Silk is a protein polymer composed of the polypeptide chains including the repeating units of glycine and alanine. Lac dye is composed mainly of two major anthraquinone based components: laccaic acids A and B. Previously, chitosan was reported and used to coat silk in the lac dyeing process for enhancing the uptake of lac dye on silk. Therefore, this work aims to explain why chitosan can help in lac dyeing process on silk by using molecular docking and molecular dynamics (MD) simulations. The molecular mechanics Poisson−Boltzmann surface area (MM-PBSA) analysis was also applied to calculate the binding free energy. The results revealed the attractive interaction between silk and chitosan. Moreover, an increasing unit of acetylglucosamine in the chitosan structure increases the binding interaction between silk and chitosan. After that, the binding between silk complexed with chitosan and laccaic acids A and B were reported. It was clearly found that the average of binding free energies between lac dyes and silk complexed with chitosan (−257.7 and −230.9 kJ/mol) was lower than those between lac dyes and silk without chitosan (−13.4 and −108.5 kJ/mol) indicating the better binding of lac dyes when chitosan is added on the silk surface. The obtained results can be explained why the existence of chitosan on silk surface could increase the binding of lac dyes. Therefore, this study can be used as a guideline in order to understand and improve the fastness properties of textiles.

丝是由包括甘氨酸和丙氨酸的重复单元的多肽链组成的蛋白质聚合物。Lac染料主要由两种主要的蒽醌基成分组成：laccaic acid A和B。以前，据报道，壳聚糖在lac染色过程中用于包覆丝绸，以增强丝绸上lac染料的吸收。因此，这项工作旨在解释为什么壳聚糖可以通过使用分子对接和分子动力学（MD）模拟来帮助丝绸上的lac染色过程。分子力学泊松-玻尔兹曼表面积（MM-PBSA）分析也用于计算结合自由能。结果表明丝绸和壳聚糖之间的吸引力相互作用。此外，壳聚糖结构中增加的乙酰氨基葡糖单元增加了丝与壳聚糖之间的结合相互作用。之后，据报道，与壳聚糖络合的蚕丝与lacacic酸A和B之间的结合。清楚地发现，紫胶染料与掺有壳聚糖的蚕丝之间的平均结合自由能（−257.7和−230.9 kJ / mol）低于紫胶染料与无壳聚糖的蚕丝之间的平均结合自由能（−13.4和−108.5 kJ / mol）表明当在丝绸表面添加壳聚糖时，紫胶染料具有更好的结合力。所获得的结果可以解释为什么在丝绸表面存在壳聚糖会增加lac染料的结合。因此，该研究可以用作指导，以了解和改善纺织品的牢度性能。9 kJ / mol）低于lac染料和不含壳聚糖的丝绸之间的相对介电常数（-13.4和-108.5 kJ / mol），表明当在丝绸表面添加壳聚糖时lac染料具有更好的结合力。所获得的结果可以解释为什么在丝绸表面存在壳聚糖会增加lac染料的结合。因此，该研究可以用作指导，以了解和改善纺织品的牢度性能。9 kJ / mol）低于lac染料和不含壳聚糖的丝绸之间的相对介电常数（-13.4和-108.5 kJ / mol），表明当在丝绸表面添加壳聚糖时lac染料具有更好的结合力。所获得的结果可以解释为什么在丝绸表面存在壳聚糖会增加lac染料的结合。因此，该研究可以用作指导，以了解和改善纺织品的牢度性能。