Molecular dynamics simulations of the interaction between polyhydroxylated compounds and Lennard-Jones walls: preferential affinity/exclusion effects and their relevance for bioprotection

Abstract

Molecular dynamics simulation is used to investigate the interaction of methanol (MET) and the polyhydroxylated cosolutes (CSLs) ethylene glycol (ETG), glycerol (GLY), glucose (GLU) and trehalose (TRH) in aqueous solution with the surface of rigid Lennard-Jones walls. The walls are designed to represent simplified models for biomolecular (membrane, protein) surfaces and include three functionalisation variants: (i) non-polar (NP, no functionalisation); (ii) semi-polar (SP, surface hydroxyl groups); and (iii) highly polar (HP, positive and negative surface charges). The simulations are performed to investigate, in a simplified context, the preferential affinity/exclusion properties of the different CSLs (compared to water), which are relevant for the phenomenon of bioprotection by polyhydroxylated compounds. The simulations are carried out at three different temperatures (300, 475 and 600 K), and a comparison with simulations involving pure water or the pure liquid CSLs MET, ETG and GLY is also undertaken. In aqueous solution, all CSLs considered evidence preferential affinity (compared to water) for the NP and SP walls. This effect increases in magnitude with increasing CSL size, and is due to the favourable driving force associated with the replacement of multiple water molecules at the wall surface by a single polyhydroxylated CSL molecule (the partial substitution occurring without a significant change in the number of wall-solution hydrogen bonds). The preferential affinity is significantly reduced for the HP wall (for MET, ETG and GLY, preferential exclusion is actually observed). This change is probably related to the higher efficiency of water (compared to the CSLs) in terms of electrostatic solvation (higher dielectric permittivity), and provides an interpretation for the observation that polyhydroxylated CSLs appear to show preferential affinity for the surface of membranes, but preferential exclusion for the surface of proteins.