Regulating copper-binding affinity with photoisomerizable azobenzene ligand by construction of a self-assembled monolayer.
Regulating copper-binding affinity with photoisomerizable azobenzene ligand by construction of a self-assembled monolayer.
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DOI：
10.1002/anie.200902048
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发表时间：
2009-08
影响因子：
--
通讯作者：
I. Takahashi;Yuichiro Honda;S. Hirota
中科院分区：
文献类型：
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作者：
I. Takahashi;Yuichiro Honda;S. Hirota
光活性分子因其允许分子性质发生显着改变和转换而引起了人们的极大兴趣。[1-5]例如，通过使用光致变色分子（例如螺吡喃和偶氮苯）的可逆结构调节，构建了既牢固结合又容易释放金属离子的功能分子和系统。[3,4]在螺吡喃衍生物的情况下，其中一种异构体通过其带负电的基团结合过渡金属离子，而另一种异构体则没有。这种光调节金属结合系统在溶液和聚合物基质中都很有用。[3]然而，由于结合位点带单个负电荷，金属结合能力相对较弱，并且需要具有两个或多个带电基团的结合位点才能更有效地调节金属结合系统。据报道，含有两个亚氨基二乙酸的偶氮苯衍生物（azo-IDA）在水溶液中能与金属离子牢固结合，但反式和顺式异构体与CuII离子的结合常数差异较小； KCu = 6.49 × 1010（反式）和 8.99 × 1010 M-1（顺式）。 [4b] 顺式配体通过溶液中的分子内相互作用与 CuII 离子配位，而反式配体可能通过分子间相互作用与 CuII 离子配位，尽管没有详细讨论。在固体表面上，配体的金属结合行为并不总是与溶液中的相同。例如，虽然偶氮吡啶衍生物的两种异构体都可以与溶液中的过渡金属离子结合，但只有一种异构体可以在金表面上与它们结合。 [5]这种结合能力的差异可能有助于金属结合调节，但它仍然相对较弱（KNi = 1.72 × 104 M-1）。 [6]为了构建光调节系统，我们合成了具有偶氮-IDA主链和二硫基团的不对称偶氮苯配体（L），并在Au表面上制备了其自组装单分子层（SAM）（图1）。偶氮-IDA主链被设计为强CuII结合位点，二硫基团被设计为表面吸附位点。 SAM 已被广泛研究，特别是在与吸附配体结合的铜离子的电化学评估和偶氮苯修饰表面的光转换性能方面。[7-10] 在这项研究中，反式 L 的 SAM 很容易释放铜离子，而顺式 L 的 SAM 则不然。因此，顺式-L的结合亲和力明显强于反式-L，并且用可见光照射顺式-L（顺式至反式光异构化）导致吸附的Cu离子数量减少。这些结果清楚地显示了将偶氮苯配体固定到金表面的铜结合亲和力的光调节。
Photoactive molecules have attracted much interest since they allow molecular properties to be changed and switched dramatically.[1-5] For example, functional molecules and systems which both strongly bind and easily release metal ions have been constructed by reversible structural regulation using photochromic molecules, such as spiropyran and azobenzene.[3,4] In the case of a spiropyran derivative, one of the isomers bound a transition metal ion through its negatively charged group, while the other isomer did not. This photoregulated metal-binding system was useful both in solution and in a polymer matrix.[3] However, the metal-binding ability was relatively weak since the binding site was singly negatively charged, and binding sites with two or more charged groups are required for a more effectively regulated metal-binding system. It has been reported that an azobenzene derivative containing two iminodiacetic acids (azo-IDA) could strongly bind to a metal ion in aqueous solution, but the difference in the binding constants of the trans and cis isomers with the CuII ion were relatively small; KCu = 6.49 × 1010 (trans) and 8.99 × 1010 M1 (cis). [4b] The cis ligand coordinates to a CuII ion by intramolecular interaction in solution, whereas the trans ligand coordinates to a CuII ion presumably through intermolecular interaction, although it was not discussed in detail. On a solid surface, the metal-binding behavior of a ligand is not always identical to that in solution. For example, although both isomers of an azopyridine derivative could bind to transition metal ions in solution, only one of the isomers could bind to them on a Au surface.[5] This difference in binding ability could be useful in metal-binding regulation, but it is still relatively weak (KNi = 1.72 × 104 M1).[6] In order to construct a photoregulated system, we synthesized an asymmetrical azobenzene ligand (L) with an azo-IDA backbone and a disulfide group, and prepared its self-assembled monolayer (SAM) on a Au surface (Figure 1). The azo-IDA backbone was designed as the strong CuII-binding site and the disulfide group as the surface adsorption site. SAMs have been widely studied especially in electrochemical evaluation of Cu ions bound to adsorbed ligands and in photoconversion properties of azobenzene-modified surfaces.[7-10] In this study, the SAM of trans-L easily released the Cu ions, whereas that of cis-L did not. The binding affinity of cis-L, therefore, is apparently stronger than that of trans-L and irradiation of cis-L with visible light (cis-to-trans photoisomerization) led to a decrease in the number of adsorbed Cu ions. These results clearly show photoregulation of the Cu-binding affinities affixing the azobenzene ligand to the Au surface.