Inclusion compounds of cyclodextrin and azo dyes. II. 1H nuclear magnetic resonance and circular dicroism spectra of cyclodextrin and azo dyes with a naphthalene nucleus.

Abstract

Azo dyes with a hydroxylated α-naphthyl group form 1 : 1 complexes with cyclodextrin. The nature of the substituent, the bulkiness of the molecule, the change of the 1H nuclear magnetic resonance (NMR) spectral pattern of cyclodextrin and the signs of the maxima in circular dicroism (CD) spectra indicate the specific orientation and freedom of motion in the cavity of the guest molecules after inclusion. For example, in orange II-β-cyclodextrin complex, the 1H NMR spectrum of β-cyclodextrin rules out inclusion from the benzenesulfonate side of orange II. The CD spectrum suggests inclusion from the short molecular axis side and tight fitting with β-cyclodextrin. The azo dyes investigated are longer than the depth of the cavity of cyclodextrin. Nevertheless, the inclusion shifts of the guest molecules are not localized at one side of the molecule. The whole H2O structure around the azo dye is probably broken down upon inclusion, or the included azo group produces inclusion shifts at all the ring protons.