Inclusion of Ethyl Acetoacetate Bearing 7-Hydroxycoumarin Dye by β-Cyclodextrin and its Cooperative Assembly with Mercury(II) Ions: Spectroscopic and Molecular Modeling Studies.

The inclusion of the fluorescent organic dye, ethyl 3-(7-hydroxy-2-oxo-2H-chromen-3-yl)-3-oxopropanoate (1) by the host -cyclodextrin (-CD), and its response toward mercuric ions (Hg2+), was studied by UV/Vis, fluorescence, and (HNMR)-H-1 spectroscopic analyses, mass spectrometry and molecular modeling studies. (HNMR)-H-1 measurements together with molecular modeling studies for dye 1 demonstrate that it exhibits two tautomeric forms (keto and enol); however, when the dye is included into the -CD cavity, the enol form predominates. Moreover, by using spectroscopic and spectrometry techniques, a 1:1 stoichiometry was determined for the complexes formed between dye 1 (enol form) and -CD, with a binding constant (K-b1=1.8x10(4)m(-1)) and for the dye 1 (keto form)-Hg2+ (K-b2=2.3x10(3)m(-1)). Interestingly, in the presence of 1--CD complex and mercuric ions, a ternary supramolecular system (Hg-1--CD complex) was established, with a 1:1:1 stoichiometry and a K-b3 value of 4.3x10(3)m(-1), with the keto form of the dye being the only one present in this assembly. The three-component system provides a starting point for the development of novel and directed supramolecular assemblies.