IQUIR   05412
INSTITUTO DE QUIMICA ROSARIO
Unidad Ejecutora - UE
artículos
Título:
New insights on the mechanism of oxidation of D-galacturonic acid by hypervalent chromium.
Autor/es:
MANGIAMELI, F; GONZÁLEZ, JUAN CARLOS; GARCIA, SILVIA; FRASCAROLI M I; S. VAN DOORSLAER; SALAS PEREGRIN, JUAN MANUEL; SALA,LUIS F.
Revista:
DALTON TRANSACTIONS
Editorial:
ROYAL SOC CHEMISTRY
Referencias:
Lugar: Londres; Año: 2011 vol. 40 p. 7033 - 7045
ISSN:
1477-9226
Resumen:
Abstract The pollutant CrVI is known to be very carcinogenic. In excess of CrVI, oxidation of D-galacturonic acid (Galur), the major metabolite of pectin, yields D-galactaric acid (Galar) and CrIII. The redox reaction takes place through a multistep mechanism involving formation of intermediate CrII/IV and CrV species. The mechanism combines one- and two-electron pathways for the reduction of CrIV by the organic substrate: CrVI ?¨ CrIV ?¨ CrII and CrVI ?¨ CrIV ?¨ CrIII. This is supported by the observation of the optical absorption spectra of CrVI esters, free radicals, CrO22+ (superoxoCrIII ion) and oxo-CrV complexes. CrIV cannot be directly detected; however, formation of CrO22+ provides indirect evidence for the intermediacy of CrII/IV. CrIV reacts with Galur much faster than CrV and CrVI do. The analysis of the reaction kinetics via optical absorption spectroscopy shows that the CrIV/Galur reaction rate inversely depends on [H+]. Nevertheless, high [H+] still does not facilitate accumulation of CrIV in the CrVI/Galur mixture. CrVI and the intermediate CrV react with Galur at comparable rates; therefore the build-up and decay of CrV accompany the decay of CrVI. The complete rate laws for the CrVI, CrV and CrIV/Galur redox reaction are here derived in detail. Furthermore, the nature of the five-co-ordinated oxo-CrV bischelate complexes formed in CrVI/Galur mixtures at pH 1-5 is investigated using continuous-wave and pulsed electron paramagnetic resonance (EPR) and density functional theory (DFT).