Dirhodium Complexes as Possible Dual-Binding Photodynamic Therapy Agents

2012 Denman Undergraduate Research Forum Winner. Third Place. Mathematical and Physical SciencesA new type of dirhodium paddlewheel complexes were synthesized that contain ligands with extended π-systems. These ligands are expected to increase the affinity of these complexes for DNA because they are known to intercalate between the DNA bases in related systems. In addition, the new complexes possess equatorial acetonitrile ligands that exchange for water molecules upon photolysis, which produces an activated form of the complex that is able to bind covalently to DNA. These features lead to dual-binding through covalent binding to DNA upon irradiation and intercalation of the extended π-system ligand between the DNA bases. Currently, there are no reports of photoactivated dual-binding agents. These complexes possess features desired of photodynamic therapy agents, primarily because they are inactive in the dark, and readily bind to DNA when irradiated. The dirhodium bis-amidate complexes cis-H,H-[Rh2(HNOCCH3)2(bpy)(CH3CN)4][BF4]2 (bpy = 2,2´-bipyridine) and cis-H,H-[Rh2(HNOCCH3)2(dpq)(CH3CN)4][BF4]2 (dpq = dipyrido[3,2-f:2',3'-h]-quinoxaline) were successfully synthesized from cis-H,H-[Rh2(HNOCCH3)2(CH3CN)6][BF4]2 with the corresponding bidentate ligand. The bpy complex was prepared in 7 days, and because it cannot intercalate between the DNA bases, it is used as a control for no intercalation, but it was shown to bind covalently to DNA upon irradiation. The dpq complex was synthesized successfully in 1 day. Studies of this complex are underway and its intercalation ability has not yet been proven. The synthesis of related complexes with other bidentate ligands is ongoing. The preparation of complexes possessing acetate bridging ligands instead of amidates were attempted from the reaction of cis-[Rh2(CH3COO)2(CH3CN)6]2+ and bpy. Cis-[Rh2(CH3COO)2(bpy)(CH3CN)4]2+ was not successfully synthesized, but it is still of interest, since its precursor cis-[Rh2(CH3COO)2(CH3CN)6]2+ binds to DNA upon irradiation and it is inactive under dark conditions.No embarg