Acyclic Cucurbit[n]uril Congeners Are High Affinity Hosts
Acyclic Cucurbit[n]uril Congeners Are High Affinity Hosts
复制标题
DOI：
10.1021/jo100760g
复制
发表时间：
2010-07-16
影响因子：
3.6
通讯作者：
Isaacs, Lyle
中科院分区：
文献类型：
--
作者：
Ma, Da;Zavalij, Peter Y.;Isaacs, Lyle
我们介绍了通过亚甲基桥联甘脲四聚体构建块的设计、合成以及非环葫芦[n]脲同系物的表征，这些同系物可以作为水中各种氨离子的宿主。自由主体及其与对二甲二胺和精胺的络合物的X射线结晶学表征确定了非环葫芦同系物的亚甲基桥联主链的灵活性，使它们能够适应客体的结构特征。我们发现，非环葫芦[n]脲同系物具有四个相邻的亚甲基桥联甘脲单元和两个含有CO(2)H取代基的芳香族邻二甲苯基团，它们与缓冲水中的氨离子结合，K(A)值从接近10(5)M(-1)到大于10(9)M(-1)。与葫芦[n]uril家族的宿主类似，我们发现，增加缓冲液中金属离子的浓度，通过在ureidyl C=O门户上的竞争结合，降低了非环葫芦[n]uril同系物对客体的亲和力。尽管非环葫芦环同系物保持了与高亲和力的氨离子结合的能力，但它们这样做的选择性低于葫芦环对宿主结构灵活性的影响。缺少取代邻二甲苯壁的亚甲基桥联甘脲四聚体模型化合物是一个亲和力低得多的宿主，这证实了这些环对无环葫芦[n]uril同系物的整体识别行为的重要性。总体而言，本文的结果证明，含有四个或更多连续的亚甲基桥联甘脲单元的非环葫芦[n]脲受体保留了葫芦[n]脲家族的许多良好的识别特性。
We present the design, synthesis via methylene bridged glycoluril tetramer building blocks, and charaterization of acyclic cucurbit[n]uril congeners that function as hosts for a wide variety of ammonium ions in water. The X-ray crystallographic characterization of the free host and its complexes with p-xylylenediamine and spermine establish the flexibility of the methylene bridged backbone of the acyclic cucurbit[n]uril congeners that allow them to adapt to the structural features of the guest. We find that the acyclic cucurbit[n]uril congeners-with their four contiguous methylene bridged glycoluril units and two aromatic o-xylylene walls bearing CO(2)H substituents-bind to ammonium ions in buffered water with values of K(a) ranging from similar to 10(5) M(-1) to greater than 10(9) M(-1). Similar to the cucurbit[n]uril family of hosts, we find that increasing the concentration of metal cations in the buffer reduces the affinity of the acyclic cucurbit[n]uril congener toward guests by competitive binding at the ureidyl C=O portals. Although the acyclic cucurbit[n]uril congeners retain the ability to bind to ammonium ions with high affinity, they do so with lower selectivity than cucurbit[n]urils presumably do to the structural flexibility of the hosts. A methylene bridged glycoluril tetramer model compound that lacks the substituted o-xylylene walls is a much lower affinity host, which establishes the importance of these rings on the overall recognition behavior of the acyclic cucurbit[n]uril congeners. Overall, the results in this paper establish that acyclic cucurbit[n]uril receptors that contain four or more contiguous methylene bridged glycoluril units retain many of the excellent recognition properties of the cucurbit[n]uril family.