Photochemical, photophysical and photobiological properties of some novel bisbipyridyl rhodium (III) complexes
Abstract
Several organic ligands and their biscomplexes of rhodium (III) have been synthesized and characterized as part of a search for new photocisplatin reagents. These complexes include OCTBP, 47TMBP, 56TMBP, TMOBP, TIOBP, BISNMe2, BISDPQ, BISDPPZ. Among these, the methylated bisphenanthroline Rh complexes, OCTBP, 47TMBP, 56TMBP were the most extensively studied. It was found that these could be photoaquated by direct excitation into the metal-based triplet manifold with long-wavelength visible light. Their enhanced triplet reactivity is also evident in their quantum efficiencies of aquation when irradiated with 311 nm light, i.e. for OCTBP, 47TMBP and BISPHEN, the quantum efficiencies of disappearance of starting material are 0.2, 0.18 and 0.02 respectively. The increased reactivity of the methylated complexes is ascribed to the electron-donor properties of the phenanthroline substituents. Also noteworthy is unusual dual phosphorescence exhibited by the BISDPPZ complex at 77 K in an aqueous-methanol glass. This emission consists of a long-lived, structured, blue emission from the ligand triplet, and a short-lived, unstructured red emission from the d,d triplet. Methylation of the aromatic ring, as in OCTBP leads to an increased association constant for these complexes with calf-thymus DNA (Kapp = 4 × 103M−1) relative to the parent bisphen complex (Kapp = 102 M−1). Irradiation of these complexes with light λ > 330 nm and λ = 311 nm leads to covalent photolytic binding to deoxyguanosme and photocytotoxicity of human nasopharyngeal (KB) and mouse (M109) cell lines in vitro . Among the compounds studied BISDPQ, BISDPPZ and TPBP photonick circular plasmid phiX-174 DNA. The photonicking ability of BISDPQ and BISDPPZ are ascribed to ILCT (n-π*) excited states, which abstract the hydrogen atom from the 3′ position of the deoxyribose sugar that leads to DNA cleavage.
Degree
Ph.D.
Advisors
Morrison, Purdue University.
Subject Area
Organic chemistry|Chemistry|Biochemistry
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