ABSTRACT Two acyclic CB[n]-type hosts (1 and 2) which possess four 2° or 3° amide arms are reported. Host 2 has four 3° amide arms that exist as a mixture of E- and Z-isomers. 1H NMR was used to qualitatively investigate the binding properties of 1 and 2 which indicates they retain the essential binding features of macrocyclic CB[n] hosts. We measured the Ka values of 1 and 2 toward guests 6–14 by ITC. Neutral hosts 1 and 2 bind less tightly than tetraanionic hosts M1, ACB1, and ACB2. We attribute the lower Ka values to the absence of secondary ion-ion electrostatic interactions for host•guest complexes of 1 and 2. The secondary amide functionality on 1 decreases affinity by the formation of intramolecular NH•••O=C H-bonds. Tertiary amide host 2 binds even more weakly than 1 due to backfolding of the amide N-CH3-groups of 2 into its own cavity. Graphical abstract

中文翻译：

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无环葫芦[n]uril型受体：仲酰胺臂与叔酰胺臂

摘要 报道了具有四个 2° 或 3° 酰胺臂的两种无环 CB[n] 型主体（1 和 2）。Host 2 有四个 3° 酰胺臂，它们以 E- 和 Z-异构体的混合物形式存在。1H NMR 用于定性研究 1 和 2 的结合特性，这表明它们保留了大环 CB[n] 主体的基本结合特征。我们测量了 ITC 对 6-14 位客人的 Ka 值 1 和 2。中性宿主 1 和 2 的结合不如四阴离子宿主 M1、ACB1 和 ACB2。我们将较低的 Ka 值归因于 1 和 2 的宿主•客体复合物没有次级离子-离子静电相互作用。1 上的二级酰胺官能团通过形成分子内 NH•••O=C 氢键降低了亲和力。由于 2 的酰胺 N-CH3-基团反向折叠到其自身的腔中，叔酰胺宿主 2 的结合甚至比 1 更弱。