research article electrochemical behavior of ni(ii)...

Hindawi Publishing CorporationInternational Journal of ElectrochemistryVolume 2013 Article ID 257926 7 pageshttpdxdoiorg1011552013257926

Research ArticleElectrochemical Behavior of Ni(II)-Salen atthe Mercury Electrode

Peacutercio Augusto Mardini Farias and Margarida Bethlem Rodrigues Bastos

Department of Chemistry Pontifıcia Universidade Catolica Rua Marques de Sao Vicente 225 22453-900 Rio de Janeiro RJ Brazil

Correspondence should be addressed to Percio Augusto Mardini Farias pfariaspuc-riobr

Received 4 February 2013 Revised 26 March 2013 Accepted 1 April 2013

Academic Editor Angela Molina

Copyright copy 2013 P A Mardini Farias and M B Rodrigues Bastos This is an open access article distributed under the CreativeCommons Attribution License which permits unrestricted use distribution and reproduction in any medium provided theoriginal work is properly cited

The complex Ni(II)-salen has been studied using cyclic and square-wave cathodic stripping voltammetry at the static mercurydrop electrode in an aqueous media of phosphate and Hepes buffers (at pH 70) The resulting voltammograms consist of a totallyirreversible one-electron transfer attributable to the coupling of Ni(II) salenNi(I) salen via an EC mechanismThe mean value forthe transfer coefficient 120572 in both supporting electrolytes was calculated as 035 plusmn 005 The amount of reactant adsorbed after 60 sof accumulation at minus700mVwas calculated to be 28 times 10minus8molsdotcmminus2 The detection limit for nickel determination was found to be34 times 10minus9mol Lminus1

1 Introduction

The effective clinical use of cis-diammine dichloro plat-inum(II) complex and other platinum complexes in thetreatment of human cancer has stimulated studies in theinteraction of DNA with different metal complexes Whilesome metal complexes possess potential antitumor activi-ties many others are persistent environmental hazards Theunderstanding of the precise nature of the interaction ofdifferent metal complexes with DNA is crucial to betterpredict their utilization for diverse purposes such as pharma-cology controlling genetic information and the elucidationof protein-DNA contacts or gene therapy [1]

Several areas of chemistry have taken great interest insalen-type Schiff bases and their complexes with transitionmetals This is mainly due to their biological activity [23] optical [4 5] catalytic [6ndash9] chromophoric [10] ther-mochromic [11] and photochromic [12] properties

In analytical chemistry this class of compounds has beenused to impregnate ion exchange resins for the study ofCu(II) Co(II) and Ni(II) complexes [13] in the fluorescentanalysis of some amines [14] and amino acids [15] and

in solvent extraction of Ga(II) and Fe(III) complexes [16]Ni(II)-selective ion sensors of salen-type Schiff base chelateshave also been developed [17]

Recently it was found that some transition metal com-plexes such as manganese [1 18] nickel [19ndash23] iron [24]ruthenium [25] and copper [26] with ligands of the salentype can selectively modify DNA and RNA [27ndash29] Theoxidative and reductive chemistry of nickel(II) complexeswith Schiff bases of salen type has been studied extensivelyin organic solvents with different coordinating strength [30ndash37] In the present work the electrochemical behavior ofNi(II)-salen (Figure 1) at a mercury electrode in an aque-ous phosphate and Hepes buffers (pH 70) by cyclic andsquare-wave stripping voltammetry has been examined Thephosphate and Hepes buffers are widely used in studiesusing biological samples and were chosen for their abilityto establish the pH 70 in aqueous solutions and they donot interact or affect ions involved in biological reactions Acomparison between the two is that the Hepes has a molec-ular structure more complex (4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid) than the phosphate buffer which isprepared at pH 7 using only monosodium phosphate and

2 International Journal of Electrochemistry

N N

Ni

O O

Figure 1 Structure of Ni(II)-salen complex

minus04 minus08 minus12 minus16 minus2Potential (V)

2 120583A

Curr

ent

Figure 2 Staircase cyclic voltammograms for 17 times 10minus6mol Lminus1of Ni(II)-salen complex in phosphate buffer (002mol Lminus1 pH 70)Equilibrium time 30 s at minus800mV Scan rate 300mVsdotsminus1

its base combined disodium phosphate The techniquesof cyclic and square-wave voltammetry are highly con-venient to understand the redox behavior of Ni(II)-salencomplex in aqueous solution proposed in this paper inaddition square-wave stripping voltammetry technique isvery sensitive and ideal for the development of an analyticalmethod for the measurement of Ni(II)-salen at trace lev-els

2 Experimental

21 Apparatus All measurements were obtained with a BAS-50W voltammetric analyzer with a hanging mercury dropelectrode The sample cell (10mL of volume) was fittedwith an AgAgCl (30mol Lminus1 KCl) reference electrode anda platinum wire auxiliary electrode A magnetic stirrer anda stirring bar provided the convective transport duringthe preconcentration step on the voltammetric strippingtechniques

22 Chemicals and Solutions All chemicals were of analyticalgrade The Ni(II)-salen complex was prepared by refluxing a01mol Lminus1 solution of nickel acetate with an equal quantityof the ligand salen in ethanol for 2 hours The precipitate

was filtered washed twice with ethanol and acetone anddried in a desiccator containing phosphorous pentoxide Thestock solution of the Ni(II)-salen complex was prepared bydissolving the crystalline complex in dimethylformamide(DMF) up to a solution containing 10mg Lminus1 Dilutionswere made with DMF or with the appropriated stock buffersolution

The stock buffer solutions of potassium dihydrogen phos-phate and 4-(2-hydroxyethyl)-1-piperazine ethanesulfonicacid (Hepes) (002mol Lminus1) were prepared by dissolving thesuitable quantities of the reagents (Sigma) in water followedby adding NaOH (02mol Lminus1) to adjust the desired pH Allsolutions were prepared with water distilled and purified bythe Milli-Q purification system

23 Procedure A known volume (10mL) of the supportingelectrolyte solution (002mol Lminus1 phosphate or Hepes buffersat pH70)was added to the cell and degassedwith nitrogen for8min (and for 30 s before each square-wave stripping cycle)The preconcentration potential (minus700mV) was applied tothe electrode for a selected time while the solution wasstirred The stirring was then stopped and after 30 s thevoltammogram was recorded by applying a negative-goingpotential scanThe scan was terminated at minus1500mV and thesquare-wave stripping cycle was repeated with a new mer-cury drop After the background stripping voltammogramshad been obtained aliquots of the Ni(II)-salen standardswere introduced The entire procedure was automated ascontrolled by the BAS stripping analyzer Throughout thisoperation nitrogen was passed over the solution surfaceThestaircase cyclic voltammograms started at minus800mV and thepotential was reversed at minus2200mV All data were obtained atambient temperature

3 Results and Discussion

The electrochemical reduction of UO2

(II) and Cu(II)-salenin buffered aqueous solution of phosphate or Hepes athanging mercury drop electrode (HMDE) was studied inour laboratory [38 40] In connection with such stud-ies the present work reports an electrochemical behav-ior of nickel(II) complexed with the Schiff base NN1015840-ethylenebis(salicylidenimine) Ni(II)-salen using cyclic andsquare-wave voltammetry

31 Cyclic Voltammetry Cyclic voltammetry (CV) is widelyused for the initial characterization of electrochemicallyactive systems Figure 2 illustrates a typical staircase cyclicvoltamogram obtained for 17 times 10minus6mol Lminus1 of Ni(II)-salencomplex in an unstirred phosphate 002mol Lminus1 buffer (pH70) The forward potential scan was started at minus800mV andits direction was reversed at minus2200mV A first cathodic peakcurrent was obtained at minus1400mV and is due to the reductionof Ni(II)-salen complex A second cathodic peak which onlyappears at a higher scan rate (gt200mV sminus1) was observed atminus2000mVThis signal is probably due the disproportionationof Ni(I)-salen (an irreversible chemical reaction) [38 39] No

International Journal of Electrochemistry 3

2000

1600

1200

800

400

00 10 20 30 40

Square root of scan rate

Curr

ent (

nA)

Figure 3 Dependence of peak current on square root of scan rateby staircase cyclic voltammetry for 17 times 10minus6mol Lminus1 of Ni(II)-salencomplex in phosphate buffer (circle) and Hepes (triangle) buffers(002mol Lminus1 pH 70) Equilibrium time of 30 s at minus800mV

peak potential was observed in the reverse scan The absenceof peaks in the backward scan can be related to irreversibleprocesses and also to the presence of a chemical step (ECmechanism)

Cyclic voltammograms also were recorded at a series ofpotential scan rates between 5 and 1000mV sminus1 at a mercuryelectrode for 17 times 10minus6mol Lminus1 of Ni(II)-salen complexFor both phosphate and Hepes aqueous media a nonlinearrelationship between reduction peak current (Ni(II)-salen)(119894119901

) and the square root of the scan rates (]12) was observed(Figure 3) A linear plot of 119894

119901

against ]12 should be obtainedwhen the electrode process is a fully reversible or irreversibleprocess atmacroelectrodes deviations from this behavior canbe due to radial diffusion quasi-reversible kinetics andorcoupled chemical reactionsadsorption [41]

The relationships between 119894119901

and scan rate (]) also wasexamined for both supporting electrolytes A linear plot of 119894

119901

against ] should be obtained when the electrode process is anadsorption-controlled process [42]

For the phosphate buffer the relationships between 119894119901

and] for both ranges of scan rate (5ndash100 and 100ndash1000mV sminus1)examined suggested a mixed adsorption- and diffusion-controlled process at the electrode surface The plots of 119894

119901

versus ] were linear with different slope values The slope ofthe log 119894

119901

versus log ] plot over the total range of scan ratesexamined was 072 This average slope clearly indicates thatthe process has more than one step This slope is between thetheoretical values of 05 and 10 for diffusion- and adsorption-controlled electrode process respectively

In theHepes buffer the height of the cathodic peak for thecomplex in the range of scan rate (5ndash100mV sminus1) examined isnot directly proportional to either the value of the scan rate orthe square root of this value A theoretical treatment [42] ofthese results suggests that there is a complex overall processcontrolled by diffusion and adsorption of the Ni(II)-salenspecies to the electrode surface From 100 to 1000mV sminus1

the 119894119901

versus ]12 plot showed a straight line suggesting adiffusion-controlled reduction process Moreover the slopeof the log 119894

119901

versus log ] plot was 043 which is very close to

800

600

400

200

00 100 200 300 400 500

Accumulation time (s)

Curr

ent (

nA)

Figure 4 The effect of accumulation time on the current ofthe square-wave stripping peak for 21 times 10minus7mol Lminus1 Ni(II)-salencomplex in phosphate buffer (002mol Lminus1 pH 70) Accumulationtime at minus700mV with stirring Potential step height (119864-step) 4mVSW-119886 30mV and SW-119891 30Hz

the theoretical of 05 for the diffusion-controlled electrodeprocess

The dependence of reduction peak potential (119864119901

) on thedecimal logarithm of the scan rate (log ]) must be a straightline [slope = (59119899120572)] mV to allow the determination of thecharge coefficient transfer 120572 [40] In phosphate buffer when119864119901

is plotted against log ] we obtain a linear relationship(correlation coefficient = 0999) with slopes of 59mV and120mV for scan rates on the ranges of 10ndash200mVsdotsminus1 (120572 =050) and of 200ndash1000mVsdotsminus1 (120572 = 025) respectively Thisdemonstrates an increase in the irreversibility of the electrodeprocess with scan rate Again the data seems to point out toa process with more than one step

For theHepes buffer the119864119901

against log ] plot was allowedto estimate the value of 120572 as 030 over all ranges of scan ratesstudied

In the phosphate buffer from 20 to 100mV sminus1 the 119894119901

]12

value is constant This also establishes the electrode processas diffusion controlled For Hepes buffer this 119894

119901

]12 value isconstant for ] gt 100mVsdotsminus1

32 Square-Wave Stripping Voltammetry (SWV) SWV alsois a powerful technique for electroanalytical purposes andfor the elucidation of the redox mechanism and adsorptionstudies [43] The relationships of peak potential and currentwith the square-wave frequency SW-119891 and pulse amplitudeSW-119886 give the characteristics of the redox mechanism [44]The adsorptive accumulation of the Ni(II)-salen complex wasinitially developed by square-wave stripping voltammetry(experimental conditions 21 times 10minus7mol Lminus1 of Ni(II)-salencomplex in an phosphate buffer (002mol Lminus1 pH 70)accumulation for 60 s at minus700mV with stirring potentialstep height (119864-step) 4mV SW-119886 30mV and SW-119891 30Hz)The results of the voltammograms showed similar behav-ior to those obtained on the staircase cyclic voltammetry(Figure 2mdashforward direction) The first reduction currentpeak of Ni(II)-salen also was observed at minus1400mV


600

500

400

300

200

100

00 20 40 60 80 100 120 140

SW amplitude (mV)

Curr

ent (

nA)

Figure 5 The effect of SW amplitude on the current of the square-wave stripping peak for 17 times 10minus7mol Lminus1 Ni(II)-salen complexOther conditions as in Figure 4

12 14 16 18 2log frequency

minus1320

minus1360

minus1400

minus1440

Pote

ntia

l (m

V)

Figure 6 The effect of decimal logarithm of the SW frequencyon the potential of the square-wave stripping peak for Ni(II)-salenOther conditions as in Figure 4

Figure 4 shows the effect of an accumulation time onthe square-wave stripping peak current (at minus1400mV) ofthe Ni(II)-salen complex The current is seen to increasefrom 0 until leveling off at 210 sec Such time-dependentprofiles represent the mercury drop saturated with a stablelayer of the complex adsorbed With higher Ni(II)-salenconcentration the reduction current reaches a plateau aftera shorter accumulation time

The relations between the peak current (Ni(II)-salen) andthe parameters of the square wave were studied to the bettercomprehension of irreversibility on the electrode processThe effect of the square-wave amplitude on stripping currentis shown in Figure 5 The current increases linearly withthe amplitude at first and then levels off This fact can becharacteristic of a totally irreversible redox reaction butseveral other systems show similar behavior [45] Square-wave amplitudes greater than 80mV yield no additionalsensitivity for analytical purposes

The peak width at half-height was observed and is acrucial parameter for assessing the reversibility or irre-versibility of the electrode process For totally irreversibleredox reactionsΔ119864

1199012

does not depend on the SW amplitudeA separate experiment using the same conditions as Figure 5also was realized The results of the voltammograms show

200

175

150

125

100

75

504 5 6 7 8 9 10 11

Square root of SW frequency

Curr

ent (

nA)

Figure 7 The effect of the square root of the SW frequency on thecurrent of the square-wave stripping peak for Ni(II)-salen Otherconditions as in Figure 4

which Δ1198641199012

after SW amplitude of 10mV remains constantThis fact is also characteristic of a totally irreversible redoxreaction with the adsorption of the reactant [45 46]

The dependence of the reduction peak current of theNi(II)-salen complex on the SW amplitude (Figure 5) alsoshows that the initial slope is (Δ119894

119901

Δ119886)119886lt40

= 39 nAmVminus1According to the following equation [45]

119894119901

= 5001199021205721198992

119865119886119891Δ119864Γ (1)

where 119886 is the SW amplitude 119902 is the surface area of theelectrode 119891 is the frequency and Δ119864 the scan increment (119864-step) the amount of the adsorbed reactant can be calculatedfrom the slope Δ119894

119901

Δ119886 using the values 120572 = 037 119899 = 2 q= 0016 cm2 119891 = 30Hz Δ119864 is 4mV and Γ is the surfaceconcentration of the complex The calculated amount of theadsorbed reactant is Γ= 28times 10minus8mol cmminus2 withNi(II)-salenconcentration of 17 times 10minus7mol Lminus1 in phosphate buffer (pH70) and using accumulation time of 60 s at minus700mV

Precise information about the electrode reaction mech-anism arises from the dependence of the reduction currenton the SW frequency At higher frequencies the signal tendsto lose its definition as the influence of the charging currentbecomes increasingly important [47]Was verified in Figure 6which the peak potential (119864

119901

) shifts linearly to more negativepotential values on the increasing frequency with indicativefor totally irreversible electrode processes and adsorption ofthe product The least-squares analysis yielded a slope of788mV sdot log119891minus1 and a correlation coefficient of 0992

The transfer coefficient (120572) can be calculated as thepeak potential depends linearly on the logarithm of the SW-frequency as shown in Figure 6 The slope is Δ119864

119901

Δ log119891 =59119899120572 [48] The half-peak width is independent of the SW-frequency In theory these characteristics are attributed to thetotally irreversible reduction processes with adsorption of thereactant Other systems can show this same behavior

Using large step heights (119864-step) greatly increases the netcurrents which is also characteristic of irreversible systems[45] A linear dependence was observed over the range from2 to 10mV of step heightsThe least-squares analysis yielded aslope of 269 nAsdotmVminus1 and a correlation coefficient of 0988A linear dependence of (119864-step) on the 119864

119901

also was observed


Table 1 Comparison of Ni(II)- Cu(II)- and UO2(II)-salen complexes in an aqueous medium

Metal-salencomplex Electrode Supporting electrolyte

(at pH 70)Detection limit

(mol Lminus1) Cathodic peak potential 119864pc (mV)

Nickel Hanging mercury drop Hepes and phosphate 34 times 10minus9 minus1400 and minus2000Copper [38 39] Hanging mercury drop Phosphate 10 times 10minus8 minus160 minus530 minus990 and minus1100Uranyl [38 40] Hanging mercury drop Hepes 10 times 10minus8 minus590 minus950 and minus1140

Curr

ent (

nA)

600

400

200

005 15 25Ni(II)-salen concentration (times10minus7 molmiddotLminus1)

(a)

minus12 minus13 minus14 minus15Potential (V)

f

e

d

c

b

a

Curr

ent

03 120583A

(b)

Figure 8 Square-wave stripping voltammograms (b) obtained for solutions of increasing Ni(II)-salen concentration from 42 times 10minus8 to 25 times10minus7mol Lminus1 (andashf) Other conditions as in Figure 4 Also shown is the resulting calibration plot (a)

The least-squares analysis yielded a slope of minus68 and acorrelation coefficient of 0993

The effect of the square root of the SW-frequency on thepeak current of the Ni(II)-salen complex also was evaluated(Figure 7) The highest peak current was observed using afrequency of approximately 60Hz

Adsorptive stripping square-wave analysis has beenshown as an importantmethod in trace analysis because of itsbroad scope of applications and relative simple instrumenta-tion It was established that the Ni(II)-salen complex adsorbsat the electrode surface and by accumulation of the complexat minus700mV the detection of lower concentration is possibleThe sensitivity of the square-wave stripping voltammetricresponse increases with accumulation time and is dependenton the character of the electrode process Figure 8 showsthe voltammograms obtained by varying the Ni(II)-salenconcentration from 42 times 10minus8 to 25 times 10minus7mol Lminus1 Theresulting calibration curve shown as the inset is seen tobe linear up to 25 times 10minus7mol Lminus1 (correlation coefficient= 0987) The detection limit was estimated to be 34 times10minus9mol Lminus1 (S2N) with 10 s of accumulation time

Table 1 compares the voltammetric behavior of Ni(II)-Cu(II)- and UO

2

(II)-salen complexes in an aqueousmedium

4 Conclusions

In the phosphate buffer the electrode process seemed to bea mixed adsorption- and diffusion-controlled one whereasin the Hepes buffer a diffusion-controlled electrode processtakes place These results indicate that Ni(II)-salen and theproduct of its reduction adsorb at the electrode surface with aone-electron reduction through an EC mechanism Thus thefollowing redox reaction could be suggested

(Ni(II) salen) ads + eminus larrrarr (Ni(I) salen) ads

(Ni(I) salen) ads 997888rarr Final products(2)

Similar results were obtained by Sweeny and Peters [49]using CV organic supporting electrolyte and glassy carbonas working electrode Azevedo et al [50] reported that inorganic media the reduction of the Ni(II)-salen complexis with one-electron diffusion-controlled and reversiblereduction process In addition the present study describesan effective assay for the determination of trace levels ofnickel(II) in presence of salen The detection limit of 34 times10minus9mol Lminus1 is comparable to that seen for other adsorptivestripping methods [39 40] The Ni(II)-salen polymeric filmcould be applied as a sensor in the determination of dissolved


oxygen dipyrone and as an electrochemical energy storagesystem [51ndash53] As the solution of Ni(II)-salen in DMF iswater-soluble we are trying to study the effect of the complexsolution on DNA cleavage This metal complex can also beimmobilized on a bismuth filmglassy carbon surface or usedto modify a carbon paste electrode in order to study itsinteractions with DNA

Acknowledgments

The authors gratefully acknowledge the CNPq and CNEN ofthe Government of Brazil and PUC-Rio for support of thiswork In addition they thank J C Moreira and M Lovric fortheir helpful discussionThe experimental assistances of A BNeves and A T da Silva are also appreciated

References

[1] S S Mandal N V Kumar U Varshney and S BhattacharyaldquoMetal-ion-dependent oxidative DNA cleavage by transitionmetal complexes of a new water-soluble salen derivativerdquo vol63 no 4 pp 265ndash272 1996

[2] V A Soloshonok and T Ono ldquoThe effect of substituentson the feasibility of azomethine-azomethine isomerizationnew synthetic opportunities for biomimetic transaminationrdquoTetrahedron vol 52 no 47 pp 14701ndash14712 1996

[3] A A Hassan ldquoChemical interactions between tetracyanoethy-lene and s-methyldithiocarbazate as well as azomethine deriva-tivesrdquo Phosphorus Sulfur and Silicon and the Related Elementsvol 101 no 1ndash4 pp 189ndash196 1995

[4] G A Shagisultanova I A Orlova and Y F Batrakov ldquoPhoto-sensitive polymers based on bis(salicylidene)ethylenediaminecomplexes of copper(II) and palladium(II)rdquoTheRussian Journalof Applied Chemistry vol 68 no 4 pp 567ndash569 1995

[5] K Bhat K J Chang M D Aggarwal W S Wang B GPenn and D O Frazier ldquoSynthesis and characterization of var-ious schiff bases for non-linear optical applicationsrdquo MaterialsChemistry and Physics vol 44 no 3 pp 261ndash266 1996

[6] R I Kureshy N H Khan S H R Abdi and A K BhattldquoAsymmetric catalytic epoxidation of styrene by dissymmetricMn(III) and Ru(III) chiral Schiff base complexes synthesis andphysicochemical studiesrdquo Journal of Molecular Catalysis A vol110 no 1 pp 33ndash40 1996

[7] G L Estiu A H Jubert J Costamagna and J VargasldquoUV-visible spectroscopy in the interpretation of the tau-tomeric equilibriumofNN1015840(bis-35-di-bromo-salicyliden)-12-diaminobenzene and the redox activity of its Co(II) complexA quantum chemical approachrdquo Journal of Molecular Structurevol 367 no 1ndash3 pp 97ndash110 1996

[8] M A Ischay M S Mubarak and D G Peters ldquoCatalyticreduction and intramolecular cyclization of haloalkynes in thepresence of nickel(I) salen electrogenerated at carbon cathodesin dimethylformamiderdquo Journal of Organic Chemistry vol 71no 2 pp 623ndash628 2006

[9] E Dunach A P Esteves M J Medeiros D Pletcher and SOlivero ldquoThe study of nickel(II) and cobalt(II) complexes witha chiral salen derivative as catalysts for the electrochemicalcyclisation of unsaturated 2-bromophenyl ethersrdquo Journal ofElectroanalytical Chemistry vol 566 no 1 pp 39ndash45 2004

[10] K Nakanishi and R Crouch ldquoApplication of artificial pigmentsto structure determination and study of photoinduced transfor-mations of retinal proteinsrdquo Israel Journal of Chemistry vol 35no 3-4 pp 253ndash272 1995

[11] J A TenonMCarles and J P Aycard ldquoN-Methyl succinimiderdquoActa Crystallographica Section C vol 56 no 5 pp 568ndash5692000

[12] S H Alarcon A C Olivieri A Nordon and R K Har-ris ldquoSolid-state electronic absorption fluorescence and13CCPMAS NMR spectroscopic study of thermo- and photo-chromic aromatic Schiff basesrdquo Journal of the Chemical Societyvol 2 no 11 pp 2293ndash2296 1996

[13] S Samal R R Das D Sahoo S Acharya R L Panda and RC Rout ldquoChelating resins III Synthesis characterization andcapacity studies of formaldehyde-condensed phenolic Schiffbases derived from 12-diamines and hydroxy benzaldehydesrdquoJournal of Applied Polymer Science vol 62 no 9 pp 1437ndash14441996

[14] T K Hwang J N Miller D T Burns and J W BridgesldquoDetermination of primary amines by means of fluorescentschiff base derivativesrdquo Analytica Chimica Acta vol 99 no 2pp 305ndash315 1978

[15] JHayashiMYamada andTHobo ldquoChemiluminescence flow-injectionmethod for the determination of amino acids based onSchiff base formation in sodium(2-ethylhexyl)sulphosuccinatereversed micellesrdquo Analytica Chimica Acta vol 259 pp 67ndash721992

[16] S Abe J Mochizuki and T Sone ldquoLiquid-liquid extractionof iron(III) and gallium(III) with macrocyclic Schiff basescontaining bisphenol A subunitsrdquo Analytica Chimica Acta vol319 no 3 pp 387ndash392 1996

[17] A K Jain V K Gupta P A Ganeshpure and J R RaisonildquoNi(II)-selective ion sensors of salen type Schiff base chelatesrdquoAnalytica Chimica Acta vol 553 no 1-2 pp 177ndash184 2005

[18] S S Mandal U Varshney and S Bhattacharya ldquoRole of thecentral metal ion and ligand charge in the DNA bindingand modification by metallosalen complexesrdquo BioconjugateChemistry vol 8 no 6 pp 798ndash812 1997

[19] M Sakamoto Y Nishida A Matsumoto et al ldquoNickel(II)-lanthanide(III) complexes of the dinucleating ligand NNrsquo-bis(3-hydroxysalicylidene)ethylenediaminerdquo Journal of Coordi-nation Chemistry vol 38 pp 347ndash354 1996

[20] J R Morrow and K A Kolasa ldquoCleavage of DNA by nickelcomplexesrdquo Inorganica Chimica Acta vol 195 no 2 pp 245ndash248 1992

[21] J G Muller S J Paikoff S E Rokita and C J BurrowsldquoDNAmodification promoted by water-soluble nickel (II) salencomplexes a switch to DNA alkylationrdquo Journal of InorganicBiochemistry vol 54 no 3 pp 199ndash206 1994

[22] J G Muller S J Paikoff S E Rokita and C J T BurrowsldquoLigand-centered oxidation of nickel salen complexes in reac-tion with DNArdquo Abstracts of Papers of the American ChemicalSociety vol 208 p 266 1994

[23] J G Muller L A Kayser S J Paikoff et al ldquoFormation of DNAadducts using nickel(II) complexes of redox-active ligandsa comparison of salen and peptide complexesrdquo CoordinationChemistry Reviews vol 185-186 pp 761ndash774 1999

[24] S Routier H Vezin E Lamour J L Bernier J P Cat-teau and C Bailly ldquoDNA cleavage by hydroxy-salicylidene-ethylendiamine-iron complexesrdquoNucleic Acids Research vol 27no 21 pp 4160ndash4166 1999


[25] C C Cheng andY L Lu ldquoNovel water-soluble 44-disubstitutedruthenium(iii)-salen complexes in dna stranded scissionrdquo Jour-nal of the Chinese Chemical Society vol 45 pp 611ndash617 1998

[26] T Tanaka K Tsurutani A Komatsu et al ldquoSynthesis of newcationic schiff base complexes of copper(II) and their selectivebinding with DNArdquo Bulletin of the Chemical Society of Japanvol 70 no 3 pp 615ndash629 1997

[27] A Sigel and H Sigel EdsMetal Ions in Biological Systems vol32 33 Dekker New York NY USA 1996

[28] J Tedim S Patrıcio R Bessada et al ldquoThird-order nonlinearoptical properties of DA-salen-type nickel(II) and copper(II)complexesrdquo European Journal of Inorganic Chemistry no 17 pp3425ndash3433 2006

[29] J E Reed A A Arnal S Neidle and R Vilar ldquoStabilizationof G-quadruplex DNA and inhibition of telomerase activity bysquare-planar nickel(II) complexesrdquo Journal of the AmericanChemical Society vol 128 pp 5992ndash5993 2006

[30] A A Isse A Gennaro and E Vianello ldquoA study of the elec-trochemical reduction mechanism of Ni(salophen) in DMFrdquoElectrochimica Acta vol 37 no 1 pp 113ndash118 1992

[31] I C Santos M Vilas-Boas M F M Piedade C Freire M TDuarte and B de Castro ldquoElectrochemical and X-ray studies ofnickel(II) Schiff base complexes derived from salicylaldehydeStructural effects of bridge substituents on the stabilisation ofthe +3 oxidation staterdquo Polyhedron vol 19 no 6 pp 655ndash6642000

[32] P Vanalabhpatana and D G Peters ldquoCatalytic reduction of16-dihalohexanes by nickel(I) salen electrogenerated at glassycarbon cathodes in dimethylformamiderdquo Journal of the Electro-chemical Society vol 152 no 7 pp E222ndashE229 2005

[33] I Correia A Dornyei T Jakusch F Avecilla T Kiss and J CPessoa ldquoWater-soluble sal

2

en- and reduced sal2

en-type ligandsstudy of their CuII and NiII complexes in the solid state and insolutionrdquo The European Journal of Inorganic Chemistry no 14pp 2819ndash2830 2006

[34] O Buriez L MMoretto and P Ugo ldquoIon-exchange voltamme-try of tris(221015840-bipyridine) nickel(II) cobalt(II) and Co(salen)at polyestersulfonated ionomer coated electrodes in acetoni-trile reactivity of the electrogenerated low-valent complexesrdquoElectrochimica Acta vol 52 no 3 pp 958ndash964 2006

[35] P Vanalabhpatana and D G Peters ldquoStoichiometric reductionof secondary alkyl monohalides by electrogenerated nickel(I)salen in the presence of oxygen and water prospects for theformation of ketonesrdquo Journal of Electroanalytical Chemistryvol 593 pp 34ndash42 2006

[36] Y Abe H Akao Y Yoshida et al ldquoSyntheses structures andmesomorphism of a series of Ni(II) salen complexes with 4-substituted long alkoxy chainsrdquo Inorganica Chimica Acta vol359 no 10 pp 3147ndash3155 2006

[37] X Feng Z X Du B X Ye and F N Cui ldquoSynthe-sis Crystal Structure and Electrochemistry Properties ofa (NNrsquo-Ethylene-bis(salicylaldiminato)) Nickel(II) Complex[Ni2

(salen)2

]sdotNCSsdotNH4

rdquo Chinese Journal of Structural Chem-istry vol 26 no 9 pp 1033ndash1038 2007

[38] M B R Bastos ldquoContribution to the study electroanalytical ofsalen schiff bases and pyridoxal-51015840-phosphate and some of itscomplexes with Cu2+ Co2+ Ni2+ and UO

2

2+rdquo [PhD thesis]Pontifical Catholic University of Rio de Janeiro Brazil 1997

[39] P A M Farias and M B R Bastos ldquoElectrochemical behaviorof copper(II) salen in aqueous phosphate buffer at the mercuryelectroderdquo International Journal of Electrochemical Science vol4 no 3 pp 458ndash470 2009

[40] M B R Bastos J C Moreira and P A M Farias ldquoAdsorptivestripping voltammetric behaviour of UO

2

(II) complexed withthe Schiff base NN1015840- ethylenebis(salicylidenimine) in aqueous4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid mediumrdquoAnalytica Chimica Acta vol 408 no 1 pp 83ndash88 2000

[41] R Greef Instrumental Methods in Electrochemistry Ellis Hor-wood Chichester England 1985

[42] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons New York NYUSA 1980

[43] A A Barros J A Rodrigues P J Almeida P G Rodriguesand A G Fogg ldquoVoltammetry of compounds confined at thehanging mercury drop electrode surfacerdquo Analytica ChimicaActa vol 385 no 1ndash3 pp 315ndash323 1999

[44] V Cueillic M Mlakar and M Branica ldquoInfluence of theHEPES Buffer on Electrochemical Reaction of the Copper(II)-Salicylaldoxime Complexrdquo Electroanalysis vol 10 no 12 pp852ndash856 1998

[45] M Lovric S Komorsky-Lovric and R W Murray ldquoAdsorptioneffects in square-wave voltammetry of totally irreversible redoxreactionsrdquo Electrochimica Acta vol 33 no 6 pp 739ndash744 1988

[46] R Djogic and M Branica ldquoSquare-wave cathodic strippingvoltammetry of hydrolyzed uranyl speciesrdquo Analytica ChimicaActa vol 305 no 1ndash3 pp 159ndash164 1995

[47] S Komorsky-Lovric and M Lovric ldquoKinetic measurements ofa surface confined redox reactionrdquo Analytica Chimica Acta vol305 no 1ndash3 pp 248ndash255 1995

[48] M Lovric and S Komorsky-Lovric ldquoSquare-wave voltammetryof an adsorbed reactantrdquo Journal of Electroanalytical Chemistryvol 248 no 2 pp 239ndash253 1988

[49] B K Sweeny and D G Peters ldquoCyclic voltammetric studyof the catalytic behavior of nickel(I) salen electrogeneratedat a glassy carbon electrode in an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate BMIM+BF

4minus

)rdquo Electro-chemistry Communications vol 3 no 12 pp 712ndash715 2001

[50] F Azevedo C Freire and B de Castro ldquoReductive electro-chemical study of Ni(II) complexes with N

2

O2

schiff basecomplexes and spectroscopic characterisation of the reducedspecies Reactivity towards COrdquo Polyhedron vol 21 no 17 pp1695ndash1705 2002

[51] M F S Teixeira and T R L Dadamos ldquoAn electrochemicalsensor for dipyrone determination based on nickel-salen filmmodified electroderdquo in Proceedings of the Eurosensors XXIIIConference J Brugger and D Briand Eds vol 1 of ProcediaChemistry 2009

[52] J L Li F Gao Y K Zhang and X D Wang ldquoElectrochemicalpolymerization of nano-micro sheafwire conducting polymerpoly[Ni(SALEN)] for electrochemical energy storage systemrdquoChinese Journal of Polymer Science vol 28 no 5 pp 667ndash6712010

[53] C S Martin T R L Dadamos and M F S TeixeiraldquoDevelopment of an electrochemical sensor for determinationof dissolved oxygen by nickel-salen polymeric film modifiedelectroderdquo Sensors and Actuators B vol 175 pp 111ndash117 2012

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


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Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


N N

Ni

O O

Figure 1 Structure of Ni(II)-salen complex

minus04 minus08 minus12 minus16 minus2Potential (V)

2 120583A

Curr

ent

Figure 2 Staircase cyclic voltammograms for 17 times 10minus6mol Lminus1of Ni(II)-salen complex in phosphate buffer (002mol Lminus1 pH 70)Equilibrium time 30 s at minus800mV Scan rate 300mVsdotsminus1

its base combined disodium phosphate The techniquesof cyclic and square-wave voltammetry are highly con-venient to understand the redox behavior of Ni(II)-salencomplex in aqueous solution proposed in this paper inaddition square-wave stripping voltammetry technique isvery sensitive and ideal for the development of an analyticalmethod for the measurement of Ni(II)-salen at trace lev-els

2 Experimental

21 Apparatus All measurements were obtained with a BAS-50W voltammetric analyzer with a hanging mercury dropelectrode The sample cell (10mL of volume) was fittedwith an AgAgCl (30mol Lminus1 KCl) reference electrode anda platinum wire auxiliary electrode A magnetic stirrer anda stirring bar provided the convective transport duringthe preconcentration step on the voltammetric strippingtechniques

22 Chemicals and Solutions All chemicals were of analyticalgrade The Ni(II)-salen complex was prepared by refluxing a01mol Lminus1 solution of nickel acetate with an equal quantityof the ligand salen in ethanol for 2 hours The precipitate

was filtered washed twice with ethanol and acetone anddried in a desiccator containing phosphorous pentoxide Thestock solution of the Ni(II)-salen complex was prepared bydissolving the crystalline complex in dimethylformamide(DMF) up to a solution containing 10mg Lminus1 Dilutionswere made with DMF or with the appropriated stock buffersolution

The stock buffer solutions of potassium dihydrogen phos-phate and 4-(2-hydroxyethyl)-1-piperazine ethanesulfonicacid (Hepes) (002mol Lminus1) were prepared by dissolving thesuitable quantities of the reagents (Sigma) in water followedby adding NaOH (02mol Lminus1) to adjust the desired pH Allsolutions were prepared with water distilled and purified bythe Milli-Q purification system

23 Procedure A known volume (10mL) of the supportingelectrolyte solution (002mol Lminus1 phosphate or Hepes buffersat pH70)was added to the cell and degassedwith nitrogen for8min (and for 30 s before each square-wave stripping cycle)The preconcentration potential (minus700mV) was applied tothe electrode for a selected time while the solution wasstirred The stirring was then stopped and after 30 s thevoltammogram was recorded by applying a negative-goingpotential scanThe scan was terminated at minus1500mV and thesquare-wave stripping cycle was repeated with a new mer-cury drop After the background stripping voltammogramshad been obtained aliquots of the Ni(II)-salen standardswere introduced The entire procedure was automated ascontrolled by the BAS stripping analyzer Throughout thisoperation nitrogen was passed over the solution surfaceThestaircase cyclic voltammograms started at minus800mV and thepotential was reversed at minus2200mV All data were obtained atambient temperature

3 Results and Discussion

The electrochemical reduction of UO2

(II) and Cu(II)-salenin buffered aqueous solution of phosphate or Hepes athanging mercury drop electrode (HMDE) was studied inour laboratory [38 40] In connection with such stud-ies the present work reports an electrochemical behav-ior of nickel(II) complexed with the Schiff base NN1015840-ethylenebis(salicylidenimine) Ni(II)-salen using cyclic andsquare-wave voltammetry

31 Cyclic Voltammetry Cyclic voltammetry (CV) is widelyused for the initial characterization of electrochemicallyactive systems Figure 2 illustrates a typical staircase cyclicvoltamogram obtained for 17 times 10minus6mol Lminus1 of Ni(II)-salencomplex in an unstirred phosphate 002mol Lminus1 buffer (pH70) The forward potential scan was started at minus800mV andits direction was reversed at minus2200mV A first cathodic peakcurrent was obtained at minus1400mV and is due to the reductionof Ni(II)-salen complex A second cathodic peak which onlyappears at a higher scan rate (gt200mV sminus1) was observed atminus2000mVThis signal is probably due the disproportionationof Ni(I)-salen (an irreversible chemical reaction) [38 39] No


2000

1600

1200

800

400

00 10 20 30 40


Curr

ent (

nA)





119901




119901




119901


119901



the 119894119901


119901


800

600

400

200

00 100 200 300 400 500


Curr

ent (

nA)









]12


119901




600

500

400

300

200

100

00 20 40 60 80 100 120 140

SW amplitude (mV)

Curr

ent (

nA)



minus1320

minus1360

minus1400

minus1440

Pote

ntia

l (m

V)





1199012


200

175

150

125

100

75

504 5 6 7 8 9 10 11


Curr

ent (

nA)


which Δ1198641199012



119901

Δ119886)119886lt40


119894119901

= 5001199021205721198992

119865119886119891Δ119864Γ (1)


119901



119901



119901



119901

also was observed







Curr

ent (

nA)

600

400

200


(a)


f

e

d

c

b

a

Curr

ent

03 120583A

(b)






2


4 Conclusions







Acknowledgments


References



































2







(salen)2

]sdotNCSsdotNH4



2




2











4minus



2

O2














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


2000

1600

1200

800

400

00 10 20 30 40


Curr

ent (

nA)





119901




119901




119901


119901



the 119894119901


119901


800

600

400

200

00 100 200 300 400 500


Curr

ent (

nA)









]12


119901




600

500

400

300

200

100

00 20 40 60 80 100 120 140

SW amplitude (mV)

Curr

ent (

nA)



minus1320

minus1360

minus1400

minus1440

Pote

ntia

l (m

V)





1199012


200

175

150

125

100

75

504 5 6 7 8 9 10 11


Curr

ent (

nA)


which Δ1198641199012



119901

Δ119886)119886lt40


119894119901

= 5001199021205721198992

119865119886119891Δ119864Γ (1)


119901



119901



119901



119901

also was observed







Curr

ent (

nA)

600

400

200


(a)


f

e

d

c

b

a

Curr

ent

03 120583A

(b)






2


4 Conclusions







Acknowledgments


References



































2







(salen)2

]sdotNCSsdotNH4



2




2











4minus



2

O2














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


600

500

400

300

200

100

00 20 40 60 80 100 120 140

SW amplitude (mV)

Curr

ent (

nA)



minus1320

minus1360

minus1400

minus1440

Pote

ntia

l (m

V)





1199012


200

175

150

125

100

75

504 5 6 7 8 9 10 11


Curr

ent (

nA)


which Δ1198641199012



119901

Δ119886)119886lt40


119894119901

= 5001199021205721198992

119865119886119891Δ119864Γ (1)


119901



119901



119901



119901

also was observed







Curr

ent (

nA)

600

400

200


(a)


f

e

d

c

b

a

Curr

ent

03 120583A

(b)






2


4 Conclusions







Acknowledgments


References



































2







(salen)2

]sdotNCSsdotNH4



2




2











4minus



2

O2














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







Curr

ent (

nA)

600

400

200


(a)


f

e

d

c

b

a

Curr

ent

03 120583A

(b)






2


4 Conclusions







Acknowledgments


References



































2







(salen)2

]sdotNCSsdotNH4



2




2











4minus



2

O2














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



Acknowledgments


References



































2







(salen)2

]sdotNCSsdotNH4



2




2











4minus



2

O2














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of











2







(salen)2

]sdotNCSsdotNH4



2




2











4minus



2

O2














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article electrochemical behavior of ni(ii)...

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