A Series of Non-Oxido V Complexes of Dibasic ONS Donor Ligands: Solution Stability, Chemical Transformations, Protein Interactions, and Antiproliferative Activity.

A series of mononuclear non-oxido vanadium(IV) complexes, [V(L)] (), featuring tridentate bi-negative ONS chelating S-alkyl/aryl-substituted dithiocarbazate ligands HL, are reported. All the synthesized non-oxido V compounds are characterized by elemental analysis, spectroscopy (IR, UV-vis, and EPR), ESI-MS, as well as electrochemical techniques (cyclic voltammetry). Single-crystal X-ray diffraction studies of - reveal that the mononuclear non-oxido V complexes show distorted octahedral ( and ) or trigonal prismatic () arrangement around the non-oxido V center. EPR and DFT data indicate the coexistence of and isomers in solution, and ESI-MS results suggest a partial oxidation of [V(L)] to [V(L)] and [VO(L)]; therefore, all these three complexes are plausible active species. Complexes - interact with bovine serum albumin (BSA) with a moderate binding affinity, and docking calculations reveal non-covalent interactions with different regions of BSA, particularly with Tyr, Lys, Arg, and Thr residues. cytotoxic activity of all complexes is assayed against the HT-29 (colon cancer) and HeLa (cervical cancer) cells and compared with the NIH-3T3 (mouse embryonic fibroblast) normal cell line by MTT assay and DAPI staining. The results suggest that complexes - are cytotoxic in nature and induce cell death in the cancer cell lines by apoptosis and that a mixture of V, V, and VO species could be responsible for the biological activity.