IQUIR   05412
INSTITUTO DE QUIMICA ROSARIO
Unidad Ejecutora - UE
artículos
Título:
Oxidation of 2-amino-2-deoxy-D-glucopyranose by hypervalent chromium: Kinetics and mechanism
Autor/es:
FRASCAROLI, M. I.; SIGNORELLA, S.; GONZÁLEZ, J. C.; MANGIAMELI, M. F.; GARCÍA, S.; RUBIN DE SELIS, E.; PIEHL, L.; SALA, L. F.; ATRIA, A. M.
Revista:
POLYHEDRON
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2011 vol. 30 p. 1914 - 1921
ISSN:
0277-5387
Resumen:
Amino sugars have been reported to occur in plants, microorganisms, and crustaceans and are an important constituent of the soil nitrogen; even, they are protected from decomposition in soils by being incorporated into the humic acid fraction. In order to obtain a more complete insight into the interaction of metal ions with these compounds a spectroscopic and kinetic study interaction of hypervalent chromium with 2-amino-2-deoxy-d-glucopyranose (Nglc) in aqueous solution was undertaken. Kinetic studies results afforded that the oxidation of Nglc by CrVI in acid media proceeded through a mechanism combining one- and two-electron pathways for the reduction of intermediate CrIV by the organic substrate: CrVI ¡ú CrIV ¡ú CrII and CrVI ¡ú CrIV ¡ú CrIII. The proposed mechanism is supported by the observation of CrVI esters, free radicals, (superoxoCrIII ion) and oxo-CrV complexes as reaction intermediates. Intermediacy of free radicals and CrII in the reaction was proved by the observation of induced polymerization of acrylamide and detection of respectively. The experimental results indicated that CrIV was a highly reactive intermediate since its disappearance rate was much faster than CrVI and CrV. Even at low [H+], CrIV intermediate was involved in fast steps and did not accumulate in the redox reaction. Oxo-CrV¨CNglc species were detected by EPR spectroscopy at low [H+]. In 0.40¨C1.00 M HClO4, CrV rapidly decomposed affording the reaction products, while, at pH 4.0 and 7.5, where the redox processes were very slow, five-coordinate oxo-CrV bis-chelates and mono-chelates of Nglc remained in solution and could be detected by EPR spectroscopy at room temperature. Kinetics results indicated that replacement of C2¨COH by C2¨CNH2 retarded the oxidation reaction of Nglc by CrVI/IV thus evidencing the role of ¨CNH2 group at C2 of the sugar frame.