The use of lucigenin luminescence as a measure of [O-2(-)] has been questio
ned because lucigenin has been shown to be capable of mediating the product
ion of O-2(-). This being the case, lucigenin can signal the presence of O-
2(-) even in systems not producing it in the absence of lucigenin, The redu
ction potential of lucigenin should be in accord with its ability to mediat
e O-2(-) production; but it has not heretofore been measured in aqueous med
ia. The problems facing such measurement are the insolubility of the divale
ntly reduced form, which deposits on the electrode, and the slow conformati
onal transition that follows the second electron transfer and which interfe
res with reversibility, We have now used rapid scan cyclic voltammetry to d
etermine that the reduction potential for lucigenin is -0.14 +/- 0.02 V ver
sus the normal hydrogen electrode. This value applies to both the first and
the second electron transfers to lucigenin and it is in accord with the fa
cile mediation of O-2(-) production by this compound. (C) 2000 Academic Pre
ss.