Covalently linked hydrogen bond donors: The other side of molecular frustration in deep eutectic solvents
Covalently linked hydrogen bond donors: The other side of molecular frustration in deep eutectic solvents
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DOI：
10.1063/5.0058165
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发表时间：
2021-08-28
影响因子：
4.4
通讯作者：
Wagle, Durgesh V.
中科院分区：
文献类型：
--
作者：
Recker, Elizabeth A.;Hardy, David;Wagle, Durgesh V.
在这项工作中，我们研究了氢键供体物种之间的单一共价键对深共晶溶剂(DESS)行为的影响，并揭示了由此产生的分子水平上的相互作用，这些相互作用影响了DES体系的整体物理性质。我们比较了糖基DES混合物，1：2氯化胆碱/葡萄糖[DES(G)]和1：1氯化胆碱/海藻糖[DES(T)]。海藻糖是一种由两个葡萄糖单元通过α-1，4-糖苷键相连的二糖，因此它是与含葡萄糖的DES(G)进行比较的理想候选者。差示扫描量热分析表明，这些化学封闭的DES体系在相变行为上存在显著差异。DES(G)的玻璃化转变温度为-58℃，在较高温度下表现为流体行为，而DES(T)在-11℃下表现出边缘相变行为，在较高温度下相行为没有变化。模拟表明，DES(T)中糖单元之间的糖苷键的存在阻碍了海藻糖中糖单元的自由移动，因此与DES(G)中的游离葡萄糖分子相比，与氯化胆碱的相互作用次数减少。在分子分析中使用原子的量子理论进一步证实了这一点，分子分析涉及到使用电子密度的拉普拉斯来确定键临界点(BCP)。分析表明，与DES(T)相比，DES(G)中氯化胆碱和糖之间的BCP数量明显更多。与DES(T)相比，DES(G)表现出更高的胆碱阳离子与糖之间的电荷转移，以及更好的相互作用能和生成热。这是由于游离葡萄糖分子能够完全包围DES(G)中的氯化胆碱并形成更多的相互作用。DES(T)的生成熵略高于DES(G)，这是由于海藻糖与氯化胆碱相互作用较少所致。总之，海藻糖中糖单元之间的糖苷键的存在限制了它们的运动，从而导致与氯化胆碱的相互作用较少。这种有限的运动反过来降低了氢键供体破坏氢键受体晶格结构中分子堆积的能力(反之亦然)，这是降低DES混合物熔点的关键因素。由于海藻糖中存在糖苷键而无法移动，这显著影响了DES(T)体系的物理状态，使其表现为半固态材料，而DES(G)在室温下表现为液体材料。
In this work, we investigated the effects of a single covalent link between hydrogen bond donor species on the behavior of deep eutectic solvents (DESs) and shed light on the resulting interactions at molecular scale that influence the overall physical nature of the DES system. We have compared sugar-based DES mixtures, 1:2 choline chloride/glucose [DES(g)] and 1:1 choline chloride/trehalose [DES(t)]. Trehalose is a disaccharide composed of two glucose units that are connected by an alpha-1,4-glycosidic bond, thus making it an ideal candidate for comparison with glucose containing DES(g). The differential scanning calorimetric analysis of these chemically close DES systems revealed significant difference in their phase transition behavior. The DES(g) exhibited a glass transition temperature of -58 degrees C and behaved like a fluid at higher temperatures, whereas DES(t) exhibited marginal phase change behavior at -11 degrees C and no change in the phase behavior at higher temperatures. The simulations revealed that the presence of the glycosidic bond between sugar units in DES(t) hindered free movement of sugar units in trehalose, thus reducing the number of interactions with choline chloride compared to free glucose molecules in DES(g). This was further confirmed using quantum theory of atoms in molecule analysis that involved determination of bond critical points (BCPs) using Laplacian of electron density. The analysis revealed a significantly higher number of BCPs between choline chloride and sugar in DES(g) compared to DES(t). The DES(g) exhibited a higher amount of charge transfer between the choline cation and sugar, and better interaction energy and enthalpy of formation compared to DES(t). This is a result of the ability of free glucose molecules to completely surround choline chloride in DES(g) and form a higher number of interactions. The entropy of formation for DES(t) was slightly higher than that for DES(g), which is a result of fewer interactions between trehalose and choline chloride. In summary, the presence of the glycosidic bond between the sugar units in trehalose limited their movement, thus resulting in fewer interactions with choline chloride. This limited movement in turn diminishes the ability of the hydrogen bond donor to disrupt the molecular packing within the lattice structure of the hydrogen bond acceptor (and vice versa), a crucial factor that lowers the melting point of DES mixtures. This inability to move due to the presence of the glycosidic bond in trehalose significantly influences the physical state of the DES(t) system, making it behave like a semi-solid material, whereas DES(g) behaves like a liquid material at room temperature.