A molecular cage consisting of two cyclic hexapeptides with an alternating sequence of (2S,4S)-4-aminoproline and 6-aminopicolinic acid subunits, covalently linked via three diglycolic acid subunits, interacts with a variety of inorganic anions in acetonitrile/water. In the respective complexes, the anion resides in a cavity between the two cyclopeptide rings where it interacts with six converging NH groups. The cage binds sulfate anions in acetonitrile/water, 2 : 1 (v/v) with a log Ka of 6.7, ca. 2.5 orders of magnitude stronger than an analogous bis(cyclopeptide) with only one linker whose sulfate affinity log Ka amounts to 4.3. The preorganization induced by the three linking units is thus beneficial for sulfate binding. In addition, these linkers cause the dissociation of the sulfate complex to have a substantial Gibbs free energy of activation ΔG≠ of 68.9 kJ mol-1 and they also seem to affect anion selectivity as illustrated by the different effects some anions produce on the 1 H NMR spectra of the triply and singly-linked bis(cyclopeptides). Such anion binding cages represent promising scaffolds to mimic natural anion receptors such as the sulfate-binding protein.

中文翻译：

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水溶液混合物中环肽衍生分子笼的阴离子结合。

由两个环状六肽组成的分子笼，具有交替的（2S，4S）-4-氨基脯氨酸和6-氨基吡啶甲酸亚基序列，通过三个二乙醇酸亚基共价连接，与乙腈/水中的多种无机阴离子相互作用。在各自的络合物中，阴离子位于两个环肽环之间的空腔中，在该空腔中它与六个会聚的NH基团相互作用。笼子在乙腈/水中以2：1（v / v）结合硫酸根阴离子，log Ka值为6.7。比仅具有一个接头的硫酸盐亲和力对数Ka为4.3的类似双（环肽）强2.5个数量级。因此，由三个连接单元诱导的预组织对于硫酸盐结合是有益的。此外，这些接头使硫酸盐络合物的解离具有68.9 kJ mol-1的大量Gibbs活化能ΔG≠，并且似乎还影响阴离子的选择性，如某些阴离子在1 H NMR光谱上产生的不同影响所说明的那样。三键和单键连接的双（环肽）。这样的阴离子结合笼代表了有前途的支架，以模仿天然阴离子受体，例如硫酸盐结合蛋白。