Does disproportionation of superoxide produce singlet oxygen

It has been claimed that the non-enzymic disproportionation of superoxide (O2-) in aqueous solution, e.g. 2O2- + 2H+ → H2O2 + O2 results in the formation of molecular oxygen in the 1Δsub(g) electronically excited state (denoted here as 1O2). However, firm experimental evidence supporting the formation of 1O2 in aqueous solutions by this reaction is somewhat lacking. Experiments have therefore been undertaken in which the presence of 1O2, if generated by this reaction, would be detected. Superoxide radicals can be generated as the sole radical species (G = 6 radicals/100 eV) by γ-irradiation of O2-saturated neutral and alkaline solutions of sodium formate. The target molecules chosen for 1O2 attack were the enzymes ribonuclease (RNase) and lysozyme. The results are presented and discussed. (U.K.)