Abstract
Thermodynamic parameters for the complexation process involving substituted sodium benzoates with a, 13 and 7 cyclodextrins have been determined in water and in N,N-dimethylformamide at 298.15 K. The increasing negative enthalpies of complexation in N,N-dimethylformamide moving from a to 7-cyclodextrin reflects the effects of substituting the cyclodextrin ligand as the cyclodextrin cavity size increases. Single-ion parameters of the new benzoate-cyclodextrin anions have been derived and the results show that these anions are solvated much better in water than in N,N-dimethylformamide. Thermodynamic parameters for the complexation of 1:1 monosaccharide-cyclodextrin complexes have been determined in water at 298.15 K. The data show the ability of the cyclodextrins to selectively distinguish between the aldopentoses and aldohexoses. Thermogravimetric analysis and differential scanning calorimetry of an isolated monosaccharide-cyclodextrin complex reveal that N,N-dimethylformamide is interacting with cyclodextrin. nuclear magnetic resonance (NMR) and spectrophotometric studies together with computer modelled calculations suggest the formation of exclusion type complexes. stability constants, free energies, enthalpies and entropies of complexation of the D-amino acids and D-amino acid trifluoromethanesulphonates in methanol at 298.15 K are discussed. No significant variations were found in the free energies of complexation of the amino acids as a result of an entropy-enthalpy compensation effect. The transfer enthalpy of the amino acid cations are negative implying that these cations are enthalpically more stable in methanol than water. However, no complexation in water was found between these guest species and 18-crown-6. This is attributed to an interaction between 18-crown-6 and water as reflected in the transfer enthalpy of this ligand from water to methanol. Electrochemical, spectrophotometric, nuclear magnetic resonance and calorimetric studies on the interaction of a resorcinol-based calix[4]arene with amines in non-aqueous media (chloroform and benzonitrile) are reported as a contribution to the area of calixarene chemistry involving the generation of new electrolytes, resulting from a combination of proton transfer and hydrogen bonding from the calixarene to the amine. A summary and suggestions for further work are also given.