Study of the Incorporation Behavior of L-Leu and D-Leu in L-Val Crystallization

Abstract

Branched-Chain Amino Acids (BCAAs) are essential amino acids mainly produced through fermentation. With respect to BCAA crystallization, the incorporation behavior of L-form BCAAs as a guest amino acid in the crystallization of L-form BCAAs is well known. However, the incorporation behavior of D-form BCAAs as a guest amino acid in the crystallization of L-form BCAAs is not clear. In this study, we focused on the crystal conformation and incorporation behavior of D-Leucine (D-Leu) and L-leucine (L-Leu) in the crystallization of L-valine (L-Val). Moreover, the difference in the incorporation behavior was investigated on the basis of the distribution ratio of crystals to mother liquor, and the crystal structure and interaction energy were calculated using a molecular dynamics method. The crystal composed of L-Leu in L-Val formed as a solid solution and L-Leu was substituted into the crystal lattice of L-Val. In the case where D-Leu was added as a guest amino acid during L-Val crystallization, D-Leu was not incorporated into the L-Vallattice because the interaction energy between a D-Leu molecule and the L-Val crystal lattice was substantially greater than that between an L-Leu molecule and the L-Val crystal lattice.