M. Kitamura et T. Ishizu, KINETIC EFFECT OF L-PHENYLALANINE ON GROWTH-PROCESS OF L-GLUTAMIC ACID POLYMORPH, Journal of crystal growth, 192(1-2), 1998, pp. 225-235
The mechanism of additive effect of L-phenylalanine (L-Phe) on the gro
wth kinetics of L-glutamic acid (L-Glu) polymorphs was investigated. W
ith L-Phe concentration the growth rate of the (1 0 1) face of the bet
a crystal decreased and finally stopped at a critical concentration C-
p. As for alpha crystal the growth rate in the [1 1 1] direction was
suppressed and the new (1 1 0) face appeared, while the growth rate of
the (0 0 1) face was not influenced by L-Phe. The fluctuation of the
growth rates was observed for both polymorphs at the higher concentrat
ion of L-Phe. The critical concentration of L-Phe for the (1 1 0) face
of alpha is about twice of that for the (1 0 1) face of beta. At the
constant L-Phe concentration each polymorph grew at higher supersatura
tions than the critical relative supersaturation sigma. The value of
sigma for the beta crystal was a few times larger than that for the a
lpha crystal. The relationship between the growth rates and the concen
tration of the additive was expressed using the growth model of a curv
ed step in connection with the adsorption density of the additive. The
dependence of the growth rate of L-Glu on the L-Phe concentration and
the relative supersaturation could be represented by Freundlich-type
equations for both polymorphs. The calculated values of the adsorption
density and the distance between the adsorbed neighboring L-Phe molec
ules also showed the preferential adsorption of L-Phe on beta crystals
. The method to determine the optional supersaturation at the certain
concentration of additives was proposed. (C) 1998 Elsevier Science B.V
. All rights reserved.