葡萄牙里斯本大学Nuno Basílio团队报道了作为葫芦脲大环客体的重氮霉素——光响应结合和热异构化的超分子催化。相关研究成果于2024年12月25日发表在国际顶尖学术期刊《美国化学会杂志》。

超分子主客体复合物的光开关是许多分子控制宏观功能的基础，如溶胶-凝胶转变、光药理学、离子或分子的主动运输、光动力分子机器等等。最常用的系统采用光活性偶氮苯客体和合成主体分子，它们暴露于紫外光后作为稳定的E异构体结合，并在Z形成时解离。

该文中，研究人员提出了一种新的、非常有效的，具有倒置稳定性的葫芦[7]脲（CB7）/重氮碱主/客体复合物，其在紫外线照射下自组装并在黑暗中解离。Z和E异构体在水中的缔合常数相差10⁴倍以上。

研究还表明，CB7显著加速了热活化的E→Z异构化，这是一种罕见的通过过渡态稳定而没有产物抑制的酶样催化。与CB7相比，葫芦素[8]脲（CB8）以高亲和力结合两种异构体，对Z异构体显示出良好的选择性（～1000倍）。

值得注意的是，相对于CB7，这种异构体优先结合CB8的倍数大于1×10⁶。研究人员还使用该系统引入了一种超分子光酸，该光酸建立在与CB7结合的客体的碱性增加，和E异构体的极高亲和力的基础上，E异构体用于从CB7中置换酸，从而改变溶液的pH值。

附：英文原文

Title: Diazocines as Guests of Cucurbituril Macrocycles: Light-Responsive Binding and Supramolecular Catalysis of Thermal Isomerization

Author: Miriam Colao, Julia Ewert, Jan-Simon von Glasenapp, Uwe Pischel, Rainer Herges, Nuno Basílio

Issue&Volume: December 25, 2024

Abstract: The photoswitching of supramolecular host–guest complexes is the basis of numerous molecularly controlled macroscopic functions, such as sol–gel transition, photopharmacology, the active transport of ions or molecules, light-powered molecular machines, and much more. The most commonly used systems employ photoactive azobenzene guests and synthetic host molecules, which bind as the stable E isomers and dissociate as the Z forms after exposure to UV light. We present a new, extraordinarily efficient cucurbit[7]uril (CB7)/diazocine host/guest complex with inverted stability that self-assembles under UV irradiation and dissociates in the dark. The association constants of the Z and E isomers in water differ by more than 104-fold. We also show that the thermally activated E → Z isomerization is significantly accelerated by CB7, which is a rare case of enzyme-like catalysis by transition state stabilization without product inhibition. In contrast to CB7, cucurbit[8]uril (CB8) binds both isomers with high affinity, showing good selectivity (～1000-fold) toward the Z isomer. Notably, this isomer preferentially binds CB8 relative to CB7 by a factor greater than 1 × 106. We also use the system to introduce a supramolecular photoacid that builds on the increased basicity of a guest bound to CB7 and on the extremely high affinity of the E isomer, which is utilized to displace the acid from CB7, thereby switching the pH of the solution.

DOI: 10.1021/jacs.4c13353

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.4c13353