Kinetic and thermodynamic analysis of the cyclodextrin-allyl isothiocyanate inclusion complex in an aqueous solution.

The decomposition of allyl isothiocyanate (AITC) in an aqueous solution was depressed in the presence of cyclodextrin (CD), it's suppression effect increasing in the order of none < beta-CD < alpha-CD. The results of kinetic and thermodynamic analysis of the CD-AITC inclusion complexes showed that the inclusion process was mostly governed by an enthalpy change (delta H degree) rather than by an entrophy change (delta S degree), and that Van der Waals forces played a primary role int he inclusion. Steric factors were important for the reaction activity of AITC inclusion into the CD cavity, especially significant being the stereospecificity between the size of the CD cavity and the AITC molecule which is the main factor concerning it's activity. Our results suggest that the association stability and activity of the included AITC molecule are important factors in the suppression mechanism for CDs. Therefore, both these factors would make an alpha-CD-AITC system more advantageous than a beta-CD-AITC system, and the marked suppression effect of alpha-CD on the decomposition of AITC can be attributed to the formation of inclusion complexes in an aqueous solution.