Polymorphic crystal structure

The solid-state properties like crystallinity, polymorphism (crystal structure), shape (morphology), and particle size of drugs are important in the stability, dissolution, and processibility of drugs. Some commonly used methods in solid-state studies include microscopy, hot stage microscopy with polarized light, x-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared FTIR/Raman, and solid-state NMR. 

Definitions always imply that limitations are imposed on the subject matter. This is very much true of polymorphism, which spans all areas of chemistry and some of mineralogy. In the case of molecule-based polymorphs, the safest approach is probably to consider polymorphic crystal structures as those leading to identical liquid (whether melt or solution) or vapour states. The definition becomes less clear cut in the cases of solvate species and of amorphous materials. Table 1 provides a basic glossary of terms that will be used throughout this chapter. 

Naphthazarin [13] is known to afford polymorphic crystal structures (Cradrick and Hall, 1971). Among them, in the polymorphic form C, both the C=0 and... 

Tautomerization of porphyrins in crystals exhibits diverse patterns of behaviour. There are polymorphic crystal structures of tetraphenylporphyrin (TPP) [19] the tetragonal and the triclinic forms (Silvers and Tlilinsky, 1967 Codding and Tulinsky, 1972 Tblinsky, 1973). In the tetragonal form. X-ray... 

A total of 163 clusters were obtained, where a cluster is a group of polymorphic crystal structures of the same compound. Of the 163 clusters, 147 contained two structures, 13 had three, and three had four structures. The authors note that these numbers are first evidence of the high frequency of polymorphism in organic crystals , although the number of clusters is a relatively small percentage of the entries in the database. The number of these clusters is probably more a measure of certain authors interest in the particular polymorphic system in question. A more realistic measure (although certainly not precise because of the caveats mentioned above) of the frequency of polymorphism in these compounds wouid be the fraction of compounds in the database known to be polymorphic, whether multiple structures have been done or not. 

The important point is that differences in external crystal shape, habit, or crystal morphology may not necessarily indicate a change in the polymorphic form or polymorphic crystal structure. An example of this distinction is given in Eig. 2.13. 

At the empirical end of the spectrum of methods employed for the theoret-ical/computational generation of possible polymorphic crystal structures is the approach taken by Gavezzotti (1991, 1994a, 1996, 1997) and co-workers (1995,... 

Oyumi, Y, Brill, T. B. and Rheingold, A. L. (1986a). Thermal decomposition of energetic materials. 9. Polymorphism, crystal structures, and thermal decomposition of polynitroazabicyclo [3.3.1]nonanes. J. Phys. Chem., 90,2526-33. [286]... 

Figure 7.4 Hydrogen bonding patterns In the polymorphic crystal structures of Iso-nlcotl-namide 6 (a) form 3A and (b) form 3B. Note that form 3A contains synthon II and form 3B contains synthon I...

The development of the new crystal structures was aecompanied by the appearance of new HS melting peaks in the DSC traces. For the HDO polymer, the new peak for the contracted form appeared at a higher temperature than that for the original extended form for the BDO and PDO polymers the new peaks for the extended forms appeared at lower temperatures than those for the contraeted forms. Only a single peak was seen for the polymer extended with EG, for which only one crystal structure was detected for the HS. These results indicated that the development of polymorphic crystal structures have to be considered in the interpretation of the multiple melting phenomena seen for the hard domains in PUs. 

We report here the macrocyclic conformation of the complexed and the uncomplexed host molecules, hostrguest interactions, the molecular columns formed by stacking of the macrocycles and the guest dependent polymorphism (crystal structure). 

Ice is considered by earth scientists, especially glaciologists, as a particular geological material (i.e., rock) which, in the form of glaciers and ice shields has important consequences for the morphology of Earth s surface. Therefore, its physical properties are briefly described here. Ice exhibits twelve different polymorphic crystal structures plus two amorphous states. Usually, at atmospheric pressure and low pressures, it exists in two polymorphic forms. Phase Ih denotes ordinary hexagonal ice obtained by direct freezing of pure water, while phase Ic denotes cubic ice obtained by crystallization of water vapor at temperatures below -130°C. 

Polymorphism is a characteristic of the solid state and the concept is immensely important in the pharmaceutical industry. Properties such as stability, solubility, bioavailability, manufacturability, tableting, formulation, and even toxicity are a function of the polymorph crystal structure. 

Levin, I. and Brandon, D. (1998) Metastable alumina polymorphs crystal structures and transition sequences. J. Am. Ceram. Soc., 81 (8), 1995-2012. 

Oyumi, Y., Brill, T.B. and Rheingold, A.L. (1986) Thermal Decomposition of Energetic Materials 9. Polymorphism, Crystal Structures and the Thermal Decomposition of Polynitroazabicyclo [3.3.1Jnonanes Journal of Physical Chemistry 90, 2526-2533. 

The enthalpy difference between two polymorphic crystal structures a and f) is ... 

Table 14.1 Problems encountered in the analysis of polymorphic crystal structures in the Cambridge Database. See text for discussion. Cell parameters in A and degrees...

Gan Z, Kuwabara K, Abe H, Iwata T, Doi Y. The role of polymorphic crystal structure and morphology in enzymatic degradation of melt-crystallized poly (butylene adipate) films. Polym Degrad Stab 2005 87 191-199. 

D. Adsorption on Fats and Polymorphism-Crystal Structure Modification... 

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