Institute of Automation and Electrometry, Siberian Branch of Russian Academy of Sciences, Novosibirsk 630090, Russia.
J Chem Phys. 2012 Aug 14;137(6):065103. doi: 10.1063/1.4739532.
Glycine phases formed when aqueous solutions were frozen and subsequently heated under different conditions were studied by Raman scattering, x-ray diffraction, and differential scanning calorimetry (DSC) techniques. Crystallization of ice I(h) was observed in all the cases. On cooling at the rates of 0.5 K∕min and 5 K∕min, glassy glycine was formed as an intermediate phase which lived about 1 min or less only, and then transformed into β-polymorph of glycine. Quench cooling of glycine solutions (15% w∕w) in liquid nitrogen resulted in the formation of a mixture of crystalline water ice I(h) and a glassy glycine, which could be preserved at cryogenic temperatures (80 K) for an indefinitely long time. This mixture remained also quite stable for some time after heating above the cryogenic temperature. Subsequent heating under various conditions resulted in the transformation of the glycine glass into an unknown crystalline phase (glycine "X-phase") at 209-216 K, which at 218-226 K transformed into β-polymorph of glycine. The "X-phase" was characterized by Raman spectroscopy; it could be obtained in noticeable amounts using a special preparation technique and tentatively characterized by x-ray powder diffraction (P2, a = 6.648 Å, b = 25.867 Å, c = 5.610 Å, β = 113.12[ordinal indicator, masculine]); the formation of "X-phase" from the glycine glassy phase and its transformation into β-polymorph were followed by DSC. Raman scattering technique with its power for unambiguous identification of the crystalline and glassy polymorphs without limitation on the crystallite size helped us to follow the phase transformations during quenching, heating, and annealing. The experimental findings are considered in relation to the problem of control of glycine polymorphism on crystallization.
当水溶液被冷冻并在不同条件下加热时，形成的甘氨酸相通过拉曼散射、X 射线衍射和差示扫描量热法（DSC）技术进行研究。在所有情况下都观察到冰 I(h)的结晶。在冷却速率为 0.5 K/min 和 5 K/min 时，形成玻璃态甘氨酸作为中间相，仅存活约 1 分钟或更短时间，然后转化为甘氨酸的 β-多晶型物。在液氮中淬火冷却甘氨酸溶液（15%w/w）导致形成结晶水冰 I(h)和玻璃态甘氨酸的混合物，该混合物可以在低温（80 K）下无限期保存。该混合物在加热超过低温后一段时间内也保持相当稳定。在各种条件下进一步加热导致甘氨酸玻璃在 209-216 K 下转化为未知的结晶相（甘氨酸“X-相”），该相在 218-226 K 下转化为甘氨酸的 β-多晶型物。“X-相”通过拉曼光谱进行表征；使用特殊的制备技术可以获得相当数量的“X-相”，并通过 X 射线粉末衍射（P2，a = 6.648 Å，b = 25.867 Å，c = 5.610 Å，β = 113.12[序数值，阳性]）进行初步表征；通过 DSC 跟踪甘氨酸玻璃相形成“X-相”及其向β-多晶型物的转变。拉曼散射技术具有在不限制晶粒尺寸的情况下明确识别结晶和玻璃多晶型物的能力，有助于我们在淬火、加热和退火过程中跟踪相变。实验结果考虑到控制甘氨酸结晶多晶型性的问题。
