A control on hydrophobic and hydrophilic interactions between HEWL and metal Schiff-base complexes comprising of different metal ions and ligands

The structural effects of different copper(II) and nickel(II) Schiff base complexes on hen egg white lysozyme (HEWL) have been investigated through steady state and time resolved absorption and fluorescence, and circular dichroism spectroscopy. The Schiff base ligands with N4 donor atoms show both hydrophobic and hydrophilic interactions, however hydrophilic interaction prevails with ligands having N2O2 donor atoms. Variation of metal ions from Cu2+ to Ni2+ with each type of Schiff base ligand increases the probability of hydrophilic over hydrophobic interactions, which supports their significance in regulating the binding affinity between HEWL and metal complexes. On photo-excitation the complexes comprising of Cu2+ ion instead of Ni2+ ion and ligands with N4 donor system rather than N2O2 donor system, increases the probability of intersystem crossing to populate the corresponding triplet state as observed from laser flash photolysis study. The better binding affinity of nickel complexes with different selectivities compared to copper complexes towards HEWL emphasizes the potentiality of less explored nickel complexes in drug-protein interactions.