Abstract

Aqueous extraction of Ahnfeltia plicata collected in the Magellan ecoregion afforded agarose devoid of sulfate groups. This neutral agarose was subjected to sulfation with SO3-pyridine complex, giving an aqueous soluble derivative with 35.5 % sulfate groups. Analysis by Fourier transform infrared spectroscopy (FT-IR) and by H-1 and C-13 NMR spectroscopy indicated that this derivative was sulfated at positions C-6 of the beta-galactopyranosyl residue and C-2 of the alpha-3,6-anhydrogalactopyranosyl residue and partially sulfated at position C-2 of the beta residue. The antioxidant capacity of sulfated agarose was evaluated by the oxygen radical absorbance capacity (ORAC) method, ABTS radical cation, hydroxyl radicals, and chelating assays. This capacity of sulfated agarose toward peroxyl radicals was higher than that of commercial lambda-carrageenan, while native agarose presented good activity, with an ORAC value similar to that of commercial kappa-carrageenan. Sulfated agarose presented good antioxidant capacity toward other radicals. Copolymerization of sulfated agarose with acrylamide was achieved using ceric ammonium nitrate as initiator. NMR spectroscopy indicated grafting of polyacrylamide at position C-4 of beta-galactopyranosyl residues.