Inclusion complex formation of 1.8-dihydroxyanthraquinone with cyclodextrins in aqueous solution and in solid state.

Complex formation between cyclodextrins and 1,8-dihy-droxyanthraquinone in buffer solution has been investigated using absorption, its second derivative (D2), and fluorescence spectroscopy. The results showed that whereas the self-association process was found for 1,8-dihydroxyanthraquinone alone, the monomeric form is microincluded in β- and γ-cyclodextrins. The interaction is more favored as the cavity size of cyclodextrins is larger, the molecule being more tightly bound with γ- than with β-cyclodextrin. The complex formation inhibits the excited-state intramolecular proton transfer process that has already been reported for 1,8-dihydroxyanthraquinone alone.