Unprecedented formation of organo-ruthenium(ii) complexes containing 2-hydroxy-1-naphthaldehyde S-benzyldithiocarbazate: synthesis, X-ray crystal structure, DFT study and their biological activities in vitro

Abstract

As a contribution to the development of new ruthenium complexes with pharmacologically interesting properties, two new mononuclear ruthenium(II) complexes of the general formula [Ru(H-Nap-sbdtc)Cl(CO)(EPh₃)₂] (1 & 2) [H-(Nap-sbdtc) = 2-hydroxy-1-naphthaldehyde-S-benzyl-dithiocarbazate; E = P or As] were synthesized. The new ruthenium(II) carbonyl complexes are remarkably stable and were obtained in good yields. Their identities have been established by satisfactory elemental analyses and various spectroscopic techniques (IR, UV/visible, (¹H, ¹³C, and ³¹P) NMR, and ESI-MS). For a better definition, the molecular structure of complexes 1 and 2 has been determined by X-ray crystallography, which confirms the coordination mode of the ligand and reveals a distorted octahedral geometry around the ruthenium ion. The molecular structure of complexes 1 and 2 has been optimized by DFT calculations. The binding affinity and binding mode of the ligand and their ruthenium(II) complexes toward calf thymus CT-DNA were determined by the emission spectral method, the fluorescent indicator displacement (FID) assay and viscosity measurements. Further, the interactions of the ligand and their complexes 1 and 2 with bovine serum albumin (BSA) were investigated using UV-Vis and fluorescence spectroscopic methods. Absorption and emission spectral studies indicate that complexes 1 and 2 interact with CT-DNA and BSA protein more strongly than their parent ligand. In addition, the interactions of the complexes with DNA/BSA were followed by electrophoretic mobility spectrometry studies and the results show that these complexes exhibited good cleavage properties. In vitro anticancer activity has been scrutinized by the MTT assay, acridine orange/ethidium bromide (AO/EB) and diamidino-2-phenylindole (DAPI) staining against the human cervical cancer (HeLa) cell line.