Exploring the solid state phase transition in dl-norvaline with terahertz spectroscopy.
Exploring the solid state phase transition in dl-norvaline with terahertz spectroscopy.
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用太赫兹光谱探索 dl-正缬氨酸的固态相变。
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
C. Schmuttenmaer
中科院分区：
文献类型：
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作者：
J. Neu;Coleen T Nemes;K. Regan;Michael R. C. Williams;C. Schmuttenmaer
dl-正缬氨酸在室温下为分子晶体，当冷却到190k以下时发生相变。这种相变被认为是马氏体的，因此对分子机器特别感兴趣。在本文中，我们通过测量其在一定温度范围内的太赫兹（THz）频谱来研究这种相变。温度相关的太赫兹时域光谱（THz- tds）测量表明，转变温度（Tβ→α）为190 K。通过测定不同晶粒尺寸分子晶体的Tβ→α，分析了成核种子的影响。与125 ~ 250 μm晶粒（Tβ→α = 190 K）相比，5 μm以下晶粒的转变温度（Tβ→α = 180 K）较低。此外，我们通过掺杂和混合分子晶体的温度依赖的太赫兹- tds光谱深入了解了相变的物理过程。分子掺杂剂与dl-正缬氨酸的不同之处在于其侧链末端位于晶体的疏水层中，其加入降低了Tβ→α。这与单位细胞沿疏水层移动的固-固相变相一致，这使我们相信dl-正缬氨酸的相变本质上是马氏体相变。
dl-Norvaline is a molecular crystal at room temperature and it undergoes a phase transition when cooled below 190 K. This phase transition is believed to be Martensitic, thus making it of particular interest for molecular machines. In this paper we investigate this phase transition by measuring its terahertz (THz) spectrum over a range of temperatures. Temperature-dependent THz time-domain spectroscopy (THz-TDS) measurements reveal that the transition temperature (Tβ→α) is 190 K. The influence of nucleation seeds was analyzed by determining the Tβ→α of molecular crystals with varying grain size. Grains of 5 μm or less result in a lower transition temperature (Tβ→α = 180 K) compared to larger grains of 125-250 μm (Tβ→α = 190 K). Additionally, we gain insight into the physical process of the phase transition via temperature-dependent THz-TDS spectra of doped and mixed molecular crystals. The addition of molecular dopants, which differ from dl-norvaline only at the end of the side chain which resides in the hydrophobic layers of the crystal, decreases Tβ→α. This is consistent with a solid-solid phase transition in which the unit cell shifts along this hydrophobic layer, and it leads us to believe that the phase transition in dl-norvaline is Martensitic in nature.