Different type-coordinated Nickel(II)dithiophosphonato complexes: Synthesis, characterization, theoretical calculations, anticancer, antioxidant and antimicrobial studies

The soft base type ligand, [(4-methoxy-2-methylphenyl)(O-3-pentyl)dithiophosphonate] (1) was synthesized from the reaction between (2,4-bis(4-methoxy-2-methylphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide) and 3-pentanol, and then reacted with NiCl2.6H(2)O to produce a new complex (2) named [(4-methoxy-2-methylphenyl)(O-3-pentyl)dithiophosphonato]Ni(II). Furthermore, the reaction of 2 with pyridine, bipyridine, and phenanthroline resulted in a series of six-coordinated, new Ni(II) complexes, denoted by 2a, 2b, 2c, and 2d. The structures were determined using spectroscopic techniques. Magnetic susceptibility measurements were also performed on the paramagnetic complexes 2a, 2b, 2c, and 2d. In addition, X-ray diffraction investigations of single-crystal of 2 and theoretical studies involving density functional theory (DFT) and molecular docking simulations were done utilising X-ray experimental data. Moreover, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity test was used to assess the antioxidant activity for 2b, 2c, 2d, and the ligand (1) involved. The antimicrobial activities of the four compounds were evaluated using agar disc diffusion and broth microdilution assays. The findings indicated high antioxidant and weak antimicrobial activity for the compounds. The evaluation of new drug candidates in colorectal (DLD-1) and hepatocellular (HepG2) carcinoma cell lines was performed to assess their anticancer potential. Within this study, IC50 values of various complexes were determined at different incubation times and compared with cisplatin, a well-known chemotherapeutic agent. In particular, complex 2d showed a time-dependent cytotoxic effect, and the highest potential was observed after 72 h of incubation. These findings indicate that complex 2d is promising as a potential anticancer agent in DLD-1 during 72 h of incubation and deserves further investigation.