Electrochemical Characteristics of Nitroheterocyclic Compounds of Biological Interest VI. The Misonidazole Radical Anion

The addition of four aprotic solvents to misonidazole in an aqueous buffer system has been examined electrochemically. Qualitatively they all result in separation of the initial irreversible 4 electron reduction step into two stages, the RNO₂/RNO₂· and RNO₂· /RNHOH couples respectively. Despite some difficulties in achieving measurements for the discrete RNO₂/RNO₂· without interference from the following reduction step, it was clear that the various aprotic solvents influenced the lifetime of the RNO₂· species to different degrees. Resolution of the two processes was best achieved using a water-acetone system and this has been employed to study the lifetimes of the misonidazole radical anion as a function of acetone content and drug concentration. Analysis of the cyclic voltammetric response showed a second order decay pathway, in line with the metronidazole system studied under similar conditions. This has been compared with results from pulse radiolysis work, which suggested a first order reaction of unknown pathway for 2-nitroimidazole radical anions.