The effect of anion on aggregation of amino acid ionic liquid: Atomistic simulation

Aggregation behavior of dodecyl betaine chloride [DB][Cl], as an amino acid ionic liquid, and dodecyl betaine N-acetyl glycinate [DB][AG], as a bio ionic liquid, in aqueous media was studied through molecular dynamics simulation. The aggregating was investigated by radial distribution function, coordination numbers, and hydrogen bond numbers. The results demonstrated the hydrogen bond between [DB]⁺ and [AG]^- that leads to aggregation. The number of hydrogen bonds of [DB][AG] is greater than [DB][Cl] and causes a decrease in the gradient of the mean square displacement, thereby the diffusion coefficient of cation, anion, and water in [DB][AG]. The results point to a stable aggregation of [DB][AG] which is in agreement with the results of root mean square deviations. The aggregation number for [DB][AG] is 50 and 44 for [DB][Cl]. Computing the radius of gyration and geometrical radius shows that the aggregation size is 23.0 Å and 26.4 Å for [DB][AG] and [DB][Cl], respectively. It was also observed that the shape of the aggregates is quasi-spherical that points to a sub-diffusive regime.