Artículo de revista
Oligo and polyuronic acids interactions with hypervalent chromium
Fecha
2009-09-02Registro en:
POLYHEDRON 28(13): 2719-2729
0277-5387
Autor
González, J. C.
García, S. I.
Bellú, Sebastián
Atria Salas, Ana María
Salas Pelegrin, Juan Manuel
Rockenbauer, A.
Korecz, L.
Signorella, Sandra
Sala, Luis F.
Institución
Resumen
Selective oxidation of galacturonic residues of oligo and polyuronic acids by Cr-VI affords CO2/HCO2H, oxidized uronic acid, and Cr-III as final redox products. Kinetic studies show that the redox reaction proceeds through a mechanism combining Cr-VI -> Cr-IV -> Cr-II and Cr-VI -> Cr-IV -> Cr-III pathways. The mechanism is supported by the observation of free radicals, CrO22+ and Cr-V as reaction intermediates. The EPR spectra show that five- and six coordinated oxo-Cr-V intermediates are formed. Penta-coordinated oxo-Cr-V species are present at any [H+], whereas hexa-coordinated ones are only observed at pH <1. At low pH Cr-V predominating species are coordinated by carboxylate groups and O-ring (g(iso) = 1.9783/5). At pH 7.5, the predominating ones are those coordinated by alcoholate groups of the ligand (g(iso) = 1.9800). Polygal can reduce Cr-VI and efficiently trap Cr-III. This behaviour represents an interesting model for the study of biomaterials, which possess a high proportion of polygal, in order to remove chromium from polluted waters.