Abstract
Thermodynamic parameters of solution (DeltaG°s, DeltaH°s, and DeltaS°s) of some haptens [ortho-, meta-, para-, 5-chloro-2-, 6-chloro-2-, 2-chloro-4- and 4-chloro-3- (parahydroxyphenylazo) sodium benzoate] and three cyclodextrins (Delta, Delta and Delta) were carried out in different reaction media. Thermodynamic parameters for the transfer (DeltaG°t, DeltaH°t, DeltaS°t) of haptens and their anions from water to methanol and from water to N,N'-Dimethylformamide were derived. In addition, transfer free energy, enthalpy and entropy of cyclodextrins from water to N,N'-Dimethylformamide are reported. Thermodynamic parameters of complexation between haptenic anions and cyclodextrins were investigated in water and in N,N'-Dimethylformamide and their transfer quantities from water to N,N'-Dimethylformamide are also given. It was found that the selected haptens (anions) are better solvated in methanol than in water than in N,N'-Dimethylformamide. The transfer enthalpies of the anions (data based on the Ph4AsPh4B convention) from water to methanol and from water to N,N'-Dimethylformamide [DeltaH°t (X-)] are largely compensated by their transfer entropies [DeltaS°t (X-)]. As far as solution thermodynamic data of cyclodextrins in water and N,N'-Dimethylformamide are concerned, it was noticed that a compensation effect between the DeltaHs and DeltaS°s values is taking place in water and in N,N'-Dimethylformamide. Only three anions complex with alpha, and gamma-cyclodextrins in water, whereas four haptens form complexes with alpha, beta and gamma-cyclodextrin in N,N'-Dimethylformamide. Again a compensation effect for cyclodextrin-anion complexes was observed in water and in N,N'-Dimethylformamide. A cavity size effect was shown during the formation of cyclodextrin-hapten complexes. Anion-cyclodextrin interaction becomes weaker with an increase in the cavity of cyclodextrin. Inclusion complexes (axial) are found to take place in water and lid-type (equatorial) complexes are found between these haptenic anions and cyclodextrins in N,N'-Dimethylformamide. The transfer parameters for the cyclodextrin-anion complexes were calculated using a thermodynamic cycle. This is the first set of data ever reported on the transfer of cyclodextrin adducts among solvents.