Polysaccharides heterogeneity

Low-molecular-weight fragments produced by chemical depolymerization and extraction of standard heparin consist of heterogeneous polysaccharide chains of molecular weight 2,000 to 9,000. The LMWH molecules contain the pentasaccharide sequence necessary for binding to antithrombin III but not the 18-saccharide sequence needed for binding to thrombin. Compared to standard heparin, LMWH has a 2- to 4-fold greater antifactor Xa activity than antithrombin activity. 

Chemoenzymatic synthesis of HS was first employed in the synthesis of structurally heterogeneous polysaccharides. In this method, a bacterial capsular polysaccharide isolated from the E. coli strain K5 is subjected to a series of enzymatic modifications, including N-sulfonation, epimerization, and 2-0-, 6-0-, and 3-O-sulfonations [26-28],... 

Jones and coworkers, in studies on mannose-containing polysaccharides, have isolated, from seeds of Iris ochroleuca and Iris sibirica, heterogeneous polysaccharides yielding on hydrolysis D-glucose and D-mannose in approximately equal amounts, as well as D-galactose (m. 3 %). These workers consider the possibility that the polysaccharides are mixtures of glucomannan with galactomannan, but, because of the similarity (in composition) between the two iris polysaccharides, tend to the view that they are... 

These extensive studies by O Dwyer have shown that part of the n-xylose-yielding materials of wood exists in heterogeneous polysaccharides of considerable complexity. Furthermore, the polysaccharides in heartwood and in sapwood differ in composition, although the fundamental structural building unit may be the same in all cases. 

Starch suspensions and other heterogeneous polysaccharide and protein systems... 

Heparin (see here) is a heterogeneous polysaccharide polymer of D-iduronate-2-sulfate linked oi l->4 to N-sulfo-D-glucosamine-6-sulfate. This repeating unit of the polymer is shown at the right. 

Xylan is a major structural heterogeneous polysaccharide found in plant biomass and represents the second most abundant polysaccharide in the biosphere, after cellulose. The abundance of xylan and its integral association within the plant cell wall makes it a key... 

Gum tragacanth is a complex mixture of highly branched, heterogeneous polysaccharides. It occurs naturally as slightly acidic calcium, magnesium, or potassium salt. 

Comparing with the glucan-type of carbohydrates, the heterogeneous polysaccharides have a different fingerprint region (1700-900 cm" ), characterized by three specific subregions, located between 900-100, 1300-1400, and around 1600 cm". ... 

Hemicelluloses are heterogeneous polysaccharides, which are located between the lignin and cellulose fibers. Depending on wood species, hemicelluloses constitute about 20-30% of the naturally occurring lignocellulosic plant biomass [19]. Lignocellulosic biomass represents a renewable, widespread, and... 

From the organochemical point of view, carbohydrates/polysaccharides are more or less substituted polyhydroxy aldehydes (e.g., glucose—>glucans) or polyhydroxy ketons (e.g., fructose-n fructans). From the physicochemical point of view, an enormous heterogeneity also exists in... 

Heparin is now recognized to be a mixture of polysaccharide chains of variable length and degree of heterogeneity. However, all of the heparin... 

From the foregoing discussion, it is apparent that heparin may be subdivided into an unlimited number of fractions when different separation approaches are applied to each fraction obtained by another procedure. More than a hundred fractions have been obtained by sequential use of affinity chromatography on antithrombin, precipitation with barium, and isoelectrofocusing.214 Although these fractions can scarcely be referred to as species, such an extensive fractionation stresses the concept of the heterogeneity of heparin, and the influence of minor differences in chemical constituents, or chain length, or both, on the physicochemical (and, conceivably, biological) properties of this polysaccharide. 

Most of the supports so far studied are conventional in the field of catalysis. Some new kinds of support have emerged including mesostructured materials,193 dendrimers, organic-inorganic hybrids, and natural polymers such as polysaccharides or polyaminoacids. Nevertheless, at the moment, supported catalysts still suffer from relatively poor stability when compared to classical heterogeneous catalysts, and from limited activity when compared to homogeneous catalysts. The driving force for this research is thus to make up some of these deficits. 

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