目的:阐明具有不同糖苷键的胶凝葡聚糖的溶胶-凝胶转变的微观机理对于理解它们的结构-性质关系和各种应用至关重要。具有不同分子链结构的葡聚糖表现出独特的凝胶化行为。在两种甲基化葡聚糖中观察到的不同的凝胶现象,Culdlan(MECD)的甲基化(1,3)-β-d-葡聚糖和纤维素(MC)的甲基化(1,4)-β-d-葡聚糖,尽管它们的替代程度相当,与它们独特的分子结构以及葡聚糖和水之间的相互作用密切相关。
方法:密度泛函理论和分子动力学模拟集中于MECD和MC之间的电子性质差异,伴随着热凝胶化过程中的构象变化。在线衰减全反射傅里叶变换红外光谱跟踪MECD和MC的二级结构变化。为了证实模拟结果,其他分析,包括圆二色性,流变学,和微量差示扫描量热法。
结果:尽管具有相似的热诱导凝胶网络,MECD和MC在凝胶化过程中显示出不同的物理凝胶化模式和分子水平的构象变化。MC凝胶网络是通过“线圈到环”过渡形成的,其次是环形堆叠。相比之下,MECD凝胶包含紧密的不规则螺旋,并伴有明显的体积收缩。凝胶化行为的这些变化归因于加热后两个系统中疏水相互作用的增强和氢键的减少。导致凝胶化。这些发现为凝胶化过程中的微观结构变化和结构相似的多糖的热凝胶化机理提供了有价值的见解。
OBJECTIVE: Elucidation of the micro-mechanisms of sol-gel transition of gelling glucans with different glycosidic linkages is crucial for understanding their structure-property relationship and for various applications. Glucans with distinct molecular chain structures exhibit unique
gelation behaviors. The disparate
gelation phenomena observed in two methylated glucans, methylated (1,3)-β-d-glucan of curdlan (MECD) and methylated (1,4)-β-d-glucan of cellulose (MC), notwithstanding their equivalent degrees of substitution, are intricately linked to their unique molecular architectures and interactions between glucan and water.
METHODS: Density functional theory and molecular dynamics simulations focused on the electronic property distinctions between MECD and MC, alongside conformational variations during thermal gelation. Inline attenuated total reflection Fourier transform infrared spectroscopy tracked secondary structure alterations in MECD and MC. To corroborate the simulation results, additional analyses including circular dichroism, rheology, and micro-differential scanning calorimetry were performed.
RESULTS: Despite having similar thermally induced gel networks, MECD and MC display distinct physical gelation patterns and molecular-level conformational changes during
gelation. The network of MC gel was formed via a \"coil-to-ring\" transition, followed by ring stacking. In contrast, the MECD gel comprised compact irregular helices accompanied by notable volume shrinkage. These variations in gelation behavior are ascribed to heightened hydrophobic interactions and diminished hydrogen bonding in both systems upon heating, resulting in
gelation. These findings provide valuable insights into the microstructural changes during
gelation and the thermo-
gelation mechanisms of structurally similar polysaccharides.