Digital Simulation Of Cyclic Voltammograms Research Articles

Redox-Induced Structural Reorganization Dictates Kinetics of Cobalt(III) Hydride Formation via Proton-Coupled Electron Transfer.

Two-electron, one-proton reactions of a family of [CoCp(dxpe)(NCCH3)]2+ complexes (Cp = cyclopentadienyl, dxpe = 1,2-bis(di(aryl/alkyl)phosphino)ethane) form the corresponding hydride species [HCoCp(dxpe)]+ (dxpe = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), and dcpe (1,2-bis(dicyclohexylphosphino)ethane)) through a stepwise proton-coupled electron transfer process. For three [CoCp(dxpe)(NCCH3)]2+ complexes, peak shift analysis was employed to quantify apparent proton transfer rate constants from cyclic voltammograms recorded with acids ranging 22 pKa units. The apparent proton transfer rate constants correlate with the strength of the proton source for weak acids, but these apparent proton transfer rate constants curiously plateau (kpl) as the reaction becomes increasingly exergonic. The absolute apparent proton transfer rate constants across both these regions correlate with the steric bulk of the chelating diphosphine ligand, with bulkier ligands leading to slower kinetics (kplateau,depe = 3.5 × 107 M-1 s-1, kplateau,dppe = 1.7 × 107 M-1 s-1, kplateau,dcpe = 7.1 × 104 M-1 s-1). Mechanistic studies were conducted to identify the cause of the aberrant kPTapp-ΔpKa trends. When deuterated acids are employed, deuterium incorporation in the Cp ring is observed, indicating protonation of the CoCp(dxpe) species to form the corresponding hydride proceeds via initial ligand protonation. Digital simulations of cyclic voltammograms show ligand loss accompanying initial reduction gates subsequent PCET activity at higher driving forces. Together, these experiments reveal the details of the reaction mechanism: reduction of the Co(III) species is followed by dissociation of the bound acetonitrile ligand, subsequent reduction of the unligated Co(II) species to form a Co(I) species is followed by protonation, which occurs at the Cp ring, followed by tautomerization to generate the stable Co(III)-hydride product [HCoCp(dxpe)]+. Analysis as a function of chelating disphosphine ligand, solvent, and acid strength reveals that the ligand dissociation equilibrium is directly influenced by the steric bulk of the phosphine ligands and gates protonation, giving rise to the plateau of the apparent proton transfer rate constant with strong acids. The complexity of the reaction mechanism underpinning hydride formation, encompassing dynamic behavior of the entire ligand set, highlights the critical need to understand elementary reaction steps in proton-coupled electron transfer reactions.

Novel electrochemical properties of an emergent mycotoxin: sterigmatocystin

The electrochemical reduction of sterigmatocystin in acetonitrile +0.1M tetrabutylammonium perchlorate at glassy carbon electrodes is studied for the first time using cyclic and square wave voltammetries, and controlled-potential electrolysis. Two reduction peaks centered at −1.77 and −2.33V vs. Ag/AgCl were found, which correspond to the formation of the radical anion and dianion, respectively. The overall electrode process was diffusion controlled. The initially formed radical anion undergoes an irreversible dimerization reaction with a rate constant of 2.06×104M−1s−1, producing a basic dimeric dianion, which is protonated by the starting molecule. An unstable dimeric reaction product was detected by UHPLC-MS/MS measurements. A value of (3.1±0.9) ×10−5cm2s−1 was calculated for sterigmatocystin diffusion coefficient from convoluted cyclic voltammograms. Thermodynamic and kinetics parameters were determined from digital simulation of cyclic voltammograms. Probable chemical structures for the dimer are proposed based on the results of theoretical calculations. The effect of the addition of tetrabutylammonium hydroxide, trifluoroacetic acid and water on the voltammetric signals was also investigated.The quantitative determination of sterigmatocystin was carried out by square wave voltammetry using the commercial reagent. The calibration curve was linear in the concentration range from 0.050 to 11.2ppm, and the limits of detection and quantification were 10 and 33ppb for signal to noise ratios of 3:1 and 10:1, respectively.

Oxygen Reduction Reactions in Aprotic Ionic Liquids Based Mixed Electrolytes for High Performance of Li–O2 Batteries

The kinetics and mechanisms of oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) in the absence and presence of Li+ have been systematically investigated in five ionic liquid (IL)/dimethyl sulfoxide (DMSO) mixed electrolytes for potential applications for high performance Li–O2 batteries. The diffusion coefficient and solubility of oxygen in these mixed electrolytes are determined by nonlinear fitting of potential-step chronoamperometry obtained at a platinum microelectrode. The mixed electrolytes exhibit enhanced oxygen diffusion coefficient (6.2–11.3 × 10–6 cm2 s–1), compared to neat ILs, and solubility (2.9–6.8 mM), compared to DMSO. Cyclic voltammetry (CV) shows that all the IL-mixed electrolytes display good stability against superoxide (O2•–) except for 1-butyl-3-methyl-pyridinium bis(trifluoromethylsulfonyl)imide [BMPy][NTf2], where the generated superoxide is found to be unstable and reacts with the cations of the IL. Using digital simulation of cyclic voltammograms for ORR, ...

Electrochemical oxidation of catecholamines in the presence of aromatic amines: interplay between inter- and intramolecular nucleophilic addition

The reactions of electrochemically generated o-quinones from oxidation of catecholamines with aniline derivatives have been studied using cyclic voltammetry. There is a close and pH-dependent interplay between intra and intermolecular Michael addition reactions of side chain amine group of catecholamines and anilines toward the electrochemically generated o-quinone. The pH dependence of reactions has been studied and the condition for domination of each reaction was obtained. The observed homogeneous rate constants of reactions were estimated by digital simulation of cyclic voltammograms for each pathway. The reactivities and the rate constants of Michael addition of anilines depend on the electron-withdrawing character of their substituent, which have been studied quantitatively.

A glance at the reactivity of osma(II)cycles [Os(C–N)x(bpy)3 − x]m + (x = 0–3) Covering a 1.8 V Potential Range toward Peroxidase through Monte Carlo Simulations (−C–N = o-2-phenylpyridinato, bpy = 2,2′-bipyridine)

Three cyclometalated and one coordination compounds [Os(C–N)x(bpy)3−x]m (x/m=0/2+ (4); 1/1+ (3); 2/1+ (2); 3/0 (1); −C–N=2-phenylpyridinato, bpy=2,2′-bipyridine) with drastically different reduction potentials have been used for analyzing the second-order rate constants for one-electron, metal-based osmium(II) to osmium(III) oxidation of the complexes by compound I (k2) and compound II (k3) of horseradish peroxidase. Previously unknown k2 and k3 have been determined by digital simulation of cyclic voltammograms measured in phosphate buffer of pH7.6 and 21±1°C. Osmium(II) species derived from osmium(III) complexes 1 and 2 were generated electrochemically in situ. Under the conditions used the reduction potentials for the OsIII/II feature equal −0.90, −0.095, 0.23 and 0.85V versus NHE (normal hydrogen electrode) for 1–4, respectively. The rate constants k2 equal ~5×107, 6×108, 2×106 and 1×105M−1s−1 and the rate constants k3 equal ~9×106, 4×107, 1×106 and 1×105M−1s−1 for complexes 1–4, respectively. Both rate constants k2 and k3 first increase with increasing the reaction driving force on going from 4 to 2 but then both decrease on going to complex 1 though the reaction driving force is the highest in this case. The system described has been explored theoretically using docking Monte Carlo simulations.

Modulation of Quinone PCET Reaction by Ca2+ Ion Captured by Calix[4]quinone in Water

Calix[4]arene-triacid-monoquinone (CTAQ), a quinone-containing water-soluble ionophore, was utilized to investigate how proton-coupled electron transfer (PCET) reactions of quinones were influenced by redox-inactive metal ions in aqueous environment. This ionophoric quinone derivative captured a Ca(2+) ion that drastically altered the voltammetric behavior of quinone, showing a characteristic response to pH and unique redox wave separation. Spectroelectrochemistry verified significant stabilization of the semiquinone, and electrocatalytic currents were observed in the presence of Ca(2+)-free CTAQ. Using digital simulation of cyclic voltammograms to clarify how the thermodynamic properties of quinones were altered, a simple scheme was proposed that successfully accounted for all the observations. The change induced by Ca(2+) complexation was explained on the basis of the combined effects of the electrostatic influence of the captured metal ion and hydrogen bonding of water molecules with the support of DFT calculation.

Electrochemical reduction of phthalide at carbon cathodes in dimethylformamide: Effects of supporting electrolyte and gas chromatographic injector-port chemistry on the product distribution

Abstract Cyclic voltammetry and controlled-potential (bulk) electrolysis have been used to investigate the direct reduction of phthalide at carbon electrodes in dimethylformamide (DMF) containing 0.10 M tetramethylammonium perchlorate (TMAP) or tetra- n -butylammonium perchlorate (TBAP). Cyclic voltammograms recorded with a glassy carbon electrode exhibit a single cathodic peak and a corresponding anodic peak that arise, respectively, from one-electron reduction of phthalide to generate a radical-anion intermediate and from reoxidation of the intermediate. At a scan rate of 100 mV s −1 , quasi-reversible behavior is observed (due to ring-opening of the radical-anion), whereas fully reversible behavior is seen at 5 V s −1 or higher. Digital simulation of cyclic voltammograms indicates that the lifetime of the radical-anion is 3.5 s. Bulk electrolysis of phthalide at a reticulated vitreous carbon cathode affords products that depend on the procedure used to analyze the catholyte. Direct injection of catholyte into a gas chromatograph shows phthalide and a 2-methylbenzoate ester bearing an alkyl moiety from the supporting-electrolyte cation. However, if the catholyte is partitioned between diethyl ether and aqueous hydrochloric acid before gas chromatographic analysis, phthalide and 2-methylbenzoic acid are observed. Thermally induced reactions that occur in the injector port of the gas chromatograph are responsible for the formation of the 2-methylbenzoate ester as well as for the phthalide found in all electrolyzed solutions.

Electrochemical Oxidation of Wine Polyphenols in the Presence of Sulfur Dioxide

Electrochemical oxidation of three representative wine polyphenols (catechin, caffeic acid, and quercetin) in the presence of sulfur dioxide in a model wine solution (pH = 3.3) was investigated. The oxidation was undertaken using chronoamperometry at a rotating glassy carbon rod electrode, and the reaction products were characterized by HPLC-MS. The mechanism of electrochemical oxidation of polyphenols in the presence of sulfur dioxide was proposed to be an ECEC mechanism. The polyphenols first underwent a one-electron oxidation to a semiquinone radical, which can be reduced back to the original polyphenol by sulfur dioxide, or further oxidized to the quinone form. In the cases of caffeic acid and catechin, the quinone combined with sulfur dioxide and produced new derivatives. The quercetin quinone underwent further chemical transformations, producing several new compounds. The proposed mechanisms were confirmed by digital simulation of cyclic voltammograms.

Voltammetric analysis of the possibility of derivatization of levodopa in the presence of aniline derivatives

Electrochemical oxidation of levodopa (LD) as one of the most well-known neurotransmitters has been studied in the presence of some aniline derivatives. The electron transfer of LD is followed by two competitive reactions in the presence of these amines. The reactions are the Michael additions of side chain amine group of LD and/or aromatic amines to electrochemically generated o-quinone. There are two ECE mechanisms for both pathways and the competition between these inter and intramolecular reactions drastically depends on the pH of the medium. The pH dependence of reactions has been studied and the observed homogeneous rate constants of the reactions were estimated by digital simulation of cyclic voltammograms. The effect of aniline substituents was also studied with regard to their reactivities toward o-quinone of LD and the competitive reactions. Based on the obtained results, the products of intermolecular reactions are electroactive diphenylamine derivatives and their half-wave potentials depend on the nature of the aniline substituent.

Efficient Factors on the Reaction Rate and Site-Selectivity in Sulfonylation of Catechol and Hydroquinone Derivatives: Experimental and Theoretical Studies

Electrochemical oxidation of some catechol (1a-1e) and hydroquinone (5a,5b) derivatives in the presence of arylsulfinic acids has been investigated both experimentally and theoretically to provide insight into the influence of some factors on the chemical reaction rate of electrogenerated benzoquinones with arylsulfinic acids and site-selectivity of the sulfination of some derivatives of catechol and hydroquinone. The results of this work show that the chemical reaction rate between electrogenerated o-benzoquinones and 4-chlorobenzenesulfinic acid is dependent on the substituent group on the catechol ring. The observed homogeneous rate constants (kobs) of benzoquinones with 4-chlorobenzenesulfinic acid were determined using digital simulation of cyclic voltammograms. In this work, the effect of the change of Gibbs free energy of the chemical reaction and charge on the reaction site were also studied in detail. ΔGaq of the Michael addition reactions and charge of each site of reaction of studied species were calculated using 6–311G (p,d) basis set DFT(B3LYP, BP86) levels of theory. The results show that the charge of the reaction site not only dictates the site of reaction but also indicates the value of the homogeneous rate constants (kobs) of the Michael addition reaction.

Electrochemical Study of Esculetin Nitration by Digital Simulation of Cyclic Voltammograms

The reaction of electrochemically generated o-quinones from oxidation of esculetin as Michael acceptor with nitrite ion as nucleophile has been studied using cyclic voltammetry. The reaction mechanism is believed to be EC, including oxidation of catechol moiety of esculetin followed by Michael addition of nitrite ion. The observed homogeneous rate constants (𝑘obs) for reactions were estimated by comparing the experimental voltammetric responses with the digitally simulated results based on the proposed mechanism. Also the effects of pH and nucleophile concentration on voltammetric behavior and the rate constants of chemical reactions were described.

Kinetic Study of the Oxidation of 4-Morpholinoaniline and N,N–Dialkyl-p-phenylenediamines in the Presence of Barbituric Acids Derivatives by Digital Simulation of Cyclic Voltammograms

Electrochemical oxidation of 4-morpholinoaniline, N,N-diethyl-p-phenylenediamine and N,N-dimethyl-p-phenylenediamine in the presence of barbituric acid, 1,3-dimethylbarbituric acid and 2-thiobarbituric acid as nucleophiles have been studied in various pHs using cyclic voltammetry and controlled-potential coulometry. The reaction mechanism is believed to be ECEC including oxidation of 4-morpholinoaniline, (N,N-diethyl-p-phenylenediamine or N,N-dimethyl-p-phenylenediamine), intermolecular Michael addition, oxidation of adduct and intramolecular Michael addition. Final products are compounds containing barbiturates. The observed homogeneous rate constants (kobs) of reactions are estimated by digital simulation of cyclic voltammograms. Also the effects of nucleophile and electrophile structures on the rate constants of chemical reactions are described.

Electron dopable molecular wires based on the extended viologens

Facile electron transfer in molecules with one dimension greatly exceeding the other two is essential in the development of new molecular electronic devices as these molecules can serve as so-called molecular wires. In this communication the electrochemical behavior of a series of molecules with multiple extended viologen moieties has been studied. We show that the electron transfer in the shortest wire is due to reduction of two identical communicating pyridinium moieties leading to a full charge delocalization, whereas the electron transfer in molecules with n≥ 2 is due to reduction of initially non-communicating centers. This was confirmed by digital simulation of cyclic voltammograms. All studied molecules accept reversibly at least four and up to ten electrons without any long-term chemical changes, which is a prerequisite for their future application. Chemical stability of these molecules after multiple electron transfer was confirmed by in situ UV-Vis spectroelectrochemical detection.

Kinetic Study of the Oxidation of Catechols in the Presence of Some Aza‐crown Ethers by Digital Simulation of Cyclic Voltammograms

AbstractThe electrochemical oxidation of catechols (1) have been studied in the presence of diaza‐18‐crown‐6 (DA18C6) (3a), diaza‐15‐crown‐5 (DA15C5) (3b), and aza‐15‐crown‐5 (A15C5) (3c) as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically generated o‐benzoquinones (2) in Michael‐type reaction with aza‐crown ethers (3) to form the corresponding new o‐benzoquinone‐aza‐crown ether adducts (5). Based on ECE mechanism, the observed homogeneous rate constants (kobs) of the reaction of o‐bezoquinones (2) with aza‐crown ethers (3) were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated observed homogeneous rate constants (kobs) was found to vary in the order DA18C6>DA15C5>A15C5.

Electrochemical oxidation of catechols in the presence of cyanoacetone and methyl cyanoacetate

Electrochemical oxidation of catechols is studied in the presence of cyanoacetone and methyl cyanoacetate as nucleophiles in aqueous solutions by means of cyclic voltammetry and controlled-potential coulometry. The reaction mechanism is believed to be ECEC including oxidation of catechol, intermolecular Michael addition, oxidation of adduct and intramolecular Michael addition. Final products are nitrile containing benzofurans. The observed homogeneous rate constants ( k obs) of reactions are estimated by digital simulation of cyclic voltammograms. Also the effects of nucleophile and catechol structures on the rate constants of chemical reactions are described.

A digital simulation study of steady-state voltammograms for the ion transfer across the liquid–liquid interface formed at the orifice of a micropipette

Digital simulation of cyclic voltammograms for the ion transfer across the micro liquid–liquid interface formed at the orifice of a glass micropipette shows that the electrochemically driven flow of ions from the inside of the micropipette to the infinitely large outer phase gives steady-state current–potential characteristics, when the shape of the tip is not cylindrical but truncated conical as usual micropipettes. Such steady-state behavior well explains experimentally observed voltammograms for ion transfer across the hydrophobic ionic liquid–water interface formed at the orifice of a micropipette with a small radius. Both the limiting current and the half-wave potential of the voltammogram vary with the angle of the inner wall of the micropipette with respect to the axis of rotational symmetry of the pipette, θ 1 , and both reach the limits predicted by the radial diffusion of the ions to the inlaid disk, that is, θ 1 = 90 ° in an asymptotic manner. The conditions for obtaining such steady-state voltammograms depend on the size of the interface and the scan rate of the applied voltage, aside from θ 1 .

Study of the oxidation of some catechols in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole by digital simulation of cyclic voltammograms

AbstractElectrochemical oxidation of catechol and its derivatives (1a–d) has been studied in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole (3) at various pHs. Some electrochemical techniques such as cyclic voltammetry using the diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled‐potential coulometry were used. Results indicate the participation of catechols (1a–d) with 3 in an intramolecular cyclization reaction to form the corresponding 1,2,4‐triazino[5,4‐b]‐1,3,4‐thiadiazine derivatives. In various scan rates, based on an electron transfer–chemical reaction–electron transfer–chemical reaction mechanism, the observed homogeneous rate constants (kobs) for Michael addition reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. The oxidation reaction mechanism of catechols (1a–d) in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole (3) was also studied. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 340–345, 2007

Electrochemical nitration of catechols: Kinetic study by digital simulation of cyclic voltammograms

Electrochemical nitration of catechols has been studied in the presence of nitrite ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of produced o -benzoquinones in Michael reaction with nitrite ion to form the corresponding nitrocatechols. Based on EC mechanism, the observed homogeneous rate constants of nitration reaction were estimated by comparing the experimental cyclic voltammograms with the digital simulated results.

Kinetic study of the oxidation of some catecholamines by digital simulation of cyclic voltammograms

AbstractElectrochemical oxidation of some catecholamines such as dopamine (1), L‐dopa (2), and methyldopa (3) has been studied in various pH values, using cyclic voltammetry. The results indicate participation of catecholamines (1–3) in intramolecular cyclization reaction to form the corresponding o‐quinone derivatives (1d–3d). In various pHs, based on ECE mechanism, the observed homogeneous rate constants (kobs) of cyclization reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital‐simulated results. Also, the cyclization rate constants (kcyc) were calculated using microscopic acidic dissociation constant of ammonium groups. The significant differences in electrochemical behavior, kobs and kcyc, of L‐dopa (2) and methyldopa (3) with dopamine (1) are due to the effects of the side chain carboxyl group. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 17–24, 2005

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlled-potential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (kobs) for the reaction of o-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.