Retarding effects of cyclodextrins on the decomposition of organic isothiocyanates in an aqueous solution.

Abstract

One- and two-dimensional (1)H nuclear magnetic resonance ((1)H NMR) spectra were measured in order to estimate the dissociation constants (K(diss)) and molecular geometries of cyclodextrin (CD) with three organic isothiocyanates (ITC), allyl-ITC, 3-butenyl-ITC, and 4-pentenyl-ITC, in an aqueous solution (pH 5.0, I(c)=0.75 M). In every ITC, the K(diss) values decreased in the order of alpha-CD>beta-CD>gamma-CD, and the three rod-like linear molecules of ITCs were accommodated with the best fit into the smallest cavity of alpha-CD. By rotating-frame nuclear Overhauser enhancement spectroscopy, cross peaks were found between the H-3 of alpha-CD and the H-1 of AITC. From the result, the molecular geometry of alpha-CD-AITC complex presume that the isothiocyanate group of AITC is located some where around the widening rim and a hydrophobic allyl group is included within the hydrophobic cavity of alpha-CD.