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Molecular mechanisms for the adhesion of chitin and chitosan to montmorillonite clay

机译：甲壳素和壳聚糖粘附到蒙脱石粘土的分子机制

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Molecular dynamics simulations have been performed to investigate molecular adhesion of chitin and chitosan oligomers to montmorillonite (Mnt) clay at different degrees of acetylation (DA, 0%, 20%, 40%, 60%, 80% and 100%) and different degree of protonation (DPr, 0%, 50%, 100% mimicking pH > 6.5, pH = 6.5, pH < 4, respectively) under fully hydrated conditions. Although the Mnt surface is negatively charged and a variation in DA also implies going from a positively charged oligomer at DA = 0% to a neutral oligomer at DA = 100%, the simulations show unexpectedly small variation of the total molecular adhesion as a function of DA. From our analysis we propose that this quantitatively similar adhesion arises from two different mechanisms. At low DA, the oligomer is rich in positively charged amino groups interacting strongly with the negatively charged surface by direct electrostatic interaction. On the other hand, at high DA, electrically neutral acetyl groups are strongly correlated with the Na ~(+) counter ions, which are in all cases stuck at the surface and the counter ions seem to act as ‘glue’ between the acetyl groups and the Mnt. However, when protonation was decreased, adhesion was affected and significantly lowered at neutral conditions (DPr = 0%). The reason is concluded to be differences in charge distributions of the respective functional groups. A further investigation on the intramolecular hydrogen bonds formed in CHT or CHS shows that the adsorbed conformation of the polymer is also highly affected by DA. This work provides fundamental insights into adhesion mechanisms and is of potential importance for the development of polymer–clay based composite materials.
机译：已经进行了分子动力学模拟，以研究丁蛋白和壳聚糖低聚物在不同乙酰化（DA，0％，20％，40％，60％，80％和100％）和不同程度下的甲藻和壳聚糖低聚物对甲状腺炎酸盐（MNT）粘土的分子粘附质子化（DPR，0％，50％，100％模拟PH> 6.5，pH = 6.5，pH = 6.5，pH <4，pH <4，分别）在完全水合条件下。虽然MnT表面是带负电的，并且DA的变化也意味着从DA = 0％的带正电荷的低聚物在DA = 100％的中性低聚物上，模拟显示出总分子粘附的常量变化达。根据我们的分析，我们提出了这种定量类似的粘附，产生了两种不同的机制。在低DA时，低聚物通过直接静电相互作用与带负电的表面相互作用的正电荷的氨基富含正电荷的氨基。另一方面，在高DA中，电中性乙酰基与Na〜（+）抗衡离子强烈相关，在所有情况下都卡在表面上，抗衡离子似乎充当乙酰基之间的“胶水”和mnt。然而，当质子化减少时，在中性条件下受到粘附并显着降低（DPR = 0％）。结论原因是各种官能团的电荷分布差异。进一步研究CHT或CHS中形成的分子内氢键，表明聚合物的吸附构象也受到DA的高度影响。这项工作为粘附机制提供了根本的见解，并且对聚合物 - 粘土的复合材料的发展具有潜在的重要性。

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