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首页> 外文期刊>Crystal growth & design >Leapfrogging Ostwald's rule of stages: Crystallization of stable γ-glycine directly from microemulsions
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Leapfrogging Ostwald's rule of stages: Crystallization of stable γ-glycine directly from microemulsions

机译：跨越奥斯特瓦尔德的阶段法则：直接从微乳液中结晶稳定的γ-甘氨酸

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Crystallization of glycine from aqueous Span 80 (sorbitan monooleate) /Brij 30 (polyethylene glycol dodecyl ether) and AOT (sodium dioctyl sulfosuccinate) microemulsions by adding the antisolvent methanol has been studied as a function of increasing initial supersaturation. All three polymorphs of glycine obtainable at ambient pressure could be crystallized using the Span 80/Brij 30 microemulsions. Crystallization in the Span 80/Brij 30 microemulsions only occurred at initial supersaturations that were significantly higher than those required for glycine crystallization in bulk solution. Crystallization of the most stable γ-glycine polymorph was achieved when crystallization was only just possible in these microemulsions, corresponding to mean initial supersaturation ratios, (c/c_(sat))_(initial), of 2.3 with respect to γ-glycine. The γ-glycine crystallization occurred even though the water, the methanol, and the surfactants, Span 80 and Brij 30, favored crystallization of the metastable α- and β-polymorphs and despite the glycine solutions being highly supersaturated initially with respect to all three polymorphs. The γ-glycine crystallization arises because crystallization is brought under thermodynamic control under conditions where crystallization is only just possible in the microemulsions. With (c/c _(sat))_(initial) ≈ 2.6 and above, the α- and β-polymorphs became the dominant products in the Span 80/Brij 30 microemulsions for methanol/water mass ratios of 2:1 and 3.8:1, respectively. In contrast, microemulsions stabilized with AOT, which is known to aid γ-glycine crystallization at planar interfaces, led to γ-glycine crystallization at a much lower (c/c_(sat))_(initial) of 1.2. The nonionic Span 80/Brij 30 surfactants were less able to induce nucleation of the metastable forms in the microemulsions due to the high interfacial curvature and ultralow interfacial tension that hindered glycine adsorption at the surfactant interface. The longer range electrostatic interactions in the AOT system, however, could still operate effectively to aid the crystallization of polar γ-glycine.
机译：通过添加抗溶剂甲醇，研究了Span 80（脱水山梨糖醇单油酸酯）/ Brij 30（聚乙二醇十二烷基醚）和AOT（二辛基磺基琥珀酸钠）微乳液中甘氨酸的结晶，该作用与增加初始过饱和度有关。在室温下可获得的甘氨酸的所有三种多晶型物都可以使用Span 80 / Brij 30微乳液进行结晶。 Span 80 / Brij 30微乳液的结晶仅在初始过饱和时发生，该过饱和度明显高于本体溶液中甘氨酸结晶所需的过饱和度。当仅在这些微乳液中仅可能结晶时，就可以实现最稳定的γ-甘氨酸多晶型物的结晶，这对应于相对于γ-甘氨酸为2.3的平均初始过饱和率（c / c_（sat））_（initial）。尽管水，甲醇和表面活性剂Span 80和Brij 30有利于亚稳态α-和β-多晶型物的结晶，但尽管甘氨酸溶液最初相对于所有三种多晶型物都高度过饱和，但仍发生γ-甘氨酸结晶。 。 γ-甘氨酸结晶的产生是因为在仅微乳液中仅可能结晶的条件下将结晶置于热力学控制下。当（c / c _（sat））_（初始）≈2.6或更高时，对于甲醇/水质量比为2：1和3.8的Span 80 / Brij 30微乳液，α和β多晶型物成为主要产物。 ：1。相反，已知用AOT稳定的微乳液有助于平面界面上的γ-甘氨酸结晶，导致γ-甘氨酸的结晶度低得多（c / c_（sat））_（初始）1.2。非离子型Span 80 / Brij 30表面活性剂由于高的界面曲率和超低的界面张力阻碍了甘氨酸在表面活性剂界面的吸附，因此在微乳状液中诱导亚稳态形式的成核的能力较弱。然而，在AOT系统中，更长距离的静电相互作用仍然可以有效地帮助极性γ-甘氨酸的结晶。

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