Structure polysaccharide structural

Structural Polysaccharides Structural (fibrous) components are found in cell walls of plants and are represented by the linear p (1—4)-linked homopolysaccharides (a) cellulose, (b) chitin, (c) xylan, (d) mannan (10.20). Of these, cellulose is by far the most universally abundant and the most important. Starch (10.20e) derivatives are important in food technology (Chapter 12.4). 

Cation (Section 1 2) Positively charged ion Cellobiose (Section 25 14) A disacchande in which two glu cose units are joined by a 3(1 4) linkage Cellobiose is oh tamed by the hydrolysis of cellulose Cellulose (Section 25 15) A polysaccharide in which thou sands of glucose units are joined by 3(1 4) linkages Center of symmetry (Section 7 3) A point in the center of a structure located so that a line drawn from it to any element of the structure when extended an equal distance in the op posite direction encounters an identical element Benzene for example has a center of symmetry Cham reaction (Section 4 17) Reaction mechanism m which a sequence of individual steps repeats itself many times usu ally because a reactive intermediate consumed m one step is regenerated m a subsequent step The halogenation of alkanes is a chain reaction proceeding via free radical intermediates... 

Globular protein (Section 27 20) An approximately spheri cally shaped protein that forms a colloidal dispersion in water Most enzymes are globular proteins Glycogen (Section 25 15) A polysaccharide present in animals that IS denved from glucose Similar in structure to amy lopectin... 

R. Moothouse, in M. Yalpani, ed.. Industrial Polysaccharides Genetic Engineering, Structure Property delations and Applications, Elsevier Science PubHshets BV, Amsterdam, the Netherlands, 1987. 

Table 1. Classification of Selected, Native Polysaccharides by Structure...

Separation of enantiomers by physical or chemical methods requires the use of a chiral material, reagent, or catalyst. Both natural materials, such as polysaccharides and proteins, and solids that have been synthetically modified to incorporate chiral structures have been developed for use in separation of enantiomers by HPLC. The use of a chiral stationary phase makes the interactions between the two enantiomers with the adsorbent nonidentical and thus establishes a different rate of elution through the column. The interactions typically include hydrogen bonding, dipolar interactions, and n-n interactions. These attractive interactions may be disturbed by steric repulsions, and frequently the basis of enantioselectivity is a better steric fit for one of the two enantiomers. ... 

Glycogen (Section 25.15) A polysaccharide present in animals that is derived from glucose. Similar in structure to amy-lopectin. 

The macromolecules of cells are built of units—amino acids in proteins, nucleotides in nucleic acids, and carbohydrates in polysaccharides—that have structural polarity. That is, these molecules are not symmetrical, and so they can be thought of as having a head and a tail. Polymerization of these units to form macromolecules occurs by head-to-tail linear connections. Because of this, the polymer also has a head and a tail, and hence, the macromolecule has a sense or direction to its structure (Figure 1.9). 

What structural features allow biological polymers to be informational macromolecnles Is it possible for polysaccharides to be informational macromolecnles ... 

By far the majority of carbohydrate material in nature occurs in the form of polysaccharides. By our definition, polysaccharides include not only those substances composed only of glycosidically linked sugar residues but also molecules that contain polymeric saccharide structures linked via covalent bonds to amino acids, peptides, proteins, lipids, and other structures. 

FIGURE 7.21 Amylose and amylopectin are the two forms of starch. Note that the linear linkages are o (1 4), but the branches in amylopectin are o (1 6). Branches in polysaccharides can involve any of the hydroxyl groups on the monosaccharide components. Amylopectin is a highly branched structure, with branches occurring every 12 to 30 residues. 

The structural polysaccharides have properties that are dramatically different from those of the storage polysaccharides, even though the compositions of these two classes are similar. The structural polysaccharide cellulose is the most... 

As shown in Figure 9.24, the outer membrane of Gram-negative bacteria is coated with a highly complex lipopolysaccharide, which consists of a lipid group (anchored in the outer membrane) joined to a polysaccharide made up of long chains with many different and characteristic repeating structures... 

Many proteins found in nature are glycoproteins because they contain covalently linked oligo- and polysaccharide groups. The list of known glycoproteins includes structural proteins, enzymes, membrane receptors, transport proteins, and immunoglobulins, among others. In most cases, the precise function of the bound carbohydrate moiety is not understood. 

By clicking the appropriate buttons on the form, the user can combine molecular structure queries of sample, CSP and solvent, using operators AND, OR, NOT with data queries in one search. A query for the search of chiral separations of alpha-aromatic acids on any polysaccharide phases coated on silica gel providing an alpha value superior to 1.2 is shown in Eig. 4-4. 

Polysaccharide-based CSPs incorporate derivatives of cellulose and amylose adsorbed on silica gel. The selectivity of these CSPs depends upon the nature of the substituents introduced during the derivatization process. The secondary structure of the modified polysaccharide is believed to play a role in selectivity, but the chiral recognition mechanisms have not been fully elucidated [55]. 

A number of other polysaccharides, such as glycogen, dextran, chitin, etc., possess interesting structures for chemical modification [103,104]. Dextran has been used as a blood plasma substitute. Although it can be converted to films and fibers, chitin s relatively small resource restricts its commercialization. 

Acetylated polysaccharides form part of the structure of wood, the acetyl radical constituting some 2-5Vo by weight of the dry wood. Hydrolysis to free acetic acid occurs in the presence of moisture at a rate varying from one species to another a wood of lower acetyl content can liberate acetic acid much faster under given conditions than another wood of higher content Small quantities of formic, propionic and butyric acids are also formed but their effects can be neglected in comparison with those of acetic acid. There is a broad, but only a broad, correlation between the corrosivity of a wood and its acidity. The chemistry of acetyl linkage in wood and of its hydrolysis has been examined in some detail. ... 

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