Molecular dynamics simulations of glycine crystal-solution interface.

Glycine is an amino acid that has several applications in the pharmaceutical industry. Hence, growth of alpha-glycine crystals through solution crystallization is an important process. To gain a fundamental understanding of the seeded growth of alpha-glycine from aqueous solution, the (110) face of alpha-glycine crystal in contact with a solution of glycine in water has been simulated with molecular dynamics. The temporal change in the location of the interface of the alpha-glycine crystal seed has been characterized by detecting a density gradient. It is found that the alpha-glycine crystal dissolves with time at a progressively decreasing rate. Diffusion coefficients of glycine adjacent to (110) face of alpha-glycine crystal have been calculated at various temperatures (280, 285, 290, 295, and 300 K) and concentrations (3.6, 4.5, and 6.0 mol/l) and compared to that in the bulk solution. In order to gain a fundamental insight into the nature of variation in such properties at the interface and the bulk, the formation of hydrogen bonds at various temperatures and concentrations has been investigated. It is found that the nature of interaction between various atoms of glycine molecules, as characterized by radial distribution functions, can provide interesting insight into the formation of hydrogen bonds that in turn affect the diffusion coefficients at the interface.