Interaction Between Cucurbit[N1urils With Some Chain Organic Numerators

A hydrophobic cavity, and polar carbonyl groups surrounding the opening portals are common characteristic features for a new receptor family—Cucurbit[n]urils (Q[n]s). The varying cavity and portal sizes, particularly, the ability to form inclusion or exclusion complexes with organic species or inorganic ions lead to Q[n]s remarkable molecular recognition properties and the building block for supramolecular chemistry that promoted quite a few researchers to focus on this area. In this work, six 1,(?)-alkylenedipyridinium dibromide guests and a series of viologen derivates were synthesized , while structures and interaction of cucurbit[6,7,8]urils with the guests were investigated by ¹H NMR techniques, UV-Vis spectroscopy, X-ray diffraction analysis and conductivity in details.1. The host-guest complexes were formed between six 1,? -alkylenedipyridinium dibromide guests and cucurbit[6,7,8]urils, while the interaction types were different for the six guests and cucurbit[6]uril, cucurbit[7]uril or cucurbit[8]uril respectively.2. The interaction between a symmetrical substituted cucurbit[6]uril (TMeQ[6]) and the guest of dibromine salt of 1,4-butyldipyridine (Bdpy) was studied. The X-ray crystallographic determination reveals that each TMeQ[6] host includes only one of pyridine ring of a Bdpy guest, the rest part of the Bdpy guest is located at one portal of the TMeQ[6] to form a unsymmetrical host-guest inclusion complex. Contrary to expectations, the ¹H NMR results show that both of pyridine rings of the Bdpy guest seem to be included in the cavity of the TMeQ[6] host.3. The binding site on the guests depended strongly on the length of the aliphatic substituents on the bipyridinium nucleus: a 1:1 complex was formed for Q[8]-viologen derivates with chains shorter that four carbon atoms, while a 1:2 complex for Q[8]-BPY²⁺ was observed under acidic condition. However, two or three Q[8] molecules could be threaded on a viologen derivates with chains longer that four carbon atoms molecule to form a 2:1, even 3:1 complex respectively.