Electrochemical behaviour of pyridoxal-5'-phosphate: Influence of the medium composition

Abstract A study of the reduction of pyridoxal-5'-phosphate in a mercury electrode in buffered ethanol + water solutions was carried out. At low ethanol content, the polarographic and voltammetric results show a slight kinetic effect in the limiting zone. The absorption spectra show a decrease of the free aldehyde concentration as the ethanol content increases. Hemiacetal formation is indicated by an increase in the absorption band at 295 nm. The band was characterized on the basis of a log normal distribution and a quantitative determination of species in solution was obtained. At high ethanol content, pure kinetic control is observed in the limiting zone, due to the hydrolysis of hemiacetal to aldehyde. Equilibrium and rate constants of the chemical reaction preceding the electrode process were obtained. The results of logarithmic analysis, i - t curves, Tafel plot, differential pulse polarography and cyclic voltammetry correspond to a prekinetic irreversible process.