Recognition of Cucurbit[7 and 8]urils Toward Methylene Blue with Spectroscopy
FENG Yan1, XUE Sai-feng1, 2*, MU Lan1, 2, ZHU Qian-jiang1, 2, TAO Zhu1, 2
1. Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025, China 2. Institute of Applied Chemistry, Guizhou University, Guiyang 550025, China
Abstract：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=1.34×1012 L2·mol-2 and KQ[8]-g=5.34×1012 L2·mol-2 respectively based on the absorption spectrophotometric analysis, while the calculated binding constants are KQ[7]-g=1.53×1012 L2·mol-2 and KQ[8]-g=6.11×1012 L2·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.
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