Kapustin E A, Minkov V S, Boldyreva E V
Novosibirsk State University, Pirogov street, 2, Novosibirsk 630090, Russian Federation.
Phys Chem Chem Phys. 2015 Feb 7;17(5):3534-43. doi: 10.1039/c4cp05094k. Epub 2014 Dec 23.
The crystal structures of N-methyl derivatives of the simplest amino acid glycine, namely sarcosine (C3H7NO2) and betaine (C5H11NO2), were studied upon cooling by single-crystal X-ray diffraction and single-crystal polarized Raman spectroscopy. The effects of decreasing temperature and increasing hydrostatic pressure on the crystal structures were compared. In particular, we have studied the behavior upon cooling of those structural motifs in the crystals, which are involved in structural rearrangement during pressure-induced phase transitions. In contrast to their high sensitivity to hydrostatic compression, the crystals of both sarcosine and betaine are stable to cooling down to 5 K. Similarly to most α-amino acids, the crystal structures of the two compounds are most rigid upon cooling in the direction of the main structural motif, namely head-to-tail chains (linked via the strongest N-H···O hydrogen bonds and dipole-dipole interactions in the case of sarcosine, or exclusively by dipole-dipole interactions in the case of betaine). The anisotropy of linear strain in betaine does not differ much upon cooling and on hydrostatic compression, whereas this is not the case for sarcosine. Although the interactions between certain structural motifs in sarcosine and betaine weaken as a result of phase transitions induced by pressure, the same interactions strengthen when volume reduction results from cooling.
通过单晶X射线衍射和单晶偏振拉曼光谱，研究了最简单的氨基酸甘氨酸的N-甲基衍生物，即肌氨酸（C3H7NO2）和甜菜碱（C5H11NO2）在冷却时的晶体结构。比较了温度降低和静水压力增加对晶体结构的影响。特别地，我们研究了晶体中那些在压力诱导的相变过程中参与结构重排的结构基序在冷却时的行为。与它们对静水压缩的高敏感性相反，肌氨酸和甜菜碱的晶体在冷却至5 K时都是稳定的。与大多数α-氨基酸类似，这两种化合物的晶体结构在沿主要结构基序方向冷却时最为刚性，即头对尾链（在肌氨酸的情况下通过最强的N-H···O氢键和偶极-偶极相互作用连接，或在甜菜碱的情况下仅通过偶极-偶极相互作用连接）。甜菜碱中线性应变的各向异性在冷却和静水压缩时变化不大，而肌氨酸则不然。尽管肌氨酸和甜菜碱中某些结构基序之间的相互作用由于压力诱导的相变而减弱，但当冷却导致体积减小时，相同的相互作用会增强。
