Inclusion behavior of alpha-cyclodextrin with 2-methylnaphthalene in aqueous solutions

By means of absorption and fluorescence spectroscopy, 2-methylnaphthalene (2MN) was found to be incorporated into the cavity of alpha-cyclodextrin (alpha-CD) to form a 1 : 1 inclusion complex. The 1 : 1 inclusion complex further associated with another alpha-CD molecule, resulting in the formation of a 2 : 1 alpha-CD-2MN inclusion complex. The equilibrium constants for the formation of the 1 : 1 and 2 : 1 inclusion complexes were estimated to be 44.6 and 376 mol(-1) dm(3), respectively, on the basis of a simulation of the observed 2MN fluorescence intensities. The induced circular dichroism spectra suggested that 2MN, buried within the alpha-CD inclusion complexes, resided in a different orientation relative to the CD symmetry axis, as compared to 2MN within a beta-CD inclusion complex.