Oligo and polyuronic acids interactions with hypervalent chromium

GONZÁLEZ, J. C.; GARCÍA, S. I.; BELLÚ, S.; ATRIA, A. M.; SALAS PEREGRIN, J. M.; ROCKENBAUER, A.; KORECZ, L.; SIGNORELLA, S.; SALA, L. F.

POLYHEDRON

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2009 vol. 28 p. 2719 - 2729

0277-5387

Selective oxidation of galacturonic residues of oligo and polyuronic acids by CrVI affords CO2/HCO2H, oxidized uronic acid, and CrIII as final redox products. Kinetic studies show that the redox reaction proceeds through a mechanism combining CrVI-CrIV-CrII and CrVI-CrIV-CrIII pathways. The mechanism is supported by the observation of free radicals, CrO22+ and CrV as reaction intermediates. The EPR spectra show that five- and six coordinated oxo-CrV intermediates are formed. Penta-coordinated oxo-CrV species are present at any [H+], whereas hexa-coordinated ones are only observed at pH <1. At low pH CrV predominating species are coordinated by carboxylate groups and Oring (giso = 1.9783/5). At pH 7.5, the predominating ones are those coordinated by alcoholate groups of the ligand (giso = 1.9800). Polygal can reduce CrVI and efficiently trap CrIII. 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.