ROD-LIKE IRON(III) OXYHYDROXIDE PARTICLES IN IRON(III)-POLYSACCHARIDESOLUTIONS

The interaction of iron(III) with different anionic polysaccharides ha s been studied by pH-metric, UV-vis, Fourier transform infrared, visco metric, and conductometric methods. The formation of water-soluble com pounds containing surprisingly high numbers of iron(III) ions even at physiological pH has been observed. The complex formation involves car boxylate, sulfonate, and probably alcoholic hydroxylate moieties. The metal binding starts in the acidic pH region with the complex precipit ating at 3.5 less than or equal to pH less than or equal to 6. The pre cipitate dissolves at pH > 6. The compositions of the complexes formed at pH 7 were found to be L[Fe(OH)(3)](n), where L is the repeating un it of the polymer. The maximum value of n proved to be dependent not o nly on the coordination ability, but also on the molar mass of the lig ands. Viscometric and conductometric data suggest that the structure-d etermining element of these complexes is the polysaccharide rather tha n an iron oxyhydroxide cluster. Their solution structure can be descri bed as independent rod-like particles comprising an unfolded polysacch aride backbone and polymerized iron(III)-oxyhydroxide particles.