Metal ions play a crucial role in forming hydrogels, and their effects on fucoidan (FUC): κ-carrageenan (KC) mixed gels were investigated. The results indicated that the FUC: KC mixed gels (FC) were promoted by K+ and Ca2+ but destroyed by Fe3+. The gel strength of FC was enhanced by K+ and Ca2+, with G' and G″ being highest at 50 mmol/L KCl and 25 mmol/L CaCl2, respectively. Water mobility was weakened after the addition of KCl and CaCl2 in accordance with the decrease in T23 relaxation time (free water, 100-1000 ms). After addition of KCl and CaCl2, the FC groups presented a typical three-dimensional network structure in contrast to the lamellar, disordered, and broken structure of FUC. Moreover, the FT-IR spectrum certified the enhancement of hydrogen bonds and the occurrence of electrostatic interactions during gel formation by the red-shift of the OH stretching vibration of the Ca2+ group and the blue-shift of the COS vibrations. The XRD results confirmed that the binding of Ca2+ to FC was tighter than that of K+ at the same charge content. These results provide a theoretical basis for understanding the interaction mechanism of FC with metal ions.
Keywords: Fucoidan; Interaction; Metal ion; κ-carrageenan mixed gels.
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