1H-NMR investigation of the binding of 2-methylnaphthalene to α-cyclodextrin in D2O solutions

As alpha-cyclodextrin (alpha-CD) was added to D2O solutions of 2-methylnaphthalene, its proton signals shifted to lower fields at low concentrations of alpha-CD. At 2.0 x 10(-2) mol dm(-3) of alpha-CD, however, a reverse, higher-field shift was observed for the H-8 signal, indicating the formation of 1 : 1 and 2: 1 alpha-CD-2-methylnaphthalene inclusion complexes. Intrinsic chemical shift differences of all the protons in 2-methylnaphthalene have been evaluated for both the 1:1 and the 2:1 alpha-CD-2-methylnaphthalene inclusion complexes. These intrinsic chemical shift differences suggest that the first alpha-CD molecule has no selectivity in accommodating one end of uncomplexed 2-methylnaphthalene; alpha-CD binds to a methyl group, as well as a naphthalene ring-end having no methyl group, to form the 1 : 1 inclusion complex, resulting in the formation of two kinds of 1 : 1 complexes.