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 dm
3 mol
? 1) and βCD.BNS
2 2 ? (10
? 2 K 2′ = 2.31 dm
3 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 dm
3 at 298.2 K. (The dimerisation of BNS
? is characterised by 10
? 2 K d = 2.65 dm
3 mol
? 1.) For
N,
N-bis((2
AS,3
AS)-3
A-deoxy-3
A-β-cyclodextrin)succinamide, 33βCD
2su,
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, 66βCD
2su,
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, 66βCD
2ur, the analogous 10
? 4 K 1 = 11.0, 101, 330, 29.6 and 435 dm
3 mol
? 1 and 10
? 2 K 2′ = 2.56, 2.31, 2.59, 1.82 and 1.72 dm
3 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.
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