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)Re^I(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, K_b ∼ 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˙)Re^I(CO)₃(dppz)] and fac-[(4,4′-bpy)Re^I(CO)₃(dppz˙)], were produced by e⁻_aq and C˙H₂OH, respectively. A Re(II) species, fac-[(4,4′-bpy)Re^II(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.