Aqueous Imidazole Solutions: A Structural Perspective from Simulations with High-Rank Electrostatic Multipole Moments

Imidazole is a small but important molecule occurring as a structure fragment in systems from amino acids, over ionic liquids, to synthetic polymers. Here we focus on the structure and dynamics of imidazole in water at ambient conditions, using both radial and spatial distribution functions. Molecular dynamics simulations were carried out for various imidazole concentrations, using a traditional point-charge potential and a high-rank multipolar potential. The difference in the description of the electrostatics leads to sizable quantitative differences (e.g., the diffusion coefficient) but also qualitative differences in the local structure. In contrast to a point-charge potential, the multipolar potential favors hydrogen-bonded chainlike imidazole dimers over stacked dimers.