ELECTROCHEMISTRY OF NADH - NAD+ ANALOGS - A DETAILED MECHANISTIC KINETIC AND THERMODYNAMIC ANALYSIS OF THE 10-METHYLACRIDAN - 10-METHYLACRIDINIUM COUPLE IN ACETONITRILE

The electrochemical oxidation of 10-methylacridan (AH) at platinum and gold electrodes in acetonitrile containing various pyridine bases is investigated by means of cyclic voltammetric and potential step techniques. The conversion of AH to the 10-methylacridinium ion (A+) proceeds along an electron-proton-electron transfer mechanism, the second electron being abstracted by the initial cation radical, AH+, rather than by the electrode itself in most cases. The use of ultramicroelectrodes (in the 10 μm diameter range) allows the determination of the standard potential of the AH+/AH couple and of the rate constant of the deprotonation of AH.+; the latter was measured as a function of the pKa of a series of pyridine bases. Investigation of the reduction of A+ by the same techniques led to the determination of the standard potential of the A+/A. couple and of the dimerization rate constant of A+. The oxidation of AH as well as the reduction of A+ are kinetically controlled by follow-up homogeneous chemical steps rather than by the initial electron transfer, which appears as quite fast in both cases. The combination of an ultraslow spectrometric technique with the ultrafast electrochemical techniques allowed the determination of the pKa of the AH+/A+ couple from that of the standard potential of the overall reaction AH ⇌ A+ + 2e- + H+ and hence the construction of a Bronsted plot with a known driving force origin for the deprotonation of AH+. © 1990, American Chemical Society. All rights reserved.