Circular-dichroism studies of pectin solutions

The influence of pH, temperature, ionic strength, and some additives on the c.d. spectra of aqueous solutions of pectins of various degrees of esterification has been studied. On changing the pH 7.5 → 2.0, hyper- and hypso-chromic effects are observed. The molecular ellipticity ([θ]) contributions of the CO2H and CO2Me groups are equal. Differences in the type of concentration-dependence of pectins of low ester content and fully esterified pectins have been found. The gelling of pectins following the change of solvent composition (addition of propan-2-ol or 5M sodium perchlorate) leads to an increase of [θ]. At a constant level of ionization, [θ] of the carboxylic chromophore can be used as a probe for intermolecular interactions in pectin solutions.