Small-angle X-ray scattering and rheological characterization of alginate gels

• Published in: Macromolecular symposia. Vol. 120; no. 1; pp. 91 - 101
• Main Authors: Stokke, B.T, Drager, K.I, Yuguchi, Y, Urakawa, H, Kajiwara, K
• Format: Journal Article
• Language: English
• Published: Hüthig & Wepf Verlag 01.07.1997
• ISSN: 1022-1360; 1521-3900
• DOI: 10.1002/masy.19971200111

The wide applicability of alginates is due to the ease of which gelation can be introduced and that the gelation conditions are compatible with requirements imposed by for instance living cells. The “egg-box” model describes the gel-inducing ions embodied in cavities formed by sequences of α-L-GulA of the alginate copolymers in a pairing reaction yielding junction zones. Small-angle X-ray scattering showed that the cross-sectional radius of gyration for an alginate with fraction of α-L-GulA, FG, = 0.39, increased from Rg,c = 3.5Å for alginate in solution to 7.6Å for homogeneous Ca-gels at [Ca²⁺] = 10 mM. The homogeneous Ca-alginate gels were obtained by in situ release of Ca²⁺ from Ca-EGTA or CaCO₃ using a slowly hydrolyzing lactone. Either increasing the [Ca²⁺] for a given FG or increasing FG by selection of an alginate from a different seaweed specie and using constant [Ca²⁺], yielded larger initial slopes and curvature in the cross-sectional plots of the SAXS data. This indicate the coexistence of junction zones differing in multiplicity characterized by shifting the distribution towards larger multiplicity either for increasing FG or [Ca²⁺]. The present finding of junction zone formation by lateral condensation of α-L-GulA sequences depending on the composition of alginate and Ca-concentration are significant extensions of the “egg-box” model that correlate the sequential arrangement of α-L-GulA and β-D-ManA in alginate to the structure of the junction zones in the Ca-alginate gels.