Inclusion excluded: Chiroptical sensing of the external surface of sulfated cyclodextrins

It is shown that the heparin antagonist bis-aminoquinoline derivative surfen interacts with sulfated cyclodextrins in a unique fashion. Analysis of the UV spectroscopic data revealed exceptionally strong association (K(a) ∼ 10(7) M(-1)) of several surfen molecules to the external surface of the cyclodextrin hosts. H-bonded to the sulfate groups in 1:1 stoichiometry, the drug molecules form a chiral layer around the macrocycles. Due to the steric proximity, dipole-dipole coupling occurs between the adjacent aminoquinoline rings that accounts for the large UV hypochromism and the induced exciton couplet in the circular dichroism spectra.