Formation Constants of Cyclodextrin Inclusion Complexes with Iodine in Aqueous Solutions

Abstract
Formation constants of cyclodextrin (CyD) inclusion complexes with iodine were determined by measuring solubilities of iodine vapor in water. The formation constants at 25 °C are 8.3×103 (α-CyD), 1.0×102 (β-CyD), and 13 dm3 mol−1 (γ-CyD). The temperature dependence of α-CyD–I2 complexation was studied. ΔH and ΔS, being 9.52 kJ mol−1 and 107 J K−1 mol−1 at 25 °C, respectively, are both largely dependent on temperature even within a rather small temperature range 15–35 °C studied. For the complexation with α-CyD, contribution of dehydration of iodine was estimated. The method proposed here is useful to study the formation of CyD association complexes with such substrates as are slightly soluble in water and easily vaporize from the aqueous phase.

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