Polymeric carbohydrates

Tannins are polyhydroxyphenols. They are soluble in water, aleohols and aeetone and ean eoagulate proteins. They are yielded by extraetion from wood substanee, bark, leaves and fruits. Other components of the extraction solutions are sugars, pectins and other polymeric carbohydrates, amino acids and other substances. The content of non-tannins can reduce wood failure and water resistance of glued bonds. The polymeric carbohydrates especially increase the viscosity of the extracts. 

The remainder of this chapter will deal with natural polymers. These are large molecules, produced by plants and animals, that carry out the many life-sustaining processes in a living cell. The cell membranes of plants and the woody structure of trees are composed in large part of cellulose, a polymeric carbohydrate. We will look at the structures of a variety of different carbohydrates in Section 23.3. Another class of natural polymers are the proteins. Section 23.4 deals with these polymeric materials that make up our tissues, bone, blood, and even hair. ... 

Polymeric carbohydrates are usually encountered as distributions, so high resolution is rarely important. Of all biological macromolecules, carbohydrates are particularly amenable to analysis by GPC because hydrophobic interactions are typically weak. A section below is devoted to the analyses of carboxymethylcellulose and xanthan. Other examples of polysaccharides of interest are hyaluronic acid,62 polymers of (l-glucose,121125 heparin,126127 cellulose and chitin,128 and Mucorales extracellular polysaccharides.129... 

The main constituent of all fibers of vegetable origin (see Table 88) is, almost exclusively, cellulose, a polymeric carbohydrate (see Textbox 53). Vegetable fibers are resistant to alkalies and to most organic acids but are destroyed by strong mineral acids. 

Vegetable Cotton, linen Fine fibers Cellulose, a polymeric carbohydrate... 

Immobilisation of the matrix in the SPREAD process, this takes place not at the surface of minerals, but at thiosepharose, a polymeric carbohydrate which... 

Cationic zirconocenes serve as useful reagents in such diverse fields as alkene polymerization, carbohydrate chemistry, asymmetric catalysis, and so on. Reagents that were originally developed for polymerization reactions (MAO, ansa-metallocenes, non-nucleophi-lic borate counterions) have now found use in organic synthesis and are being employed for carbometalation reactions, hydrogenation, and Diels—Alder catalysis. 

Suppose we start with a starch-rich meal, say one containing a lot of pasta or bread. The digestion of starches begins in the mouth. Saliva contains an enzyme, salivary amylase (aka ptyalin), which catalyzes the conversion of starch to simple sugars such as glucose. This process is completed in the small intestine under the influence of other enzymes in the amylase class. This completes the first phase of carbohydrate catabolism the conversion of complex, polymeric carbohydrates (e.g., starches) to their simple monomeric units, the sugars. 

Carbohydrates are among the most abundant constituents of plants, animals, and microorganisms. Polymeric carbohydrates function as important food reserves, and as stmctural components in cell walls. Animals and most microorganisms are dependent upon the carbohydrates produced by plants for their very existence. Carbohydrates are the first products formed in photosynthesis, and are the products from which plants S5mthesize their own food reserves, as well as other chemical constituents. These materials then become the foodstuffs of other organisms. The main pathways of carbohydrate biosynthesis and degradation comprise an important component of... 

Amylase, the most important endoglyco-sidase in the pancreas, catalyzes the hydrolysis of al 4 bonds in the polymeric carbohydrates starch and glycogen. This releases maltose, maltotriose, and a mixture of other oligosaccharides. 

It is worth pointing out that, besides o-sorbitol 19 and D-mannitol 36, other low-molecular weight building blocks have been already obtained on the ton-scale from low cost or waste polymeric carbohydrates (starch, cellulose, hemicellulose, chitin) [80, 81]. Most of these compounds are densely functionalized enantiopure molecules that can be easily converted into high-value added products, including chiral ionic liquids. Therefore, further studies are required to develop other synthetic approaches to environmentally sustainable ionic liquids based on renewable raw materials. 

Molecules consist of six Joined carbon atoms and six water molecules. Their molecules are made up of two joined monosaccharides. Aiso ioiown as polysaccharides or polymeric carbohydrates-, their molecules are blopoly-mers made up of many monosaccharides joined together. ... 

Frederick M. Swain The furfurals are believed to be represented by polymeric carbohydrate compounds in the rocks and to have been produced by distillation of the rock samples with hydrochloric acid (6). 

C. Fayet and J. Gelas, Reaction of mono- and oligo-saccharides with keto or ethylenic enol ethers as a route to functionalized acetals and monomers for polymerization, Carbohydr. Res. 259 177 (1993). 

The procedure is limited to materials that dissolve, or in the case of polymers, which swell in dimethylsulfoxide. Jones has reviewed the GLC of the methyl ethers and pointed out that the free reducing methyl sugars adsorb on columns and are thus of limited utility (74). Methods to avoid this problem will be discussed in section 9.3.3. It has also been pointed out that mixed ether acetyl ester derivatives are useful for the determination of bonding in polymeric carbohydrates. This also will be treated in section 9.3.3. 

The actual position of the linkages in a branched polymer, such as (2), will depend on the relative reactivities of the hydroxyl groups. These reactivities are known to be different both in monomeric and polymeric carbohydrates.28 In a study24 of the condensation polymerization of undo) W. II. Carothers, Trans. Faraday Soc., S3, 39 (1936) Chem. Rev., 8, 353 (1931) Ref. 12, pp. 31—132. 

Polymeric carbohydrates are major structural components in plant and bacterial cell walls and in the extracellular matrix of vertebrates. Branched-chain polymeric carbohydrates covalently linked to proteins are used to give proteins unique signatures that guide them to their final destination and that facilitate specific interactions between free proteins or proteins attached to cells. 

---