Identification of ferrihydrite in polysaccharide iron complex by mossbauer spectroscopy and x-ray diffraction

A polysaccharide-iron complex (PIC), synthesized by the neutralization of an FeCl3−carbohydrate solution, is marketed as an oral hematimic (“Niferex”). The iron component was examined using Mössbauer Spectroscopy (12.8-295 K) and X-ray diffraction. From the Mössbauer spectra (a) the iron is high-spin Fe3+; (b) there is a continuous distribution of hyperfine fields at low T with a maximum field approaching 500 k0e as T approaches 0 K; (c) low-temperature spectra have small quadrupole interaction (2ϵ ≅ —0.08 mm/sec); (d) at T ⩾ 77 K the spectrum collapses to a broadened doublet; (e) high-temperature spectra require ⩾ 3 doublets for a good fit. Except for (a) all the above points are inconsistent with akagenéite (even though the syntheses are similar) and are consistent with ferrihydrite. The X-ray diffraction spectrum has peaks at 1.48, 2.25, and 2.52 Å (broad) and is consistent with ferrihydrite. No akaganéite peaks are present. Except for a slightly larger particle size (evidenced by smaller doublet component above 20 K), PIC resembles ferritin in all of the above characteristics. It may therefore serve as a useful model for the iron core of ferritin.