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Purple acid phosphatase, (PAP), is known to contain dinuclear Fe2 + 2, + 3 site with characteristic Fe + 3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe2 + 2, + 3 (o-NQCH3ox) (o-NSQCH3ox)2 (CAT) H2O]. Fe-2: [Fe + 3(o-NQCH3ox) (p-NQCH3ox)2]2 a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. 57Fe Mossbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. 57Fe Mossbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe + 3]A and [Fe + 2]B sites. The hyperfine interaction parameters are δ A = 0.152, (ΔE Q)A = 0.598 mm/s with overlapping doublet at δ B = 0.410 and (ΔE Q)B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe + 3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQCH3ox ligand surrounding Fe + 3(h.s.) state generates small field gradient indicated by quadrupole split ΔE Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe2 + 2, + 3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g 1 = 4.17 and g 2 = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe + 3(h.s.) configuration. SQUID data of \(\chi _m^{{\rm corr}} \mbox{.T}\) were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = −13.5 cm − 1 with an agreement factor of R = 1.89 × 10 − 5). The lower J value of antiferromagnetic exchange leads to Fe+3μ-(OH) Fe + 2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe + 3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = −12.4 cm − 1, g = 2.3 with R = 3.58 × 10 − 5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.

Microwave-hydrothermal (MH) route was employed to synthesize various iron oxide phases in ultra-fine crystalline powders by using ferrous sulphate and sodium hydroxide as starting chemicals. All chemical reactions were carried out under identical MH conditions, namely, at 190°C, 154 psi, 30 min, by varying the molar ratio (MR) of FeSO4/NaOH in the aqueous solutions. The variation of MR has a dramatic effect on the crystallization behavior of various phases of iron oxides under MH processing conditions. For example, spherical agglomerates of Fe3O4 powder were obtained if MR equal to 0.133 (pH>10 sample A). On the other hand non-stoichiometric Fe3O4 powders (Sample B) were obtained for all higher MR of FeSO4/NaOH between 0.133 and 4.00 (6.6

Films of nanocrystalline γ-Fe2O3 were deposited on silicon substrates by using the technique of electrophoretic deposition. The precursor powder was nanocrystalline γ-Fe2O3, which was synthesized, using DC arc plasma in the oxygen ambient by vapour–vapour interaction in gas phase condensation; at a stabilized arc current of 40 A. This powder was characterized by X-ray diffraction, Transmission Electron Microscopy, Vibrating Sample Magnetometer and Mossbauer Spectroscopy. An increase in directional coercivity was observed in case of films deposited on silicon substrates, which is dramatically significant. Preferred orientation of almost similar sized nanocrystalline magnetic domains in deposited films is evident from the results of X-ray diffraction and Transmission Electron Microscopy results. The preferred alignment of the nanocrystallites seems to be responsible for the significant changes observed in magnetic properties of films.

The effects of ion beam induced atomic mixing at the Fe-Polyethylene interface have been investigated by means of conversion electron Mossbauer spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed composites exhibit distinctly different features. In particular, the ion beam mixed composite shows that presence of Fe2+ state in polyethylene matrix along with the Fe−C austenite like phase.

The effect of ion beam induced atomic mixing and subsequent thermal transformations at the Fe:Al2O3 interface have been investigated by means of conversion electron Mossbauer spectroscopy [CEMS]. It is shown that the asdeposited and ion beam mixed samples exhibit distinctly different features. In particular, the ion beam mixed sample in as-mixed state shows the presence of FeAl2O4 along with non-stoichiometric FeO. Upon annealing at 600°C it shows precipitation of α-Fe with reduced contribution of FeAl2O4. The study of dose dependence of ion beam mixing has also revealed interesting features regarding the ion beam induced interface reactions.

Oxide layers are produced on iron surface, under discharge in water ambient, applying both anodic and cathodic potentials to iron foil. Non-stoichiometric Fe1−xO containing different ratios of Fe3+ and Fe2+ has been detected by using CEMS. Corrosion of these samples in 0.5 M H2SO4 shows that, cathodically discharge treated iron foil has higher corrosion resistance as compared to the anodically treated sample. This is attributed to the microstructural differences in the Fe1−xOx films formed during the discharge.

Highly unstable FeO is chemically passivated by incorporating Cr3+ ions by solid solution technique and forming FexO∶Cr3+ single phase material. XRD, chemical analysis and Mossbauer spectroscopy are used for the characterization of the freshly prepared as well as samples aged in the desiccator for nearly three months. Optimum concentration range — 0.25 to 0.75 mole% — of Cr2O3 has been found to be necessary for stabilizing FexO∶Cr3+. x is determined by chemical analysis. Mossbauer and XRD studies have confirmed the chemical passivation of unstable FeO.

The nuclear hyperfine structure of dilute impurity iron ions in ferroelectric lithium niobate is investigated via57Fe Mossbauer effect (ME). The ME spectra exhibit typical slow electron spin relaxation effects associated with Fe3+ ions in the6S5/2 state, which are analysed using spin-Hamiltonian formalism. For Fe3+ ions, the principal axis of EFG tensor is found to be parallel to the crystallographic c-axis. The strong external magnetic field of 47 KOe is used to study magnetic and crystal field effects on the ME hyperfine structure.

Magnetic Ferrite — polymer composites are synthesised using platelet type barium ferrite with four different polymers with and without treating with silane and titanate surface modifiers. Fe57 Mossbauer and bulk magnetic measurements have been carried out at room temperature to study polymer-filler interactions, both at macro- and microscopic levels. Hyperfine interaction parameters did not show any noticeable change except for the few percent change in intensities. On the other hand, significant changes in remanence, coercivity and (BH)max value of these composites are observed as a function of processing parameters.