摘要
基于冠醚和二级铵盐的轮烷体系是一类重要的超分子机器.理解外力作用下该轮烷体系的解离及结合机制,将有助于开发基于轮烷体系的力学响应材料.基于原子力显微镜(AFM)的单分子力谱(SMFS)是研究这种超分子弱相互作用的有效方法.为了提升实验效率并降低界面非特异性相互作用对单分子力谱实验的干扰,通过合理的分子设计和聚合方法,将单体轮烷结构单元聚合,形成轮/轴首尾相连的聚互锁结构.通过将该聚合物桥联于AFM针尖与固体基片之间,并对该聚合物进行恒速拉伸操纵,实现了聚轮烷互锁结构的动态打开与形成过程的原位观测.实验结果显示,外力作用下聚轮烷结构中的重复单元依次打开,产生了具有锯齿状平台的力学信号,该锯齿状信号的力值体现出对拉伸过程中力加载速率的依赖性,随着力加载速率从600 pN/s升高至90000 pN/s,其力值从~84 pN升高至142 pN.往复拉伸实验结果显示,该聚轮烷结构的形成是一个自发、可逆的过程,且结合力值随着松弛速率的增加而降低.通过结合动态力学谱及相关动力学模型,得到该轮烷体系的结合速率常数为1.3×10^(4)s^(-1),解离速率常数为0.26 s^(-1),平衡态自由能为-34.6 kJ/mol,并绘制出其解离与结合的能量路径.本研究深化了对基于冠醚和二级铵盐的轮烷体系力学稳定性及结合与解离机制的认识,为基于轮烷的材料体系力学性质调控及理性设计提供了重要参考.
Rotaxane system that is based on benzo-21-crown-7(B21C7)and dialkylammonium salts(DAAs)is one of the important molecular machines.Understanding the mechanism of force-induced unbinding and rebinding of such rotaxane system will facilitate the development of rotaxane-based force-responsive materials.In this paper,we have investigated the mechanochemistry and unbinding-rebinding process of a tandem polyrotaxane with B21C7/DAAs repeat units.The binding mode and binding strength have been also revealed.Through the atomic force microscopy(AFM)-based single molecule force spectroscopy(SMFS)method,we are able to get the unbinding information of each rotaxane unit on the whole tandem chain and quantify the strength of the host-guest complexation.A force plateau containing sawtooth peaks was observed,which corresponds to the sequential unbinding of the B21C7/DAAs unit,and the peak force was found in the range of 84-142 pN depending on the force loading rate.Consecutive stretching-relaxation experiments reveal that after detaching from the binding point and sliding along the axle,crown ether moieties can travel back to their original binding sites once the chain is relaxed.The loading rate dependence tells us that the unbinding force increases linearly with the increase of the force loading rate,whereas the rebinding force decreases linearly with the increase of the force loading rate.Furthermore,we can get the kinetic parameters governing the dynamic motion of the polyrotaxane with a dissociation rate constant of 0.26 s-1 and an association rate constant of 1.3×104 s-1.With these kinetic parameters,the potential energy landscape for the unbinding/rebinding of rotaxane was drawn with an equilibrium free energy of-34.6 kJ/mol.These results deepen the understanding of B21C7/DAAs system,and are helpful for the rational design of functional materials with rotaxane molecular machine building blocks.The established method can also be applied in other rotaxane systems.
作者
李占东
鞠华强
黄飞鹤
张文科
Zhan-dong Li;Hua-qiang Ju;Fei-he Huang;Wen-ke Zhang(State Key Laboratory of Supramolecular Structure and Materials,College of Chemistry,Jilin University,Changchun 130012;State Key Laboratory of Chemical Engineering,Department of Chemistry,Zhejiang University,Hangzhou 310027)
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2022年第10期1279-1286,共8页
Acta Polymerica Sinica
基金
国家自然科学基金(基金号21827805,21525418,21474041,91127031)资助项目.
关键词
聚轮烷
超分子材料
单分子力谱
力化学
Polyrotaxanes
Supramolecular materials
Single molecule force spectroscopy
Mechanochemistry
