129Xe and 1H NMR study of the reversible trapping of xenon by cryptophane-A in organic solution
129Xe and 1H NMR study of the reversible trapping of xenon by cryptophane-A in organic solution
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DOI：
10.1021/ja972377j
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发表时间：
1998-02-04
影响因子：
15
通讯作者：
Reisse, J
中科院分区：
文献类型：
--
作者：
Bartik, K;Luhmer, M;Reisse, J
用Xe-129和H-1核磁共振谱研究了I，1,2,2-四氯乙烷-d(2)中氙与隐烷- a的相互作用。在278 K时，氙被可逆地捕获到宿主腔中，形成1对1的主客体复合物，其表观结合常数K至少为3 × 10(3) M-1。在氙-129核磁共振时间尺度上，自由氙和束缚氙之间的交换是缓慢的，并且束缚氙共振相对于自由氙共振大约移位了160 ppm到更低的频率。在相同条件下，氙配合物比相应的氯仿和甲烷配合物分别至少稳定4倍和20倍。这种氙配合物的稳定性似乎比先前描述的α -环糊精在水中的氙配合物要大得多，这可能是由于三个有利效应的结合：(1)在最松弛的构象中，客体和隐烷腔之间的尺寸匹配良好，导致高极化客体和宿主的富电子芳香环之间的伦敦力优化（焓稳定）；（ii）隐晶腔中单原子客体无旋转或振动熵损失；（iii）由于主体构象自由度的降低，没有（或很少）熵损失。分析自由氙和束缚氙对应的信号的线宽与相对氙/隐烷比的函数关系表明，进入的氙原子必须取代离开的氙原子才能进入隐烷腔，并且空的隐烷不参与络合平衡。
The interaction of xenon with cryptophane-A in I,1,2,2-tetrachloroethane-d(2) is investigated by Xe-129 and H-1 NMR spectroscopy. Xenon is reversibly trapped into the cavity of this host to form a 1 to 1 host-guest complex with an apparent association constant K of the order of at least 3 x 10(3) M-1 at 278 K. The exchange between the free and bound xenon is slow on the Xe-129 NMR time scale, and the bound xenon resonance is shifted by approximately 160 ppm to lower frequencies with respect to the free xenon resonance, The xenon complex is at least 4 and 20 times more stable, respectively, than the corresponding chloroform and methane complexes under the same conditions. The stability of this xenon complex appears to be much greater than that of the previously described xenon complex of alpha-cyclodextrin in water, This is probably due to the combination of three favorable effects: (i) good size matching between the guest and the cryptophane cavity in its most relaxed conformation, resulting in the optimization of the London forces between the highly polarizable guest and the electron rich aromatic rings of the host (enthalpic stabilization); (ii) no rotational or vibrational entropy loss of the monatomic guest in the cryptophane cavity; and (iii) no (or little) entropy loss due to reduction of the conformational freedom of the host, Analysis of the line widths of the signals corresponding to the free and bound xenon as a function of the relative xenon/cryptophane ratio suggests that the incoming xenon atom must displace the departing one to enter the cryptophane cavity, and that the empty cryptophane is not involved in the complexation equilibrium.