title: Synthesis and spectroelectrochemistry of Ir(bpy)(phen)(phi)(3+), a tris(heteroleptic) metallointercalator.
abstract: A tris(heteroleptic) phenanthrenequinone diimine (phi) complex of Ir(III), Ir(bpy)(phen)(phi)(3+), was synthesized through the stepwise introduction of three different bidentate ligands, and the Lambda- and Delta-enantiomers were resolved and characterized by CD spectroscopy. Like other phi complexes, this tris(heteroleptic) iridium complex binds avidly to DNA by intercalation. Electrochemical studies show that Ir(bpy)(phen)(phi)(3+) undergoes a reversible one-electron reduction at E(0) = -0.025 V in 0.1 M TBAH/DMF (versus Ag/AgCl), and spectroelectrochemical studies indicate that this reduction is centered on the phi ligand. The EPR spectrum of electrochemically generated Ir(bpy)(phen)(phi)(2+) is consistent with a phi-based radical. The electrochemistry of Ir(bpy)(phen)(phi)(3+) was also probed at a DNA-modified electrode, where a DNA binding affinity of K = 1.1 x 10(6) M(-1) was measured. In contrast to Ir(bpy)(phen)(phi)(3+) free in solution, the complex bound to DNA undergoes a concerted two-electron reduction, to form a diradical species. On the basis of UV-visible and EPR spectroscopies, it is found that disproportionation of electrochemically generated Ir(bpy)(phen)(phi)(2+) occurs upon DNA binding. These results underscore the rich redox chemistry associated with metallointercalators bound to DNA.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: C
authors.initials: C
authors.lastname: Stinner
authors.forename: M D
authors.initials: MD
authors.lastname: Wightman
authors.forename: S O
authors.initials: SO
authors.lastname: Kelley
authors.forename: M G
authors.initials: MG
authors.lastname: Hill
authors.forename: J K
authors.initials: JK
authors.lastname: Barton
mesh_terms: D004247:DNA / Q000737:chemistry; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D007364:Intercalating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010616:Phenanthrenes / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D007364:Intercalating Agents; D009942:Organometallic Compounds; D010616:Phenanthrenes; C441192:iridium(bpy)(phen)(phi)(3+); C005399:9,10-phenanthrenequinone; D007495:Iridium; D004247:DNA