title: On the interaction of anisyl-3,4-semiquinone with oxygen.
abstract: Pulse radiolysis studies of anisyl-3,4-semiquinone, formed in the metabolic activation of 4-hydroxyanisole, a possible melanocytotoxic drug under current assessment as a treatment for malignant melanoma, have shown this semiquinone to be unreactive towards oxygen (k less than or equal to 10(5) M-1 s-1), although the reverse reaction of O2- with anisyl-3,4-quinone is very rapid (k = 8.7 x 10(8) M-1 s-1). Since 1,4 benzoquinone is also unreactive towards anisyl-3,4-semiquinone (k less than or equal to 10(5) M-1 s-1), the one-electron reduction potential, E17 (anisyl-3,4-quinone/anisyl-3,4-semiquinone), is likely to be considerably more positive than 0.1 V. This suggests that the cytotoxicity mechanism does not involve the generation of O2- and possible subsequent production of H2O2 and/or OH., leading to lipid peroxidation, as previously proposed, but rather involves as yet unknown reactions of anisyl-3,4-quinone. This quinone is unstable in water and its absorption spectrum was measured immediately (less than 0.1 s) following disproportionation of anisyl-3,4-semiquinone, before significant decay of the quinone had occurred.
authors.affiliation: Department of Chemistry, University College, London, U.K.
authors.forename: C J
authors.initials: CJ
authors.lastname: Cooksey
authors.forename: E J
authors.initials: EJ
authors.lastname: Land
authors.forename: P A
authors.initials: PA
authors.lastname: Riley
authors.forename: T
authors.initials: T
authors.lastname: Sarna
authors.forename: T G
authors.initials: TG
authors.lastname: Truscott
mesh_terms: D010084:Oxidation-Reduction; D010100:Oxygen; D011675:Pulse Radiolysis; D011809:Quinones; D013481:Superoxides
chemical_list: D011809:Quinones; D013481:Superoxides; D010100:Oxygen