Stabilization of the ruthenium (II) and -(III) centres by chelating N-donor ligands: Synthesis, characterization, biomolecular affinities and computational studies

Anti-Amyloid Aggregation and Anti-Hyperglycemic Activities of Novel Ruthenium Uracil Schiff Base Compounds

The formation and characterization of new diamagnetic ruthenium uracil mono-imine compounds: [(η6-p-cymene)RuII(L)Cl][BF4] (L=H2urpda=5-((pyridin-2-yl)methyleneamino)-6-aminouracil) for 1, urdpy=6-amino-1,3-dimethyl-5-((pyridin-2-ylmethylene)amino)uracil) for 2 or urqda=5-((quinolin-2-yl)methyleneamino)-6-aminouracil) for 3); cis-[Ru(bipy)2(urpy)](BF4)2 (4) (urpy=5-((pyridin-2-yl)methyleneamino)uracil) and cis-[Ru(bipy)2(dapd)] (5) (H2dadp=5,6-diaminouracil) are described. A ruthenium(IV) uracil Schiff base compound, trans-[Ru(urpda)(PPh3)Cl2] (6) was also formed. Various physicochemical techniques were utilized to characterize the novel ruthenium compounds. Similarly, the stabilities of 1-3 and 6 monitored in chloro-containing and the non-coordinating solvent, dichloromethane show that they are kinetically inert, whereas, in a high nucleophilic environment, the chloride co-ligands of these ruthenium complexes were rapidly substituted by DMSO. In contrast, the substitution of the labile co-ligands for these ruthenium complexes by DMSO molecules in a high chloride content was suppressed. Solution chemical reactivities of the different ruthenium complexes were rationalized by density functional theory computations. Furthermore, the binding affinities and strengths between BSA and the respective ruthenium complexes were monitored using fluorescence spectroscopy. In addition, the in vitro anti-diabetic activities of the novel metal complexes were assessed in selected skeletal muscle and liver cell lines.

Bovine serum albumin uptake and polypeptide disaggregation studies of hypoglycemic ruthenium(II) uracil Schiff-base complexes

Our prior studies have illustrated that the uracil ruthenium(II) diimino complex, [Ru(H3ucp)Cl(PPh3)] (1) (H4ucp = 2,6-bis-((6-amino-1,3-dimethyluracilimino)methylene)pyridine) displayed high hypoglycemic effects in diet-induced diabetic rats. To rationalize the anti-diabetic effects of 1, three new derivatives have been prepared, cis-[Ru(bpy)2(urdp)]Cl2 (2) (urdp = 2,6-bis-((uracilimino)methylene)pyridine), trans-[RuCl2(PPh3)(urdp)] (3), and cis-[Ru(bpy)2(H4ucp)](PF6)2 (4). Various physicochemical techniques were utilized to characterize the structures of the novel ruthenium compounds. Prior to biomolecular interactions or in vitro studies, the stabilities of 1-4 were monitored in anhydrous DMSO, aqueous phosphate buffer containing 2% DMSO, and dichloromethane (DCM) via UV-Vis spectrophotometry. Time-dependent stability studies showed ligand exchange between DMSO nucleophiles and chloride co-ligands of 1 and 3, which was suppressed in the presence of an excess amount of chloride ions. In addition, the metal complexes 1 and 3 are stable in both DCM and an aqueous phosphate buffer containing 2% DMSO. In the case of compounds 2 and 4 with no chloride co-ligands within their coordination spheres, high stability in aqueous phosphate buffer containing 2% DMSO was observed. Fluorescence emission titrations of the individual ruthenium compounds with bovine serum albumin (BSA) showed that the metal compounds interact non-discriminately within the protein's hydrophobic cavities as moderate to strong binders. The metal complexes were capable of disintegrating mature amylin amyloid fibrils. In vivo glucose metabolism studies in liver (Chang) cell lines confirmed enhanced glucose metabolism as evidenced by the increased glucose utilization and glycogen synthesis in liver cell lines in the presence of complexes 2-4.