Voltammetric behavior of a 4-nitroimidazole derivative - Nitro radical anion formation and stability

Abstract

A new synthesized compound, 1-methyl-4-nitro-2-hydroxymethylimidazole (4-MNImOH), was electrochemically reduced at the mercury electrode in aqueous, mixed, and aprotic media. In an aqueous medium, only one voltammetric peak was observed because of the four-electron, four-proton reduction of the nitro group to the hydroxylamine derivative in the 2-12 pH range. For the mixed and nonaqueous media, it was possible to observe a reversible couple due to the first one-electron reduction step of the nitro group to the nitro radical anion. The nitro radical anion decays by a disproportionation reaction in mixed media and by dimerization in a nonaqueous medium. Both disproportionation and dimerization rate constants, k(2), were determined according to Olmstead's approach, obtaining a value of 1460 ± 110 M-1 s(-1) in aprotic medium. In mixed media, the values were dependent both on pH and on the nature of the cosolvent. After comparison of 4-MNImOH with the parent compound, 4-nitroimidazole, we concluded that the substitution with 1-methyl and 2-hydroxymethyl produces a more easily reducible nitro compound and a less stable nitro radical anion than the unsubstituted 4-nitroimidazole. According to the electrochemical results, the 4-MNImOH derivative would be more suitable for enzymatic reduction and less toxic to the host than 4-nitroimidazole.