Interactions of cucurbit[7]uril and β-cyclodextrin with some nucleobases

The binding affinity of both macrocyclic receptors, cucurbit[7]uril (CB[7]) and β-cyclodextrin (β-CD), respectively, towards guanine and cytosine was investigated in solution by means of UV spectroscopy and fluorescence spectroscopy. The association constants and the stoichiometry of host–guest complexes were determined. Thus by the Job’s method of continuous variations, the stoichiometry of CB[7]-cytosine and β-cyclodextrin-guanine was found to be 1:1 for both complexes under study. The UV absorption and fluorescence intensity of guanine increased in the presence of β-cyclodextrin highlighting the formation of the complex between guanine and β-cyclodextrin. Correlating the results obtained by UV absorption spectroscopy with the findings from fluorescence measurements leads to concluding that formation of an inclusion complex of β-cyclodextrin with guanine at pH 3.0 is possible.