ELECTROCHEMICAL OXIDATION OF MICROCRYSTAL LINE CHLOROPHYLL-A

The films of microcrystalline chlorophyll a (absorption maximum at 740 -750 nm) were prepared by electrodeposition from isooctane solutions o n optically transparent ITO electrodes and carbon glass electrode, and their electrochemical oxidation was studied by cyclic voltammetry. Th ree main waves were found at the anodic branch of voltammetic curves i n the potential range from +0.5 to 1.0 V (S.C.E.). The first wave was reversible, the second and third waves displayed the anodic-cathodic p eak potential splitting of 0,7 and 1,3 V, respectively. The spectral c hanges observed indicated the formation of a chlorophyll cation-radica l; they were reversible for the first ware and less reversible for the second and third waves. The existence of three the populations of chl orophyll molecules possessing similar optical spectra and redox potent ials, but different kinetics of the electron transfer was proposed. Th e E((Chl/Chl).+(surf) value of microcrystalline chlorophyll a (0.5 V) was the same as E((Chl/Chl).+)(surf) of weakly interacting chlorophyll a aggregates (absorption at 672-676 nm) which were studied by us earl ier. Our data confirmed that the aggregation of chlorophylls does not affect substantially their oxidation potential.