α-Cyclodextrin/aminobenzoic acid binding in salt solutions at different pH: dependence on guest structure

Influence of Na(+) and K(+) cations on α-cyclodextrin guest-host complex formation with isomeric aminobenzoic acids was examined at different pH and temperature of 298.15 K by (1)H NMR and calorimetry methods. More pronounced influence of Na(+) on inclusion complex formation of α-CD with aminobenzoic acid anions compare to the effects of Na(+) on α-CD complex formation with zwitterionic aminobenzoic acid molecules was revealed. For the first time, the dependence of salt effects on the structure, ionization and the hydration state of the guest molecule was demonstrated and analysed on the basis of the obtained thermodynamic parameters of complex formation and calculated free energy of hydration of different ionized forms of aminobenzoic acids.