Insights into the Thermodynamics of Polymer Nanodot–Human Serum Albumin Association: A Spectroscopic and Calorimetric Approach

July 28, 2017

Title

Insights into the Thermodynamics of Polymer Nanodot–Human Serum Albumin Association: A Spectroscopic and Calorimetric Approach

Author

Arpan Bhattacharya, Somnath Das, Tushar Kanti Mukherjee

Year

2016

Journal

Langmuir

Abstract

With the advent of newer luminescent nanoparticles (NPs) for bioimaging applications, their complex interactions with the individual biomolecules need to be understood in great detail, prior to their direct application into the cellular environments. Here we have present a systematic and detailed study of the interaction between luminescent polymer nanodot (PND) and human serum albumin (HSA) in its free and ligand-bound state with the help of spectrophotometric and calorimetric techniques. At physiological pH (pH=7.4), PND quenches the intrinsic fluorescence of HSA as a consequence of ground-state complex formation. The binding stoichiometry and various thermodynamic parameters have been evaluated by using isothermal titration calorimetry (ITC) as well as van’t Hoff equation. It has been found that the association of PND with HSA is spontaneous (ΔG0 = -32.48 ± 1.24 kJ mol-1) and is driven by a favorable negative standard enthalpy change (ΔH0 = -52.86 ± 2.12 kJ mol-1) and unfavorable negative standard entropy change (ΔS0 = -68.38 ± 2.96 J mol-1 K-1). These results have been explained by considering hydrogen bonding interactions between amino and hydroxyl groups (–NH2 and –OH) of PND and carboxylate groups (-COO-) of glutamate (Glu) and aspartate (Asp) residues of HSA. The binding constant of PND with HSA is estimated to be 4.90 ± 0.19 × 105 M-1. Moreover, it has been observed that warfarin bound HSA (war-HSA) shows a significantly lower binding affinity (Kb= 1.15 ± 0.19 × 105 M-1) towards PND, while ibuprofen bound HSA (ibu-HSA) shows a slightly lower affinity (Kb= 3.47 ± 0.13 × 105 M-1) compared to the free HSA. In addition, our results reveal that PND displaces warfarin from the site I (subdomain IIA) of HSA due to the partial unfolding of the war-HSA. We hope that the present study will be helpful to understand the fundamental interactions of these biocompatible PNDs with various biological macromolecules.

Instrument

J-815

Keywords

Circular dichroism, Secondary structure, Ligand binding, Nanostructures, Materials, Biochemistry