X-ray Raman scattering: a new in situ probe of molecular structure during nucleation and crystallization from liquid solutions
X-ray Raman scattering: a new in situ probe of molecular structure during nucleation and crystallization from liquid solutions
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DOI：
10.1039/c8ce00929e
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发表时间：
2018-11-21
期刊：
影响因子：
3.1
通讯作者：
Schroeder, Sven L. M.
中科院分区：
文献类型：
--
作者：
Al-Madhagi, Laila H.;Chang, Sin-Yuen;Schroeder, Sven L. M.
用X射线拉曼散射(XRS)原位探测了冷却结晶过程中溶液中溶质分子的形态。测量了咪唑水溶液的C和N K边随温度的变化，以监测从不饱和状态到过饱和到结晶的转变。使用了一种新的夹套容器结晶器，具有内部流动，能够实现热控制并将辐射损害降至最低。我们证明了咪唑的C和N K边对局域键的变化很敏感。与此相一致，N-K边精细结构的突变表明过饱和溶液开始解溶和结晶。相反，在冷却过程中观察到的C和N K边光谱的变化可以忽略不计，这表明咪唑分子周围的平均溶剂化结构在穿过热力学亚稳态过饱和区时没有显著变化。据我们所知，这是第一次用X射线拉曼散射来研究结晶过程中有机水溶液中的分子形态。用含时密度泛函理论(TD-DFT)对水分子的近边光谱进行了隐式、显式和组合溶剂化模型的计算，以阐明水分子可能的结合位置。用一个水分子配位咪唑环上每个氮基的显式溶剂化模型精确地再现了咪唑水溶液的XRS谱峰位置和强度。
X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization. The C and N K-edges of aqueous imidazole were measured as a function of temperature to monitor the transition from the undersaturated state through supersaturation to crystallization. A new jacketed-vessel crystallizer with internal flow was used, which enables thermal control and minimizes radiation damage. We have demonstrated that the C and N K-edges of imidazole are sensitive to changes in local bonding. In line with this, an abrupt change in the N K-edge fine structure indicates the onset of desolvation and crystallization from the supersaturated solution. In contrast, negligible changes are observed in the C and N K-edge spectra acquired during cooling, indicating that the average solvation structure around imidazole molecules does not change significantly while traversing the thermodynamically metastable supersaturated zone. To the best of our knowledge this is the first time X-ray Raman scattering has been used for studying molecular speciation in organic aqueous solutions during crystallization. Time-dependent density functional theory (TD-DFT) calculations of the near-edge spectra were performed using implicit, explicit and combined solvation models to elucidate the likely binding sites of the water molecules. An explicit solvation model with one water molecule coordinating each nitrogen moiety in the imidazole ring accurately reproduces the peak positions and intensities of the XRS spectra of aqueous imidazole solution.