Polymorph , additive effect crystallization

Nakano, K., Sada, K. and Miyata, M. (1996). Novel additive effect of inclusion crystals on polymorphs of cholic acid crystals having different hydrogen-bonded networks with the same organic guest. Chem. Commun., 989-90. [58]... 

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-fl). However, the effect of additives espeddly on the kinetic behavior of polymorphism has not usually been treated quantitatively and the mechanisms are not known. 

Aronhime, J, S Sarig, N Garti. (1990). Emulsifiers as additives in fats Effect on polymorphic transformations and crystal properties of fatty acids and triglycerides. Food Struct 9 337-352. 

FIG. 2 Polymorphism in ammonium nitrate (top) and effect of additives on crystal habit modifications (bottom). 

Another problem is explaining the mechanism of solvation of an organic molecule at a molecular level. It is well known that even for the same compound, different polymorphic crystals have different solubility characteristics. In addition the rate of solvation varies according to the face of the crystals this is also observed in crystal growth. These phenomena could be influenced by kinetic factors, which have a significant effect on the efficiency of resolution. Thus treatment of the kinetic factors of solvation is another problem that must be explored. 

Black and Davey (1988) describe a number of the interrelationships and practical aspects of the control of nucleation, crystal growth, and polymorphic transformation of amino acids. The factors described and demonstrated for primary nucleation of L-glutamic acid include temperature, critical nucleus, relationship of interfacial tension to solubility, thermal history, induction time, agitation, and effect of additive. 

In this section, the polymorphic properties of natural fats are briefly discussed by highlighting miMat, cocoa butter, and palm oil fraction based on recent research into the effects of external factors on the polymorphic crystallization such as shear stress, ultrasound stimulation, and addition of food emulsifiers. 

---