Polymorphism occurrence

Figure 18. Diagram of the polymorphic occurrence for the LLUPPP mixtures.

Figure 19 shows the phase behavior of the polymorphic occurrence for the LLL/ MMM mixtures obtained from DSC and SR X-ray scattering experiments. This diagram indicates the following three points ... 

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). 

Polymorphic Occurrence of Saturated-Elaidic Mixed-Acid Triacylgiycerols (TAG) ... 

Polymorphism describes a naturally occurring variation in the DNA sequence among individuals which leads to the occurrence of two or more allelic forms of a gene. 

The following section deals with the crystallization and interconversion of polymorphic forms of polymers, presenting some thermodynamic and kinetic considerations together with a description of some experimental conditions for the occurrence of solid-solid phase transitions. 

Some relevant effects of the polymorphism on the properties of polymeric materials are shown in the final section. In particular, it is shown that, while the occurrence of transitions between polymorphic forms can be detrimental for some systems, a precise knowledge of the polymorphic behavior and of the physical properties of the single forms can be used advantageously to improve the in use properties as well as the processing conditions of some polymeric materials,... 

In the following, various Fe(III) compounds of R-substituted salicylaldehyde thiosemicarbazones will be discussed according to the criteria mentioned above, although it should be pointed out that a comparison of these materials may be rendered less meaningful due to the possible occurrence of different polymorphs. Moreover, upon variation of one substitution parameter, several other structural features may also be changed simultaneously. For instance, a change in outer-sphere cation or the introduction of a substituent at the salicylaldehyde moiety is frequently associated with increased hydration of the Fe(III) material. 

Investigations for the occurrence of polymorphism have been undertaken by ir spectroscopy, differential scanning calorimetry and x-ray powder diffraction (Guinier-de Wolff). No polymorphism has been observed so far. An amorphous form may be prepared artificially by rapid evaporation of a methanolic solution of the drug substance. 

No detailed studies on the crystal structure of methimazole is reported in the literature. Methimazole can be microscopically identified using Kofler s method, the occurrence of polymorphous modification is indicated in methimazole. 

First, drug-induced lengthening of the QT interval has been associated with the occurrence of ventricular tachyarrhythmias, namely TdP, a polymorphous ventricular arrhythmia that may cause syncope and degenerate into ventricular fibrillation and sudden death although the incidence of TdP is a rare event (usually, less than 1 in 100 000) [32], even a low risk is not justified for drugs with uncertain benefits or drugs providing only symptomatic improvement of a mild disease. 

The rate of nucleation is dependent on the degree of supersaturation as described in section 2.4.1, and because this will always be larger for Form 1 it may be incorrectly assumed that Form I will always precipitate first. The true situation is somewhat more complicated because the critical size, activation energy and nucleation rate also depend on the solid state that is being formed [6]. It is quite feasible and a regular occurrence, that a less stable polymorph will have a higher rate of nucleation than a more stable form, as illustrated in figure 6. 

Polymorphism The occurrence together of two or more distinct forms in the same population. [NIH]... 

Crystalline or amorphous forms of fhe drug substance can affect product efficacy. Polymorphic forms usually exhibif different physical-chemical properties, including melting point and solubility. The occurrence of polymorphic forms with drugs is relatively... 

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