Singh Ratna, Smiatek Jens, Moerschbacher Bruno M
Institute for Biology and Biotechnology of Plants, University of Münster, Schlossplatz 8, 48143 Münster, Germany.
Institute for Computational Physics, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany.
Int J Mol Sci. 2023 Sep 7;24(18):13792. doi: 10.3390/ijms241813792.
Chitosans are partially acetylated polymers of glucosamine, structurally characterized by their degree of polymerization as well as their fraction and pattern of acetylation. These parameters strongly influence the physico-chemical properties and biological activities of chitosans, but structure-function relationships are only poorly understood. As an example, we here investigated the influence of acetylation on chitosan-copper complexation using density functional theory. We investigated the electronic structures of completely deacetylated and partially acetylated chitosan oligomers and their copper-bound complexes. Frontier molecular orbital theory revealed bonding orbitals for electrophiles and antibonding orbitals for nucleophiles in fully deacetylated glucosamine oligomers, while partially acetylated oligomers displayed bonding orbitals for both electrophiles and nucleophiles. Our calculations showed that the presence of an acetylated subunit in a chitosan oligomer affects the structural and the electronic properties of the oligomer by generating new intramolecular interactions with the free amino group of neighboring deacetylated subunits, thereby influencing its polarity. Furthermore, the band gap energy calculated from the fully and partially deacetylated oligomers indicates that the mobility of electrons in partially acetylated chitosan oligomers is higher than in fully deacetylated oligomers. In addition, fully deacetylated oligomers form more stable complexes with higher bond dissociation energies with copper than partially acetylated ones. Interestingly, in partially acetylated oligomers, the strength of copper binding was found to be dependent on the pattern of acetylation. Our study provides first insight into the influence of patterns of acetylation on the electronic and ion binding properties of chitosans. Depending on the intended application, the obtained results can serve as a guide for the selection of the optimal chitosan for a specific purpose.
壳聚糖是葡糖胺的部分乙酰化聚合物，其结构特征在于聚合度以及乙酰化的比例和模式。这些参数强烈影响壳聚糖的物理化学性质和生物活性，但结构 - 功能关系却知之甚少。例如，我们在此使用密度泛函理论研究了乙酰化对壳聚糖 - 铜络合的影响。我们研究了完全脱乙酰化和部分乙酰化的壳聚糖低聚物及其与铜结合的络合物的电子结构。前沿分子轨道理论揭示了完全脱乙酰化的葡糖胺低聚物中亲电试剂的成键轨道和亲核试剂的反键轨道，而部分乙酰化的低聚物则同时显示了亲电试剂和亲核试剂的成键轨道。我们的计算表明，壳聚糖低聚物中乙酰化亚基的存在通过与相邻脱乙酰化亚基的游离氨基产生新的分子内相互作用来影响低聚物的结构和电子性质，从而影响其极性。此外，由完全和部分脱乙酰化的低聚物计算出的带隙能量表明，部分乙酰化壳聚糖低聚物中电子的迁移率高于完全脱乙酰化的低聚物。另外，完全脱乙酰化的低聚物与铜形成的络合物比部分乙酰化的低聚物具有更高的键解离能，因而更稳定。有趣的是，在部分乙酰化的低聚物中，发现铜结合的强度取决于乙酰化模式。我们的研究首次深入了解了乙酰化模式对壳聚糖电子和离子结合特性的影响。根据预期应用，所得结果可为特定目的选择最佳壳聚糖提供指导。
