Title

Supramolecular ruthenium(II) and osmium(II) complexes : synthesis, characterization, DNA binding and DNA photocleavage

Author

Kaiyu Li

Date of Award

2017

Degree Name

M.S. in Chemistry

Department

Department of Chemistry

Advisor/Chair

Advisor: Shawn Swavey

Abstract

Two new bridging ligands have been synthesized by combining substituted benzaldehydes with phenanthrolinopyrrole (php), resulting in new polyazine bridging ligands. The ligands have been characterized by 1H NMR, mass spectroscopy, and elemental analysis. These new ligands display π-π* transitions above 500 nm with modest molar absorptivities. Upon excitation at the ligand-centered charge-transfer transition, weak emission with a maximum wavelength of 612 nm is observed. When coordinated to two ruthenium (II) bis-(2,2’-bipyridine) groups, the new bimetallic complexes generated give an overall 4+ charge. The electronic transitions of the bimetallic ruthenium (II) complexes display traditional π-π* transitions at 287 nm and metal-to-ligand charge-transfer transitions at 452 nm with molar absorptivities greater than 30000 M-1 cm-1. Oxidation of the ruthenium (II) metal centers to ruthenium (III) occurs at potentials above 1.4 V versus the Ag/AgCl reference electrode. Spectroscopic and electrochemical measurements indicate that the ruthenium (II) moieties behave independently. Both complexes are water-soluble and show the ability to photo-nick plasmid DNA when irradiated with low-energy light above 550 nm. In addition, one of the complexes, [Ru(bpy)2php]2Van4+, shows the ability to linearize plasmid DNA and gives evidence, by gel electrophoresis, of photoinduced binding to plasmid DNA. Coordination of two Osmium(II) bis-(bipyridine) complexes to the peripheral phenanthroline of (4-hydroxy-3- methoxyphenyl)diphenanthropyrromethane ligand yields the bimetallic Os(II) complex. 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 photo- cleavage 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.

Keywords

DNA-ligand interactions, Photosensitizing compounds, Metal complexes, Supramolecular organometallic chemistry, Chemistry, Photosensitizer, Ruthenium, Osmium, Bimetallic complexes, DNA Photocleavage

Rights Statement

Copyright 2017, author

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