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 adsorbed on mercury by using cyclic voltammetry. 2-Mercaptopyridine penetrates into monolayer in the zone of stability of the phospholipid layer and shows an quasi-reversible behaviour while reversibility is observed in the absence of a monolayer. This fact is reflected in the occurrence of voltammetric 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 when the potential was scanned to values positive to -0.2 V. Beyond this potential the cyclic voltammograms show a series of anodic peaks, due to a rearrangement 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 peaks was analized.