Conductometric detection of coil-to-helix transition of anionic polysaccharides.: κ-carrageenan

The conformational coil-to-helix transition of an ionic polysaccharide, kappa-carrageenan, as effected by temperature and concentration of the polyion, was studied using conductance measurements in solutions of low ionic strength. Interactions between counterions, Na+, and polyions during such a transition were quantified by the ratio of the diffusion coefficient of Na+ counterions in the pobelectrolyte solution (kappa-carrageenan sodium salt) to that in the solution without polyelectrolyte (NaCl), Structural characterization of kappa-carrageenan conformers, expressed by the charge separation distance, was performed based on Manning's theory for polyelectrolytes. The conformational transition was a reversible coil-to-double helix process resulting from temperature decrease. This process did not depend on the concentration of kappa-carrageenan for the concentration range from 10 to 40 mM, The determined charge separation distance for kappa-carrageenan in solution was 0.89 and 0.40 nm for a coil and a double-helix form, respectively.