Chapter 9
Growth Process and Morphological Change of β-Glutamic Acid in the Presence of L-Phenylalanine
Downloaded by MONASH UNIV on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1997 | doi: 10.1021/bk-1997-0667.ch009
M . Kitamura and Y. Sumi Department of Chemical Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739, Japan The growth rate of β crystal of L-glutamic acid(L-Glu) was measured using a single crystal method in a flow system at 25°C. The growth rate in the longitudinal direction(A), which corresponds to (101) face, was measured under the experimental conditions, however, the growth rates in the directions of thickness(C) and width(B) were too low to be observed. The growth process in pure solutions was found to be controlled by the surface reaction step. It was observed that with increasing of L -phenylalanine(L-Phen) concentration (Cp) the growth rate decreased and finally stopped at the critical concentrations (Cp*). At higher concentrations of L-Phen, the growth of L-Glu became irregular and a fluctuation of the growth rates with time appeared. The fluctuation was attributed to the complex surface structure, i.e. on the surface adsorption of L-Phen is not homogeneous and the growth of L-Glu is occurring competitively. Furthermore, a morphological change occurred, i.e. the growing face of (101) tended to separate. It is considered that the adsorption of L-Phen occurs at a specific point on the advancing front of the crystals. When the value of Cp* for β crystal was compared with that for α crystal in the direction parallel to the main face. it was cleared that Cp* for β is smaller than that for α . This fact coincides well with the batch crystallization behaviors of these polymorphs. In the crystallization of polymorphs influence with some special additives is observed(i-3). Such effect is due to the relative change of nucleation rate and growth rate of the polymorphs,' the effect also contains the change in transformation rate(4,5). Furthermore, a morphological change occurs in many cases. On the other hand, a crystallographic approach has been applied to effect of various type of additives on crystal growth(6-8). However, the effect of additives especially on the kinetic behavior of polymorphism has not usually been treated quantitatively and the mechanisms are not known. From this pointof view we have dealt with the crystallization and the transformation processes of amino acids such as L-glutamic acid(L-Glu)(9.70) and L-histidine(77). With respect to L-Glu, the effects of temperature, supersaturation, and stirring on the crystallization behavior of the polymorphs(metastable α and stable β) were clarified(9). At 45 C in pure solutions both polymorphs tended to crystallize and the e
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© 1997 American Chemical Society
In Separation and Purification by Crystallization; Botsaris, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
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K I T A M U R A & SUMI
Growth Process of ^Glutamic Acid
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transformation occurred by "solution-mediated mechanism". However, in the presence of L-phenylalanine (L-Phen) the crystallization of β type was selectively suppressed and the transformation rate was retarded(70). This means that L-Phen suppresses preferentially both the nucleation rate and growth rate of β L-Glu. In this work the effect of L-Phen on the growth kinetics and morphology of β L Glu crystals was investigated using a single crystal method in a flow system and the results were compared with those for
