Cyclic Bis-porphyrin-Based Flexible Molecular Containers: Controlling Guest Arrangements and Supramolecular Catalysis by Tuning Cavity Size
Cyclic Bis-porphyrin-Based Flexible Molecular Containers: Controlling Guest Arrangements and Supramolecular Catalysis by Tuning Cavity Size
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DOI：
10.1002/chem.201700577
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发表时间：
2017-05-23
影响因子：
4.3
通讯作者：
Rath, Sankar Prasad
中科院分区：
文献类型：
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作者：
Mondal, Pritam;Sarkar, Sabyasachi;Rath, Sankar Prasad
具有高柔性连接体的三环锌双卟啉（CB）被用作人工分子容器，在其腔内有效地封装/配位各种芳香醛。有趣的是，来宾的排列及其在分子间隙内的反应性受到循环容器腔大小的显著影响。当多环芳香族醛（如3-甲酰苝）作为客体存在时，具有较小空腔（CB1）的环双卟啉宿主形成1:1的夹心复合物。在稍微增加间隔长度从而增加空腔大小后，环寄主（CB2）包裹两个3-甲酰苝分子，由于它们之间的强pi-pi相互作用和与卟啉环的CH-pi相互作用，它们也堆叠在一起。然而，在具有更大空腔的环状宿主（CB3）中，双卟啉的两个金属中心在其空腔内轴向协调两个3-甲酰苝分子。采用UV/Vis、ESI-MS、H-1 NMR等方法研究了环双卟啉宿主体内客体的不同排列方式，并对主-客体配合物进行了x射线结构测定。此外，环双卟啉宿主体内的客体强结合支持了溶液中主客体组合的鲁棒性。双卟啉腔通过包封/配位对芳香醛的这种优先结合已被成功地用于在环境条件下催化一系列多环醛与活性亚甲基化合物（如Meldrum酸和1,3 -二甲基巴比妥酸）的Knoevenagel缩合。有趣的是，随着环双卟啉间隔长度的增加，缩合产物的产率显著增加，因为更多的底物可以被封装在腔内。这种可控制腔体大小的循环容器对构建高功能和模块化的酶模拟物具有深远的意义。
Three cyclic zinc(II) bis-porphyrins (CB) with highly flexible linkers are employed as artificial molecular containers that efficiently encapsulate/coordinate various aromatic aldehydes within their cavities. Interestingly, the arrangements of guests and their reactivity inside the molecular clefts are significantly influenced by the cavity size of the cyclic containers. In the presence of polycyclic aromatic aldehydes, such as 3-formylperylene, as a guest, the cyclic bisporphyrin host with a smaller cavity (CB1) forms a 1:1 sandwich complex. Upon slightly increasing the spacer length and thereby the cavity size, the cyclic host (CB2) encapsulates two molecules of 3-formylperylene that are also stacked together due to strong pi-pi interactions between them and CH-pi interactions with the porphyrin rings. However, in the cyclic host (CB3) with an even larger cavity, two metal centers of the bis-porphyrin axially coordinate two molecules of 3-formylperylene within its cavity. Different arrangements of guest inside the cyclic bis-porphyrin hosts are investigated by using UV/Vis, ESI-MS, and H-1 NMR spectroscopy, along with X-ray structure determination of the host-guest complexes. Moreover, strong binding of guests within the cyclic bis-porphyrin hosts support the robust nature of the host-guest assemblies in solution. Such preferential binding of the bis-porphyrinic cavity towards aromatic aldehydes through encapsulation/coordination has been employed successfully to catalyze the Knoevenagel condensation of a series of polycyclic aldehydes with active methylene compounds (such as Meldrum's acid and 1, 3-dimethylbarbituric acid) under ambient conditions. Interestingly, the yields of the condensed products significantly increase upon increasing spacer lengths of the cyclic bis-porphyrins because more substrates can then be encapsulated within the cavity. Such controllable cavity size of the cyclic containers has profound implications for constructing highly functional and modular enzyme mimics.