These groups were shown to be solely responsible
for oxidation reduction reactions of Eu3+/Eu2+, V3+/V2+, and
Fe3+/Fe2+, with E0¢ values ranging from -430 to +771 mV
(19). Also S2- (E0¢)-270 mV) is known to be oxidized by AC,
although quinone moieties have not yet been implicated
(21-23).