Synthesis and spectroelectrochemistry of Ir(bpy)(phen)(phi)(3+), a tris(heteroleptic) metallointercalator.
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.
Stinner
C
C
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Wightman
M D
MD
Kelley
S O
SO
Hill
M G
MG
Barton
J K
JK
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
D007364:Intercalating Agents; D009942:Organometallic Compounds; D010616:Phenanthrenes; C441192:iridium(bpy)(phen)(phi)(3+); C005399:9,10-phenanthrenequinone; D007495:Iridium; D004247:DNA