Interaction Thermodynamics Studies of Different Surface-Modified ZnSe QDs with BSA by Spectroscopic and Molecular Simulation Methods

Three types of ZnSe quantum dots (QDs) modified with L-glutathione (GSH), thioglycolic acid (TGA) and L-cysteine (Cys) as capping agents on their surface were synthesized in aqueous solution by microwave irradiation. The interactions between the QDs and bovine serum albumin (BSA) were explored by spectroscopic and molecular simulation methods, to calculate their thermodynamic constants and binding distances. The experimental results suggest that binding is an enthalpy-driven process, mainly via hydrogen bonding and van der Waals interactions. The interaction forces vary with the type of capping agent used for surface modification, being strongest for GSH, weakest for TGA, and intermediate for Cys. These results were confirmed by molecular modeling. The TGA-modified QDs interact with BSA at multiple binding sites on its surface, mainly via van der Waals forces and hydrogen bonding. The Cys-modified QDs also bind with BSA at multiple binding sites on its surface, but mainly through hydrogen bonding and hydrophobic interactions. The GSH-modified QDs bind with BSA on the surface and in the pocket of BSA, which is dominated by hydrogen bonding. These experimental and molecular modeling studies shed new light on the interactions of BSA with QDs modified with different ligands.