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首页> 外文期刊>Chemistry: A European journal >Quantitative conformational study of redox-active [2]rotaxanes, part 2: Switching in flexible and rigid bistable [2]rotaxanes
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Quantitative conformational study of redox-active [2]rotaxanes, part 2: Switching in flexible and rigid bistable [2]rotaxanes

机译：氧化还原活性[2]轮烷的定量构象研究，第2部分：切换柔性和刚性双稳态[2]轮烷

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摘要

Translational movement of the macrocycle in two structurally similar bistable [2]rotaxanes, which is induced by a four-step electrochemical process in solution, has been investigated by using a methodology developed in the preceding article (Chem. Eur. J 2008, 14, 1107-1116). Both [2]rotaxanes contain a crown ether that can be accommodated by either of two interconnected viologen recognition sites. These sites are substantially different in terms of their affinity towards the crown ether and they possess considerably different electrochemical reduction potentials. The two [2]rotaxanes differ in the length and the rigidity of a bridge that links these sites. A combination of molecular mechanics modelling and NOE spectroscopy data provides information about the conformations of both [2]rotaxanes in the parent oxidation state when the crown ether exclusively populates the strong recognition site. To determine the population of the recognition sites at subsequent stages of reduction, a paramagnetic NMR technique and cyclic voltammetry were used. ne key finding is that the flexibility of the connecting bridge element between the recognition sites interferes with shuttling of the crown ether in [2]rotaxanes. It can be demonstrated that the more flexible trimethylene bridge is folded, thus limiting the propensity of the crown ether to shuttle. Consequently, the crown ether populates the original site even in the second reduced state of the flexible [2]rotaxane. On the contrary, in the [2]rotaxane in which two viologen sites are connected by a larger and more rigid p-terphenylene bridge, the predominant location of the crown ether at the weak recognition site is achieved after just one single electron reduction.
机译：通过使用在前一篇文章中开发的方法研究了两种在结构上相似的双稳态[2]轮烷中由四步电​​化学过程诱导的大环的平移运动（Chem。Eur。J 2008，14， 1107-1116）。两种[2]轮烷均含有冠状醚，可被两个相互连接的紫精识别位点之一容纳。这些位点对冠醚的亲和力显着不同，并且它们具有明显不同的电化学还原电势。两种[2]轮烷的长度和连接这些位点的桥的刚性不同。分子力学建模和NOE光谱数据的结合可提供有关当冠醚专门位于强识别位点时母体氧化态中[2]轮烷的构象的信息。为了确定还原反应后续阶段识别位点的数量，使用了顺磁NMR技术和循环伏安法。一个重要发现是，识别位点之间的连接桥元件的柔韧性会干扰冠状醚在[2]轮烷中的穿梭。可以证明，更灵活的三亚甲基桥是折叠的，因此限制了冠醚穿梭的倾向。因此，即使在柔性[2]轮烷的第二还原状态下，冠醚也会填充原始位点。相反，在[2]轮烷中，两个大分子位点通过一个更大，更刚性的对-三亚苯基桥连接，仅一次电子还原后，冠醚就位于弱识别位点上。

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