A voltammetric study of 6-mercaptopurine monolayers on polycrystalline gold electrodes

6-Mercaptopurine (6MP) monolayers were formed spontaneously on different gold surfaces by chemisorption from 6MP solutions. The present cyclic voltammetric study reveals that the monolayer formed is stable in a wide potential range up to values where the oxidative desorption occurs. The reductive desorption of 6MP at a polyfaceted gold electrode shows a multi-wave response. This has been analysed by comparing the observed peak potentials with those obtained at low-index single crystal gold electrodes. The film has no apparent effect on the electron transfer rate constant of RU(NH3)(6)(3+/2+) and Fe(CN)(6)(3-/4-) at the substrates studied, but modifies the electron transfer rate of the benzoquinone redox couple. This behaviour is typical of thin films where only the slower reactions should display a larger apparent decrease of the rate constant. In contrast, the GMP-monolayer shows a strong ability to inhibit electroreduction of dioxygen at polyfaceted gold while it remains stable. (C) 2001 Elsevier Science B.V. All rights reserved.