Products from Polysaccharide Degradation

A polysaccharide can be conveniently degraded for purposes of structural determinations in a rather simple way. The polysaccharide to be examined is dissolved in an excess of an oxygen-free solution of a base, usually saturated lime-water, and allowed to stand at 25-37° for several months. Cations are then removed from the solution with a suitable cation-exchange resin. Residual polysaccharide may be precipitated with three volumes of ethanol, and the degradation products separated by cellulose-column chromatography, or by fractional reprecipitation of their calcium salts.  

Degradation occurs more readily in lime-water than in a potassium hydroxide solution of similar normalityand lime-water directs the degradation of (1 — 3)- and (1 — 4)-linked glycans toward saccharinates which contain the same number of carbon atoms as the sugar units involved in the parent glycan. 

Alkaline degradation of polysaccharides usually stops before the degra- 

less likely, (c) the formation of stable, ordinary saccharinate end-groups in (1 — 4)-linked glycans (see Fig. 6). 

Alkaline degradation of cellulose is important during alkaline pulping it produces non-volatile acids which are, for the most part, D-gluco-isosaccharinates.  

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It is known that the qualitative and quantitative composition of the thennal degradation products from polysaccharides can be altered by use of different catalysts [1]. Inorganic acids are not well selective catalysts as they affect both the degradation and condensation reactions in the pyrolysis process. A relationship between dehydration, degradation and condensation reactions is determined by the individual properties of the acid, the characteristics of the cellulose structure and by the pyrolysis conditions... 

In 1947, L-rhamnose was first recognized by Stacey as a constituent of Pneumococcus Type II specific polysaccharide. This finding was confirmed, in 1952, by Kabat et al. and in 1955 again by Stacey when 2,4- and 2,5-di-O-methyl-L-rhamnose were synthesized and the former was shown to be identical with a di-O-methylrhamnose, obtained by hydrolysis of the methylated polysaccharide. This result indicated a pyranose ring structure for the rhamnose units in the polysaccharide. Announcement of the identification of D-arabinofuranose as a constituent of a polysaccharide from M. tuberculosis aroused considerable interest. The L-enantiomer had been found extensively in polysaccharides, but reports of the natural occurrence of D-arabinose had been comparatively rare. To have available reference compounds for comparison with degradation products of polysaccharides, syntheses of derivatives (particularly methyl ethers) of both d- and L-arabinose were reported in 1947. 

Y. Aoki and Y. Kamei, Preparation of recombinant polysaccharide-degrading enzymes from the marine bacterium, Pseudomonas sp. ND137 for the production of protoplasts of Porphyra yezoensis, Eur. J. Phycol., 41 (2006) 321-328. 

Chemical studies reported by Karrer, in 1921, indicated that glycogen and starch have closely related structures. Acidic or enzymic hydrol3reis gave similar products from both polysaccharides, and, on methylation with methyl sulfate and barium or sodium hydroxide, methyl ethers of similar composition were isolated. Furthermore, both glycogen and starch degraded by acetyl bromide gave acetobromomaltose (in about 60 % yield). 

Definitive proof of the location of L-rhamnopyranosyl residues in gum arabic was obtained on acetolysis of the carboxyl-reduced polysaccharide, from which degradation, 4-O-L-rhamnopyranosyl-D-glu-cose (19) and 0-L-rhamnopyranosyl-(l — 4)-0-D-glucopyranosyl-(1 — 6)-D-galactose (20) were identified as products of partial... 

Koll and Metzger (1978) report on the use of supercritical acetone as the reaction medium for the thermal degradation of cellulose and chitin. Since the pyrolysis of these polysaccharides occurs at such high temperatures, it is necessary to remove the primary products from the reaction zone as soon as they are formed to avoid degradation of the products into coke. The high operating temperature also adversely affects both yield and product distribution. It is possible to reduce the carbon formation by carrying out the pyrolysis under vacuum but the reaction rate is also reduced because of the poor heat transfer to the reactants. 

The enzymatic hydrolysis of poly-p-hydroxybutyrate, PHB, by several different bacteria, which are known to secrete active esterases, has been studied in some detail by several research groups [7, 8]. As with the polysaccharides, the final products of these degradation reactions are the monomers, dimers and trimers, which are removed by hydrolysis only from hydroxyl-end of the polymer chain, as follows ... 

The general pyrolysis mechanisms of polysaccharides have been determined from model studies on cellulose and involve the splitting of the polysaccharide structure by three basic chemical reaction mechanisms dehydration, retroaldolization, and decarboxylation. Using these basic pyrolysis mechanisms, it is possible to explain the pyrolysis of polysaccharides and evolved pyrolysis products. The hexose degradation pathway for cellulose results in formation of furan- and pyran-type fragments and smaller acyclic aldehyde and ketone fragments. ... 

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