Twenty Natural Amino Acids Adsorption on Representative Surfaces: Dependence of Entropy–Enthalpy Compensation on Interface Properties

Despite extensive studies on the protein adsorption on the surface, a thermodynamic understanding of the crucial relationship between interface properties and entropy-enthalpy compensation during adsorption remains elusive. Herein, we calculated the key thermodynamic parameters for adsorption of 20 amino acids on two representative surfaces by molecular dynamics simulations. Our simulation results demonstrate the dependence of free energy including entropy-enthalpy compensation on the side chain properties of amino acids, which could be categorized into three groups: hydrophobic, polar, and charged. The adsorption free energies increase with molecular size within their respective categories on gold and graphene surfaces. The adsorption of charged amino acids on gold and graphene surfaces is predominantly an entropy-driven process. For polar amino acids, smaller molecules are primarily driven by the enthalpy change, whereas larger molecules are mainly dominated by entropy effects on these two surfaces. For hydrophobic amino acids, the adsorption driving force on the graphene surface is consistent with the observed features for polar amino acids. However, on the gold surface, the size effect of the hydrophobic amino acids exhibits a trend contrasting with that observed on the graphene surface. Our study highlights the importance of the distinct features of solid-liquid interfaces in determining the relationship between the entropy and enthalpy variations.