Associations of Water-Soluble Macrocyclic Hosts with 4-Aminoazobenzene: Impact of pH

An investigation of the pH effect on the inclusion complexes of β-cyclodextrins and calixarenesulfonates with 4-aminoazobenzene was conducted both by experiments and molecular simulations. The whole thermodynamic characterizations of the association between hosts and 4-aminoazobenzene ( K, Δ_r G⁰, Δ_r H⁰, and TΔ_r S⁰) were determined by UV-visible spectroscopy. β-Cyclodextrin inclusion complexes are not affected by pH change unlike those obtained with calixarenes. All the studied systems were enthalpically favored. Nevertheless, the entropic behavior is different depending on the host. In order to interpret these experimental results, molecular simulations were used to calculate the number of atoms inserted into the cage-like host compounds and the number of water molecules expelled from the cavity.