NMR studies of inclusion complexes: naphthalene and natural cyclodextrins

Inclusion complexes of naphthalene (NP) with cyclodextrins (CD) have been investigated so far using non-NMR techniques resulting in inconsistent data. Here, the first application of high-field NMR spectroscopy in combination with a precise analysis of the results has allowed us to determine accurately the stoichiometry of complexes and their association constants. Titration measurements have been performed by H-1 NMR spectroscopy in D2O at a magnetic field B-0 of 18.8 T. NP and alpha CD form a 1 : 2 complex in which a single NP molecule is closed in a capsule made up of two alpha CD macrocycles. NP and beta CD build coexisting 2 : 1 and 2 : 2 complexes with large binding constants. Larger gamma CD host molecules form essentially similar complexes with NP as the beta CD but corresponding binding constants are smaller.