Photosensitized generation of superoxide radical in aprotic solvents: an EPR and spin trapping study

• Published in: Free radical research communications Vol. 19 Suppl 1; p. S33
• Main Authors: Reszka, K, Bilski, P, Sik, R H, Chignell, C F
• Format: Journal Article
• Language: English
• Published: Switzerland 01.10.1993
• Subjects: Photochemistry; Solvents; Spin Labels; Superoxides - chemistry
• ISSN: 8755-0199
• DOI: 10.3109/10715769309056s33

The UV or visible irradiation of pigments such as curcumin, anthralin, benzanthrone, 1,8-dihydroxyanthraquinone, and rose bengal- or eosine-complexes with cationic surfactants in aerated aprotic solvents, such as benzene, toluene, acetone, n-heptane, cyclohexane, in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generates EPR spectra with hyperfine splitting constants (hfsc's) aN = 12.75 G, a beta H = 10.50 G, a gamma H = 1.26 G in toluene, 12.83 G, 10.64 G, 1.24 G in benzene, 12.75 G, 10.19 G, 1.35 G in acetone and 12.54 G, 10.46 G, 1.38 G in n-heptane and cyclohexane. These spectra are similar to those observed when DMPO reacts with 18-crown-6 ether-solubilized KO2 in the respective solvents and suggests that the photoinduced EPR spectra can be safely assigned to the DMPO/superoxide radical adduct (1). A correlation between the hfsc's of 1 and solvent parameters, the solvent acceptor number AN and the Kosower Z value, has been evaluated in terms of its usefulness for the identification of the DMPO/superoxide adduct in organic media.