Ferromagnetic resonance for the quantification of superparamagnetic iron oxide nanoparticles in biological materials

The aim of the present work is the presentation of a quantification methodology for the control of the amount of superparamagnetic iron oxide nanoparticles (SPIONs) administered in biological materials by means of the ferromagnetic resonance technique (FMR) applied to studies both in vivo and in vitro. The in vivo study consisted in the analysis of the elimination and biodistribution kinetics of SPIONs after intravenous administration in Wistar rats. The results were corroborated by X-ray fluorescence. For the in vitro study, a quantitative analysis of the concentration of SPIONs bound to the specific AC133 monoclonal antibodies was carried out in order to detect the expression of the antigenic epitopes (CD133) in stem cells from human umbilical cord blood. In both studies FMR has proven to be an efficient technique for the SPIONs quantification per volume unit (in vivo) or per labeled cell (in vitro).

The metal content of bulge field stars from FLAMES-GIRAFFE spectra - I. Stellar parameters and iron abundances

Aims. We determine the iron distribution function (IDF) for bulge field stars, in three different fields along the Galactic minor axis and at latitudes b = -4 degrees, b = -6 degrees, and b = -12 degrees. A fourth field including NGC 6553 is also included in the discussion. Methods. About 800 bulge field K giants were observed with the GIRAFFE spectrograph of FLAMES@VLT at spectral resolution R similar to 20 000. Several of them were observed again with UVES at R similar to 45 000 to insure the accuracy of the measurements. The LTE abundance analysis yielded stellar parameters and iron abundances that allowed us to construct an IDF for the bulge that, for the first time, is based on high-resolution spectroscopy for each individual star. Results. The IDF derived here is centered on solar metallicity, and extends from [Fe/H] similar to -1.5 to [Fe/H] similar to + 0.5. The distribution is asymmetric, with a sharper cutoff on the high-metallicity side, and it is narrower than previously measured. A variation in the mean metallicity along the bulge minor axis is clearly between b = -4 degrees and b = -6 degrees ([Fe/H] decreasing similar to by 0.6 dex per kpc). The field at b = -12 degrees. is consistent with the presence of a gradient, but its quantification is complicated by the higher disk/bulge fraction in this field. Conclusions. Our findings support a scenario in which both infall and outflow were important during the bulge formation, and then suggest the presence of a radial gradient, which poses some challenges to the scenario in which the bulge would result solely from the vertical heating of the bar.

Nonmonotonic thickness dependence of spin wave energy in ultrathin Fe films: Experiment and theory

High wave-vector spin waves in ultrathin Fe/W(110) films up to 20 monolayers (MLs) thick have been studied using spin-polarized electron energy-loss spectroscopy. An unusual nonmonotonous dependence of the spin wave energies on the film thickness is observed, featuring a pronounced maximum at 2 ML coverage. First-principles theoretical study reveals the origin of this behavior to be in the localization of the spin waves at the surface of the film, as well as in the properties of the interlayer exchange coupling influenced by the hybridization of the electron states of the film and substrate and by the strain.

Tris(N-benzoyl-N ',N ''-diphenylthioureato-kappa O-2,S)cobalt(III)

In the title compound, [Co(C20H15N2OS)(3)], the Co-III atom is coordinated by the S and O atoms of three N-benzoyl-N',N'-diphenylthiourea ligands in a slightly distorted octahedral geometry. The O and S atoms are in cis positions, while the positions between the O and S atoms are trans.

Nanostructured Films Based on Carbon Nanotubes and Cobalt for the Electrocatalytic Reduction of H(2)O(2)

This paper presents the fabrication of a nanothick Co-modified film electrochemically synthesized on layer-by-layer (LbL) structures made with dendrimer polyamidoamine/carbon nanotubes (PAMAM/CNT), and its electrocatalytic properties toward H(2)O(2) reduction. Scanning electron microscopy indicated the formation of a homogeneous, 14 nm thick Co film. The porous nature of the PAMAM/CNT LbL film allowed the electrolyte access to the bottom of the electrode, generating a homogenous Co electrodeposit. In addition, the nanostructure based on Co-modified PAMAM/CNT LbL exhibited high electrocatalytic activity for H(2)O(2) reduction when compared to the Co-free PAMAM/CNT LbL film, which demonstrates the suitability of the system studied for biosensing. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3602200] All rights reserved.

Partial magnetic ordering and crystal structure of the ludwigites Co(2)FeO(2)BO(3) and Ni(2)FeO(2)BO(3)

We present an extensive study of the structural, magnetic, and thermodynamic properties of the two heterometallic oxyborates: Co(2)FeO(2)BO(3) and Ni(2)FeO(2)BO(3). This has been carried out through x-ray diffraction at room temperature (RT) and 150 K, dc and ac magnetic susceptibilities, and specific-heat experiments in single crystals above 2 K. The magnetic properties of these iron ludwigites are discussed in comparison with those of the other two known homometallic ludwigites: Fe(3)O(2)BO(3) and Co(3)O(2)BO(3). In both ludwigites now studied we have found that the magnetic ordering of the Fe(3+) ions occurs at temperatures very near to which they order in Fe(3)O(2)BO(3). A freezing of the divalent ions (Co and Ni) is observed at lower temperatures. Our x-ray diffraction study of both ludwigites at RT and 150 K showed very small ionic disorder in apparent contrast with the freezing of the divalent ion spins. The structural transition that occurs in homometallic Fe(3)O(2)BO(3) has not been found in the present mixed ludwigites in the temperature range investigated.

DNA damage by sulfite autoxidation catalyzed by cobalt complexes

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 mu M) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O(2), DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO(3)(center dot)-S-, HO(center dot) and H(center dot) radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO(center dot) adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.

Contrasting photoelectrochemical behaviour of two isomeric supramolecular dyes based on meso-tetra(pyridyl)porphyrin incorporating four (mu(3)-oxo)- triruthenium(III) clusters

A saddle shaped tetracluster porphyrin species containing four [Ru(3)O(OAc)(6)(py)(2)](+) clusters coordinated to the N-pyridyl atoms of 5,10,15,20-tetra(3-pyridyl)porphyrin, H(2)(3-TCPyP), has been investigated in comparison with the planar tetra(4-pyridyl) porphyrin analogue H(2)(4-TCPyP). The steric effects from the bulky peripheral complexes play a critical role in the H(2)(3-TCPyP) species, determining a non-planar configuration around the porphyrin centre and precluding any significant pi-electronic coupling, in contrast with the less hindered H(2)(4-TCPyP) species. Both systems exhibit a photoelectrochemical response in the presence of nanocrystalline TiO(2) films, involving the porphyrin excitation around 450 nm. However, only in the H(2)(4-TCPyP) case do the cluster moieties also contribute to the photoinduced electron injection process at 670 nm, reflecting the relevance of the electronic coupling between the porphyrin centre and the peripheral complexes.

Response of Wolfiporia cocos to iron availability: alterations in growth, expression of cellular proteins, Fe3+-reducing activity and Fe3+-chelators production

Aims: The main objective of this study was to evaluate the behaviour of the brown-rot fungus Wolfiporia cocos under differential iron availability. Methods and Results: W. cocos was grown under three differential iron conditions. Growth, catecholate and hydroxamate production, and mycelial and extracellular Fe3+-reducing activities were determined. Iron starvation slowed fungal growth and accelerated pH decline. Some mycelial proteins of low molecular weight were repressed under iron restriction, whereas others of high molecular weight showed positive iron regulation. Mycelial ferrireductase activity decreased as culture aged, while Fe3+-reducing activity of low molecular reductants constantly increased. Hydroxamates production suffered only limited iron repression, whereas catecholates production showed to be more iron repressible. Conclusions: W. cocos seems to possess more than one type of iron acquisition mechanism; one involving secretion of organic acids and ferrireductases and/or extracellular reductants, and another relying on secretion of catecholates and hydroxamates chelators. Significance and Impact of the Study: This paper is the first to report the kinetic study of brown-rot fungus grown under differential iron availability, and the information provided here contributes to address more traditional problems in protecting wood from brown decay, and also makes a contribution in the general area of the physiology of brown-rot fungi.

Niobium hydrogenation process Effect of temperature and cooling rate from the hydrogenation temperature

High-purity niobium powder can be produced via the hydrogenation and dehydrogenation processes The present work aimed at the effect of temperature and cooling rate conditions on the niobium hydrogenation process using hydrogen gas The hydrogen contents of the materials were evaluated by weight change and chemical analysis X ray diffraction (XRD) was performed to identify and determine the lattice parameters of the formed hydride phases No hydrogenation took place under isothermal conditions only during cooling of the materials Significant hydrogenation occurred in the 500 C and 700 C experiments leading to the formation of a beta NbH(x) single phase material (C) 2010 Elsevier Ltd All rights reserved

Impact of transition oxides on growth stresses and texture of alumina scales formed during oxidation of iron aluminides

The internal stresses and crystallographic texture in alpha-Al(2)O(3) scales grown on iron aluminides at 1100 degrees C were determined in situ using synchrotron X-ray diffraction. In the first hour of oxidation, alpha-Al(2)O(3) was formed by direct nucleation and by conversion from transition oxides (either theta-Al(2)O(3) or a mixed Fe-Al oxide). A sharp texture develops connected with the direct nucleation of alpha-Al(2)O(3), in contrast to the weaker texture observed in alpha-Al(2)O(3) originated by previous transformations, which also yielded tensile stresses in early oxidation stages. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tempering temperature effects on abrasive wear of mottled cast iron

The effects of different tempering temperatures (300-600 degrees C) on abrasive wear resistance of mottled cast iron were studied. Abrasive wear tests were carried out using the rubber-wheel test on quartz sand and the pin test on Al(2)O(3) abrasive cloths. The retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of the specimens was examined by scanning electron microscopy for identifying the wear micromechanism. Bulk hardness and matrix hardness before and after the tests were measured. The results showed that in the two-body (pin-on-disc test) system, the main wear mechanism was microcutting and high matrix hardening was presented. The wear rates presented higher correlation with the retained austenite than with the bulk and matrix hardness. In the three-body system (sand-rubber wheel), the wear surfaces presented indentations due to abrasive rolling. The wear rates had better correlation with both the bulk and matrix hardness (before and after the wear test) than with the retained austenite content. There are two groups of results, high and low wear rates corresponding to each tribosystem, two-body abrasive wear and three-body abrasive wear, respectively. (C) 2009 Elsevier B.V. All rights reserved.

Particle size effect on abrasion resistance of mottled cast iron with different retained austenite contents

Effects of particle abrasive sizes on wear resistance of mottled cast iron with different retained austenite contents were studied. Abrasive wear tests using a pin test on alumina paper were carried out, using abrasive sizes between 16 mu m and 192 mu m. Retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of samples and the alumina paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results show that at lower abrasive sizes the mass loss was similar for the iron with different austenite contents. However, at higher abrasive sizes the samples with higher retained austenite content presented higher abrasion resistance. For lower abrasive sizes tested, samples with higher and lower retained austenite content both presented microcutting. On the other hand, the main wear micromechanism for the samples with higher retained austenite content and higher abrasive sizes was microploughing. The samples with lower retained austenite content presented microcutting and wedge formation at higher abrasive sizes. Higher abrasive size induced more microcutting in samples with lower retained austenite. The iron with lower retained austenite content presented wider grooves for the different abrasive sizes measured. SEM on the abrasive paper used on samples with higher retained austenite showed continuous and discontinuous microchips and the samples with lower retained austenite showed discontinuous microchips at 66 and 141 mu m. This research demonstrates the relation between abrasive size, wear resistance, groove width and wear micromechanism for mottled cast iron with different retained austenite contents. (C) 2009 Elsevier B.V. All rights reserved.

Abrasive wear study of white cast iron with different solidification rates

The abrasive wear resistance of white cast iron was studied. The iron was solidified using two solidification rates of 1.5 and 15 degrees C/s. Mass loss was evaluated with tests of the type pin on abrasive disc using alumina of different sizes. Two matrices were tested: one predominantly austenitic and the other predominantly martensitic, containing M(3)C carbides. Samples with cooling rate of 15 degrees C/s showed higher hardness and more refined microstructure compared with those solidified at 1.5 degrees C/s. During the test, the movement of successive abrasives gave rise to the strain hardening of the austenite phase, leading to the attainment of similar levels of surface hardness, which explains why the wear rate showed no difference compared to the austenite samples with different solidification rates. For the austenitic matrix the wear rate seems to depend on the hardness of the worn surface and not on the hardness of the material without deformation. The austenitic samples showed cracking and fracture of M(3)C carbides. For the predominantly martensitic matrix, the wear rate was higher at the solidification rate of 1.5 degrees C/s, for grain size of 66 and 93 mu m. Higher abrasive sizes were found to produce greater penetration and strain hardening of austenitic matrices. However, martensitic iron produces more microcutting, increasing the wear rate of the material. The analysis of the worn surface by scanning electron microscopy indicated abrasive wear mechanisms such as: microcutting, microfatigue and microploughing. Yet, for the iron of austenitic matrix, the microploughing mechanism was more severe. (C) 2009 Elsevier B.V. All rights reserved.

Load effect in abrasive wear mechanism of cast iron with graphite and cementite

In this study four irons were casted with different chromium and vanadium contents: 2.66% Cr, 5.01% Cr, 2.51% V and 5.19% V. Their microstructure is composed of: ledeburite, graphite and M(3)C carbides (cementite). Pin-abrasion tests were carried out using fixed alumina abrasive grains at different loads: 1, 2, 4.6 and 10 N. The wear surface and the abrasive paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results reveal that the mass loss increased with the load increase, and the effect of the percentage of chromium on mass loss is inverted when the load is increased from 4.6 to 10 N; for 4.6 N the mass loss decreased when the chromium percentage was increased from 2.66% to 5.01%. Nevertheless, for 10 N the mass loss increased when the chromium percentage was increased. The worn surfaces of the materials tested at 1 N show microcutting caused by the abrasive tip that produces continuous microchips. The worn surfaces and the abrasive paper tested at 10 N show continuous microchips and brittle debris. The results show that high pressures produce a brittle wear mechanism and low pressures produce a more ductile wear micromechanism, for this, the applied pressure defines the dependence between the wear resistance and wear micromechanism. (C) 2009 Elsevier B.V. All rights reserved.