Polysaccharides, constitution

X-Ray diffraction analysis of oriented polysaccharide fibers has had a long history. Marchessault and Sarko discussed this topic in Volume 22 of Advances, and a series of articles by Sundararajan and Marchessault in Volumes 33, 35, 36, and 40 surveyed ongoing developments. The comprehensive account presented here by Chandrasekaran (West Lafayette, Indiana) deals with some 50 polysaccharides, constituting a wide range of structural types, where accurate data and reliable interpretations are available. The regular helical structures of the polysaccharide chains, and associated cations and ordered water molecules, are presented in each instance as stereo drawings and discussed in relation to observed functional properties of the polymers. 

Some of the polysaccharides constituting intermediate stages in the biosynthesis of heparin have been physically isolated.23 Their structure is strikingly similar to those of heparan sulfates,24 thus re-opening the often-raised question as to whether heparan sulfate indeed represents products of incomplete biosynthesis of heparin. A detailed account of the structure and biological properties of heparan sulfate is beyond the scope of this article. However, in view of similarities of structural fea-... 

Some polysaccharides classified by degree of water solubility are given in Table I. The list includes only a few of the known polysaccharides. Those listed have a reasonably high molecular weight, having DP of 100 to several thousand. Highly branched polysaccharides, constituting the majority of polysaccharides, are almost always very soluble in water. 

Polysaccharides constitute an important class of natural macromolecules present in all living organisms, with a wide range of functions, some... 

Microbial polysaccharides constitute a specific class of biopolymers. These biopolymers are formed during the growth of the living organisms, and are thus, called natural polymers. Their synthesis usually involves enzymatic catalysis and an increase in the chain through polymerization reactions of the monomers, typically inside the cells, mediated by complete metabolic processes (3,4). 

Noncovalent wrapping with polysaccharides is another commonly used approach in the carbohydrate functionalization and solubilization of carbon nanotubcs.39-42 For example, Liu et al. used alginic acid (AA), a natural polysaccharide constituted with repeated (3-D-mannuronic acid ((3M) and a-L-guluronic acid (aG) segments, to... 

Chitin is a polysaccharide constituted of N -acctylglucosamine, which forms a hard, semitransparent biomaterial found throughout the natural world. Chitin is the main component of the exoskeletons of crabs, lobsters and shrimps. Chitin is also found also in insects (e.g. ants, beetles and butterflies), and cephalopods (e.g. squids and octopuses) and even in fungi. Nevertheless, the industrial source of chitin is mainly crustaceans. 

In 1977, Ohnishi and Kato (2850) described the identification of several carbonyl compounds in the pyrolysates from the tobacco cell-wall polysaccharides cellulose, hemicellu-lose, and pectins. They noted that these biopolymeric polysaccharides constituted 30% to 50% of the dry weight of the tobacco they were studying. Sakuma et al. pyrolyzed tobacco-derived cellulose (3401), chlorogenic acid, and rutin (3400) and reported various aldehydes and ketones plus numerous phenols in the pyrolysates. Many of the pyrolysate components identified have also been identified in cigarette MSS. 

The amylaceous polysaccharides constitute the best example of the successful application of enzymic techniques. The fundamental, structural features of these polysaccharides were established nonenzymically, to a large extent by Haworth and Hirst, before any enzymic degradation studies were undertaken. Subsequent use of well characterized enzymes, particularly by Peat and Whelan and their coworkers, has led to the elucidation of the fine structures. 

Extraction of botanical polysaccharides has traditionally been successfully carried out using the popular method of hot water extraction [1,2,5,71-77,85] and it is applicable in a variety of plant cell wall structures and water solubility of polysaccharide constitutes [65]. Briefly, the procedure involves large quantity of medicinal plant material/mushroom to be powdered, and then homogenized to maintain uniformity within and between the samples collected at different times. The powdered sample is then subjected to hot water extraction by autoclaving for approximately 2 h at 121 °C [5]. Autoclaved sample is filtered after allowing it to cool to room temperature, and the supernatant is then precipitated using 95% aqueous ethanol (supema-tant EtOH=l 4, v/v) for about 15 h at 2.5 °C to remove nonpolar... 

Cellulose, the most widely distributed plant skeletal polysaccharide, constitutes almost half of the cell-wall material of wood. Cotton is almost pure cellulose. 

Cellulose is the main component of the cell walls of plants. The so-called hemicelluloses and other related polysaccharides constitute a considerable proportion of plants (Chapter XII). Therefore, these substances are present in nearly all dietaries. None of the higher forms of life appears to be... 

Cellulose is the main constituent of plant cell walls, where it usually occurs together with hemi-celluloses, pectin and lignin. Since cellulase enzymes are absent in the human digestive tract, cellulose, together with some other inert polysaccharides, constitute the indigestible carbohydrate of plant food (vegetables, fruits or cereals), referred to as dietary fiber. Cellulases are also absent in the digestive tract of animals, but herbivorous an-... 

The polysaccharides constitute 0.2-0.3% of the fresh gel (0.8-1.2% of dry matter content). Postproduction autodegradation of the glucomannan polysaccharides produces mainly mannans. The gel polysaccharides, consisting mainly of mannose and glucose in a 1 3 ratio, can degrade in 48 h at room temperature, with a decrease in glucose content and an increase in mannose glucose ratio to >10. ... 

A disaccharide is derived from two monosaccharides by the formation of an ether (usually, acetal) bridge (Sections 17-7 and 24-11). Hydrolysis regenerates the monosaccharides. Ether formation between a mono- and a disaccharide results in a trisaccharide, and repetition of this process eventually produces a natural polymer (polysaccharide). Polysaccharides constitute the framework of cellulose and starch (Section 24-12). 

Table 7 shows results obtained when data were fit to Cross model,. The upper Newtonian plateau was, as usually, inaccessible. Structural relaxation times, , showed that hydrated polysaccharides constituted a network which relaxed after attainment of its corresponding onset value. 

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