Polymorphs measurement

M. Sheikhzadeh, S. Rohani, M. Taffish, S. Murad. Solubility analysis of buspirone hydrochloride polymorphs Measurements and prediction. Int. J. Pharm. 338 (2007) 55-63. 

Table 12.2 The diffraction planes of cellulose polymorphs measured by WAXS...

The solid is polymorphic, with a cubic structure above 1.4°C. A bond length of 1.816 A has been obtained from EXAFS measurements at 10K, while vapour phase measurements give Os-F of 1.831 A [22],... 

In the identification of different polymorphs in polymers the FTIR technique presents, with respect to the diffraction techniques, the advantage of easier and more rapid measurements. In particular, the high speed of the measurements allows to study the polymorphic behavior under dynamic conditions. As an example let us recall the study of the transition from the a toward the P form of PBT induced by tensile stresses, evaluated by quantitative analysis of the infrared spectra [83],... 

SNP Single nucleotide polymorphism. Refers to the fact that single nucleotide genetic variation in genome sequence exists at discrete loci throughout the chromosomes. Measurement of allelic SNP differences is useful for gene mapping studies. 

This technique provides an easy and convenient method to evaluate the association of small molecules to various polymorphic forms of nucleic acid structures from the measurement of absorbance changes in the absorption maximum of the hgand, where the nucleic acid has no absorbance. Information about overall DNA/RNA base preference and nature of binding can also... 

There are other soUd states which sometimes confuse the measurement and definition of solubiUty. The dmg may crystaUize as a hydrate, i.e. under inclusion of water molecules. If the hydrate form is more stable than the pure form it may be difficult to measure the intrinsic solubility of the drug at all. Often drugs tend to precipitate in an amorphous form, often under the inclusion of impurities. As with metastable polymorphs, such amorphous precipitates may lead to erroneously high solubility measurements. CommerciaUy, drugs are often crystallized in salt form, e.g. as the hydrochloride salt, a cation with a chloride anion. In these co-crystallized salts, a much lower solubility than the intrinsic solubility will typi-... 

Measurements of the dissolution behavior of polymorphic forms of relatively insoluble drugs are a convenient way of measuring thermodynamic parameters which, in turn, provide a rational approach to selection of the more energetic polymorphic forms of these drugs for absorption. Large differences in free energy... 

The importance of temperature-controlled scanning calorimetry for measurements of heat capacity and of scanning transitiometry for simultaneous caloric and pVT analysis has been demonstrated for polymorphic systems [9]. This approach was used to study an enantiotropic system characterized by multiphase (and hindered) transitions, the role of heat capacity as a means to understand homogeneous nucleation, and the creation of (p, T) phase diagrams. The methodology was shown to possess distinct advantages over the more commonly used combination of characterization techniques. 

The photostability of two polymorphs of nicardipine hydrochloride have been studied using a number of techniques [95]. After irradiation, the drug substance decomposes to a pyridine derivative, and the photodegradation of the /1-form exceeded that of the x-form. It was also found that the color of the two different forms differed with the polymorphic state, but that grinding the two forms lessened the difference in their photochemistries. A correlation between the heat of fusion (measured by differential scanning calorimetry) and the photodegradation rate constant was observed. 

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