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. SALA. Can. J. Chem. 69, 1994 (199 1). The equilibrium reactions between rutin, 3-[6-0-(6-deoxy-a-~-mannopyranosyl)-(~-~-glucopyranosyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4H-l-benzopyran4one, and quercetin (rutin aglycone) with ironw), copper(II), cobalto, and nickel@) have been studied by potentiometric and spectrophotometric methods in aqueous solution. All measurements were carried out at t = 20°C and p = 0.10 M, and the corresponding stability constants were calculated by applying computational methods. The interactions between the proposed cations with both biological ligands and other related ones are compared, with simultaneous postulation of the probable structures.Key words: chelate stability constants of rutin, chelate stability constants of quercetin, transition metal ion interaction with flavonoids, stability constant determinations, potentiometric and spectrophotometric studies. Introduction Flavonoids are structures of recognized biological activity (1). Rutin (Scheme I), one of the typical glucosides in the flavonoids series widely distributed in natural plants, is a potent inhibitor of lens aldose reductase (potentially useful for prevention of diabetic cataracts) (2). Pharmacologically, rutin as well . as quercetin has a direct constructor action on the capillary bed and decreases the permeability and fragility of the vessels (3). We thought it of value to determine the stability constants of rutin and quercetin metal-ion complexes of biological interest, which have not yet been reported in the literature. The study was performed with the intention of applying the results to possible clinical and biological situations. For these reasons the chelate stability constants of rutin and quercetin with common divalent and trivalent metal ions have been determined.

LUIS F. SALA, SANDRA R. SIGNORELLA, MARCELA RIZZOT~O, M A R~A I. FRASCAROLI, and FABIO GANDOLFO. Can. J. Chem. 70, 2046Chem. 70, (1992.The oxidation of L-rhamnose and D-mannose by Cr(V1) in perchloric acid follows the rate law: M -~ S-I pour le L-rhamnose. Cette equation de vitesse correspond a la reaction conduisant a la formation de la L-1 ,4-rhamnonelactone et de la D-1 ,4-mannonelactone. I1 ne se produit pas de clivage en dioxyde de carbone lorsque la quantite d'aldose utilisee depasse de 20 fois ou plus la quantite de Cr(V1). On interprkte les valeurs relatives des constantes cinktiques en fonction d'une participation du groupe hydroxyle primaire dans 1.kster chromique qui se forme au cours de la premikre Ctape de la reaction. Les radicaux libres qui se forment au cours de la reaction reagissent avec le Cr(V1) pour former du Cr(V). On attribue deux signaux (gi,, = 1,977 et gi,, = 1,970) observes par resonance paramagnetique Clectronique (rpe) sur des solutions de 0,25 1 N de HC10, saturees en L-rhamnose et en c~,o,'-, aux complexes du Cr(V) intermediaire. A des pH supkrieurs (3-7), on n'a detecte que le signal a g = 1,977. Pour le D-mannose, on n'observe que le signal a g = 1,978 ti toutes les concentrations de HC104.[Traduit par la redaction]

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