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Chemphyschem. 2014 Jan 13;15(1):139-50. doi: 10.1002/cphc.201300871. Epub 2013 Dec 2.
Viologens readily thread bis-p-phenylene crown ethers to form [2]pseudorotaxanes. However, the binding of sterically hindered 3,3'-dimethylviologens is very weak. Density functional theory (DFT) calculations indicated that the additional energy cost of "flattening" is substantial, 55 kJ mol(-1), and prevents the formation of a stable host-guest complex. The structures of [2]pseudorotaxanes determined by X-ray crystallography are in good agreement with the NMR characterisation and DFT results. Their association constants and thermodynamic parameters in solution were measured by using a dilution method and, for the first time, by host-guest nuclear Overhauser effect (NOE) correlations. The NOE approach was subsequently applied to study the sterically hindered analogues and it was shown that the binding in 3,3'-dimethyl-N,N-dibenzyl [2]pseudorotaxane is by 8.5 kJ mol(-1) weaker than in its regular analogue. The proposed technique helps to quantify weak interactions in [2]pseudorotaxanes and can be applied to other host-guest complexes.
Viologen 很容易将双对苯撑冠醚穿成 [2] 伪轮烷。然而，空间位阻较大的 3,3'- 二甲基 Viologen 的结合非常弱。密度泛函理论 (DFT) 计算表明，“变平”的额外能量成本很大，为 55 kJ/mol，这阻止了稳定的主客体络合物的形成。通过 X 射线晶体学确定的 [2] 伪轮烷的结构与 NMR 特征和 DFT 结果非常吻合。通过稀释法和首次使用主客体核 Overhauser 效应 (NOE) 相关，测量了它们在溶液中的缔合常数和热力学参数。随后，该方法被应用于研究空间位阻类似物，并表明 3,3'- 二甲基-N,N-二苄基 [2] 伪轮烷的结合比其常规类似物弱 8.5 kJ/mol。该技术有助于量化 [2] 伪轮烷中的弱相互作用，并可应用于其他主客体络合物。
