Philip J. Elving

Electrochemical Oxidation of Adenine: Reaction Products and Mechanisms

The electrochemical oxidation of adenine (6‐aminopurine), which gives a single well‐defined voltammetric wave at the pyrolytic graphite electrode (PGE), was investigated by macroscale controlled electrode potential at the PGE in aqueous 1M acetic acid solution (pH 2.3) with exhaustive isolation, identification, and determination of reaction products and intermediates. The electrochemical oxidation of adenine appears to follow initially the same path as the enzymatic oxidation, but further oxidation and fragmentation of the purine ring system occur. Thus, adenine is oxidized in a process involving a total of 6 electrons per adenine molecule to give as the primary product a dicarbonium ion intermediate, which, being unstable, undergoes a further series of reactions: (a) electrochemical oxidation to parabanic acid (some of which is further hydrolyzed to oxaluric acid), urea, carbon dioxide, and ammonia; (b) electrochemical reduction to give ultimately 4‐aminopurpuric acid, carbon dioxide, and ammonia; and (c) hydrolysis to allantoin, carbon dioxide, and ammonia.

Nicotinamide-Nad Sequence: Redox Processes and Related Behavior: Behavior and Properties of Intermediate and Final Products

I. INTRODUCTION The senior author and his collaborators have long been concerned with the use of analytical chemical techniques – more specifically, experimental approaches and methodologies primarily based on polarography – to study problems of general chemical interest. Currently, electroanalytical approaches are being used in a systematic investigation of chemical phenomena involving biologically significant compounds, where such approaches seem to offer distinct advantages. Attention has been focused on the behavior of nucleic acid components, pyridine coenzymes, and relevant model compounds in solution as well as the electron-transfer interface. Behavior at the interface involves (a) adsorption of original, intermediate, and product species, (b) association in the adsorbed state, (c) mechanisms and kinetics of electron-transfer (redox) processes, and (d) chemical reactions (kinetics and mechanisms) involving reactant, intermediate (free radical, carbanion), and product species preceding, accompanying...

Electrochemical Reduction of 6‐Substituted Purines Correlation with Structural and Energetic Characteristics

The electrochemical reduction of 6‐substituted purines has been examined over the available pH range by direct‐ and alternating‐current polarography, and the effects of substitution evaluated in respect to significant electrochemical characteristics. Where the bonds are available in the pyrimidine moiety, a four‐electron polarographic wave due to hydrogenation of these bonds is observed; purine itself and 6‐methylpurine give two twoelectron waves. The energy‐controlling step involves reduction of the protonated bond. The current is essentially diffusion controlled at low pH where the wave is relatively constant in height and kinetically controlled at higher pH where it begins to disappear. Correlation of the ease of reduction, as measured by , with total polar substituent constant and polar substituent constant (σ*) indicates either an absence of mesomeric and steric effects due to the substituents or their transmittal by an inductive mechanism and, further, that none of the substituents exerts any specific effect different from those exerted by the other substituents. Substitution in the 6‐position influences mostly the bond order and the electronic charge distributions on N(1) and N(3), which, in turn, largely determine the reducibility; correlates linearly with the quantum mechanically calculated magnitudes of these quantities, but not with other bond orders and charges. also correlates linearly with electron‐acceptor properties as represented by the calculated energy of the lowest empty molecular orbital ( coefficients) and with for proton acquisition (the protonation, which occurs prior to electron transfer, seems to have no significant role in the potential‐determining step except in the region where the wave has nearly disappeared). Isoguanine generally deviates from the various correlations. Adsorption involving an uncharged site in the molecule is markedly greater with derivatives having bulky substituents.

Electrochemical Behavior of the Quinone‐Hydroquinone System in Pyridine

The electrochemical behavior of quinone, hydroquinone, and quinhydrone in pyridine solution at the stationary pyrolytic graphite electrode has been studied by conventional and cyclic voltammetry. In the absence of available protons, quinone is somewhat reversibly reduced in a probable 1e process to a free radical anion; in the presence of protons, the free radical produced on 1e reduction is thought to be oxidized to an N‐dihydroxyphenyl pyridinium ion. The latter is also a likely product from the oxidation of hydroquinone. The quinone‐hydroquinone system itself is irreversible, e.g., quinhydrone behaves as a mixture of quinone and hydroquinone, the potentials of whose waves are 0.5v apart.

Jaroslav Heyrovsky: Nobel laureate

Examines the life and scientific contributions of Jaroslav Heyrovsky, particularly with respect to the development of polarography.