Research ArticleA CV Study of Copper Complexation with Guanine UsingGlassy Carbon Electrode in Aqueous Medium
Md Sohel Rana1 Mohammad Arifur Rahman2 and A M Shafiqul Alam2
1 Department of Chemistry Chittagong University of Engineering amp Technology Chittagong 4349 Bangladesh2Department of Chemistry University of Dhaka Dhaka 1000 Bangladesh
Correspondence should be addressed to Md Sohel Rana mdsohelrananbdgmailcom andA M Shafiqul Alam amsalam2010gmailcom
Received 22 February 2014 Accepted 18 March 2014 Published 2 April 2014
Academic Editors H Karimi-Maleh and B Lakard
Copyright copy 2014 Md Sohel Rana et alThis is an open access article distributed under the Creative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Voltammetric behaviors of Copper (II) nitrogen bearing nucleobases such as Guanine (C5H4N5O2) was studied in electro analyzer
using cyclic voltammetry (CV) on a Glassy Carbon Electrode Assessment of the chemical and physical conditions that may favoroptimum current enhancement was done by studying the effect of variation of concentration of metal and ligand ions variation ofscan rate variation of step height variation of pHvalues and variation of supporting electrolyte as (NH
4)2SO4 KCl andNaCl It was
observed that Copper and Guanine forms a 1 2 ratio complex The work reflects that increasing the concentration of either metalion or ligand ion increases the corresponding current Increasing the scan rate increases the corresponding current linearly with thesquare root of the scan rate As the step height decreases the peaks become sharp Anodic and cathodic current increases linearlywith decreasing step height For the complexmixture the complexation occursmaximum at a pH of 23ndash70 and is badly restricted inthe slightly alkaline medium and the complexing order of the supporting electrolyte showed a trend as (NH
4)2SO4gt NaCl gt KCl
1 Introduction
The complexation of organic compounds with selected metalion has a wide variety of application in medicinal chemistrysurface chemistry and analytical chemistry Complexation ofmedicinal substances with ions influence the bioavailabilityof drugs in the body and the biological action that affectsthe stability of medicinal compounds since a large numberof metals are taken into the body system either with drugsor in the form of diet The complex formation has beensuggested as one of the important mechanisms for certaindrug action [1] The metal chelating phenomena are usedto reduce the toxic effect of drugs in human physiologyThe studies of redox behavior biologically and biochemicallyimportant compound are gaining importance because suchredox phenomena are close to natural processes occurring inhuman and living organism
Toxicmetals are generallymore important than abundantmetals in terms of environmental pollution because of theireffects on living organismsThe study of trace metals toxicity
on biological system [2 3] indicates that an under supplywould not yield steady growth and over supply would notabove the threshold level generate toxicity with lethality atthe end At least twenty metals are known to be toxic and halfof these including As Cd Cr Cu Pb Ni Ag Se Mn and Znare released into the environment in sufficient quantities topose a risk to human health [4ndash6]
Copper (II) ions (Cu2+) are soluble in water where theyfunction at low concentration as bacteriostatic substancesfungicides and wood preservatives In sufficient amountscopper salts can be poisonous to higher organisms as wellHowever despite universal toxicity at high concentrationsthe Cu2+ ion at lower concentrations is an essential tracenutrient to all higher plant and animal life In animals includ-ing humans it is found widely in tissues with concentrationin liver muscle and bone It functions as a co-factor invarious enzymes and in copper-based pigments
Nucleobases are nitrogen-containing biological com-pounds found within DNA RNA nucleotides and nucleo-sides They are also termed as nitrogenous bases or simply
Hindawi Publishing CorporationISRN ElectrochemistryVolume 2014 Article ID 308382 7 pageshttpdxdoiorg1011552014308382
2 ISRN Electrochemistry
HN
N
O
NH
N
H2N
Scheme 1 Chemical structure of guanine
bases due to their ability to form base-pairs and to stackupon one another leading directly to the helical structure ofDNA and RNAThe primary Nucleobases bases are cytosineguanine (Scheme 1) adenine (DNA and RNA) thymine(DNA) and uracil (RNA) abbreviated as C G A T and Urespectively
In DNA guanine is paired with cytosine With the for-mula C
5H5N5O guanine is a derivative of purine consisting
of a fused pyrimidine-imidazole ring system with conjugateddouble bonds Being unsaturated the bicyclic molecule isplanar Guanine has the C-6 carbonyl group that acts as thehydrogen bond acceptor while a group at N-1 and the aminogroup at C-2 act as the hydrogen bond donors
Metals in the ionic forms have essential catalytic phys-iological functions to perform in living systems includinghuman [7] Excess metal ions in human system can damagespecific organs Free metal ions are more toxic than metalchelates Thus the chelating agents are used in medicine forthe formation of soluble easily extractable metal chelates bysequestering metal ions in the circulation of blood In thepresent research guanine have been used to form complexwith the free metal ion and to study how it can be made non-toxic in the body Since chelation is the elimination of all thebinding sites in the metal ion and as such chemical bonds toessential enzymes cannot be formed lowering of toxicity bychelation of metal ions is ensured [8 9]
Guanine is a critical component of DNA it has extraduties to perform in the cell including defying the charac-teristics of the living body In other words they functionas character determiner Interestingly guanine functions bybinding to phosphate group and form guanosine and takespart in cell mechanism with thymine This later involvesnumerous enzymatic reactions necessary for sustaining lifeand protecting the cell from toxins either that produced byour cells or carcinogenic in our environment
Thus researches on synthesis and properties of variousmetal-amino acid complexes are important from the viewpoint of chemistry bio-chemistry and medical scienceAttempts have been made in the present work to synthesizecopper complex of guanine in order to gain greater insightin the metal interaction with guanine which could helpto understand the role of metal ions and Nucleobases inthe biological process Not too much research work wascarried out with metal-ligand complex in searching theirelectrochemical behavior
Electrochemical techniques based on electrochemicalsensors are the most versatile analytical tool to study the
redox behavior and to diagnose electro-active species in thefield of chemistry biochemistry pharmacy food science [10]and environmental science Electrochemical sensors [11] aremostly based on the redox behavior of the analytes forexample gas molecules ions and drugs Sensitivity to a widerange of chemical species has made electrochemical sensoran essential tool for analysis and monitoring of pollutantsmedicine narcotics neurotransmitters and so forth
In this present work we are interested in investigatingthe electrochemical behavior of those complexes and theirinfluence in our body system Hence the study the redoxbehavior of guanine at GCE electrode and its complexationwith Cu has been investigated in aqueous medium byusing electrochemical methods Cyclic voltammetric studiesof copper (II) and its complex with guanine to reveal theredox behavior in aqueous environment Thus a systematicapproachwith themode of formation and structural relation-ship with properties of this new compound may be derivedfrom such study
chased from China Extra pure acetic acid (BDH England)and phosphoric acid (BDH England) were procured forbuffer
22 Measurements CuSO4sdot5H2Owas dissolved in deionized
water to prepare 05ndash20mM solutions Guanine solutionswere prepared in slightly acidic medium (dil HCl) uponwarmingThe sodium acetate buffer solutionwas prepared bytaking 01MCH
3COONa and 01MCH
3COOHof solutions
at different ratiosThephosphate buffer solutionwas preparedby mixing 01M di-sodium hydrogen phosphate 01M HCland 01M NaOH solutions in different ratios Milli-Q deion-ized water used throughout the experiment
GCE was polished with fine alumina powder of 03 andthen 003 micron sized on a wet polishing lather surfaceFor doing so a part of the lather surface was made wetwith deionized water and alumina powder was sprinkledover it The GCE was then polished on this surface forabout 10ndash20 minutes by pressing softly the electrode againstthe polishing surface A shiny black mirror like electrodesurface was then thoroughly washed with deionized waterUnder computer controlled magnetic stirring experimentalsolution was deaerated by purging for at least 10 minutes with999977 pure nitrogen gas before performing every exper-iment Traces of dissolved oxygen gas were thus removedfrom the solutionThus interference due tomolecular oxygendissolved in the solutions was eliminated from the CyclicVoltammograms
Three electrodes system consists of a GCE as the workingelectrode AgAgCl (satd KCl) as the reference electrodeand platinum wire as the counter electrode was used CyclicVoltammetricmeasurementwas performedusingComputer-ized Electrochemical System Model HQ-2040 developed byAdvanced Analytics USA
Figure 1 Cyclic Voltammogram of 05mM Cu2+ in presence of02MKCl atminus800mV to 650mVpotential window 5mV step heightand 100mV sminus1 scan rate
05mM guanine with 02M KCl
8
6
4
2
0
minus2
minus4
minus6
minus8
minus10minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
Figure 2 Cyclic Voltammogram of 05mM guanine in presenceof 02M KCl at minus1000mV to 800mV potential window 5mV stepheight and 100mV sminus1 scan rate
3 Results and Discussion
The redox behavior of Cu (II) in copper (II) sulphate wasexamined in 02M KCl by Cyclic Voltammetric technique onglassy carbon electrode at room temperature
From Figure 1 it is observed that Cu2+ solution iselectroactive as it gives two cathodic and two anodic peaksFirst anodic peak current is 80760120583Aandpotential is 125mVSecond anodic peak current is 317697 120583A and potential isminus185mV First cathodic peak current is 755120583A and potentialis 55mV Second cathodic peak current is 1260 120583A andpotential is minus425mV This implies that the Cu2+ system is atwo electron reversible system
Figure 3 Cyclic Voltammograms of copper ion copper-guaninecomplex and guanine in presence of 02M KCl
HN HN
N
O
NH
N1
2
4
56
7
8
9
6
3N
O
NH
N1
2
4
56
7
8
9
6
3H2N H2N
(a) (b)H+
Scheme 2 Structure of guanine (a) non-protonated (b) protonated
31 Characterization of Copper-Guanine Complex CyclicVoltammogram of 05mM guanine in presence of 02M KClat minus1000mV to 800mV potential window 5mV step heightand 100mVsminus1 scan rate was taken
From Figure 2 it is observed that it has an anodic peak atminus200mVpotential having peak current of 37511 120583A It provesthat guanine is an electroactive compound and an irreversiblesystem [12]The complexation ratio of copper-guanine is 1 2confirmed by Jobs Continuous Variation Method and MoleRatio Method
311 Proposed Structure of the Copper-Guanine Complex InFigure 3 a comparison has been depicted to understand thebehavior of changing peak current
Figure 3 illustrates that due to complex formation peakcurrent of copper ion decreases while that of guanineincreases
In acidic medium ring nitrogen N(3) of guanine isprotonated (Scheme 2)
The guanine complexes of several metal ions such asAl(III) Co(II) Cu(II) Zn(II) Pt(II) and Pd(II) have beenreported earlier [13 14] It is found from the literature [15 16]
4 ISRN Electrochemistry
N
HN
N
O
Cu2+ N
NH
N
NH2O
[(C5H4N5 O)2Cu]
H2N
Nminus
Nminus
Scheme 3 Proposed structure of copper (II) and guanine complex
that guanine binds with metal ions through carbonyl oxygenO(6) andor imidazolyl nitrogen N(7) Early transitionmetalions show a preference for the O(6) position while later onesprefer N(7) However the information available in this regardis very limited to understand the potential binding sites ofguanine and the possible mechanism of interaction betweenguanine and the various metal ions
Attempts have been made to obtain the complex insolid form for further structural analysis but due to theinstable nature of the complex as the individual componentsprecipitate out with increasing pH it was not possible toaccumulate more structural analysis data to confirm thestructure of the complex
However from our observations and literature reviewScheme 3 could be proposed as the structure of copper (II)and guanine complex [17 18]
312 Variation of Cu2+ Concentration Cyclic Voltammo-gram of 025mM guanine at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent Cu2+ ion concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofthe Cu2+ increases more reactions take place [19] and moreelectrons are transferred so anodic and cathodic currentsincrease As the complex is formed the anodic and cathodicpotential shifts their position to more positive direction
313 Variation of Guanine Concentration Cyclic Voltam-mogram of 025mM Cu2+ at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent guanine concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofguanine increases the more reactions take place [20] andmore electrons are transferred so anodic and cathodic currentincrease As the complex is formed the anodic and cathodicpotential shifts their position to more negative direction Asguanine is a least electroactive substance the addition ofguanine increases less amount of current compared to theaddition of Cu2+ in guanine
mm m
m m
80
60
40
20
0
minus20
minus40
Scan rate 25Scan rate 50Scan rate 75
Scan rate 100Scan rate 125
minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
V sminus1V sminus1V sminus1
V sminus1V sminus1
Figure 4 Cyclic Voltammogram of 06mM Cu2+ and 12mMguanine at minus1000mV to +600mV potential window and 20mVstep height in presence of 02M KCl as supporting electrolyte anddifferent scan rates (25 50 75 100 and 125mV sminus1)
314 Variation of Scan Rate Cyclic Voltammogram of06mM Cu2+ and 12mM guanine at minus1000mV to +600mVpotential window and 20mV step height in presence of 02MKCl as supporting electrolyte and different scan rates (25 5075 100 and 125mV sminus1) was taken (Figure 4)
The intensity for both the anodic and cathodic peaks iscontrolled by the following equation
119894119901= 269 times 10
5sdot 11989932sdot 119860 sdot 119863
12sdot 119862 sdot V12 (1)
where 119894119901= peak current in ampere 119899 = electron stoichiome-
try119860 = area of the electrode in cm2119863 = diffusion coefficientin cm2s 119862 = concentration of the species in molcm3 andV = scan rate in voltss
Two plots of anodic peak current versus square root ofthe scan rate and cathodic peak current versus square rootof the scan rate are shown in the Figure 5 which depictthe comparison of their increasing and decreasing trendrespectively
The electrochemical processes are diffusion controlledwhich can be explained from the graph of 119894
119901versus V12
as shown in Figure 4 First anodic current increases from1358 120583A to 3464 120583A and second anodic current increasesfrom 1643 120583A to 5713 120583A First cathodic current increasesfrom 427120583A to 1106 120583A and second cathodic currentincreases from 1284 120583A to 2426120583A From Figure 4 it canbe explained that as the scan rate of the complex mixturesincreases the corresponding current increases but anodicand cathodic potential shift very little [21 22]
315 Variation of Step Height Cyclic Voltammogram of025mMCu2+and 050mM guanine at minus800mV to +600mVpotential window at 100mVS scan rate at different stepheight (20 25 30 35 and 40mV) was taken It is observed
ISRN Electrochemistry 5
40
30
20
10
0
minus10
minus204 5 6 7 8 9 10 11 12
First anodic peak current First cathodic peak current
Peak
curr
enti p
(120583A
)
v12
versus v12
versus v12
Figure 5 Peak current versus square root of the scan rate for copperand guanine complex
Second anodic current Second cathodic current
50
50 60
40
40
30
30
20
20
10
10
0
minus10
minus20
Step height (mV)
Peak
curr
ent (120583
A)
versus step heightversus step height
Figure 6 Peak current versus step height for Cu2+ and guanineComplex
as the anodic and cathodic current decreases linearly withincreasing step height
Moreover in the lower step height the peak becomessharper This might happen as the interaction between themetal ions and ligand ions decreases with increasing stepheight and complex formation decrease and consequentlyanodic and cathodic current decreases with increasing stepheight [23]
Plotting peak current versus step height Figure 6 isobtained and it shows a straight line with negative slopewhich indicates that the increase in step height decreases thepeak current
316 Variation of pH Cyclic Voltammogram of 025mMCu2+and 050mM guanine at minus800mV to +600mV potential
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
40
30
20
10
0
minus10
minus20
minus30
minus40
pH 230
pH 700
pH 100
Curr
ent (120583
A)
Figure 7 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVS scanrate and 20mV step height at different pH Values ( 230 700 and100)
window at 100mVS scan rate and 20mV step height atdifferent pH Values (230 700 and 100) was taken (Figure 7)to see the effect of pH on the complex At lower pH theH+ ion can compete with Cu2+ ion for ligand in solutionBut an increase in pH value will reduce the concentrationof hydrogen ions which allows greater complex formationbetween Cu2+ and guanine There was a little increase inpeak current of Cu2+ guanine complex species below pH70From pH 70 onwards the peak current increased sharply theoptimum pH range appears to be between pH 23 and 70
317 Variation of Supporting Electrolyte Figure 8 illustratesthe effect of variation of supporting electrolyte on the elec-trochemical behavior of copper complexation with guanine
Any species that compete with metal ion for the surfaceof the electrode would inevitably interfere in the adsorptionof metal thyminate complex species hence leading to adecrease in the increase in current effect [24] This explainswhy the supporting electrolyte such as (NH
4)2SO4 which
is weakly complexing produce higher current as comparedto NaCl and KCl More over in case of NaCl and KCl bothare Chloride containing Supporting electrolyte but NaCl isweakly complexing compared to KCl produces more currentin the anodic and cathodic peak So the order of the anodicand cathodic current enlargement is (NH
4)2SO4gt NaCl gt
KCl
4 Conclusions
The results indicated that guanine is electroactive atminus1000mV to 800mV potential window and 100mV sminus1 scanrate as it has an anodic peak at minus200mV potential havingpeak current of 37511120583A in the Cyclic Voltammogram Cu
6 ISRN Electrochemistry
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
30
20
10
0
minus10
minus20
minus30
minus40
02 M KCl02 M NaCl02 M (NH4)2SO4
Curr
ent (120583
A)
Figure 8 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVSscan rate and 20mV step height in presence of different Supportingelectrolytes (02M KCl 02M NaCl and 02M (NH
4)2SO4)
(II) is electroactive as it gives two cathodic and two anodicpeaks Two anodic peaks are at 125 mV and minus185 mV and twocathodic peaks at 55mV and minus425mV which indicate thatCu (II) is two electron processes
Complex formation of metal ion and ligands wereobserved according to Jobs Method and Mole Ratio MethodCu (II) forms 1 2 complexes with guanine Probable struc-tures of the complexes of copper with guanine have beenproposed which is being supported by the previous works
As the concentration of any component increases inter-action between the metal and ligand increases more com-plexes are formed more electrons are transferred and con-sequently current increases Scan rate was varied for all themetal and ligand pairs which indicates the increase in scanrate increases the number of time of current scanning inthe system per second increases Hence the correspondingcurrent also increases Plot of the peak current versus squareroot of scan rate gives straight line with positive slope passingthrough origins which indicate that the peak current isdirectly proportional to the square root of the scan rate
Step height was varied from 20mV to 40mV for copperand guanine complex which implies that the correspondinganodic and cathodic current decreases with increasing stepheight it is due to less interaction between the metal andligand ions and fewer complexes are formed
The pH value of the complex mixture was varied from23 to 100 for all metal and ligand complex mixture by usingacetate and phosphate buffers At a lower pH the H+ioncompete with metal ions and less complexes are formed lesscurrent is obtained increasing pH value from 23 to 100 andcurrent increases and becomesmaximum and then decreasesrapidly with increasing pH value That implies the complexis favored to slightly acidic medium and slightly alkaline
medium The optimum pH range can be considered as 23 to70 for the complexes of copper with guanine and thymine
The supporting electrolytes were used as (NH4)2SO4
NaCl and KCl for all metal and ligand pair complex ratioMore interaction occurs when SO2minus
4containing supporting
electrolyte (NH4)2SO4is used compared to chloride contain-
ing supporting electrolyte KCl and NaCl As Na is below K inthe electrochemical series has higher tendency to be reducedcompared to K so less current is found for KCl than NaClSo the complexation tendency of the supporting electrolytesfollows the decreasing order (NH
4)2SO4gt NaCl gt KCl
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] N FarrellTransitionMetal Complexes as Drugs and Chemother-apeutic Agents vol 11 Springer 1989
[2] U C Gupta and S C Gupta ldquoTrace element toxicity rela-tionships to crop production and livestock and human healthimplications for managementrdquo Communications in Soil Scienceand Plant Analysis vol 29 no 11ndash14 pp 1491ndash1522 1998
[3] B A Chowdhury and R K Chandra ldquoBiological and healthimplications of toxic heavy metal and essential trace elementinteractionsrdquo Progress in Food amp Nutrition Science vol 11 no 1pp 57ndash113 1987
[4] V Mudgal N Madaan A Mudgal R B Singh and S MishraldquoEffect of toxic metals on human healthrdquoThe Open Nutraceuti-cals Journal vol 3 pp 94ndash99 2010
[5] J O Nriagu ldquoA silent epidemic of environmental metal poison-ingrdquo Environmental Pollution vol 50 no 1-2 pp 139ndash161 1988
[6] J N Galloway J DThornton S A Norton H L Volchok andR A N McLean ldquoTrace-metals in atmospheric deposition areview and assessmentrdquo Atmospheric Environment vol 16 no7 pp 1677ndash1700 1982
[7] W Zheng M Aschner and J-F Ghersi-Egea ldquoBrain barriersystems a new frontier in metal neurotoxicological researchrdquoToxicology and Applied Pharmacology vol 192 no 1 pp 1ndash112003
[8] H V Aposhian R M Maiorino D Gonzalez-Ramirez et alldquoMobilization of heavy metals by newer therapeutically usefulchelating agentsrdquo Toxicology vol 97 no 1ndash3 pp 23ndash38 1995
[9] S J S Flora M Mittal and A Mehta ldquoHeavy metal inducedoxidative stress amp its possible reversal by chelation therapyrdquoIndian Journal of Medical Research vol 128 no 4 pp 501ndash5232008
[10] M Elyasi M A Khalilzadeh and H Karimi-Maleh ldquoHigh sen-sitive voltammetric sensor based on PtCNTs nanocompositemodified ionic liquid carbon paste electrode for determinationof Sudan I in food samplesrdquo Food Chemistry vol 141 no 4 pp4311ndash4317 1996
[11] H Karimi-Maleh P Biparva andMHatami ldquoA novelmodifiedcarbon paste electrode based onNiOCNTs nanocomposite and(9 10-dihydro-9 10-ethanoanthracene-11 12-dicarboximido)-4-ethylbenzene-1 2-diol as a mediator for simultaneous deter-mination of cysteamine nicotinamide adenine dinucleotideand folic acidrdquo Biosensors and Bioelectronics vol 48 pp 270ndash275 2013
ISRN Electrochemistry 7
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
bases due to their ability to form base-pairs and to stackupon one another leading directly to the helical structure ofDNA and RNAThe primary Nucleobases bases are cytosineguanine (Scheme 1) adenine (DNA and RNA) thymine(DNA) and uracil (RNA) abbreviated as C G A T and Urespectively
In DNA guanine is paired with cytosine With the for-mula C
5H5N5O guanine is a derivative of purine consisting
of a fused pyrimidine-imidazole ring system with conjugateddouble bonds Being unsaturated the bicyclic molecule isplanar Guanine has the C-6 carbonyl group that acts as thehydrogen bond acceptor while a group at N-1 and the aminogroup at C-2 act as the hydrogen bond donors
Metals in the ionic forms have essential catalytic phys-iological functions to perform in living systems includinghuman [7] Excess metal ions in human system can damagespecific organs Free metal ions are more toxic than metalchelates Thus the chelating agents are used in medicine forthe formation of soluble easily extractable metal chelates bysequestering metal ions in the circulation of blood In thepresent research guanine have been used to form complexwith the free metal ion and to study how it can be made non-toxic in the body Since chelation is the elimination of all thebinding sites in the metal ion and as such chemical bonds toessential enzymes cannot be formed lowering of toxicity bychelation of metal ions is ensured [8 9]
Guanine is a critical component of DNA it has extraduties to perform in the cell including defying the charac-teristics of the living body In other words they functionas character determiner Interestingly guanine functions bybinding to phosphate group and form guanosine and takespart in cell mechanism with thymine This later involvesnumerous enzymatic reactions necessary for sustaining lifeand protecting the cell from toxins either that produced byour cells or carcinogenic in our environment
Thus researches on synthesis and properties of variousmetal-amino acid complexes are important from the viewpoint of chemistry bio-chemistry and medical scienceAttempts have been made in the present work to synthesizecopper complex of guanine in order to gain greater insightin the metal interaction with guanine which could helpto understand the role of metal ions and Nucleobases inthe biological process Not too much research work wascarried out with metal-ligand complex in searching theirelectrochemical behavior
Electrochemical techniques based on electrochemicalsensors are the most versatile analytical tool to study the
redox behavior and to diagnose electro-active species in thefield of chemistry biochemistry pharmacy food science [10]and environmental science Electrochemical sensors [11] aremostly based on the redox behavior of the analytes forexample gas molecules ions and drugs Sensitivity to a widerange of chemical species has made electrochemical sensoran essential tool for analysis and monitoring of pollutantsmedicine narcotics neurotransmitters and so forth
In this present work we are interested in investigatingthe electrochemical behavior of those complexes and theirinfluence in our body system Hence the study the redoxbehavior of guanine at GCE electrode and its complexationwith Cu has been investigated in aqueous medium byusing electrochemical methods Cyclic voltammetric studiesof copper (II) and its complex with guanine to reveal theredox behavior in aqueous environment Thus a systematicapproachwith themode of formation and structural relation-ship with properties of this new compound may be derivedfrom such study
chased from China Extra pure acetic acid (BDH England)and phosphoric acid (BDH England) were procured forbuffer
22 Measurements CuSO4sdot5H2Owas dissolved in deionized
water to prepare 05ndash20mM solutions Guanine solutionswere prepared in slightly acidic medium (dil HCl) uponwarmingThe sodium acetate buffer solutionwas prepared bytaking 01MCH
3COONa and 01MCH
3COOHof solutions
at different ratiosThephosphate buffer solutionwas preparedby mixing 01M di-sodium hydrogen phosphate 01M HCland 01M NaOH solutions in different ratios Milli-Q deion-ized water used throughout the experiment
GCE was polished with fine alumina powder of 03 andthen 003 micron sized on a wet polishing lather surfaceFor doing so a part of the lather surface was made wetwith deionized water and alumina powder was sprinkledover it The GCE was then polished on this surface forabout 10ndash20 minutes by pressing softly the electrode againstthe polishing surface A shiny black mirror like electrodesurface was then thoroughly washed with deionized waterUnder computer controlled magnetic stirring experimentalsolution was deaerated by purging for at least 10 minutes with999977 pure nitrogen gas before performing every exper-iment Traces of dissolved oxygen gas were thus removedfrom the solutionThus interference due tomolecular oxygendissolved in the solutions was eliminated from the CyclicVoltammograms
Three electrodes system consists of a GCE as the workingelectrode AgAgCl (satd KCl) as the reference electrodeand platinum wire as the counter electrode was used CyclicVoltammetricmeasurementwas performedusingComputer-ized Electrochemical System Model HQ-2040 developed byAdvanced Analytics USA
Figure 1 Cyclic Voltammogram of 05mM Cu2+ in presence of02MKCl atminus800mV to 650mVpotential window 5mV step heightand 100mV sminus1 scan rate
05mM guanine with 02M KCl
8
6
4
2
0
minus2
minus4
minus6
minus8
minus10minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
Figure 2 Cyclic Voltammogram of 05mM guanine in presenceof 02M KCl at minus1000mV to 800mV potential window 5mV stepheight and 100mV sminus1 scan rate
3 Results and Discussion
The redox behavior of Cu (II) in copper (II) sulphate wasexamined in 02M KCl by Cyclic Voltammetric technique onglassy carbon electrode at room temperature
From Figure 1 it is observed that Cu2+ solution iselectroactive as it gives two cathodic and two anodic peaksFirst anodic peak current is 80760120583Aandpotential is 125mVSecond anodic peak current is 317697 120583A and potential isminus185mV First cathodic peak current is 755120583A and potentialis 55mV Second cathodic peak current is 1260 120583A andpotential is minus425mV This implies that the Cu2+ system is atwo electron reversible system
Figure 3 Cyclic Voltammograms of copper ion copper-guaninecomplex and guanine in presence of 02M KCl
HN HN
N
O
NH
N1
2
4
56
7
8
9
6
3N
O
NH
N1
2
4
56
7
8
9
6
3H2N H2N
(a) (b)H+
Scheme 2 Structure of guanine (a) non-protonated (b) protonated
31 Characterization of Copper-Guanine Complex CyclicVoltammogram of 05mM guanine in presence of 02M KClat minus1000mV to 800mV potential window 5mV step heightand 100mVsminus1 scan rate was taken
From Figure 2 it is observed that it has an anodic peak atminus200mVpotential having peak current of 37511 120583A It provesthat guanine is an electroactive compound and an irreversiblesystem [12]The complexation ratio of copper-guanine is 1 2confirmed by Jobs Continuous Variation Method and MoleRatio Method
311 Proposed Structure of the Copper-Guanine Complex InFigure 3 a comparison has been depicted to understand thebehavior of changing peak current
Figure 3 illustrates that due to complex formation peakcurrent of copper ion decreases while that of guanineincreases
In acidic medium ring nitrogen N(3) of guanine isprotonated (Scheme 2)
The guanine complexes of several metal ions such asAl(III) Co(II) Cu(II) Zn(II) Pt(II) and Pd(II) have beenreported earlier [13 14] It is found from the literature [15 16]
4 ISRN Electrochemistry
N
HN
N
O
Cu2+ N
NH
N
NH2O
[(C5H4N5 O)2Cu]
H2N
Nminus
Nminus
Scheme 3 Proposed structure of copper (II) and guanine complex
that guanine binds with metal ions through carbonyl oxygenO(6) andor imidazolyl nitrogen N(7) Early transitionmetalions show a preference for the O(6) position while later onesprefer N(7) However the information available in this regardis very limited to understand the potential binding sites ofguanine and the possible mechanism of interaction betweenguanine and the various metal ions
Attempts have been made to obtain the complex insolid form for further structural analysis but due to theinstable nature of the complex as the individual componentsprecipitate out with increasing pH it was not possible toaccumulate more structural analysis data to confirm thestructure of the complex
However from our observations and literature reviewScheme 3 could be proposed as the structure of copper (II)and guanine complex [17 18]
312 Variation of Cu2+ Concentration Cyclic Voltammo-gram of 025mM guanine at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent Cu2+ ion concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofthe Cu2+ increases more reactions take place [19] and moreelectrons are transferred so anodic and cathodic currentsincrease As the complex is formed the anodic and cathodicpotential shifts their position to more positive direction
313 Variation of Guanine Concentration Cyclic Voltam-mogram of 025mM Cu2+ at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent guanine concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofguanine increases the more reactions take place [20] andmore electrons are transferred so anodic and cathodic currentincrease As the complex is formed the anodic and cathodicpotential shifts their position to more negative direction Asguanine is a least electroactive substance the addition ofguanine increases less amount of current compared to theaddition of Cu2+ in guanine
mm m
m m
80
60
40
20
0
minus20
minus40
Scan rate 25Scan rate 50Scan rate 75
Scan rate 100Scan rate 125
minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
V sminus1V sminus1V sminus1
V sminus1V sminus1
Figure 4 Cyclic Voltammogram of 06mM Cu2+ and 12mMguanine at minus1000mV to +600mV potential window and 20mVstep height in presence of 02M KCl as supporting electrolyte anddifferent scan rates (25 50 75 100 and 125mV sminus1)
314 Variation of Scan Rate Cyclic Voltammogram of06mM Cu2+ and 12mM guanine at minus1000mV to +600mVpotential window and 20mV step height in presence of 02MKCl as supporting electrolyte and different scan rates (25 5075 100 and 125mV sminus1) was taken (Figure 4)
The intensity for both the anodic and cathodic peaks iscontrolled by the following equation
119894119901= 269 times 10
5sdot 11989932sdot 119860 sdot 119863
12sdot 119862 sdot V12 (1)
where 119894119901= peak current in ampere 119899 = electron stoichiome-
try119860 = area of the electrode in cm2119863 = diffusion coefficientin cm2s 119862 = concentration of the species in molcm3 andV = scan rate in voltss
Two plots of anodic peak current versus square root ofthe scan rate and cathodic peak current versus square rootof the scan rate are shown in the Figure 5 which depictthe comparison of their increasing and decreasing trendrespectively
The electrochemical processes are diffusion controlledwhich can be explained from the graph of 119894
119901versus V12
as shown in Figure 4 First anodic current increases from1358 120583A to 3464 120583A and second anodic current increasesfrom 1643 120583A to 5713 120583A First cathodic current increasesfrom 427120583A to 1106 120583A and second cathodic currentincreases from 1284 120583A to 2426120583A From Figure 4 it canbe explained that as the scan rate of the complex mixturesincreases the corresponding current increases but anodicand cathodic potential shift very little [21 22]
315 Variation of Step Height Cyclic Voltammogram of025mMCu2+and 050mM guanine at minus800mV to +600mVpotential window at 100mVS scan rate at different stepheight (20 25 30 35 and 40mV) was taken It is observed
ISRN Electrochemistry 5
40
30
20
10
0
minus10
minus204 5 6 7 8 9 10 11 12
First anodic peak current First cathodic peak current
Peak
curr
enti p
(120583A
)
v12
versus v12
versus v12
Figure 5 Peak current versus square root of the scan rate for copperand guanine complex
Second anodic current Second cathodic current
50
50 60
40
40
30
30
20
20
10
10
0
minus10
minus20
Step height (mV)
Peak
curr
ent (120583
A)
versus step heightversus step height
Figure 6 Peak current versus step height for Cu2+ and guanineComplex
as the anodic and cathodic current decreases linearly withincreasing step height
Moreover in the lower step height the peak becomessharper This might happen as the interaction between themetal ions and ligand ions decreases with increasing stepheight and complex formation decrease and consequentlyanodic and cathodic current decreases with increasing stepheight [23]
Plotting peak current versus step height Figure 6 isobtained and it shows a straight line with negative slopewhich indicates that the increase in step height decreases thepeak current
316 Variation of pH Cyclic Voltammogram of 025mMCu2+and 050mM guanine at minus800mV to +600mV potential
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
40
30
20
10
0
minus10
minus20
minus30
minus40
pH 230
pH 700
pH 100
Curr
ent (120583
A)
Figure 7 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVS scanrate and 20mV step height at different pH Values ( 230 700 and100)
window at 100mVS scan rate and 20mV step height atdifferent pH Values (230 700 and 100) was taken (Figure 7)to see the effect of pH on the complex At lower pH theH+ ion can compete with Cu2+ ion for ligand in solutionBut an increase in pH value will reduce the concentrationof hydrogen ions which allows greater complex formationbetween Cu2+ and guanine There was a little increase inpeak current of Cu2+ guanine complex species below pH70From pH 70 onwards the peak current increased sharply theoptimum pH range appears to be between pH 23 and 70
317 Variation of Supporting Electrolyte Figure 8 illustratesthe effect of variation of supporting electrolyte on the elec-trochemical behavior of copper complexation with guanine
Any species that compete with metal ion for the surfaceof the electrode would inevitably interfere in the adsorptionof metal thyminate complex species hence leading to adecrease in the increase in current effect [24] This explainswhy the supporting electrolyte such as (NH
4)2SO4 which
is weakly complexing produce higher current as comparedto NaCl and KCl More over in case of NaCl and KCl bothare Chloride containing Supporting electrolyte but NaCl isweakly complexing compared to KCl produces more currentin the anodic and cathodic peak So the order of the anodicand cathodic current enlargement is (NH
4)2SO4gt NaCl gt
KCl
4 Conclusions
The results indicated that guanine is electroactive atminus1000mV to 800mV potential window and 100mV sminus1 scanrate as it has an anodic peak at minus200mV potential havingpeak current of 37511120583A in the Cyclic Voltammogram Cu
6 ISRN Electrochemistry
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
30
20
10
0
minus10
minus20
minus30
minus40
02 M KCl02 M NaCl02 M (NH4)2SO4
Curr
ent (120583
A)
Figure 8 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVSscan rate and 20mV step height in presence of different Supportingelectrolytes (02M KCl 02M NaCl and 02M (NH
4)2SO4)
(II) is electroactive as it gives two cathodic and two anodicpeaks Two anodic peaks are at 125 mV and minus185 mV and twocathodic peaks at 55mV and minus425mV which indicate thatCu (II) is two electron processes
Complex formation of metal ion and ligands wereobserved according to Jobs Method and Mole Ratio MethodCu (II) forms 1 2 complexes with guanine Probable struc-tures of the complexes of copper with guanine have beenproposed which is being supported by the previous works
As the concentration of any component increases inter-action between the metal and ligand increases more com-plexes are formed more electrons are transferred and con-sequently current increases Scan rate was varied for all themetal and ligand pairs which indicates the increase in scanrate increases the number of time of current scanning inthe system per second increases Hence the correspondingcurrent also increases Plot of the peak current versus squareroot of scan rate gives straight line with positive slope passingthrough origins which indicate that the peak current isdirectly proportional to the square root of the scan rate
Step height was varied from 20mV to 40mV for copperand guanine complex which implies that the correspondinganodic and cathodic current decreases with increasing stepheight it is due to less interaction between the metal andligand ions and fewer complexes are formed
The pH value of the complex mixture was varied from23 to 100 for all metal and ligand complex mixture by usingacetate and phosphate buffers At a lower pH the H+ioncompete with metal ions and less complexes are formed lesscurrent is obtained increasing pH value from 23 to 100 andcurrent increases and becomesmaximum and then decreasesrapidly with increasing pH value That implies the complexis favored to slightly acidic medium and slightly alkaline
medium The optimum pH range can be considered as 23 to70 for the complexes of copper with guanine and thymine
The supporting electrolytes were used as (NH4)2SO4
NaCl and KCl for all metal and ligand pair complex ratioMore interaction occurs when SO2minus
4containing supporting
electrolyte (NH4)2SO4is used compared to chloride contain-
ing supporting electrolyte KCl and NaCl As Na is below K inthe electrochemical series has higher tendency to be reducedcompared to K so less current is found for KCl than NaClSo the complexation tendency of the supporting electrolytesfollows the decreasing order (NH
4)2SO4gt NaCl gt KCl
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] N FarrellTransitionMetal Complexes as Drugs and Chemother-apeutic Agents vol 11 Springer 1989
[2] U C Gupta and S C Gupta ldquoTrace element toxicity rela-tionships to crop production and livestock and human healthimplications for managementrdquo Communications in Soil Scienceand Plant Analysis vol 29 no 11ndash14 pp 1491ndash1522 1998
[3] B A Chowdhury and R K Chandra ldquoBiological and healthimplications of toxic heavy metal and essential trace elementinteractionsrdquo Progress in Food amp Nutrition Science vol 11 no 1pp 57ndash113 1987
[4] V Mudgal N Madaan A Mudgal R B Singh and S MishraldquoEffect of toxic metals on human healthrdquoThe Open Nutraceuti-cals Journal vol 3 pp 94ndash99 2010
[5] J O Nriagu ldquoA silent epidemic of environmental metal poison-ingrdquo Environmental Pollution vol 50 no 1-2 pp 139ndash161 1988
[6] J N Galloway J DThornton S A Norton H L Volchok andR A N McLean ldquoTrace-metals in atmospheric deposition areview and assessmentrdquo Atmospheric Environment vol 16 no7 pp 1677ndash1700 1982
[7] W Zheng M Aschner and J-F Ghersi-Egea ldquoBrain barriersystems a new frontier in metal neurotoxicological researchrdquoToxicology and Applied Pharmacology vol 192 no 1 pp 1ndash112003
[8] H V Aposhian R M Maiorino D Gonzalez-Ramirez et alldquoMobilization of heavy metals by newer therapeutically usefulchelating agentsrdquo Toxicology vol 97 no 1ndash3 pp 23ndash38 1995
[9] S J S Flora M Mittal and A Mehta ldquoHeavy metal inducedoxidative stress amp its possible reversal by chelation therapyrdquoIndian Journal of Medical Research vol 128 no 4 pp 501ndash5232008
[10] M Elyasi M A Khalilzadeh and H Karimi-Maleh ldquoHigh sen-sitive voltammetric sensor based on PtCNTs nanocompositemodified ionic liquid carbon paste electrode for determinationof Sudan I in food samplesrdquo Food Chemistry vol 141 no 4 pp4311ndash4317 1996
[11] H Karimi-Maleh P Biparva andMHatami ldquoA novelmodifiedcarbon paste electrode based onNiOCNTs nanocomposite and(9 10-dihydro-9 10-ethanoanthracene-11 12-dicarboximido)-4-ethylbenzene-1 2-diol as a mediator for simultaneous deter-mination of cysteamine nicotinamide adenine dinucleotideand folic acidrdquo Biosensors and Bioelectronics vol 48 pp 270ndash275 2013
ISRN Electrochemistry 7
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
Figure 1 Cyclic Voltammogram of 05mM Cu2+ in presence of02MKCl atminus800mV to 650mVpotential window 5mV step heightand 100mV sminus1 scan rate
05mM guanine with 02M KCl
8
6
4
2
0
minus2
minus4
minus6
minus8
minus10minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
Figure 2 Cyclic Voltammogram of 05mM guanine in presenceof 02M KCl at minus1000mV to 800mV potential window 5mV stepheight and 100mV sminus1 scan rate
3 Results and Discussion
The redox behavior of Cu (II) in copper (II) sulphate wasexamined in 02M KCl by Cyclic Voltammetric technique onglassy carbon electrode at room temperature
From Figure 1 it is observed that Cu2+ solution iselectroactive as it gives two cathodic and two anodic peaksFirst anodic peak current is 80760120583Aandpotential is 125mVSecond anodic peak current is 317697 120583A and potential isminus185mV First cathodic peak current is 755120583A and potentialis 55mV Second cathodic peak current is 1260 120583A andpotential is minus425mV This implies that the Cu2+ system is atwo electron reversible system
Figure 3 Cyclic Voltammograms of copper ion copper-guaninecomplex and guanine in presence of 02M KCl
HN HN
N
O
NH
N1
2
4
56
7
8
9
6
3N
O
NH
N1
2
4
56
7
8
9
6
3H2N H2N
(a) (b)H+
Scheme 2 Structure of guanine (a) non-protonated (b) protonated
31 Characterization of Copper-Guanine Complex CyclicVoltammogram of 05mM guanine in presence of 02M KClat minus1000mV to 800mV potential window 5mV step heightand 100mVsminus1 scan rate was taken
From Figure 2 it is observed that it has an anodic peak atminus200mVpotential having peak current of 37511 120583A It provesthat guanine is an electroactive compound and an irreversiblesystem [12]The complexation ratio of copper-guanine is 1 2confirmed by Jobs Continuous Variation Method and MoleRatio Method
311 Proposed Structure of the Copper-Guanine Complex InFigure 3 a comparison has been depicted to understand thebehavior of changing peak current
Figure 3 illustrates that due to complex formation peakcurrent of copper ion decreases while that of guanineincreases
In acidic medium ring nitrogen N(3) of guanine isprotonated (Scheme 2)
The guanine complexes of several metal ions such asAl(III) Co(II) Cu(II) Zn(II) Pt(II) and Pd(II) have beenreported earlier [13 14] It is found from the literature [15 16]
4 ISRN Electrochemistry
N
HN
N
O
Cu2+ N
NH
N
NH2O
[(C5H4N5 O)2Cu]
H2N
Nminus
Nminus
Scheme 3 Proposed structure of copper (II) and guanine complex
that guanine binds with metal ions through carbonyl oxygenO(6) andor imidazolyl nitrogen N(7) Early transitionmetalions show a preference for the O(6) position while later onesprefer N(7) However the information available in this regardis very limited to understand the potential binding sites ofguanine and the possible mechanism of interaction betweenguanine and the various metal ions
Attempts have been made to obtain the complex insolid form for further structural analysis but due to theinstable nature of the complex as the individual componentsprecipitate out with increasing pH it was not possible toaccumulate more structural analysis data to confirm thestructure of the complex
However from our observations and literature reviewScheme 3 could be proposed as the structure of copper (II)and guanine complex [17 18]
312 Variation of Cu2+ Concentration Cyclic Voltammo-gram of 025mM guanine at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent Cu2+ ion concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofthe Cu2+ increases more reactions take place [19] and moreelectrons are transferred so anodic and cathodic currentsincrease As the complex is formed the anodic and cathodicpotential shifts their position to more positive direction
313 Variation of Guanine Concentration Cyclic Voltam-mogram of 025mM Cu2+ at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent guanine concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofguanine increases the more reactions take place [20] andmore electrons are transferred so anodic and cathodic currentincrease As the complex is formed the anodic and cathodicpotential shifts their position to more negative direction Asguanine is a least electroactive substance the addition ofguanine increases less amount of current compared to theaddition of Cu2+ in guanine
mm m
m m
80
60
40
20
0
minus20
minus40
Scan rate 25Scan rate 50Scan rate 75
Scan rate 100Scan rate 125
minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
V sminus1V sminus1V sminus1
V sminus1V sminus1
Figure 4 Cyclic Voltammogram of 06mM Cu2+ and 12mMguanine at minus1000mV to +600mV potential window and 20mVstep height in presence of 02M KCl as supporting electrolyte anddifferent scan rates (25 50 75 100 and 125mV sminus1)
314 Variation of Scan Rate Cyclic Voltammogram of06mM Cu2+ and 12mM guanine at minus1000mV to +600mVpotential window and 20mV step height in presence of 02MKCl as supporting electrolyte and different scan rates (25 5075 100 and 125mV sminus1) was taken (Figure 4)
The intensity for both the anodic and cathodic peaks iscontrolled by the following equation
119894119901= 269 times 10
5sdot 11989932sdot 119860 sdot 119863
12sdot 119862 sdot V12 (1)
where 119894119901= peak current in ampere 119899 = electron stoichiome-
try119860 = area of the electrode in cm2119863 = diffusion coefficientin cm2s 119862 = concentration of the species in molcm3 andV = scan rate in voltss
Two plots of anodic peak current versus square root ofthe scan rate and cathodic peak current versus square rootof the scan rate are shown in the Figure 5 which depictthe comparison of their increasing and decreasing trendrespectively
The electrochemical processes are diffusion controlledwhich can be explained from the graph of 119894
119901versus V12
as shown in Figure 4 First anodic current increases from1358 120583A to 3464 120583A and second anodic current increasesfrom 1643 120583A to 5713 120583A First cathodic current increasesfrom 427120583A to 1106 120583A and second cathodic currentincreases from 1284 120583A to 2426120583A From Figure 4 it canbe explained that as the scan rate of the complex mixturesincreases the corresponding current increases but anodicand cathodic potential shift very little [21 22]
315 Variation of Step Height Cyclic Voltammogram of025mMCu2+and 050mM guanine at minus800mV to +600mVpotential window at 100mVS scan rate at different stepheight (20 25 30 35 and 40mV) was taken It is observed
ISRN Electrochemistry 5
40
30
20
10
0
minus10
minus204 5 6 7 8 9 10 11 12
First anodic peak current First cathodic peak current
Peak
curr
enti p
(120583A
)
v12
versus v12
versus v12
Figure 5 Peak current versus square root of the scan rate for copperand guanine complex
Second anodic current Second cathodic current
50
50 60
40
40
30
30
20
20
10
10
0
minus10
minus20
Step height (mV)
Peak
curr
ent (120583
A)
versus step heightversus step height
Figure 6 Peak current versus step height for Cu2+ and guanineComplex
as the anodic and cathodic current decreases linearly withincreasing step height
Moreover in the lower step height the peak becomessharper This might happen as the interaction between themetal ions and ligand ions decreases with increasing stepheight and complex formation decrease and consequentlyanodic and cathodic current decreases with increasing stepheight [23]
Plotting peak current versus step height Figure 6 isobtained and it shows a straight line with negative slopewhich indicates that the increase in step height decreases thepeak current
316 Variation of pH Cyclic Voltammogram of 025mMCu2+and 050mM guanine at minus800mV to +600mV potential
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
40
30
20
10
0
minus10
minus20
minus30
minus40
pH 230
pH 700
pH 100
Curr
ent (120583
A)
Figure 7 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVS scanrate and 20mV step height at different pH Values ( 230 700 and100)
window at 100mVS scan rate and 20mV step height atdifferent pH Values (230 700 and 100) was taken (Figure 7)to see the effect of pH on the complex At lower pH theH+ ion can compete with Cu2+ ion for ligand in solutionBut an increase in pH value will reduce the concentrationof hydrogen ions which allows greater complex formationbetween Cu2+ and guanine There was a little increase inpeak current of Cu2+ guanine complex species below pH70From pH 70 onwards the peak current increased sharply theoptimum pH range appears to be between pH 23 and 70
317 Variation of Supporting Electrolyte Figure 8 illustratesthe effect of variation of supporting electrolyte on the elec-trochemical behavior of copper complexation with guanine
Any species that compete with metal ion for the surfaceof the electrode would inevitably interfere in the adsorptionof metal thyminate complex species hence leading to adecrease in the increase in current effect [24] This explainswhy the supporting electrolyte such as (NH
4)2SO4 which
is weakly complexing produce higher current as comparedto NaCl and KCl More over in case of NaCl and KCl bothare Chloride containing Supporting electrolyte but NaCl isweakly complexing compared to KCl produces more currentin the anodic and cathodic peak So the order of the anodicand cathodic current enlargement is (NH
4)2SO4gt NaCl gt
KCl
4 Conclusions
The results indicated that guanine is electroactive atminus1000mV to 800mV potential window and 100mV sminus1 scanrate as it has an anodic peak at minus200mV potential havingpeak current of 37511120583A in the Cyclic Voltammogram Cu
6 ISRN Electrochemistry
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
30
20
10
0
minus10
minus20
minus30
minus40
02 M KCl02 M NaCl02 M (NH4)2SO4
Curr
ent (120583
A)
Figure 8 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVSscan rate and 20mV step height in presence of different Supportingelectrolytes (02M KCl 02M NaCl and 02M (NH
4)2SO4)
(II) is electroactive as it gives two cathodic and two anodicpeaks Two anodic peaks are at 125 mV and minus185 mV and twocathodic peaks at 55mV and minus425mV which indicate thatCu (II) is two electron processes
Complex formation of metal ion and ligands wereobserved according to Jobs Method and Mole Ratio MethodCu (II) forms 1 2 complexes with guanine Probable struc-tures of the complexes of copper with guanine have beenproposed which is being supported by the previous works
As the concentration of any component increases inter-action between the metal and ligand increases more com-plexes are formed more electrons are transferred and con-sequently current increases Scan rate was varied for all themetal and ligand pairs which indicates the increase in scanrate increases the number of time of current scanning inthe system per second increases Hence the correspondingcurrent also increases Plot of the peak current versus squareroot of scan rate gives straight line with positive slope passingthrough origins which indicate that the peak current isdirectly proportional to the square root of the scan rate
Step height was varied from 20mV to 40mV for copperand guanine complex which implies that the correspondinganodic and cathodic current decreases with increasing stepheight it is due to less interaction between the metal andligand ions and fewer complexes are formed
The pH value of the complex mixture was varied from23 to 100 for all metal and ligand complex mixture by usingacetate and phosphate buffers At a lower pH the H+ioncompete with metal ions and less complexes are formed lesscurrent is obtained increasing pH value from 23 to 100 andcurrent increases and becomesmaximum and then decreasesrapidly with increasing pH value That implies the complexis favored to slightly acidic medium and slightly alkaline
medium The optimum pH range can be considered as 23 to70 for the complexes of copper with guanine and thymine
The supporting electrolytes were used as (NH4)2SO4
NaCl and KCl for all metal and ligand pair complex ratioMore interaction occurs when SO2minus
4containing supporting
electrolyte (NH4)2SO4is used compared to chloride contain-
ing supporting electrolyte KCl and NaCl As Na is below K inthe electrochemical series has higher tendency to be reducedcompared to K so less current is found for KCl than NaClSo the complexation tendency of the supporting electrolytesfollows the decreasing order (NH
4)2SO4gt NaCl gt KCl
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] N FarrellTransitionMetal Complexes as Drugs and Chemother-apeutic Agents vol 11 Springer 1989
[2] U C Gupta and S C Gupta ldquoTrace element toxicity rela-tionships to crop production and livestock and human healthimplications for managementrdquo Communications in Soil Scienceand Plant Analysis vol 29 no 11ndash14 pp 1491ndash1522 1998
[3] B A Chowdhury and R K Chandra ldquoBiological and healthimplications of toxic heavy metal and essential trace elementinteractionsrdquo Progress in Food amp Nutrition Science vol 11 no 1pp 57ndash113 1987
[4] V Mudgal N Madaan A Mudgal R B Singh and S MishraldquoEffect of toxic metals on human healthrdquoThe Open Nutraceuti-cals Journal vol 3 pp 94ndash99 2010
[5] J O Nriagu ldquoA silent epidemic of environmental metal poison-ingrdquo Environmental Pollution vol 50 no 1-2 pp 139ndash161 1988
[6] J N Galloway J DThornton S A Norton H L Volchok andR A N McLean ldquoTrace-metals in atmospheric deposition areview and assessmentrdquo Atmospheric Environment vol 16 no7 pp 1677ndash1700 1982
[7] W Zheng M Aschner and J-F Ghersi-Egea ldquoBrain barriersystems a new frontier in metal neurotoxicological researchrdquoToxicology and Applied Pharmacology vol 192 no 1 pp 1ndash112003
[8] H V Aposhian R M Maiorino D Gonzalez-Ramirez et alldquoMobilization of heavy metals by newer therapeutically usefulchelating agentsrdquo Toxicology vol 97 no 1ndash3 pp 23ndash38 1995
[9] S J S Flora M Mittal and A Mehta ldquoHeavy metal inducedoxidative stress amp its possible reversal by chelation therapyrdquoIndian Journal of Medical Research vol 128 no 4 pp 501ndash5232008
[10] M Elyasi M A Khalilzadeh and H Karimi-Maleh ldquoHigh sen-sitive voltammetric sensor based on PtCNTs nanocompositemodified ionic liquid carbon paste electrode for determinationof Sudan I in food samplesrdquo Food Chemistry vol 141 no 4 pp4311ndash4317 1996
[11] H Karimi-Maleh P Biparva andMHatami ldquoA novelmodifiedcarbon paste electrode based onNiOCNTs nanocomposite and(9 10-dihydro-9 10-ethanoanthracene-11 12-dicarboximido)-4-ethylbenzene-1 2-diol as a mediator for simultaneous deter-mination of cysteamine nicotinamide adenine dinucleotideand folic acidrdquo Biosensors and Bioelectronics vol 48 pp 270ndash275 2013
ISRN Electrochemistry 7
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
Scheme 3 Proposed structure of copper (II) and guanine complex
that guanine binds with metal ions through carbonyl oxygenO(6) andor imidazolyl nitrogen N(7) Early transitionmetalions show a preference for the O(6) position while later onesprefer N(7) However the information available in this regardis very limited to understand the potential binding sites ofguanine and the possible mechanism of interaction betweenguanine and the various metal ions
Attempts have been made to obtain the complex insolid form for further structural analysis but due to theinstable nature of the complex as the individual componentsprecipitate out with increasing pH it was not possible toaccumulate more structural analysis data to confirm thestructure of the complex
However from our observations and literature reviewScheme 3 could be proposed as the structure of copper (II)and guanine complex [17 18]
312 Variation of Cu2+ Concentration Cyclic Voltammo-gram of 025mM guanine at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent Cu2+ ion concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofthe Cu2+ increases more reactions take place [19] and moreelectrons are transferred so anodic and cathodic currentsincrease As the complex is formed the anodic and cathodicpotential shifts their position to more positive direction
313 Variation of Guanine Concentration Cyclic Voltam-mogram of 025mM Cu2+ at minus800mV to 650mV potentialwindow and 20mV step height and 100mV sminus1 scan rate inpresence of 02M KCl as supporting electrolyte and differ-ent guanine concentrations (025mM 050mM 075mM100mM and 125mM) reflects that as the concentration ofguanine increases the more reactions take place [20] andmore electrons are transferred so anodic and cathodic currentincrease As the complex is formed the anodic and cathodicpotential shifts their position to more negative direction Asguanine is a least electroactive substance the addition ofguanine increases less amount of current compared to theaddition of Cu2+ in guanine
mm m
m m
80
60
40
20
0
minus20
minus40
Scan rate 25Scan rate 50Scan rate 75
Scan rate 100Scan rate 125
minus1200 minus800 minus400 0 400 800
E (mV) versus AgAgCl (satd KCl)
Curr
ent (120583
A)
V sminus1V sminus1V sminus1
V sminus1V sminus1
Figure 4 Cyclic Voltammogram of 06mM Cu2+ and 12mMguanine at minus1000mV to +600mV potential window and 20mVstep height in presence of 02M KCl as supporting electrolyte anddifferent scan rates (25 50 75 100 and 125mV sminus1)
314 Variation of Scan Rate Cyclic Voltammogram of06mM Cu2+ and 12mM guanine at minus1000mV to +600mVpotential window and 20mV step height in presence of 02MKCl as supporting electrolyte and different scan rates (25 5075 100 and 125mV sminus1) was taken (Figure 4)
The intensity for both the anodic and cathodic peaks iscontrolled by the following equation
119894119901= 269 times 10
5sdot 11989932sdot 119860 sdot 119863
12sdot 119862 sdot V12 (1)
where 119894119901= peak current in ampere 119899 = electron stoichiome-
try119860 = area of the electrode in cm2119863 = diffusion coefficientin cm2s 119862 = concentration of the species in molcm3 andV = scan rate in voltss
Two plots of anodic peak current versus square root ofthe scan rate and cathodic peak current versus square rootof the scan rate are shown in the Figure 5 which depictthe comparison of their increasing and decreasing trendrespectively
The electrochemical processes are diffusion controlledwhich can be explained from the graph of 119894
119901versus V12
as shown in Figure 4 First anodic current increases from1358 120583A to 3464 120583A and second anodic current increasesfrom 1643 120583A to 5713 120583A First cathodic current increasesfrom 427120583A to 1106 120583A and second cathodic currentincreases from 1284 120583A to 2426120583A From Figure 4 it canbe explained that as the scan rate of the complex mixturesincreases the corresponding current increases but anodicand cathodic potential shift very little [21 22]
315 Variation of Step Height Cyclic Voltammogram of025mMCu2+and 050mM guanine at minus800mV to +600mVpotential window at 100mVS scan rate at different stepheight (20 25 30 35 and 40mV) was taken It is observed
ISRN Electrochemistry 5
40
30
20
10
0
minus10
minus204 5 6 7 8 9 10 11 12
First anodic peak current First cathodic peak current
Peak
curr
enti p
(120583A
)
v12
versus v12
versus v12
Figure 5 Peak current versus square root of the scan rate for copperand guanine complex
Second anodic current Second cathodic current
50
50 60
40
40
30
30
20
20
10
10
0
minus10
minus20
Step height (mV)
Peak
curr
ent (120583
A)
versus step heightversus step height
Figure 6 Peak current versus step height for Cu2+ and guanineComplex
as the anodic and cathodic current decreases linearly withincreasing step height
Moreover in the lower step height the peak becomessharper This might happen as the interaction between themetal ions and ligand ions decreases with increasing stepheight and complex formation decrease and consequentlyanodic and cathodic current decreases with increasing stepheight [23]
Plotting peak current versus step height Figure 6 isobtained and it shows a straight line with negative slopewhich indicates that the increase in step height decreases thepeak current
316 Variation of pH Cyclic Voltammogram of 025mMCu2+and 050mM guanine at minus800mV to +600mV potential
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
40
30
20
10
0
minus10
minus20
minus30
minus40
pH 230
pH 700
pH 100
Curr
ent (120583
A)
Figure 7 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVS scanrate and 20mV step height at different pH Values ( 230 700 and100)
window at 100mVS scan rate and 20mV step height atdifferent pH Values (230 700 and 100) was taken (Figure 7)to see the effect of pH on the complex At lower pH theH+ ion can compete with Cu2+ ion for ligand in solutionBut an increase in pH value will reduce the concentrationof hydrogen ions which allows greater complex formationbetween Cu2+ and guanine There was a little increase inpeak current of Cu2+ guanine complex species below pH70From pH 70 onwards the peak current increased sharply theoptimum pH range appears to be between pH 23 and 70
317 Variation of Supporting Electrolyte Figure 8 illustratesthe effect of variation of supporting electrolyte on the elec-trochemical behavior of copper complexation with guanine
Any species that compete with metal ion for the surfaceof the electrode would inevitably interfere in the adsorptionof metal thyminate complex species hence leading to adecrease in the increase in current effect [24] This explainswhy the supporting electrolyte such as (NH
4)2SO4 which
is weakly complexing produce higher current as comparedto NaCl and KCl More over in case of NaCl and KCl bothare Chloride containing Supporting electrolyte but NaCl isweakly complexing compared to KCl produces more currentin the anodic and cathodic peak So the order of the anodicand cathodic current enlargement is (NH
4)2SO4gt NaCl gt
KCl
4 Conclusions
The results indicated that guanine is electroactive atminus1000mV to 800mV potential window and 100mV sminus1 scanrate as it has an anodic peak at minus200mV potential havingpeak current of 37511120583A in the Cyclic Voltammogram Cu
6 ISRN Electrochemistry
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
30
20
10
0
minus10
minus20
minus30
minus40
02 M KCl02 M NaCl02 M (NH4)2SO4
Curr
ent (120583
A)
Figure 8 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVSscan rate and 20mV step height in presence of different Supportingelectrolytes (02M KCl 02M NaCl and 02M (NH
4)2SO4)
(II) is electroactive as it gives two cathodic and two anodicpeaks Two anodic peaks are at 125 mV and minus185 mV and twocathodic peaks at 55mV and minus425mV which indicate thatCu (II) is two electron processes
Complex formation of metal ion and ligands wereobserved according to Jobs Method and Mole Ratio MethodCu (II) forms 1 2 complexes with guanine Probable struc-tures of the complexes of copper with guanine have beenproposed which is being supported by the previous works
As the concentration of any component increases inter-action between the metal and ligand increases more com-plexes are formed more electrons are transferred and con-sequently current increases Scan rate was varied for all themetal and ligand pairs which indicates the increase in scanrate increases the number of time of current scanning inthe system per second increases Hence the correspondingcurrent also increases Plot of the peak current versus squareroot of scan rate gives straight line with positive slope passingthrough origins which indicate that the peak current isdirectly proportional to the square root of the scan rate
Step height was varied from 20mV to 40mV for copperand guanine complex which implies that the correspondinganodic and cathodic current decreases with increasing stepheight it is due to less interaction between the metal andligand ions and fewer complexes are formed
The pH value of the complex mixture was varied from23 to 100 for all metal and ligand complex mixture by usingacetate and phosphate buffers At a lower pH the H+ioncompete with metal ions and less complexes are formed lesscurrent is obtained increasing pH value from 23 to 100 andcurrent increases and becomesmaximum and then decreasesrapidly with increasing pH value That implies the complexis favored to slightly acidic medium and slightly alkaline
medium The optimum pH range can be considered as 23 to70 for the complexes of copper with guanine and thymine
The supporting electrolytes were used as (NH4)2SO4
NaCl and KCl for all metal and ligand pair complex ratioMore interaction occurs when SO2minus
4containing supporting
electrolyte (NH4)2SO4is used compared to chloride contain-
ing supporting electrolyte KCl and NaCl As Na is below K inthe electrochemical series has higher tendency to be reducedcompared to K so less current is found for KCl than NaClSo the complexation tendency of the supporting electrolytesfollows the decreasing order (NH
4)2SO4gt NaCl gt KCl
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] N FarrellTransitionMetal Complexes as Drugs and Chemother-apeutic Agents vol 11 Springer 1989
[2] U C Gupta and S C Gupta ldquoTrace element toxicity rela-tionships to crop production and livestock and human healthimplications for managementrdquo Communications in Soil Scienceand Plant Analysis vol 29 no 11ndash14 pp 1491ndash1522 1998
[3] B A Chowdhury and R K Chandra ldquoBiological and healthimplications of toxic heavy metal and essential trace elementinteractionsrdquo Progress in Food amp Nutrition Science vol 11 no 1pp 57ndash113 1987
[4] V Mudgal N Madaan A Mudgal R B Singh and S MishraldquoEffect of toxic metals on human healthrdquoThe Open Nutraceuti-cals Journal vol 3 pp 94ndash99 2010
[5] J O Nriagu ldquoA silent epidemic of environmental metal poison-ingrdquo Environmental Pollution vol 50 no 1-2 pp 139ndash161 1988
[6] J N Galloway J DThornton S A Norton H L Volchok andR A N McLean ldquoTrace-metals in atmospheric deposition areview and assessmentrdquo Atmospheric Environment vol 16 no7 pp 1677ndash1700 1982
[7] W Zheng M Aschner and J-F Ghersi-Egea ldquoBrain barriersystems a new frontier in metal neurotoxicological researchrdquoToxicology and Applied Pharmacology vol 192 no 1 pp 1ndash112003
[8] H V Aposhian R M Maiorino D Gonzalez-Ramirez et alldquoMobilization of heavy metals by newer therapeutically usefulchelating agentsrdquo Toxicology vol 97 no 1ndash3 pp 23ndash38 1995
[9] S J S Flora M Mittal and A Mehta ldquoHeavy metal inducedoxidative stress amp its possible reversal by chelation therapyrdquoIndian Journal of Medical Research vol 128 no 4 pp 501ndash5232008
[10] M Elyasi M A Khalilzadeh and H Karimi-Maleh ldquoHigh sen-sitive voltammetric sensor based on PtCNTs nanocompositemodified ionic liquid carbon paste electrode for determinationof Sudan I in food samplesrdquo Food Chemistry vol 141 no 4 pp4311ndash4317 1996
[11] H Karimi-Maleh P Biparva andMHatami ldquoA novelmodifiedcarbon paste electrode based onNiOCNTs nanocomposite and(9 10-dihydro-9 10-ethanoanthracene-11 12-dicarboximido)-4-ethylbenzene-1 2-diol as a mediator for simultaneous deter-mination of cysteamine nicotinamide adenine dinucleotideand folic acidrdquo Biosensors and Bioelectronics vol 48 pp 270ndash275 2013
ISRN Electrochemistry 7
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
First anodic peak current First cathodic peak current
Peak
curr
enti p
(120583A
)
v12
versus v12
versus v12
Figure 5 Peak current versus square root of the scan rate for copperand guanine complex
Second anodic current Second cathodic current
50
50 60
40
40
30
30
20
20
10
10
0
minus10
minus20
Step height (mV)
Peak
curr
ent (120583
A)
versus step heightversus step height
Figure 6 Peak current versus step height for Cu2+ and guanineComplex
as the anodic and cathodic current decreases linearly withincreasing step height
Moreover in the lower step height the peak becomessharper This might happen as the interaction between themetal ions and ligand ions decreases with increasing stepheight and complex formation decrease and consequentlyanodic and cathodic current decreases with increasing stepheight [23]
Plotting peak current versus step height Figure 6 isobtained and it shows a straight line with negative slopewhich indicates that the increase in step height decreases thepeak current
316 Variation of pH Cyclic Voltammogram of 025mMCu2+and 050mM guanine at minus800mV to +600mV potential
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
40
30
20
10
0
minus10
minus20
minus30
minus40
pH 230
pH 700
pH 100
Curr
ent (120583
A)
Figure 7 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVS scanrate and 20mV step height at different pH Values ( 230 700 and100)
window at 100mVS scan rate and 20mV step height atdifferent pH Values (230 700 and 100) was taken (Figure 7)to see the effect of pH on the complex At lower pH theH+ ion can compete with Cu2+ ion for ligand in solutionBut an increase in pH value will reduce the concentrationof hydrogen ions which allows greater complex formationbetween Cu2+ and guanine There was a little increase inpeak current of Cu2+ guanine complex species below pH70From pH 70 onwards the peak current increased sharply theoptimum pH range appears to be between pH 23 and 70
317 Variation of Supporting Electrolyte Figure 8 illustratesthe effect of variation of supporting electrolyte on the elec-trochemical behavior of copper complexation with guanine
Any species that compete with metal ion for the surfaceof the electrode would inevitably interfere in the adsorptionof metal thyminate complex species hence leading to adecrease in the increase in current effect [24] This explainswhy the supporting electrolyte such as (NH
4)2SO4 which
is weakly complexing produce higher current as comparedto NaCl and KCl More over in case of NaCl and KCl bothare Chloride containing Supporting electrolyte but NaCl isweakly complexing compared to KCl produces more currentin the anodic and cathodic peak So the order of the anodicand cathodic current enlargement is (NH
4)2SO4gt NaCl gt
KCl
4 Conclusions
The results indicated that guanine is electroactive atminus1000mV to 800mV potential window and 100mV sminus1 scanrate as it has an anodic peak at minus200mV potential havingpeak current of 37511120583A in the Cyclic Voltammogram Cu
6 ISRN Electrochemistry
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
30
20
10
0
minus10
minus20
minus30
minus40
02 M KCl02 M NaCl02 M (NH4)2SO4
Curr
ent (120583
A)
Figure 8 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVSscan rate and 20mV step height in presence of different Supportingelectrolytes (02M KCl 02M NaCl and 02M (NH
4)2SO4)
(II) is electroactive as it gives two cathodic and two anodicpeaks Two anodic peaks are at 125 mV and minus185 mV and twocathodic peaks at 55mV and minus425mV which indicate thatCu (II) is two electron processes
Complex formation of metal ion and ligands wereobserved according to Jobs Method and Mole Ratio MethodCu (II) forms 1 2 complexes with guanine Probable struc-tures of the complexes of copper with guanine have beenproposed which is being supported by the previous works
As the concentration of any component increases inter-action between the metal and ligand increases more com-plexes are formed more electrons are transferred and con-sequently current increases Scan rate was varied for all themetal and ligand pairs which indicates the increase in scanrate increases the number of time of current scanning inthe system per second increases Hence the correspondingcurrent also increases Plot of the peak current versus squareroot of scan rate gives straight line with positive slope passingthrough origins which indicate that the peak current isdirectly proportional to the square root of the scan rate
Step height was varied from 20mV to 40mV for copperand guanine complex which implies that the correspondinganodic and cathodic current decreases with increasing stepheight it is due to less interaction between the metal andligand ions and fewer complexes are formed
The pH value of the complex mixture was varied from23 to 100 for all metal and ligand complex mixture by usingacetate and phosphate buffers At a lower pH the H+ioncompete with metal ions and less complexes are formed lesscurrent is obtained increasing pH value from 23 to 100 andcurrent increases and becomesmaximum and then decreasesrapidly with increasing pH value That implies the complexis favored to slightly acidic medium and slightly alkaline
medium The optimum pH range can be considered as 23 to70 for the complexes of copper with guanine and thymine
The supporting electrolytes were used as (NH4)2SO4
NaCl and KCl for all metal and ligand pair complex ratioMore interaction occurs when SO2minus
4containing supporting
electrolyte (NH4)2SO4is used compared to chloride contain-
ing supporting electrolyte KCl and NaCl As Na is below K inthe electrochemical series has higher tendency to be reducedcompared to K so less current is found for KCl than NaClSo the complexation tendency of the supporting electrolytesfollows the decreasing order (NH
4)2SO4gt NaCl gt KCl
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] N FarrellTransitionMetal Complexes as Drugs and Chemother-apeutic Agents vol 11 Springer 1989
[2] U C Gupta and S C Gupta ldquoTrace element toxicity rela-tionships to crop production and livestock and human healthimplications for managementrdquo Communications in Soil Scienceand Plant Analysis vol 29 no 11ndash14 pp 1491ndash1522 1998
[3] B A Chowdhury and R K Chandra ldquoBiological and healthimplications of toxic heavy metal and essential trace elementinteractionsrdquo Progress in Food amp Nutrition Science vol 11 no 1pp 57ndash113 1987
[4] V Mudgal N Madaan A Mudgal R B Singh and S MishraldquoEffect of toxic metals on human healthrdquoThe Open Nutraceuti-cals Journal vol 3 pp 94ndash99 2010
[5] J O Nriagu ldquoA silent epidemic of environmental metal poison-ingrdquo Environmental Pollution vol 50 no 1-2 pp 139ndash161 1988
[6] J N Galloway J DThornton S A Norton H L Volchok andR A N McLean ldquoTrace-metals in atmospheric deposition areview and assessmentrdquo Atmospheric Environment vol 16 no7 pp 1677ndash1700 1982
[7] W Zheng M Aschner and J-F Ghersi-Egea ldquoBrain barriersystems a new frontier in metal neurotoxicological researchrdquoToxicology and Applied Pharmacology vol 192 no 1 pp 1ndash112003
[8] H V Aposhian R M Maiorino D Gonzalez-Ramirez et alldquoMobilization of heavy metals by newer therapeutically usefulchelating agentsrdquo Toxicology vol 97 no 1ndash3 pp 23ndash38 1995
[9] S J S Flora M Mittal and A Mehta ldquoHeavy metal inducedoxidative stress amp its possible reversal by chelation therapyrdquoIndian Journal of Medical Research vol 128 no 4 pp 501ndash5232008
[10] M Elyasi M A Khalilzadeh and H Karimi-Maleh ldquoHigh sen-sitive voltammetric sensor based on PtCNTs nanocompositemodified ionic liquid carbon paste electrode for determinationof Sudan I in food samplesrdquo Food Chemistry vol 141 no 4 pp4311ndash4317 1996
[11] H Karimi-Maleh P Biparva andMHatami ldquoA novelmodifiedcarbon paste electrode based onNiOCNTs nanocomposite and(9 10-dihydro-9 10-ethanoanthracene-11 12-dicarboximido)-4-ethylbenzene-1 2-diol as a mediator for simultaneous deter-mination of cysteamine nicotinamide adenine dinucleotideand folic acidrdquo Biosensors and Bioelectronics vol 48 pp 270ndash275 2013
ISRN Electrochemistry 7
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
E (mV) versus AgAgCl (satd KCl)minus1000 minus800 minus600 minus400 minus200 0 200 400 600 800
30
20
10
0
minus10
minus20
minus30
minus40
02 M KCl02 M NaCl02 M (NH4)2SO4
Curr
ent (120583
A)
Figure 8 Cyclic Voltammogram of 025mM Cu2+and 050mMguanine at minus800mV to +600mV potential window at 100mVSscan rate and 20mV step height in presence of different Supportingelectrolytes (02M KCl 02M NaCl and 02M (NH
4)2SO4)
(II) is electroactive as it gives two cathodic and two anodicpeaks Two anodic peaks are at 125 mV and minus185 mV and twocathodic peaks at 55mV and minus425mV which indicate thatCu (II) is two electron processes
Complex formation of metal ion and ligands wereobserved according to Jobs Method and Mole Ratio MethodCu (II) forms 1 2 complexes with guanine Probable struc-tures of the complexes of copper with guanine have beenproposed which is being supported by the previous works
As the concentration of any component increases inter-action between the metal and ligand increases more com-plexes are formed more electrons are transferred and con-sequently current increases Scan rate was varied for all themetal and ligand pairs which indicates the increase in scanrate increases the number of time of current scanning inthe system per second increases Hence the correspondingcurrent also increases Plot of the peak current versus squareroot of scan rate gives straight line with positive slope passingthrough origins which indicate that the peak current isdirectly proportional to the square root of the scan rate
Step height was varied from 20mV to 40mV for copperand guanine complex which implies that the correspondinganodic and cathodic current decreases with increasing stepheight it is due to less interaction between the metal andligand ions and fewer complexes are formed
The pH value of the complex mixture was varied from23 to 100 for all metal and ligand complex mixture by usingacetate and phosphate buffers At a lower pH the H+ioncompete with metal ions and less complexes are formed lesscurrent is obtained increasing pH value from 23 to 100 andcurrent increases and becomesmaximum and then decreasesrapidly with increasing pH value That implies the complexis favored to slightly acidic medium and slightly alkaline
medium The optimum pH range can be considered as 23 to70 for the complexes of copper with guanine and thymine
The supporting electrolytes were used as (NH4)2SO4
NaCl and KCl for all metal and ligand pair complex ratioMore interaction occurs when SO2minus
4containing supporting
electrolyte (NH4)2SO4is used compared to chloride contain-
ing supporting electrolyte KCl and NaCl As Na is below K inthe electrochemical series has higher tendency to be reducedcompared to K so less current is found for KCl than NaClSo the complexation tendency of the supporting electrolytesfollows the decreasing order (NH
4)2SO4gt NaCl gt KCl
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] N FarrellTransitionMetal Complexes as Drugs and Chemother-apeutic Agents vol 11 Springer 1989
[2] U C Gupta and S C Gupta ldquoTrace element toxicity rela-tionships to crop production and livestock and human healthimplications for managementrdquo Communications in Soil Scienceand Plant Analysis vol 29 no 11ndash14 pp 1491ndash1522 1998
[3] B A Chowdhury and R K Chandra ldquoBiological and healthimplications of toxic heavy metal and essential trace elementinteractionsrdquo Progress in Food amp Nutrition Science vol 11 no 1pp 57ndash113 1987
[4] V Mudgal N Madaan A Mudgal R B Singh and S MishraldquoEffect of toxic metals on human healthrdquoThe Open Nutraceuti-cals Journal vol 3 pp 94ndash99 2010
[5] J O Nriagu ldquoA silent epidemic of environmental metal poison-ingrdquo Environmental Pollution vol 50 no 1-2 pp 139ndash161 1988
[6] J N Galloway J DThornton S A Norton H L Volchok andR A N McLean ldquoTrace-metals in atmospheric deposition areview and assessmentrdquo Atmospheric Environment vol 16 no7 pp 1677ndash1700 1982
[7] W Zheng M Aschner and J-F Ghersi-Egea ldquoBrain barriersystems a new frontier in metal neurotoxicological researchrdquoToxicology and Applied Pharmacology vol 192 no 1 pp 1ndash112003
[8] H V Aposhian R M Maiorino D Gonzalez-Ramirez et alldquoMobilization of heavy metals by newer therapeutically usefulchelating agentsrdquo Toxicology vol 97 no 1ndash3 pp 23ndash38 1995
[9] S J S Flora M Mittal and A Mehta ldquoHeavy metal inducedoxidative stress amp its possible reversal by chelation therapyrdquoIndian Journal of Medical Research vol 128 no 4 pp 501ndash5232008
[10] M Elyasi M A Khalilzadeh and H Karimi-Maleh ldquoHigh sen-sitive voltammetric sensor based on PtCNTs nanocompositemodified ionic liquid carbon paste electrode for determinationof Sudan I in food samplesrdquo Food Chemistry vol 141 no 4 pp4311ndash4317 1996
[11] H Karimi-Maleh P Biparva andMHatami ldquoA novelmodifiedcarbon paste electrode based onNiOCNTs nanocomposite and(9 10-dihydro-9 10-ethanoanthracene-11 12-dicarboximido)-4-ethylbenzene-1 2-diol as a mediator for simultaneous deter-mination of cysteamine nicotinamide adenine dinucleotideand folic acidrdquo Biosensors and Bioelectronics vol 48 pp 270ndash275 2013
ISRN Electrochemistry 7
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
[12] AMOliveira-Brett VDiculescu and J A P Piedade ldquoElectro-chemical oxidation mechanism of guanine and adenine using aglassy carbon microelectroderdquo Bioelectrochemistry vol 55 no1-2 pp 61ndash62 2002
[13] AA ShaikhKDilip PaulM S Rahman andK PradipBakshildquoInteractions of guanine with Cr(VI) Ag(I) Cd(II) and Hg(II)in acidic aqueous mediumrdquo Journal of Bangladesh ChemicalSociety vol 24 no 2 pp 106ndash114 2011
[14] P Kamalakannan and D Venkappayya ldquoSynthesis and char-acterization of cobalt and nickel chelates of 5-dimethylamino-methyl-2-thiouracil and their evaluation as antimicrobial andanticancer agentsrdquo Journal of Inorganic Biochemistry vol 90 no1-2 pp 22ndash37 2002
[15] A Robertazzi and J A Platts ldquoBinding of transitionmetal com-plexes to guanine and guanine-cytosine Hydrogen bondingand covalent effectsrdquo Journal of Biological Inorganic Chemistryvol 10 no 8 pp 854ndash866 2005
[16] S Zhu A Matilla J M Tercero V Vijayaragavan and J AWalmsley ldquoBinding of palladium(II) complexes to guanineguanosine or guanosine 51015840 -monophosphate in aqueous solu-tion potentiometric and NMR studiesrdquo Inorganica ChimicaActa vol 357 no 2 pp 411ndash420 2004
[17] T F Mastropietro D Armentano E Grisolia et al ldquoGuanine-containing copper(ii) complexes synthesis X-ray structuresand magnetic propertiesrdquo Dalton Transactions vol 8 no 4 pp514ndash520 2008
[18] E Sletten and B Lie ldquoCopper complex of guanosine-51015840-monophosphaterdquoActa Crystallographica vol 32 pp 3301ndash33041976
[19] A Habib T Shireen A Islam N Begum and A M ShafiqulAlam ldquoCyclic voltammetric studies of copper and manganesein the presence of L-leucine using glassy carbon electroderdquoPakistan Journal of Analytical amp Environmental Chemistry vol7 pp 96ndash102 2006
[20] A A Abdullah ldquoSynthesis and structural studies of somenucleic acids metal complexesrdquo Basrah Journal of Scienec vol24 no 1 pp 115ndash128 2006
[21] R B Sumathi and M B Halli ldquoMetal (II) complexes derivedfrom naphthofuran-2-carbohydrazide and diacetylmonoximeSchiff base synthesis spectroscopic electrochemical and bio-logical investigationrdquo Bioinorganic Chemistry and Applicationsvol 2014 Article ID 942162 11 pages 2014
[22] T Al Tanvir M Elius Hossain M Al Mamun and M QEhsan ldquoPreparation and characterization of Iron(Iii) complexof Saccharinrdquo Journal of Bangladesh Academy of Sciences vol37 no 2 pp 195ndash203 2013
[23] I Cukrowski J R Zeevaart and N V Jarvis ldquoA potentiometricand differential pulse polarographic study of Cd(II) with 1-hydroxyethylenediphosphonic acidrdquo Analytica Chimica Actavol 379 no 1-2 pp 217ndash226 1999
[24] A A Shaikh M Badrunnessa J Firdaws M Shahidur Rah-man N Ahmed Pasha and P K Bakshi ldquoA cyclic voltammetricstudy of the influence of supporting electrolytes on the redoxbehaviour of Cu(II) in aqueous mediumrdquo Journal of BangladeshChemical Society vol 24 no 2 pp 158ndash164 2011
