Unraveling the effect of non-specific counterions in the Ca²⁺-induced gelation of high-content alternating sequence alginate.

Authors

Xiaoyang Li, Jiangbing Xu, Cuixia Sun, Yiguo Zhao, Wei Lu, Yapeng Fang

Published in

International journal of biological macromolecules. Pages 155039. Oct 25, 2026. Epub Oct 25, 2026.

Abstract

Alginate gelation is typically governed by the "egg-box" model, wherein Ca²⁺ crosslinks G-blocks to form junction zones. However, for alginates with limited G-block length, this model alone may be insufficient. Here, we investigate the influence of monovalent counterions (Li⁺, Na⁺, K⁺) on the Ca²⁺-induced gelation of a high-GM alginate (ALG) with an average G-block length (N_G = 6) below the threshold for stable egg-box formation. Rheological measurements reveal that the Na⁺ form (ALGNa) exhibits the fastest gelation kinetics and highest mechanical strength, forming a finer and more compact network than Li⁺ (ALGLi) and K⁺ (ALGK) counterparts. Molecular dynamics simulations indicate that Na⁺ promotes the aggregation of poly-GM chains more effectively than Li⁺ or K⁺. The underlying mechanism is attributed to the balance between ion-carboxylate coordination and ion-hydration effects, which is composition-dependent and leads to the most effective association of GM-rich segments when Na⁺ serves as the counterion. Atomic force microscopy indicates that chain rigidity follows the order ALG-Na < ALG-Li < ALG-K, consistent with the proposed order of counterion effectiveness. Given the limited G-block length, it is inferred that Na⁺ promotes interchain proximity of GM-rich segments, increasing the local concentration of G-blocks to enable weak, transient "egg-box"-like interactions that collectively contribute to network connectivity, while GM/GM and mixed GG/GM junction zones serve as the primary structural elements. These findings extend the understanding of counterion-dependent Ca²⁺ gelation to a high-GM, short-G-block alginate and provide guidance for the preparation and mechanical regulation of alginate hydrogels derived from this specific composition.

PMID:
42927816
Bibliographic data and abstract were imported from PubMed on 26 Oct 2026.

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