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[摘要]：The fluorescent properties of a trinitrophenylated Meisenheimer complex of adenosine (TNP-Ado) in water were examined in the presence of alpha-, beta-, and gamma-cyclodextrins (CDs). The TNP-Ado complex exhibits minimal fluorescence in water, whereas addition of 10 m M alpha-CD, beta-CD, and gamma-CD enhances fluorescence by factors of 1 2, 7, and 110, respectively. The large enhancement by gamma-CD is attributed to its larger hydrophobic cavity, which is able to accommodate the TNP moiety of TNP-Ado. H-1 NMR spectra demonstrate 1:1 stoichiometry of the complex, which undergoes slow exchange on the NMR time scale. H-1 NMR and 2D ROESY spectra reveal substantial interaction of the TNP hydrogens with gamma-CD. Equilibrium constants were determined by fluorimetry from 10 to 20 degrees C by nonlinear curve fitting. Fluorescence is temperature dependent, with maximum fluorescence increasing with decreasing temperature. Complexation is exothermic with large negative entropy, consistent with formation of a tight complex between TNP-Ado and gamma-CD. Rate constants and activation parameters for both complexation and dissociation were determined by a combination of fluorimetry and 2D NM R exchange spectroscopy (EXSY). |
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