Fluorescence enhancement of coumarin-6-sulfonyl chloride amino acid derivatives in cyclodextrin media

Coumarin-6-sulfonyl (6-CS) amino acid derivatives form inclusion complexes with α- and β-cyclodextrins (CD) in aqueous solution. The stoichiometry of the inclusion complex and the equilibrium constant were investigated. Using a fluorescence technique and alanine-β-CD as a model, a 1:2 guest-host complex was established, and K = 4.7 × 10⁵ mol^-2 l² was obtained. Fluorescence enhancement was observed for all derivatives studied, with glycine exhibiting a greater enhancement, and tyrosine showing the least. The stability of the inclusion complex was found to depend on the respective sizes of the guest-host complex and their interaction.