Inhibition ionic interaction

In weakly solvating solvents interionic interactions between organic molecular ions can lead to fixation of the ionic end of the molecule. The Tl values of pertinent and neighboring 13C nuclei become smaller. In contrast, strongly solvating solvents such as water and alcohols inhibit interionic interaction and lead to an enhanced mobility of the ions solvated by ion-dipole interactions 13C spin-lattice relaxation is consequently slower in such solvents. Thus the T, values of n-butylammonium trifluoroacetate increase with the polarity of the solvent, as shown in Table 3.19 [148]. 

In vitro studies have shown that dextran sulfate inhibits HIV binding, replication and syncytium formation, probably because they interfere with the ionic interaction between cell surface components such as CD4 or sulfated polysaccharides and positively charged amino acids concentrated in the V3 region of HIV gpl20 [ 127-129]. Again, low molecular weight derivatives with... 

Collectively, the direct thrombin inhibitors are prototypically represented by hirudin, the antithrombotic molecule found in the saliva of the medicinal leech (Hirudo medicinalis), This protein is a 65 amino acid molecule that forms a highly stable but noncovalent complex with thrombin (7). With two domains, the NH2-terminal core domain and the COOH-terminal tail, the hirudin molecule inhibits the catalytic site and the anion-binding exosite in a two-step process. The first step is an ionic interaction that leads to a rearrangement of the thrombin-hirudin complex to form a tighter bond that is stoi-chiometrically I I and irreversible. The apolar-binding site may also be involved in hirudin binding. This complex and... 

For aqueous SEC, ionic interactions need to be suppressed and the eluent usually modihed by the addition of salt and/or the adjustment of pH. For water-soluble polymers with hydrophobic character, the addition of a weak organic solvent (methanol) is sometimes required to inhibit hydrophobic interactions. A general approach for the separation of the aqueous polymeric samples is shown in Figure 6-8. 

Elevated pressures can induce functional and structural alterations of proteins. The effects of pressure are governed by Le Chatelier s principle. According to this principle, an increase in pressure favours processes which reduce the overall volume of the system, and conversely increases in pressure inhibit processes which increase the volume. The effects of pressure on proteins depend on the relative contribution of the intramolecular forces which determine their stability and functions. Ionic interactions and hydrophobic interactions are disrupted by pressure. On the other hand, stacking interactions between aromatic rings and charge-transfer interactions are reinforced by pressure. Hydrogen bonds are almost insensitive to pressure. Thus, pressure acts on the secondary, tertiary, and quaternary structure of proteins. The extent and the reversibility, or irreversibility, of pressure effects depend on the pressure range, the rate of compression, and the duration of exposure to increased pressures. These effects are also influenced by other environmental parameters, such as the temperature, the pH, the solvent, and the composition of the medium. 

Phosphonates may be viewed as structural analogues of phosphate or carboxylates. They are chosen as inhibitors of enzymes which catalyse reactions of carboxylates or phosphates following the recognition that ionic interactions are an important component in enzymic specificity and thus a major factor in the design of inhibitors. They may be expected to interfere with enzymatic processes involving phosphates due to the substitution of the P—O—C bond by the hydrolytically stable P—C bond. On the other hand, the combination of the electrostatic similarity with the stereochemical difference between the tetrahedral phosphonic groups and the planar carboxy groups makes it likely that phosphonates can inhibit enzymes which catalyse reactions of carboxylic acids. 

B. Clouet-d Orval, T. K. Stage, and O. C. Uhlenbeck, Neomycin inhibition of the hammerhead ribozyme involves ionic interactions, Biochemistry, 34 (1995) 11186-11190. 

Owing to the presenee of a perfluorinated alkyl substituent, surfaee energy decreases, increasing metal hydrophobicity. However, the heterocyclie ring of triazole inhibits this process and keeps molecules from the adsorbed layer on the metal due to covalent and ionic interactions. These processes increase the corrosion resistance of... 

The ability to inhibit wall interaction is demonstrated in Fig. 5. The complete tryptic digest of cytochrome c is analyzed at pH 4.0, with optimization accomplished by modifying the ionic strength of the buffer and separation field strength. A dramatic improvement in the separation is achieved by increasing the ionic strength. From these data, the best separation conditions can easily be identified, and the complex mixture spiked with the isolated peptides to identify them within the mixture. 

The enzymes belonging to a metabolic system may be attached to either side of a given membrane. Sequences spanning a membrane can sequester the products from the initial enzymes to avoid interactions like feedback inhibition (A 4.3) and maintain differences in the microenvironment needed for optimal catalysis, such as pH. Loose binding of enzymes to membranes may be brought about by ionic interactions, which are easily destroyed during purification. 

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