Beta-cyclodextrin complexes with chlorogenic and caffeic acids from coffee brew : spectroscopic, thermodynamic and molecular modelling study

Coffee brew is rich in chlorogenic and cinnamic acids, potent antioxidants. Its interaction with beta-cyclodextrin leads to formation of inclusion complexes which affect the physicochemical properties of the guest molecule. We investigated spectral changes in coffee-originated phenols, chlorogenic (CHA) and caffeic (CA) acids, due to complexation with beta-cyclodextrin (betaCD) in aqueous solutions and studied thermodynamic properties of the complexes formed. The spectroscopic data (absorption and fluorescence) were used for deducing the position of both phenols inside the beta-cyclodextrin cavity, as well as to calculate the binding constants of the complexes. The obtained data indicate the formation of a 1:1 complex between betaCD and CHA or CA. The temperature-dependence of the latter allowed the calculation of thermodynamic parameters (Δ H , Δ S and Δ G ) of the complexation. The negative values of all the thermodynamic parameters indicated that the formation of these inclusion complexes was an enthalpy-driven process in which a crucial role is played by weak van der Waals forces and hydrogen bonds. Molecular modelling confirmed experimental observations that, in aqueous phase, betaCD–CHA and –CA complexes are stable and energetically favourable, and additionally provided information regarding conformation and interaction between atoms forming the complexes. The experimental data were used to characterise the molecular mechanism of the complexation.