Diazacoronand-Linked α- and β-Cyclodextrin Dimer Complexes of the Brilliant Yellow Tetraanion

Abstract

Complexation of the Brilliant Yellow tetraanion, 1^4–, 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 · 1^4– and 3 · 1^4– 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.