Syntheses, x-ray structures, spectroscopy, DFT electronic configuration, and biological relevance of photolabile ruthenium and iron nitrosyls derived from ligands containing carboxamido-N donors

The interactions of nitric oxide (NO) with metal centers like Ruthenium (Ru) and Iron (Fe) is of importance due to their biological relevance of the resulting complexes, namely ruthenium or iron nitrosyls. Iron nitrosyls are often formed in biological context as an integral part of biochemical signaling pathways, enzyme regulation, neurological signaling and host-inflammatory response. The Introduction (Chapter 1, Part I) describes some known experimental approaches towards generating Ru-based "synthetic NO carriers", which can deliver NO upon photolysis with UV light. The second portion of the Introduction (Chapter 1, Part II) describes the interaction of NO with a unique enzyme, iron-containing nitrile hydratase (Fe-NHase). Fe-NHase is photoregulated by the bonding of NO to the active site Fe, and the overall "synthetic enzyme modeling" approach is discussed.;The next two chapters (Chapters 2 and 3) describe our efforts towards isolating Ru-based NO donors that are sensitive to visible light, instead of UV light. Such complexes are potentially much more useful in biological NO transfer experiments, or as potential therapeutics in photodynamic therapy (PDT). One major focus has been the direct coordination of visible-light-harvesting chromophores to the Ru-center, which has aided in photosensitizing Ru-nitrosyls up to wavelengths of 600 nm (red light).;Chapter 4 re-focuses on one endogenous role of NO, with regard to our efforts towards isolating synthetic models of "dark" form Fe-NHase (Fe-NHase dark), wherein NO is bound to the active site iron, along with two carboxamido-N and two sulfur donors (S, SO, or SO2 depending on oxygenation state) in the equatorial plane. We have found that {Fe-NO}6 nitrosyls derived from an mixed carboxamido-N/thiolato-S donor set are not photolabile (but are thermally labile), while the same {Fe-NO}6 unit does exhibit NO photolability after the thiolato-S donors have been oxygenated to sulfinic donors (SO2). On the basis of these experimental photochemistry experiments, as well as density functional theory (DFT) calculations, we have gained insight as to the chemical factors leading to NO photolability in our model complexes, as well as one possible important role of such unusual post-translational modification (S→SO2) found in the active site of Fe-NHase.