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.
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