| Abstract
| - Interaction between tetramethylcucurbit[6]uril (TMeQ[6], host) with hydrochloride salts of 2-phenylpridine(G1), 2-benzylpyridine (G2), and 4-benzylpyridine (G3) (guests) have been investigated by using 1H NMRspectroscopy and electronic absorption spectroscopy and theoretical calculations. The 1H NMR spectra analysisestablished an interaction model in which the host selectively included the phenyl moiety of the HCl salt ofthe above three guests, and formed inclusion complexes with a host−guest ratio of 1:1. Absorptionspectrophotometric analysis allowed quantitative measurement of the stability of these host−guest inclusioncomplexes. Particularly, we have established a competitive interaction in which one host−guest inclusioncomplex pair is much more stable than another host−guest inclusion complex pair. The stability constantsfor the three host−guest inclusion complexes of TMeQ[6]-G1, TMeQ[6]-G2, and TMeQ[6]-G3 are ∼2 ×106, 60.7, and 19.9 mol-1·L, respectively. To understand how subtle differences in the structure of the titleguests lead to a significant difference in the stability of the corresponding host−guest inclusion complexeswith the TMeQ[6], ab initio theoretical calculations have been performed, not only for the gas phase but alsothe solution phase (water as solvent) in all cases. The calculation results revealed that when the phenyl moietyof the three pyridine derivate guests was included, the host−guest complexation reached the minimum, andthe corresponding energy differences for the formation of the title host−guest inclusion complexes arequalitatively consistent with the experimental results.
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