Fluorescent Molecular Sensory System Based on Bis Pyrene-Modified γ-Cyclodextrin Dimer for Steroids and Endocrine Disruptors

Abstract

A γ-cyclodextrin dimer modified with two pyrene moieties, 6-(2-pyrenebutylate-aminoethyl)pyrenebutylate-amino-6-deoxy-bis-γ-cyclodextrin, has been synthesized in the presence of N,N′-dicyclohexycarbodiimide from γ-cyclodextrin dimer linked with ethylenediamine at an upper rim. The sensing ability and binding property of the titled dimer were investigated for bile acids and endocrine disruptors. This cyclodextrin dimer showed both monomer and excimer fluorescence; the guest-induced emissions were observed as increases or decreases depending on the guest. The values ΔI_m/I⁰_m and ΔI_ex/I⁰_ex, where I⁰_m and I_m are fluorescence intensities of monomer emission in the absence and presence of a guest and I⁰_ex and I_ex are those of excimer emission and ΔI_m and ΔI_ex were I_m - I⁰_m and I_ex - I⁰_ex, respectively, were used as a parameter of sensitivity. This host exhibited highly sensitive molecular recognition ability for bile acids and endocrine disruptors, in which the sensing parameters obtained from monomer emission were plus or minus values, whereas the parameters obtained as excimer emission were minus ones. The behavior of the appended moieties of the host during a host-guest complexation was studied by induced circular dichroism (ICD) and fluorescence spectra. The ICD intensities of the titled dimer were decreased upon an addition of a guest. The guest-induced variations in the fluorescence and ICD intensity suggest that the appended moieties move by altering the spatial relationship in the hydrophobic space between two linked cyclodextrins.