Spectrophotometric determination of binding constants between some aminocyclodextrins and nitrobenzene derivatives at various pH values

The inclusion capacity of three modified cyclodextrins—namely mono-(6-N,N-dimethylamino-6-deoxy)- (3), mono-6-(2-aminoethyl)-amino-6-deoxy- (4) and mono-6-(2-N,N-dimethylaminoethyl)-amino-6-deoxy- (5) β-cyclodextrin, with six para-substituted nitrobenzenes (A–F) has been investigated at three different pH values. Molecular interactions in inclusion complexes have also been investigated by means of molecular mechanics (MM2/QD) models. The desolvation of the cyclodextrin is the most important factor in determining the binding ability of the various hosts. However, for a given host, electrostatic and van der Waals interactions and the formation of a hydrogen bond between the donor amino group and the oxygen atom of a secondary hydroxyl group are the most important contributions in determining the binding constant of different guests.