UV-VISIBLE SPECTROSCOPIC INVESTIGATION OF THE 1,3,6,8-TETRAHYDROXYXANTHYLIUM ION IN AQUEOUS-SOLUTION - STRUCTURAL TRANSFORMATIONS AND MOLECULAR COMPLEXATION WITH CYCLODEXTRINS AND CAFFEINE

1,3,6,8-tetrahydroxyxanthylium chloride, a polyphenolic dye, has been investigated by UV-vis spectroscopy in strongly acidic to slightly alk aline aqueous solutions. Variations in the dye concentration, solvent effects and molecular complexation experiments using cyclodextrins and caffeine have made it clear that the dye exists essentially as a dime r in aqueous solution except in the presence of beta-cyclodextrin and caffeine, which form stable molecular complexes with the monomer. By c ontrast, strong binding between gamma-cyclodextrin and the dimer has b een demonstrated. Moreover, encapsulation into the cyclodextrins appea rs to be the most convenient way to distinguish the monomer from the d imer on the basis of their spectral properties.