minus1
(4)
36 Effect of pH Complexation reactions involvingmetals byligands of aminopolycarboxylic acids are very dependent onpH such that according to the acidity of the reaction med-ium there will be a greater or lesser prevalence of a species ofligand at equilibrium At very low pH the nonionized speciesof the ligand predominates so that for the reaction to occurthemetal ionsmust be able to remove the ionizable hydrogens
Journal of Chemistry 7
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
Figure 5 Structures of the isomer ldquoBrdquo of the Cr-EDTA complex (a) Cr-collagen complex (b) and Cr-NTA complex (c)
electronic density at BCP (120588) the Laplacian of the electrondensity (nabla2120588) the potential energy (Vc) kinetic energy (Gc)and the total electron energy (Hc) are useful for detect-ing and characterizing the chemical bonds such as cova-lent bonds metal-ligand interactions hydrogen bonds andother weak noncovalent intramolecular interactions [41] Forexample for bonds predominantly covalent 120588 is generallygt020 nabla2120588 lt 0 and Hc lt 0 while for the bond of an electro-static nature (ionic) 120588 is generally lower (sim10minus2 for hydrogenbonding and sim10minus3 for Van der Waals interaction) withnabla
2120588 gt 0 and Hc relatively higher [13 42] Table 3 shows
the properties of BCPs for the most relevant interactionsthat occur among the atoms in the Cr+6 complexes shownin Figure 5 As with the data in Table 4 it can be seenthat the interactions established between chromium and theoxygen atom are electrostatic in nature with ionic bondingcharacteristics wherein the core supports the entire loadconcentration (nabla2120588 gt 0 and relatively high Hc) in contrast
for example with the values of the covalent bond O1ndashC5TheQTAIM analysis did not reveal relevant intramolecular inter-action such as hydrogen bonding for example However thetopological analysis revealed a greater electron density in thecoordination sphere region for Cr-EDTA complex than withthe complexes collagen-Cr and Cr-(NTA)(H
2O)2 Moreover
the electron density (120588) values in the coordination sphere ofBCPs for these two complexes were much lower indicatingthat electrostatic interactions are less
35 Formation Kinetics of Cr-EDTA Complex
351 Experimental Since our theoretical findings point outEDTA as the best ligand used for the complexation reactionwith chromium at both oxidation states Cr+3 and Cr+6 wehave performed the experimental part focused on EDTAcomplex The formation of the Cr-EDTA complex in relationto time can be evidenced by the gradual formation of its
6 Journal of Chemistry
18
16
14
12
10
08
06
04
02
00
400 450 500 550 600 650 700 750 800
Abso
rban
ce
Wavelength (nm)
180min
60min
15min10min
5min
1min
Figure 6 UV-Vis spectra of the Cr-EDTA complex at 70∘C
18
16
14
12
10
08
06
04
02
00
Abso
rban
ce
0 5000 10000 15000 20000 25000 30000
Time (s)
50∘C
70∘C
60∘C
40∘C
25∘C
(a)
Time (s)
50∘C70
∘C
60∘C
40∘C
25∘C
0 50 100 150 200 250 300 350 400 450 500 550 600
00
minus05
minus10
minus15
minus20
minus25
ln A
bs
k = 000389 sminus1
k = 000356 sminus1
k = 000144 sminus1
k = 000077 sminus1
k = 000020 sminus1
(b)
Figure 7The formation kinetics of the Cr-EDTA complex at different temperatures (a) and the linearization of the equation speed (ln [Abs]= 119896119905) with the respective constants (b)
absorption band in the visible region at 546 nm (Figure 6)The spectra show that at 70∘C the formation of the complexcan be studied with extreme speed only 5min of reactionis necessary The formation kinetics of Cr-EDTA complexwas studied at 546 nm at various temperatures as shownin Figure 7(a) It can be observed that increasing the tem-perature increases the rate of complex formation observingthe increase in absorbance for the same time In additionconsidering an approximately linear curve in short timesone can determine the rate constants for complex formationby linearizing the velocity equation ln [Abs] = 119896119905 shownin Figure 7(b) Using the Arrhenius equation [43] (4) andwith the data obtained in this experiment it was possible to
determine the activation energy required for the formationof the complex (119864
119886= 59 kJsdotmolminus1)
ln119870 = ln119860 minus119864at119877
119879
minus1
(4)
36 Effect of pH Complexation reactions involvingmetals byligands of aminopolycarboxylic acids are very dependent onpH such that according to the acidity of the reaction med-ium there will be a greater or lesser prevalence of a species ofligand at equilibrium At very low pH the nonionized speciesof the ligand predominates so that for the reaction to occurthemetal ionsmust be able to remove the ionizable hydrogens
Journal of Chemistry 7
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
Figure 6 UV-Vis spectra of the Cr-EDTA complex at 70∘C
18
16
14
12
10
08
06
04
02
00
Abso
rban
ce
0 5000 10000 15000 20000 25000 30000
Time (s)
50∘C
70∘C
60∘C
40∘C
25∘C
(a)
Time (s)
50∘C70
∘C
60∘C
40∘C
25∘C
0 50 100 150 200 250 300 350 400 450 500 550 600
00
minus05
minus10
minus15
minus20
minus25
ln A
bs
k = 000389 sminus1
k = 000356 sminus1
k = 000144 sminus1
k = 000077 sminus1
k = 000020 sminus1
(b)
Figure 7The formation kinetics of the Cr-EDTA complex at different temperatures (a) and the linearization of the equation speed (ln [Abs]= 119896119905) with the respective constants (b)
absorption band in the visible region at 546 nm (Figure 6)The spectra show that at 70∘C the formation of the complexcan be studied with extreme speed only 5min of reactionis necessary The formation kinetics of Cr-EDTA complexwas studied at 546 nm at various temperatures as shownin Figure 7(a) It can be observed that increasing the tem-perature increases the rate of complex formation observingthe increase in absorbance for the same time In additionconsidering an approximately linear curve in short timesone can determine the rate constants for complex formationby linearizing the velocity equation ln [Abs] = 119896119905 shownin Figure 7(b) Using the Arrhenius equation [43] (4) andwith the data obtained in this experiment it was possible to
determine the activation energy required for the formationof the complex (119864
119886= 59 kJsdotmolminus1)
ln119870 = ln119860 minus119864at119877
119879
minus1
(4)
36 Effect of pH Complexation reactions involvingmetals byligands of aminopolycarboxylic acids are very dependent onpH such that according to the acidity of the reaction med-ium there will be a greater or lesser prevalence of a species ofligand at equilibrium At very low pH the nonionized speciesof the ligand predominates so that for the reaction to occurthemetal ionsmust be able to remove the ionizable hydrogens
Journal of Chemistry 7
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
of the molecule On the other hand in strongly basic solu-tions such hydrogens are removed by reaction with hyd-roxide ions However the ligand in its anionic form willldquocompeterdquo with the hydroxyl in the complexation with themetal andmanymetal ions tend to hydrolyze and precipitateas hydroxides [2] The formation of [Cr+3(EDTA)] complexshows to be favored between pH 45 and 7 and accordingto the basicity increase the species is gradually replacedby [Cr+3(EDTA)(OH)] tending to form the hydroxide Cr+3[44]
4 Conclusion
In this work the stability of complexation of chromium (triva-lent and hexavalent) with the structures of the polydentateligands EDTA and NTA and collagen was studied Accordingto our results we observe that the formation of the Cr-EDTAcomplex from theCr+6 is energeticallymore favorable that isthe complex ismore stableThe fact that the Cr+6 has a similarelectronic configuration to a representative element and asmaller ionic radius compared to Cr+3 can justify this greaterstability The kinetics of formation of complex with Cr+3was also investigated The results showed that increasing thetemperature increases the rate of formation of the complexand at 70∘C only 5min of reaction is required with a rateconstant equal to 119896 = 000389 sminus1
By comparing the Gibbs free energy of Cr-EDTA[Cr(NTA)(H
2O)2] and Cr-collagen structures complexation
the following order of stability was found [Cr+6(EDTA)] gt[Cr+3(EDTA)] gt [Cr+6(NTA)(H
2O)2] gt [Cr+3(NTA)(H
2O)2]
gt [Cr+6(collagen)] gt [Cr+3(collagen)] Thus in this workit was noticed that although the EDTA and NTA ligandscan be used in the process the formation of the Cr-EDTAcomplex is energetically more favorable therefore EDTA hasgreater ability to ldquosequesterrdquo Cr3+ as well as Cr6+ whichare connected to the waste from the leather industry (chipsshavings and dust from sanding) before they are discardedor reused for other purposes Thus from a thermodynamicsas well as kinetics point of view our theoretical and exper-imental findings point out EDTA as a promising scavengerfor chromium forming a more stable metallic complex withchromium with a lower activation energy from ldquowet bluerdquoleather waste
Conflict of Interests
The authors declare that there is no conflict of interestregarding the publication of this paper
Acknowledgments
The authors thank the Brazilian agencies FAPEMIG CAPESand CNPq for funding part of this work
References
[1] C Durante M Cuscov A A Isse G Sandona and A GennaroldquoAdvanced oxidation processes coupledwith electrocoagulation
for the exhaustive abatement of Cr-EDTArdquoWater Research vol45 no 5 pp 2122ndash2130 2011
[2] R Dai J Liu C Yu R Sun Y Lan and J-D Mao ldquoAcomparative study of oxidation of Cr(III) in aqueous ionscomplex ions and insoluble compounds by manganese-bearingmineral (birnessite)rdquo Chemosphere vol 76 no 4 pp 536ndash5412009
[3] J P Thyssen M Strandesen P B Poulsen T Menne and J DJohansen ldquoChromium in leather footwear-risk assessment ofchromium allergy and dermatitisrdquo Contact Dermatitis vol 66no 5 pp 279ndash285 2012
[4] K Kolomaznik M Adamek I Andel and M UhlirovaldquoLeather wastemdashPotential threat to human health and a newtechnology of its treatmentrdquo Journal of Hazardous Materialsvol 160 no 2-3 pp 514ndash520 2008
[5] RM Dallago A Smaniotto and L C A de Oliveira ldquoResıduossolidos de curtumes como adsorventes para a remocao decorantes emmeio aquosordquoQuımicaNova vol 28 no 3 pp 433ndash437 2005
[6] M Erdem and A Ozverdi ldquoLeaching behavior of chromium inchrome shaving generated in tanning process and its stabiliza-tionrdquo Journal of HazardousMaterials vol 156 no 1ndash3 pp 51ndash552008
[7] L F Cabeza M M Taylor G L Dimaio et al ldquoProcessing ofleather waste pilot scale studies on chrome shavings Isolationof potentially valuable protein products and chromiumrdquoWasteManagement vol 18 no 3 pp 211ndash218 1998
[8] DQ L deOliveira K TGCarvalhoA R R Bastos L CA deOliveira J J G de Sa eMeloMarques and R S deMelo Pereirado Nascimento ldquoUse of leather industry residues as nitrogensources for elephantgrassrdquo Revista Brasileira de Ciencia do Solovol 32 no 1 pp 417ndash424 2008
[9] A Kovacs D S Nemcsok and T Kocsis ldquoBonding inter-actions in EDTA complexesrdquo Journal of Molecular StructureTHEOCHEM vol 950 no 1ndash3 pp 93ndash97 2010
[10] M Korolczuk and M Grabarczyk ldquoEvaluation of ammoniabuffer containing EDTA as an extractant for Cr(VI) from solidsamplesrdquo Talanta vol 66 no 5 pp 1320ndash1325 2005
[11] C-C Liu and Y-C Lin ldquoReclamation of copper-contaminatedsoil using EDTA or citric acid coupled with dissolved organicmatter solution extracted from distillery sludgerdquo EnvironmentalPollution vol 178 pp 97ndash101 2013
[12] L Chen T Liu and C Ma ldquoMetal complexation and biodegra-dation of EDTA and SS-EDDS a density functional theorystudyrdquo The Journal of Physical Chemistry A vol 114 no 1 pp443ndash454 2010
[13] I Cukrowski and K K Govender ldquoA density functional theory-and atoms in molecules-based study of NiNTA and NiNTPAcomplexes toward physical properties controlling their stabilityA new method of computing a formation constantrdquo InorganicChemistry vol 49 no 15 pp 6931ndash6941 2010
[14] S Cataldo C de Stefano A Gianguzza and A PettignanoldquoSequestration of (CH
3)Hg+ by amino-polycarboxylic chelating
agentsrdquo Journal of Molecular Liquids vol 172 pp 46ndash52 2012[15] Z-G Shen X-D Li C-C Wang H-M Chen and H Chua
ldquoLead phytoextraction from contaminated soil with high-biomass plant speciesrdquo Journal of Environmental Quality vol31 no 6 pp 1893ndash1900 2002
[16] S C Hoops K W Anderson and K M Merz Jr ldquoForce FieldDesign for Metalloproteinsrdquo Journal of the American ChemicalSociety vol 113 no 22 pp 8262ndash8270 1991
8 Journal of Chemistry
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
[17] J Sponer and P Hobza ldquoMP2 and CCSD(T) study on hydrogenbonding aromatic stacking and nonaromatic stackingrdquo Chem-ical Physics Letters vol 267 no 3-4 pp 263ndash270 1997
[18] T C Ramalho E F F da Cunha and R B de AlencastroldquoA density functional study on the complexation of etham-butol with divalent cationsrdquo Journal of Molecular StructureTHEOCHEM vol 676 no 1ndash3 pp 149ndash153 2004
[19] P Comba and R Remenyi ldquoInorganic and bioinorganic molec-ular mechanics modelingmdashthe problem of the force fieldparameterizationrdquo Coordination Chemistry Reviews vol 9 pp238ndash239 2003
[20] P Carloni and W Andreoni ldquoPlatinum-modified nucleobasepairs in the solid state a theoretical studyrdquo Journal of PhysicalChemistry vol 100 no 45 pp 17797ndash17800 1996
[21] M S Caetano T C Ramalho D F Botrel E F F da Cunhaand W C de Mello ldquoUnderstanding the inactivation processof organophosphorus herbicides a DFT study of glyphosatemetallic complexes with Zn2+ Ca2+ Mg2+ Cu2+ Co3+ Fe3+Cr3+ and Al3+rdquo International Journal of Quantum Chemistryvol 112 no 15 pp 2752ndash2762 2012
[22] W S Ohlinger P E Klunzinger B J Deppmeier and W JHehre ldquoEfficient calculation of heats of formationrdquoThe Journalof Physical Chemistry A vol 113 no 10 pp 2165ndash2175 2009
[23] T A Yousef G M Abu El-Reash and R M El MorshedyldquoStructural spectral analysis and DNA studies of heterocyclicthiosemicarbazone ligand and its Cr(III) Fe(III) Co(II) Hg(II)and U(VI) complexesrdquo Journal of Molecular Structure vol 1045pp 145ndash159 2013
[24] F Fontaine-Vive F Merzel M R Johnson and G J KearleyldquoCollagen and component polypeptides low frequency andamide vibrationsrdquo Chemical Physics vol 355 no 2-3 pp 141ndash148 2009
[25] L C A Oliveira M C Guerreiro M Goncalves D Q LOliveira and L C M Costa ldquoPreparation of activated carbonfrom leather waste a new material containing small particle ofchromium oxiderdquoMaterials Letters vol 62 no 21-22 pp 3710ndash3712 2008
[26] M J Frisch G W Trucks H B Schlegel et al GaussianWallingford Conn USA 2009
[27] T C Ramalho E F F da Cunha R B de Alencastro and AEspınola ldquoDifferential complexation between Zn2+ and Cd2+with fulvic acid a computational chemistry studyrdquo Water Airand Soil Pollution vol 183 no 1ndash4 pp 467ndash472 2007
[28] M Ghosh S Sproules T Weyhermuller and K Wieghardtldquo(120572-diimine)chromium complexes molecular and electronicstructures a combined experimental and density functionaltheoretical studyrdquo Inorganic Chemistry vol 47 no 13 pp 5963ndash5970 2008
[29] R Ditchfie W J Hehre and J A Pople ldquoSelf-consistentmolecular-orbital methods IX An extended Gaussian-typebasis for molecular-orbital studies of organic moleculesrdquo Jour-nal of Chemical Physics vol 54 p 724 1971
[30] Y I Ishikawa and K Kawakami ldquoStructure and infraredspectroscopy of group 6 transition-metal carbonyls in the gasphase DFT studies on M(CO)
119899(M = Cr Mo and W n = 6 5
4 and 3)rdquo Journal of Physical Chemistry A vol 111 no 39 pp9940ndash9944 2007
[31] H Sun X Tian J Wang J Zhang Y Yuan and Z-R SunldquoTheoretical studies on molecular and structures of mono- andbinuclear chromium carbazole derivatives for optoelectronicsrdquoThe Journal of Physical Chemistry A vol 115 no 50 pp 14495ndash14501 2011
[32] K Shimizu A A Freitas J P S Farah and L G DiasldquoPredicting hydration free energies of neutral compounds bya parametrization of the polarizable continuum modelrdquo TheJournal of Physical Chemistry A vol 109 no 49 pp 11322ndash113272005
[33] NBO Version 50 Included in the Gaussian09 Package ofPrograms Gaussian Wallingford Conn USA 2009
[34] T H Dunning and P J Hay ldquoGaussian basis sets for molecularcalculationsrdquo inModern Theoretical Chemistry vol 3 pp 1ndash28Plenum New York NY USA 1976
[35] T A Keith AIMAll (Version 111016) TK Gristmill SoftwareOverland Park Kan USA 2011 httpaimtkgristmillcom
[36] R E Hamm ldquoComplex ions of chromium IV The ethylenedi-aminetetraacetic acid complex with chromium (III)rdquo Journal ofthe American Chemical Society vol 75 no 22 pp 5670ndash56721953
[37] H Irving and R J PWilliams ldquoThe stability of transition-metalcomplexesrdquo Journal of the Chemical Society pp 3192ndash3210 1953
[38] C Quintelas Z Rocha B Silva B Fonseca H Figueiredo andT Tavares ldquoRemoval of Cd(II) Cr(VI) Fe(III) and Ni(II) fromaqueous solutions by an E coli biofilm supported on kaolinrdquoChemical Engineering Journal vol 149 no 1ndash3 pp 319ndash3242009
[39] M S Aksoy and U Ozer ldquoPotentiometric and spectroscopicstudies with chromium(iii) complexes of hydroxysalicylic acidderivatives in aqueous solution rdquo Turkish Journal of Chemistryvol 27 no 6 pp 667ndash673 2003
[40] T C Ramalho T L C Martins L E Pizarro Borgesand J D Figueroa-Villar ldquoInfluence of nonbonded inter-actions in the kinetics of formation of chalcogenol estersfrom chalcogenoacetylenesrdquo International Journal of QuantumChemistry vol 95 no 3 pp 267ndash273 2003
[41] B Bankiewicz P Matczak and M Palusiak ldquoElectron densitycharacteristics in bond critical point (QTAIM) versus interac-tion energy components (SAPT)mdashthe case of charge-assistedhydrogen bondingrdquo Journal of Physical Chemistry A vol 116 no1 pp 452ndash459 2012
[42] P R Varadwaj and H M Marques ldquoThe physical chemistry of[M(H
2O)4(NO3)2] (M = Mn2+ Co2+ Ni2+ Cu2+ Zn2+) com-
plexes computational studies of their structure energetics andthe topological properties of the electron densityrdquo TheoreticalChemistry Accounts vol 127 no 5-6 pp 711ndash725 2010
[43] P Atkins Fısico-Quımica vol 3 of H Macedo ed chapter 2LTC Rio de Janeiro Brazil 1999
[44] R F Carbonaro B N Gray C F Whitehead and A TStone ldquoCarboxylate-containing chelating agent interactionswith amorphous chromium hydroxide adsorption and disso-lutionrdquo Geochimica et Cosmochimica Acta vol 72 no 13 pp3241ndash3257 2008
