Dilute solution properties of κ-carrageenan polysaccharides: effect of potassium and calcium ions on chain conformation

The effect of added ions (0.5 mM K+ or 0.25 mM Ca2+) and temperature (25 or 60 °C) on the solution properties of κ-carrageenan (0.2%, w/w) were investigated using static light scattering, circular dichroism and viscometry. At 60 °C (coil conformation), added salts caused a decrease in the radius of gyration (Rg), as chains became less spatially extended. As temperatures declined (60–25 °C), κ-carrageenan underwent a temperature-induced transition whereby Rg decreased by ∼18% with or without added K+, and 2.7% with added Ca2+. Temperature dependence of the molecular ellipticity [θ] at 620 nm, described by the vanʹt Hoff relationship, estimated enthalpic changes for the unraveling of the ordered conformation of 2.3–4.1 kJ/mole depending on the ionic conditions. At 25 °C (ordered conformation), Rg decreased and [θ] increased with added salts. No significant effect of ionic strength on intrinsic viscosity was found.