Investigation of the Electronic Structure and Photolability of Copper-,Manganese-, and Ruthenium-Nitrosyl Complexes.

[摘要] NO, a highly reactive diatomic, can readily react with biological molecules. This reactivity has led to the investigation of metal-nitrosyl complexes in biological systems. The electronic and geometric structures of Cu-NOx adducts in CuNIR and corresponding model complexes are discussed, followed by the analysis of the electronic structures and photolability of manganese- and ruthenium-nitrosyl complexes. In order to understand the binding mode of NO to copper, a computational analysis using two models of Cu(I)-NO in the CuNIR active site was utilized. The end-on and side-on Cu(I)-NO geometries were found to be the global energy minimum and local minimum, respectively. Isoleucine-257 severely interacts sterically within the CuNIR active site when the Cu(I)-NO unit is bound end-on and thus is responsible for the observed side-on coordination of NO in the CuNIR crystal structure. This analysis is followed by a spectroscopic and computational study of Cu-NOx model complexes using hydrotris(triazolyl)borate and hydrotris(pyrazolyl)borate type ligands. We found that hydrotris(triazolyl)borate is a slightly stronger sigma donor than hydrotris(pyrazolyl)borate when bound to copper.Detailed spectroscopic and theoretical studies of two photolabile Mn(II)-nitrosyl complexes provide insight into the mechanism of NO photolability upon Vis-NIR excitation. Using the assigned electronic spectra of a Mn(II)-nitrosyl, the release of NO upon irradiation in the Vis-NIR region is found to be due to an excitation into dxy to L(Py/Q_π*) CT transitions between Mn and the coligand. Then, an interconversion into the dxy to π*_dπ singlet excited states, which show strong spin-orbit coupling with the analogous dxy to π*_dπ triplet excited states, promotes intersystem crossing. Since these states are strongly Mn-NO antibonding in nature, dissociation of the NO ligand is observed.Finally, the analysis and photolabilization of NO in water-soluble and -insoluble ruthenium-nitrosyl complexes are presented. The effect solvents have on the photolabilization of Ru-NO complexes and how these results compare to other published results contribute to the understanding of the molecular characteristics necessary for a suitable photodynamic Ru-NO complex. We found that photolabilization of ruthenium-nitrosyl complexes in aqueous solutions may not increase the amount of NO released, however, photolabilization in a myoglobin assay allows for an accurate determination of photolabilized NO.

[发布机构] University of Michigan

[效力级别] Copper Electronic Structure

[关键词] Photolabilization of Ruthenium and Manganese;Copper Electronic Structure;Chemistry;Science;Chemistry