ELECTROCHEMICAL REDUCTION OF 2,5-DIMETHOXY NITROBENZENES - NITRO RADICAL-ANION GENERATION AND BIOLOGICAL-ACTIVITY

The electrochemical reduction of four 2,5-dimethoxy nitrobenzene 6-sub stituted derivatives in aqueous and mixed media by cyclic voltammetry, tast and differential pulse polarography were studied. In aqueous med ia, pH > 8, it was possible to observe a polarographic peak or wave du e to the nitro radical anion formation. This fact is not very common i n nitro aromatic compounds where the observation of the nitro radical anion formation peak (or wave) requires the presence of inhibitors or aprotic solvent, besides alkaline pH. In mixed media, all the studied compounds show a well-defined reversible couple, due to the one electr on reduction of the nitro group to produce the corresponding nitro rad ical anion. Cyclic voltammetric studies show that the nitro radical an ion generated was relatively stable, although this intermediate specie shows a tendency to undergo further chemical reactions. From these ex periments, the kinetic behaviour of the nitro radical anions electroch emically generated was characterized and permitted us to calculate the rate constant k(2) of the second order chemical reaction of the radic al anions and their half-life. The electrochemical behaviour is correl ated with the in vivo studies of oxygen consumption on Trypanosoma cru zi cell suspensions. (C) 1998 Elsevier Science S.A. All rights reserve d.