Synthesis, characterization, antimicrobial and antitubercular evaluation of nickel (II) complexes of ON donor quinoline-hydrazide core

In the current work, non-toxic and safe Ni(II) complexes of unsymmetrical Schiff base ligand derived from Quinoline hybrid and isoniazid, viz. [Ni^II(Quibal-INH)₂] (1), [Ni^II(Quibal-INH)(cat)] (2) and [Ni^II(Quibal-INH)(bha)] (3), were synthesized. The complexes were characterized by elemental analysis and ATR-IR spectroscopy. These novel complexes were further preliminary evaluated for their solution stability in varied pH conditions. Furthermore, the interactions between Ni (II) complexes with human serum albumin (HSA) have been explored by using UV–visible spectroscopy. It was inferred that the complexes could quench the intrinsic fluorescence of HSA in a steady quenching process. The compounds were tested for their therapeutic potentials, viz. antibacterial, antifungal and anti-TB potential. In preliminary screening, nickel complexes (1) and (3) were active against Candida albicans with excellent growth inhibition. Nickel complex (1) was established as active and was assigned for further validation. For complexes 1 and 3, a toxicity test was performed on human embryonic kidney cells, and a hemolytic test was conducted on human red blood cells. Both complexes (1 and 3) were found to be non-toxic and safe. Nickel Complex (2) exhibited excellent anti-TB activity against the MTB H₃₇R_v strain, which was comparable to the standard TB drugs.