A deep, water-soluble cavitand acts as a phase-transfer catalyst for hydrophobic species
A deep, water-soluble cavitand acts as a phase-transfer catalyst for hydrophobic species
复制标题
DOI：
10.1002/anie.200600405
复制
发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Rebek, Julius, Jr.
中科院分区：
文献类型：
--
作者：
Hooley, Richard J.;Biros, Shannon M.;Rebek, Julius, Jr.
产物抑制通常是合成受体催化的一个问题超分子催化剂对高周转率所需的过渡结构和产物没有精确的识别能力，除了少数例外，[2,3]它们的反应会减慢，然后停止。我们现在已经遇到了与水溶性四羧酸盐腔体和1相转移催化的情况（方案1）这些反应产生的阴离子产物被中性反应物所取代，从而迫使高周转率。结果表明，在识别事件中超越形状互补性可以导致有效的催化剂。正构烷烃本质上不溶于水，可被萃取到含有1的水溶液中，形成1:1的化学计量配合物疏水稳定性驱动这种结合并导致非常高的结合常数。受体的开放性使一部分客体暴露在水环境中。当客体通过化学转化获得水溶性功能时，客体的疏水稳定性随着结合亲和力的降低而降低。这允许客体被起始材料取代，从而导致周转和使用空腔体作为相转移催化剂（图1）。例如，十二烷基硫酸钠（SDS）在低于其临界胶束浓度[8]时是一个很好的客体，但在更高浓度时没有观察到结合；只有在不适宜溶于水的情况下才会粘结。b[9]我们使用了“两部分”的反应物来影响这一过程：疏水锚（为空腔体提供水不溶性和形状互补性）和反应官能团n取代马来酰亚胺。通过核磁共振光谱分析，n - adamantylmale亚胺3等物质没有水溶性，而3 - 9均被提取到1 / 2o的溶液中。它们的核磁共振光谱表明，底物3-9的碳氢化合物部分结合在腔内，而马来酰亚胺功能暴露在溶剂中。
Product inhibition is generally a problem for catalysis by synthetic receptors.[1] Supramolecular catalysts do not show the exquisite recognition of transition structures versus products required for high turnover and, with few exceptions,[2, 3] their reactions slow down, then stop. We have now encountered cases of phase-transfer catalysis [4] with the watersoluble tetracarboxylate cavitand 1 (Scheme 1).[5] The reactions produce anionic products that are replaced with a neutral reactant, thus forcing high turnover. The results suggest that moving beyond shape complementarity in the recognition event can lead to efficient catalysts. Normal alkanes, which are essentially insoluble in water, can be extracted into aqueous solutions containing 1 and form stoichiometric 1: 1 complexes.[7] Hydrophobic stabilization drives this binding and leads to very high association constants. The open-ended nature of the receptor exposes a portion of the guest to the aqueous environment. When the guest gains a water-soluble functionality by chemical transformation, the hydrophobic stabilization of the guest is decreased along with the binding affinity. This allows the guest to be replaced by the starting material, thus leading to turnover and the use of the cavitand as a phase-transfer catalyst (Figure 1). For example, sodium decyl sulfate (SDS) is a good guest for 1 below its critical micelle concentration,[8] but no binding is observed at higher concentrations; the guest only binds if dissolution in water is unfavorable.[9]We used a “two-part” reactant to effect the process: a hydrophobic anchor (to provide water insolubility and shape complementarity for the cavitand) and a reactive functionality, N-substituted maleimides. Species such as N-adamantylmaleimide 3 show no water solubility by NMR spectroscopic analysis, yet maleimides 3–9 are all extracted into a solution of 1 in D2O. Their NMR spectra show that the hydrocarbon portions of substrates 3–9 are bound inside the cavity, whereas the maleimide function is exposed to the solvent.