Wagner Brian D, Boland Patricia G, Lagona Jason, Isaacs Lyle
Department of Chemistry, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada.
J Phys Chem B. 2005 Apr 28;109(16):7686-91. doi: 10.1021/jp044369c.
This paper describes the host properties of a new cucurbit[6]uril analogue, studied by fluorescence and 1H NMR spectroscopy. This host has an elongated cavity with oval-shaped portals. It is intrinsically fluorescent, and more importantly, this fluorescence is sensitive to guest encapsulation, allowing for the study of the inclusion of nonfluorescent guests by fluorescence spectroscopy. In the case of benzene as guest, significant enhancement of the cucurbit[6]uril analogue host fluorescence was observed upon addition of benzene; this allowed for the determination of the binding constant for 1:1 host-guest complexation, yielding a value of K = 6900 +/- 1100 M(-1). This complexation was also studied by 1H NMR, yielding a similar value of K = 8980 +/- 500 M(-1). The binding of a much larger guest, the dye Nile Red, was also studied, but in this case using guest fluorescence. Significant suppression of the Nile Red fluorescence was observed upon 1:1 complexation with the cucurbit[6]uril analogue, with an extremely large binding constant of 8.2 +/- 0.5 x 10(6) M(-1), indicating a very strong host-guest interaction and an excellent size and shape match. In both cases, binding was much stronger than in the case of the same guests with cucurbit[6]uril itself, and in the case of Nile Red, binding was also much stronger than with modified beta- or gamma-cyclodextrins. This is partly a result of the partial aromatic nature of the host walls, which allow for pi-pi interactions not possible in cucurbiturils or cyclodextrins. The ability to study its inclusion complexes using either host or guest fluorescence, and the very high binding constants observed, illustrates the versatility and potential usefulness of this new host compound.
本文描述了一种新型葫芦[6]脲类似物的主体性质，通过荧光光谱和¹H NMR光谱进行了研究。该主体具有一个带有椭圆形入口的细长空腔。它本身具有荧光，更重要的是，这种荧光对客体包封敏感，从而能够通过荧光光谱研究非荧光客体的包合情况。以苯作为客体时，加入苯后观察到葫芦[6]脲类似物主体荧光显著增强；这使得能够测定1:1主体 - 客体络合的结合常数，得到的值为K = 6900 ± 1100 M⁻¹。这种络合也通过¹H NMR进行了研究，得到的K值类似，为8980 ± 500 M⁻¹。还研究了一种大得多的客体染料尼罗红的结合情况，但在这种情况下使用的是客体荧光。当尼罗红与葫芦[6]脲类似物以1:1络合时，观察到尼罗红荧光显著猝灭，结合常数极大，为8.2 ± 0.5 × 10⁶ M⁻¹，表明主体 - 客体相互作用非常强，且尺寸和形状匹配极佳。在这两种情况下，结合都比相同客体与葫芦[6]脲本身的情况要强得多，对于尼罗红来说，结合也比与修饰的β - 或γ - 环糊精的情况要强得多。这部分是由于主体壁的部分芳香性质，使得在葫芦脲或环糊精中不可能发生的π - π相互作用成为可能。利用主体或客体荧光研究其包合物的能力以及观察到的非常高的结合常数，说明了这种新型主体化合物用途广泛且具有潜在实用性。
