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使用慢扫描速率循环伏安法测量双稳态机械互锁分子中的基态分布。

Measurement of the ground-state distributions in bistable mechanically interlocked molecules using slow scan rate cyclic voltammetry.

机构信息

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA.

出版信息

Proc Natl Acad Sci U S A. 2011 Dec 20;108(51):20416-21. doi: 10.1073/pnas.1109795108. Epub 2011 Nov 30.

Abstract

In donor-acceptor mechanically interlocked molecules that exhibit bistability, the relative populations of the translational isomers--present, for example, in a bistable [2]rotaxane, as well as in a couple of bistable [2]catenanes of the donor-acceptor vintage--can be elucidated by slow scan rate cyclic voltammetry. The practice of transitioning from a fast scan rate regime to a slow one permits the measurement of an intermediate redox couple that is a function of the equilibrium that exists between the two translational isomers in the case of all three mechanically interlocked molecules investigated. These intermediate redox potentials can be used to calculate the ground-state distribution constants, K. Whereas, (i) in the case of the bistable [2]rotaxane, composed of a dumbbell component containing π-electron-rich tetrathiafulvalene and dioxynaphthalene recognition sites for the ring component (namely, a tetracationic cyclophane, containing two π-electron-deficient bipyridinium units), a value for K of 10 ± 2 is calculated, (ii) in the case of the two bistable [2]catenanes--one containing a crown ether with tetrathiafulvalene and dioxynaphthalene recognition sites for the tetracationic cyclophane, and the other, tetrathiafulvalene and butadiyne recognition sites--the values for K are orders (one and three, respectively) of magnitude greater. This observation, which has also been probed by theoretical calculations, supports the hypothesis that the extra stability of one translational isomer over the other is because of the influence of the enforced side-on donor-acceptor interactions brought about by both π-electron-rich recognition sites being part of a macrocyclic polyether.

摘要

在表现出双稳态的给体-受体机械互锁分子中,可以通过慢扫描速率循环伏安法阐明平移异构体的相对丰度——例如,在双稳态[2]轮烷中存在,以及在一对双稳态[2]具有给体-受体 vintage 的索烃中存在——可以通过慢扫描速率循环伏安法阐明平移异构体的相对丰度。从快速扫描速率转变为缓慢扫描速率的做法允许测量中间氧化还原对,该对是在所有三种机械互锁分子中,两个平移异构体之间存在的平衡的函数。这些中间氧化还原电位可用于计算基态分布常数 K。然而,(i)在由包含富π电子四硫富瓦烯和二氧萘识别位点的哑铃组件组成的双稳态[2]轮烷的情况下,对于环组件(即包含两个π电子缺电子的联吡啶单元的四阳离子环),计算出 K 的值为 10 ± 2,(ii)在两个双稳态[2]索烃的情况下——一个包含具有四硫富瓦烯和二氧萘识别位点的冠醚对于四阳离子环,另一个含有四硫富瓦烯和丁二炔识别位点——K 的值分别为数量级(分别为一和三)更大。这一观察结果也通过理论计算进行了探究,支持了这样一种假设,即一个平移异构体相对于另一个的额外稳定性是由于富π电子的识别位点都作为大环聚醚的一部分而产生的强制性侧给体-受体相互作用的影响。

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