Ascorbate-quinone interactions: electrochemical, free radical, and cytotoxic properties.

Standard midpoint potentials have been determined for p-benzoquinone, methoxy-p-benzoquinone and 2,3-, 2,5-, and 2,6-dimethoxy-p-benzoquinones in aqueous solution. ESR studies have been made of the ascorbate and semiquinone radicals produced when these quinones interact with sodium ascorbate. Direct correlations are found between the electrochemical potentials, generated semiquinone lifetimes, and cytotoxic action in Ehrlich ascites-bearing mice.