ACS Biomater Sci Eng. 2020 Jan 13;6(1):298-307. doi: 10.1021/acsbiomaterials.9b01101. Epub 2019 Oct 25.
Chitosan is a natural polycationic linear polysaccharide deacetylated from chitin. Glycol chitosan is a derivative of chitosan and has been extensively investigated in the biomaterials and hydrogel field for many bioengineering applications because of their unique material and biological properties. However, the molecular structure and network of glycol chitosan hydrogels remain unclear. Here, we explored the molecular structures and network of glycol chitosan with different protonation percentages by using full atomistic simulations. Hydrogel and xerogel models are constructed to understand the interactions between the water molecules and glycol chitosan chains. We calculated the radius of gyration and radial distribution function of hydrogel and xerogel models to understand the swelling behavior from molecular level. We find that when the pH is close to neutral and becomes basic, greater flexibility of glycol chitosan chains leads to a high swelling ratio. The slight contracting behavior of glycol chitosan chains and the dispersive distribution above 40% protonation can be interpreted to indicate a poor swelling ratio. The protonated amino groups inhibit the hydrogen-bond formation between water molecules and adjacent oxygen-containing groups of glycol chitosan main chains. On the other hand, the glycol groups of glycol chitosan are not affected by the electrostatic interaction, and the number of hydrogen bonds between glycol groups and water molecules does not vary with pH. The van der Waals interaction between glycol chitosan chains is dominant when the protonation percentages are lower than 40%, while the electrostatic interaction of amino groups is dominant when the protonation percentages are higher than 40%. Our results explain the effects of pH on the molecular structures of glycol chitosan and provide useful information regarding the design strategy of novel glycol chitosan and its derivatives for biomedical applications.
壳聚糖是一种从甲壳素中脱乙酰化得到的天然聚阳离子线性多糖。乙二醇壳聚糖是壳聚糖的衍生物，由于其独特的材料和生物学特性，在生物材料和水凝胶领域得到了广泛的研究，用于许多生物工程应用。然而，乙二醇壳聚糖水凝胶的分子结构和网络仍不清楚。在这里，我们通过使用全原子模拟探索了不同质子化率的乙二醇壳聚糖的分子结构和网络。构建水凝胶和干凝胶模型，以了解水分子与乙二醇壳聚糖链之间的相互作用。我们计算了水凝胶和干凝胶模型的旋转半径和径向分布函数，以从分子水平理解溶胀行为。我们发现，当 pH 值接近中性并变为碱性时，乙二醇壳聚糖链的更大灵活性导致高溶胀比。在质子化率高于 40%时，乙二醇壳聚糖链的轻微收缩行为和分散分布可以解释为低溶胀比。质子化的氨基基团抑制水分子与乙二醇壳聚糖主链相邻含氧基团之间氢键的形成。另一方面，乙二醇壳聚糖的乙二醇基团不受静电相互作用的影响，并且乙二醇基团与水分子之间氢键的数量不随 pH 值而变化。当质子化率低于 40%时，乙二醇壳聚糖链之间的范德华相互作用占主导地位，而当质子化率高于 40%时，氨基基团的静电相互作用占主导地位。我们的结果解释了 pH 值对乙二醇壳聚糖分子结构的影响，并为新型乙二醇壳聚糖及其衍生物在生物医学应用中的设计策略提供了有用的信息。
