Chemical Entity

Apart from fatty acids, straight-chain molecules containing other hydrophilic end groups have been employed in numerous studies. In order to stabilize LB films chemical entities such as tlie alcohol group and tlie metliyl ester group have been introduced, botli of which are less hydrophilic tlian carboxylic acids and are largely unaffected by tlie pH of tlie subphase. 

The electronic wave functions of the different spin-paired systems are not necessarily linearly independent. Writing out the VB wave function shows that one of them may be expressed as a linear combination of the other two. Nevertheless, each of them is obviously a separate chemical entity, that can he clearly distinguished from the other two. [This is readily checked by considering a hypothetical system containing four isotopic H atoms (H, D, T, and U). The anchors will be HD - - TU, HT - - DU, and HU -I- DT],... 

An example of a chiral compound is lactic acid. Two different forms of lactic acid that are mirror images of each other can be defined (Figure 2-69). These two different molecules are called enantiomers. They can be separated, isolated, and characterized experimentally. They are different chemical entities, and some of their properties arc different (c.g., their optical rotation),... 

Mixtures containing up to several thousand distinct chemical entities are often synthesized and tested in mix-and-split combinatorial chemistry. The descriptor representation of a mixture may be approximated as the descriptor average of its individual component molecules, e.g., using atom-pair and topological torsion descriptors. 

Ab-initio calculations are particularly usefiil for the prediction of chemical shifts of unusual species". In this context unusual species" means chemical entities that are not frequently found in the available large databases of chemical shifts, e.g., charged intermediates of reactions, radicals, and structures containing elements other than H, C, O, N, S, P, halogens, and a few common metals. 

Cellulose triacetate is obtained by the esterification of cellulose (qv) with acetic anhydride (see Cellulose esters). Commercial triacetate is not quite the precise chemical entity depicted as (1) because acetylation does not quite reach the maximum 3.0 acetyl groups per glucose unit. Secondary cellulose acetate is obtained by hydrolysis of the triacetate to an average degree of substitution (DS) of 2.4 acetyl groups per glucose unit. There is no satisfactory commercial means to acetylate direcdy to the 2.4 acetyl level and obtain a secondary acetate that has the desired solubiUty needed for fiber preparation. 

Flavoringingredient. Any single chemical entity or natural mixture added to food, dmgs, or other products taken in the mouth, the clearly predominant purpose and effect of which is to provide all or part of the particular flavor of the final product. 

Specialty chemicals, however, differ in that they are used for thek performance properties and usuaHy are not specified chemical entities. Products from different suppHers usuaHy differ somewhat, and free interchangabHity is not always possible. Special chemical systems also exist in the market and these are formulated products that contain both commodity and specialty chemicals. 

Dmg receptors are chemical entities which are typically, but not exclusively, small molecules that interact with cellular components, frequently at the plasma membrane level (1,2). There are many types of receptors heat, light, immune, hormone, ion channel, toxin, and vims are but a few that can excite a cell. The receptor concept can be appHed generally to signal recognition processes where a chemical or physical signal is recognized. This recognition is translated into response (Fig. 3) and the process can be seen as a flow of information. 

In contrast to prescription dmgs, OTC dmgs and cosmetics are not subject to preclearance in the United States. However, the rules covering OTC dmgs preclude introduction of untested dmgs or new combinations. A "new chemical entity" that appears suitable for OTC dmg use requires work-up via the new dmg appHcation (NDA) process. In contrast, the use of ingredients in cosmetics is essentially unrestricted and may include less well known substances. 

Nitrate is one of the facts of life. It is essential for the growth of many plant species, including most of those we eat, but it becomes a problem if it gets into water in which it is not wanted. It is perceived mainly as a chemical fertilizer used by farmers, but much of the nitrate found in soil is produced by the microbes that break down plant residues and other nitrogen-containing residues in the soil. There is no difference between nitrate from fertilizer and that produced by microbes, but, whatever its origin, this rather commonplace chemical entity has now become a major environmental problem and is also treated as a health hazard. 

Not all models are physical or pictorial objects. For example, the Sn2 mechanism is a simple model for a particular class of reactions that successfully explains a lot of chemistry. What all of these things have in common is that they use a set of pre-defined objects and rules to approximate real chemical entities and processes. 

The hydrogen atom has a high ionization energy (1312kJmol ) and in this it resembles the halogens rather than the alkali metals. Removal of the Is electron leaves a bare proton which, having a radius of only about 1.5 x 10 pm, is not a stable chemical entity in the condensed phase. However, when bonded to other species it is well known in solution and in... 

The development of a single enantiomer as a new active substance should be described in the same manner as for any other new chemical entity. Studies should be carried out with the single enantiomer, but if development began with the race-mate then these studies may also be taken into account. Chiral conversion should be considered early on so that enantiospecific bioanalytical methods may be developed. These methods should be described in chemistry and pharmacy part of the dossier. If the opposite enantiomer is formed in vivo, then it should be evaluated in the same way as other metabolites. For endogenous human chiral compounds, enantiospecific analysis may not be necessary. The enantiomeric purity of the active ingredient used in preclinical and clinical studies should be stated. 

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