Oligo and polyuronic acids interactions with hypervalent chromium.

JUAN C. GONZÁLEZ; SILVIA I. GARCÍA; SEBASTIÁN BELLÚ; ANA MARÍA ATRIA; JUAN MANUEL SALAS PELEGRÍN; ANTAL ROCKENBAUER; LAZLO KORECZ; SANDRA SIGNORELLA; LUIS F. SALA

POLYHEDRON

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, CrO2 2+ 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.VI 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, CrO2 2+ 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.