The inclusion of tropaeolin 000 no. 2 by permethylated β-cyclodextrin. A kinetic and equilibrium study

Abstract

Temperature-jump visible spectrophotometric studies show the monoanionic form of the dye tropaeolin (TR) to be included by permethylated β-cyclodextrin (βPCD) in a fast step to form a 1:1 complex (TR·βPCD), which is followed by the slower formation of the 2:1 complex (TR)₂·βPCD, in which tropaeolin dimerizes: [graphic omited] At 298.2 K K₁=(1.24 ± 0.05)× 10² dm³ mol^–1, K₂=(4.82 ± 0.42)× 10⁴ dm³ mol^–1, k₂=(1.68 ± 0.09)× 10⁸ dm³ mol^–1 s^–1 and k_–2=(3.48 ± 0.11)× 10³ s^–1 in aqueous solutions buffered at pH 5.50 by 0.100 mol dm^–3 phosphate and 0.200 mol dm^–3 K₂SO₄ supporting electrolyte. U.v.–visible spectrophotometric equilibrium measurements yield K₁=(1.36 ± 0.11)× 10² dm³ mol^–1 and K₂=(2.29 ± 0.38)× 10⁴ dm³ mol^–1. A similar study of inclusion of the dye pyronine B was attempted, but the u.v.–visible spectral changes were too small for a quantitative study. These results are compared with those obtained from the analogous β- and γ-cyclodextrin systems.