BIOLOGICAL DEACTIVATION AND SINGLE-STRAND BREAKAGE OF PLASMID DNA BY PHOTOSENSITIZATION USING TRIS(2,2′- BIPYRIDYL)RUTHENIUM(II) AND PEROXYDISULFATE

— Single-strand break formation and biological deactivation of plasmid pBR322 DNA in the presence of tris(2,2′-bipyridyl)-ruthenium(II), Ru(bpy)2/3;+, and K2S2O8, upon irradiation with visible light(400–500 nm), were studied in aqueous solution at room temperature. Conditions of complete binding of Ru(bpy)2/3;+ to the strand were employed. The damage is initiated mainly by the SO2/3;; radical anion. Under anoxic conditions at a ratio of nucleotide to sensitizer concentrations (N/S) of 18 and S2O2/8- concentrations of 0.5 mM the quantum yield of single-strand break (ssb) formation is φssb= 8.4 times 10-3 while that of biological deactivation (bd) is Obd= 7.6 times 10-3 (φssb= 5.2 times 10-36.4 times 10-3, 6.0 times 10-3 and φbd= 4.2 times 10-3, 5.2 times 10-3, 4.8 times 10-3 at N/S=3, 6, and 9, respectively). The quantum yields are approximately 2.5 times smaller in air-saturated solutions. At N/S = 18 about 33 SO4-radical anions are required per one lethal event. φbd increases linearly with the S2Oφ- concentration (up to 0.5 mM). The damage to DNA is drastically reduced on addition of mono- or divalent salts (e.g. NaC104, MgCl2). These additives cause the release of Ru(bpy)2+ from the strand. The observed damage to DNA is thus the result of a site specific reaction. When the phenanthroline analogue, Ru(phen)φ+, is used as sensitizer, φssb and φbd are three times smaller.