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Associative behaviour of κ-carrageenan in aqueous solutions and its modification by different monovalent salts as reflected by viscometric parameters.

M. Bercea,B. Wolf

Published 2019 in International Journal of Biological Macromolecules

ABSTRACT

The viscometric behaviour of κ-carrageenan in aqueous solutions and in the presence of monovalent salts was investigated at 25 °C. Coil, helix or double helix conformations were induced by cooling hot κ-carrageenan solutions under appropriate ionic conditions. A new viscometric approach was used for modeling the behaviour of κ-carrageenan solutions. The intrinsic viscosity, [η], is markedly changed by the presence of different monovalent salts (NaCl, NaI and CsI). In pure water, the intrinsic viscosity amounts to 48 dL·g-1. In 0.1 M NaCl solutions (single helix state) [η] is 6.2 dL·g-1, whereas in 0.1 M NaI (double helix conformation) it is approximately twice as large. In 0.1 M CsI (dissimilar cation and counter-ion) the intrinsic viscosity is three times larger, suggesting the formation of the associated κ-carrageenan helices. Stepwise association of κ-carrageenan helices was followed in presence of NaI/CsI mixtures of different compositions. The value of Smidsrød-Haug stiffness parameter (B) measured for κ-carrageenan in NaCl solutions is 4.47 × 10-2, higher than that of DNA (5.5 × 10-3), but lower than those reported for carboxymethyl cellulose (6.3 × 10-2), indicating that the chain conformation is moderately rigid.

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