Kinetics and electrochemical studies on superoxide

Rate constants for the reaction of superoxide O-2(-) with various substrates were obtained through stationary electrode polarography theory and technique. In solvent acetonitrile, the substrate and the rate constants of the reaction O-2(-) + AH --> (k2) Product, are, AH = isopropanol (k(2) less than or equal to 0.01 M-1 s(-1)); ethanol(k(2) = 1.42 x 10(2) M-1 s(-1)); methanol (k(2) = 1.1 X 10(7) M-1 s(-1)) H2O (k(2) = 1.0 x 10(5) M-1 s(-1)). In MeCN, O-2(-) was found to be rather unreactive towards glucose and acetone but it reacts with fructose and sucrose catalytically. However, in DMF2, O-2(-) reacts with glucose and fructose with k(2) order of 10(5) M-1 s(-1). The mechanism of the reaction of O-2(-) with the substrates (AH) is proposed as O-2(-)+AH reversible arrow (k2)(k-1)[O-2, AH](-) --> (k2 ') O2H + A(-), with k(1) = 10(9) M(-1)s(-1) and k(-1) = 10(8 -)10(9) s(-1). With these values of k(-1) and k(1), k ' (2) similar or equal to k(2)(obs). The reversible E-1/2 for O-2 + e reversible arrow O-2(-) in various solvents: MeCN, acetone, isopropanol, methanol, H2O were obtained either directly from the reversible voltammogram or from experimental voltammograms and the rate constants obtained las above) using stationary electrode polargraphy theory; E-1/2 being -0.82 (MeCN), -0.85 (acetone), -0.72 (isopropanol); -0.66 (MeOH), -0.56 (H2O) vs SCE.