Highly selective recognition of diols by a self-regulating fine-tunable methylazacalix[4]pyridine cavity: guest-dependent formation of molecular-sandwich and molecular-capsule complexes in solution and the solid state.
Highly selective recognition of diols by a self-regulating fine-tunable methylazacalix[4]pyridine cavity: guest-dependent formation of molecular-sandwich and molecular-capsule complexes in solution and the solid state.
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DOI：
10.1002/chem.200700498
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发表时间：
2007-09
期刊：
影响因子：
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通讯作者：
H. Gong;De‐Xian Wang;Jun-feng Xiang;Qi-Yu Zheng;Mei-Xiang Wang
中科院分区：
文献类型：
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作者：
H. Gong;De‐Xian Wang;Jun-feng Xiang;Qi-Yu Zheng;Mei-Xiang Wang
用核磁共振氢谱和X射线衍射研究了甲基氮杂杯[4]吡啶（MACP-4; 1）对多种二元醇的分子识别作用。MACP-4是一种独特的大环主体分子，在溶液中能迅速发生构象反转，通过四个桥氮原子与相邻吡啶环形成不同的共轭，形成一个与客体分子通过分子间氢键、C-H键、氢键和氢键相互作用的空穴，从而自我调节其构象。π，以及宿主和客体之间的π-π相互作用。因此，根据二醇结构和几何形状，MACP-4与客体形成1：1分子三明治、2：1分子胶囊和1：2蝶形层状复合物。由于良好的焓和熵效应，MACP-4在识别间苯二酚方面表现出优异的选择性，从而导致与间苯二酚的非常稳定的1：1夹心复合物，结合常数为6000（M-1）。动态1H NMR研究表明，MACP-4间苯二酚配合物（13）的大环1，3-交替构象在低温（T<243 K）下是稳定的，其构象转化需要较大的活化能（Δ G ++=（45.5+/-2.2）kJ mol（-1））.当间苯二酚过量时，MACP-4间苯二酚络合物的构象转化更容易进行，活化能降低（Δ G ++=（33.5+/-1.5）kJ mol（-1）），这很可能是由于[3]-[4]-间苯二酚络合物的有利焓效应。1... 3]++过渡态。
The molecular recognition of methylazacalix[4]pyridine (MACP-4; 1) towards various diols was investigated by using (1)H NMR spectroscopic and X-ray diffraction analysis. As a unique macrocyclic host molecule that undergoes conformational inversions very rapidly in solution, MACP-4 has been shown to self-regulate its conformation, through the formation of different conjugations of the four bridging nitrogen atoms with their adjacent pyridine rings, to form a cavity that best fits the guest species through intermolecular hydrogen-bond, C-H...pi, and pi-pi interactions between the host and guest. As a consequence, depending upon the diol structure and geometry, MACP-4 forms a 1:1 molecular sandwich, 2:1 molecular capsule, and 1:2 butterfly-layered complex with the guests. As a result of favorable enthalpy and entropy effects, MACP-4 exhibits excellent selectivity in the recognition of resorcinol, thus resulting in a very stable 1:1 sandwich complex with resorcinol with a binding constant of 6000 (M-1). The dynamic (1)H NMR spectroscopic study demonstrated that the 1,3-alternate conformation of the macrocyclic ring of the MACP-4resorcinol complex (13) is stable at low temperature (T<243 K), and its conformational inversion requires a larger activation energy (DeltaG++=(45.5+/-2.2) kJ mol(-1)). In the presence of an excess amount of resorcinol, however, the conformational inversion of the MACP-4resorcinol complex proceeds more readily with a decreased activation energy (DeltaG++=(33.5+/-1.5) kJ mol(-1)) owing most probably to the favorable enthalpy effect of the [3...1...3]++transition state.