Dimerisation and complexation of 6-(4'-t-butylphenylamino)naphthalene-2-sulphonate by β-cyclodextrin and linked β-cyclodextrin dimers

Abstract

This study shows that stereochemical factors largely determine the extent to which 6-(4′-t-butylphenylamino)-naphthalene-2-sulphonate, BNS− and its dimer, (BNS− )2, are complexed by β-cyclodextrin, βCD, and a range of linked βCD dimers. Fluorescence and 1H NMR studies, respectively, show that BNS− and (BNS− )2 form host–guest complexes with βCD of the stoichiometry βCD.BNS− (10− 4 K 1 = 4.67 dm3 mol− 1) and βCD.BNS2 2 − (10− 2 K 2′ = 2.31 dm3 mol− 1), where the complexation constant K 1 = [βCD.BNS− ]/([βCD][BNS− ]) and K 2′ = [βCD. (BNS− )2]/([βCD.BNS− ][BNS− ]) in aqueous phosphate buffer at pH 7.0, I = 0.10 mol dm3 at 298.2 K. (The dimerisation of BNS− is characterised by 10− 2 K d = 2.65 dm3 mol− 1.) For N,N-bis((2AS,3AS)-3A-deoxy-3A-β-cyclodextrin)succinamide, 33βCD2su, N-((2AS,3AS)-3A-deoxy-3A-β-cyclodextrin)-N′-(6A-deoxy-6A-β-cyclodextrin)urea, 36βCD2su, N,N-bis(6A-deoxy-6A-β-cyclodextrin)succinamide, 66βCD2su, N-((2AS,3AS)-3A-deoxy-3A-β-cyclodextrin)-N′-(6A-deoxy-6A-β-cyclodextrin)urea, 36βCD2ur, and N,N-bis(6A-deoxy-6A-β-cyclodextrin)urea, 66βCD2ur, the analogous 10− 4 K 1 = 11.0, 101, 330, 29.6 and 435 dm3 mol− 1 and 10− 2 K 2′ = 2.56, 2.31, 2.59, 1.82 and 1.72 dm3 mol− 1, respectively. A similar variation occurs in K 1 derived by UV–vis methods. The factors causing the variations in K 1 and K 2 are discussed in conjunction with 1H ROESY NMR and molecular modelling studies.