Polysaccharides are ubiquitous in nature; they serve fundamental roles in vivo and are used for a multitude of food, pharmaceutical, cosmetic biomaterials, and biomedical applications. Here, the structure–property function for low acetylated Gellan gum hydrogels induced by divalent ions was established by means of optical, rheological, and microscopic techniques. The hydrogels interacted with visible light as revealed by birefringence and multiple scattering, as a consequence of quaternary, supramolecular fibrillar structures. The molecular assembly and structure were elucidated by statistical analysis and polymer physics concepts applied to high-resolution AFM height images and further supported by FTIR. This revealed intramolecular coil-to-single helix transitions, followed by lateral aggregation of single helices into rigid, fibrillar quaternary structures, ultimately responsible for gelation of the system. Calcium and magnesium chloride were shown to lead to fibrils up to heights of 6.0 nm and persistence lengths of several micrometers. The change in molecular structure affected the macroscopic gel stiffness, with the plateau shear modulus reaching ∼10⁵ Pa. These results shed light on the two-step gelation mechanism of linear polysaccharides, their conformational molecular changes at the single polymer level and ultimately the macroscale properties of the ensued gels.

中文翻译：

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羧化线性多糖中二价离子诱导的刚性、纤维状四级结构

多糖在自然界中无处不在；它们在体内发挥基本作用，并用于多种食品、药物、化妆品生物材料和生物医学应用。在这里，通过光学、流变学和显微镜技术建立了由二价离子诱导的低乙酰化结冷胶水凝胶的结构-性能函数。由于四元超分子纤维状结构，水凝胶与可见光相互作用，如双折射和多重散射所示。通过应用于高分辨率 AFM 高度图像的统计分析和聚合物物理概念阐明了分子组装和结构，并得到了 FTIR 的进一步支持。这揭示了分子内线圈到单螺旋的转变，随后单螺旋横向聚集成刚性，纤维状四元结构，最终导致系统的凝胶化。氯化钙和氯化镁被证明会导致高达 6.0 nm 的原纤维和几微米的持续长度。分子结构的变化影响宏观凝胶刚度，平台剪切模量达到~10⁵ Pa。这些结果揭示了线性多糖的两步凝胶机制、它们在单一聚合物水平上的构象分子变化以及最终凝胶的宏观性质。