Interactions Between Polyamine-modified β-Cyclodextrins and Anionic Surfactants

The binding constants between several polyamine-modified beta-cyclodextrins, i.e., mono(6-amino-6-deoxy)-beta-cyclodextrin (NH2-beta-CD), mono [6-(ethylenediamino)-6-deoxy]-beta-cyclodextrin (EN-beta-CD), mono [6-(diethylenetriamino)-6-deoxy]-beta-cyclodextrin (DETA-beta-CD), mono [6-(triethylene tetraamino)-6-deoxy]-beta-cyclodextrin(TETA-beta-CD) and three anionic surfactants (CnH2n+1SO3Na: n = 8, OAS; n = 10, TDS; n = 12, SDS) in phosphate buffer solution (25 degrees C, pH = 7.2) and carbonic acid buffer solution (25 degrees C, pH = 10.5) were measured by the methods of UV-Vis and fluorescence spectroscopy titration using phenolphthalein and neutral red as spectral probes. The 1: 1 stoichiometry of hosts and guests was validated by Job's experiments, and the inclusion modes were determined by 2D NMR spectroscpy. The obtained results show that the binding constants between polyamine-modified beta-cyclodextrins and anion surfactants were in the region of 2.6 x 10(2)-4.35 x 10(4) L/mol in neutral condition, whereas in basic condition the binding would become weaker(1.5 x 10(2)-1.42 x 10(4) L/mol). In both of two pH conditions, the binding ability became much stronger with increasing the carbon number of anionic surfactants. The different binding abilities can be derived from the cooperative effect of hydrophobic, electrostatic and hydrogen bonding interactions.