Inducing Ferrimagnetic Exchange in 1D-FeSe2 Chains Using Heteroleptic Amine Complexes: [Fe(en)(tren)][FeSe2]2

[Fe(en)(tren)][FeSe2]2 (en = ethylenediamine, C2H8N2, tren = tris(2-aminoethyl)amine, C6H18N4) has been synthesized by a mixed-ligand solvothermal method. Its crystal structure contains heteroleptic [Fe(en)(tren)]2+ complexes with distorted octahedral coordination, incorporated between 1D-FeSe2 chains composed of edge-sharing FeSe4 tetrahedra. The twisted octahedral coordination environment of the Fe-amine complex leads to partial dimerization of Fe-Fe distances in the FeSe2 chains so that the FeSe4 polyhedra deviate strongly from the regular tetrahedral geometry. 57Fe Mössbauer spectroscopy reveals oxidation states of +3 for the Fechain atoms and +2 for the Fecomplex atoms. The close proximity of Fe atoms in the chains promotes ferromagnetic nearest neighbor interactions, as indicated by a positive Weiss constant, θ = +53.8(6) K, derived from the Curie-Weiss fitting. Magnetometry and heat capacity reveal two consecutive magnetic transitions below 10 K. DFT calculations suggest that the ordering observed at 4 K is due to antiferromagnetic intrachain interactions in the 1D-FeSe2 chains. The combination of two different ligands creates an asymmetric coordination environment that induces changes in the structure of the Fe-Se fragments. This synthetic strategy opens new ways to explore the effects of ligand field strength on the structure of both Fe-amine complexes and surrounding Fe-Se chains.

As-Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe-Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering

A novel mixed-valent hybrid chiral and polar compound, Fe₇As₃Se₁₂(en)₆(H₂O), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [Fe₅Se₉] chains connected via [As₃Se₂]-Se pentagonal linkers and charge-balancing interstitial [Fe(en)₃]²⁺ complexes (en = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing. Magnetic polarizability of the produced compound was confirmed by X-ray magnetic circular dichroism (XMCD) spectroscopy. X-ray absorption spectroscopy (XAS) and ⁵⁷Fe Mössbauer spectroscopy showed the presence of mixed-valent Fe²⁺/Fe³⁺ in the Fe-Se chains. Magnetic susceptibility measurements reveal strong antiferromagnetic nearest neighbor interactions within the chains with no apparent magnetic ordering down to 2 K. Hidden short-range magnetic ordering below 70 K was found by ⁵⁷Fe Mössbauer spectroscopy, showing that a fraction of the Fe³⁺/Fe²⁺ in the chains are magnetically ordered. Nevertheless, complete magnetic ordering is not achieved even at 6 K. Analysis of XAS spectra demonstrates that the fraction of Fe³⁺ in the chain increases with decreasing temperature. Computational analysis points out several competing ferrimagnetic ordered models within a single chain. This competition, together with variation in the Fe oxidation state and additional weak intrachain interactions, is hypothesized to prevent long-range magnetic ordering.

Atomic structure of an FeCrMoCBY metallic glass revealed by high energy x-ray diffraction

Amorphous bulk metallic glasses with the composition Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂have been of interest due to their special mechanical and electronic properties, including corrosion resistance, high yield-strength, large elasticity, catalytic performance, and soft ferromagnetism. Here, we apply a reverse Monte Carlo technique to unravel the atomic structure of these glasses. The pair-distribution functions for various atomic pairs are computed based on the high-energy x-ray diffraction data we have taken from an amorphous sample. Monte Carlo cycles are used to move the atomic positions until the model reproduces the experimental pair-distribution function. The resulting fitted model is consistent with ourab initiosimulations of the metallic glass. Our study contributes to the understanding of functional properties of Fe-based bulk metallic glasses driven by disorder effects.

Atomic arrangements in an amorphous CoFeB ribbon extracted via an analysis of radial distribution functions

We discuss the atomic structure of amorphous ferromagnetic FeCoB alloys, which are used widely in spintronics applications. Specifically, we obtain the pair-distribution functions for various atomic pairs based on high-energy x-ray diffraction data taken from an amorphous Co₂₀Fe₆₁B₁₉specimen. We start our reverse Monte Carlo cycles to determine the disordered structure with a two-phase model in which a small amount of cobalt is mixed with Fe₂₃B₆as a second phase. The structure of the alloy is found to be heterogeneous, where the boron atoms drive disorder through the random occupation of the atomic network. Our analysis also indicates the presence of small cobalt clusters that are embedded in the iron matrix and percolating the latter throughout the structure. This morphology can explain the enhanced spin polarization observed in amorphous magnetic materials.

Magnetic properties of γ-Fe2O3 nanoparticles in a porous SiO2 shell for drug delivery

A method is presented for synthesizing core-shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple γ-Fe2O3 nanoparticles (∼15 nm) enclosed in a SiO2 (∼100-200 nm) matrix using either methyl (denoted TMOS-γ-Fe2O3) or ethyl (TEOS-γ-Fe2O3) template groups. Low-temperature Mössbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, γ-Fe2O3, with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of γ-Fe2O3 was greater in the TMOS-γ-Fe2O3 nanoparticles than TEOS-γ-Fe2O3 nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS-γ-Fe2O3 and around 250 K for the TEOS-γ-Fe2O3. Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core-shell structure.

Tuning Fe-Se Tetrahedral Frameworks by a Combination of [Fe(en)3]2+ Cations and Cl- Anions

A one-dimensional (1D) chain compound [Fe(en)3]3(FeSe2)4Cl2 (en = ethylenediamine), featuring tetrahedral FeSe₂ chains separated by [Fe(en)₃]²⁺ cations and Cl^- anions, has been synthesized by a low temperature solvothermal method using simple starting materials. The degree of distortion in the Fe-Se backbone is similar to previously reported compounds with isolated 1D FeSe₂ chains. ⁵⁷Fe Mössbauer spectroscopy reveals the mixed-valent nature of [Fe(en)₃]₃(FeSe₂)₄Cl₂ with Fe³⁺ centers in the [FeSe₂]^- chains and Fe²⁺ centers in the [Fe(en)₃]²⁺ complexes. SQUID magnetometry indicates that [Fe(en)3]3(FeSe2)4Cl2 is paramagnetic with a reduced average effective magnetic moment, μ_eff = 9.51 μ_B per formula unit, and a negative Weiss constant, θ = -10.9(4) K, indicating antiferromagnetic (AFM) nearest neighbor interactions within the [FeSe₂]^- chains. Weak antiferromagnetic coupling between chains, combined with rather strong intrachain AFM coupling, leads to spin-glass behavior at low temperatures, as indicated by a frequency shift of the peak observed at 3 K in AC magnetic measurements. A combination of [Fe(en)₃]²⁺ and Cl^- ions is also capable of stabilizing mixed-valent 2D Fe-Se puckered layers in the crystal structure of [Fe(en)₃]₄(Fe₁₄Se₂₁)Cl₂, where Fe₁₄Se₂₁ layers have a unique topology with large open pores. Property measurements of [Fe(en)₃]₄(Fe₁₄Se₂₁)Cl₂ could not be performed due to the inability to either grow large crystals or synthesize this material in single-phase form.

Structural properties of PbTe quantum dots revealed by high-energy x-ray diffraction

High-energy x-ray diffraction (HE-XRD) experiments combined with an analysis based on atomic-pair-distribution functions can be an effective tool for probing low-dimensional materials. Here, we show how such an analysis can be used to gain insight into structural properties of PbTe nanoparticles (NPs). We interpret our HE-XRD data using an orthorhombic Pnma phase of PbTe, which is an orthorhombic distortion of the rocksalt phase. Although local crystal geometry can vary substantially with particle size at scales below 10 nm, and for very small NPs the particle size itself influences x-ray diffraction patterns, our study shows that HE-XRD can provide a unique nano-characterization tool for unraveling structural properties of nanoscale systems.

Size-dependent magnetic properties of γ-Fe2O3 nanocrystallites

A route for synthesizing monodisperse magnetic nanocrystallites of maghemite, [Formula: see text]-Fe₂O₃, with various sizes has been revisited. A systematic investigation of three [Formula: see text]-Fe₂O₃ nanocrystalline samples by different techniques has been performed to characterize their size-dependent magnetic properties. Zero-field-cooled and field-cooled magnetization measurements reveal that the superparamagnetic blocking temperatures are around 230 K, 170 K, and 50 K for the 15.0 nm, 11.8 nm, and 6.1 nm nanocrystallites, respectively. Low-temperature Mössbauer spectra show that all three nanocrystallites have the maghemite structure with all the vacancies in the B-sites. Furthermore, detailed analysis shows that there are more vacancies on the B-sites for the 6.1 nm nanocrystallites compared to 0.33 for the bulk maghemite.

Bimetallic Fe/Al system: An all-in-one solid-phase Fenton reagent for generation of hydroxyl radicals under oxic conditions

In the classic Fenton reaction, both H₂O₂ and ferrous ion (Fe(II)) are required under a narrow low pH range to produce hydroxyl radicals (OH). The modified Fenton processes including heterogeneous Fenton-like reaction, photo-Fenton reaction and electro-Fenton reaction developed to overcome the drawbacks of the homogeneous Fenton reaction have recently received increasing attention. However, all the modifications of the classic Fenton reaction cannot be assembled into one system and require external supply of reagents or energy. We present here, bimetallic Fe/Al, a novel solid-phase Fenton reagent capable of in situ generation of H₂O₂ and Fe(II) to form OH under near neutral pH conditions without an external energy supply. Aluminum acts as an electron donor to maintain the electron supply and preserve the outer layer of iron at the zero-valence state with enhanced surface areas. The production of OH by bimetallic Fe/Al was quantified and further detected by an electron paramagnetic resonance (EPR) analysis under oxic conditions. Radical scavenging tests were performed by adding isopropanol or 1,4‑benzoquinone in the system to investigate the nature of the oxidants produced during the oxidative process. Bimetallic Fe/Al system for the Fenton reaction in water involves both surface-mediated and aqueous-phase reactions. A pilot scale test using a continuous-flow column packed with Fe/Al (9.8 kg) demonstrated the capability of bimetallic Fe/Al for COD removal of acidic dye solutions. The novelty of bimetallic Fe/Al is that it is an all-in-one solid-phase Fenton reagent that can be readily applied to a wide variety of environmental applications.

Nitrosylation of Nitric-Oxide-Sensing Regulatory Proteins Containing [4Fe-4S] Clusters Gives Rise to Multiple Iron-Nitrosyl Complexes

The reaction of protein-bound iron-sulfur (Fe-S) clusters with nitric oxide (NO) plays key roles in NO-mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe-S clusters has been hampered by a lack of information about the nature of the iron-nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe-4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe2 (NO)4 (Cys)2 ]) and Roussin's Black Salt (RBS, [Fe4 (NO)7 S3 ]. In the latter case, the absence of 32 S/34 S shifts in the Fe-S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates.

Characterization of the [3Fe-4S](0/1+) cluster from the D14C variant of Pyrococcus furiosus ferredoxin via combined NRVS and DFT analyses

The D14C variant of Pyrococcus furiosus ferredoxin provides an extraordinary framework to investigate a [3Fe-4S] cluster at two oxidation levels and compare the results to its physiologic [4Fe-4S] counterpart in the very same protein. Our spectroscopic and computational study reveals vibrational property changes related to the electronic and structural aspects of both Fe-S clusters.

Extracting the cation distributions in NiFe2-xAlxO4 solid solutions using magnetic Compton scattering

We discuss the ground state electronic structure and magnetization properties of a series of NiFe2-x Al x O4 solid solutions (x  =  0.0, 0.4, 0.8, 1.2, 1.6, and 2.0) using magnetic Compton scattering measurements, together with parallel first-principles computations. In this way, we systematically extract the complicated cation distributions in this ferrite system as a function of x. The relationship between the electronic ground state, magnetism, and cation distributions is explained in terms of a model, validated by our first-principles computations, wherein the magnetic properties of the three cation distributions are assumed to be different. A good accord is found between the computed and measured magnetic Compton profiles.

Synthesis and controllable oxidation of monodisperse cobalt-doped wüstite nanoparticles and their core-shell stability and exchange-bias stabilization

Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ∼4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (H(E)), an enhanced coercivity field (H(C)), and a pronounced vertical shift, thus indicating the presence of a strong exchange bias coupling effect. More importantly, the onset temperature of H(E) was found to be higher than 200 K, which suggests that cobalt doping increases the Néel temperature (T(N)) of the CWT core. In general, the results show that the homogeneous dispersion of Co in iron precursors improves the stability of the final CWT nanoparticles. Moreover, the CoFe2O4 shells formed following oxidation increase the oxidation resistance of the CWT cores and enhance their anisotropy energy.

Quasi-three-coordinate iron and cobalt terphenoxide complexes {Ar(iPr8)OM(μ-O)}2 (Ar(iPr8) = C6H-2,6-(C6H2-2,4,6-(i)Pr3)2-3,5-(i)Pr2; M = Fe or Co) with M(III)2(μ-O)2 core structures and the peroxide dimer of 2-oxepinoxy relevant to benzene oxidation

The bis(μ-oxo) dimeric complexes {Ar(iPr8)OM(μ-O)}2 (Ar(iPr8) = C6H-2,6-(C6H2-2,4,6-(i)Pr3)2-3,5-(i)Pr2; M = Fe (1), Co (2)) were prepared by oxidation of the M(I) half-sandwich complexes {Ar(iPr8)M(η(6)-arene)} (arene = benzene or toluene). Iron species 1 was prepared by reacting {Ar(iPr8)Fe(η(6)-benzene)} with N2O or O2, and cobalt species 2 was prepared by reacting {Ar(iPr8)Co(η(6)-toluene)} with O2. Both 1 and 2 were characterized by X-ray crystallography, UV-vis spectroscopy, magnetic measurements, and, in the case of 1, Mössbauer spectroscopy. The solid-state structures of both compounds reveal unique M2(μ-O)2 (M = Fe (1), Co(2)) cores with formally three-coordinate metal ions. The Fe···Fe separation in 1 bears a resemblance to that in the Fe2(μ-O)2 diamond core proposed for the methane monooxygenase intermediate Q. The structural differences between 1 and 2 are reflected in rather differing magnetic behavior. Compound 2 is thermally unstable, and its decomposition at room temperature resulted in the oxidation of the Ar(iPr8) ligand via oxygen insertion and addition to the central aryl ring of the terphenyl ligand to produce the 5,5'-peroxy-bis[4,6-(i)Pr2-3,7-bis(2,4,6-(i)Pr3-phenyl)oxepin-2(5H)-one] (3). The structure of the oxidized terphenyl species is closely related to that of a key intermediate proposed for the oxidation of benzene.

NsrR from Streptomyces coelicolor is a nitric oxide-sensing [4Fe-4S] cluster protein with a specialized regulatory function

The Rrf2 family transcription factor NsrR controls expression of genes in a wide range of bacteria in response to nitric oxide (NO). The precise form of the NO-sensing module of NsrR is the subject of controversy because NsrR proteins containing either [2Fe-2S] or [4Fe-4S] clusters have been observed previously. Optical, Mössbauer, resonance Raman spectroscopies and native mass spectrometry demonstrate that Streptomyces coelicolor NsrR (ScNsrR), previously reported to contain a [2Fe-2S] cluster, can be isolated containing a [4Fe-4S] cluster. ChIP-seq experiments indicated that the ScNsrR regulon is small, consisting of only hmpA1, hmpA2, and nsrR itself. The hmpA genes encode NO-detoxifying flavohemoglobins, indicating that ScNsrR has a specialized regulatory function focused on NO detoxification and is not a global regulator like some NsrR orthologues. EMSAs and DNase I footprinting showed that the [4Fe-4S] form of ScNsrR binds specifically and tightly to an 11-bp inverted repeat sequence in the promoter regions of the identified target genes and that DNA binding is abolished following reaction with NO. Resonance Raman data were consistent with cluster coordination by three Cys residues and one oxygen-containing residue, and analysis of ScNsrR variants suggested that highly conserved Glu-85 may be the fourth ligand. Finally, we demonstrate that some low molecular weight thiols, but importantly not physiologically relevant thiols, such as cysteine and an analogue of mycothiol, bind weakly to the [4Fe-4S] cluster, and exposure of this bound form to O2 results in cluster conversion to the [2Fe-2S] form, which does not bind to DNA. These data help to account for the observation of [2Fe-2S] forms of NsrR.

Favourable pregnancy outcome in Takayasu arteritis: a single-centre experience

OBJECTIVES

Takayasu arteritis is a chronic large-vessel vasculitis in young women of reproductive age. We aimed to obtain information on pregnancy in TA retrospectively.

METHODS

Takayasu arteritis patients with history of pregnancy were included in this study. The evaluations included physical findings, serum C-reactive protein, erythrocyte sedimentation rate as well as history and symptoms. Information about pregnancies, abortus, deliveries and newborns was obtained from medical records. Disease activity score, disease damage index appraised Kerr's criteria and vasculitis damage index (VDI) and medication were recorded.

RESULTS

Thirty-six Takayasu arteritis patients who had a total of 84 pregnancies were evaluated. The mean age of patients ranged 24.5 ± 6.6 years. Subclavian arteries (86%) were the most frequently involved vessels. We were able to complete the follow-up of ten patients who had a pregnancy after diagnosis during the period of pregnancy. Two patients who had renal artery involvement and active disease in third trimester suffered from preeclampsia and a worsening of hypertension. In one of them, disease flared up in the third trimester. There was no active disease in the postpartum sixth month. Maternal heart failure, cerebrovascular accident, death or cerebral hypoperfusion at the time of delivery, asphyxia and newborn anomalies were not seen in any of these patients.

CONCLUSIONS

TA pregnancies may have a favourable outcome with regular follow-up schedule and close monitorisation of blood pressure.

Controlling spin polarized band-structure by variation of vacancy intensity in nanostructures

In this study, the magnetic properties of FeAl alloys with different grain sizes produced by high-pressure torsion were probed by means of magnetic Compton scattering. The measurements were performed at 300 and 10 K. Magnetic Compton profiles of nanocrystalline (35 nm) and ultrafine-grained (160 nm) FeAl alloys were analyzed in terms of the integral area, the width, and the distinctive dip intensity at low momenta. The changes in total magnetic moment and the strength of spin-polarization of itinerant electrons are assumed to be caused by vacancies induced during the preparation of the samples. Despite local disordering due to interfacial regions and deviations in perfect stoichiometry for B2 structure, the effect of vacancies is considered as the major magnetic state contributor.

Control over connectivity and magnetism of tetrahedral FeSe2 chains through coordination Fe–amine complexes

Magnetic interactions in compounds containing tetrahedral _∞¹(FeSe₂) chains separated by Fe–amine complexes are controlled by the denticity of the amine.

High-Temperature Magnetism as a Probe for Structural and Compositional Uniformity in Ligand-Capped Magnetite Nanoparticles

To investigate magnetostructural relationships in colloidal magnetite (Fe₃O₄) nanoparticles (NPs) at high temperature (300-900 K), we measured the temperature dependence of magnetization (M) of oleate-capped magnetite NPs ca. 20 nm in size. Magnetometry revealed an unusual irreversible high-temperature dependence of M for these NPs, with dip and loop features observed during heating-cooling cycles. Detailed characterizations of as-synthesized and annealed Fe₃O₄ NPs as well as reference ligand-free Fe₃O₄ NPs indicate that both types of features in M(T) are related to thermal decomposition of the capping ligands. The ligand decomposition upon the initial heating induces a reduction of Fe³⁺ to Fe²⁺ and the associated dip in M, leading to more structurally and compositionally uniform magnetite NPs. Having lost the protective ligands, the NPs continually sinter during subsequent heating cycles, resulting in divergent M curves featuring loops. The increase in M with sintering proceeds not only through elimination of a magnetically dead layer on the particle surface, as a result of a decrease in specific surface area with increasing size, but also through an uncommonly invoked effect resulting from a significant change in Fe³⁺/Fe²⁺ ratio with heat treatment. The interpretation of irreversible features in M(T) indicates that reversible M(T) behavior, conversely, can be expected only for ligand-free, structurally and compositionally uniform magnetite NPs, suggesting a general applicability of high-temperature M(T) measurements as an analytical method for probing the structure and composition of magnetic nanomaterials.

Use of ductoscopy as an additional diagnostic method and its applications in nipple discharge

AIM

About 1/10 of the patients apply to breast clinics with the complaint of nipple discharge (ND). Surgery is the most frequently preferred treatment method in case of suspicious ND. The contribution of ductoscopy to identify the patients who are candidates for surgery was evaluated and its role to limit the surgery was assessed.

METHODS

From November 2005 to December 2010 430 patients with ND were assessed by 456 ductoscopic investigations and the results were analyzed. Complete ductoscopic evaluation was achieved in 84% of cases and 28 patients were offered surgery but did not accept (N.=355). Patients with bloody or serous discharges from a single duct were investigated by ductoscopy under local anesthesia as an office procedure. The patients were grouped according to discharge characteristics and the ductoscopic diagnoses.

RESULTS

A total of 223 patients had all three criteria of pathologic ND (PND: single duct, spontaneous and bloody/serous discharge). Twenty-two potential neoplastic or malignant lesion (PNML) and 79 papillomatous lesion (solitary or multiple papilloma) were identified. In 132 patients with just two of the PND criteria, 5 PNML and 18 papillomatous lesions were identified. Twenty-three patients with solitary papilloma that were removed by ductoscopic papillomectomy (DP) are followed up without surgery.

CONCLUSION

Ductoscopy helped to identify the patients who required surgical treatment and decreased the number of operations. DP was successfully performed in select group of patients who otherwise would have required surgical resection. Patients with normal ductoscopy findings and patients who were treated with DP successfully can be followed up without the need of surgery.

NH4FeCl2(HCOO): synthesis, structure, and magnetism of a novel low-dimensional magnetic material

Solvothermal synthesis was used to create a low-dimensional iron(II) chloride formate compound, NH4FeCl2(HCOO), that exhibits interesting magnetic properties. NH4FeCl2(HCOO) crystallizes in the monoclinic space group C2/c (No. 15) with a = 7.888(1) Å, b = 11.156(2) Å, c = 6.920(2) Å, and β = 108.066(2)°. The crystal structure consists of infinite zigzag chains of distorted Fe(2+)-centered octahedra linked by μ2-Cl and syn-syn formate bridges, with interchain hydrogen bonding through NH4(+) cations holding the chains together. The unique Fe(2+) site is coordinated by four equatorial chlorides at a distance of 2.50 Å and two axial oxygens at a distance of 2.08 Å. Magnetic measurements performed on powder and oriented single-crystal samples show complex anisotropic magnetic behavior dominated by antiferromagnetic interactions (TN = 6 K) with a small ferromagnetic component in the direction of chain propagation. An anisotropic metamagnetic transition was observed in the ordered state at 2 K in an applied magnetic field of 0.85-3 T. (57)Fe Mössbauer spectroscopy reveals mixed hyperfine interactions below the ordering temperature, with strong electric field gradients and complex noncollinear arrangement of the magnetic moments.

Oxidation states and quality of upper interfaces in magnetic tunnel junctions: oxygen effect on crystallization of interfaces

In this study, we have deposited an 57Fe sensor layer at the upper interface, i.e. the interface between the oxide barrier and the upper electrode in selected magnetic tunnel junctions (MTJs), in order to perform nuclear resonant scattering with the aim of obtaining direct information on the magnetic properties and quality of this interface. This is a unique approach as it makes use of this powerful technique to give information at the atomic level, and specifically from the interface where the sensor layer is deposited. By varying sample tunnel barrier thicknesses and oxidation times in the preparation of this barrier, we have observed that longer oxidation time results in not only an increase of the magnetic hyperfine fields, but also causes an interesting crystallization and smoothing of the interface. We also observed that boron atoms diffuse away from the lower part of the upper FeCoB electrode toward the capping layer. An important observation, which has a crucial effect in tunnel magnetoresistance values, is the absence of any magnetically dead FeO layer at the interface. Another finding is that the deposition of Fe on MgO is much smoother than the deposition of MgO on Fe.

Frequency of Celiac Disease in Children with Beta Thalassemia major

BACKGROUND

We aimed to investigate the frequency of celiac disease in children with β-thalassemia major (B-TM) in Shiraz, southern Iran.

MATERIALS AND METHODS

In this study, the prevalence of celiac disease in children with B-TM was evaluated. Children with B-TM were screened for celiac disease by ant-tissue transglutaminase (anti-tTG) IgA antibody, IgA level and anti-tTG IgG. A total of 1500 school healthy children in Shiraz with age/sex matched were selected as control group.

RESULTS

A total of 215 B-TM patients with mean age of 12.7 ± 4.4 years, were included into the study (52.1% was male). None of the patients were positive for anti-tTG IgA. Eight cases were IgA deficient in whom anti-tTG IgG was investigated but none of them were positive for anti-tTG IgG. The finding in control group has a seroprevalence of 2% and biopsy proven disease of 0.6%.

CONCLUSION

Many patients with thalassemia major have multiple non specific symptom that are not justifiable with underlying disease and might be due to atypical celiac disease. We didn't find any case of celiac disease among more than 200 children with β-thalassemia major in Shiraz, southern Iran. So it seems reasonable to screen only those who have features, even not classical, of celiac disease.

Chemical excision of tetrahedral FeSe(2) chains from the superconductor FeSe: synthesis, crystal structure, and magnetism of Fe(3)Se(4)(en)(2)

Fragments of the superconducting FeSe layer, FeSe2 tetrahedral chains, were stabilized in the crystal structure of a new mixed-valent compound Fe3Se4(en)2 (en = ethylenediamine) synthesized from elemental Fe and Se. The FeSe2 chains are separated from each other by means of Fe(en)2 linkers. Mössbauer spectroscopy and magnetometry reveal strong magnetic interactions within the FeSe2 chains which result in antiferromagnetic ordering below 170 K. According to DFT calculations, anisotropic transport and magnetic properties are expected for Fe3Se4(en)2. This compound offers a unique way to manipulate the properties of the Fe-Se infinite fragments by varying the topology and charge of the Fe-amino linkers.

Oxidation states and the quality of lower interfaces in magnetic tunnel junctions: oxygen effect on crystallization of interfaces

Lower interfaces in magnetic tunnel junctions (MTJs), which are the basic components in many spintronic devices such as magnetoresistive random access memories, have crucial effects on the performance of these devices. To obtain more insight into such interfaces, we have introduced an ultrathin sensor layer of (57)Fe at the interface between the lower electrode and the oxide barrier in selected MTJs. This allowed us to perform nuclear resonant scattering measurements, which provide direct information on the magnetic properties and quality of the interfaces. The application of nuclear resonant scattering to study interfaces in MTJs is a unique approach in the sense that it gives information at the atomic level, and specifically from the interface where the sensor layer is deposited. Samples with different tunnel barrier thicknesses and varied oxidation times in the preparation of this barrier have been studied. These show that oxidation can not only increase the magnetic hyperfine fields but also cause an interesting smoothing and crystallizing of the interface. Another interesting finding is the observation of boron diffusion into the lower part of the FeCoB lower electrode towards the Ta seed layer.

Characterization of [4Fe-4S] cluster vibrations and structure in nitrogenase Fe protein at three oxidation levels via combined NRVS, EXAFS, and DFT analyses

Azotobacter vinelandii nitrogenase Fe protein (Av2) provides a rare opportunity to investigate a [4Fe-4S] cluster at three oxidation levels in the same protein environment. Here, we report the structural and vibrational changes of this cluster upon reduction using a combination of NRVS and EXAFS spectroscopies and DFT calculations. Key to this work is the synergy between these three techniques as each generates highly complementary information and their analytical methodologies are interdependent. Importantly, the spectroscopic samples contained no glassing agents. NRVS and DFT reveal a systematic 10-30 cm(-1) decrease in Fe-S stretching frequencies with each added electron. The "oxidized" [4Fe-4S](2+) state spectrum is consistent with and extends previous resonance Raman spectra. For the "reduced" [4Fe-4S](1+) state in Fe protein, and for any "all-ferrous" [4Fe-4S](0) cluster, these NRVS spectra are the first available vibrational data. NRVS simulations also allow estimation of the vibrational disorder for Fe-S and Fe-Fe distances, constraining the EXAFS analysis and allowing structural disorder to be estimated. For oxidized Av2, EXAFS and DFT indicate nearly equal Fe-Fe distances, while addition of one electron decreases the cluster symmetry. However, addition of the second electron to form the all-ferrous state induces significant structural change. EXAFS data recorded to k = 21 Å(-1) indicates a 1:1 ratio of Fe-Fe interactions at 2.56 Å and 2.75 Å, a result consistent with DFT. Broken symmetry (BS) DFT rationalizes the interplay between redox state and the Fe-S and Fe-Fe distances as predominantly spin-dependent behavior inherent to the [4Fe-4S] cluster and perturbed by the Av2 protein environment.

Observation of the Fe-CN and Fe-CO vibrations in the active site of [NiFe] hydrogenase by nuclear resonance vibrational spectroscopy

Nuclear inelastic scattering of (57)Fe labeled [NiFe] hydrogenase is shown to give information on different states of the enzyme. It was thus possible to detect and assign Fe-CO and Fe-CN bending and stretching vibrations of the active site outside the spectral range of the Fe-S cluster normal modes.

Development of iron-doped silicon nanoparticles as bimodal imaging agents

We demonstrate the synthesis of water-soluble allylamine-terminated Fe-doped Si (Si(xFe)) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single-source iron-containing precursor, Na(4)Si(4) with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH(4)Br to produce hydrogen-terminated Si(xFe) nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy indicates that the average particle diameter is ∼3.0 ± 1.0 nm. The Si(5Fe) nanoparticles show strong photoluminescence quantum yield in water (∼10%) with significant T(2) contrast (r(2)/r(1) value of 4.31). Electron paramagnetic resonance and Mössbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity.

A randomized, placebo controlled study: EMLA in minor breast surgery

AIM

Patients undergoing excision for breast lumps prefer general anesthesia or local anesthesia plus sedation, because of the fear of pain for local anesthesia alone. The aim of this study is to show the efficacy of an eutectic mixture of local anesthetic lignocaine and prilocaine (EMLA®) in these patients.

METHODS

This study has been designed randomized, placebo-controlled. Forty five patients undergoing excision for breast lumps were divided into three groups. The first group was administered local EMLA cream preoperatively (Group I, N.=15), the second group (Group II, N.=15) had no preoperative preparation and the third group was placebo group (Group III, N.=15). All groups underwent the operation under local anesthesia. Pain during the local anesthesia and three hours after the operation were assessed using the visual analog scale. The amount of local anesthetic used during the operation and the anesthetic need of patients after the operation were assessed.

RESULTS

When the three groups were compared, it was found that the intensity of pain in the group with EMLA was considerably lower during and after the operation (P<0.05). The amount of local anesthetic used during the operation was lower (P<0.05) and the need for post-operative analgesic was also less than the usual (P<0.05).

CONCLUSION

Topical EMLA use decreases the pain, provides per-operative and postoperative patient and physician comfort, improved patient's compliance, and simplifies the surgical procedure. This is the first study demonstrating that a topical anesthetic provides a non-invasive analgesia during benign breast mass excision.

Real sample temperature: a critical issue in the experiments of nuclear resonant vibrational spectroscopy on biological samples

There are several practical and intertangled issues which make the experiments of nuclear resonant vibrational spectroscopy (NRVS) on biological samples difficult to perform. The sample temperature is one of the most important issues. In NRVS the real sample temperatures can be very different from the readings on the temperature sensors. In this study the following have been performed: (i) citing and analyzing various existing NRVS data to assess the real sample temperatures during the NRVS measurements and to understand their trends with the samples' loading conditions; (ii) designing several NRVS measurements with (Et(4)N)[FeCl(4)] to verify these trends; and (iii) proposing a new sample-loading procedure to achieve significantly lower real sample temperatures and to balance among the intertangled experimental issues in biological NRVS measurements.

Shape induced symmetry in self-assembled mesocrystals of iron oxide nanocubes

Grazing incidence small-angle scattering and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal mesocrystals. Energy models accounting for the directionality and magnitude of the van der Waals and dipolar interactions as a function of the degree of truncation of the nanocubes illustrated the importance of the directional dipolar forces for the formation of the initial nanocube clusters and the dominance of the van der Waals multibody interactions in the dense packed arrays.