Atomistic molecular dynamic simulations of polyethylene glycol monododecanoate in water, methanol, ethanol, and 2-propanol

Polyethylene glycol monododecanoate (PEGMD) is a widely used nonionic surfactant in the industry and this study aims to examine its physicochemical properties in water and organic solvents namely methanol, ethanol, and 2-propanol. Simulations were carried out via GROMACS simulation package. A multitude of tests were carried out to evaluate the dihedral angle distribution, radius of gyration, spatial density function (SDF) and solvent accessible surface areas (SAS) calculation. It was found that gyration radius shows that water has the highest degree of compactness followed by methanol, ethanol, and propanol. Dihedral angle distribution instead shows that PEGMD in water exists in three conformations i.e., gauche-, gauche +  and trans states while in organic alcohols only in gauche- and gauche +  states, albeit at differing population preferences, with methanol being almost equally distributed, ethanol preferring gauche +  and propanol gauche- . SDF maps show an irregular, bean-shaped density distribution covering a single PEGMD molecule while the SAS revealed that surface area available for hydrophobic interaction in all four systems exceed that of hydrophilic systems at a ratio of 3:1. Reasons and explanations for the observations are discussed.