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Issue
J. Chim. Phys.
Volume 96, Number 8, September 1999
Page(s) 1367 - 1386
DOI http://dx.doi.org/10.1051/jcp:1999216
DOI: 10.1051/jcp:1999216


J. Chim. Phys. Vol. 96, N°8  p. 1367-1386

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

R. Herrero1, J.L. Barriada1, M.R. Moncelli2, J.M. López-Fonseca3 and M.E. Sastre de Vicente1

1  Departamento de Química Fundamental e Industrial, University of La Coruña, 15071 A Coruña, Spain
2  Dipartimento di Chimica, University of Florence, 50121 Florence, Italy
3  Departamento de Química Física y Analítica, University of Oviedo, 33006 Oviedo, Spain

Abstract
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.

Résumé
Le comportement voltampérometrique de la 2-mercaptopyridine et de l'aminoacid L-cysteine a eté etudié sur l'électrode de mercure couverte par une monocouche de dioleoylphosphatidylcholine. Pour la 2-mercaptopyridine on peut constater la pénétration de ce composé dans la zone de stabilité de la monocouche. La constante de vitesse a eté calculée seulement pour des basses concentrations. Lorsque la concentration augmente le comportement devient très compliqué. Par contre, pour la cysteine on observe seulement un signal de courant pour des potentiels superieurs à -0.2 V oú la monocouche de phospholipide ne peut pas être considerée très stable. La differente structure chimique des deux substances permet de rendre compte du different comportement voltammetrique observé.


Key words: 2-mercaptopyridine -- L-cysteine -- phospholipid monolayer on mercury -- permeability model
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