Spectroscopic studies on the interaction of green synthesized-gold nanoparticles with human serum albumin

The interaction of gold nanoparticles, synthesized using Curcuma mangga extract (CM-AuNPs) with human serum albumin (HSA) was investigated with the help of fluorescence, UV absorption and circular dichroism (CD) spectroscopy. In view of the positive correlation of Stern-Volmer constant with temperature, quenching of protein fluorescence observed upon addition of CM-AuNPs seems to occur through collisional mechanism. The quenching mechanism was further substantiated by UV absorption spectral results, where no significant change in the absorption spectrum of HSA was observed upon addition of CM-AuNPs. Analysis of the fluorescence quenching titration data revealed moderate binding affinity (Ka = 0.97 × 104 M−1 at 298 K) between CM-AuNP and HSA. The complexation between CM-AuNP and HSA was predicted to be stabilized by hydrophobic forces, as reflected from the thermodynamic data (ΔH = +35.5 kJ mol−1 and ΔS = +195.62 J mol−1 K−1). Three-dimensional fluorescence spectral analysis demonstrated perturbation of microenvironment around Trp and Tyr residues in HSA upon CM-AuNPs addition. While interaction between CM-AuNP and HSA produced significant tertiary structural change in the protein, secondary structures remained unaltered, as elucidated by near-UV and far-UV CD spectral analyses, respectively. ANS displacement experiments suggested Sudlow's Site II, located in subdomain IIIA, as the preferred binding site of CM-AuNP on HSA