Interaction of biosynthesized gold nanoparticles with BSA and CTDNA: A multi-spectroscopic approach

The interaction between biosynthesized gold nanoparticles (GNP) with bovine serum albumin (BSA) and calf thymus DNA (CTDNA) was investigated from a multi-spectroscopic approach. The apparent binding constant (K) were 2.69 x 10(4) L/mol and 15.84 x 10(4) L/mol at 293 K, respectively for BSA and CTDNA, and the number of binding sites were similar to 1. According to the Van't Hoff equation, the thermodynamic parameters were calculated (Delta H = -119.496 kJ/mol, Delta S = -320.92 J/mol/K for BSA and Delta H = -225.89 kJ/mol; AS = 673 J/mol/K for CTDNA) and the results indicated hydrogen bonds and van der Waals forces are the main stabilizing force in both of the BSA-GNP and CTDNA-GNP complex. The average binding distance (r = 4.45 nm) and the critical energy transfer distance (R-0 = 2.94 nm) between GNP and BSA were also evaluated according to Forster's non-radiative energy transfer theory. What is more, UV-Visible, and circular dichroism spectra showed that the addition of GNP changed the secondary structure of BSA and led to a decrease in alpha-helix. Circular dichroism spectra also indicated conformational changes of CTDNA in the presence of the GNP. Furthermore, the GNP induces small changes in DNA viscosity and melting temperature which is indicative of groove binding mode of GNP with CTDNA. (C) 2016 Elsevier Ltd. All rights reserved.