结冷胶聚集两步机理的分子起源
Molecular origin of the two-step mechanism of gellan aggregation
摘要：
在水胶体中，结冷胶是最常用的阴离子多糖之一，因为其能够在相对低的浓度下形成机械稳定的凝胶。尽管其长期的使用和重要性，结冷胶的聚集机制仍然没有在微观水平上理解，由于缺乏原子信息。在这里，我们将填补这一空白，报告分子动力学模拟结冷链在不同的聚合物和盐的含量，能够揭示发生的两个步骤的过程中，与现有的假设。首先，发生双螺旋的形成，随后聚集成超结构。对于这两个步骤，二价阳离子的作用似乎是至关重要的，也显示了流变学和原子力显微镜测量：它们不仅有利于连接的链成双螺旋，但也促进通过桥接它们的安排成较大的聚集体。另一方面，一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能形成双螺旋，而不会积极参与凝胶的形成。因此，我们的模拟提供了第一个完整的结冷胶聚集的微观概述，并将是重要的结冷胶为基础的系统，用于各种各样的应用，从食品科学到艺术修复的未来使用。
英文摘要：
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.
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