The Influence of pH on the Rate of Hydrolysis of Acidic Polysaccharides.

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Abstract
The rate of hydrolysis was determined for a number of poly-and oligosaccharides as a function of the pH. Neutral carbohydrates were hydrolysed at a rate nearly proportional to the acid concentration. At low pH-values, carbohydrates containing sulphate or carboxyl groups were hydrolysed at a lower rate while the opposite was the case at low acid concentrations. Poly- and oli-gouronides showed a particularly high rate of hydrolysis at pH-values above 2, and the results indicate that the rate depends on the degree of dissociation of the carboxyl group. The higher rate of hydrolysis of charged polysaccharides at low acid concentrations is supposed to be due to a higher proton concentration near the negatively charged polysaccharide chain than in the bulk of the solution. An intramolecular catalysis by the undissociated carboxyl groups is proposed as the mechanism responsible for the specific effect obtained with 1,4-linked uronic acids.

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