Binding of coumarin 334 with β-cyclodextrin and with C-hexylpyrogallol[4]arene: Opposite fluorescence behavior

Abstract

We report here the structure of the host-guest complexes of Coumarin 334 (C334) with β-cyclodextrin (β-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 β-CD or C-HPA to C334 and by 2D ROESY spectroscopy. Opposite fluorescence behaviors, that is, quenching of fluorescence in β-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 p K a values for the protonation equilibrium of C334 in water and the difficulty of protonation in the presence of the host molecules are discussed. © 2013 Chandrasekaran Sowrirajan and Enoch Israel Vijayaraj Muthu Vijayan.