Spectroscopy and Molecular Modeling Study on Binding of Nickel Phthalocyanine to Human Serum Albumin.

The interaction of nickel tetra sulfunated phthalocyanine( NiTSPc) with human serum albumin (HSA), in 20 mM phosphate buffer pH 7.4 was investigated using advanced techniques including fluorescence, synchronous fluorescence, Fourier transform infrared (FT-IR), circular dichroism (CD) spectroscopy and molecular docking. The fluorescence quenching measurements showed a single binding site on HSA for NiTSPc with the binding constant (K<sub>b</sub>) value equals to 1.26×106 at 25°C. The results showed that quenching mechanism of HSA by NiTSPc was of dynamic type. The results from FTIR and CD spectroscopies demonstrated that NiTSPc binds to amino acid residues of the main polypeptide chain in protein destroying the hydrogen bonding network. The corresponding thermodynamic parameters were then calculated by analysis of fluorescence data using van't Hoff plot. These data indicated that driving force for interaction was mainly hydrophobic in nature and the process was entropy driven. The information obtained from CD, FT-IR and synchronous fluorescence spectroscopies revealed that both microenvironment and conformation of HSA was changed. Molecular docking study confirmed the binding mode obtained by experimental data.