Theoretical and biological investigations of newly synthesized Co(II)-salphen complexes derived from salphen ligands

A series of five cobalt(II)-salphen complexes, C1-C5 were synthesized from the known salphen ligands, L1-L5 [N, N’-(X)bis(salicylidene)1,2-phenylenediamine] {where X = H (L 1 ), Cl( L2 ), Br( L3 ), CH 3 ( L4 ), OCH 3 ( L5 )} and characterized by elemental analyses, magnetic moments, molar conductance, UV–visible, FT-IR, H 1 NMR, ESI-MS and PXRD spectral measurements. The theoretical stabilities and optimized structures of the complexes were explored from Density Functional Theory (DFT) calculations. The binding propensities of the synthesized complexes with Bovine Serum Albumin (BSA) were investigated via absorption titration, fluorescence and electrochemical studies. The values of the Stern-Volmer constant, binding constant and number of binding sites determined were indicative of significant binding of all the complexes. The higher values (in the order of 10 12 M -1 s -1 ) of Kq, indicate the behavior of static quenching via ground state complex formation of BSA with complexes. Molecular modeling studies predicted the affinity energies for suitable binding conformations ranging from -7.4 to -8.2 kcal/mol for the system. Although all complexes exhibit binding ability, C2 and C3 bearing electron withdrawing groups seems to bind more favorably to BSA interaction. The antimicrobial screening results demonstrate that the complexes, C 1-C5 exhibited well defined inhibitory effect than the free ligands. The observed percentage of cell viability (IC 50 values ranging 14–123 µM) against A549 cell lines suggests the potential efficacy of all the complexes. Notably, C2 and C3 possessing electron withdrawing moiety exhibited superior anticancer potency than the other complexes.