Molecular hybridization approach of bio-potent Cu(II)/Zn(II) complexes derived from N, O donor bidentate imine scaffolds: Synthesis, spectral, human serum albumin binding, antioxidant and antibacterial studies.

Novel bio-relevant monometallic Schiff base complexes of the type, [Cu(L(1))2] (1), [Zn(L(1))2]·2H2O (2), [Cu(L(2))2]·2H2O (3) and [Zn(L(2))2]·H2O (4) [L(1)(E)-3-(((3-chloro-4-hydroxyphenyl)imino)methyl)naphthalen-2-ol and L(2)(E)-2-chloro-4-((1-(5-chloro-2-hydroxyphenyl)ethylidene)amino)phenol] were synthesized and characterized. A comparative account of analytical, spectroscopic (FT-IR, (1)H and (13)C NMR, Mass, UV-vis and EPR), thermal (TGA/DTA), XRD and SEM studies revealed a correlation between the structure and function of these biologically active molecular entities. HSA (Human serum albumin) binding profiles of the metal complexes (1-4) were monitored using biophysical techniques viz., absorbance, fluorescence, circular dichromism (CD) and foster resonance energy transfer (FRET). The intrinsic binding constant (Kb) demonstrated substantial binding propensity of L(1) linked complexes (1 and 2) in comparison to L(2) complexes (3 and 4) suggesting L(1) to be more bio-active pharmacophore due to higher planarity and conjugation as compared to L(2) ligand. The outcome of fluorescence study revealed static quenching mechanism on the basis of the quenching of HSA by the complexes (1-4). However, modifications in the secondary structure of HSA by complexes (1-4) inferred via CD measurements which revealed the enhancement of α-helicity (67.47% to 69.20%) with the preference order of 1>2>3>4. Furthermore, in-vitro antibacterial study against different bacteria and antioxidant activities against DPPH and superoxide radical (O2(-)) at variable concentrations outspread discernible bio-potencies of the metal complexes as compared to free ligand scaffolds due to the chelation effect.