Hyaluronic acid (hyaluronan, HA) is a negatively charged polysaccharide forming highly swollen random coils in aqueous solutions. Their size decreases along with growing salt concentration, but the mechanism of this phenomenon remains unclear. We carry out molecular-dynamics simulations of a 48-monosaccharide HA oligomer in varying salt concentration and temperature. They identify the interaction points of Na+ ions with the HA chain and reveal their influence on the HA solvation-shell structure. The salt-dependent variation of the molecular size does not consist in the distribution of the dihedral angles of the glycosidic connections but is driven by the random flips of individual dihedral angles, which cause the formation of temporary hairpin-like structures effectively shortening the chain. They are induced by the frequency of cation-chain interactions that grow with the salt concentration, but is reduced by the simultaneous decrease of ions' activities. This leads to an anomalous random-coil shrinkage at 0.6 M salt concentration.

中文翻译：

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溶剂和离子对透明质酸分子结构和动力学的影响。

透明质酸（hyaluronan，HA）是带负电荷的多糖，在水溶液中形成高度溶胀的无规卷曲。它们的大小随着盐浓度的增加而减小，但是这种现象的机理仍不清楚。我们在盐浓度和温度变化的情况下，对48种单糖HA低聚物进行了分子动力学模拟。他们确定了Na +离子与HA链的相互作用点，并揭示了它们对HA溶剂化壳结构的影响。分子大小的盐依赖性变化不在于糖苷连接的二面角的分布，而是由各个二面角的随机翻转驱动的，这导致形成临时发夹状结构，从而有效地缩短了链。它们是由与盐浓度成正比的阳离子-链相互作用的频率诱导的，但是由于离子活性的同时降低而降低。这导致盐浓度为0.6 M时，随机线圈收缩异常。