Descamps Marc, Correia Natalia T, Derollez Patrick, Danede Florence, Capet Frédéric
Laboratoire de Dynamique et Structure des Matériaux Moléculaires, UMR CNRS 8024, Université de Lille 1, Bât. P5, 59655 Villeneuve d'Ascq Cedex, France.
J Phys Chem B. 2005 Aug 25;109(33):16092-8. doi: 10.1021/jp040494c.
The present paper focuses on the high temperature form I of caffeine and on its low temperature metastable form. Structural, dynamic, and kinetic information has been obtained by X-ray, dielectric, and calorimetric investigations. This study shows the following features: (1) The high temperature phase (I) of caffeine is in a state of dynamically orientationally disordered crystalline state (so-called "plastic, or rotator, phase"). (2) This high-symmetry hexagonal phase can be maintained at low temperature in a metastable situation. (3) Under deep undercooling of form I a glass transition occurs in the disordered crystalline state near room temperature. It is associated with the orientational freezing in of the molecular motions. Otherwise stated, the metastable state I enters into a nonergodic unstable state, so-called "glassy crystal" state. These findings rationalize the difficulties seen with caffeine in pharmaceutical science.
本文聚焦于咖啡因的高温晶型I及其低温亚稳晶型。通过X射线、介电和量热研究获得了结构、动力学和动力学信息。本研究显示了以下特征：（1）咖啡因的高温相（I）处于动态取向无序的晶态（所谓的“塑性或旋转相”）。（2）这种高对称六方相在低温下可以在亚稳状态下保持。（3）在晶型I的深度过冷条件下，在接近室温的无序晶态中会发生玻璃化转变。它与分子运动的取向冻结有关。换句话说，亚稳态I进入了一种非遍历的不稳定状态，即所谓的“玻璃态晶体”状态。这些发现解释了在药物科学中咖啡因所面临的困难。
