Polymorphism/polymorphs

Infiltrate Polymorphous Polymorphous Polymorphous Monomorphic with fibrosis/polymorphous... 

Polymerisierbarkeit, /. polymerizability, polymerisieren, v.t. i. polymerize, Polymerisierung, /. polymerization. Polymolybdansaure, /. polymolybdic acid, polymorph, polymorphisch, a. polymorphous, polymorphic. 

Any two samples of a particular mineral, whatever their source or place of origin, have the same basic composition and characteristic crystal structure moreover, no two different minerals have identical chemical composition and crystal structure (see Textboxes 8 and 21). Quartz, for example, is a common and abundant mineral composed of silicon dioxide, a compound that occurs naturally not only as quartz but also in other crystal structures, known as polymorphs (polymorphs are minerals that have the same chemical composition but different crystal structure), some of which, listed in Table 23, have been used for a variety of purposes. The crystal structure, which is essential for the characterization of solid materials, is just one of a wide range of physical properties, that is, properties not involving chemical differences, which provide convenient criteria for characterizing and identifying solids. 

Genes/polymorphisms polymorphism Clinical effects Reference... 

A dione 74 also undergoes ODPM rearrangement under direct irradiation to give compound 75 in 94% yield (Scheme 4.30) [44]. The product 75 was crystallized from ethyl acetate/hexane at room temperature to lead to two polymorphs. Polymorphism is recognized as being a vital branch of solid-state supramolecular chemistry. 

The second polymorph, polymorph B, can be considered as homeotypic with CaCuP (AlB2-type) structure. The structure consists of undulating hexagonal sheets. Five such nets interpenetrate to file the void space in a single net. see Venkataraman, D. Lee, S. Moore, J. S. Zhang, P. Hirsch, K. A. Gardner, G. B. Covey, A. C. Prentice, C. L. Submitted for publication to Chemistry of Materials. 

Polymorphism refers to the arrangement of a drug in various crystal forms (polymorphs). Polymorphs have the same chemical structure but different physical properties, such as solubility, density, hardness, and compression characteristics. Some polymorphic crystals may have much lower aqueous solubility than the amorphous forms, causing a product to be incompletely absorbed. Chloramphenicol, for example, has several crystal forms, and when given orally as a suspension, the drug concentration in the body depended on the percentage of p-polymorph in the suspension. The p-form is more soluble and better absorbed (Fig. 7). In general, the crystal form that has the lowest... 

Polymorphism. Polymorphs are substances with essentially identical compositions, but with different crystal structures. 

Internal structure (unit cell) can be different in crystals that are chemically identical. This is called polymorphism. Polymorphs can vary substantially in physical and chemical properties such as bioavailability and solubility. They can be identified by analytical techniques such as X-ray diffraction, infrared, Raman spectro, and microscopic techniques. For the same internal structure, very small amounts of foreign substances will often completely change the crystal habit. The selective adsorption of dyes by different faces of a crystal or the change from an alkaline to an acidic environment will often produce pronounced changes in the crystal habit. The presence of other soluble anions and cations often has a similar influence. In the crystallization of ammonium sulfate, the reduction in soluble iron to below 50 ppm of ferric ion is sufficient to cause significant change in the habit of an ammonium sulfate costal from a long, narrow form to a relatively chunky and compact form. Additional information is available in the patent literature and Table 18-4 lists some of the better-known additives and their influences. 

Genetic polymorphism polymorphism due to two or more alleles in a gene leading to more than one phenotype with respect to biological target reactivity to drugs. 

Polymorphism, as applied to the sohd state, can be defined as the ability of the same chemical substance to exist in different crystalline structures (Findlay et al. 1951) (regular, repeating arrangement of atoms or molecules in the solid state). The different structures are generally referred to as polymorphs, polymorphic modifications, crystal forms, or forms (Verma and Krishna 1966). Strict adherence to this definition of polymorphism excludes solvates and hydrates (specific water solvate) as polymorphs because they correspond to different chemical substances. Solvates and hydrates are sometimes referred to as pseudopolymorphs. Molecule A is a different chemical substance than molecule A coordinated with a solvent. 

A large proportion of drug substances, whether neutral molecules, free adds, free bases or salts, are capable of exhibiting polymorphism or pseudopolymorphism (hydrate or solvate formation). It has been reported that 70% of barbiturates, 60% of sulfonamides and 23% of steroids exhibit polymorphism." Polymorphism often influences a range of physicochemical properties such as solubility, dissolution rate, stability and powder properties as well as bioavailability. Usually, it is possible to determine the most stable polymorph and discover recrystallization solvents that uniquely produce this form and improve the physicochemical and physicome-chanical properties and chemical stability of the drug. 

Genetic variations occur as either rare defects or polymorphisms. Polymorphisms are defined as variations occurring at a frequency of... 

Polymorphism. Polymorphic literally means multiform, but the term does not refer to variation in external shape. It indicates that crystals of the same molecules have different unit cells, be it of the same or of a different crystal system. The phenomenon is quite common. There are two types of polymorphism. Enantiotropic polymorphs each are stable within a certain range of temperature and pressure. Consequently, a phase diagram of the various polymorphs can be made. The prime example is ice (Section 15.3.1). If monotropic polymorphs exist, all but one of these are unstable. There is no phase diagram and, given time, only the most stable form will remain. The prime examples are compounds with long paraffinic chains, including most lipids (especially acylglycerols), where three main polymorphs exist (a, (F, and (3). 

Different crystalline forms containing the same molecules or ions are called polymorphs. Polymorphism is of major industrial importance today.With the exception of review articles published by some of us in 1999/ the subject of organometallic polymorphism has never been reviewed. The investigation of crystal polymorphism requires a crystal-engineering approach the formation of different crystal forms implies that different sets of supramolecular interactions are established between the same building blocks. Under this viewpoint, therefore, polymorphs are crystal isomers. ... 

Blood group GTs Blood group polymorphism Polymorphism in ABO bgl (Aa3T), H Secrtor bgl (Fa2T), Lewis bgl (Fa3/4FT), P bgj (AT)... 

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