Ruggiero Michael T, Sibik Juraj, Zeitler J Axel, Korter Timothy M
Department of Chemistry, Syracuse University , 1-014 Center for Science and Technology, Syracuse, New York 13244-4100, United States.
Department of Chemical Engineering and Biotechnology, University of Cambridge , New Museums Site, Pembroke Street, Cambridge CB2 3RA, United Kingdom.
J Phys Chem A. 2016 Sep 29;120(38):7490-5. doi: 10.1021/acs.jpca.6b05702. Epub 2016 Sep 19.
The ability of l-glutamic acid to crystallize in two different forms has long been the subject of study due to its commercial importance. While a solvent-mediated phase transformation between the α and β polymorphs is the prevailing theory, recent reports indicate a thermal solid-solid transformation between the two may be possible. However, determining accurate thermodynamic stabilities of these crystals has been challenging. Here new low-temperature single-crystal X-ray diffraction data coupled to solid-state density functional theory simulations have enabled a detailed description to be achieved for the energetic parameters governing the stabilization of the two l-glutamic acid solids. The temperature-dependent Gibbs free-energy curves show that α-glutamic acid is the preferred form at low temperatures (<222 K) and the β form is most stable at ambient temperatures. Terahertz time-domain spectroscopy was utilized to evaluate the quality of the intermolecular force modeling as well as to provide characteristic low-frequency spectral data that can be used for quantification of polymorph mixtures or crystal growth monitoring.
由于L-谷氨酸在商业上的重要性，其以两种不同形式结晶的能力长期以来一直是研究的主题。虽然α和β多晶型物之间的溶剂介导相变是主流理论，但最近的报告表明两者之间可能存在热固-固转变。然而，确定这些晶体准确的热力学稳定性一直具有挑战性。在这里，新的低温单晶X射线衍射数据与固态密度泛函理论模拟相结合，使得能够详细描述控制两种L-谷氨酸固体稳定性的能量参数。温度依赖性吉布斯自由能曲线表明，α-谷氨酸在低温（<222 K）下是优选形式，而β形式在环境温度下最稳定。太赫兹时域光谱被用于评估分子间力建模的质量，并提供可用于多晶型混合物定量或晶体生长监测的特征低频光谱数据。
