Rigidity and Flexibility in Rotaxanes and Their Relatives; On Being Stubborn and Easy-Going.
Rigidity and Flexibility in Rotaxanes and Their Relatives; On Being Stubborn and Easy-Going.
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DOI：
10.3389/fchem.2022.856173
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发表时间：
2022
影响因子：
5.5
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中科院分区：
文献类型：
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轮烷是一类新兴的分子，由两种结构单元组成：大环和螺纹。轮烷及其伪轮烷和聚轮烷亲属可作为分子级开关和机器的原型，以及弹性聚合物和3D打印油墨等材料的成分。这些分子的刚性和柔性是其设计的特征。然而，组装轮烷及其组分的机械性能很少被直接检查，并且这些性能从分子到块体材料的转化研究不足。在这篇综述中，我们考虑轮烷的机械性能，利用借用的概念，从物理有机化学。刚性分子具有较少的可及构象和较高的能垒，而柔性分子具有更多的可及构象和较低的能垒。大环和螺纹成为刚性螺纹在一起时，轮烷，其中形成的分子间相互作用和增加的空间接触共同减少构象空间和提高障碍。相反，轮烷的旋转和平移异构增加了新的灵活性模式。我们发现，硬化轮烷几乎是普遍的，但可以引入新的灵活性程度。两者都在轮烷的功能中发挥作用。
Rotaxanes are an emerging class of molecules composed of two building blocks: macrocycles and threads. Rotaxanes, and their pseudorotaxane and polyrotaxane relatives, serve as prototypes for molecular-level switches and machines and as components in materials like elastic polymers and 3D printing inks. The rigidity and flexibility of these molecules is a characteristic feature of their design. However, the mechanical properties of the assembled rotaxane and its components are rarely examined directly, and the translation of these properties from molecules to bulk materials is understudied. In this Review, we consider the mechanical properties of rotaxanes by making use of concepts borrowed from physical organic chemistry. Rigid molecules have fewer accessible conformations with higher energy barriers while flexible molecules have more accessible conformations and lower energy barriers. The macrocycles and threads become rigidified when threaded together as rotaxanes in which the formation of intermolecular interactions and increased steric contacts collectively reduce the conformational space and raise barriers. Conversely, rotational and translational isomerism in rotaxanes adds novel modes of flexibility. We find that rigidification in rotaxanes is almost universal, but novel degrees of flexibility can be introduced. Both have roles to play in the function of rotaxanes.