NMR studies of complex formation between natural cyclodextrins and benzene

Abstract

Inclusion complexes of benzene (Bz) with cyclodextrins (CD) have been investigated so far using non-NMR techniques in various solvents resulting in conflicting data. Here, the first application of NMR spectroscopy, combined with rigorous statistical analysis of the results, has allowed us to determine accurately the stoichiometry of complexes and their association constants. Titration measurements have been performed by 1H NMR spectroscopy in D2O at a magnetic field B0 of 14.1 T. αCD and γCD host molecules form weak 1 : 1 complexes with Bz. In contrast, Bz and βCD build 1 : 1 and 2 : 1 complexes coexisting in solution with large binding constants. The binding of the second benzene molecule is strongly cooperative.