Diazacoronand-linked α- And β-cyclodextrin dimer complexes of the brilliant yellow tetraanion

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 298.2K, pH 10.0, and I 0.10 mol dm ^-3 (NEt₄C1O₄). 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) × 10 ²,(1.52 ± 0.36) × 10⁵, (1.49 ± 0.03) × 10⁵, and (4.28 ± 0.07) × 10⁴ dm ³ mol^-1 for Mg²⁺, Ca²⁺, Sr ²⁺, 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.