Saccharide monomers

Our original approach to polysaccharide C-13 n.m.r. spectral analysis consisted of making a minimum number of hypotheses about expected structure-to-spectra relationships (8). By then comparing spectra to known structure for a series of D-glucans, we attempted to establish the validity of these hypotheses and to establish how diverse a structural difference could be accommodated The hypotheses were as follows. Firstly, that each polymer could be considered as an assembly of independent saccharide monomers. Secondly, that these hypothetical saccharide monomers would be 0 alkylated (0 -methylated) in the same positions as the actual saccharide linked residues (it had previously been established that 0-methylation of any a-D-glucopyranosyl carbon atom position resulted in a down-field displacement of vlO p.p.m. for the associated resonance). Thirdly, that each differently substituted residue would have a completely different set of chemical shift values for each carbon atom position (different from the unsubstituted saccharide) but that only the carbon atom positions involved in inter-saccharide linkages would have A6 greater that 1 p.p.m. And, fourthly, that the hypothetical 0-alkylated residues would contribute resonances to the total spectrum proportional to their mole ratio in the polymers. 

The same procedure of catalyst synthesis applied to other polysaccharides, such as -carrageenan and chitosan, allowed data on the influence of the chemical structure of the support to be obtained. The differences in turnover numbers (moles of product per moles of Pd per hour), close to 500 for alginates, 190 for carrageenan, and only 40 for chitosan, indicated that the activities were correlated to the electrostatic properties of the support. Carrageenans only bear one sulfate group per two saccharide monomers, while alginate presents one carboxylic group... 

The binding affinity of lectins to saccharide monomers is in the order of millimolar. It rises to nanomolar when carbohydrate clusters are provided. The... 

It is widely held that polysaccharides (frequently thousands of saccharide monomers aU linked together) serve two functions. Not only do polysaccharides serve plants as structural components (stems, trunks, etc.), but they also serve as a food reserve (e.g., starch). 

In contrast to proteins and nucleic acids, the linkages formed between saccharide monomers are made at stereogenic centers, and so stereochemical control of the polymerization step is critical. The crucial carbon, the anomeric center, is highlighted in Figure 6.18, which defines the nomenclature convention for this stereogenic center. This stereochemical distinc-... 

A potential challenge in using funetionalized polymers in biologieal environments is the hydrolytic sensitivity of the ester or anhydride funetionalities commonly used to tether pendant funetionalities to the norbomene ring [9]. In model studies. Week and cowoikers reported hydrolysis of ester, acetal, and 0-amino ester groups at different pH ranges saccharide monomers were also affected [12]. 

The fact that the neutral saccharide residue is trapped on the column and subsequently can be eluted as though it contains carboxylate functionality frirther supports the thesis that the saccharide monomer is incorporated into the poly(acrylic acid). In a control experiment, glucose was not retained on the ion exchange column in the presence of the copolymer while the copolymer was. These observations were used to advantage in the determination of saccharide monomer incorporation into the acrylic acid copolymer. A solution of polymer made from a feed containing 2 mole% monomer 5f that was not otherwise purified was subjected to the solid phase extraction technique. Forty-six percent of the saccharide present in the copolymer solution prior to solid phase extraction was not retained on the solid phase extraction medium 54% of the saccharide was retained and therefore bound to the copolymer. This indicates that a feed of 2 mole% of this saccharide monomer leads to the incorporation of 1.1 mole% monomer in the copolymer. Similar levels of monomer incorporation were observed in other copolymerizations of monomer 5f and with monomer 5e (75). 

A very practical and broadly applicable two-step synthesis of a new family of monofunctional saccharide monomers was developed (16). In this synthesis, all reactions are done in water, no protecting groups are employed, and no by-products are formed. These saccharide-derived monomers were found to be useful as tags for water treatment polymers (7 7). 

Figure 6 Structure of cellulose/consisting of glucose monomers regularly linked by 3-1,4 -glycosidic bonds. (In contrast, hemicellulose consists of varying types of saccharide monomers and has a branched structure overall see Ref. 171.)...

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