| dc.description.abstract | Carbon monoxide (CO) is a recognized gasotransmitter, similar to nitric oxide (NO) and hydrogen sulphide (H₂S). It is endogenously produced in mammals as a result of haem catabolism, catalysed by haem oxygenase enzymes. At low concentrations (nM range), CO exhibits physiological effects, including vasodilation, redox signalling, and inhibition of platelet aggregation. At higher concentrations (M range), CO is known to exhibit adverse effects on biological systems. Recently, many CO-releasing molecules (CORMs) have been employed for site-specific CO delivery as they can be activated by various external stimuli such as light, pH, solvent interactions, and enzymes. This thesis deals with a structure-activity correlation study involving Mn(I) carbonyl complexes as CO-releasing molecules.
The first part of the thesis describes a detailed study on the effect of a single atom substitution in the ligand backbone on the back-donation ability and CO-releasing properties of Mn(I) complexes. The effect of electron-withdrawing, π-conjugated, and rigid ligands and their influence on the CO release are discussed. Further, the role of metal-to-ligand charge transfer (MLCT) is analysed with respect to the number of CO molecules released. The complexes release CO in mammalian cells under photo-irradiation.
The next part highlights the coordination preferences of Mn(I) carbonyl complexes, particularly their tendency to form bidentate octahedral structures even in the presence of ligands with three potential donor sites. A detailed structure-activity relationship (SAR) was drawn to assess how ligand substitution affects the rate and mechanism of CO release. It was observed that changes in the ligand structure influence the electron density on the Mn(I) center, leading to solvent-triggered CO release instead of photoinduced release.
The third part of the work deals with the formation of an unusual tetrel bond (TtB) in a series of Mn (I) carbonyl complexes. The nature and strength of these non-covalent interactions were systematically evaluated using NMR, single-crystal X-ray diffraction studies and density functional theory (DFT) calculations. In the final part of the thesis, the strength of TtB is further explored by comparing five-membered and six-membered ring systems. This study led to the identification of unusual TtB between carbon and sulfur/selenium atoms, where the sulfur and selenium atoms act as TtB acceptors. Overall, the thesis provides several insights into the role of primary and secondary coordination sphere on the photo-induced release of CO in Mn(I) complexes and their applications in CO delivery in mammalian cells. | en_US |
