Studies of protolytic equilibria and investigations of stability of flavonoids at different acidities are necessary to better understand their antioxidant efficiencies and autoxidation characteristics. The protonation constant of carbonyl group and dissociation constants of OH groups of quercetin in aqueous solutions were determined spectrophotometrically. The distribution diagram of ionic species in aqueous solutions of various acidities was calculated. Study of the effects of UV irradiation on quercetin at pH 5.00, 7.50 and 10.00 indicated that UV irradiation accelerated quercetin autoxidation via the formation of the oxidation product. The stability of quercetin and oxidation product was investigated as a function of irradiation time by using spectrophotometric and HPLC techniques. The apparent pseudofirst-order rate constants for quercetin degradation and oxidation product formation were calculated and discussed.

Tiling modification in fullerene modeling can be achieved by some map operations. In this respect, sequences of classical operations, or single generalized operations, were used to obtain corannulene-like azulenic patterns. The aromaticity of such cages tessellated by "corazulenic" supra-faces is discussed in terms of several criteria. Particularly, the number of Kekulé valence structures, was considered as a rough measure of the fullerene aromaticity and implicitely of their stability. The covering was given as a pi-electron partition within some Kekulé valence structures. The well-known geometric index of aromaticity HOMA (harmonic oscillator model of aromaticity) enabled the evaluation of local aromaticity of the discussed supra-faces and brought evidence for several dominant Kekulé valence structures.