Aza‐Bambusurils En Route to Anion Transporters

Abstract

Previous calculations of anion binding with various bambusuril analogs predicted that the replacement of oxygen by nitrogen atoms to produce semiaza-bambus[6]urils would award these new cavitands with multiple anion binding properties. This study validates the hypothesis by efficient synthesis, crystallography, thermogravimetric analysis and calorimetry. These unique host molecules are easily accessible from the corresponding semithio-bambusurils in a one-pot reaction, which converts a single anion receptor into a potential anion channel. Solid-state structures exhibit simultaneous accommodation of three anions, linearly positioned within the cavity along the main symmetry axis. The ability to hold anions at a short distance of about 4 Å is reminiscent of natural chloride channels in E. coli, which exhibit similar distances between their adjacent anion binding sites. The calculated transition-state energy for double-anion movement through the channel suggests that although these host-guest complexes are thermodynamically stable they enjoy high kinetic flexibility to render them efficient anion channels.

Bambusurils Bearing Nitro Groups and Their Further Modifications

“…The BU [4] cavity is too small for the inclusion of any anion. On the other hand, BU [6] is able to encapsulate inorganic anions of different sizes to form BU [6] anion complexes. That is why inorganic anions are used as templates to favor the formation of BU [6] over BU [4].…”

“…On the other hand, BU [6] is able to encapsulate inorganic anions of different sizes to form BU [6] anion complexes. That is why inorganic anions are used as templates to favor the formation of BU [6] over BU [4]. In other words, six glycoluril units assemble around a template as a result of 12 stabilizing C-H···anion hydrogen bonds, giving rise to the six-membered macrocycle BU [6].…”

“…That is why inorganic anions are used as templates to favor the formation of BU [6] over BU [4]. In other words, six glycoluril units assemble around a template as a result of 12 stabilizing C-H···anion hydrogen bonds, giving rise to the six-membered macrocycle BU [6]. [2,3] BU[n] derivatives differing in the substituents attached to the nitrogen atoms on their portals have been prepared.…”

“…The type of substituent significantly influences the solubility of the macrocycle. For example, bambusurils bearing benzyl groups, BU [4]d and BU [6]d [3] (Figure 1), show good solubility in chloro-which provided the macrocycles with water solubility and allowed their further modification. For example, we have demonstrated the conversion of amino groups on the bambusurils into the corresponding urea-functionalized bambusuril derivatives.…”

“…form, whereas the macrocycle BU [6]f containing carboxybenzyl groups [2] is soluble in neutral and basic water. Besides our group, other research teams have explored the chemistry of bambusurils.…”