Synthesis, characterization and molecular dynamics simulation of layered double hydroxides intercalated with aspartic acid
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摘要:
传统实验手段在水滑石超分子结构与水合膨胀性能研究上存在不足，无法得知层间阴离子排布形态以及结构水分子的信息。采用共沉淀法和离子交换法两种方法合成了天冬氨酸插层镁铝水滑石，用X射线粉末衍射、差热分析、红外光谱表征了水滑石前驱体及其与天冬氨酸插层复合材料的结构，并用Materials Studio软件分子动力学模拟方法对复合材料的微观结构和水合特性进行研究。制得的复合材料层状结构规整、晶相单一，天冬氨酸插层后其层间距从0.84 nm增至1.13~1.17 nm；插层后天冬氨酸的热分解温度由249 ℃升高至334 ℃，其热稳定性大大提高。通过复合材料结构分子动力学模拟得到水滑石层间阴离子的分布状态以及水分子的结合状况。实验所得插层后水滑石层间距与分子动力学模拟结果水分子与天冬氨酸比(Nw)为3~4时接近；水滑石层间水分子数量越多，层间距越大；水合能逐渐呈增大趋势，且趋于一定值；水合过程层板与阴离子间氢键数量减少，而层板与水分子间氢键增多，总氢键数逐渐增多。通过模拟所得结果与实验结论接近，可为水滑石基药物复合材料设计合成奠定基础。
Abstract:Traditional experimental methods are insufficient in the study of layered double hydroxides (LDHs) supramolecular structure and hydration expansion performance, and information on interlayer anionic arrangement and structural water molecules cannot be obtained. Aspartic acid intercalated magnesium aluminum hydrotalcite was synthesized using coprecipitation and ion exchange. The structure of hydrotalcite precursor and its aspartic acid composite materials was characterized by X-ray powder diffraction, differential thermal analysis, and infrared spectroscopy, and Materials Studio software was used to simulate the molecular dynamics of microstructure and hydration properties of LDHs intercalated with the aspartic acid drug. The prepared composite material had a regular layered structure and a single crystal phase. After intercalation with aspartic acid, the interlayer spacing increased from 0.84 nm to 1.13−1.17 nm; after intercalation, the thermal decomposition temperature of aspartic acid increased from 249 °C to 334 °C, greatly improving its thermal stability. The interlayer spacing of the intercalated hydrotalcite obtained from the experiment was close to the molecular dynamics simulation results when Nw=3−4. As more water molecules were inserted between the layers, the greater the interlayer distance became. Hydration energy increased gradually and tended to a certain value. The total number of hydrogen bonds increased gradually, the hydrogen bonds between laminates and anions decreased gradually, but the hydrogen bonds between laminates and water molecules increased gradually. The simulation results are close to the experimental results, which can lay a foundation for the design and synthesis of LDHs-based drug composites.
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Figure 1. Initial layer model of magnesium aluminum layered double hydroxides (LDHs)
Green ball: Mg; Peach ball:Al; Red ball:O;White ball:H
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Figure 2. Picture of chloride intercalated magnesium aluminum layered double hydroxides (Mg3Al-Cl-LDHs) structure optimized
A：Side view; B:Top view
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Figure 3. NPT dynamic model of aspartic acid intercalated layered double hydroxides (Mg3Al-Asp-LDHs) after simulation
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Figure 5. DTA patterns of LDHs-Asp(ie) (a), LDHs-Asp(co) (b), Asp (c), and LDHs-NO3− (d)
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Figure 6. FTIR patterns of LDHs-NO3− (a), LDHs-Asp(ie) (b), LDHs-Asp(co) (c), and Asp (d)
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Figure 7. Molecular dynamic simulation results of Mg3Al-Asp-nH2O-LDHs models
Green ball: Mg; Peach ball:Al; Red ball:O;White ball:H; Blue ball:N
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