Acid/base properties of flavonoids hydroxylated at positions 2 and 3:: a novel quantum mechanical study in gas-phase and solution

The protonated and deprotonated forms of 4H-1-benzopyran-4-one, 2-hydroxy-4H-1-benzopyran-4-one, 3-hydroxy-4H-1-benzopyran-4-one and 2,3-dihydroxy-4H-1 -benzopyran-4-one in the gas-phase and in solution have been examined by theoretical methods. Ab initio calculations at the MP2/6-31+G(d) level have been used to study the acid/base properties of these compounds in the gas-phase. The influence of the solvent has been examined using a self-consistent reaction-field. Two different solvents (water and chloroform) were used to investigate the effect of varying the dielectric constant of the surrounding media. The results provide a complete and accurate picture of the acid/base properties of the investigated compounds. Furthermore, the optimized geometries have been analyzed in order to investigate some relevant structural features. (C) 2000 Elsevier Science B.V. All rights reserved.