Li Yuanchao, Sheiko Sergei S
Department of Chemistry, University of North Carolina, Chapel Hill, NC, 27599-3290, USA.
Top Curr Chem. 2015;369:1-36. doi: 10.1007/128_2015_627.
Mechanical activation of chemical bonds is usually achieved by applying external forces. However, nearly all molecules exhibit inherent strain of their chemical bonds and angles as a result of constraints imposed by covalent bonding and interactions with the surrounding environment. Particularly strong deformation of bonds and angles is observed in hyperbranched macromolecules caused by steric repulsion of densely grafted polymer branches. In addition to the tension amplification, macromolecular architecture allows for accurate control of strain distribution, which enables focusing of the internal mechanical tension to specific chemical bonds and angles. As such, chemically identical bonds in self-strained macromolecules become physically distinct because the difference in bond tension leads to the corresponding difference in the electronic structure and chemical reactivity of individual bonds within the same macromolecule. In this review, we outline different approaches to the design of strained macromolecules along with physical principles of tension management, including generation, amplification, and focusing of mechanical tension at specific chemical bonds.
化学键的机械活化通常通过施加外力来实现。然而,由于共价键的限制以及与周围环境的相互作用,几乎所有分子的化学键和键角都存在固有应变。在超支化大分子中,由于密集接枝的聚合物支链的空间排斥作用,观察到键和键角有特别强烈的变形。除了张力放大外,大分子结构还允许精确控制应变分布,这使得内部机械张力能够集中到特定的化学键和键角上。因此,自应变大分子中化学性质相同的键在物理上变得不同,因为键张力的差异导致同一大分子内各个键的电子结构和化学反应性产生相应差异。在这篇综述中,我们概述了设计应变大分子的不同方法以及张力管理的物理原理,包括在特定化学键处产生、放大和集中机械张力。