M. Ciszkowska, M. D. Guillaume, I. Kotlyar, Chem. Anal.  2000, 45, 167-174.

Chemical Analysis, Volume 45, Number 2



 Coil-to-Helix Transition of Anionic Polysaccharides: Comparison of Voltammetric and Conductometric Results for Kappa-Carrageenan
Malgorzata Ciszkowska Melissa D. Guillaume, and Igor Kotlyar
Department of Chemistry, Brooklyn College, The City University of New York, Brooklyn, NY 11210-2889

Two electroanalytical techniques, steady-state voltammetry and conductance measurements were utilized to study conformational coil to double helix transition of an ionic polysaccharide kappa-carrageenan, kappa-car, in solutions of low ionic strengths as effected by temperature and concentration of the polyion.  Interactions between counterions, Na+, or electroactive probe ions, Tl+, and polyanions during such transition were quantified by the ratio of the diffusion coefficient of Na+ or Tl+ ions in the polyelectrolyte solution (kappa-car sodium salt) to that in the solution without polyelectrolyte (NaCl or NaClO4).  Results for native counterions, Na+, from conductance measurements were very close to those obtained from voltammetry of Tl+ probe ions.  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-car for the concentration range from 10 to 40 mM.  The charge spacing in kappa-car conformers was determined based on Manning’s theory for polyelectrolytes.  The average charge spacing from conductivity and voltammetric results was 0.39 nm and 0.90 nm for a double helix and a coil form of kappa-car, respectively.