Specific Chemical Structure

2 Molecular Structure and Higher Order Structure 2.1 Specific Chemical Structure 

---

The term benzodiazepine refers to a specific chemical structure. Numerous benzodiazepine-receptor ligands exist which have different structures. These include the jS-carbolines (e.g. methyl-6,7-dimethoxy-4-ethyl-jS-carboline 3-carboxylate DMCM), triazolopyridazines (e.g. CL 218872), imidazopyridines (e.g. zolpidem), and pyrazolo-quinolinones (e.g. CGS 8216). In experimental animals these compounds produce... 

Since many essential nutrients (e.g., monosaccharides, amino acids, and vitamins) are water-soluble, they have low oil/water partition coefficients, which would suggest poor absorption from the GIT. However, to ensure adequate uptake of these materials from food, the intestine has developed specialized absorption mechanisms that depend on membrane participation and require the compound to have a specific chemical structure. Since these processes are discussed in Chapter 4, we will not dwell on them here. This carrier transport mechanism is illustrated in Fig. 9C. Absorption by a specialized carrier mechanism (from the rat intestine) has been shown to exist for several agents used in cancer chemotherapy (5-fluorouracil and 5-bromouracil) [37,38], which may be considered false nutrients in that their chemical structures are very similar to essential nutrients for which the intestine has a specialized transport mechanism. It would be instructive to examine some studies concerned with riboflavin and ascorbic acid absorption in humans, as these illustrate how one may treat urine data to explore the mechanism of absorption. If a compound is... 

There are two different oligomer series present in all spectra. The oligomer series can be identified by calculating the masses of the end groups and assigning them to specific chemical structures (Pasch and Schrepp, 2003 Weidner et al., 2004). In the present example, the two species are the propionic amide-acid (R-am-ac) and the propionic amide-propionic amide polyamides (R-am-am-R). The use of MALDI-TOF MS as a structure-sensitive detector allows the resolution to be indirectly enhanced since several species coelute, as shown in Fig. 17.21. The polarity of the... 

Few of us recognize that the fascinating glow of a lightstick at a carnival or fair arises from a complex series of chemical reactions. The chemist s palette—a variety of ingredients with specific chemical structures—produces the rainbow of colors seen in these novelties. 

These drugs are most commonly classified according to their principal pharmacological effect rather than by specific chemical structure (Table 10.4). The exception to this is the tricyclic antidepressants which share a common chemical structure and also common pharmacological effects. The other important type of drug used in the treatment of mood disorders is the mood stabilisers (lithium compounds and some anticonvulsants) which are discussed in the next section of this chapter. Tricyclic antidepressants... 

The widespread use of infrared spectroscopy at that time was probably due to the observation that many chemical groups absorb in a very narrow range of frequency. Furthermore, within this frequency range, the observed frequency may be correlated to specific chemical structures. For example, aldehydes can be differentiated from ketones by the characteristic stretching frequency of the carbonyl group near 1700 cm-1, and the spectral pattern may be likened to a molecular fingerprint. ... 

In the case of polycarbonates, it has been observed that by adding miscible low molecular weight additives, with specific chemical structures, it is possible to increase the yield stress of the polymer, as well as to reduce the local molecular motions that are responsible for the secondary relaxation processes... 

In a way similar to that described for polyethylene fere-phthalate (Sect. 4.2), some antiplasticiser small molecules with a specific chemical structure are able to affect the ft transition and the yield stress of epoxy resins, but they do not have any effect on the y transition. In the case of HMDA networks, an efficient antiplasticiser, EPPHAA, whose chemical structure is shown in Table 8, has been reported [69]. The investigation of such antiplasticised epoxy networks by dynamic mechanical analysis as well as solid-state NMR experiments [70] can lead to a deeper understanding of the molecular processes involved in the ft transition and of their cooperativity. 

Chemical name A drug name that is derived from the specific chemical structure of the compound. Chemical names are not used clinically but are shortened in some way to form the drug s generic name. 

Recently, a common but specific chemical structural pattern has been observed among a large number of biologically, pharmacologically, and clinically active compounds from both the natural and synthetic origin. This structural pattern may lead to the design of novel molecules with pertinent biomedical implications. A preliminary account of this observation has been published [51]. 

The PMN review process has evolved over time within the constraints set by TSCA. An important constraint is that submitters are required to furnish only test data already in their possession (if any) and are not required to conduct a battery of tests as a precondition for approval. This generalization holds true for basic chemical property data as well as toxicity data, and it is the main reason why TSCA has been such a powerful impetus for developing estimation methods for many of the parameters needed in environmental assessment. To illustrate how extreme the situation is, in one study of more than 8,000 PMNs for class 1 chemical substances (i.e., those for which a specific chemical structure can be drawn) that were received from 1979 through 1990,Lynch et al. (1991) found only 300 that contained any of the property data noted earlier as needed for environmental assessment. The U.S. is unique among industrialized nations in requiring its assessors to work in the virtual absence of test data. 

Carrier proteins are highly selective, transporting solutes with specific chemical structures. As they are normally involved in the transport of many naturally occurring compounds they will often transport drugs with structures related to these natural products. This type of structural relationship can be use in the approach to the design of new drugs. 

Despite the quantitative victory of molecular orbital (MO) theory, much of our qualitative understanding of electronic structure is still couched in terms of local bonds and lone pairs, that are key conceptual elements of the valence bond (VB) picture. VB theory is essentially the quantum chemical formulation of the Lewis concept of the chemical bond [1,2]. Thus, a chemical bond involves spin-pairing of electrons which occupy valence atomic orbitals or hybrids of adjacent atoms that are bonded in the Lewis structure. In this manner, each term of a VB wave function corresponds to a specific chemical structure, and the isomorphism of the theoretical elements with the chemical elements creates an intimate relationship between the abstract theory and the nature of the... 

Fluorochromes can be attached to antibodies which will then bind to specific chemical structures on or inside cells. Many other chemical and physical properties of fluorochromes determine when and where these dyes are useful in various biological assays. For example, some of the fluorochromes that bind to DNA, such as Hoechst 33342, can get into living cells, but most DNA-binding fluorochromes cannot get past the cell membrane. Those fluorescent dyes that cannot get past an intact cell membrane, such as propidium iodide (PI), are often used to distinguish live from dead and dying cells. 

NMR spectroscopy is ideally suited for characterizing the silicate and aluminosilicate species present in the media from which zeolites are formed. The nuclei observable include 29si, 27 Al, and all of the alkali metal cations. The largest amount of information has come from 29gi spectra ri-31. This nucleus has a spin of 1/2, no quadrupole moment, and a chemical shift range of about 60 ppm. As a consequence, it is possible to identify silicon atoms in specific chemical structures. 27 Al, on the other hand, is a spin 3/2 nucleus and has a sizeable quadrupole moment. This results in broad lines and limits the amount of information that can be extracted from 27Al spectra. 

Another approach to predict toxicity is basing on structure-activity-relationship (SAR), which means the qualitative relationship between a specific chemical structure and their biological/toxicological activity, e.g. the expert system DEREK is based on SAR prediction. In SAR the occurrence of specific substructures in a molecule are correlated to be responsible and necessary for a biological/toxicological activity. 

The inhibition must depend upon the specific chemical structure of the antibiotic molecule in precisely the same manner as does the growth-inhibitory effect. 

Because of the unique growth mechanism of material formation, the monomer for plasma polymerization (luminous chemical vapor deposition, LCVD) does not require specific chemical structure. The monomer for the free radical chain growth polymerization, e.g., vinyl polymerization, requires an olefinic double bond or a triple bond. For instance, styrene is a monomer but ethylbenzene is not. In LCVD, both styrene and ethylbenzene polymerize, and their deposition rates are by and large the same. Table 7.1 shows the comparison of deposition rate of vinyl compounds and corresponding saturated vinyl compounds. 

It is important to reiterate here that chemical structure of a species that deposits on a substrate depends on the kinetic pathlength described in Chapter 5, which is greatly influenced by the energy input to the luminous gas phase and the temperature of the substrate as shown in Figure 5.6. In other words, a monomer with a certain structure does not yield a deposition with a specific chemical structure... 

Although no specific chemical structure can be assigned to humic substances, several models were proposed, such as the one shown below for a humic acid [3] ... 

Step 4. Given s, i, and c of a specific chemical structure, a set of operations B establishes the set of potential instances of chemical-behavior (or cb) for the specific chemical structure ... 

With the exception of glycine, all amino acids are asymmetrical, having a hydrogen atom, a carboxyl group, an amino group, and a distinctive R group of a specific chemical structure. 

---