Effects of additives on the growth of L-glutamic acid crystals (beta-form)

To elucidate the mechanism of polymorph-selective crystallization of L-glutamic acid (L-Glu) crystals by the additives, the effects of various L-amino acids, carboxylic acids, and a di-peptide, gamma-L-glutamyl-L-glutamic acid (gamma-Glu-Glu) on the growth of the {1 0 1}, {0 1 0}, and {0 0 1}, three dominant faces of the beta-form of L-Glu crystals have been investigated experimentally and structurally. gamma-Glu-Glu and L-phenylalanine (L-Phe) showed nearly the same strong inhibitory effects on the three faces of the P-form in contrast to their different behavior on the two dominant faces of the alpha-form of L-Glu. These phenomena were explained in terms of the characteristics of the hydrogen bonds of each face and it was found that the beta-form has less discriminating capacity than the alpha-form for the recognition of the molecules. Finally, the cause of the polymorph-selective crystallization by the additives in the L-Glu is attributed mainly to the difference in the inhibitory effects of the additives on the two dominant faces of the alpha-form.