Photodelivery of CO by designed PhotoCORMs: correlation between absorption in the visible region and metal-CO bond labilization in carbonyl complexes.
The therapeutic potential of photoactive CO-releasing molecules (photoCORMs) have called for close examination of the roles of the ligand(s) and the central metal atoms on the overall photochemical labilization of the metal-CO bonds. Along this line, we have synthesized four metal complexes, namely, [MnBr(azpy)(CO)3 ] (1), [Mn(azpy)(CO)3 (PPh3 )]ClO4 (2), [ReBr(azpy)(CO)3 ] (3), and [Re(azpy)(CO)3 (PPh3 )]ClO4 (4), derived from 2-phenylazopyridine. These complexes were characterized by spectroscopic and crystallographic studies. Although both 1 and 3 exhibit strong metal-to-ligand charge-transfer bands in the 500-600 nm region, only 1 photoreleases CO upon illumination with visible light. Results of theoretical studies were used to gain insight into this surprising difference. Strong spin-orbit coupling (prominent in heavy metals) appears to promote intersystem crossing to a triplet state in 3, a step that discourages CO release upon illumination with visible light. Slow release of CO from 2 and 4 also indicates that strong σ-donating ligands, such as Br(-) , accelerate the rate of CO photorelease relative to π-acid ligands, such as PPh3 .
Department of Chemistry and Biochemistry, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (USA).
Indranil
I
Chakraborty
Samantha J
SJ
Carrington
Pradip K
PK
Mascharak
D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008027:Light; D008345:Manganese / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008968:Molecular Conformation; D010782:Photolysis; D011725:Pyridines / Q000737:chemistry; D011789:Quantum Theory; D012211:Rhenium / Q000737:chemistry
D056831:Coordination Complexes; D008024:Ligands; D008670:Metals; D011725:Pyridines; D008345:Manganese; D012211:Rhenium; D002248:Carbon Monoxide
carbonyl ligands; drug design; manganese; photolysis; rhenium