Exploratory studies in the synthesis and characterization of a series of polysaccharide stereoregular polyelectrolytes

A series of sodium dextran sulfates was synthesized under a variety of reaction conditions using as the sulfating agent a complex of N,N-dimethylformamide-sulfur trioxide in a mixed solvent system of dimethylsulfoxide and N,N-dimethylformamide. The reaction temperature, polysaccharide reaction pre-treatment, and ratio of reactant to substrate were varied to obtain a polysaccharide sulfate having a degree of substitution equal to one and without (or minimal) polysaccharide degradation. Methods for the analysis of the sulfate distribution were investigated to allow total characterization of the polyelectrolytes to establish any specificity for substitution under the reaction conditions studied. Periodate oxidation analysis on sedium dextran sulfate exhibited anomalous underoxidation behavior that did not allow this technique to be used in the normal analytical manner. Further investigations of the periodate oxidation behavior of five other dextran derivatives showed the anomalous underoxidation behavior to occur as a result of the electron withdrawing ability of the substituent, the electrostatic interaction of the polyelectrolyte with the reagent, and hemiacetal-hemialdal formation. The major contributing factor to the observed anomalous oxidation behavior was attributed to the hemiacetal-hemialdal formation. The problem was solved by isolation and sodium borohydride reduction of the underoxidized sample followed by further periodate oxidations. ..