A study has been made of the internal fields acting on Fe 57 nuclei in some spinel ferrites, with particular reference to the low-temperature order-disorder transition in magnetite, using the techniques of Mossbauer absorption. For the Fe 3+ ions at both the octahedral and tetrahedral sites in nickel ferrite (NiFe 2 0 4 ) at 300°K, 7Fe20 3 at 85° and 300°K, and magnetite (Fe30 4 ) at 85 °K, the effective magnetic field at the Fe 67 nuclei is the same and equal to about 5.1 XlO 5 oe. In magnetite, the value of H e u in the Fe 2+ ions is about 4.5X10 5 oe at 85°K. Measurements on Fe 3 04 at room temperatures provide a microscopic confirmation of Verwey's hypothesis that above the transition temperature of magnetite there is a fast exchange between the ferrous and ferric ions in the octahedral sites.

The reaction of isonicotinoyl hydrazone of pyridoxal (PIH), a biologically active iron‐carrier, with FeSO4‐7H20 at pH ∼ 6 generates the delta, lamda species of the N,N‐trans‐O,O‐cis‐cis coordination isomer of an iron(III) complex with iron‐to‐ligand ratio of 1:2. The dark red‐brown crystals are monoclinic, space group C2/c, with unit‐cell dimensions a = 14.487(2), b = 18.586(2), c = 27.508(4) Å, β = 102.76(3)°, and Z = 8. The coordination around the metal is distorted octahedral and involves the protonated organic ligands, which are chelated through the phenolic oxygen [Fe‐O1 1.941(6), Fe‐O1′ 1.938(6)], an enolic form of the carbonyl oxygen [Fe‐O3 2.017(6), Fe‐O3′ 2.018(6)] and the azomethinic nitrogen [Fe‐N2 2.133(8), Fe‐N2′ 2.133(8)]. Packing is determined by systems of N‐H….O and O‐H….O hydrogen bonds involving the protonated pyridoxal nitrogens, the pyridoxal hydroxymethyl group, and the [SO4]2− group. The Mössbauer spectra at different temperatures (300 K, 88 K and 4.1 K) clearly prove that the iron atom in the complex is in a high‐spin trivalent state.

Mouse (MEL) and human (K-562) erythroleukemia cell lines can be induced to undergo erythroid differentiation, including hemoglobin (Hb) synthesis, by extra cellular hemin. In order to study the effect of extracellular hemin on intracellular ferritin and Hb content, we have used Mossabauer spectroscopy to measure the amount of 57Fe incorporated into ferritin or Hb and a fluorescent enzyme-linked immunosorbent assay (ELISA) to measure the ferritin protein content. When K-562 cells were cultured in the presence of a 57Fe source either as transferrin or citrate, in the absence of a differentiation inducer, all the intracellular 57Fe was detected in ferritin. When the cells were cultured in the presence of 57Fe-hemin, 57Fe was found in both ferritin and Hb. 57Fe in ferritin increased rapidly, and after 2 days it reached a plateau at 5 X 10(-14) g/cell. 57Fe in Hb increased linearly with time and reached the same value after 12 days. Addition of other iron sources such as iron-saturated transferrin, iron citrate, or iron ammonium citrate caused a much lower increase in ferritin protein content as compared to hemin. When K-562 cells were induced by 57Fe-hemin in the presence of 56Fe-transferrin, 57Fe was found to be incorporated in equal amounts into both ferritin and Hb. However, when the cells were induced by 56Fe-hemin in the presence of 57Fe-transferrin, 57Fe was incorporated only into ferritin, but not into Hb, which contained 56Fe iron. These results indicate that in K-562 cells, when hemin is present in the culture medium it is preferentially incorporated into Hb, regardless of the availability of other extra- or intracellular iron sources such as transferrin or ferritin. In MEL cells induced to differentiate by dimethylsulfoxide (DMSO) a different pattern of iron incorporation was observed; 57Fe from both transferrin and hemin was found to incorporate in ferritin as well as in Hb.

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