title: Photoinduced interaction of Ru(bpy)3 2+ with nucleotides and nucleic acids in the presence of S2O8 2-; a transient conductivity study.
abstract: The photochemical reactions of Ru(bpy)3(2+) with single- and double-stranded DNA, polynucleotides and purine-containing nucleotides in argon-saturated aqueous solution in the presence of S2O8(2-) were studied using time-resolved absorption and conductivity methods. The conversion of Ru(bpy(3(3+) to Ru(bpy)3(2+), monitored spectroscopically either after rapid mixing with substrate or after laser flash excitation (lambda exc = 353 nm) is quantitative at nucleotide-to-sensitizer ratios [N]/[S] of 1-2 for DNA and other guanine-containing compounds. Conductivity measurements following the laser pulse revealed a fast conductivity increase (rise time, less than 0.1 ms) due to the formation of protons and, to a lesser degree, to charged species of much lower ion mobility. A slower component in the 0.01-1 s range was observed for nucleic acids; its amplitude is markedly reduced at pH 6-9. In buffered neutral solution the signal is replaced by a slight decrease in conductivity. Electronically excited Ru(bpy)3(2+) bound to DNA reacts with S2O8(2-) to form Ru(bpy)3(3+) and SO4(.-) as primary oxidizing species both of which react with bases. The resulting base radicals react subsequently with Ru(bpy)3(3+) and Ru(bpy)3(2+) or the ligands in the ruthenium complex, producing protons which give rise to the slower conductivity increase. The formation of single-strand breaks and the ensuing release of condensed counterions does not appear to contribute significantly to the slow component. The transient conductivity behaviour is sensitive to the single- or double-stranded nature of DNA.
authors.affiliation: Max-Planck-Institut für Strahlenchemie, Germany.
authors.forename: A B
authors.initials: AB
authors.lastname: Tossi
authors.forename: H
authors.initials: H
authors.lastname: Görner
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives; D056831:Coordination Complexes; D004247:DNA / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000737:chemistry; D003848:Deoxyguanine Nucleotides / Q000737:chemistry* / Q000528:radiation effects; D003849:Deoxyguanosine / Q000737:chemistry / Q000528:radiation effects; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D008027:Light; D010777:Photochemistry; D011131:Polyribonucleotides / Q000737:chemistry* / Q000528:radiation effects; D012265:Ribonucleotides / Q000737:chemistry* / Q000528:radiation effects; D012428:Ruthenium; D013464:Sulfuric Acids; D017975:Ruthenium Compounds
chemical_list: D015082:2,2'-Dipyridyl; D056831:Coordination Complexes; D004247:DNA; D004277:DNA, Single-Stranded; D003848:Deoxyguanine Nucleotides; D003849:Deoxyguanosine; D011131:Polyribonucleotides; D012265:Ribonucleotides; D012428:Ruthenium; D013464:Sulfuric Acids; C547232:tris(2,2-bipyridine)-ruthenium(II); D017975:Ruthenium Compounds; C007257:2'-deoxyguanosine 5'-phosphate