Intercalation of fac-[(4,4′-bpy)ReI(CO)3(dppz)]+, dppz = dipyridyl[3,2-a:2′3′-c]phenazine, in polynucleotides. On the UV-vis photophysics of the Re(i) intercalator and the redox reactions with pulse radiolysis-generated radicals
Abstract
The intercalation of fac-[(4,4′-bpy)ReI(CO)3(dppz)]+ (dppz = dipyridyl[3,2-a:2′3′-c]phenazine) in polynucleotides, poly[dAdT]2 and poly[dGdC]2, where A = adenine, G = guanine, C = cytosine and T = thymine, is a major cause of changes in the absorption and emission spectra of the complex. A strong complex–poly[dAdT]2 interaction drives the intercalation process, which has a binding constant, Kb ∼ 1.8 × 105 M−1. Pulse radiolysis was used for a study of the redox reactions of e−aq, C˙H2OH and N3˙ radicals with the intercalated complex. These radicals exhibited more affinity for the intercalated complex than for the bases. Ligand-radical complexes, fac-[(4,4′-bpy˙)ReI(CO)3(dppz)] and fac-[(4,4′-bpy)ReI(CO)3(dppz˙)], were produced by e−aq and C˙H2OH, respectively. A Re(II) species, fac-[(4,4′-bpy)ReII(CO)3(dppz)]2+, was produced by N3˙ radicals. The rate of annihilation of the ligand-radical species was second order on the concentration of ligand-radical while the disappearance of the Re(II) complex induced the oxidative cleavage of the polynucleotide strand.