Inclusion complexes of pyrenylbutyrate with γ-cyclodextrin

Abstract

Mixing 4-pyren-1-ylbutyrate ion with γ-cyclodextrin in aqueous solution leads to inclusion complexes that become evident from changed absorption spectra as well as protection of the included pyrene moieties from fluorescence quenchers. The inclusion proceeds in stages, yielding first a 1:1 complex, which then dimerizes to form a 2:2 complex. At 25 °C the respective equilibrium constants of complex formation are 1.3 × 10³ and 5.2 × 10⁴ l mol^–1. The dimerization equilibrium has an unusual temperature dependence, with ΔH^≠–16.7 kcal mol^–1 and ΔS^≠–35 cal K^–1 mol^–1.