Syntheses and Photophysical Properties of Schiff Base Ni(II) Complexes: Application for Sustainable Antibacterial Activity and Cytotoxicity

Five
new imine-linked ligands (H2L1, H4L2,
and L3–L5) were synthesize in two step reactions and final
products were fully characterized with spectroscopic techniques. The
binding behavior of these ligands was evaluated with the library of
metal ions. However, substantial photophysical modulations were observed
with the coordination of [Ni2+] ion to the ligand pocket.
The fact that Ni2+ induced remarkable modulation in photophysical
studies encouraged us to prepare the nickel complexes of respective
ligands. The resultant coordination complexes offered interesting
properties like tunable coordination geometry, variable stereochemistry,
and possibility of electrostatic interactions which are important
for biomolecular recognition. These properties of coordination complexes
encouraged us to evaluate the antimicrobial activity of nickel complexes.
All nickel complexes have shown appreciable antibacterial activity
against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). The SEM imaging studies were performed
to know the mechanism of cell death, and results revealed that the
cell wall inhibition is the main reason for bacterial cell death.
The cytotoxicity of these complexes and their respective ligands for
human cell lines was established with the HeLa cell, and observations
affirm 85–90% cell viability after 24 h.