Electrochemical Titration Research Articles

Oxygen nonstoichiometry and chemical expansion of mixed conducting La0.1Sr0.9Co0.8Fe0.2O3 − δ

The chemical diffusivity and surface exchange constant of La0.1Sr0.9Co0.8Fe0.2O3−δ (LSCF1982) were successfully extracted by using the chemical expansion relaxation method, and the oxygen nonstoichiometry was determined by electrochemical coulometric titration as a function of oxygen partial pressure (pO2) and temperature. The oxygen chemical diffusivity and surface exchange constants were 3.16×10−4cm2/s and 6.31×10−3cm/s at 1000°C in air, respectively. These values and the activation energies for oxygen diffusion were in good agreement with our own previously reported values determined from the 4-probe D.C. conductivity relaxation method. The oxygen nonstoichiometry was increased with decreasing pO2 and increasing temperature, due to the thermal and chemical release of lattice-site oxygen from the lattice sites. The oxygen self-diffusion coefficient and ionic conductivity were successfully extracted from the relation between the oxygen nonstoichiometry and the chemical diffusion coefficient, and are best expressed by the following equations:DO/cm2/s=(1.75±0.05)×10−4exp−0.68±0.10eVkT|pO2=0.21atmσionT/cm2/sK−1=(4.01±0.02)×105exp−0.65±0.04eVkT|pO2=0.21atm.

Ferrocene conjugated imidazolephenols as multichannel ditopic chemosensor for biologically active cations and anions

Two chemosensor molecules with the capability of sensing cations and anions have been synthesized by coupling an electroactive unit based on ferrocene and a sensor unit based on imidazolyl and phenol moieties through a linker. The two receptor molecules have been characterized crystallographically. The sensing of the cations or anions is achieved by monitoring the electrochemical wave or optical signal of the ferrocenyl moiety present in the molecule. Results of electrochemical and spectral titration of the chemosensors with cations and anions show that the response of the chemosensors to cations and anions can be tuned by changing the substituents in the phenolic ring.

Synthesis, structure, DNA-binding properties and cytotoxic activities of a new one-dimensional polymeric copper(II) complex with N-benzoate-N′-[3-(2-hydroxyl-ethylammino)propyl]oxamide as ligand

A new one-dimensional polymeric copper(II) complex, [Cu2(bhpox)(phen)]+n·nClO4−·nH2O, where bhpox3− and phen stand for N-benzoate-N′-[3-(2-hydroxyethylammino)propyl]oxamide and 1,10-phenanthroline, respectively, has been synthesized and characterized by elemental analysis, molar conductivity measurement, IR and electronic spectra studies, and single-crystal X-ray diffraction. The complex crystallizes in monoclinic space group P21/c with crystallographic data: a=13.8500(2)Å, b=13.3321(2)Å, c=15.8532(2)Å, and Z=4. In the crystal structure, the cation [Cu2(bhpox)(phen)]nn+ exhibits a one-dimensional zigzag-like structure for copper(II) ions alternately bridged by cis-oxamido and carboxylato groups, with the Cu⋯Cu separations of 5.1928(4) and 5.5240(5)Å, respectively. Each copper(II) ion is located in a slightly distorted square–pyramidal environment. Hydrogen bonds and π–π stacking interactions contribute to a three-dimensional supramolecular structure in the crystal. The interactions between the copper(II) complex and herring sperm DNA (HS-DNA) have been investigated by using electronic absorption titration, fluorescence titration, electrochemical titration and viscometry. All the experiments reveal that the copper(II) complex interacts with HS-DNA in the mode of intercalation with the intrinsic binding constant Kb=2.67×104M−1. The copper(II) complex exhibits potent anticancer activities against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549.

A 1,2,3,4,5‐Pentaphenylferrocene‐Stoppered Rotaxane Capable of Electrochemical Anion Recognition

The chloride anion templated synthesis of an electrochemical anion sensory interlocked host system, prepared by the integration of redox-active 1,2,3,4,5-pentaphenylferrocene stopper groups into the structure of a rotaxane capable of binding anionic guests is described. Extensive (1)H NMR and electrochemical titration investigations were used to probe the anion recognition and sensing properties of the rotaxane, compared to the axle and model system components. A characteristic electrochemical response was observed for chloride binding by the rotaxane, which was attributed to the topologically constrained cavity of the interlocked host molecule.

Synthesis, structure, and DNA-binding studies of a dicopper(II) complex with N-phenolato-N′-[2-(dimethylamino) ethyl]oxamide as ligand

A new µ-oxamido-bridged dicopper(II) complex, [Cu2(pdmaeox)(bpy)(H2O)](pic) · H2O [H3pdmaeox = N-phenolato-N′-[2-(dimethylamino)ethyl]oxamide, Hpic = 2,4,6-trinitrophenol, bpy = 2,2′-bipyridine], has been synthesized and characterized by elemental analyses, molar conductivity measurement, infrared, and electronic spectra studies, and X-ray single-crystal diffraction. The complex crystallizes in the triclinic system, P 1 space group, with crystallographic data: a = 10.7815(2) Å, b = 11.3598(2) Å, c = 14.1389(3) Å, and z = 2. In [Cu2(pdmaeox)(bpy)(H2O)]+, one copper(II) resides in the inner site with a square-planar coordination geometry and the other is chelated by the two exo-oxygen atoms of the cis-pdmaeox3− ligand in a square-pyramidal environment. The Cu···Cu separation through cis-pdmaeox3− bridge is 5.1834(4) Å. The crystal structure is stabilized by hydrogen bonds and π–π stacking interactions. The interaction of the dicopper(II) complex with herring sperm-DNA (HS-DNA) has been investigated by electronic absorption titration, fluorescence titration, electrochemical titration, and viscosity measurements. The results reveal that the interaction of the dicopper(II) complex with HS-DNA might be electrostatic binding. The effects of bridging ligand on the interaction of the dinuclear complex with HS-DNA were preliminarily investigated.

Direct electrochemical analyses of human cytochromes b5 with a mutated heme pocket showed a good correlation between their midpoint and half wave potentials

BackgroundCytochrome b5 performs central roles in various biological electron transfer reactions, where difference in the redox potential of two reactant proteins provides the driving force. Redox potentials of cytochromes b5 span a very wide range of ~400 mV, in which surface charge and hydrophobicity around the heme moiety are proposed to have crucial roles based on previous site-directed mutagenesis analyses.MethodsEffects of mutations at conserved hydrophobic amino acid residues consisting of the heme pocket of cytochrome b5 were analyzed by EPR and electrochemical methods. Cyclic voltammetry of the heme-binding domain of human cytochrome b5 (HLMWb5) and its site-directed mutants was conducted using a gold electrode pre-treated with β-mercarptopropionic acid by inclusion of positively-charged poly-L-lysine. On the other hand, static midpoint potentials were measured under a similar condition.ResultsTitration of HLMWb5 with poly-L-lysine indicated that half-wave potential up-shifted to -19.5 mV when the concentration reached to form a complex. On the other hand, midpoint potentials of -3.2 and +16.5 mV were obtained for HLMWb5 in the absence and presence of poly-L-lysine, respectively, by a spectroscopic electrochemical titration, suggesting that positive charges introduced by binding of poly-L-lysine around an exposed heme propionate resulted in a positive shift of the potential. Analyses on the five site-specific mutants showed a good correlation between the half-wave and the midpoint potentials, in which the former were 16~32 mV more negative than the latter, suggesting that both binding of poly-L-lysine and hydrophobicity around the heme moiety regulate the overall redox potentials.ConclusionsPresent study showed that simultaneous measurements of the midpoint and the half-wave potentials could be a good evaluating methodology for the analyses of static and dynamic redox properties of various hemoproteins including cytochrome b5. The potentials might be modulated by a gross conformational change in the tertiary structure, by a slight change in the local structure, or by a change in the hydrophobicity around the heme moiety as found for the interaction with poly-L-lysine. Therefore, the system consisting of cytochrome b5 and its partner proteins or peptides might be a good paradigm for studying the biological electron transfer reactions.

Determination of the surface acidity of a free-base corrole in a self-assembled monolayer

Mixed self-assembled monolayers (SAMs) containing a corrole moiety have been prepared to examine their electrochemical properties and surface acidity, with the eventual goal of biosensor development. Mixed SAMs consisting of 6-mercapto-hexanol (6-MHO) and 8-amino-1-octanethiol (8-AOT) in varying ratios were modified with a free-base corrole and characterized via Osteryoung square-wave voltammetry and contact angle measurements. The surface acidity of the free-base corrole was determined using an electrochemical titration method, with pKa values established at 6.4 when using Fe(CN)64−/Fe(CN)63− as a redox probe and at 6.7 when using iodide, and assigned to the CorH4+ ⇌ CorH3 + H+ equilibrium.

Multi-tool formaldehyde measurement in simulated and real atmospheres for indoor air survey and concentration change monitoring

Formaldehyde is of particular health concern since it is carcinogenic for human and ubiquitous in indoor air where people spend most of their time. Therefore, it is important to have suitable methods and techniques to measure its content in indoor air. In the present work, four different techniques have been tested in the INERIS exposure chamber and in indoor environments in comparison to a standard active method: passive sampling method based on the reaction of 2,4-dinitrophenylhydrazine with formaldehyde, two on-line continuous monitoring systems based on fluorescence and UV measurements and a portable commercialised analyser based on electrochemical titration. Two formaldehyde concentrations, about 10 and 25 μg m−3 were generated in an exposure chamber under controlled conditions of temperature, relative humidity, and wind speed to simulate real conditions and assess potential influence on passive sampling and continuous systems response. Influence of sampling periods on passive sampling has also been evaluated. The real atmosphere experiments have been performed in four different indoor environments: an office, a furniture shop, a shopping mall, and residential dwellings in which several potential formaldehyde sources linked to household activities have been tested. The analytical and sampling problems associated with each measurement method have been identified and discussed. An overall agreement between each technique has been observed and continuous analyzers allowed for formaldehyde concentrations change monitoring and secondary formation of that pollutant observation.

Evaluation of Electronics, Electrostatics and Hydrogen Bond Cooperativity in the Binding of Cyanide and Fluoride by Lewis Acidic Ferrocenylboranes

Synthetic approaches based on the direct borylation of ferrocene by BBr(3), followed by boryl substituent modification, or on the lithiation of ferrocene derivatives and subsequent quenching with the electrophile FBMes(2), have given access to a range of ferrocene derivatized Lewis acids with which to conduct a systematic study of fluoride and cyanide binding. In particular, the effects of borane electrophilicity, net charge, and ancillary ligand electronics/cooperativity on the binding affinities for these anions have been probed by a combination of NMR, IR, mass spectrometric, electrochemical, crystallographic, and UV-vis titration measurements. In this respect, modifications made at the para position of the boron-bound aromatic substituents exert a relatively minor influence on the binding constants for both fluoride and cyanide, as do the electronic properties of peripheral substituents at the 1'- position (even for cationic groups). By contrast, the influence of a CH(2)NMe(3)(+) substituent in the 2- position is found to be much more pronounced (by >3 orders of magnitude), reflecting, at least in part, the possibility in solution for an additional binding component utilizing the hydrogen bond donor capabilities of the methylene CH(2) group. While none of the systems examined in the current study display any great differentiation between the binding of F(-) and CN(-) (and indeed some, such as FcBMes(2), bind both anions with equal affinity within experimental error), much weaker boronic ester Lewis acids will bind fluoride (but give a negative response for cyanide). Thus, by the incorporation of an irreversible redox-matched organic dye, a two-component [BMes(2)/B(OR)(2)] dosimeter system can be developed capable of colorimetrically signaling the presence of fluoride and cyanide in organic solution by Boolean AND/NOT logic.

Electron Fluxes in a Microbial Fuel Cell Performing Carbon and Nitrogen Removal

The electron recovery in microbial fuel cells (MFCs) is decreased by processes like methanogenesis, bacterial growth, and the accumulation of intermediates. Using a suite of analytical techniques, including electrochemical monitoring, chemical analysis, microsensor analysis, and Titration and Off-Gas Analysis (TOGA), this study aimed to (a) identify and quantify the electron losses occurring at the anode and the cathode of a MFC removing acetate and nitrate (NO3-), respectively, and (b) to investigate the impact of the operational characteristics of the cathode on the denitrification process. Our results show that methane (CH4) production and estimated biomass formation at the anode and nitrous oxide (N2O) accumulation at the cathode were responsible for the reduction of Coulombic efficiency (epsilon) during continuous feeding conditions. At the anode, up to 40.1% of the acetate consumed was released as methane at closed circuit. At the cathode, N2O accumulation represented instead the main loss accounting for up to 10.0 +/- 2.1% of the oxidation capacity of the electron acceptor provided as NO3-. Batch experiments at controlled potentials and currents revealed that for a given current the fraction of electron transferred and released as N2O is significantly reduced by low cathodic potentials.

Silyl Radicals by Reverse and One-Electron Electrochemistry

Silicon-centered radicals R3Si•, both as short-lived intermediates and as persistent species, were produced by means of electrochemistry. The one-electron electrochemical oxidation of silyl anions prepared by various methods (sonochemical cleavage of disilanes with K, reductive electrochemical titration of monochlorosilanes and by reverse electrochemistry in a flow-through cell) resulted in R3Si• radicals, which were involved in radical silylation of double bonds or trapped with PTBN as shown by EPR-spectroelectrochemistry. The same radical species were produced by oxidation-reduction of hexaphenyldisilane in a flow-through teo-compartment cell. The possibility of generating silyl radicals by direct one-electron cathodic reduction has been demonstrated.

Electrostatic Interactions Between FeS Clusters in NADH:Ubiquinone Oxidoreductase (Complex I) from Escherichia coli

The redox properties of the cofactors of NADH:ubiquinone oxidoreductase (complex I) from Escherichia coli were studied by following the changes in electron paramagnetic resonance (EPR) and optical spectra upon electrochemical redox titration of the purified protein. At neutral pH, the FMN cofactor had a midpoint redox potential ( E m) approximately -350 mV ( n = 2). Binuclear FeS clusters were well-characterized: N1a was titrated with a single ( n = 1) transition, and E m = -235 mV. In contrast, the titration of N1b can only be fitted with the sum of at least two one-electron Nernstian curves with E m values of -245 and -320 mV. The tetranuclear clusters can also be separated into two groups, either having a single, n = 1, or more complex redox titration curves. The titration curves of the EPR bands attributed to the tetranuclear clusters N2 ( g = 2.045 and g = 1.895) and N6b ( g = 2.089 and g = 1.877) can be presented by the sum of at least two components, each with E m (app) approximately -200/-300 mV and -235/-315 mV, respectively. The titration of the signals at g = 1.956-1.947 (N3 or N7, E m = -315 mV), g = 2.022, and g = 1.932 (Nx, -365 mV) and the low temperature signal at g = 1.929 (N4 or N5, -330 mV) followed Nernstian n = 1 curves. The observed redox titration curves are discussed in terms of intrinsic electrostatic interactions between FeS centers in complex I. A model showing shifts of E m due to the electrostatic interaction between the centers is presented.

Kinetics and mechanism of the reaction between 4‐hexadecylbenzenediazonium ions and vitamin C in emulsions: further evidence of the formation of diazo ether intermediates in the course of the reaction

AbstractThe kinetics and mechanism of the reaction between hydrophobic 4‐hexadecylarenediazonium ions, 16‐ArN and vitamin C, VC, in a model emulsion prepared by mixing octane, acidic (HCl) water and the non‐ionic surfactant hexaethyleneglycol monododecyl ether, C12E6, were investigated. Because emulsions are opaque, linear sweep voltammetry, LSV, was employed to monitor the reaction. Voltammograms of 16‐ArN in emulsions show two reduction peaks as in aqueous systems. The half‐life for the spontaneous decomposition of 16‐ArN in the emulsion was estimated as t1/2 = 14.5 h at T = 25 °C. Upon addition of VC to the system, the first reduction peak of 16‐ArN disappears almost immediately and a new reduction peak is detected at Ep = −0.25 V. Electrochemical titration of 16‐ArN shows that the new peak corresponds to the formation of a 1:1 adduct. The iP(Ep = −0.25 V) values can be linearly correlated with [16‐ArN] and the observed rate constants, kobs, were determined by fitting the (ip, t) data to the integrated first order equation. The variation of kobs with [VC] follows a saturation kinetics profile, consistent with the formation of an intermediate in a pre‐equilibrium step. All the evidence is consistent with a reaction mechanism comprising two competitive pathways, the spontaneous DN + AN mechanism and the unimolecular decomposition of a transient diazo ether (DE) formed in a pre‐equilibrium step. The data allowed estimations of the interfacial rate constant for the reaction between 16‐ArN and VC− but did not allow the determination of the equilibrium constant for the DE formation. Copyright © 2008 John Wiley & Sons, Ltd.

Ternary MgTiX‐Alloys: A Promising Route towards Low‐Temperature, High‐Capacity, Hydrogen‐Storage Materials

In the search for hydrogen-storage materials with a high gravimetric capacity, Mg(y)Ti((1-y)) alloys, which exhibit excellent kinetic properties, form the basis for more advanced compounds. The plateau pressure of the Mg--Ti--H system is very low (approximately 10(-6) bar at room temperature). A way to increase this pressure is by destabilizing the metal hydride. The foremost effect of incorporating an additional element in the binary Mg--Ti system is, therefore, to decrease the stability of the metal hydride. A model to calculate the effect on the thermodynamic stability of alloying metals was developed by Miedema and co-workers. Adopting this model offers the possibility to select promising elements beforehand. Thin films consisting of Mg and Ti with Al or Si were prepared by means of e-beam deposition. The electrochemical galvanostatic intermittent titration technique was used to obtain pressure-composition isotherms for these ternary materials and these isotherms reveal a reversible hydrogen-storage capacity of more than 6 wt. %. In line with the calculations, substitution of Mg and Ti by Al or Si indeed shifts the plateau pressure of a significant part of the isotherms to higher pressures, while remaining at room temperature. It has been proven that, by controlling the chemistry of the metal alloy, the thermodynamic properties of Mg-based hydrides can be regulated over a wide range. Hence, the possibility to increase the partial hydrogen pressure, while maintaining a high gravimetric capacity creates promising opportunities in the field of hydrogen-storage materials, which are essential for the future of the hydrogen economy.

A role for cytochrome c and cytochrome c peroxidase in electron shuttling from Erv1

Erv1 is a flavin-dependent sulfhydryl oxidase in the mitochondrial intermembrane space (IMS) that functions in the import of cysteine-rich proteins. Redox titrations of recombinant Erv1 showed that it contains three distinct couples with midpoint potentials of -320, -215, and -150 mV. Like all redox-active enzymes, Erv1 requires one or more electron acceptors. We have generated strains with erv1 conditional alleles and employed biochemical and genetic strategies to facilitate identifying redox pathways involving Erv1. Here, we report that Erv1 forms a 1:1 complex with cytochrome c and a reduced Erv1 can transfer electrons directly to the ferric form of the cytochrome. Erv1 also utilized molecular oxygen as an electron acceptor to generate hydrogen peroxide, which is subsequently reduced to water by cytochrome c peroxidase (Ccp1). Oxidized Ccp1 was in turn reduced by the Erv1-reduced cytochrome c. By coupling these pathways, cytochrome c and Ccp1 function efficiently as Erv1-dependent electron acceptors. Thus, we propose that Erv1 utilizes diverse pathways for electron shuttling in the IMS.

Direct ethylene glycol fuel-cell stack—Study of oxidation intermediate products

In the present paper, a ten 10 cm 2 direct ethylene glycol fuel-cell (DEGFC) stack based on a nanoporous proton-conducting membrane (NP-PCM) is used to study the electro-oxidation of ethylene glycol (EG) in acid medium under initial and steady-state conditions, and under the operating conditions of electrochemical titration. Ethylene glycol (EG) has a theoretical capacity 17% higher than that of methanol in terms of Ah ml −1 (4.8 and 4, respectively); this is especially important for portable electronic applications. EG (bp 198 °C) is also a safer fuel for direct-oxidation fuel-cell (DOFC) applications than is methanol. A maximal power of 12 W (at 0.3 V cell −1) at 80 °C has been achieved for a DEGFC fresh stack fed with 0.5 M EG/1.7 M triflic acid solution at ambient dry air pressure. The formation of oxidation by-products – glycolic and oxalic acids (most likely in parallel reactions) – has been proven by ion-chromatography analysis. On continuous feed of EG in order to maintain a concentration of about 0.5 M, the concentration of intermediates reached a maximum after about two fuel (EG) turnovers. After discharging without feeding the stack with EG, there was no further accumulation of these acids and their concentration decreased to almost zero. This is clear evidence that EG is a real fuel that can be converted completely to CO 2.

Electrochemical titration of hydrogen adsorbed on supported platinum catalysts

A method for the surface area determination of platinum on 5% Pt/Al2O3 catalysts by electrochemically generated oxygen has been tested. This method is based on the oxidation of adsorbed hydrogen on a platinum surface area by oxygen that is generated electrochemically. The course of the titration was followed by measurement the potential of a catalyst suspended in a sulphuric acid solution. The applicability and the accuracy of this method were tested by a measurement of platinum particle sizes using XRD and electron microscopy.

Reaction of lithium with FeAsS, a quaternary system

Electrochemical titration and X-ray diffraction experiments have been performed on the reaction of lithium with arsenopyrite, FeAsS. The results obtained on this quaternary system have been interpreted in terms of the Li-Fe-As-S composition tetrahedron. It was found that 1.8 mol of Li can reversibly react rapidly at a potential of 1.75 V vs pure lithium. Two additional plateaus were found at 0.95 and 0.75 V vs lithium that do not make important contributions to the theoretical specific energy.

Structural and Spectroscopic Evidence for the Formation of Trinuclear and Tetranuclear Vanadium(III)/Carboxylate Complexes of Acetate and Related Derivatives in Aqueous Solution

The formation of vanadium(III) complexes with nuclearity greater than two is believed to occur in aqueous solution on the basis of potentiometric, electrochemical, and/or UV-vis spectroscopy titration measurements, although structural evidence for this is limited. Upon the addition of 1-2 equiv of acetate, propionate, chloroacetate, trifluoroacetate, or bromoacetate to an aqueous, acidic solution of vanadium(III), trinuclear and tetranuclear complexes are formed. The structures of [V4(mu-OH)4(mu-OOCCF3)4(OH2)8]Cl4.7.5H2O (1), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.CH3COOH.12H2O (2), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.3H2O (3), [V3(mu3-O)(mu-OOCCH2Br)6(OH2)3]CF3SO3.H2O (4), [V3(mu3-O)(mu-OOCCH2CH3)6(OH2)3]Cl.2H2O (5), [V3(mu3-O)(mu-OOCCH3)6(OH2)3]Cl.3.5H2O (6), and [V3(mu3-O)(mu-OOCCH2Cl)6(OH2)3]CF3SO3.H2O (7) have been determined by X-ray diffraction. Importantly, electrospray mass spectrometry and 1H NMR measurements suggest that these complexes are not purely solid-state phenomena but are also present in solution. For the vanadium(III)/acetate and vanadium(III)/propionate systems, two paramagnetic 1H NMR signals corresponding to two distinct complexes (species A and B) are observed in the 40-55 ppm region for 0.20 mol equiv of acetate or propionate, at pD 3.44. No corresponding signals are observed for the vanadium(III)/bromoacetate and vanadium(III)/chloroacetate systems under the same conditions or for the vanadium(III)/ trifluoroacetate system using 19F NMR spectroscopy. UV-vis spectra suggest that species B are structurally analogous for the vanadium(III)/acetate and vanadium(III)/propionate systems, whereas structurally different complexes are the major species for the other systems. Diffusion coefficients of species B for the vanadium(III)/acetate and vanadium(III)/propionate systems determined by pulsed-field-gradient spin-echo NMR spectroscopy measurements are (3.0 +/- 0.1) x 10-6 and (3.23 +/- 0.01) x 10-6 cm2 s-1, respectively, and are most consistent with species B being trimeric, rather than tetranuclear, complexes.

Spectroscopic, viscositic and electrochemical studies of DNA interaction with a novel mixed-ligand complex of nickel (II) that incorporates 1-methylimidazole and thiocyanate groups

A novel mixed-ligand nickel(II) complex that contains 1-methylimidazole and thiocyanate, Ni(NCS) 2(Mim) 4 (Mim = 1-methylimidazole), was synthesized and its structure was determined by X-ray crystallography, IR spectrum and elemental analysis, etc. Its DNA-binding properties were studied by electronic absorption spectral, viscositive and electrochemical measurements. The absorption spectral and viscositive results suggest that the nickel(II) complex binds to DNA via partial intercalation. The addition of DNA results in the decrease of the peak current of the nickel(II) complex proved their interaction. The slight differences of peak profiles and electrochemical parameters between free and DNA-bound Ni(NCS) 2(Mim) 4 showed the formation of an electrochemical inactive complex between Ni(NCS) 2(Mim) 4 and DNA. The binding site and binding constant of the complex to DNA were determined by electrochemical titration method.