Complexation of 6-(4′-(toluidinyl)naphthalene-2-sulfonate by β-cyclodextrin and linked β-cyclodextrin dimers

The complexation of 6-(4′-(toluidinyl)naphthalene-2-sulfonate, TNS^-, by β-cyclodextrin (βCD) and five linked βCD-dimers is characterized by UV-Vis, fluorescence and ¹H NMR spectroscopy. In aqueous phosphate buffer at pH 7.0, I = 0.10 mol dm ^-3 and 298.2 K, TNS^- forms host-guest complexes with βCD of stoichiometry βCD·TNS^- {K₁ = [βCD·TNS^-]/([βCD][TNS^-]) = 3300 dm ³ mol^-1} and βCD₂·TNS^- {K₂ = [βCD₂·TNS^-]/([βCD] [βCD·TNS^-]) = 11 dm³ mol^-1} as shown by fluorescence studies. For N,N-bis((2^Adextrin)-S,3 ^AS)-3^A-deoxy-3^A-β-cyclodextrin) succinamide, 33βCD₂su, N-((2^AS,3^AS)-3 ^A-deoxy-3^A-β-cyclodextrin)N′-(6 ^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD ₂su, N,N-bis(6^A-deoxy-6^A-β-cyclodextrin) succinamide, 66βCD₂su, N-((2^AS,3^AS)-3 ^A-deoxy-3^A-β-cyclodextrin)-N′-(6 ^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD ₂ur, and N,N-bis(6^A-deoxy-6^A-β- cyclodextrin)urea, 66βCD₂ur, the analogous K₁ = 9600, 8700, 12 500, 9800, and 38 000 dm³ mol^-1, respectively. ¹H NMR ROESY studies provide evidence for variation of the mode of complexation of the TNS^- guest as the host is changed. The factors affecting complexation are discussed and the synthesis of the new linked βCD-dimer 36βCD₂su is reported.