Thermodynamic insight into the origin of the inclusion of monosulfonated isomers of triphenylphosphine into the beta-cyclodextrin cavity.

Formation of inclusion complexes between the beta-cyclodextrin and the potassium salt of o-, m-, and p-substituted monosulfonated triphenylphosphine derivatives was investigated in aqueous solution by NMR spectroscopy. Titration and continuous variation plots obtained from 31P and 1H NMR data indicate the formation of a 1:1 inclusion complex for the three phosphine isomers. T-ROESY NMR experiments show that in all cases a non-sulfonated aromatic ring was included into the hydrophobic cavity of beta-cyclodextrin from the secondary hydroxyl groups side. The standard enthalpy and entropy of the inclusion process were estimated from the temperature dependence of the association constant. All inclusion complexes were enthalpy stabilized, but highly entropy destabilized.