ELECTROCHEMICAL OXIDATION OF CAROTENOIDS CONTAINING DONOR ACCEPTOR SUBSTITUENTS/

Cyclic voltammetry and square wave voltammetry of the carotenoids beta -carotene (I), 7',7'-dimethyl-7'-apo-beta-carotene (II), 7',7'-hexadeu terodimethyl-7'-apo-beta-carotene (III), 7'-cyano-7'-ethoxycarbonyl-7' -apo-beta-carotene (IV), 7',7'-dicyano-7'-apo-beta-carotene (V) and ca nthaxanthin (VI) show that the electrochemical properties of the synth etic dimethyl and hexadeuterodimethyl compounds are similar to those o f the naturally occurring beta-carotene, while the properties of the s ynthetic dicyano carotenoid are similar to those of the naturally occu rring canthaxanthin, and those of the cyanoester compound are of an in termediate nature. The difference in oxidation potentials for the form ation of the cation radical and the dication is small for the first se t of compounds (less than 36 mV) and large (up to about 200 mV) for th e second. Simulation of the CVs with the DigiSim(R) program led to eva luation of the half-wave potentials, heterogeneous rate constants and homogeneous equilibrium constants which describe the oxidation propert ies of the carotenoids.