Host−Guest Interactions between β-Cyclodextrin and the (Z)-Phenylhydrazone of 3-Benzoyl-5-phenyl-1,2,4-oxadiazole:  The First Kinetic Study of a Ring−Ring Interconversion in a “Confined Environment”

Abstract

The effect of beta-cyclodextrin (beta-CD) on the mononuclear heterocyclic rearrangement of the (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1) in aqueous borate buffer at pH = 9.6 has been analyzed at temperatures ranging from 293.15 to 313.15 K. The trend of the absorption spectra of 1 as a function of time has been accounted for with the formation of two different 1:1 complexes between beta-CD and 1, the first, "unreactive" complex being formed faster than the "reactive" one. The occurrence of negative activation enthalpy values for the studied interconversion evidences the kinetic relevance of inclusion processes. Computational models elaborated using the MM2 molecular mechanics force field give an idea of the relative importance of the different complexes, additionally helping us to formulate a suitable reaction scheme.

Supramolecular Complex Formation: A Study of the Interactions between β‐Cyclodextrin and Some Different Classes of Organic Compounds by ESI‐MS, Surface Tension Measurements, and UV/Vis and 1H NMR Spectroscopy

“…In view of the increasing interest in the use of cyclodextrins (CDs) as hosts in drug, food and cosmetic chemistry [3] and the changes in the physicochemical properties [4] of many chemicals produced by the ability of cyclodextrins to interact strongly and stably with different guests, we have recently examined the course of the rearrangement of the (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (essentially insoluble in water) in water solutions of β-cyclodextrin (β-CD) at pH 9.6, [5] taking advantage of the ability of the β-cyclodextrin to dissolve organic compounds. On studying the reaction at different β-CD concentrations of the guest in the host to be gained.…”

A deep insight into the mechanism of the acid‐catalyzed rearrangement of the Z‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole in a non‐polar solvent

“…Among ring‐to‐ring interconversions, the monocyclic rearrangements of heterocycles (MRH, as named by Boulton and Katritzky)40–53 play an important role in the syntheses of heterocycles containing one nitrogen atom together with other heteroatoms such as nitrogen atoms, oxygen, sulphur, and so on. For this reason, our research group has long been involved in the study of synthetic applications of MRH54, 55, 64–67 as well as their mechanisms, either collecting kinetic data54–71 in very different experimental conditions (e.g., in conventional polar or apolar solvents,54–63 in room‐temperature ionic liquids,64–67 and in the presence of micelles68 or of β ‐cyclodextrins)69–71 or by means of ab initio calculations 72, 73. The results collected by our research group has enabled us to define the reaction mechanism of MRH, which clearly appears to be a S N i process, whose course is favored by its intramolecularity and by thermodynamic factors 59–63, 72, 73.…”

Host—Guest Interactions Involving Cyclodextrins: Useful Complementary Insights Achieved by Polarimetry.

“…They are employed in widespread research and industrial applications, spanning from reaction microenvironments 2 and enzyme modeling 3 to separation technologies 4 and to additives for pharmaceutical, cosmetic, and food industries. 5 Studies on CDs are the object of an immense literature that is periodically reviewed.…”