A study of the interaction of carbon rich polymer nanodots with serum albumins:a spectroscopc investigation

Abstract

Here, we investigate the interaction of carbon rich polymer nanodots (PNDs) with bovine serum albumin (BSA) and human serum albumin (HSA) under physiological conditions by means of fluorescence spectroscopy, circular dichroism (CD) and FT-IR spectroscopy. It has been observed that the steady-state fluorescence quenching of BSA and HSA by PNDs is a result of ground state complex formation and this leads to static quenching mechanism which is further supported by lifetime measurements. The binding parameters are estimated from Stern-Volmer and Scatchard equation. The binding constant of both the albumins with PNDs is in the order of 105 M-1. The calculated thermodynamic parameters reveal that the enthalpy change (ΔH) and entropy change (ΔS) are negative and these results have been explained by considering specific hydrogen bonding (H- bonding) interactions between amine (–NH2) and hydroxyl (˗OH) groups of PNDs and carboxylate (–COO − ) groups of aspartate (Asp) and glutamate (Glu) residues of BSA/HSA. Moreover, salt effect study confirms that, electrostatic interaction doesn’t play any role in the protein-PNDs association process. The observed H-bonding interaction is spontaneous since the overall free energy change (ΔG) is negative. Competitive experiments using warfarin and ibuprofen as site markers indicate that association of BSA and HSA with PNDs occurs selectively through site I of the proteins. Furthermore, the CD spectral analysis indicates that the secondary structure of BSA/HSA changes considerably in the presence of PNDs probably due to partial unfolding of the albumins proteins at the nanoparticle surface, although the overall tertiary structure remains intact.