Cyclic Voltammetric Data Research Articles

Standard electrochemical behavior of high-quality, boron-doped polycrystalline diamond thin-film electrodes

Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 1019 B/cm3 range, and the boron-doping level of the USU films was approximately 5 x 10(20) B/cm(-3) based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe-(CN)6(3-/4-), Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, dopamine, ascorbic acid, Fe(3+/2+), and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, k0(app), observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, and chlorpromazine all involve electron transfer that is insensitive to the diamond surface microstructure and chemistry with k0(app) in the 10(-2)-10(-1) cm/s range. The rate constants are mainly influenced by the electronic properites of the films. Fe(CN)6(3-/4-) undergoes electron transfer that is extremely sensitive to the surface chemistry with k0(app) in the range of 10(-2)-10(-1) cm/s at the hydrogen-terminated surface. An oxygen surface termination severely inhibits the rate of electron transfer. Fe(3+/2+) undergoes slow electron transfer at the hydrogen-terminated surface with k0(app) near 10(-5) cm/s. The rate of electron transfer at sp2 carbon electrodes is known to be mediated by surface carbonyl functionalities; however, this inner-sphere, catalytic pathway is absent on diamond due to the hydrogen termination. Dopamine, like other catechol and catecholamines, undergoes sluggish electron transfer with k0(app) between 10(-4) and 10(-5) cm/s. Converting the surface to an oxygen termination has little effect on k0(app). The slow kinetics may be related to weak adsorption of these analytes on the diamond surface. Ascorbic acid oxidation is very sensitive to the surface termination with the most negative Ep(ox) observed at the hydrogen-terminated surface. An oxygen surface termination shifts Ep(ox) positive by some 250 mV or more. An interfacial energy diagram is proposed to explain the electron transfer whereby the midgap density of states results primarily from the boron doping level and the lattice hydrogen. The films were additionally characterized by scanning electron microscopy and micro-Raman imaging spectroscopy. The cyclic voltammetric and kinetic data presented can serve as a benchmark for research groups evaluating the electrochemical properties of semimetallic (i.e., conductive), hydrogen-terminated, polycrystalline diamond.

Spectroscopic and electrochemical characterization of the interaction of nitrogen monoxide and cobalt tetrasulfonated phthalocyanine in aqueous solutions and surfactant films

Cobalt(II) tetrasulfonated phthalocyanine (Co(II)TSPc) was attached to didodecyldimethylammonium (DDA) and dodecyltrimethylammonium (DTA) films. Spectroscopic data suggest that monomeric Co(II)TSPc is the major species in the surfactant films. Differential pulse voltammetry for CoTSPc/DTA films in phosphate buffer solution at pH 6 shows reduction peaks at +0.61, +0.06 and −0.64 V attributed to Co(III)/Co(II), Co(II)/Co(I) and TSPc reduction, respectively. In CoTSPc/DDA films, Co(II) is reduced at −0.03 V and TSPc at −0.68 and −0.84 V, and the peak for Co(III)/Co(II) is undetectable. The reaction of Co(II)TSPc with NO was studied for dissolved CoTSPc as well as for CoTSPc/DDA and CoTSPc/DTA films using spectroscopic and electrochemical techniques. From cyclic voltammetric data for Co(II)TSPc/DDA films in NO containing solution at pH 9, the stability constant of the Co(II)TSPc(NO) adduct was estimated to be 1.3×10 8 M −1. A slow shift of the FTIR band located at 1646–1700 cm −1 for solid Co(II)TSPc/DDA films exposed to NO is attributed to a conformation from a bent to linear configuration for the CoTSPc(NO) adduct. The rate of this transformation as obtained from UV–Vis experiments conducted for CoTSPc dissolved in aqueous solution as well as from FTIR and electrochemical data for CoTSPc/DDA films is 0.015±0.002 min −1. The Co(II)TSPc(NO) adduct formed in these films in solutions at pH 9 at NO concentrations <7×10 −5 M is reduced at −0.17 V. Higher NO concentrations cause reductive nitrosylation and the formation of a Co(I)TSPc(NO +) complex which is reduced at −0.72 and −0.46 V, in DDA and DTA films, respectively. The electroreduction of NO at these potentials is positively shifted by 100 and 450 mV relatively to that obtained for DDA and DTA films devoid of CoTSPc, respectively.

D2-Symmetric Dimer of 1,1‘-Binaphthyl and Its Chiral π-Conjugated Carbodianion

The synthesis of a chiral, nonracemic π-conjugated system with D2 point group of symmetry and the corresponding chiral carbodianion is described. Cu(II)-mediated oxidation of (R)-2,2‘-dilithio-1,1‘-binaphthyl (prepared from (R)(+)- 2,2‘-dibromo-1,1‘-binaphthyl) gives the corresponding dimer, (R)(+)-3, which is a chiral π-conjugated derivative of o-tetraphenylene, a saddle shaped molecule. When partially resolved 2,2‘-dibromo-1,1‘-binaphthyl is used, amplification of the enantiomeric excess (ee) is observed in the coupling product (3). The dihedral angles between the naphthalene moieties in (R)(+)-3 are about 70 °, as determined by the X-ray crystallography. However, CD and UV spectra, and cyclic voltammetric data of (R)(+)-3 are consistent with small, but far from negligible, conjugation (or homoconjugation) between the naphthalene moieties. The melting points of (R)(+)-3 and its racemate differ by more than 200 °C. Reaction of (R)(+)-3 with Li or Na in tetrahydrofuran (THF) gives the corresponding chiral...

Electrochemical determination of the stability of complexes formed by proton-ionizable ligands of 3,5-disubstituted 1H-pyrazole with phenethylamine

The application of two extreme models for diffusion in two-component systems to electrochemically determine equilibrium constants is discussed. The application of cyclic voltammetric, diferential pulse and rotating-disc electrode voltammetric data to elucidate the stoichiometry and formation constant of complex species by applying a generalization of the molar-ratio method is described. Molar-ratio experiments permit the distinction between the limiting diffusive regimes. The values of the equilibrium stability constants for complexation of phenethylamine and phenethylammonium ions by a 26-membered dioxotetraester crown of 3,5-disubstituted 1H-pyrazole as free ligand 1[L] and as dipyrazolate anion 1′[L 2−]2Na +, respectively, were determined.

The Use of Cyclic Voltammetry and Principal Component Analysis for the Rapid Evaluation of Selectivity of Conductive Polymer Sensors

Principal component analysis (PCA) was applied to cyclic voltammetric data obtained using a microelectrode array containing nine different conducting electroactive polymers. The array was immersed into two different supporting electrolytes containing potassium and methylamine. The objective was to build a method for selection of conducting electroactive polymers and predict favorable potential ranges for operation at a microelectrode array detector that discriminates between potassium and methylamine. The important advantage of this approach is that the analyst is presented with PC model options to produce ‘purpose built’ microelectrode arrays. The approach should be widely applicable.

New ruthenium(III) complexes containing tetradentate Schiff bases and their antibacterial activity

Ruthenium(III) complexes, [RuX(EPh3)(LL′)] (X = Cl, Br; E = P, As; LL′-acactet, dbm-tet, dbm-o-ph), have been synthesised by reacting [RuCl3(PPh3)3], [RuCl3(AsPh3)3], [RuBr3(AsPh3)3] or [RuBr3(PPh3)2(MeOH)] with tetradentate Schiff bases such as bis(acetylacetone)tetramethylenediimine (H2acactet), bis(dibenzoylmethane)tetramethylenediimine (H2dbmtet) and bis(dibenzoylmethane)-o-phenylenediimine (H2dbm-o-ph). All the complexes have been characterised by elemental analysis, i.r., electronic spectra, e.p.r., magnetic moment and cyclic voltammetric data and an octahedral structure has been tentatively proposed. These new complexes have been tested for their antibacterial activities.

Synthesis and characterization of polymer supported vitamin B12 model compounds

A series of polymer supported cobalt complexes have been synthesized by the reaction of Co(II)-SALEN (salicylaldehyde ethylenediimine) and other variations thereof with the chelating resin containing vinyl pyridine. The polymer supported complexes have been characterized by electronic and infrared spectra. The presence of polymer supports has a marked influence on the UV-visible bands observed in the electronic spectra of cobalt complexes. These polymer supported complexes are also investigated by cyclic voltammetry. The electronic spectral data and cyclic voltammetric data for free complexes and polymer supported complexes are compared. The discernible differences in the spectral and electrochemical data suggest the presence of pentacoordinate cobalt in the polymer matrix.

Synthesis and electrochemical studies of heterobinuclear complexes containing copper and molybdenum nitrosyl groups linked by Schiff base ligands

The reaction of [MoCl(NO)Tp* = tris(3,5-dimethylpyrazolylborate] with copper Schiff base complexes derived by condensation of one mole each of 2,5-dihydroxybenzaldehyde and salicylaldehyde with α,ω diamines [NH2(CH2)nNH2, n = 2–4] yields heterobinuclear complexes with two potential redox centres. I.r., electronic and e.s.r. spectroscopic properties of these complexes are described. Cyclic voltammetric data of the base complexes in DMSO reveal that the copper redox centres undergo irreversible one electron reduction at potentials which vary slightly with the polymethylene carbon chain backbone of the Schiff base ligands. Incorporation of [MoCl(NO)Tp*]+ groups in the copper Schiff base complexes, results to a slight anodic shift (100 mV) in the reduction potential of the copper centre which remains invariant as the polymethylene carbon chain lengthens. Electrochemical data of the heterobinuclear complexes using CH2Cl2 and DMSO as solvents indicate the solvent dependence of the reduction potentials of these complexes. In CH2Cl2, the reduction potential of the copper centre shifts cathodically by 100 mV, while that of the molybdenum centre shifts anodically by 200 mV. However, accumulated electrochemical data of the heterobinuclear complexes indicate minimal electronic interactions between the copper and molybdenum redox centres.

Electrodeposition and dissolution of Co–W alloy films

Cyclic voltammetric studies were carried out on platinum in alkaline solution containing cobalt sulphate, sodium tungstate, dimethyl sulphoxide and triammonium citrate. Spectral u.v. absorption studies of cobalt citrate complex indicate the species to be [Co L (H2O)3]2+, where L is triammonium citrate. The deposition of cobalt involves a stepwise electron transfer mechanism. The observed cyclic voltammetric data show that the alloy deposition is possibly from cobalt–tungstate complex. The citrate ions and dimethyl sulphoxide hinder the alloy deposition. Dimethyl sulphoxide, which specifically adsorbs on the electrode surface, favours the hydrogen evolution reaction (HER), whereas tungstate hinders the HER. Stripping voltammograms show the existence of cobalt rich alloy phases. X-ray diffraction studies further confirm the phases to be Co3W and Co7W.

New redox materials based on functionalized 9,10-anthracenediylidenes

Abstract

Multivariate Curve Resolution of Cyclic Voltammetric Data: Application to the Study of the Cadmium-Binding Properties of Glutathione

Multivariate curve resolution is applied to cyclic voltammetry (CV) data obtained in the study of Cd(II) complexation by glutathione (GSH). The relatively poor resolution of CV hinders the direct interpretation of raw data. The use of CV is improved by the combination of several chemometric techniques based on factor analysis: singular-value decomposition, evolving factor analysis, and multivariate curve resolution with constrained alternating least squares optimization including a new peak-shape constraint. This multivariate analysis data treatment simultaneously reveals the formation of Cd(GSH)2 and Cd2(GSH)2 complexes, through the calculated concentration profiles, and allows the assignment of numerically obtained pure individual CV signals for the different Cd(II) ions present in solution (free and bound) and involved in the electrochemical process.

1,3-Dithiol-2-ylidene derivatives of 1,3-indanedione

The synthesis is described of a series of mono-, bis-, and tris(1,3-dithiol-2-ylidene) derivatives 7,9 and 10 starting from 1,3-indanedione. Cyclic voltammetric data establish that the π-electron donor ability of these molecules increases in the sequence 7 < 9 < 10, which is consistent with stabilisation of the cationic species by the presence of additional 1,3-dithiole units. The X-ray crystal structure of a complex ( 7a) 2.TCNQ is reported. Short intramolecular S…O contacts are observed within moiety 7a. The mean planes of 7a and TCNQ are almost parallel forming planar layers within which ribbons of TCNQ molecules are intercalated by double ribbons of molecule 7a all stretched along thex direction. Mono-, bis-, and tris(1,3-dithiol-2-ylidene) derivatives of 1,3-indanedione have been synthesised, and their π-electron donor ability studied by cyclic voltammetry. The crystal structure of a complex ( 7a) 2·TCNQ is reported. [Display omitted]

4-Ethoxycarbonyl-4′,5,5′-trimethyltetrathiafulvalene and its radical cation: Langmuir–Blodgett film studies, EPR spectra and the X-ray crystal structure of (Me3TTF-CO2Et)2·TCNQ complex

Langmuir–Blodgett films of the title trimethyltetrathiafulvalene derivative 10 have been assembled without the need for added fatty acid: room temperature, in-plane, dc conductivity values of the films before and after doping with iodine vapour were σrt = 10–5 S cm–1 and 10–1 S cm–1, respectively. Over the temperature range 300–100 K the films exhibited a linear current versus voltage relationship, with an activation energy for conductivity Ea = 0.11 eV. Cyclic voltammetric data were obtained for LB films of 10 and the best response was recorded for a 2-layer film; electroactivity gradually disappeared after a few cycles, which is consistent with film desorption from the electrode. UV–vis and IR spectra of the LB films are consistent with a conjugative intramolecular charge-transfer interaction between the triMe-TTF (donor) and ester (acceptor) moieties of 10 (see structure 10′). This increases the amphiphilic nature of 10 and is believed to play an important role in stabilising the LB film structure. Iodine doping of the LB films leads to the formation of radical cations 10·+, and polarised spectra show that the molecules are aligned at a high angle to the substrate surface. Simultaneous electrochemistry and EPR (SEEPR) studies provide insight into the electronic structure of the radical cation species 10·+ in solution; the ethoxycarbonyl group strongly polarises the spin density, and these data are supported by ab initio UHF and B3LYP calculations. The single crystal X-ray structure of the complex (10)2·TCNQ (TCNQ = tetracyano-p-quinodimethane) reveals a mixed ⋯ADDADD⋯ stacking motif with a low degree of charge transfer between the D and A moieties. Analysis of the bond lengths in the donor moiety confirms a contribution from the zwitterionic structure 10′.

Donor-π-Acceptor Species Derived from Functionalised 1,3-Dithiol-2-ylidene Anthracene Donor Units Exhibiting Photoinduced Electron Transfer Properties: Spectroscopic, Electrochemical, X-Ray Crystallographic and Theoretical Studies

Steric interactions between the anthraquinoid core and the 1,3-dithiole and dicyanomethylene groups play a key role in determining the physical properties of system 1. The intramolecular charge transfer properties of this donor–π-acceptor species have been explored and cyclic voltammetric data, X-ray crystal structures and ab initio calculations are also reported.

Electrochemical study on cytochrome c peroxidase from Paracoccus denitrificans: a shifting pattern of structural and thermodynamic properties as the enzyme is activated

The di-haem cytochrome c peroxidase of Paracoccus denitrificans is a calcium binding dimer of 37.5 kDa subunits. It is responsible for reduction of H2O2 to H2O with oxidation of cytochrome c 550 and is isolated in a fully oxidised state (inactive) in which one haem (centre I) is in a high-spin/low-spin equilibrium and high potential and the other (centre II) is low-spin and low potential. The enzyme undergoes direct electron transfer (without the need for mediators) with a 4,4′-dithiodipyridine-modified gold electrode and the response of both haem groups can be observed. By combination of the cyclic and pulse voltammetric data with the established spectroscopic information, it was demonstrated that entry of one electron to the high potential haem leads (in a mechanism involving strong haem-haem interactions) to a complex change of spin states and redox potentials of both haems in order to attain a "ready state" for binding, reduction and cleavage of the hydrogen peroxide. In the absence of endogenous calcium, haem communication can be completely disconnected and is recovered only when Ca2+ is added, an essential step for the formation of the peroxidatic site. The intricate electrochemical behaviour of this enzyme was interpreted as a mechanism involving, both reduction and oxidation of the high potential haem, an interfacial electron transfer coupled to a homogenous chemical reaction (EC mechanism). We discuss two different models for the sequence of events leading to the appearance of the active pentacoordinated peroxidatic haem.

Epr, cyclic voltammetric and biological activities of copper(II) complexes of salicylaldehyde N(4)-substituted thiosemicarbazone and heterocyclic bases

An interesting series of heterocyclic base adducts of copper(II) complexes have been synthesised by the reaction of copper(II) acetate with salicylaldehyde N(4)-phenylthiosemicarbazone in presence of heterocyclic bases like pyridine (py), piperidine (pip), β/ γ-picoline ( β/ γ-pic), 1,10-phenanthroline (phen) and 2,2′-bipyridine (bipy). IR, electronic, 1H and 13C NMR spectra of the thiosemicarbazone, as well as IR, electronic and EPR spectra of the complexes have been obtained. Based on EPR studies spin Hamiltonian and bonding parameters have been calculated. The g values, calculated for all the complexes in frozen DMF, indicate the presence of the unpaired electron in the d x 2− y 2 orbital. The metal-ligand bonding parameters evaluated showed strong in-plane sigma and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for the four-coordinate and a distorted square pyramidal for five-coordinate complexes. From cyclic voltammetric data reversible copper(II)/copper(I) couples are observed for these complexes. The thiosemicarbazone and its copper(II) complexes show growth inhibitory activity against human pathogenic bacteria Salmonella typhi, Shigella dysentariae, non-coagulace Staphylococcus, Photobacterium sp. and Staphylococcus aureus and plant pathogenic fungi Rhizoctonia, Collectotrichium and Aspergillus sp.

Electrochemistry of the bis(1,4,7-triazacyclodecane) cobalt(III) complex and its role in the catalytic reduction of hydrogen

The electrochemistry of the bis(1,4,7-triazacyclodecane) cobalt(III) complex at a mercury electrode, HMDE, in aqueous Britton–Robinson buffer solutions was investigated using cyclic voltammetry, double-potential-step chronoamperometry and chronocoulometry. The cyclic voltammetric data were analyzed by digital simulation to confirm and to measure the heterogeneous and homogeneous parameters for the suggested electrode mechanism. Generally, the complex is electrochemically reduced giving rise to two cyclic voltammetric waves. The first wave is a diffusion-controlled reversible wave. It is assigned to the stable Co(III)/Co(II) redox couple. The second one is found to be irreversible and corresponding to a reduction of Co(II) to Co(I) species. The monovalent cobalt, highly unstable, is rapidly protonated, and then forms cobalt hydride. The hydride decomposes to hydrogen molecules and regenerates Co(II) species following a disproportionation pathway. The overall reduction mechanism is concluded to be an EECC kinetics.

Multi-technique study of the anodic degradation of polyaniline films

Polyaniline (PANI) films, formed by potential cycling methods on Au electrodes in sulfuric acid solutions, were anodically degraded with time at ca. 1 V versus RHE. Ellipsometric and cyclic voltammetric data suggest that colored species are formed within the film, perhaps containing quinone endgroups, and the bulk of the film dissolves uniformly creating greater porosity. This model of film degradation has been supported by transmission electron microscopy (TEM) studies of cross-sectional samples of PANI films. Both TEM and ellipsometry also showed that the PANI film is not delaminated, and is very resistant to anodic dissolution/degradation. Concurrent in situ mass measurements suggest that, in the early stages of film degradation, some regions of the film become electrochemically inactive, although the nature of the charge compensation mechanism of the PANI redox reaction remains unaltered. When no further film degradation can be accomplished, the mass data show that a substantial quantity of largely inactive film material is still present on the electrode surface. Furthermore, the change in the redox potential and the invariant charge compensation stoichiometry suggests that, although the final degraded film is a different material from the newly formed PANI film, only those portions of the film that have PANI characteristics are electrochemically active.

Zeolite-encapsulated manganese(III)salen complexes

Manganese(III) complexes of [ N, N′-ethylenebis(salicylidene-aminato)] (salen), [ N, N′-ethylenebis(5-chloro-salicylidene-aminato)] (Cl 2Salen), [ N, N′-ethylenebis(5-bromo-salicylidene-aminato)] (Br 2Salen) and [ N, N′-ethylenebis(5-nitro-salicylidene-aminato)] [(NO 2) 2Salen] have been encapsulated in the supercages of zeolite X by the zeolite synthesis method. The catalysts have been characterized by FTIR, UV–Vis and EPR spectroscopic techniques, XRD, SEM, thermal and elemental analysis, as well as nitrogen adsorption and cyclic voltammetric studies. The extent of encapsulation of the Mn(III)Salen complexes in zeolite X varies with the nature of the substituent group on the aromatic ring. While bromo groups enhance encapsulation, substitution with –NO 2 groups decreases the amounts of Mn(III) complexes encapsulated in the cavities of the zeolites. Cyclic voltammetric data indicate that the zeolite matrix facilitates the reduction of Mn(III) to Mn(II), suggesting that it behaves like an electron-withdrawing substituent. The aerobic oxidation of styrene to benzaldehyde, styrene oxide and phenylacetaldehyde over these catalysts is also reported.

Selective oxidation over copper and manganese salens encapsulated in zeolites

Abstract Copper and Mn(III)(X 2 -salen) complexes, where salen 2− =N,N′-ethylenebis(salicylideneaminato) and X=H, Cl, Br or (NO 2 ), encapsulated in the cavities of zeolites NaX and NaY, have been synthesized and characterized by various physicochemical measurements. Samples obtained by synthesizing the complexes `in situ' in the cavities of the zeolite by the `flexible ligand' method contain a higher concentration of the complex than those obtained by synthesizing the zeolites around the preformed copper complex. Substitution of the aromatic hydrogen atoms of the salen ligand by electron-withdrawing groups like -Cl, -Br and NO 2 has two major effects: (1) retention and concentration of the copper complex in the zeolite cavities is enhanced (due to the larger size of the substituents); and (2) the spectral properties of the encapsulated complex are modified. Cyclic voltammetric data indicate that the zeolite matrix facilitates the reduction of Mn(III) to Mn(II), suggesting that it behaves like an electron-withdrawing substituent. The rates of decomposition of H 2 O 2 and tert-butyl hydroperoxide as well as the selective, low-temperature oxidation of phenol, styrene and para-xylene are all enhanced by electron-withdrawing substituents on the salen ligand.