Binding of Coumarin 334 withβ-Cyclodextrin and with C-Hexylpyrogallol[4]arene: Opposite Fluorescence Behavior release_u5d66jptmnf3zdmcqoj7oevkha

Abstract

We report here the structure of the host-guest complexes of Coumarin 334 (C334) with<jats:italic>β</jats:italic>-cyclodextrin (<jats:italic>β</jats:italic>-CD) and with C-hexylpyrogallol[4]arene (C-HPA) and the effect of acidity on the neutral-cation equilibrium of C334 in water and in the presence of the host molecules. The structures of the host-guest complexes are proposed on the basis of the change of fluorescence on the addition of<jats:italic>β</jats:italic>-CD or C-HPA to C334 and by 2D ROESY spectroscopy. Opposite fluorescence behaviors, that is, quenching of fluorescence in<jats:italic>β</jats:italic>-CD and enhancement of fluorescence in C-HPA are observed. Time-resolved fluorescence analysis is done for the complexation, and biexponential decay pattern is observed. The possible strong inclusion complexation with C-HPA is explained. The ground and the excited state<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>p</mml:mi><mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mi>a</mml:mi></mml:mrow></mml:msub></mml:math>values for the protonation equilibrium of C334 in water and the difficulty of protonation in the presence of the host molecules are discussed.
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