APPARENT FORMATION CONSTANTS CORRELATION OF ORGANIC LIGAND-TRIVALENT METAL COMPLEXES

FERRARI GABRIELA V.; PAPPANO NORA B.; MONTAÑA M.PAULINA; GARCÍA NORMAN A.; DEBATTISTA NORA B.

Florianópolis

Conferencia; 10th Latinamerican Conference on Physical Organic Chemistry; 2009

Universidade Federal de Santa Catarina

Flavonoids are a wide variety of polyphenolic compounds which have many biological properties. These compounds show an interesting capacity: the metal ion complexation. The study of this capacity is important because it has been found that biological properties of these ligands can be enhanced when complexation occurs. In this work two flavonoids?Ga(III) complexes were studied: 2´,4´,3-trihydroxychalcone-Ga(III) and 3,7,3´-trihydroxyflavone-Ga(III). The chalcone was synthesized through Claisen-Schmidt´s reaction, method involving reaction between acetophenone and benzaldehyde, both appropriately substituted, and watery alkaline solution. The flavone was synthesized cycling the chalcone in alkaline medium. Both compounds were properly purified and indentified. Ga(III) complexes formation and their stoichiometry were determined spectrophotometrically using Yoe?Jones method. The apparent formation constants, K, were evaluated in methanolic solutions at 25 ºC by means of a easy and of extensive applicability spectrophotometric method, previously developed by this work group. The system 2´,4´,3-trihydroxichalcone?Ga(III) presented 1:1 L:M stoichiometry, while the other system presented 2:1 L:M stoichiometry. The determined constant values of both systems are: 2´,4´,3-trihydroxichalcone?Ga(III) 5.21x10^4 and 3,7,3´-trihydroxiflavone?Ga(III) 2.59x10^7. This sistems werecompered with other two previously studied2: 2´3-dihidroxichalcona?Ga(III)[Stoichiometry 1:1, K=3.95x10^3] and 3,3´-dihidroxiflavona?Ga(III) [Stoichiometry 2:1, K=1.50x10^8] Both chalcones presented stoichiometry 1:1 and the K values show that introducing an hydroxyle group in the 4´ position of the ligand increases the oxygen electronegativity of the carbonyl and, thus, the complex stability. These values also show that trihydroxylated chalcone can be considered as analytical reagent of Ga(III). Flavones-Ga(III) complexes are formed involving a 5-membered ring and presented 2:1 stoichiometry. According to the values in the table, the introduction of an additional hydroxyle group has no effect in the complexation capacity of flavones. Their K values are substantially lower than expected to be considered analytical reagents.