Unexchangeable Interlayer Anions; Synthesis and Characterization of Zn/Al- and Mg/Al-Layered Double Hydroxides with Interlayer Alizarin red S

The formation of complexes between -cyclodextrin and 1-alkanols hasbeen studied calorimetrically at 298 K in water and in concentrated aqueoussolutions of ethanol or urea. When a complex is formed, calorimetry enables thecalculation of both the enthalpy and the association constant, from which thefree energy and the entropy of the process can be obtained. The effects ofethanol and urea on the hydration cospheres of the interacting substances havebeen investigated through the study of the binary solutions of the involvedsolutes in water and in the mixed solvents. The findings obtained are, then,related to the consequent changes in the association parameters.The forces involved in the association process are discussed in the light of the signsand values of the thermodynamic parameters obtained. The most important featurescoming out from this study are: (i) association in water is an entropy-driven process;(ii) in concentrated aqueous solutions of cosolvent, the enthalpic term contributessignificantly to the Gibbs energy, while the entropic contribution is smaller; (iii) forevery solvent medium employed, the invariance of the entropic contribution withincreasing alkyl chain length of the alkanol is an indication that the relaxation ofwater molecules from the cavity of the macrocycle mainly determines the associationprocess.