Electrochemical and UV-spectrophotometric study of oxygen and superoxide anion radical interaction with anthraquinone derivatives and their radical anions
T. Ossowski et al., Electrochemical and UV-spectrophotometric study of oxygen and superoxide anion radical interaction with anthraquinone derivatives and their radical anions, ELECTR ACT, 45(21), 2000, pp. 3581-3587
One-electron reduction of dihydroxyanthraquinone derivatives was studied in
dimethylsulfoxide solution by means of electrochemical and spectrophotomet
ric methods. It was found that dihydroxyanthraquinone reduction in the pres
ence of oxygen occurs according to an EC mechanism, the second step being o
xygen reaction with semiquinone anion radical. This mechanism was confirmed
by the dependence of CV curves on dihydroxyanthraquinone and oxygen concen
tration. Supplementary spectrophotometric and electrochemical studies of th
e dihydroxyanthraquinone-potassium superoxide system have shown that no cov
alent compound is formed between seminquinone anion radical and molecular o
xygen and therefore the reaction following dihydroxyanthraquinone reduction
involves electron and proton transfer from semiquinone anion radical to mo
lecular oxygen to form hydroperoxyl radical and deprotonated dihydroxyanthr
aquinone. The rate constants of the electron-transfer reactions from semiqu
inone anion radical to molecular oxygen were determined from the dependence
of anthraquinone cathodic reduction peak potential and the corresponding a
nodic peak current on oxygen concentration. It was found that the rate cons
tants increase with decreasing pK(a) of the hydroxyanthraquinones, which co
nfirms the postulated mechanism. (C) 2000 Elsevier Science Ltd. hll rights
reserved.