Henry N. Blount

Interfacial electrochemistry of cytochrome c at tin oxide, indium oxide, gold, and platinum electrodes

Abstract Cyclic voltammetry has been used to study the heterogeneous electron transfer kinetics of horse heart cytochrome c in pH 7 tris/cacodylate media at several electrode surfaces. Reversible voltammetric responses (formal heterogeneous electron transfer rate constant>10−2 cm/s) were observed at bare gold electrodes and at tin-doped indium oxide semiconductor electrodes for certain experimental conditions. Quasireversible voltammetric responses were more typically observed at fluorine-doped tin oxide semiconductor electrodes, bare platinum electrodes, and at the indium oxide electrodes. Reaction rates at bare metal electrodes were strongly dependent on pretreatment procedures and experimental protocol. Reaction rates at metal oxide electrodes were strongly dependent on solution conditions, pretreatment procedures, and on the hydration state of the electrode surface. A general mechanistic scheme involving both interfacial electrostatic and chemical interactions is proposed for cytochrome c electrode reactions. The asymmetric distribution of surface charges on cytochrome c appears to play a dominant role in controlling electron transfer rates by its interaction with the electric field at the electrode surface. Electron transfer distances are also considered, and it is concluded that electron transfer between an electrode surface and the exposed heme edge of properly oriented cytochrome c molecules involves maximum distances of ca. 0.6–0.9 nm.

The anodic pyridination of 9,10-diphenylanthracene in acetonitrile: The spectroelectrochemical view

Summary The mechanism of the anodic pyridination of 9,10-diphenylanthracene in acetonitrile has been examined using hybrid spectral-electrochemical techniques and has been found to be of the “half-regeneration” type previously reported for the anodic hydroxylation of the same substrate.

On the mechanism of the electrochemical reduction of N-methylpyridinium ion

The electrochemical reduction of N-methylpyridinium ion (NMP+) at concentrations <2 × 10−4 M in aqueous solution in the pH range of 5–11 has been shown to he a one-electron process which gives rise to 1-methyl-1,4-dihydropyridinyl radicals. These pyridinyl radicals undergo rapid dimerization for which the bimolecular rate constant has been shown to be in excess of 1 × 107 M−1 s−1. The formal potential for the reduction of NMP+ in aqueous 1.0 M KCl is found to be −1.372 V vs. NHE. The formation of the pyridinyl radical as a transient intermediate in the electroreduction of NMP+ has been established by spin trapping using α-phenyl-N-tert-butyl nitrone.

Derivative cyclic voltabsorptometry of cytochrome c.

Abstract The recently reported method of derivative cyclic voltabsorptometry has been applied to horse heart cytochrome c at fluoride doped tin oxide optically transparent electrodes. The advantages of the derivative cyclic voltabsorptometric method compared to voltammetric methods in analytical, kinetic and mechanistic studies are discussed.

The electropreparation and characterization of 9,10-dihydro-9,10-diphenyl-9,10-dipyridiniumanthracene diperchlorate: The product of the anodic pyridination of 9,10-diphenylanthracene

Summary The product of the anodic pyridination of 9,10-diphenylanthracene at a platinum electrode in acetonitrile has been isolated and characterized as 9,10-dihydro-9,10-diphenyl-9,10-dipyridiniumanthracene diperchlorate. Macroscale electrolyses using tetraethylammonium perchlorate as the supporting electrolyte gave rise to a mixed product comprised of the titled compound and the corresponding triethylamine adduct. The source of the triethyl amine was found to be the cathodic discharge of the cation of the supporting electrolyte. A reversible equilibrium was shown to exist between 9,10-dihydro-9,10-diphenyl-9,10-dipyridiniumanthracene diperchlorate and 9,10-dihydro-9,10-diphenyl-9,10-di(triethyl)ammoniumanthracene diperchlorate.

Electrochemical Aspects of Bioenergetics

The application of electrochemical techniques to the study of biological systems finds its roots in work done more than fifty years ago.(1) This early work, based principally on potentiometric studies, provided extensive thermodynamic information for a number of biological molecules. More recently there has been a remarkable expansion in the application of electrochemical techniques to problems in biological systems. A number of scientific disciplines that focus on the thermodynamics, kinetics, and mechanisms of biological electron transfer are responsible for this enhanced activity. The basic processes by which energy is transduced between chemical and electrical domains in biological systems are being intensely investigated.

The electrochemical formation and electron spectroscopic characterization of the platinum sulfide electrode

Summary The anodic voltammetry of acetonitrile solutions containing hydrogen sulfide shows that modification of the platinum electrode surface occurs at potentials sufficiently anodic to oxidize hydrogen sulfide (≥1.25 V vs . SCE). The cathodic voltammetry of these electrodes which have been subjected to anodic polarization shows the reductive discharge of the modified surface at −0.70 V vs . SCE. Comparison of the electron energy (e.s.c.a.) spectra of the modified surface with those of various authentic samples indicates that the anodic modification of the surface is the oxidative formation of PtS.

Interfacial spin trapping in model membrane systems

Summary Spatially resolved spin trapping in ordered media has been demonstrated by using an amphiphilic nitrone derived spin trap co-assembled with other amphiphiles to form either micelles or vesicles. The ability of α-(4-dodecyloxyphenyl)-N- tert -butyl nitrone to trap transient phenyl radicals generated either in the bulk aqueous phase or in the hydrophobic region of the vesicle or micelle confirms its location and function at the “membrane”/solution interface. These results establish that reactions involving transient free radicals occurring at the interface of ordered systems can be studied using spatially resolved spin trapping.

The Solubility of Hydrogen Sulfide in Acetonitrile at 25°C

Abstract The solubility of hydrogen sulfide in acetonitrile at 25°C has been determined both gravimetrically and titrimetrically to be 0. 528 M. The effects of the presence of water and an electrolyte (LiClO4) on this parameter are reported.

Heterogeneous electron transfer kinetics of sperm whale myoglobin

Abstract Very little information has been reported describing the heterogeneous electron transfer kinetics of biological molecules at electrodes. We report here the first application of a recently developed spectroelectrochemical technique to the measurement of the heterogeneous electron transfer kinetics of a biological molecule, sperm whale myoglobin, at a methyl viologen modified gold minigrid electrode. The overpotential dependence of the heterogeneous electron transfer rate constant for the reduction of myoglobin at this surface gives rise to values of the formal heterogeneous electron transfer rate constant [ko′f,h = 3.88 (± 0.07) × 10−11 cm/s] and the transfer coefficient [α = 0.88 (± 0.01)] for this electrocatalyzed process. The importance of studying the heterogeneous electron transfer kinetics of biological molecules lies in the fact that many physiological electron transfer reactions occur heterogeneously. Though myoglobin does not function in this manner physiologically, our initial study has been directed at this molecule owing to its stability and ready availability. It is expected that this technique will be applied to other optically transparent electrodes and other biological molecules thereby providing new insights into understanding biological redox reactions.