Diazacoronand-linked α- and β-cyclodextrin dimer complexes of the Brilliant Yellow tetraanion

Abstract

<jats:p>Complexation of the Brilliant Yellow tetraanion, 14–, by the new coronand-linked α- and β-cyclodextrin (αCD and βCD) dimers 4,13-bis(6 A-deoxy-α-cyclodextrin-6 A-ylamidomethyl)-4,13-diaza-1,7,10-trioxacyclodecapentane and 4,13-bis(6 A-deoxy-β-cyclodextrin-6 A-ylamidomethyl)-4,13-diaza-1,7,10-trioxacyclodecapentane, 2 and 3, respectively, has been studied in aqueous solution. The complexation constants for 2 · 14– and 3 · 14– are K1 = (3.20 ± 0.05) × 105 and (2.76 ± 0.09) × 104 dm3 mol–1, respectively, at 298.2 K, pH 10.0, and I 0.10 mol dm–3 (NEt4ClO4). The pK a values of 2 · H22+ are 6.57 ± 0.04 and 5.88 ± 0.05, and of 3 · H22+ are 6.70 ± 0.03 and 6.08 ± 0.02. Complexation of the alkaline earth metal ions by 2 is characterized by complexation constants (2.73 ± 0.51) × 102, (1.52 ± 0.36) × 105, (1.49 ± 0.03) × 105, and (4.28 ± 0.07) × 104 dm3 mol–1 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively. These data are compared with those reported for analogous coronand-linked βCD dimer complexes to establish the hierarchy of the factors determining the stability of such complexes.</jats:p>