Photosensitization by anticancer agents--10. ortho-semiquinone and superoxide radicals produced during anthrapyrazole-sensitized oxidation of catechols.

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— Photosensitized oxidation of catechol, 3,4-dihydroxybenzoic acid (DHBA), 3,4-dihydroxy-dihydrocinnamic acid (DHCA), and 3,4-dihydroxy-phenylalanine (DOPA) by novel anticancer agents, anthrapyrazoles (AP), has been studied employing EPR and the spin trapping technique. The formation of o -semiquinone radicals, the one-electron oxidation products of the catechols, stabilized in the form of zinc ion complexes, has been demonstrated. Rate constants for the disproportionation of the semiquinone radical/Zn 2+ complexes in (DMSO)/acetate buffer (pH 4.5, 1:1 vol/vol; 100 m M Zn 2+ ) mixture have been determined to be 0.35 × 10 4 14 × 10 4 8.8 × 10 4 3 × 10 4 M -1 s -1 for catechol, DHBA, DHCA and DOPA respectively. The presence of oxygen enhanced rather than inhibited the photogeneration of the o-semiquinone radicals and facilitated their EPR detection. The EPR spectrum of the superoxide radical adduct with the spin trap 5,5-dimethyl-1-pyrroline- N -oxide was observed for the first time during photosensitized oxidation of the catechols in acidic aqueous solutions and in DMSO/acetate buffer mixture.

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SUBSTANCE-P TACHYKININS CAPSAICIN NK1 RECEPTORS SUBMANDIBULAR GLAND URINARY BLADDER GASTROINTESTINAL SMOOTH MUSCLE RADIOLIGAND BINDING SENSORY NEURONS