Thermodynamic Implications and Time Evolution of the Interactions of Near-Infrared PbS Quantum Dots with Human Serum Albumin

Abstract

Near-infrared (NIR)-emitting PbS quantum dots (QDs) are endowed with good stability, high quantum yield, and long lifetime in the body, so they are promising agents in biological imaging. They quickly form the so-called “protein corona” through nonspecific adsorption with proteins in biological fluids once upon exposure to the biological system. Here, PbS QDs and human serum albumin (HSA) were selected as the model system. Fluorescence quenching spectroscopic studies indicated a static quenching process caused by the addition of PbS QDs, which was corroborated by the UV–vis absorption spectroscopy and fluorescence lifetime. Thermodynamic parameters were obtained by the fluorescence quenching method. The enthalpy change and entropy change were well correlated with the “enthalpy–entropy compensation” (EEC) equation summarized in this work. The slope (α = 1.08) and the intercept (TΔS 0 = 34.44 kJ mol–1) indicated that the interaction resembled a protein–protein association. The both negative signs of enthalpy change and entropy change were elucidated by a proposed “two-step association–interaction” (TSAI) model. Agarose gel electrophoresis (AGE) and dynamic light scattering (DLS) showed that the binding ratio was roughly 2:1 (HSA/QDs), resembling sandwich-like structures. Furthermore, the secondary structure of HSA depended on the concentration of added QDs and the incubation time. The results preliminarily uncovered the physicochemical properties of QDs in the presence of proteins and elucidated the role of time evolution. These will inspire us to make the fluorescent QDs more biocompatible and use them in a proper way.

Isothermal titration calorimetry investigation of the interactions between vitamin B6-derived hydrazones and bovine and human serum albumin

“…In principle, a linear correlation between ∆S and ∆H in the binding process for a series of homologous compounds is considered as strong evidence of H-S compensation. The linear correlation occurring for the binding of PLPderived hydrazones with both BSA and HSA clearly indicates enthalpy-entropy compensation, that is, a change in enthalpy is compensated by a corresponding change in the entropic term, as reported for similar systems [55,56].…”

Positive Sorption Behaviors in the Ligand Exchanges for Water-Soluble Quantum Dots and a Strategy for Specific Targeting

“…Desolvation will cause the increase of entropy, that is, Δ S 1 > 0, which is favorable for the free energy. We reported in a recent article that the association of two hydrated species was an endothermic process . With the increase of exposed sites, K d1 (stage I) increases obviously.…”

Regulation of the Enzymatic Activities of Lysozyme by the Surface Ligands of Ultrasmall Gold Nanoclusters: The Role of Hydrophobic Interactions

“…According to Ross theory, the interaction forces could be distinguished by the sign and value of thermodynamic parameters, i.e., enthalpy change (Δ H ) and entropy change (Δ S ). Furthermore, our group recently proposed a two-step association–interaction (TSAI) model for the interactions of nanoparticles with proteins and summarized the thermodynamic parameters of the interactions between nanoparticles and serum albumins and brought up a linear relationship between Δ H and T Δ S , that is, the “enthalpy–entropy compensation” (EEC) equation which may provide a useful guidance for better elucidating the driving forces happen in the protein–nanomaterials system.…”

“…Furthermore, our group recently proposed a two-step association−interaction (TSAI) model for the interactions of nanoparticles with proteins and summarized the thermodynamic parameters of the interactions between nanoparticles and serum albumins and brought up a linear relationship between ΔH and TΔS, that is, the "enthalpy−entropy compensation" (EEC) equation. 36…”