Computational Observation of Pockets of Enhanced Water Concentration at the 1-Octanol/Water Interface

Abstract

Molecular dynamics simulations with polarizable potentials were carried out to investigate the 1-octanol-water interface in which a significant amount of water migrated into the 1-octanol phase. A region of enhanced water concentration, around three times the average concentration in water saturated 1-octanol, was present 18 Å from the Gibbs dividing surface into the 1-octanol phase. This coincided with two layers of 1-octanol molecules, forming a somewhat ordered bilayer with the first layer having its hydroxyl group pointed toward the water phase. The second layer of 1-octanol had hydroxy groups pointed in the opposite direction on average. A consequence of this was a region of high alkyl concentration and reduced polarity, as has been previously observed. Water structure in the octanol phase contracted as it approached the 1-octanol phase, opposite what was observed at the n-octane-water interface with polarizable potentials. In contrast, 1-octanol hydroxy structure expanded as it came in contact with water.