FLAVONOLS AND CROWN-FLAVONOLS AS METAL CATION CHELATORS - THE DIFFERENT NATURE OF BA2+ AND MG2+ COMPLEXES

The derivatives of 3-hydroxyflavone exhibit excited-state intramolecul ar proton transfer (ESIPT) reaction with significant (60-80 nm) shifts of fluorescence spectra between normal and phototautomer forms. This fact makes these compounds attractive as fluorescence probes in analyt ical chemistry, biophysics, and molecular biology. Different flavonol derivatives, including 4'-(monoaza-15-crown-5)flavonol; were synthesiz ed, and their absorption and fluorescent spectra were studied in aceto nitrile in the presence of different concentrations of Mg2+ and Ba2+ i ons. It was shown that the general feature of flavonols is the ability to form two types of complexes with alkaline-earth cations: the low-s tability ''external'' and high-stability chelating complexes. On the f ormation of the complexes, parent flavonols and their 4'-dialkylamino derivatives undergo different perturbations of their electronic struct ures. 4'-(Monoaza-15-crown-5)flavonol forms two types of complexes wit h both Mg2+ and Ba2+ ions; the sequence of steps in formation of Ba2and Mg2+ complexes is different.