光谱法研究七、八元瓜环对亚甲基蓝的分子识别

Recognition of Cucurbit[7 and 8] urils Toward Methylene Blue with Spectroscopy

利用紫外-可见吸收光谱和荧光光谱法考察了七、八元瓜环(Q[7],Q[8])对客体亚甲基蓝染料(g)的分子识别作用。结果表明,Q[7]与g作用形成物质的量比为2∶1的主客体配合物,Q[8]与g作用形成的是物质的量之比为1∶2的主客体配合物。吸收光谱法测得的包结常数分别为KQ[7]-g=1.34×1012L2·mol-2,KQ[8]-g=5.34×1012L2·mol-2;荧光光谱法测得的KQ[7]-g=1.53×1012L2·mol-2,KQ[8]-g=6.11×1012L2·mol-2,两种方法结果一致。随着Q[7或8]浓度的增加,瓜环对客体有明显的荧光增敏作用,而Q[8]对客体有明显的荧光猝灭作用。从Q[7]和Q[8]分别与客体作用体系的紫外-可见吸光度和荧光强度随pH值改变的变化规律可以看出,体系在pH在0.5～13范围内均能观察到主客体的相互作用,且作用比例不发生变化。

The molecular recognition of cucurbit[7,8]urils toward a methylene blue dye was investigated by using electronic absorption spectroscopy and fluorescence spectroscopy. The experimental results revealed that the formation of host-guest complexes between Q[7] and the methylene blue dye were formed with a stoichiometry of 2∶1,while the formation of host-guest complexes between Q[8] and the methylene blue dye were formed with a stoichiometry of 1∶2. The calculated binding constants are KQ[7]-g=1.34×10^12 L^2·mol^-2 and KQ[8]-g=5.34×10^12 L^2·mol^-2 respectively based on the absorption spectrophotometric analysis,while the calculated binding constants are KQ[7]-g=1.53×10^12 L^2·mol^-2 and KQ[8]-g=6.11×10^12 L^2·mol^-2 respectively based on the fluorescence spectroscopy analysis. The values of K are reasonably consistent. The fluorescence of the guest was found to rapidly increase with the increase in the concentration of Q[7],while the fluorescence of the guest was found to rapidly decrease with the increase in the concentration of Q[8]. Based on the variation of the absoption or fluorecence of the host-guest complexes of Q[7] or Q[8]-methylene blue dye with the variation of pH,the interaction of the Q[7] or Q[8] and the methylene blue dye with an unchangeable ratio can be observed in the range of pH between 0.5 and 13.