Experimental and theoretical study of the inclusion complexes of 3-carboxycoumarin acid with β- and 2-hydroxypropyl-β-cyclodextrins

The association process of a host–guest system, cyclodextrins (CyD) – 3-carboxycoumarin acid (3CCA) was followed by means of UV–vis, circular dichroism and steady-state fluorescence spectroscopies in buffer solution at pH = 1. The experimental data were analyzed in order to get information on the stoichiometry, the equilibrium constants and the geometry of the inclusion complexes. In the circular dichroism spectra, a positive induced signal was obtained reflecting that the guest penetrates the cavity in such a way that the transition moment of the electronic band is quasi parallel to the host main axis. The experimental data are supported by the DFT and TDDFT (B3LYP/6-31G) calculations performed on the isolated ligand and by TDDFT (ZINDO) calculations carried out on the supramolecular ligand-cyclodextrin system.

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► Estimation of the stoichiometry and association constants at pH = 1 by spectral methods.
► Characterization of the inclusion mode by circular dichroism and TDDFT calculations.
► Molecular modeling of the supramolecular system ligand-cyclodextrin.
► TDDFT(ZINDO) simulation of the ICD spectrum.