Electrochemical control of recognition processes. A three-component molecular switch
Electrochemical control of recognition processes. A three-component molecular switch
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DOI：
10.1021/ja9728740
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发表时间：
1997-11-05
影响因子：
15
通讯作者：
Rotello, VM
中科院分区：
文献类型：
--
作者：
Deans, R;Niemz, A;Rotello, VM
近年来，人们对有机分子器件的创造产生了浓厚的兴趣，这些器件有可能在分子级计算机和其他应用中充当信息存储/交换系统。为此，已经建造了许多装置，包括分子穿梭器、开关和电线。生物系统利用氧化还原和分子识别的相互作用来调节各种各样的过程和转化。在我们继续努力了解这些系统的过程中，我们设计了合成受体，其中非共价相互作用（氢键和芳香堆叠）已被证明可以调节黄素辅助因子的氧化还原电位。利用这些受体，我们确定了黄素自由基阴离子通过氢键稳定。与这种稳定同时，我们观察到相对于完全氧化的黄素，自由基阴离子的识别增强。史密斯和他的同事在一个类似的系统中量化了这种效应。在最近的研究中，我们观察到黄素自由基阴离子通过芳香层的不稳定性。氢键和芳香族堆积对黄素还原电位的相反影响表明，在氧化还原态变化的识别调节中存在互补。为了检验这种效应并探索氧化还原过程对分子识别的控制，我们创建了一个系统，其中两个宿主之间的竞争由客体的氧化还原状态调节。本研究中使用的两种宿主是蒽受体A和酰基化二氨基吡啶受体d。这两种宿主都可以与客体萘酰亚胺进行3点氢键相互作用，无论是氧化的Nox还是自由基阴离子nrad形式（图1）。此外，寄主A能够形成芳香堆叠相互作用。我们在此报告了该系统中氧化还原控制的识别以及三组分、两极分子开关的创建（图2）。在我们最初的研究中，我们确定了孤立双组分系统的热力学常数。通过CDCl3中的核磁共振滴定实验获得了Nox与A和D的缔合常数（Ka）（表1）。8研究发现，由于良好的芳香-芳香相互作用，A与Nox的结合强度比D强一个数量级以上。为了量化Nrad-的结合，我们研究了添加A和D后Nox的标准还原电位（E1/2）的变化。添加D导致E1/2向更小的负值显著转变，表明自由基阴离子的基本稳定。相比之下，A的加入对萘酰亚胺的还原电位影响不大（表1）。这是由于氢键的有利作用抵消了芳香族堆积对还原过程的不利影响。使用关联常数（Ka）和E1/2值，可以为两个主客系统构建热力学平方（图3）
In recent years, considerable interest has been devoted to the creation of organic based molecular deVices1 that have the potential to function as information storage/switching systems2 in molecular scale computers3 and other applications. 4 To this end, a number of devices have been constructed, including molecular shuttles, switches, and wires. 5 Biological systems use the interplay of redox and molecular recognition to regulate a wide variety of processes and transformations. In our continued efforts to understand these systems, we have designed synthetic receptors where noncovalent interactions (hydrogen-bonding and aromatic stacking) have been demonstrated to modulate the redox potentials of flavin cofactors. 6 Using these receptors, we have established that the flavin radical anion is stabilized by hydrogen bonding. Concurrent with this stabilization, we observed enhanced recognition of the radical anion relative to the fully oxidized flavin. 6a This effect was quantified in an analogous system by Smith and co-workers. 7 In recent studies, we have observed destabilization of the flavin radical anion by aromatic stacking. 6b The opposite effects of hydrogen bonding and aromatic stacking on flavin reduction potentials suggest a complementarity in the modulation of recognition upon redox state change. To examine this effect and explore the control of molecular recognition through redox processes, we have created a system where the competition between two hosts is regulated by the redox state of the guest. The two hosts used in this study were anthracene receptor A and acylated diaminopyridine receptor D. Both hosts can undergo three-point hydrogen-bonding interactions with guest naphthalimide, either in its oxidized Nox or radical anion Nrad-form (Figure 1). In addition, host A is capable of forming aromatic stacking interactions. We report here redox-controlled recognition in this system and the creation of a three-component, two-pole, molecular switch (Figure 2).In our initial studies, we determined the thermodynamic constants for the isolated two-component systems. Association constants (Ka) of Nox with A and D were obtained via NMR titration experiments in CDCl3 (Table 1). 8 It was found that A binds Nox more than an order of magnitude stronger than D, due to favorable aromatic-aromatic interactions. To quantify the binding of Nrad-, we investigated the change in standard reduction potential (E1/2) of Nox upon addition of A and D. Addition of D resulted in a significant shift of E1/2 to less negative values, indicating substantial stabilization of the radical anion. Addition of A, in contrast, had little effect on the reduction potential of naphthalimide (Table 1). This results from the offsetting favorable effect of hydrogen bonding and unfavorable effect of aromatic stacking on the reduction process. Using the association constants (Ka) and E1/2 values, it is possible to construct thermodynamic squares for the two host-guest systems (Figure 3). 9