Polymorphs properties

TABLE 8. Polymorphic properties of stilbene and azo derived compounds... 

The polymorphic nature of the multicomponent TAG systems is related to phase behavior that is affected by molecular interactions among the component TAGs. The fat crystals in a miscible phase may exhibit simple polymorphic properties. By contrast, the immiscile eutectic phase may show complicated polymorphic properties as a superposition of the polymorphic forms of the component TAGs. Furthermore, if the molecular compound is formed by specific TAG components, the polymorphic behavior becomes complicated, as shown for the case of POP-OPO (see Section 5.2). Therefore, knowing the phase behavior of the principal TAG components is a prerequisite for precise understanding of the polymorphism of natural fats. 

The phase behavior of the mixed TAG system is influenced by polymorphism. For example, a miscible phase is formed in a and p polymorphs, but it transforms into a eutectic phase in p, as revealed in the SSS-PPP mixture. Then, the polymorphic occurrence is largely affected by cooling rate and temperature fluctuation, and it is therefore necessary to observe the polymorphic properties of the natural fats by varying the rate of coohng or by fluctuating the temperature (so-called tempering). 

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. 

This chapter described polymorphic properties of principal TAGs and natural fats based on recent research work to clarify fundamental aspects of polymorphsim of fats and oils. The authors hope that the basic understanding of the polymorphism of the principal TAGs would be useful to elucidate rather complicated polymorphic properties of natural fats and oils that contain TAGs with very heterogeneous fatty acid compositions. 

While establishing molecular networks for cocrystal design and determining crystal structures is very important, the value of cocrystals of pharmaceutical components lies in the ability to tailor the functionality of materials. In contrast to polymorphs that have the same chemical composition, cocrystals do not. As such, one would expect that with cocrystals one could introduce greater changes in material properties than with polymorphs. Properties that relate to pharmaceutical performance and that can be controlled by cocrystal formation include melting point, solubility, dissolution, chemical stability, hygroscopicity, mechanical properties, and bioavailability. The cocrystals for which pharmaceutical properties have been studied are few and some of these are presented below. Clearly further research in this area is needed. 

Table 1 shows the polymorphic behavior of the three TAG in which the saturated fatty acid at the the in-1 and in-2,3 positions is stearic and the sn-2 acid varied from oleic (SOS), ricinoleic (SRS) to linoleic (SLS). As a reference, a typical feature of polymorphic transformation of SOS from a to 3j forms through y, P and P2 is illustrated in Table 1 (10). As briefly mentioned in die previous section, one of the unique polymorphic properties in SOS is that the chainlength structure converted from DCL (a) to TCL (y, P, P2, and Pj), and the subcell structures of stearic and unsaturated acid leaflets in the TCL polymorphs changed in different manners. This transformation behavior is caused by the steric hindrance of steric and unsaturated acid chains, as well as by the structural stabilization of the aliphatic chains and glycerol groups altogether, as briefly summarized in the following.

The chocolate paste needs tempering before further operations take place. Tempering is required because of the polymorph property of the cocoa butter. Polymorphy is a phenomenon when a given material is able to produce crystal-modifications of different physical properties. Out of four possible modifications only one, the P-crystal modification is stable. Through tempering it is possible to obtain P -crystal modification which is transformed into stable P-modification in the finished product. 

Gosselin PM, Thibert R, Preda M, and McMullen JN. Polymorphic Properties of Micronized Carbamazepine Produced by RESS. Int JPharm 2003 252 225-233. 

C. Gamero, A.K. Chattah, M. Longhi, Improving farosemide polymorphs properties through supramolecular complexes of p-cyclodextrin, J. Pharm. Biomed. Anal. 95 (2014) 139-145. 

It is possible to show that the amorphous form is less stable than any crystalline form over all temperatures by considering the following. FromEqs. (1.19) and (1.20), the relative stability of the amorphous or any polymorph compared to the more stable form, as given by 5/u., depends on the temperature. Polymorph pairs can be classified as either monotropic or enantiotropic. A monotropic pair is one in which one form is more stable at all temperatures up to the melting temperature of the less stable form. An enantiotropic pair is one in which there is a crossover or transition temperature Tx such that for temperatures lower than Tx one form is more stable while above Tx the other form is more stable. An implied requirement for enantiotropic pairs is that neither form melts below the crossover temperature, otherwise, the pair would be monotropic. (Once melted, there is no solid structure, so there can be no amorphous or polymorphic properties.)... 

This review mainly focuses on the structural aspects, such as configurational, conformational, and polymorphic properties, in addition to the interacting forces on many heterocyclic molecules studied in our group using X-ray crystallographic techniques. 

Kawahata, M., Endo, T., Seki, H., Nishikawa, K. and Yamaguchi, K., Polymorphic properties of ionic liquid of l-isopropyl-3-methylimidazolium bromide, Chem. Lett. 38 (12), 1136-1137 (2009). 

SCN, n = 1 X = NH3, n = 2) [152]. McMillin and coworkers recently reported the photophysical properties of a series of platinum] n) terpyridyl complexes with different counter ions [153]. These classes of platinum]n) complexes have also been found to exhibit rich polymorphic properties and have been studied by Gray and coworkers [154]. 

The main objectives of this chapter are to clarify the roles of the hydrophobic emulsifier additives added in the oil phase of O/W emulsions how they modify fat crystallization and where they interact within the emulsion droplets. One may ask why the hydrophobic emulsifiers accelerate the nucleation process. The answer may not be straightforward, because their influences on fat crystallization are controlled by their physical and chemical properties and the nature of the interactions with the fat molecules occurring in the oil phase and at the oil/water interfaces. However, the results we have obtained so far indicate that the addition of hydrophobic emulsifiers in the oil phase has remarkable effects on crystallization. Fat crystals typically form a number of polymorphs, whose crystallization properties are influenced by many factors, such as temperature, rate of crystallization, time evolution for transformation, and impurity effects, as is commonly revealed in various examples [27,28], It is reasonable to expect that these polymorphic properties of fats may interfere with the clarification of the essential properties of the interface heterogeneous nucleation that occurs in O/W emulsions. 

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