Dynamic aspects in host–guest interactions. Part 4. Kinetic and 1H NMR evidence for multi-step directional binding in the molecular recognition of some 2-naphthylazophenol guests with α-cyclodextrin

Abstract

Detailed solution kinetic and equilibria data in aqueous solution are presented for the molecular recognition by α-cyclodextrin (α-CD_x) of structually different types of 2-naphthylazophenol guest. ¹H NMR equilibrium titrations and stopped-flow data have allowed the determination of the proposed structure of the intermediate, equilibrium constants, and the rate and mechanism for the molecular recognition by α-cyclodextrin. Some kinetic data are consistent with a two-step inclusion process wherein the intramolecular structural reorganization from the intermediate to the final inclusion complex is the rate-controlling step.¹H NMR data also support the existence of stable intermediate species. The steric and charge factors affecting the directional inclusion process are discussed.