Inclusion complex of 1,2,3-trihydroxybenzene with α- and β-cyclodextrins

Abstract

Effect of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) on the absorption and fluorescence spectra of pyrogallol (THB) has been discussed. The solid inclusion complex of THB with CD has been investigated by UV -visible, fluorimetry, FT-IR, scanning electron microscopy and semiempirical methods. The thermodynamic parameters (Δ<i>G</i>, Δ<i>H</i> and Δ<i>S</i>) values indicate that the inclusion processes are exothermic and spontaneous. β-CD studies reveal that THB forms 1:1 inclusion complex with β-CD. The small formation constant of THB shows that this molecule is not tightly embedded in the β-CD cavity. In β-CD medium, neutral, monoanion and dianion maxima are blue shifted as compared to in aqueous medium. Also, the <i>pK</i>_a<i> </i>(<i>pK</i>_a<i>*</i>)<i> </i>values in β-CD medium are greater than in aqueous medium. Of the two COs, β-CD can more readily include THB than α-CD. Dual luminescence observed in α-CD shows that intramolecular hydrogen bonding interactions of THB in α-CD is greater than in β-CD. The study also shows that THB is more tightly embedded in α-CD than in β-CD.