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

Abstract

Anticancer activities of ruthenium Schiff base metal complexes have been closely correlated to their steric factors and physicochemical properties. The core objectives of our research study were to synthesize and characterize new ruthenium Schiff base compounds derived from cinnamaldehyde, cuminaldehyde or 4-aminoantipyrine. In addition, the stereo-electronic features of the aforementioned metal compounds and two selected previously reported ruthenium Schiff base compounds were related to their antioxidant and biomolecular interaction capabilities. Therefore, we demonstrated the formation of novel mononuclear ruthenium(III) compounds with chelating N-donor ligands: fac-[RuCl3(PPh3)(ap)] (1) (ap = 4-aminoantipyrine), trans-P-[Ru(PPh3)2(cinap)2](PF6) (2) (cinap = 1,5-dimethyl-2-phenyl-4-{[3-phenylprop-2-en-1-ylidene]amino}-1,2-dihydro-3H-pyrazol-3-one) and cis-Cl, trans-P-[RuCl2(PPh3)2(cumbh)] (3) (cumbh = N'-(4-isopropylbenzylidene)benzohydrazide). Structural confirmations were conducted primarily by spectroscopic techniques while the single crystal X-ray analysis revealed the distorted octahedrons of the respective metal compounds. Voltammetry experiments of 1–3 illustrated one-electron quasi-reversible redox waves which are attributed to metal oxidation state interconversions. CT-DNA binding affinities and modes of the novel metal complexes 1–3 as well as the formerly published ruthenium Schiff base compounds, trans-P, cis-Cl-[Ru(pch)Cl2(PPh3)2] (4) (pch = 4-((pyridine-2yl-imino)methylene)-chromone) and cis-[RuCl2(bpap)(PPh3)] (5) (bpap = 2,6-bis-((antipyrine-imino)methylene)pyridine) were experimentally and computationally investigated. The paramagnetism of 1–4 and the proton-donor abilities of all the metal compounds promoted significantly higher NO and DPPH radical scavenging activities than the natural antioxidant, vitamin C. Experimental electronic BSA titrations revealed that the metal compounds are ideal binders which preferentially bind to site IIA. The X-ray and spectroscopic data were supported by the computed data which was simulated using the density functional theory method.