The proposed research focuses on the use of ligand-bridged neutral and cationic d7-d7 and d8-d8 bimetallic metal complexes for photochemotherapy. Initiation of anti-tumor drug activity utilizing light has been an area of intense research with mixed success. The systems previously chosen for these studies have typically been fluorescent singlet excited states of organic molecules, their respective triplet states, or luminescent inorganic complexes. Problems encountered include short excited state lifetimes, high energy ultraviolet photons necessary for excitation, and the reaction of the photogenerated intermediates at undesired sites. A new avenue of research can be opened with the investigation of the non- or weakly-emissive excited states of mononuclear and bimetallic complexes, whose photophysical properties and reactivity remain largely unexplored. The potential advantages of these systems presented here include their increased redox reactivity through the presence of the metal center, their ability to be excited with visible light (lambda > 600 nm), and the ease with which they can be chemically modified to permit binding at selective DNA sites and to improve the excited state properties. Bimetallic systems that can be photoexcited with visible light to afford a reactive diradical excited state that can act as inorganic enediyne analogs, and whose reaction can be photoactivated. All of the molecules currently utilized in photodynamic therapy require oxygen for their activity since the excited states themselves are not reactive, therefore when the oxygen supply is depleted their reactivity is shut down. Our preliminary results show that the d7-d7 (RhII)2 systems can photocleave DNA effectively through the formation of singlet oxygen, however, the excited states themselves can photocleave duplex DNA. In addition to various dirhodium(II) complexes, we will also explore the excited state reactivity and DNA photocleavage by cationic d7-d7 (PtIII)2 and neutral d8-d8 (PtII)2 Systems
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