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Isothermal titration calorimetry study of the polyelectrolyte complexation of xanthan and chitosan samples of different degree of polymerization

Authors

  • Gjertrud Maurstad,

    1. Department of Physics, Biophysics and Medical Technology, The Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway
    2. Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan
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  • Shinichi Kitamura,

    1. Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan
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  • Bjørn T. Stokke

    Corresponding author
    1. Department of Physics, Biophysics and Medical Technology, The Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway
    • Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan
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  • This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley. com

Abstract

Mixing oppositely charged polyelectrolytes in aqueous solutions leads to the spontaneous formation of polyelectrolyte complexes. Here, we characterize the interaction between xanthan of two different chain lengths, a tri-glucosamine and a chitosan polymer by isothermal titration calorimetry (ITC). Analysis of the experimental thermodynamic data assuming a single set of identical sites indicated both enthalpic and entropic contributions to the overall interaction in the interaction between xanthan and tri-glucosamine. The relative contribution of entropy compared to enthalpy was found to be largest for the shortest chain length of xanthan. Using a chitosan polymer instead of tri-glucosamine gave rise to two different stages in the interaction process. A model where the first stage of the ITC curve represent an initial polyelectrolyte complexation stage followed by aggregation on further titration of chitosan to the xanthan is suggested. Ultrastructure images by applying atomic force microscopy at some selected extents of titration are consistent with the two-stage interpretation of the thermodynamic data. © 2011 Wiley Periodicals, Inc. Biopolymers 97: 1–10, 2012.

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