Protein binding and cytotoxic activities of monomeric and dimeric oxido-vanadium(V) salan complexes: Exploring the solution behavior of monoalkoxido-bound oxido-vanadium(V) complex

Three ONNO donor tetradentate diamino bis(phenolato) “salan” ligands, N, N′-dimethyl-N, N′-bis-(5-chloro-2-hydroxy-3-methyl-benzyl)-1,2-diaminoethane (H2L1), N, N′-dimethyl-N, N′-bis-(5-chloro-2-hydroxy-3-isopropyl-6-methyl-benzyl)-1,2-diamino-ethane (H2L2) and N, N′-bis-(5-chloro-2-hydroxy-3-isopropyl-6-methyl-benzyl)-1,2-diaminocyclohexane (H2L3) have been synthesized by following Mannich condensation reaction. Reaction of these ligands with their corresponding vanadium metal precursors gave one oxidomethoxidovanadium(V) [VVOL1(OCH3)] (1) and two monooxido-bridged divanadium (V, V) complexes [VVOL2–3]2(μ-O) (2–3). The complexes were characterized by IR, UV–vis, NMR and ESI mass spectrometry. Also, the structure of all the complexes (1–3) was confirmed by the Single-Crystal X-ray diffraction analysis, which revealed a distorted octahedral geometry around the metal centres. The solution behavior of the [VVOL1(OCH3)] (1) reveals the formation of two different types of V(V) species in solution, the structurally characterized compound 1 and its corresponding monooxido-bridged divanadium (V, V) complex [VVOL1]2(μ-O), which was further studied by IR, and NMR spectroscopy. The electrochemical behavior of all the complexes was evaluated through cyclic voltammetry. Interaction of the salan-V(V) complexes with human serum albumin (HSA) and bovine serum albumin (BSA) were analysed through fluorescence quenching, UV–vis absorption titration, synchronous fluorescence, circular dichroism studies, and förster resonance energy transfer (FRET). Finally, the in vitro cytotoxicity of the complexes was investigated against MCF-7 and HT-29 and NIH-3T3 cell lines. Cytotoxicity value of complexes in both MCF-7 and HT-29 follows the same trend that is 3 > 1 > 2 which is in line with protein binding affinity of the complexes. Some new monomeric, [VVOL1(OCH3)] (1) and dimeric, [VVOL2–3]2(μ-O) (2 and 3) V(V) complexes of salan ligands are reported, showing solution behaviors of complex 1. Biological potential has been explored in terms of their human serum albumin (HSA) and bovine serum albumin (BSA) interaction, and cytotoxicity against MCF-7 and HT-29. [Display omitted] •Novel mono- and dinuclear vanadium(V) complexes (1–3) of salan ligands (H2L1–3).•Solution behavior of oxidomethoxidovanadium(V) [VVOL1(OCH3)] (1), L1 = salan ligand.•Investigation of protein binding.•Cytotoxic potential.