Polysaccharides partially acetylated

Note. The name ending in -an refers to the unsubstituted polysaccharide. Thus xylan occurs in nature in unacetylated and partially acetylated forms. Xylan designates the unacetylated material, and xylan acetate an acetylated derivative. 

Starch is an abundant, inexpensive polysaccharide that is readily available from staple crops such as com or maize and is thus is mostly important as food. Industrially, starch is also widely used in papermaking, the production of adhesives or as additives in plastics. For a number of these applications, it is desirable to chemically modify the starch to increase its hydrophobicity. Starch modification can thus prevent retrodegradation improve gel texture, clarity and sheen improve film formation and stabilize emulsions [108], This may, for example, be achieved by partial acetylation, alkyl siliconation or esterification however, these methods typically require environmentally unfriendly stoichiometric reagents and produce waste. Catalytic modification, such as the palladium-catalyzed telomerization (Scheme 18), of starch may provide a green atom-efficient way for creating chemically modified starches. The physicochemical properties of thus modified starches are discussed by Bouquillon et al. [22]. 

The pectic substances are polysaccharides composed principally of a-1,4 linked galacturonic acid or its methyl ester. The term pectin refers to material with a significant amount of esterification in contrast to unesterified polymers called pectic or polygalacturonic acids (Figure 1). The esterification degree of a particular pectin depends upon its source and extraction method. Some pectic substances are partially acetylated at the C2 and C3 positions of galacturonide residues. 

Chem. Soc. 1953, 2332. Structure is a partially acetylated polysaccharide containing about 8% acetyl groups and about 37% uronic acid residues. Reviews F. Smith, R. Montgomery, The Chemistry of Plant Gums and Mucilages (Reinhold, New York, 1959)1 Goldstein, Alter, in Industrial Gums. R. L. Whistler, Ed. (Academic Press, New York, 2nd ed., 1973) pp 273-287. 

Chitin, the second most abundant natural polysaccharide, is widely distributed in nature as the principal component of exoskeletons of crustaceans and insects as well as of cell walls of some bacteria and fungi. Like cellulose, it is a glucose-based unbranched polysaccharide. Partial deacetylation of chitin results in the production of chitosan, which is a polysaccharide comprising copolymers of glucosamine and N-acetyl glucosamine. It is also naturally present in some microorganisms and fungi. 

Pectin is a complex class of plant cell wall polysaccharides, composed of galacturonans and rhamnogalacturonans. Pectin has a backbone of P-(l-4)-D-galacturonic acid with a-(l-2)-L-rhamnose units interspersed (Figure 2.12). The galacturonic acid units are partially acetylated and methylated, and the L-rhamnose units contain side chains containing arabinose and/or galactose [82]. 

Four partially acetylated D-gluco-D-mannans have been isolated from the leaves of Aloe vera The polysaccharides differed in the ratio of D-glucose to D-mannose as well as in their acetyl content. The results of methylation and periodate-ion oxidation analyses sTiowed that the polymers were all linear with only (1 -> 4) linkages present. 

Gum Karaya is a complex, partially acetylated polysaccharide with a branched structure obtained as a calcium and magnesium salt. 

Partially acetylated homopolymer of Caryophyllose, C-31. O-Specific polysaccharide from the lipopolysaccharide fraction of Pseudomonas caryophylli (Burkholderia caryophylli). 

A partially acetylated polysaccharide containing D-galactouronic acid, D-galactose and L-rhamnose units. The dried exudate of the tree Sterculia mens. Emulsifier, thickener, flavouring and gelling agent in food manuf... 

In a search for new vaccine antigens, the partially acetylated form of the p-(1 6)-poly-D-glucosamine polysaccharide 39 was found to be crucial for tbe virulence of bacterial biofilms produced by coagulase-negative strains. Protective antibodies to 39 are elicited when a deacetylated glycoform (<30% acetyl) is used in conjugate vaccines, whereas highly acetylated 39 does not induce such antibodies (Scheme 13). ... 

Chitosan (CS) is a partially acetylated glucosamine obtained by deacetylation of chitin, one of the most abundant natural polymers. As a polysaccharide of natural origin, chitosan has many useful features such as nontoxicity, biocompatibility, biodegradability, good mechanical strength and antimicrobial properties. Blends of chitosan (CS) and NR obtained by solvent casting improved the thermal resistance of chitosan. Johns and Rao have also developed chitosan and NR blends vulcanized with dicumyl peroxide (DCP) and... 

In the past SO years wood chemists have learned much about the composition and physical properties of hardwood xylans. Partially acetylated glucuronoxylans are model native hardwood xylans. They exhibit thermoplasticity, film forming properties, crystallization potential and are oriented in the secondary cell wall. Their crystal structure has been determined and the hydration of this crystalline polysaccharide has been defined. The structural regularity of these abundant polysaccharides can be interpreted using the principle of optical superposition. 

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