Structural characterization and iron(III) binding ability of dimeric and polymeric lignin models

To understand the complexation in solution and the sorption of iron(III) on soluble and solid fractions of lignin, a dimeric model (guaiacyl-beta -gua iacylglycerol ether, called beta -O-4) and a polymeric model (dehydrogenati on polymer resulting from polymerization of coniferyl alcohol) of lignin ha ve been synthesized and characterized with chromatographic, solution, and s olid state C-13 CP-MAS NMR and XPS spectroscopies. The beta -O-4 dimer is a monoacid (HL). Potentiometric studies in aqueous solution at 25 degreesC a nd 1 mol L-1 ionic strength (KNO3) indicated formation of two stable comple xes, FeL2+ and probably FeL(OH)(+) which shows that the soluble fraction of lignin binds metals, indicating that they are transported by water through the soils. The binding of iron(III) on the DHP polymer was then investigat ed. The sorption experiments have shown a great affinity of iron for the so lid with a maximum of adsorption since pH 5. A pulsed-ESR study has reveale d surface oxidation by the iron(III) cation, which leads to iron(II) and se miquinonic radicals on the polymer surface, with a radical concentration of about 5 x 10(17) spin/g. (C) 2001 Academic Press.