Research Article Reversible Oxygenation of -Amino Acid...

Research ArticleReversible Oxygenation of 120572-Amino AcidndashCobalt(II) Complexes

Xincun Zhang1 Fan Yue1 Hui Li1 Yan Huang1 Yi Zhang2 Hongmei Wen1 and Jide Wang1

1Key Laboratory of Oil and Gas Fine Chemicals Ministry of Education and Xinjiang Uyghur Autonomous RegionCollege of Chemistry and Chemical Engineering Xinjiang University Urumqi Xinjiang 830046 China2College of Chemistry and Chemical Engineering Central South University Changsha Hunan 410083 China

Correspondence should be addressed to Jide Wang awangjdsinacn

Received 27 October 2015 Revised 21 December 2015 Accepted 22 December 2015

Academic Editor Luigi Casella

Copyright copy 2016 Xincun Zhang et al This 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

We systematically investigated the reversibility time lapse and oxygenation-deoxygenation properties of 15 natural 120572-amino acidndashCo(II) complexes through UV-vis spectrophotometer polarographic oxygen electrode and DFT calculations respectively toexplore the relationship between the coordinating structure and reversible oxygenation of 120572-amino acidndashCo(II) complexes Resultsrevealed that the 120572-amino acid structure plays a key role in the reversible oxygenation properties of these complexes The specificconfiguration of the 120572-amino acid group affects the eg

1 electron of Co(II) transfer to the 120587lowast orbit of O2 this phenomenon also

favors the reversible formation and dissociation of CondashO2bond when O

2coordinates with Co(II) complexes Therefore the co-

coordination of amino and carboxyl groups is a determinant of Co complexes to absorb O2reversibly The group adjacent to the

120572-amino acid unit evidently influences the dioxygen affinity and antioxidation ability of the complexes The presence of amino (orimino) and hydroxy groups adjacent to the 120572-amino acid group increases the oxygenation-deoxygenation rate and the numberof reversible cycles Our findings demonstrate a new mechanism to develop reversible oxygenation complexes and to reveal theoxygenation of oxygen carriers

1 Introduction

Oxygenated complexes should be investigated whether asa model compound of natural oxygen carriers or as anenvironmentally friendly catalyst [1ndash6] The oxygenationrelated mechanism and configuration of oxygenated com-plexes as a model compound of natural oxygen carriers havebeen extensively explored [7ndash13] Nam synthesized crystalsof mononuclear oxygenated complexes and speculated theiroxygenation mechanism by systematically investigating theiraging process that is the process of activation of dioxygenand then the oxidation of the oxygenated complex [1 14ndash17]For example metalloenzymes activate dioxygen to performvarious biological reactions [8 10 18ndash20] The activationof dioxygen at enzyme active sites occurs through severalsteps (1) O

2binds to a reduced metal center (2) superoxo

and peroxo species are then generated the OndashO bond ofmetal hydroperoxo complexes is cleaved and high-valentmetal-oxo oxidants are formed [2 3 21ndash26] Studies havedemonstrated the mechanisms by which biological enzymesactivate oxygen molecules However reversible oxygenation

complexes which can be used as a model compound ofhemoglobin have been rarely reported because availableoxygenation complexes are unstable as a result researchersexperience difficulty in characterizing the exact structuresof products [27 28] Two major problems are encounteredin studies involving the oxygenation of cobalt complexesin an aqueous solution (1) complexes absorb dioxygenimmediately when they are formed under ambient conditionsand (2) aging phenomenon or the oxidation of the oxy-genated complex occurs until the aging process is completed[29 30] Although the rates of the aging or oxidation ofthese cobalt complexes differ oxygenated complexes exist invarying states As such oxygenated compounds should becharacterized immediately after these compounds are formedin solutions rather than after they become separated fromsolutions UV-vis spectrophotometer and polarographic oxy-gen electrode are used to monitor oxygenation and deoxy-genation online through the continuous alternation of O

2

and N2atmospheres A mass spectrometer is utilized to

characterize complexes and to determine their structures[29ndash31]

Hindawi Publishing CorporationBioinorganic Chemistry and ApplicationsVolume 2016 Article ID 3585781 10 pageshttpdxdoiorg10115520163585781

2 Bioinorganic Chemistry and Applications

Glycine (Gly) Alanine (Ala) Valine (Val)

XS

Methionine (Met)

HN O

OHProline (Pro)Serine (Ser)

X

HO

Threonine (Thr)

X

Asparagine (Asn)

X

OGlutamine (Gln)

X

HS

Cysteine (Cys)

X

Lysine (Lys)

XHN

NHArginine (Arg)

X

HN

N

Histidine (His)

O

HO

Aspartate (Asp)

X

O

HO

Glutamate (Glu)

COOH

H

R

H X X XHO X

R X

O

Abbr

X

NH2

H2N

H2N

H2N

H2N

H3C

Scheme 1 Structures of 15 natural amino acids

Schiff base ligands and porphyrins are mostly confined inthe reversible oxygenation of oxygenated complexes [11 24]however the reversible oxygenation property of these com-plexes is poor in aqueous solutions and at room temperatureBurk et al investigated histidinendashCo(II) and demonstratedthat oxygenation reversibility occurs in an aqueous solutionat room temperature [32] Considering this previous studyMartell and other researchers examined Co(II) complexeswith amino acids and dipeptides which can reversibly uptakeoxygen [33 34] In our study four groups of ligands withdifferent NO NN and OO difunctional groups [35] suchas amino acids amino alcohols polyamines and multicar-boxylic acids were selected The oxygenation performancesof their Co(II) complexes were comparatively analyzedThe following results were obtained the OO difunctionalgroup of the Co(II) complexes does not possess oxygenationproperties the NN difunctional group of the complexescan uptake oxygen but cannot undergo reversibility theNO-type difunctional group of the complexes is relativelydifferent 120572-amino acidndashCo(II) complexes exhibit evidentreversible oxygen performance and 120572-amino alcoholndashCo(II)complexes uptake oxygen weakly and show no reversibilityHowever studies have yet to determine the factor causing 120572-amino acidndashCo complexes to exhibit oxygenation reversibil-ity

Among Co complexes 120572-amino acidndashCo complexes dis-play different oxygenation reversibilities On the basis of thisunusual finding we supposed that the 120572-amino acid group in

a ligand could be a key group associated with the reversibleoxygenation of such complexes Therefore we synthesized aseries of novel amino acidndashCo(II) complexes and found thatCo complexes can reversibly uptake dioxygen [28 35 36]Indeed the 120572-amino acid unit in a ligand is a key structuralcomponent related to the reversible oxygenation property ofthese complexes

To explore the factors and coordinating structure thatdetermine the oxygenation reversibility of 120572-amino acidndashCo complexes we selected 15 natural water-soluble 120572-aminoacids (Scheme 1) and performed a detailed investigation oftheir oxygenation properties in aqueous solutions at roomtemperature Measurements were conducted at a specific pHrange at which these complexes are in their major states Wealso conducted a thorough comparative analysis to determinethe relationship between the structures of ligands and thedioxygen affinity of Co complexes

This study aimed to determine the basic structural unitresponsible for the reversible dioxygen uptake This studyalso aimed to identify the auxiliary functional groups thatimprove the reversibility of dioxygen uptake We believe thatour findings would remarkably contribute to elucidating andrevealing the oxygenation mechanism of oxygen carriers

2 Experimental

21 Materials Amino acids and Co(CH3COO)

2sdot4H2O were

purchased from Shanghai Aladdin Reagents Co Ltd

Bioinorganic Chemistry and Applications 3

Table 1 Concentrations of 15 amino acids and cobalt salts

LA Gly Ala Val Ser Thr His Pro Met Cys Arg Lys Glu Gln Asn AspMr 75 89 117 105 119 155 115 149 121 174 146 147 146 132 133119888BCo times 10

minus3 60 033 05 10 10 0028 033 10 01 025 02 10 10 20 20119888L times 10

minus3 180 10 15 30 30 0056 10 30 03 075 06 30 30 60 60NotesA amino acids ligandsB 119888 molsdotLminus1

(China) Amino acids and Co aqueous solutions were pre-pared with distilled water High-purity (9999) O

2and N

2

were used All of the chemicals were used without furtherpurification

The following instruments were used in the experimentUV-vis spectrometer (UV-2450 Shimadzu Japan) infraredspectrometer (VERTEX70-RAMAN II Bruker CompanyGermany test conditions dpi 40 cmminus1 number of scans100 and ATR with water as background) peristaltic pump(PS19-2 Pgeneral China) (PP2) portable dissolved oxygenmeter (HI 9146 Hanna Instruments Italy) and pH Meter(PHS-3C Shanghai Shengci Instrument Co China)

22 UV-vis Spectrophotometry Table 1 provides a list of theconcentrations of the120572-amino acids andCo(II) to prepare thecorresponding complex solutionsThe spectra were recordedat 250 plusmn 01∘C by using a UV2450 spectrophotometer witha 1 cm cuvette within the spectral range of 200ndash600 nm or atthe maximum absorption peak (120582max) of each complex at acertain pH

23 Mass Spectrometry Mass spectrometry was performedwith Waters Quattro Premier XE mass spectrometerequipped with an electrospray ionization source (MicromassManchester UK)

24 Construction of the Absorption (119860)-pH Curves For eachamino acid the Co(II) solution with a known concentrationwas mixed with the 120572-amino acid solution at a molar ratio of1 3 or 1 2 depending on the 120572-amino acid species (Table 1)The 119860 versus pH curve was constructed in accordance witha previously described method [28] and the suitable pHranges to examine each complex were selected from the 119860-pH curves

25 Determination of the Reversibility of Dioxygen Uptake andRelease The oxygenation and deoxygenation kinetics weredetermined using a PP2 flow injection apparatus [28] Thereversibility of the oxygenation and deoxygenation of the 120572-amino acidndashCo(II) complexes was identified by recording thechanges in the absorbance of O

2and N

2saturated solutions

The absorbance difference (Δ119860 = 119860O minus 119860N) betweenthe absorbances in O

2(119860O) and N

2atmospheres (119860N) was

considered to evaluate the ability of the complexes to uptakeO2 The number of oxygenation-deoxygenation cycles (119862)

was obtained to estimate the endurance of each complex toantioxidation

26 Oxygenometry The concentration of the dissolved O2in

the solution corresponded to the evolution of the oxygenationof the complexes The concentration of the dissolved O

2in

the solution was measured in accordance with a previouslydescribed method [28]

27 DFT Calculation Calculations were performed with theGaussian 03W program package [37] Full geometry opti-mization computations were conducted via a B3LYPmethodIn all of the calculations a LANL2DZ basis set along with thecorresponding effective core potential was used for Cometalatoms The 6-31G(d) basis set was utilized for C H N and Oatoms

3 Results and Discussion

The oxygenation and reversible performances of the 15 120572-amino acidndashCo complexes were investigated in this paperThe AlandashCo complex was used as an example to demonstratethe experimental processes

31 Complex Formation

311 UV-vis Spectra Figure S1A (in Supplementary Mate-rial available online at httpdxdoiorg10115520163585781)shows the UV-vis spectra of Ala and Co(II) salt solutionalone and their mixtures The spectra of the mixture aredistinctly different from those of Co or ligands alone thisresult confirmed that the complexes were formed Similarresults were observed in the other amino acidndashCo systems asindicated by theUV-vis spectra Figure S1 presents theUV-visspectra of SerndashCo HisndashCo and LysndashCo

312 IR Spectroscopy Figure S2 shows the IR spectra of Land AlandashCo(II) SerndashCo HisndashCo and LysndashCo Clearly thespectra of these complexes are significantly different fromthose of amino acids alone which refers to the formation ofthe complexes

313 Mass Spectrometry Analysis All amino acidndashCo com-plexes were determined by MS and the results exhibited theformation of the complexes Figures S3 and S4 present the ESImass spectrum of HisndashCo and AlandashCo

32 Determination of the Suitable pHCondition for the Forma-tion of Each 120572-Amino AcidndashCo Complex Co(II) complexescould be formed at different pH because of the differences


Table 2 Suitable pH 120582max and reversibility for the dioxygen uptake of 15 complexes

L Gly Ala Val Ser Thr His Pro Met Cys Arg Lys Glu Gln Asn Asp120582max 362 365 368 368 366 320374 380 365 347442 366 365 365 365 365 365pHC 85 95 90 95 95 80 105 100 70 95 105 105 100 100 115OUD Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes YesUVE Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes YesOXF Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes YesNotesC suitable pH value for the testD oxygen uptake performanceE reversible performance tested by UV-vis spectrumF reversible performance testedby oxygen electrode

in the coordinating abilities of amino acids to Co(II) 119860-pH curves of all the complexes were recorded by UV-visspectrophotometry according to the part of experiment Thesuitable pH for each complex was selected according to these119860-pH curves Table 2 lists the suitable pH for the formationof oxygenated complexes and 120582max

Figure S5 presents the figure of 119860-pH curves for AlandashCo (curve 1) SerndashCo (curve 2) HisndashCo (curve 3) and LysndashCo (curve 4) The suitable pH for the formation of thesecomplexes was concluded to be as follows 93ndash12 (AlandashCo) 95ndash98 (SerndashCo) 78ndash103 (HisndashCo) and 103ndash108 (LysndashCo) their compositions were also determined via molarratio method in corresponding pH and their formulae areCo(Ala)

3 Co(Ser)

2 Co(His)

2 and Co(Lys)

3 respectively

Other amino acidndashCo systems were tested in the samemethod

33 Determination of Reversibility for the Uptake and Releaseof Dioxygen In the N

2atmosphere when Ala and Co(II) salt

solutions were mixed at pH 95 the AlandashCo complex solutionshowed a distinct spectrum with two main absorption peaksat 365 and 540 nm in an aqueous solution thereby indicatingthe formation of the complex (Figure 1(a) curve 1) Whendioxygen was added the absorption intensity of the AlandashCo complex increased abruptly at 365 nm (Figure 1(a) curve11015840) and the color of the solution rapidly changed fromlight pink to orange-yellow hence indicating that AlandashCocould be easily oxygenated in an aqueous solution at roomtemperature This spectral change is caused by the chargetransfer from oxygen to Co(II) (LMCT) [24] When theatmosphere was changed from dinitrogen to dioxygen andsubsequently back to dinitrogen (defined as one cycle) thespectrum changed regularly according to the change of thegas atmosphere (Figure 1(a) curves 2 and 3 for N

2and 21015840

and 31015840 for O2)These results confirmed that the oxygenation-

deoxygenation reactions of AlandashCo are reversible Other 120572-amino acidndashCo complexes were tested in the same mannerThe spectral changes of SerndashCo HisndashCo and LysndashCo dis-played that the oxygenation of these three cobalt complexeswas reversible (Figures 1(b) 1(c) and 1(d)) The spectra ofother cobalt complexes dropped evidently after three cyclesbut the spectra of HisndashCo remained the same after 15 cyclesThese results showed that autoxidation occurred during oxy-genation andHisndashCohad an excellent reversible oxygenation

ability Table 2 provides the results of reversibility for all the15 amino acid complexes

34 OxygenometryMethod Evolution of the dissolved dioxy-gen concentration in airtight complex solutions was exam-ined using a dissolved oxygen meter within the pH rangeof 3ndash11 and subsequently from 11 back to 3 at 250 plusmn 01∘CFigure S6 exhibits the diagrams of the dissolved dioxygenconcentration as a function of pH (from 3 to 11 and back to3) of the AlandashCo SerndashCo HisndashCo and LysndashCo complexesThese concentration curves of the dissolved dioxygen inoxygenation coincidedwell with those of deoxygenation thusindicating that the oxygenation of the complex is reversible

The reversibility of oxygenation for other 120572-amino acidndashCo complexes was also examined in the same procedure andthe results are listed in Table 2 The results obtained fromoxygenometry also agreedwell with those obtained fromUV-vis spectrophotometry

The 15 120572-amino acid complexes have affinities to dioxy-gen and 14 of them could reversibly bind dioxygen at suitablepH values however CysndashCo could only take oxygen but didnot release it (Table 2)

35 Dynamics of Oxygenation-Deoxygenation of the 120572-AminoAcidndashCoComplexes After three oxygenation-deoxygenationcycles the AlandashCo(II) complex still maintained reversibleperformance The time-dependent cycle numbers ofoxygenation-deoxygenation of AlandashCo(II) were determinedto elucidate the complete oxygenation process and antiagingability of the oxygenated complex The time elapsingchanges of absorbance were recorded as N

2and O

2

were alternately bubbled into the system to observe theevolution of the oxygenation species The difference ofabsorbance (Δ119860) under N

2and O

2in one cycle was used

to identify the oxygenation ability of the complex Figure 2represents the oxygenation-deoxygenation kinetics of theAlandashCo(II) complex The AlandashCo(II) complex took about84min to complete one oxygenation-deoxygenation cycleOxygenation spent about 28min whereas deoxygenationtook twice times to complete Kinetics results (Figure 2(a))showed that the AlandashCo complex could sustain eightcontinuous oxygenation-deoxygenation cycles over 10 h inan aqueous solution at room temperature SerndashCo sustained27 cycles in 20 hours (Figure 2(b)) and HisndashCo (Figure 2(c))


1

32

1998400

2998400

3998400

00

02

04

06

08

10Ab

sorb

ance

400 500 600300Wavelength (nm)

(a) AlandashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(b) SerndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

12

14

Abso

rban

ce


(c) HisndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(d) LysndashCo

Figure 1 Reversible performance of LndashCo was determined by UV-vis spectrophotometry (curves 1 2 and 3 were tested in nitrogen andcurves 11015840 21015840 and 31015840 were tested in an oxygen atmosphere)

and LysndashCo (Figure 2(d)) did 550 in 110 h and 20 in 45 hrespectively Other 120572-amino acidndashCo complexes were alsoexamined in the same procedures and the results are listedin Table 3

36 Comparative Study All 15 120572-amino acidndashcobalt com-plexes except for Cys displayed reversible oxygenation prop-erties but exhibited different affinities to dioxygen thereforea systematic comparative study was conducted to revealthe relationship between the structures of amino acids andoxygenation properties of complexes AlandashCo complex onlyhas a methyl connected with 120572-amino acid group thus it wasused as a reference of other 120572-amino acidndashcobalt complexesIn the comparative study except for reversibility the timesof oxygenation and deoxygenation and number of reversiblecycles were involved as the contrast parameters Some ruleswere concluded from the comparative study

4 Discussion

All120572-amino acidndashcobalt complexes exhibit reversible bindingability to dioxygen except for CysndashCo(II) Generally theoxygenation time (119905o) of a complex is shorter than thedeoxygenation time (119905d) for almost all complexes HisndashCoyields the minimum 119905o and 119905d of 1 and 75min respectivelyGlundashCo and AspndashCo reach the maximum 119905o and 119905d of 93 and100min respectively The ligands of the Co complexes werearranged from the shortest to the longest on the basis of theduration dioxygen uptake saturation (119905o min) His (1) Ser(17) Thr (18) Gly (22) Ala (28) (Pro = Arg) (33) Val (35)Met (37) Lys (42) Asn (50) Asp (83) Gln (87) and Glu (93)Likewise the ligands of theCo complexeswere arranged fromthe shortest to the longest on the basis of the duration of thecomplete dioxygen release (119905d min) His (75) Ser (17) Thr(25) Pro (33) Val (50) Ala (56) Met (57) (Arg = Lys) (58)Asn (67) Gly (75) Glu (87) Gln (92) andAsp (100)TheHisndashCo complex requiresmuch less time than the other complexes


50

2nd

100

1st

936586

20

5th

204

5

8th

Time (h)103

O2

O2

O2

O2

O2O2

N2

N2

N260min

60min

00

05

10

15

20

25Ab

sorb

ance

(a) AlandashCo

1st100

044

3rd50

132Time (h)

11th20

553

27th5

1976

O2

O2

O2

O2

O2

N2

00

05

10

15

20

25

30

Abso

rban

ce

(b) SerndashCo

0083 110 715

200th50

30

350th 20

560th 5

Time (h)

O2

O2

O2

N2

1st100

O2

O2

02

04

06

08

10

Abso

rban

ce

557 s

(c) HisndashCo

167 675 1343 4501Time (h)

4th50

8th25

20th5

1st100

O2

O2

O2

O2

O2

N2

00

05

10

15

20

Abso

rban

ce

(d) LysndashCo

Figure 2 Absorbance changes at 120582max when N2and O

2were alternately introduced

do in the oxygenation-deoxygenation process this findingsuggested that the HisndashCo complex is an excellent modelof oxygen carriers According to the theoretical calculationresults 119905d is usually longer than 119905o of these complexeswhen anH bond forms between ligands and when O

2binding occurs

Another important characteristic parameter to evaluatethe oxygenation property of a complex is the number ofoxygenation-deoxygenation cycles Our results suggest thatHisndashCo has the maximum cycle number of 550 whereasGly displays only 2 cycles The ligands of the Co complexeswere arranged from the highest to the lowest dependingon whether they could sustain 5 to 100 of the originaloxygenation capacity His (550) Pro (40) Arg (33) Ser (27)(Glu = Gln) (24) (Val = Lys) (20)Thr (17) Met (16) Asp (12)Asn (11) Ala (8) and Gly (2)

Tables 2 and 3 reveal the results of the comparativeanalyses of one cycle time (119905

119879 119905119879= 119905o+119905d) and cycle numbers

(119862) of 14 120572-amino acidndashcobalt complexesAlandashCo complex took 84min to complete one oxygen-

ation-deoxygenation cycle This complex could also sustain

eight reversible cycles (Table 3) Furthermore GlyndashCo ValndashCo and ProndashCo (97 85 and 66min resp) showed a similarcycle time to that of AlandashCo All of these amino acidshave a similar alkyl radical to Ala thus all these complexeshave a similar coordinating structure Nevertheless the cyclenumbers are decreased in the order of the decrease ofnumbers of carbon atoms in alkyl chain

The oxygenation properties of cobalt complexes of HisSer and Thr are improved evidently when compared withAlandashCo these complexes have cycle times of 85 34 and43min as well as reversible cycle numbers of 550 27 and 17respectively In this study we suppose that this improvementis because they have a heteroatomic group adjacent to theiramino acid group The presence of one more atom fromthe heteroatomic group (NH

2or OH) that coordinates with

amino acid together with Co(II) is helpful to form thecomplexes and enhance the oxygenation ability

The CysndashCo complex could bind to dioxygen but showsno reversibility although it has also one more coordinatingatom this observation is probably because S atom is larger


Table 3 Oxygenation parameters of 15 amino acid complexes

L Gly Ala Val Ser Thr Pro His Cys Met Arg Lys Glu Gln Asn Asp119905o

G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862

1 2 8 20 27 17 40 550 16 33 20 24 24 11 12Notes G 119905o for oxygenation time (minutes) H 119905d for deoxygenation time (minutes) 0 119905119879 for one oxygenation-deoxygenation circulation units minutes1 119862 cycle numbers

and more basic compared with N and O atoms whichincreased the electron density between the metal ions andmolecular oxygen thereby increasing the bond strength ofCondashO

2and making it more difficult to release dioxygen

This result is consistent with the report that the coordinationability will be modestly increased for metal complexes whena ligand contains S group [38]

In contrast to the CysndashCo complex the MetndashCo complexshowed reversible oxygenation patterns similar to that ofAlandashCo with nearly the same time for one oxygenation-deoxygenation cycle (95min and 16 reversible cycles) Thisfinding may be caused by the fact that the aliphatic S atomcannot coordinate with Co(II) because it is far from theamino acid group instead only the 120572-amino acid unit of Metcan coordinate with Co(II) and it behaves the same as Aladoes However the aliphatic S plays a role in the resistanceof the complex to autoxidation by increasing its number ofreversible cycles to 16

Arg and Lys have another ndashNH2group that could act

as a potential coordinating group for the ligands HoweverndashNH2is far from the 120572-amino acid unit as in MetndashCo

hence the coordination between the amino acid and Co(II)is much weaker Thus the dioxygen affinity of the Co(II)complexes for Arg and Lys is similar to that of AlandashCo andtheir cycle times are also almost the same as AlandashCo Theresistance to autoxidation of ArgndashCo and LysndashCo is improvedby their ndashNH

2group and the numbers of their reversible

cycles increased to 33 and 20 respectivelyGlu and Gln have additional ndashCONH

2and ndashCOOH

groups in their structures respectively and they exhibitsimilar oxygenation abilities The second carbonyl in Gluand Gln can be used as coordination group however itdoes not coordinate with its amino acid group together withthe same Co(II) ion Instead this group coordinates withanother Co(II) ion to form linear macromolecule during theformation of the Co(II) complexes Therefore the times forone oxygenation-deoxygenation cycle of Glu and Gln areextended to 180 and 179min respectively and the numbersof their reversible cycles are also improved to 24

Asn also contains one more ndashCONH2group but it

possesses one ndashCH2group less than Glu in its chain The

carbonyl groups inAsn can promote its coordinationwith theCo(II) ion Hence one cycle time of Asn is 117min which isfaster than that of Glu Asp also behaves as Gln and its onecycle time remains at 183min which is nearly the same as thatofGlnNevertheless the reversible cycle numbers of bothAspand Asn are retained at 11 and 12 respectively

All of above 14 oxygenated 120572-amino acidndashcobalt com-plexes have UV-vis absorptionThe characteristic absorptionpeaks of all aliphatic 120572-amino acidndashcobalt complexes aresimilar to one another and appeared at about 365 nm therebyrevealing that oxygenated species of these 120572-amino acidndashcobalt complexes have considerable similarity in terms oftheir coordinating structures and patterns

Somedifferences exist between the oxygenated complexesof HisndashCo and ProndashCo and other oxygenated complexes andthe UV-vis absorption peaks appeared at 374 and 380 nmrespectively The result is attributed to the fact that both ofthese amino acids have an aromatic ring that can stabilizethe complexes and make the absorption band shift to redwaves Based on these results the absorption peak at 365 nmwould be a characteristic absorption peak for the oxygenatedspecies of the complex In such case the UV-vis spectra at365 nmcould be used to characterize the aliphatic oxygenatedcomplexes

On the basis of the comparative studies we proposedthat the 120572-amino acid group is the basic unit responsible forthe reversible oxygenation properties in these 14 complexesOther functional groups can also affect the rate cycle timesand other oxygenation properties The rates and cycle timesof the reversible oxygenation process are mainly determinedby the coordination ability of amino acids Groups suchas imidazole in histidine that can cooperate with the 120572-amino acid to form more stable complexes with Co(II) willcause the HisndashCo complex to exhibit faster oxygenation anddeoxygenation rates

The presence of additional coordinating groups in theamino acids may also affect the oxygenation abilities of thecomplexes The presence of ndashNH

2(or ndashNH) and ndashOH

at a position adjacent to the 120572-amino acid unit couldincrease both oxygenation-deoxygenation rates and numberof reversible cycles The heteroatom group linked with thechain of the 120572-amino acid can inhibit oxidation and increasethe number of cycles

5 Reversible Oxygenation Mechanism

The DFT calculations were conducted for the structuralmodels of the studied compounds and the results of AlandashCo and HisndashCo have been reported [28 39 40] Basedon the theoretical calculation and experimental results theoxygenation mechanism of the Co(II) complexes is proposedas follows


O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+

Figure 3 Formation and oxygenation of the AlandashCo complex

N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N

CoIII CoIIICoIIICoII

CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+

Figure 4 Formation and oxygenation of the HisndashCo complex

When a complex binds to dioxygen the d-orbitals ofCo(II) are split and the distribution of the electrons on the3d orbital is t

2g6eg1 For the oxygenated complexes the energy

level of eg orbitals of Co(II) is fairly close to the energy level of120587lowast orbitals for dioxygenTherefore the electron of eg orbitals

can transfer to 120587lowast orbitals of dioxygen to form the CondashO2

bond [24]The 120572-amino acidndashCo(II) complexes can reversibly bind

to O2depending on the co-coordination of 120572-amino and

carboxyl groups The electronegativity of N atom is smallerthan that of O atom and its lone pair electrons in N arecloser to the central Co(II) as a result the electron clouddensity on Co(II) is increasedThis phenomenon is helpful totransfer the eg

1 electron fromCo(II) to the 120587lowast orbit of O2and

form the CondashO2bond when O

2coordinates with the Co(II)

complex According to the theoretical calculation before andafter oxygenation the bond lengths of NndashC CndashO CondashO andCondashN in the complexes shortened for AlandashCo [39] CondashOandCondashNhave 20889ndash2266 and 22131ndash22137 lengths in thecomplex respectively after oxygenation CondashO and CondashNbecome 1941ndash1984 and 21368ndash22059 respectively For HisndashCo [40] CondashO CondashN and CondashN (imidazole) are 2272320113 and 20775 22847 and 19847 19910 respectivelyin the complex after oxygenation CondashO CondashN and CondashN (imidazole) become 19519 19286 19361 20006 and19632 19580 respectively These results showed that the 120572-amino and carboxyl groups have conjugation in oxygenationThe conjugation of coordinated carboxyl can make CondashO2bond more stable where the peroxo complex forms

With the transition of the electron and conjugation the O2

binding becomes reversible when O2and N

2atmospheres

are alternatively changed The reversible oxygenation of thecomplexes would occur as shown in Figures 3 and 4

6 Conclusions

Our study revealed that the structural detail of 120572-aminoacid plays a key role in determining the reversible oxy-genationdeoxygenation ability of the complexes formed byCo(II) and amino acidWe observed that the auxiliary groupslinked to the 120572-amino acid group can affect the affinitiesof the complexes to dioxygen and their abilities to undergoantiautoxidation In particular the presence of ndashNH

2(or ndash

NH) or ndashOH group at a position adjacent to the aminoacid unit enhances the oxygenation-deoxygenation rates andnumber of reversible cycles A heteroatomgroup linked to thechain of the amino acid improves the resistance to oxidationand may increase the number of reversible cycles Thereforea reversible oxygenation mechanism of amino acidndashCo(II)complexes is proposed that is the coaction of the strongelectron donor of the amino group and conjugation of thecarboxyl group is an important phenomenon of the reversibleoxygenation of these complexes This strategy may provide auseful basis of novel oxygen carriers

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

Financial support from the National Natural Science Foun-dation of China (nos 21162027 and 21261022) is gratefullyacknowledged


References

[1] W Nam Y-M Lee and S Fukuzumi ldquoTuning reactivity andmechanism in oxidation reactions by mononuclear nonhemeiron(IV)-oxo complexesrdquo Accounts of Chemical Research vol47 no 4 pp 1146ndash1154 2014

[2] K P Bryliakov and E P Talsi ldquoActive sites and mechanismsof bioinspired oxidation with H

2O2 catalyzed by non-heme Fe

and related Mn complexesrdquo Coordination Chemistry Reviewsvol 276 pp 73ndash96 2014

[3] S Kim J W Ginsbach A I Billah et al ldquoTuning of the copper-thioether bond in tetradentate N

3S(thioether) Ligands OndashO bond

reductive cleavage via a [CuII2(120583-12-peroxo)]2+[CuIII

2(120583-

oxo)2]2+ equilibriumrdquo Journal of the AmericanChemical Society

vol 136 no 22 pp 8063ndash8071 2014[4] D Das Y-M Lee K Ohkubo W Nam K D Karlin and

S Fukuzumi ldquoTemperature-independent catalytic two-electronreduction of dioxygen by ferrocenes with a copper(II) tris[2-(2-pyridyl)ethyl]amine catalyst in the presence of perchloric acidrdquoJournal of the American Chemical Society vol 135 no 7 pp2825ndash2834 2013

[5] S Fukuzumi L Tahsini Y-M Lee K Ohkubo W Nam andK D Karlin ldquoFactors that control catalytic two-versus four-electron reduction of dioxygen by copper complexesrdquo Journal ofthe American Chemical Society vol 134 no 16 pp 7025ndash70352012

[6] MBaumgartenC JWinscom andWLubitz ldquoProbing the sur-rounding of a cobalt(II) porphyrin and its superoxo complex byEPR techniquesrdquo Applied Magnetic Resonance vol 20 no 1-2pp 35ndash70 2001

[7] N Kindermann S Dechert S Demeshko and F MeyerldquoProton-induced reversible interconversion of a 120583-12-peroxoand a 120583-11-hydroperoxo dicopper(II) complexrdquo Journal of theAmerican Chemical Society vol 137 no 25 pp 8002ndash8005 2015

[8] M Rolff and F Tuczek ldquoHow do copper enzymes hydroxylatealiphatic substrates Recent insights from the chemistry ofmodel systemsrdquo Angewandte ChemiemdashInternational Editionvol 47 no 13 pp 2344ndash2347 2008

[9] B M T Lam J A Halfen V G Young Jr et al ldquoLigandmacrocycle structural effects on copperndashdioxygen reactivityrdquoInorganic Chemistry vol 39 no 18 pp 4059ndash4072 2000

[10] J P Klinman ldquoHow do enzymes activate oxygen withoutinactivating themselvesrdquo Accounts of Chemical Research vol40 no 5 pp 325ndash333 2007

[11] M R Tine ldquoCobalt complexes in aqueous solutions as dioxygencarriersrdquo Coordination Chemistry Reviews vol 256 no 1-2 pp316ndash327 2012

[12] AM J Devoille and J B Love ldquoDouble-pillared cobalt Pacmancomplexes synthesis structures and oxygen reduction cataly-sisrdquo Dalton Transactions vol 41 no 1 pp 65ndash72 2012

[13] M Tonigold Y Lu A Mavrandonakis et al ldquoPyrazolate-based cobalt(II)-containing metal-organic frameworks in het-erogeneous catalytic oxidation reactions elucidating the role ofentatic states for biomimetic oxidation processesrdquo ChemistrymdashA European Journal vol 17 no 31 pp 8671ndash8695 2011

[14] S Hong H So H Yoon et al ldquoReactivity comparison ofhigh-valent iron(iv)-oxo complexes bearing N-tetramethylatedcyclam ligands with different ring sizerdquo Dalton Transactionsvol 42 no 22 pp 7842ndash7845 2013

[15] S P de Visser J-U Rohde Y-M Lee J Cho and W NamldquoIntrinsic properties and reactivities of mononuclear nonheme

ironndashoxygen complexes bearing the tetramethylcyclam ligandrdquoCoordination Chemistry Reviews vol 257 no 2 pp 381ndash3932013

[16] J Cho R Sarangi and W Nam ldquoMononuclear metalndashO2com-

plexes bearing macrocyclic N-tetramethylated cyclam ligandsrdquoAccounts of Chemical Research vol 45 no 8 pp 1321ndash1330 2012

[17] J Cho R Sarangi H Y Kang et al ldquoSynthesis structural andspectroscopic characterization and reactivities of mononuclearcobalt(III)-peroxo complexesrdquo Journal of the American Chemi-cal Society vol 132 no 47 pp 16977ndash16986 2010

[18] A Kunishita M Z Ertem Y Okubo et al ldquoActive site modelsfor the CuA site of peptidylglycine 120572-hydroxylating monooxy-genase and dopamine 120573-monooxygenaserdquo Inorganic Chemistryvol 51 no 17 pp 9465ndash9480 2012

[19] M Martinho G Blain and F Banse ldquoActivation of dioxygen bya mononuclear non-heme iron complex characterization of aFeIII(OOH) intermediaterdquo Dalton Transactions vol 39 no 6pp 1630ndash1634 2010

[20] J A Kovacs ldquoHow iron activates O2rdquo Science vol 299 no 5609

pp 1024ndash1025 2003[21] J Park Y Morimoto Y-M Lee W Nam and S Fukuzumi

ldquoUnified view of oxidative C-H bond cleavage and sulfoxidationby a nonheme iron(IV)-oxo complex via lewis acid-promotedelectron transferrdquo Inorganic Chemistry vol 53 no 7 pp 3618ndash3628 2014

[22] J Park Y-M Lee W Nam and S Fukuzumi ldquoBroslashnsted acid-promotedCndashHbond cleavage via electron transfer from toluenederivatives to a protonated nonheme iron(IV)-oxo complexwith no kinetic isotope effectrdquo Journal of the American ChemicalSociety vol 135 no 13 pp 5052ndash5061 2013

[23] N Kitajima and Y Moro-oka ldquoCopper-dioxygen complexesInorganic and bioinorganic perspectivesrdquo Chemical Reviewsvol 94 no 3 pp 737ndash757 1994

[24] E C Niederhoffer J H Timmons and A E Martell ldquoThermo-dynamics of oxygen binding in natural and synthetic dioxygencomplexesrdquo Chemical Reviews vol 84 no 2 pp 137ndash203 1984

[25] A L Gavrilova C J Qin R D Sommer A L Rheingold andB Bosnich ldquoBimetallic reactivity One-site addition two-metaloxidation reaction of dioxygen with a bimetallic dicobalt(II)complex bearing five- and six-coordinate sitesrdquo Journal of theAmerican Chemical Society vol 124 no 8 pp 1714ndash1722 2002

[26] X Zhang H Furutachi S Fujinami et al ldquoStructural andspectroscopic characterization of (120583-hydroxo or 120583-oxo)(120583-peroxo)diiron(III) complexes models for peroxo intermediatesof non-heme diiron proteinsrdquo Journal of the American ChemicalSociety vol 127 no 3 pp 826ndash827 2005

[27] J Simplicio and R GWilkins ldquoKinetics of the rapid interactionof bis(histidinato)-cobalt(II) with oxygenrdquo Journal of the Amer-ican Chemical Society vol 89 no 24 pp 6092ndash6095 1967

[28] F Yue N Song Y Huang et al ldquoReversible oxygenation ofbis[120573-(2-pyridyl)-120572-alaninato]Co(II) complex in aqueous solu-tion at room temperaturerdquo Inorganica Chimica Acta vol 398pp 141ndash146 2013

[29] J F Li J H Fu C XWang H Li and J DWang ldquoOxygenationreaction and aging mechanism of the triethylenetetraminecobalt complexrdquo Chinese Journal of Inorganic Chemistry vol 31no 4 pp 673ndash680 2015

[30] E Vinck E Carter D M Murphy and S Van DoorslaerldquoObservation of an organic acid mediated spin state transitionin a Co(II)-Schiff base complex an EPR HYSCORE and DFTstudyrdquo Inorganic Chemistry vol 51 no 15 pp 8014ndash8024 2012


[31] C Comuzzi A Melchior P Polese R Portanova and MTolazzi ldquoCobalt(II) dioxygen carriers based on simple diaminoligands kinetic and ab initio studiesrdquo Inorganic Chemistry vol42 no 25 pp 8214ndash8222 2003

[32] D Burk J Z Hearon L Caroline and A L Schade ldquoReversiblecomplexes of cobalt histidine and oxygen gasrdquo The Journal ofBiological Chemistry vol 165 no 2 pp 723ndash724 1946

[33] M SMichailidis and R BMartin ldquoOxygenation and oxidationof cobalt(II) chelates of amines amino acids and dipeptidesrdquoJournal of the American Chemical Society vol 91 no 17 pp4683ndash4689 1969

[34] W R Harris G McLendon and A E Martell ldquoOxygenationequilibriums of cobalt(II) complexes of amino acids and dipep-tidesrdquo Journal of the American Chemical Society vol 98 no 26pp 8378ndash8381 1976

[35] H M Wen X Zhang H Li F Yue and J D Wang ldquoContraststudy of the oxygenation of Co(II) complexes with different bi-poly-dentate ligandsrdquo Chemical Journal of Chinese Universitiesvol 34 no 10 pp 2262ndash2269 2013

[36] X C Zhang F Yue Y Huang et al ldquoReversible oxygenationproperties of 23-diaminopropanoic acid cobalt complexrdquo Chi-nese Journal of Inorganic Chemistry vol 29 no 11 pp 2387ndash2393 2013

[37] M J Frisch G W Trucks H B Schlegel et al GAUSSIAN 03Revision E01 Gaussian Inc Wallingford Conn USA 2004

[38] R D Hancock and A E Martell ldquoLigand design for selectivecomplexation of metal ions in aqueous solutionrdquo ChemicalReviews vol 89 no 8 pp 1875ndash1914 1989

[39] Y L Deng Y Yang and F Yue ldquoCoordination environmenginfluence to the oxygenation performance of alanine cobaltrdquoComputers and Applied Chemistry vol 31 no 3 pp 325ndash3282014

[40] Y Yang Y L Deng F Yue H M Chen D C Sun and J DWang ldquoTheoretical research of cobalt(II)-hisditine oxygenationprocessrdquo Computers and Applied Chemistry vol 30 no 6 pp633ndash637 2013

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


Glycine (Gly) Alanine (Ala) Valine (Val)

XS

Methionine (Met)

HN O

OHProline (Pro)Serine (Ser)

X

HO

Threonine (Thr)

X

Asparagine (Asn)

X

OGlutamine (Gln)

X

HS

Cysteine (Cys)

X

Lysine (Lys)

XHN

NHArginine (Arg)

X

HN

N

Histidine (His)

O

HO

Aspartate (Asp)

X

O

HO

Glutamate (Glu)

COOH

H

R

H X X XHO X

R X

O

Abbr

X

NH2

H2N

H2N

H2N

H2N

H3C

Scheme 1 Structures of 15 natural amino acids

Schiff base ligands and porphyrins are mostly confined inthe reversible oxygenation of oxygenated complexes [11 24]however the reversible oxygenation property of these com-plexes is poor in aqueous solutions and at room temperatureBurk et al investigated histidinendashCo(II) and demonstratedthat oxygenation reversibility occurs in an aqueous solutionat room temperature [32] Considering this previous studyMartell and other researchers examined Co(II) complexeswith amino acids and dipeptides which can reversibly uptakeoxygen [33 34] In our study four groups of ligands withdifferent NO NN and OO difunctional groups [35] suchas amino acids amino alcohols polyamines and multicar-boxylic acids were selected The oxygenation performancesof their Co(II) complexes were comparatively analyzedThe following results were obtained the OO difunctionalgroup of the Co(II) complexes does not possess oxygenationproperties the NN difunctional group of the complexescan uptake oxygen but cannot undergo reversibility theNO-type difunctional group of the complexes is relativelydifferent 120572-amino acidndashCo(II) complexes exhibit evidentreversible oxygen performance and 120572-amino alcoholndashCo(II)complexes uptake oxygen weakly and show no reversibilityHowever studies have yet to determine the factor causing 120572-amino acidndashCo complexes to exhibit oxygenation reversibil-ity

Among Co complexes 120572-amino acidndashCo complexes dis-play different oxygenation reversibilities On the basis of thisunusual finding we supposed that the 120572-amino acid group in

a ligand could be a key group associated with the reversibleoxygenation of such complexes Therefore we synthesized aseries of novel amino acidndashCo(II) complexes and found thatCo complexes can reversibly uptake dioxygen [28 35 36]Indeed the 120572-amino acid unit in a ligand is a key structuralcomponent related to the reversible oxygenation property ofthese complexes

To explore the factors and coordinating structure thatdetermine the oxygenation reversibility of 120572-amino acidndashCo complexes we selected 15 natural water-soluble 120572-aminoacids (Scheme 1) and performed a detailed investigation oftheir oxygenation properties in aqueous solutions at roomtemperature Measurements were conducted at a specific pHrange at which these complexes are in their major states Wealso conducted a thorough comparative analysis to determinethe relationship between the structures of ligands and thedioxygen affinity of Co complexes

This study aimed to determine the basic structural unitresponsible for the reversible dioxygen uptake This studyalso aimed to identify the auxiliary functional groups thatimprove the reversibility of dioxygen uptake We believe thatour findings would remarkably contribute to elucidating andrevealing the oxygenation mechanism of oxygen carriers

2 Experimental

21 Materials Amino acids and Co(CH3COO)

2sdot4H2O were

purchased from Shanghai Aladdin Reagents Co Ltd




minus3 60 033 05 10 10 0028 033 10 01 025 02 10 10 20 20119888L times 10



2and N

2







2and N



2(119860O) and N






2in















3 Co(Ser)

2 Co(His)

2 and Co(Lys)

3 respectively





2and 21015840








2and O

2


2and O




1

32

1998400

2998400

3998400

00

02

04

06

08

10Ab

sorb

ance


(a) AlandashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(b) SerndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

12

14

Abso

rban

ce


(c) HisndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(d) LysndashCo




4 Discussion



50

2nd

100

1st

936586

20

5th

204

5

8th

Time (h)103

O2

O2

O2

O2

O2O2

N2

N2

N260min

60min

00

05

10

15

20

25Ab

sorb

ance

(a) AlandashCo

1st100

044

3rd50

132Time (h)

11th20

553

27th5

1976

O2

O2

O2

O2

O2

N2

00

05

10

15

20

25

30

Abso

rban

ce

(b) SerndashCo

0083 110 715

200th50

30

350th 20

560th 5

Time (h)

O2

O2

O2

N2

1st100

O2

O2

02

04

06

08

10

Abso

rban

ce

557 s

(c) HisndashCo

167 675 1343 4501Time (h)

4th50

8th25

20th5

1st100

O2

O2

O2

O2

O2

N2

00

05

10

15

20

Abso

rban

ce

(d) LysndashCo




2binding occurs














G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862











2and ndashCOOH














O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




minus3 60 033 05 10 10 0028 033 10 01 025 02 10 10 20 20119888L times 10



2and N

2







2and N



2(119860O) and N






2in















3 Co(Ser)

2 Co(His)

2 and Co(Lys)

3 respectively





2and 21015840








2and O

2


2and O




1

32

1998400

2998400

3998400

00

02

04

06

08

10Ab

sorb

ance


(a) AlandashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(b) SerndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

12

14

Abso

rban

ce


(c) HisndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(d) LysndashCo




4 Discussion



50

2nd

100

1st

936586

20

5th

204

5

8th

Time (h)103

O2

O2

O2

O2

O2O2

N2

N2

N260min

60min

00

05

10

15

20

25Ab

sorb

ance

(a) AlandashCo

1st100

044

3rd50

132Time (h)

11th20

553

27th5

1976

O2

O2

O2

O2

O2

N2

00

05

10

15

20

25

30

Abso

rban

ce

(b) SerndashCo

0083 110 715

200th50

30

350th 20

560th 5

Time (h)

O2

O2

O2

N2

1st100

O2

O2

02

04

06

08

10

Abso

rban

ce

557 s

(c) HisndashCo

167 675 1343 4501Time (h)

4th50

8th25

20th5

1st100

O2

O2

O2

O2

O2

N2

00

05

10

15

20

Abso

rban

ce

(d) LysndashCo




2binding occurs














G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862











2and ndashCOOH














O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






3 Co(Ser)

2 Co(His)

2 and Co(Lys)

3 respectively





2and 21015840








2and O

2


2and O




1

32

1998400

2998400

3998400

00

02

04

06

08

10Ab

sorb

ance


(a) AlandashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(b) SerndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

12

14

Abso

rban

ce


(c) HisndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(d) LysndashCo




4 Discussion



50

2nd

100

1st

936586

20

5th

204

5

8th

Time (h)103

O2

O2

O2

O2

O2O2

N2

N2

N260min

60min

00

05

10

15

20

25Ab

sorb

ance

(a) AlandashCo

1st100

044

3rd50

132Time (h)

11th20

553

27th5

1976

O2

O2

O2

O2

O2

N2

00

05

10

15

20

25

30

Abso

rban

ce

(b) SerndashCo

0083 110 715

200th50

30

350th 20

560th 5

Time (h)

O2

O2

O2

N2

1st100

O2

O2

02

04

06

08

10

Abso

rban

ce

557 s

(c) HisndashCo

167 675 1343 4501Time (h)

4th50

8th25

20th5

1st100

O2

O2

O2

O2

O2

N2

00

05

10

15

20

Abso

rban

ce

(d) LysndashCo




2binding occurs














G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862











2and ndashCOOH














O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


1

32

1998400

2998400

3998400

00

02

04

06

08

10Ab

sorb

ance


(a) AlandashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(b) SerndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

12

14

Abso

rban

ce


(c) HisndashCo

1

32

1998400

2998400

3998400

00

02

04

06

08

10

Abso

rban

ce


(d) LysndashCo




4 Discussion



50

2nd

100

1st

936586

20

5th

204

5

8th

Time (h)103

O2

O2

O2

O2

O2O2

N2

N2

N260min

60min

00

05

10

15

20

25Ab

sorb

ance

(a) AlandashCo

1st100

044

3rd50

132Time (h)

11th20

553

27th5

1976

O2

O2

O2

O2

O2

N2

00

05

10

15

20

25

30

Abso

rban

ce

(b) SerndashCo

0083 110 715

200th50

30

350th 20

560th 5

Time (h)

O2

O2

O2

N2

1st100

O2

O2

02

04

06

08

10

Abso

rban

ce

557 s

(c) HisndashCo

167 675 1343 4501Time (h)

4th50

8th25

20th5

1st100

O2

O2

O2

O2

O2

N2

00

05

10

15

20

Abso

rban

ce

(d) LysndashCo




2binding occurs














G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862











2and ndashCOOH














O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


50

2nd

100

1st

936586

20

5th

204

5

8th

Time (h)103

O2

O2

O2

O2

O2O2

N2

N2

N260min

60min

00

05

10

15

20

25Ab

sorb

ance

(a) AlandashCo

1st100

044

3rd50

132Time (h)

11th20

553

27th5

1976

O2

O2

O2

O2

O2

N2

00

05

10

15

20

25

30

Abso

rban

ce

(b) SerndashCo

0083 110 715

200th50

30

350th 20

560th 5

Time (h)

O2

O2

O2

N2

1st100

O2

O2

02

04

06

08

10

Abso

rban

ce

557 s

(c) HisndashCo

167 675 1343 4501Time (h)

4th50

8th25

20th5

1st100

O2

O2

O2

O2

O2

N2

00

05

10

15

20

Abso

rban

ce

(d) LysndashCo




2binding occurs














G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862











2and ndashCOOH














O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




G 22 28 35 17 18 33 1 2 37 33 42 93 87 50 83119905d

H 75 56 50 17 25 33 75 57 58 58 87 92 67 100119905119879

0 97 84 85 34 43 66 85 95 91 100 180 179 117 183119862











2and ndashCOOH














O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


O

O O

OO

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

OO

O

2minus

Step 1 Step 2

O O

OO

O

O

O2

N2 NH2H2 H2N

CoIICoIIOminus

minusH+

NH3

N

H2N

H2N

H2N

H2N H2N

CoIII CoIII CoIII

H2N H2N

NH2

H2

N

minus

+


N

NH

O O

N

HN

OO

N

NH

O

OO

NNH

OO N

HN

O

O

NHN

O

O

NNH

O

O

N NHO

O

NHN

O

O

O

O

Step 1 Step 2

O2

N2

H2N H2N


CoII

NH3

Ominus

minusH+

H2

NH2N

H2N NH2

NH2NH2

+















2atmospheres


6 Conclusions


2(or ndash




Acknowledgment



References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


References








2(120583-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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