Secondary binding

Although the clam structures are of interest as ammonium ion binders, they are by no means the only azacrown compounds of interest in this application. Sutherland and coworkers have examined a number of azacrowns as primary ammonium ion bind-ers - . In addition, Metcalfe and Stoddart have utilized bis-azacrowns to bind secondary ammonium cations. 

Because it is generally assumed that only unbound drug is available for uptake across cell membranes and therefore determines distribution and possibly elimination of a drug, it is likely that changes in drug plasma binding (secondary to alterations in plasma lipoprotein binding) will affect pharmacokinetic parameters such as volume of distribution (VD) and clearance (CL). 

An interaction of heparin with digitoxin has been described and ascribed to altered protein binding, secondary to changes in fatty acid concentrations, but the clinical relevance, for example in patients undergoing hemodialysis, is unclear (207). 

The cap of mRNA binds, secondary structures unwind, and the ribosomal subunit moves along... 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

When nickel hydroxide is oxidized at the nickel electrode in alkaline storage batteries the black trivalent gelatinous nickel hydroxide oxide [12026-04-9], Ni(0H)0, is formed. In nickel battery technology, nickel hydroxide oxide is known as the nickel active mass (see Batteries, secondary cells). Nickel hydroxide nitrate [56171-41-6], Ni(0H)N02, and nickel chloride hydroxide [25965-88-2], NiCl(OH), are frequently mentioned as intermediates for the production of nickel powder in aqueous solution. The binding energies for these compounds have been studied (55). 

In secondary wastewater treatment plants receiving silver thiosulfate complexes, microorganisms convert this complex predominately to silver sulfide and some metallic silver (see Wastes, INDUSTRIAL). These silver species are substantially removed from the treatment plant effluent at the settling step (47,48). Any silver entering municipal secondary treatment plants tends to bind quickly to sulfide ions present in the system and precipitate into the treatment plant sludge (49). Thus, silver discharged to secondary wastewater treatment plants or into natural waters is not present as the free silver ion but rather as a complexed or insoluble species. 

Filtration. Filtration is usually a misnomer for tertiary processes that remove particulate matter. Small particles are removed by adsorption rather than by physical straining. If secondary effluents contain a high concentration of soHds, filter beds clog and binding occurs at the bed surface. 

Simple combinations of a few secondary strucfure elements with a specific geometric arrangement have been found to occur frequently in protein structures. These units have been called either supersecondary structures or motifs. We will use the term "motif" throughout this book. Some of these motifs can be associated with a particular function such as DNA binding others have no specific biological function alone but are part of larger strucfural and functional assemblies. 

Sauer, R.T., et al. Homology among DNA-binding proteins suggests use of a conserved super-secondary structure. Nature 298 447-451, 1982. 

In more recent work, Lockhart and Thompson have formed derivatives of 3 by substituting the secondary nitrogen. Substituents include CO—CH2—CH2—CH2—COOH and CH2CH2CH2 0Et. The latter compound should exhibit quite interesting binding properties for alkali metals, but binding constants for these compounds do not appear to have been determined. 

The way in which molecular chaperones interact with polypeptides during the folding process is not completely understood. What is clear is that chaperones bind effectively to the exposed hydrophobic regions of partially folded structures. These folding intermediates are less compact than the native folded proteins. They contain large amounts of secondary and even some tertiary... 

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