Sulfate groups, determination polysaccharides

Native polysaccharides with acid groups other than the uronic type are not very common except for the sulfate esters. Total acidity may be estimated by direct titration, but erroneous results are obtained if the polysaccharide is alkali-labile as is the case with many oxidized polysaccharides. Addition of calcium acetate (7, 8) or sodium bromide 8, 9) to the polysaccharide solution increases the accuracy of the titration. Other methods for the estimation of carboxyl and other acidic groups involve determination of the amount of methylene blue absorbed, or determination of the amount of silver salt formed by exchange from a solution which contains silver in combination with a very weak acid. The sulfate content of polysaccharide sulfates, such as agar, is obtained by ordinary sulfate analysis of the completely hydrolyzed or ashed polysaccharide. 

Once assignments of polysaccharide signals are known, they may be used as a basis in determination of the position of substitution by such groups as acetate, malonate, phosphate, and sulfate, whose a- and /3-shifts may be estimated by referral to suitable monosaccharide models. For phosphate, the phosphated carbon atoms and adjacent resonances may be identified, as they give coupled signals and are subject to lanthanide-induced shifts. These data are described in Section VI, 8. 

Core chain trisaccharide related to human blood group antigenic determinants. Constit. of a sulfated polysaccharide from an ovarian cyst glycoprotein exhibiting blood group A activity. 

Ionic polymers (polyelectrolytes and polyampholytes) constitute an important class of water-soluble maaomole-cules. ° Their monomer units are capable of ionization in polar solvents, for example, in water. The ionization occurs via either dissociation of hydrogen ions H from the acidic groups or dissociation of water molecules and protonation of the basic groups on the polymer chain. The solubility of polyelectrolytes in polar solvents is determined first of all by a huge gain in translational entropy of the counterions. The majority of bio-maaomolecules (proteins, nucleic acids, and polysaccharides) operating in aqueous environment carry ionizable groups (carboxyl, sulfate, amine, etc.) and are included in this class of polymers. 

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