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首页> 外文期刊>Crystal growth & design >The Rich Solid-State Phase Behavior of L-Phenylalanine: Disappearing Polymorphs and High Temperature Forms
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The Rich Solid-State Phase Behavior of L-Phenylalanine: Disappearing Polymorphs and High Temperature Forms

机译：L-苯丙氨酸的富含固态相行为：消失多晶型物和高温形式

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摘要

After years of controversy over the solid state structure of the essential amino acid L-phenylalanine, four different polymorphic forms were published recently. The common form I has symmetry P2(1) with four molecules in the asymmetric unit (Z' = 4), similar to form III, but with a different arrangement of molecular bilayers. Form II, obtained from the hydrate at very low humidity, is unrelated to forms I and III, as is the high-density form IV. The present investigation demonstrates that this prototype aromatic amino acid has two additional high-temperature phases Ih and IIIh obtained from form I and form III above 458 and 440 K, respectively, when flipping between two alternative side-chain conformations becomes dynamic and causes pairs of molecules, initially crystallographically independent, to become equivalent above a sharp transition temperature. These abrupt and reversible phase changes occur with a reduction of Z' from 4 (low T) to 2 (high T) and modified crystal symmetry. We furthermore experienced an example of disappearing polymorph for form I which after growing form III in one of our laboratories could no longer be crystallized at room temperature. In contrast, form III crystals may be irreversibly converted to form I crystals as a result of sliding of molecular bilayers in the crystal at elevated temperature. No conversions between the high-temperature forms Ih and IIIh were found. The remarkable crystallographic results are here corroborated by Molecular Dynamics and metadynamics simulations of the form I - form III system.
机译：经过多年的争议，在必需氨基酸L-苯丙氨酸的固态结构上，最近发表了四种不同的多态形式。常见的形式I具有对称p2（1），其在不对称单元（z'= 4）中具有四个分子，类似于形式III，但具有不同的分子双层排列。在非常低湿度下从水合物获得的形式II与形成I和III不相关，同样是高密度形式IV。本研究表明，该原型芳族氨基酸分别具有两种另外的高温相IH和IIIH，分别在258和440k的形式III中获得，当在两个替代的侧链构象之间变为动态并且导致对分子最初在晶体上独立，以变得等同于高于急剧的过渡温度。这些突然和可逆的相位变化发生在4（低T）到2（高T）和改性晶体对称性的Z'中的变化。我们进一步经历了一种消失的多晶型物的例子，其形式I在我们的一个实验室中生长的形式后，在我们的实验室中不再在室温下结晶。相反，由于在晶体在升高温度下晶体中的分子双层滑动，可以不可逆地转化为不可逆地转化以形成I晶体。未发现高温形式IH和IIH之间的转换。这里的晶体动力学和I形式III系统形式III系统的分子动力学和Metadnynamics模拟有了显着的结晶结果。

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  • 来源
    《Crystal growth & design》 |2019年第3期|共11页
  • 作者

    Cuppen Herma M.; Smets Mireille M. H.; Krieger Annika M.; van den Ende Joost A.; Meekes Hugo; van Eck Ernst R. H.; Gorbitz Carl Henrik;

  • 作者单位

    Radboud Univ Nijmegen Inst Mol &

    Mat Heyendaalseweg 135 NL-6525 AJ Nijmegen Netherlands;

    Radboud Univ Nijmegen Inst Mol &

    Mat Heyendaalseweg 135 NL-6525 AJ Nijmegen Netherlands;

    Radboud Univ Nijmegen Inst Mol &

    Mat Heyendaalseweg 135 NL-6525 AJ Nijmegen Netherlands;

    Radboud Univ Nijmegen Inst Mol &

    Mat Heyendaalseweg 135 NL-6525 AJ Nijmegen Netherlands;

    Radboud Univ Nijmegen Inst Mol &

    Mat Heyendaalseweg 135 NL-6525 AJ Nijmegen Netherlands;

    Radboud Univ Nijmegen Inst Mol &

    Mat Heyendaalseweg 135 NL-6525 AJ Nijmegen Netherlands;

    Univ Oslo Dept Chem N-0315 Oslo Norway;

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  • 正文语种 eng
  • 中图分类 晶体学;
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