葫[n]环联脲(n=5,6,7,8)与两种重氮氟硼酸盐的包合作用研究

Inclusion Complexation Between Cucurbit[n]uril(n=5,6,7,8) and Two Diazonium Tetrafluoroborates

用核磁共振氢谱和紫外 -可见光谱滴定法考察了葫 [n]环联脲 ( Cucurbit[n]uril,n=5 ,6,7,8)与对甲苯重氮氟硼酸盐和 4,4′-联苯二重氮氟硼酸盐的配位情况 ,并用曲线拟合求得形成的包结配合物的稳定常数 .结果表明 ,不同空腔的葫 [n]环联脲对不同尺寸的重氮氟硼酸盐具有很显著的选择性包结作用 .在相同条件下 ,与葫 [6]环联脲相比 ,葫 [7]环联脲更易于容纳苯环 .同时 ,随着酸性的增强 ,葫 [n]环联脲上的脲羰基质子化程度加大 ,使得其配位能力有所减弱 .

Inclusion complexation between cucurbit[n]uril(CB[n], n=5,6,7,8) and two diazonuim salts in various acid solutions was investigated by 1H NMR spectroscopy and UV-Vis spectrophotometric titration. The binding constants were obtained by using a non-linear least squares curve fitting. The inclusion of diazonuim ions in the cavity of CB[n] made 1H NMR spectra of diazonuim ions moving towards a higher magnetic field. The results indicated that CB[5] and CB[8] couldn′t include the two kinds of diazonium ions efficiently. The cavity of CB[6] was too small to accommodate 4,4′-biphenylene-bis-diazonium ions. CB[7] could contain both p-methylbenzene diazonium and 4,4′-biphenylene-bis-diazonium ions. In contrast to CB[6], CB[7] was more suitable for holding p-methylbenzenediazonium ion, showing that the complex stability is dominated by the size/shape-matching between the host and guest. With increasing the concentration of the acid, the measured binding constants decreased notablely, due to the competitive complex of protons with carbonyls of CB[n].