SIMULTANEOUS ELECTROCHEMICAL AND ELECTRON-PARAMAGNETIC-RESONANCE STUDIES OF CAROTENOIDS - EFFECT OF ELECTRON-DONATING AND ACCEPTING SUBSTITUENTS

A series of substituted phenyl-7'-apocarotenoids with varying electron donating and accepting substituents was examined by cyclic voltammogr am (CV) and simultaneous electrochemical electron paramagnetic resonan ce (SEEPR). Carotenoids substituted with electron donating groups are more easily oxidized than those with electron accepting substituents. Comproportionation constants for the dication and the neutral species were measured by SEEPR techniques and by simulation of the CVs. The De lta H-pp of the SEEPR spectrum of the cation radicals varies from 13.2 to 15.6 G, and the g factors are 2.0027 +/- 0.0002. These EPR paramet ers suggest a polyene pi-cation radical structure. The CVs are calcula ted using DigiSim, a CV simulation program, and the proposed mechanism involves three electrode reactions and two homogeneous reactions.