  The electrochemical behaviours of the sandwich-type complex
[As2W18(VO)3O66]11- were studied in a pH 7 medium and compared with those of
the three following Dawson-type vanadium-substituted complexes: [P2V2W16O62]8-
(P2V2W16), [P2MoV2W15O62]8- (P2MoV2W15) and [P2V3W15O62]9- (P2V3W15).
Electrochemistry shows that the sandwich-type POM contains 2 VIV centers and
one VV center and must be formulated As2V2IVVW18, in agreement with titration,
elemental analysis and magnetic measurements on this element.. All the POMs of
this work proved efficient for the oxidation of L-cysteine. Comparison of the
present results with those of mono-Vanadium substituted POMs indicates that
accumulation of vanadium atoms in the POM framework is beneficial in the
electrocatalytic process. In addition, the present work highlights the
important influence of the POM structure in the electrocatalytic oxidation of
L-cysteine. The remarkable outcome of this work is that the potential for the
oxidation of L-cysteine in the presence of the selected POMs has been
substantially driven in the negative direction compared to the case of glassy
carbon alone, a feature which is associated with faster kinetics. The stability
of the systems must also be pointed out.
