Chemical Analysis, Volume 45, Number 2

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.