The thermosalient phenomenon. "Jumping crystals" and crystal chemistry of the anticholinergic agent oxitropium bromide.
The thermosalient phenomenon. "Jumping crystals" and crystal chemistry of the anticholinergic agent oxitropium bromide.
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DOI：
10.1021/ja105508b
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发表时间：
2010-09
影响因子：
15
通讯作者：
Ž. Skoko;S. Zamir;P. Naumov;J. Bernstein
中科院分区：
文献类型：
--
作者：
Ž. Skoko;S. Zamir;P. Naumov;J. Bernstein
抗胆碱能剂溴化氧具有丰富的晶体化学性质，最显著的是表现出强烈的热显着效应（“跳晶”效应），这一力学性质在有机基致动器中具有潜在的应用前景。通过结构、微观、光谱和热分析技术的结合，研究了以高达几厘米的强力跳跃为特征的热显热效应，为提出该现象的机制提供了数据基础。对单晶效应的直接观察和两相结构的测定表明，晶体的跳跃是细胞体积高度各向异性变化的宏观表现。细胞畸变伴随着氧离子阳离子的构象变化，这引发了晶格中离子对之间的分离增加，在每个离子对中正离子和阴离子之间几乎相同的分离。在分子水平上，阳离子充当由两个刚性部分（环氧-氮杂-三环-壬基部分和苯基环）组成的分子梭子，这两个刚性部分由一个柔性酯键桥接。刚性惰性氮杂三环部分的结构几乎不受温度的影响，这表明了一种机制，在这种机制中，热积累的大应变通过酯桥转移到苯环上，苯环旋转触发相变。还介绍了高温固体现象的机理细节。高温相也可以通过研磨或紫外线照射室温相得到。此外，如果在KBr存在下用紫外光照射，高温相发生分子内光化学重排。将高温相加热到略低于熔融温度，会产生额外的固态反应，导致盐转化为中性化合物的混合物。
The anticholinergic agent oxitropium bromide possesses rich crystal chemistry, most remarkably exhibiting a strong thermosalient effect ("jumping crystal" effect), a mechanical property with potential applications in organic-based actuators. The thermosalient effect, manifested in forceful jumps of up to several centimeters, was investigated by a combination of structural, microscopic, spectroscopic, and thermoanalytical techniques, providing data on which to base a proposed mechanism for the phenomenon. Direct observation of the effect in a single crystal and structure determination of both phases revealed that the jumping of the crystals is a macroscopic manifestation of a highly anisotropic change in the cell volume. The cell distortion is accompanied by a conformational change of the oxitropium cation, which triggers increased separation between the ion pairs in the lattice at nearly identical separation between the cation and the anion within each ion pair. At the molecular level, the cation acts as a molecular shuttle composed of two rigid parts (epoxy-aza-tricyclic-nonyl portion and phenyl ring) that are bridged by a flexible ester linkage. The structure of the rigid, inert aza-tricyclic portion remains practically unaffected by the temperature, suggesting a mechanism in which the large, thermally accumulated strain is transferred over the ester bridge to the phenyl ring, which rotates to trigger the phase transition. Mechanistic details of the higher temperature solid-state phenomena are also presented. The high-temperature phase can also be obtained by grinding or UV irradiation of the room-temperature phase. In addition, if it is irradiated with UV light in the presence of KBr, the high-temperature phase undergoes intramolecular photochemical rearrangement. Heating the high-temperature phase to slightly below the melting temperature results in an additional solid-state reaction that results in the conversion of the salt to a mixture of neutral compounds.