Biological Deactivation and Single‐strand Breakage of Plasmid Dna by Photosensitization Using Tris(2,2′‐ Bipyridyl)ruthenium(ii) and Peroxydisulfate

Abstract—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 0.5mMthe quantum yield of single‐strand break (ssb) formation is φssb= 8.4 times 10‐3while that of biological deactivation (bd) is Øbd= 7.6 times 10‐3(φssb= 5.2 times 10‐36.4 times 10‐3, 6.0 times 10‐3and φbd= 4.2 times 10‐3, 5.2 times 10‐3, 4.8 times 10‐3at 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. φbdincreases linearly with the S2Oφ‐concentration (up to 0.5mM).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, φssband φbdare three times smaller.