Voltammetry of L-cysteine and 2-mercaptopyridine on a self-assembled phospholipid monolayer

The redox behaviour of 2-mercaptopyridine and the aminoacid L-cysteine was studied through a self-assembled monolayer of dioleoylphosphatidylcholine a dsorbed on mercury by using cyclic voltammetry. 2-Mercaptopyridine penetrat es into monolayer in the zone of stability of the phospholipid layer and sh ows an quasireversible behaviour while reversibility is observed in the abs ence of a monolayer. This fact is reflected in the occurrence of voltammetr ic peaks in the above mentioned region of potentials. Conversely, cysteine was found not to penetrate in the lipid layer as long as the latter behaves like a half-membrane. Voltammetric signal of cysteine was only obtained wh en the potential was scanned:to values positive to -0.2 V, Beyond this pote ntial the cyclic voltammograms Show a series of anodic peaks, due to a rear rangement of the lipid film and to the formation of Hg(RS)(2), followed by three cathodic peaks when the scan is reversal. The behaviour of these peak s was analized.