Synthesis, X-ray studies, electrochemical properties, evaluation as in vitro cytotoxic and antibacterial agents of two antimony‌(III) complexes with dipicolinic acid

Abstract

Proton-transfer compounds were prepared by the reaction of pyridine-2,6-dicarboxylic acid (pydcH2) with 1-methylimidazole (1-mim) and 2-methyimidazole (2-mim) in 1:2 molar ratio. The reaction of ligands with antimony(III)chloride led to complexes formulated as [Sb(pydcH)(pydc)(H2O)] (1) and [Sb2(pydcH)2(H2O)2(Cl)2(OH)]2·2H2O (2). Both two of complexes were characterized by elemental analysis, IR, UV–Vis and NMR spectroscopy and also their structures were confirmed by X-ray crystallography. Cyclic voltammetry measurements on the complexes revealed one redox couple corresponding to Sb(III)/Sb(V) at E0′ of −0.184 to −0.052 V versus Ag/AgCl, under argon. Aeration proved the further interaction potent of complex (2) with oxygen compared to (1), within 5 min. In this study, the cytotoxic potential of each of three compounds were evaluated, using oxaliplatin as a standard, under MTT method, against MCF7 (a human breast cancer), H1299 (a human non-small cell lung carcinoma), HT29 (a human colon adenocarcinoma), HepG2 (a human liver hepatocellular carcinoma) and βTC (a mouse beta pancreatic) cell lines. Complex (2) with E0′ about three and a half times (1) exhibited more significant toxicity compared to (1). The strongest cytotoxic effect for (2) was indicated on HepG2 cell line (IC50 = 1 μM). Antibacterial activity of the compounds was evaluated against three Gram-positive bacteria namely Staphylococcus aureus, Streptococcus pyogenes and Enterococcus faecalis and also three Gram-negative bacteria namely Escherichia coli, Pseudomonas aeruginosa and Proteus vulgaris through the established antibacterial assays including broth microdilution method using 2,3,5-triphenyl tetrazolium chloride (TTC, as chromogenic marker) and agar well diffusion method. Both two complexes showed an enhanced antibacterial activity in comparison with the standard drug chloramphenicol.