[Study on the molecular recognition of perhydroxycucurbit[6] uril with methyl orange by spectroscopic methods]

The inclusion interaction of perhydroxycucurbit[6] uril (HOCB6) with methyl orange (MO) was studied by UV spectroscopic and fluorimetric methods. Several effect factors, such as pH values, common organic solvents and surfactants on the fluorescence intensity and the stability of the complex were investigated. The results indicate that the fluorescence intensity of MO was enhanced with a blue shift as host molecules were added, showing that MO was accommodated into the hydrophobic cavities of HOCB6 and an endo-inclusion complex was formed. The hydrophobic interaction between HOCB6 and MO mainly contributed to the formation of 1 : 1 type HOCB6-MO. Its complex constant was determined to be 1.41 x 10(2) L x mol(-1). The comparative study of HOCB6 with other supramolecules, such as cucurbit[6] uril (CB6), p-(N,N-dimethyl-aminomethyl) calix [8]arene and beta-cyclodextrin, was also carried out by using MO as a guest probe. The spectra changes showed that cucurbit[6] uril (CB6) can also form 1 : 1 type endo-inclusion complex with MO, which is similar to HOCB6, but its complex constant (34.65 L x mol(-1)) is small. The spectra changes also showed that the endo-inclusion complex with 2 : 1 type was formed between beta-cyclodextrin and MO, While the exo-inclusion complex was formed between p-(N,N-dimethyl-aminomethyl) calix[8] are-ne and MO, leading to fluorescence quenching, and their complex constants were determined to be 6.14 x 10(6) L2 mol(-2) and 1.35 x 10(4) L x mol(-1), respectively.