Ecofriendly gold nanoparticles – Lysozyme interaction: Thermodynamical perspectives

Abstract

In the featured work interaction between biosynthesized gold nanoparticles (GNP) and lysozyme (Lys) has been studied using multi-spectroscopic approach. A moderate association constant (Kapp) of 2.66 × 104 L/mol has been observed indicative of interactive nature. The binding constant (Kb) was 1.99, 6.30 and 31.6 × 104 L/mol at 291, 298 and 305 K respectively and the number of binding sites (n) was found to be approximately one. Estimated values of thermodynamic parameters (Enthalpy change, ΔH = 141.99 kJ/mol, entropy change, ΔS = 570 J/mol/K, Gibbs free energy change, ΔG = − 27.86 kJ/mol at 298 K) suggest hydrophobic force as the main responsible factor for the Lys-GNP interaction and also the process of interaction is spontaneous. The average binding distance (r = 3.06 nm) and the critical energy transfer distance (Ro = 1.84 nm) between GNP and Lys was also evaluated using Förster's non-radiative energy transfer (FRET) theory and results clearly indicate that non-radiative type energy transfer is possible. Moreover, the addition of GNP does not show any significant change in the secondary structure of Lys as confirmed from circular dichroism (CD) spectra. Furthermore, NMR spectroscopy also indicates interaction between Lys and GNP. The resulting insight is important for the better understanding of structural nature and thermodynamic aspects of binding between the Lys and GNP. © 2017 Elsevier B.V.