13C-N.M.R. spectra of cyclomalto-oligosaccharides (cyclodextrins), their derivatives, and complexes with azo dyes.

The nature of the inclusion complexes of several cyclomalto-oligosaccharides (cyclodextrins, CDs) with azo dyes has been studied on the basis of 13C-n.m.r. chemical shifts, relaxation times, correlation times, and broadening and doubling of the n.m.r. signals. All CDs show the azo dye-induced shifts at the narrow-rim side of the CD, indicating that the azo dyes protrude from the cavity. CD-induced shifts of azo dyes depend on the hydrophobic nature of the cavity, van der Waals forces, as well as ring-current and deformation effects, and suggest inclusion essentially from the hydrophobic site. The broadening and the doubling of the 13C-n.m.r. signals, the altered relaxation and correlation times, as well as the temperature dependence for these phenomena, also provide particular information about the characteristic host-guest interactions.