Among hydrocolloids, gellan is one of the most used anionic polysaccharides, because of its capability of forming mechanically stable gels at relatively low concentrations. Despite its long-standing use and importance, the gellan aggregation mechanism is still not presently understood at the microscopic level due to the lack of atomistic information. Here we will fill this gap by reporting molecular dynamics simulations of gellan chains at different polymer and salt contents, being able to unveil the occurrence of the two steps in the process, in agreement with existing hypotheses. At first, the formation of double helices takes place, followed by the aggregation into super-structures. For both steps, the role of bivalent cations appears to be crucial, as also shown by rheology and atomic force microscopy measurements: they not only facilitate the junction of the chains into double helices, but also promote through bridging their arrangement into larger aggregates. On the other hand, monovalent cations have a much more reduced role, making it possible to form double helices only at very high salt content and not actively participating in the formation of gels. Our simulations thus offer the first complete microscopic overview of gellan aggregation and will be important for future use of gellan-based systems for a wide variety of applications, ranging from food science to art restoration.

中文翻译：

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结冷凝聚两步机制的分子起源

在水胶体中，结冷胶是最常用的阴离子多糖之一，因为它能够在相对低的浓度下形成机械稳定的凝胶。尽管其长期使用和重要性，但由于缺乏原子信息，目前在微观水平上仍未了解结冷凝聚机制。在这里，我们将通过报告不同聚合物和盐含量的结冷链的分子动力学模拟来填补这一空白，能够揭示该过程中两个步骤的发生，与现有假设一致。首先，形成双螺旋，然后聚集成超结构。对于这两个步骤，二价阳离子的作用似乎至关重要，流变学和原子力显微镜测量也表明：它们不仅促进了链连接成双螺旋，而且还通过将它们的排列桥接成更大的聚集体来促进。另一方面，单价阳离子的作用要小得多，这使得只有在非常高的盐含量下才有可能形成双螺旋，并且不积极参与凝胶的形成。因此，我们的模拟提供了结冷聚合的第一个完整的微观概述，并且对于未来将基于结冷的系统用于从食品科学到艺术修复的各种应用非常重要。使得只有在非常高的盐含量下才有可能形成双螺旋并且不积极参与凝胶的形成。因此，我们的模拟提供了结冷聚合的第一个完整的微观概述，并且对于未来将基于结冷的系统用于从食品科学到艺术修复的各种应用非常重要。使得只有在非常高的盐含量下才有可能形成双螺旋并且不积极参与凝胶的形成。因此，我们的模拟提供了结冷聚合的第一个完整的微观概述，并且对于未来将基于结冷的系统用于从食品科学到艺术修复的各种应用非常重要。