Conductometric Detection of Coil-to-Helix Transition of Anionic Polysaccharides.-Carrageenan

Malgorzata Ciszkowska* and Igor Kotlyar

Department of Chemistry, Brooklyn College, The City University of New York, Brooklyn,
New York 11210-2889

Abstract:

The conformational coil-to-helix transition of an ionic polysaccharide, -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 polyelectrolyte solution (-carrageenan sodium salt) to that in the solution without polyelectrolyte (NaCl). Structural characterization of -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 -carrageenan for the concentration range from 10 to 40 mM. The determined charge separation distance for -carrageenan in solution was 0.89 and 0.40 nm for a coil and a double-helix form, respectively.