Synthesis, structure and magnetic properties of β-MnO 2 nanorods

We present synthesis, structure and magnetic properties of structurally well-ordered single-crystalline β-MnO₂ nanorods of 50–100 nm diameter and several μm length. Thorough structural characterization shows that the basic β-MnO₂ material is covered by a thin surface layer (∼2.5 nm) of α-Mn₂O₃ phase with a reduced Mn valence that adds its own magnetic signal to the total magnetization of the β-MnO₂ nanorods. The relatively complicated temperature-dependent magnetism of the nanorods can be explained in terms of a superposition of bulk magnetic properties of spatially segregated β-MnO₂ and α-Mn₂O₃ constituent phases and the soft ferromagnetism of the thin interface layer between these two phases.     

Thickness dependent magnetic properties of BiFeO3 thin films prepared by pulsed laser deposition

BiFe_1 ? xMn_xO₃ thin films having thickness 65 and 130 nm was fabricated on LAO substrates using pulsed laser deposition technique and its structural and magnetic properties were examined. Atomic force microscopy images confirmed that, as the thickness of the films increases the particles size also increases resulting in the decrease of magnetization. The possible cause for the lowering of magnetization with film thickness was discussed. Increase of spontaneous magnetization in BiFeO₃ at room temperature was observed with Mn substitution for Fe. The blocking temperature was found to decrease with increasing film thickness.     

Ferromagnetic signal in nanosized Ag particles

A new technique using an inductively coupled plasma reactor equipped with a liquid-nitrogen cooling system was developed to prepare Ag nanoparticles. The magnetic signal from these Ag particles with diameters of 4 nm showed, surprisingly, a signal with combined ferromagnetic and diamagnetic components, in contrast to the signal with only one diamagnetic component from bulk Ag. The same technique was used to prepare the Ag/Cu nanoparticles, which are Ag nanoparticles coated with a Cu layer. Compared to the Ag nanoparticles, these showed a greatly enhanced superparamagnetic signal in addition to the same value of the ferromagnetism. The comparison between the Ag and the Ag/Cu nanoparticles indicated that the ferromagnetic components are a common feature of Ag nanoparticles while the greatly enhanced paramagnetic component of Ag/Cu, which dominates over the background diamagnetic component from the Ag core, is from the outer Cu shell.     

Interface effect of magnetic properties in Ni nanoparticles with a hcp core and fcc shell structure

We have fabricated hexagonal close-packed (hcp) Ni nanoparticles covered by a face-centered cubic (fcc) Ni surface layer by polyol method. The magnetic properties have been investigated as a function of temperature and applied magnetic field. The magnetic behavior reveals that the system should be divided magnetically into three distinct phases with different origins. The fcc Ni phase on the shell contributes to the superparamagnetism through a wide temperature range up to 360 K. The hcp Ni phase at the core is associated with antiferromagnetic nature below 12 K. These observations are in good agreement with the X-ray absorption spectroscopy and magnetic circular dichroism measurements. In our particular case, the unique hcp core and fcc shell structure gives rise to an additional anomaly at 20 K in the zero-field-cooled magnetization curve. Its position is barely affected by the magnetic field but its structure disappears above 30 kOe, showing a metamagnetic transition in the magnetization versus magnetic field curve. This new phase originates from the magnetic exchange at the interface between the hcp and fcc Ni sublattices.     

Facile synthesis of fully ordered L10-FePt nanoparticles with controlled Pt-shell thicknesses for electrocatalysis

We report a simple one-step approach for the synthesis of ～4 nm uniform and fully L10-ordered face-centered tetragonal (fct) FePt nanopartides (NPs) embedded in ～60 nm MCM-41 (fct-FePt NPs@MCM-41).We controlled the Pt-shell thickness of the fct-FePt NPs by treating the fct-FePt NPs@MCM-41 with acetic acid (HOAc) or hydrochloric acid (HC1) under sonication,thereby etching the surface Fe atoms of the NPs.The fct-FePt NPs deposited onto the carbon support (fct-FePt NP/C) were prepared by mixing the fct-FePt NPs@MCM-41 with carbon and subsequently removing the MCM-41 using NaOH.We also developed a facile method to synthesize acid-treated fct-FePt NP/C by using a HF solution for simultaneous surface-Fe etching and MCM-41 removal.We studied the effects of both surface-Fe etching and Pt-shell thickness on the electrocatalytic properties of fct-FePt NPs for the methanol oxidation reaction (MOR).Compared with the non-treated fct-FePt NP/C catalyst,the HOAc-treated and HCl-treated catalysts exhibit up to 34％ larger electrochemically active surface areas (ECASAs);in addition,the HCl-treated fct-FePt NP (with ～1.0 nm Pt shell)/C catalyst exhibits the highest specific activity.The HF-treated fct-FePt NP/C exhibits an ECASA almost 2 times larger than those of the other acid-treated fct-FePt NP/C catalysts and shows the highest mass activity (1,435 mA.mg~,2.3 times higher than that of the commercial Pt/C catalyst) and stability among the catalysts tested.Our findings demonstrate that the surface-Fe etching for the generation of the Pt shell on fct-FePt NPs and the Pt-shell thickness can be factors for optimizing the electrocatalysis of the MOR.     

Superparamagnetism of Cu2Se nanoparticles

Cu2Se nanoparticles were synthesized using the standard Schlenk line and glove box techniques, with the hot-injection method. The X-ray diffraction (XRD) analysis showed that the initial nanoparticles were formed in a stoichiometric Cu2Se phase with a cubic structure. When the nanoparticles are exposed to air, the diffraction peaks shift to higher angles. This suggests that the nanoparticles are changed to a nonstoichiometric Cu2-deltaSe phase with copper vacancies. The mean size of the nanoparticles was about 7 nm. The magnetic results show that the initial nanoparticles were diamagnetic, and after 1-week air exposure, they became paramagnetic. This dramatic change from diamagnetic to paramagnetic can be explained by the oxidation of Cu+ into Cu2+ at the nanoparticle surface. In addition, the superparamagnetic properties were observed to have a blocking temperature of 150 K. The coercive field decreased as the temperature approached the blocking temperature, and eventually vanished above the blocking temperature.     

Molecular characterization of bovine placental and ovarian 20α-hydroxysteroid dehydrogenase

The enzyme 20α-hydroxysteroid dehydrogenase (20α-HSD) catalyzes the conversion of progesterone to its inactive form, 20α-hydroxyprogesterone. This enzyme plays a critical role in the regulation of luteal function in female mammals. In this study, we conducted the characterization and functional analyses of bovine 20α-HSD from placental and ovarian tissues. The nucleotide sequence of bovine 20α-HSD showed significant homology to that of goats (96%), humans (84%), rabbits (83%), and mice (81%). The mRNA levels increased gradually throughout the estrous cycle, the highest being in the corpus luteum (CL) 1 stage. Northern blot analysis revealed a 1.2 kb mRNA in the bovine placental and ovarian tissues. An antibody specific to bovine 20α-HSD was generated in a rabbit immunized with the purified, recombinant protein. Recombinant 20α-HSD protein produced in mammalian cells had a molecular weight of ～37 kDa. Bacterially expressed bovine 20α-HSD protein showed enzymatic activity. The expression pattern of the 20α-HSD protein in the pre-parturition placenta and the CL1 stage of the estrous cycle was similar to the level of 20α-HSD mRNA expression. Immunohistochemical analysis also revealed that bovine 20α-HSD protein was intensively localized in the large luteal cells during the late estrous cycle.     

Magnetic properties of single-crystalline CoSi nanowires

We have observed unusual ferromagnetic properties in single-crystalline CoSi nanowire ensemble, in marked contrast to the diamagnetic CoSi in bulk. High-density freestanding CoSi nanowires with B20 crystal structure are synthesized by a vapor-transport-based method. The reaction of cobalt chloride precursor with a Si substrate produces high-aspect-ratio CoSi nanowires. The high-resolution transmission electron microscopy and electron diffraction studies reveal superlattice structure in CoSi nanowires with twice the lattice parameter of simple cubic CoSi lattice. The zero-field-cooled and field-cooled (ZFC-FC) measurements from the nanowire ensemble show freezing of the disordered surface spins at low temperatures. The magnetoresistance (MR) measurements of single nanowire devices show a negative MR whose magnitude gets larger at lower temperatures.     

Secretion of Human Protein C in Mouse Milk

To determine the production of recombinant human protein C (rec-hPC) in milk, we created two homozygous mice lines for the goat β-casein/hPC transgene. Females and males of both lines (#10 and #11) displayed normal growth, fertility, and lactated normally. The copy number of the transgene was about fivefold higher in #10 line as compared to #11 line. mRNA expression of the transgene was only detected in the mammary glands of both lines. Furthermore, mRNA expression was fourfold higher on day 7 than on day 1 during lactation. Northern blot analysis of mRNA expression in the #10 line of transgenic (Tg) mice indicated a strong expression of the transgene in the mammary glands after seven days of lactation. Comparison of rec-hPC protein level with that of mRNA in the mammary glands showed a very similar pattern. A 52-kDa band corresponding to the hPC protein was strongly detected in mammary glands of the #10 line during lactation. We also detected two bands of heavy chain and one weak band of light chain in the milk of the #10 and #11 lines. One single band at 52 kDa was detected from CHO cells transfected with hPC cDNA. hPC was mainly localized in the alveolar epithelial cell of the mammary glands. The protein is strongly expressed in the cytoplasm of the cultured mammary gland tissue. hPC protein produced in milk ranged from 2 to 28 ng/mL. These experiments indicated that rec-hPC can be produced at high levels in mice mammary glands.     

Inhibition of 2,2′-azobis(2,4-dimethylvaleronitrile)-induced lipid peroxidation by sesaminols

We found that sesaminols, a mixture of sesaminol and its stereoisomers, are potent inhibitors of the oxidation of low-density lipoprotein induced by 2,2′-azobis(2,4-dimethylvaleronitrile). Although sesaminols strongly inhibit lipid peroxidation related to their ability to scavenge free radicals, their antioxidant effects have not been investigated. To confirm the involvement of the phenolic moiety in the sesaminol structure in antioxidant activity, sesaminols were reacted with 2,2′-azobis(2,4-dimethylvaleronitrile). The reaction products were isolated by high-performance liquid chromatography and found to have a 1-cyano-1,3-dimethyl-butyl-peroxyl group in their structures. These chemical structures suggest that the sesaminols reacted with the alkylperoxyl radicals to form four major reaction products that are stereoisomers of each other, although the stereochemistry of each isomer has not yet been confirmed. Further instrumental analyses of the reaction products may increase our understanding of the antioxidant activity of sesaminols.