Adsorption Energetics of Amino Acid Analogs on Polymer/Water Interfaces Studied by All-Atom Molecular Dynamics Simulation and a Theory of Solutions

Energetics of adsorption was addressed with all-atom molecular dynamics simulation on the interfaces of poly(2-methoxyethyl acrylate) (PMEA), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) with water. A wide variety of adsorbate solutes were examined, and the free energy of adsorption was computed with the method of energy representation. It was found that the adsorption free energy was favorable (negative) for all the combinations of solute and polymer, and among PMEA, PMMA, and PBA, the strongest adsorption was observed on PMMA for the hydrophobic solutes and on PMEA for the hydrophilic ones. According to the decomposition of the adsorption free energy into the contributions from polymer and water, it was seen that the polymer contribution is larger in magnitude with the solute size. The total free energy of adsorption was correlated well with the solvation free energy in bulk water only for hydrophobic solutes. The roles of the intermolecular interaction components such as electrostatic, van der Waals, and excluded-volume were further studied, and the electrostatic component was influential only in determining the polymer dependences of the adsorption propensities of hydrophilic solutes. The extent of adsorption was shown to be ranked by the van der Waals component in the solute-polymer interaction separately over the hydrophilic and hydrophobic solutes, with the excluded-volume effect from water pointed out to also drive the adsorption.

Automated summary

The energetics of adsorption on the interfaces of PMEA, PMMA, and PBA with water were studied using all-atom molecular dynamics simulation. The adsorption free energy was found to be favorable for all combinations of solute and polymer, and PMMA exhibited the strongest adsorption for hydrophobic solutes while PMEA showed the strongest adsorption for hydrophilic solutes. The polymer contribution to the adsorption free energy was larger with increasing solute size. The total free energy of adsorption correlated well with the solvation free energy in bulk water for hydrophobic solutes only.