Crystalline form factors affecting

The factors described earlier that affect the solubility of a lead compound when choosing a particular salt form—a polymorphic form—a specific crystalline form directly affects the most critical parameter that determines the drug activity, which is the dissolution rate in the biological milieu. The first step in the commencement of dissolution is the wettability of solid particles—there is a direct correlation between wettability and bioavailability. As the milieu of drug administration sites is mostly aqueous in nature, low wettability makes the particles less hygroscopic. 

The solubility of the drug is affected by several physiological and physicochemical factors [26], Drug properties are defined not only by the chemical structure but also by the solid material, and a drug can potentially exist in many different solid state forms which may differ in solubility. Amorphous materials tend to show much higher aqueous solubility than crystalline forms of the same compound and different crystal modifications of the same compound may also have different solubility (e.g., [25]). 

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crys-... 

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crystalline structure, such as pressure, intensity of the electric field, controlled melt crystallization, precipitation from different solvents, or seeding crystallization (e.g., surfactants). The alpha and beta forms are most common in practical situations. Generally, the alpha form is generated in normal melt processing the beta form develops under mechanical deformation of melt-fabricated specimens. The gamma form arises under special circumstances, and the delta form is obtained by distortion of... 

However, the equilibrium solubility values are very difficult to obtain, because they are affected by many factors such as crystalline form of a substance, particle size distribution, temperature, composition of aqueous phase. 

Polymorphism is the ability of a molecule to take more than one crystalline form depending on its arrangement within the crystal lattice. In lipids, differences in hydrocarbon chain packing and variations in the angle of tilt of the hydrocarbon chain packing differentiate polymorphic forms. The crystallization behavior of TAG, including crystallization rate, crystal size, morphology, and total crystallinity, are affected by polymorphism. The molecular structure of the TAG and several external factors like temperature, pressure, rate of crystalhzation, impurities, and shear rate influence polymorphism (5). 

The kinetics of crystallization has been simulated by many models, including the Avrami model (House 2007). The rate of conversion from amorphous to crystalline states can be measured by using thermal analysis (differential scanning calorimetry, DSC) and/or X-ray diffraction. The rate of conversion from amorphous to crystalline form depends on a number of factors. The process occurs in two steps, nucleation and growth (Mullin 2001), which are affected by various factors and occur at different rates. Specifically, for crystallization to occur, a seed or nucleus must form, on which subsequent growth will occur. Thus, the rate of nucleation is of primary interest. By analogy with Arrhenius-type processes, the nucleation rate can be written as... 

This article reviews physical and physico - chemical studies on linear ma1to - dextrins. The various crystalline forms of the dextrins are described and the melting and glass transition behavior discussed. Solution conformations and the viscous behavior of dilute and concentrated aqueous solutions are considered. In addition factors affecting the Interaction of small solutes with the dextrins In aqueous solution are discussed and compared with the known behavior of cyclodextrins. 

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