Binding of neutral substrates by calix[4]pyrroles
Binding of neutral substrates by calix[4]pyrroles
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DOI：
10.1021/ja9632217
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发表时间：
1996-12-11
影响因子：
15
通讯作者：
Sessler, JL
中科院分区：
文献类型：
--
作者：
Allen, WE;Gale, PA;Sessler, JL
中性化合物的分子识别对超分子化学领域提出了挑战。 1 短链醇 2 和简单单酰胺 3 等底物的结合特别困难，因为这些分子几乎没有可用于氢键结合的官能化位点，并且它们缺乏参与有效疏水或 π-π 堆积相互作用所需的大烃表面。因此，中性底物/合成受体复合物的缔合常数通常是适度的， 4 尽管受体的结构复杂性通常很高。此前，我们发现R8-杯[4]吡咯（即内消旋八烷基卟啉原）很容易通过吡咯与对称酮的酸催化缩合反应制备，5可作为阴离子底物（例如氟化物、氯化物、磷酸二氢盐和羧酸盐）的受体。 6 在本文中，我们报告这些大环化合物还可以结合固态和溶液中的中性底物。结构灵活性是杯 [4] 吡咯的一个特征。 7 在固态下，已知的八甲基衍生物 Me8-calix-[4] 吡咯 (1) 在没有底物的情况下采用 1, 3-交替构象，在与 F- 或 Cl- 结合时采用锥体构象。 6 在此基础上，人们认为 1 可能会改变其形状以适应不同的中性底物，8 前提是这些底物可以充当氢键受体。在
Molecular recognition of neutral compounds presents a challenge in the area of supramolecular chemistry. 1 Binding of substrates such as short-chain alcohols2 and simple monoamides3 is particularly difficult because these molecules have few functionalized sites available for hydrogen bonding, and they lack the large hydrocarbon surfaces necessary to participate in efficient hydrophobic or π-π stacking interactions. Association constants for neutral substrate/synthetic receptor complexes are thus generally modest, 4 even though the architectural complexity of the receptors is often high. Previously, we found that the R8-calix [4] pyrroles (ie, meso-octaalkylporphyrinogens), readily made by acid-catalyzed condensation of pyrrole with symmetrical ketones, 5 act as receptors for anionic substrates such as fluoride, chloride, dihydrogen phosphate, and carboxylate. 6 In this paper, we report that these macrocycles also bind neutral substrates, both in the solid state and in solution.Structural flexibility is a characteristic of the calix [4] pyrroles. 7 In the solid state, the known octamethyl derivative Me8-calix-[4] pyrrole (1) adopts a 1, 3-alternate conformation in the absence of substrates and a cone conformation when bound to F-or Cl-. 6 On this basis, it was considered likely that 1 would modify its shape to accommodate different neutral substrates, 8 provided that these can act as hydrogen-bonding acceptors. In