Structure nonspecific

The testing of pure optical isomers can give much insight into the nature of a receptor. An example concerns the anaesthetic gases. It is widely believed that anaesthetic gases exert their action by a structurally nonspecific perturbation of the fluid character of nerve membranes. This view... 

Finally the minimum observed for the AG°t function of n-Bu4NBr in both chemical systems may be interpreted as follows the variation of AG°t(+) and AG°t(-) with solvent composition are generally not linear, so the minimum can be looked upon as the consequence of the opposite behavior of anion and cation towards the solvent molecules. However this interpretation does not take into account the fact that at low organic solvent mole fraction one has AH°t < T AS°t. This observation means that a structural (nonspecific) effect predominates in the water-rich region. This effect might be related to the cavity effect as can be evaluated from Pierrotti s scaled particle theory because the large size of the... 

We suggest therefore that for a minimum to occur in the standard free energy of transfer function of a solute in aqueous binaries we need a structural (nonspecific) effect (related here to the hydrophobic character of the cation) in the water-rich region and superposed to it, classical solute-solvent interactions with predominant water-solute interactions. 

In general we may consider pharmacological action to be of two types. One type is thought to be caused solely by the physicochemical properties of the compound without discernible relationship to chemical structure. These structurally nonspecific drugs are usually administered in relatively large doses. It is presumed that such agents form a... 

The action of certain agents whose mechanism of action does not appear related to their chemical structure (structurally nonspecific drugs) may, in some cases, be due to their accumulation in important cellular locations, leading to disorganization either internally, such as in metabolic processes, or externally, by membrane disruption. 

In general, substances depressant to our CNS tend to be structurally nonspecific, relatively inert organic compounds.4 Their CNS activity appears to depend primarily on physical properties that are not related in any obvious way to their chemical geometry. An examination of Table 12-4 makes this apparent. 

Serine proteinases such as chymotrypsin and subtilisin catalyze the cleavage of peptide bonds. Four features essential for catalysis are present in the three-dimensional structures of all serine proteinases a catalytic triad, an oxyanion binding site, a substrate specificity pocket, and a nonspecific binding site for polypeptide substrates. These four features, in a very similar arrangement, are present in both chymotrypsin and subtilisin even though they are achieved in the two enzymes in completely different ways by quite different three-dimensional structures. Chymotrypsin is built up from two p-barrel domains, whereas the subtilisin structure is of the a/p type. These two enzymes provide an example of convergent evolution where completely different loop regions, attached to different framework structures, form similar active sites. 

The great variety of structures that have by now been shown to exhibit estrogenic activity leads to the suspicion that the estrogen receptor may be unusually nonspecific compared to receptors for other steroid hormones. 

The ligand used for determination of nonspecific binding has a different molecular structure from the tracer ligand. 

The consideration made above allows us to predict good chromatographic properties of the bonded phases composed of the adsorbed macromolecules. On the one hand, steric repulsion of the macromolecular solute by the loops and tails of the modifying polymer ensures the suppressed nonspecific adsorptivity of a carrier. On the other hand, the extended structure of the bonded phase may improve the adaptivity of the grafted functions and facilitate thereby the complex formation between the adsorbent and solute. The examples listed below illustrate the applicability of the composite sorbents to the different modes of liquid chromatography of biopolymers. 

Guidelli and co-workers336-338 measured the potential of zero charge by chronocoulometry. They found that the pzc was independent of the electrolyte concentration in both NaC104 and Na2S04. However, Ea=0 in the presence of sulfates was ca. 40 mV more negative. These authors have explained this apparent discrepancy in terms of the perturbation of the solvent structure at the interface by the ions at the electrode surface, which are, however, nonspecifically adsorbed. 

Many pesticides are not as novel as they may seem. Some, such as the pyre-throid and neonicotinoid insecticides, are modeled on natural insecticides. Synthetic pyrethroids are related to the natural pyrethrins (see Chapter 12), whereas the neo-nicotinoids share structural features with nicotine. In both cases, the synthetic compounds have the same mode of action as the natural products they resemble. Also, the synthetic pyrethroids are subject to similar mechanisms of metabolic detoxication as natural pyrethrins (Chapter 12). More widely, many detoxication mechanisms are relatively nonspecific, operating against a wide range of compounds that... 

Disulfide bonds between and within polypeptides stabilize tertiary and quaternary structure. However, disulfide bond formation is nonspecific. Under oxidizing conditions, a given cysteine can form a disulfide bond with the —SH of any accessible cysteinyl residue. By catalyzing disulfide exchange, the rupture of an S— bond and its reformation with a different partner cysteine, protein disulfide isomerase facilitates the formation of disulfide bonds that stabilize their native conformation. 

Finally, it should be remarked that, as long as the interfacial region is extended sufficiently to include all structural and electronic deviations from the reservoirs, (5.18) and (5.19) are valid for any type of connection between a metallic electrode and an electrolyte. They also include the cases of nonspecific and specific adsorption on the electrode. 

Further STM and SXS smdies [Wu et al., 1998] concerning this phenomenon indicated that the presence of specifically and nonspecifically adsorbing anions as well as organic molecules (e.g., pyridine, bipyridine, and uracil) may also lift the reconstructed surface by exhibiting a structural transition, and it has been extensively studied and reviewed in [Kolb, 1996]. 

Spectral data based on at least three structurally specific ions fhaf completely define the parent molecule (may or may not include the molecular ion), or more if nonspecific ions are included. Use of water loss and isotopic ions is discouraged. 

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