Acidity terms Links

Proteins are large biomolecules made up of a-amino acid residues linked together by amide, or peptide, bonds. Chains with fewer than 50 amino acids are often called peptides, while the term protein is reserved for larger chains. Twenty amino acids are commonly found in proteins all are a-amino acids, and all except glycine have stereochemistry similar to that of l sugars. In neutral solution, amino acids exist as dipolar zwitterions. 

In peptide chemistry, the term "pseudopeptide" is commonly used to denote a peptide in which some or all of the amino acids are linked together by bonds other than the conventional peptide Linkage (13). Such pseudopeptides have found applications as specific structural... 

Amino acids become linked by reactions that occur between the amine group of one amino acid and the carboxyl group of another. As shown in Figure 22.23, this polymerization produces a molecule of water and, hence, is a condensation reaction. Naturally occurring polypeptides with molecular weights in excess of 10,000 daltons are termed proteins. These biomolecules are ubiquitous in marine organisms and are not specific to particular species. Proteins are important components of enzymes as well as of structural parts and connective tissues. 

Amides are the derivatives of the carboxylic acids. In amides the carboxylic acid is linked with ammonia or an amine. Like esters, the parent carboxylic acid is identified. This is then termed an alkanamide and includes the nitrogen atom. For example, linking ethanoic acid with ammonia gives ethanamide ... 

A new generation of cross-linked hyaluronic acids, termed Hylans, is now available [96]. It would be expected that such aggregated molecules, which consist of several hyaluronic acid chains linked via methoxy bridges to a protein core, should be more resistant to free radical-induced depolymerisation. The results of initial studies to determine the radiolytic yield of chain scission... 

Several years ago we began to express the results of our thermal and photochemical degradation experiments in terms of Equation 4. Figure 1 shows some of the initial data obtained, relating to exposure of test sheets in the Fade-ometer. Just as Daruwalla and Narsian (16) observed, there seems to be a break in the curve. If the first stage indeed represents weak links, about 3 such bonds per 10,000 in the original cellulosic chain (0.03 ) are apparent, a figure similar to the fraction of labile acid-sensitive links determined by Sharpies (21) and labile photochemically sensitive links reported by Daruwalla (16) when radiation at 2540 A was used. 

Glycosaminoglycans are solubilized from stromal or other tissues by extracting the source tissue with dilute acid or alkali. Hyaluronan is electrostatically bound to specific proteins called hyaladherins, which possess a structural domain of -100 amino acids termed a link module. Other glycosaminoglycans are O-linked to serine and threonine residues of polypeptides and these bonds hydrolyze before the rest of the polysaccharide. The protein moiety precipitates when trichloroacetic acid or ammonium sulfate is added to the cooled mixture. The composition of the GAGs (including hyaluronan) was identified by chromatographic separation of the purified polysaccharides, followed by their hydrolysis in boiling 1.0 M HC1 for 2 1 h and identification of the individual monosaccharide components. 

Protein building Amino acids, condensation of amino acids, peptide link, primary structure, D,L optical isomers, primary structure of human insulin Chemical ideas Chemistry explains macroscopic phenomena and structure of matter in terms of the microscopic/ submicro-scopic, symbolic, and process levels. 

Fibers. The principal type of phenoHc fiber is the novoloid fiber (98). The term novoloid designates a content of at least 85 wt % of a cross-linked novolak. Novoloid fibers are sold under the trademark Kynol, and Nippon Kynol and American Kynol are exclusive Hcensees. Novoloid fibers are made by acid-cataly2ed cross-linking of melt-spun novolak resin to form a fuUy cross-linked amorphous network. The fibers are infusible and insoluble, and possess physical and chemical properties that distinguish them from other fibers. AppHcations include a variety of flame- and chemical-resistant textiles and papers as weU as composites, gaskets, and friction materials. In addition, they are precursors for carbon fibers. 

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