The rate constants for the protonation of "free" (that is, solvated) superoxide ions by water and ethanol are equal to 0.5-3.5 X lO-~M-l.s-' in DMF and AN at 20'. It has been found that the protonation rates for the ion pairs of 0; with the BudN+ cation are much slower than those for "free" 0,. It is suggested that the effects of aprotic solvents on the protonation rates of 0; are mainly due to the fact that the proton donors form solvated complexes of different stability in these solvents.
Absorption spectra of the superoxide ion have been studied in dimethylformamide (DMF) and acetonitrile (AN). It was found that the superoxide ion existed in equilibrium with an ion pair in AN ( K , = 20M-', BQN+ is the cation) and as "free" (solvated) ion in DMF. The addition of DMF caused the destruction of an ion pair in AN. The addition of the proton donors HX (water or ethanol) to the 0, solutions in DMF and AN caused the formation of new ion pairs (BQN+O&HX. The equilibrium constants of these ion pairs were determined in DMF and AN.
The interaction of superoxide ion and ascorbate anion with anthracycline antibiotics (adriamycin and aclacinimycin A) as well as with their Fe3+ complexes has been studied in aprotic and protic media. It was found that both superoxide and ascorbate reduce anthracyclines to deoxyaglycons via a one-electron transfer mechanism under all conditions studied. The reaction of ascorbate anion with adriamycin and aclacinomycin A in aqueous solution proceeded only in the presence of Fe3+ ions; it is supposed that an active catalytic species was Fe3+ adriamycin. It is also supposed that the reduction of anthracycline antibiotics by O2-. and ascorbate in cells may increase their anticancer effect.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.