Conformational and spectroscopic investigation of 3-hydroxyflavone-aluminium chelates

3-Hydroxyflavone (3HF), which is the simplest molecule of the flavonol clas s, possesses chelating properties towards Al(III). Spectrophotometric metho ds have shown that the 3HF molecule forms an Al(3HF)(2) complex in purl met hanol. The structure of this complex, obtained by quantum semi-empirical AM 1 method, indicated that complexed 3HF adopts a pyronium form. Structural a nd electronic modifications induced by chelation are illustrated by the imp ortant frequency shifts observed between free and complexed 3HF FT- Raman s pectra and by the chemical shifts variations in the C-13 NMR spectra of the two species. Complexes with the same stoichiometry were formed when AcO- o r MeO- are present in the medium. However, in acidic medium the chelate com position is Al-2(3HF). (C) 2000 Elsevier Science B.V. All rights reserved.