A Dimetallic Osmium(II) Complex as a Potential Phototherapeutic Agent: Binding and Photocleavage Studies with Plasmid DNA

Abstract

AbstractA new dimetallic OsII complex bridged by (4‐hydroxy‐3‐methoxyphenyl)diphenanthropyrromethane [{Os(bpy)2php}2van](PF6)4 has been synthesized and characterized by UV/Vis spectroscopy, cyclic voltammetry, and elemental analysis. The spectroscopic properties are similar to those of [Os(bpy)3]2+ with ligand‐centered π–π* transitions in the UV region of the spectrum and three metal‐to‐ligand charge‐transfer (1MLCT) transitions in the visible region. A broad 3MLCT is observed stretching from 550 to 700 nm with modest intensity. Binding studies with calf thymus DNA (ctDNA) show binding constants as high as 105 M–1 indicating a strong interaction of the complex with DNA. When aqueous solutions of the complex and plasmid DNA are irradiated with low‐energy light for brief periods of time complete photocleavage of the DNA is observed. Studies indicate that the mechanism of this photoreaction requires molecular oxygen and results from both the formation of 1O2 and oxygen radicals offering multiple modes for DNA destruction.