ExCage
详细信息    查看全文
文摘
Cyclophanes, especially those where pyridinium units in conjugation with each other are linked up face-to-face within platforms that are held approximately 7 脜 apart by rigid linkers, are capable of forming inclusion complexes with polycyclic aromatic hydrocarbons (PAHs) with high binding affinities as a result of a combination of noncovalent bonding interactions, including face-to-face [蟺路路路蟺] stacking and orthogonal [C鈥揌路路路蟺] interactions. Here, we report the template-directed, catalyst-assisted synthesis of a three-fold symmetric, extended pyridinium-based, cage-like host (ExCage6+) containing a total of six 蟺-electron-deficient pyridinium units connected in a pairwise fashion by three bridging p-xylylene linkers, displayed in a trigonal (1,3,5) fashion around two opposing and parallel 1,3,5-tris(4-pyridinium)benzene platforms. The association constants (Ka) of eight complexes have been measured by isothermal titration calorimetry (ITC) in acetonitrile and were found to span the range from 2.82 脳 103 for naphthalene up to 5.5 脳 106 M鈥? for perylene. The barriers to decomplexation, which were measured in DMF-d7 for phenanthrene, pyrene, triphenylene, and coronene by dynamic 1H NMR spectroscopy undergo significant stepwise increases from 11.8 鈫?13.6 鈫?15.5 鈫?>18.7 kcal mol鈥?, respectively, while complexation experiments using rapid injection 1H NMR spectroscopy in DMF-d7 at 鈭?5 掳C revealed the barriers to complexation for pyrene and coronene to be 6.7 and >8 kcal mol鈥?, respectively. The kinetic and thermodynamic data reveal that, in the case of ExCage6+, while the smaller PAHs form complexes faster than the larger ones, the larger PAHs form stronger complexes than the smaller ones. It is also worthy of note that, as the complexes become stronger in the case of the larger and larger PAHs, the Rebek 55% solution formula for molecular recognition in the liquid state becomes less and less relevant.

© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号

地址:北京市海淀区学院路29号 邮编:100083

电话:办公室:(+86 10)66554848;文献借阅、咨询服务、科技查新:66554700