ELECTROCHEMICAL PROPERTIES OF THE HERBICIDE CACALOL AND ITS DERIVATIVES IN PROTIC AND APROTIC-SOLVENTS BY USING CYCLIC VOLTAMMETRY - CORRELATION WITH HILLS REACTION ACTIVITIES

The redox behavior of cacalol, a natural product, and its semisyntheti c derivatives, which were found acting as electron transport inhibitor s in photosystem II, was examined by cyclic voltammetry. The studied c ompounds were cacalol (1), 2-acetylcacalol (2), cacalol acetate (3), 2 -acetylcacalol acetate (4), and cacalol methyl ether (5). The voltammo grams of 1 and 2 in a protic solvent were indicative of an electrochem ically irreversible oxidation of the phenolic system. The electrooxida tion of compounds 1-5 in an aprotic solvent was irreversible and more complex than in the protic solvent but presented similar oxidation pat terns; however, compounds containing an unsubstituted phenolic system presented E(pa), which is near the potential for the water-splitting e nzyme. This suggests that these compounds suffer oxidation and act as inhibitors to the oxygen evolution complex enzyme. Compounds 3-5 with higher oxidation potentials could not form a redox pair with the enzym es of photosystem II. Therefore, it is believed that these derivatives acted as inhibitors without any oxidation or reduction reaction.