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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The oxidation of D-ribose and 2-deoxy-D-ribose by CrVI yields the aldonic acid and Cr3+ as final products when an excess of sugar over CrVI is used. The redox reaction occurs through CrVI–>CrIII and CrVI–>CrV–>CrIII paths. The complete rate laws for the CrVI oxidation reactions are expressed by -d[CrVI]/dt = kH[H+]2 [ribose][CrVI], where kH = (5.9 ± 0.1) × 10-2 mol-3 dm9 s-1, and -d[CrVI]/dt = (k0 + kH'[H+]2) [2-deoxyribose][CrVI], where k0 = (1.3 ± 0.5) × 10-3 mol-1 dm3 s-1 and kH' = (4.2 ± 0.1) × 10-2 mol-3 dm9 s-1, at 33°C. An intermediate sugar alkoxide radical could be trapped with DMPO and observed by EPR as a multiline signal at g = 2.003. CrV is formed in a rapid step by reaction of the sugar radical with CrVI. CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxochromate(V) intermediates are formed, and the distribution of these CrV species in the reaction mixture essentially depends on the solution acidity.Key words: ribose, 2-deoxyribose, chromium, redox, mechanism, kinetics.

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Recebido em 4/3/02; aceito em 14/10/02The interaction of mercury(II) with sulfathiazole has been analyzed. IR and NMR spectral studies suggest a coordination of Hg(II) with the N thiazolic atom, unlike related Hg-sulfadrugs compounds. The complex was screened for its activity against Escherichia coli, showing an appreciable antimicrobial activity compared with the ligand.