Ex2Box: Interdependent Modes of Binding in a Two-Nanometer-Long Synthetic Receptor

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• 作者：Michal Jur铆膷ek ; Jonathan C. Barnes ; Edward J. Dale ; Wei-Guang Liu ; Nathan L. Strutt ; Carson J. Bruns ; Nicolaas A. Vermeulen ; Kala C. Ghooray ; Amy A. Sarjeant ; Charlotte L. Stern ; Youssry Y. Botros ; William A. Goddard ; III ; J. Fraser Stoddart
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：August 28, 2013
• 年：2013
• 卷：135
• 期：34
• 页码：12736-12746
• 全文大小：631K
• 年卷期：v.135,no.34(August 28, 2013)
• ISSN：1520-5126

文摘

Incorporation of two biphenylene-bridged 4,4鈥?bipyridinium extended viologen units into a para-phenylene-based cyclophane results in a synthetic receptor that is 2 nm long and adopts a box-like geometry. This cyclophane, Ex²Box⁴⁺, possesses the ability to form binary and ternary complexes with a myriad of guest molecules ranging from long 蟺-electron-rich polycyclic aromatic hydrocarbons, such as tetracene, tetraphene, and chrysene, to 蟺-electron-poor 2,6-dinitrotoluene, 1,2,4-trichlorobenzene, and both the 9,10- and 1,4-anthraquinone molecules. Moreover, Ex²Box⁴⁺ is capable of forming one-to-one complexes with polyether macrocycles that consist of two 蟺-electron-rich dioxynaphthalene units, namely, 1,5-dinaphtho[38]crown-10. This type of broad molecular recognition is possible because the electronic constitution of Ex²Box⁴⁺ is such that the pyridinium rings located at the 鈥渆nds鈥?of the cyclophane are electron-poor and prefer to enter into donor鈥揳cceptor interactions with 蟺-electron-rich guests, while the 鈥渕iddle鈥?of the cyclophane, consisting of the biphenylene spacer, is more electron-rich and can interact with 蟺-electron-poor guests. In some cases, these different modes of binding can act in concert to generate one-to-one complexes which possess high stability constants in organic media. The binding affinity of Ex²Box⁴⁺ was investigated in the solid state by way of single-crystal X-ray diffraction and in solution by using UV鈥搗is and NMR spectroscopy for 12 inclusion complexes consisting of the tetracationic cyclophane and the corresponding guests of different sizes, shapes, and electronic compositions. Additionally, density functional theory was carried out to elucidate the relative energetic differences between the different modes of binding of Ex²Box⁴⁺ with anthracene, 9,10-anthraquinone, and 1,4-anthraquinone in order to understand the degree with which each mode of binding contributes to the overall encapsulation of each guest.