This report describes cucurbit[7]uril (CB7) complexation of azobenzene dyes that have a 4-(N,N′-dimethylamino) or 4-amino substituent. Absorption and NMR data show that CB7 encapsulates the protonated form of the azobenzene and that the complexed dye exists as its azonium tautomer with a trans azo conformation and substantial quinoid resonance character. Because CB7 complexation stabilizes the dye conjugate acid, there is an upward shift in its pK_a, and in one specific case, the pK_a of the protonated azobenzene is increased from 3.09 to 4.47. Molecular modeling indicates that the CB7/azobenzene complex is stabilized by three major noncovalent factors: (i) ion-dipole interactions between the partially cationic 4-(N,N′-dimethylamino) or 4-amino group on the encapsulated protonated azobenzene and the electronegative carbonyl oxygens on CB7, (ii) inclusion of the upper aryl ring of the azobenzene within the hydrophobic CB7 cavity, and (iii) a hydrogen bond between the proton on the azo nitrogen and CB7 carbonyls. CB7 complexation enhances azobenzene stability and increases azobenzene hydrophilicity; thus, it is a promising way to improve azobenzene performance as a pigment or prodrug. In addition, the striking yellow/pink color change that accompanies CB7 complexation can be exploited to create azobenzene dye displacement assays with naked eye detection.

中文翻译：

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葫芦[7]脲超分子络合偶氮苯染料

该报告描述了具有 4-( N , N '-二甲基氨基) 或 4-氨基取代基的偶氮苯染料的葫芦[7]脲 (CB7) 络合。吸收和核磁共振数据表明，CB7 封装了偶氮苯的质子化形式，并且络合染料以其氮互变异构体的形式存在，具有反式偶氮构象和显着的醌型共振特征。由于 CB7 络合稳定了染料共轭酸，因此其 p K _a向上移动，并且在一种特定情况下，p K _a质子化偶氮苯的摩尔分数从3.09增加到4.47。分子模型表明 CB7/偶氮苯复合物通过三个主要非共价因子稳定：(i) 部分阳离子 4-( N , N包封的质子化偶氮苯上的 '-二甲氨基）或 4-氨基和 CB7 上的负电羰基氧，（ii）疏水性 CB7 空腔内包含偶氮苯的上芳环，以及（iii）质子之间的氢键在偶氮氮和CB7羰基上。CB7络合增强偶氮苯稳定性并增加偶氮苯亲水性；因此，它是提高偶氮苯作为颜料或前药性能的有前途的方法。此外，CB7 络合所伴随的显着黄色/粉色颜色变化可用于通过肉眼检测进行偶氮苯染料置换测定。