Preparation et etude d'un oxyphosphate Fe4(PO4)2O

This compound is obtained in several ways, at 900°C, from the components of the FePO system when the oxygen pressure is made suitable, or from Fe₃(PO₄)₂ + Fe + Fe₂O₃ in a sealed tube under vacuum. It crystallizes under these latter conditions with a trace of FeCl₂. The cell is monoclinic; a = 6.564(1), b = 11.271(2), c = 9.383(2) Å, β = 103.95 (2)°, with Z = 4, group $\text{P2}{}_1\text{c}$. The structure is determined thanks to the use of a direct method and Fourier synthesis and is refined to R = 0.033. The PO₄ tetrahedra are isolated; the iron fills four crystallographic sites: three are more or less distorted octahedra, the fourth is a trigonal bipyramid. The oxyphosphate character is ascertained by the presence of some oxygen atoms connected to iron only, with, moreover, a low site potential. This compound is paramagnetic above 90°K. Its Mössbauer spectrum exhibits four doublets in good agreement with the structure; in order to identify which one corresponds to the hexahedral site, the phase Fe₃Zn(PO₄)₂O has been prepared, but its Mössbauer spectrum, in spite of the zinc affinity for the V coordination, shows that two sites are modified, which does not allow conclusions to be made.     

Reactions of collman complex with tin(IV) and germanium(IV) porphyris,formation of [tin(II) and germanium(II) porphyrins] tetracarbonyliron and crystal structure of [2,3,7,8,12,13,17,18-octaethylporphinato tin(II)] tetracarbonyliron

The action of Na₂Fe(CO)₄ with tin(IV) and germanium(IV) porphyrins affords metal(II) porphyrin complexes [(por)M(II)Fe(CO)₄] (por = porphyrinate, M - Sn(II) or Ge(II)). The molecular structure of [(oep)Sn(II)Fe(CO)₄] was solved by X-ray diffraction techniques. The molecular structure of [(oep)Sn(II)Fe(CO)₄] was solved by X-ray diffraction techniques : the Sn coordination is square pyramidal with the iron in axial position (Sn-Fe = 2.492(1)Å) whereas the Fe coordination is trigonal bipyramidal. Mössbauer parameters provide convincing evidence for the formal zero oxidation state of the iron atom.     

Surface hydrophobicity modulates the operation of actomyosin-based dynamic nanodevices

We studied the impact of surface hydrophobicity on the motility of actin filaments moving on heavy-meromyosin (HMM)-coated surfaces. Apart from nitrocellulose (NC), which is the current standard for motility assays, all materials tested are good candidates for microfabrication: hydrophilic and hydrophobic glass, poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBuMA), and a copolymer of O-acryloyl acetophenone oxime with a 4-acryloyloxybenzophenone (AAPO). The most hydrophilic (hydrophilic glass, contact angle 35 degrees) and the most hydrophobic (PtBuMA, contact angle 78 degrees) surfaces do not maintain the motility of actin filaments, presumably because of the low density of adsorbed HMM protein or its high levels of denaturation, respectively. The velocity of actin filaments presents higher values in the middle of this "surface hydrophobicity motility window" (NC, PMMA), and a bimodal distribution, which is more apparent at the edges of this motility window (hydrophobic glass and AAPO). A molecular surface analysis of HMM and its S1 units suggests that the two very different, temporally separated conformations of the HMM heads could exacerbate the surface-modulated protein behavior, which is common to all microdevices using surface-immobilized proteins. An explanation for the above behavior proposes that the motility of actin filaments on HMM-functionalized surfaces is the result of the action of three populations of motors, each in a different surface-protein conformation, that is, HMM with both heads working (high velocities), working with one head (low velocities), and fully denatured HMM (no motility). It is also proposed that the molecularly dynamic nature of polymer surfaces amplifies the impact of surface hydrophobicity on protein behavior. The study demonstrates that PMMA is a good candidate for the fabrication of future actomyosin-driven dynamic nanodevices because it induces the smoothest motility of individual nano-objects with velocities comparable with those obtained on NC.     

Effects of electric field and hydrostatic pressure on donor binding energies in a spherical quantum dot

The binding energies of a hydrogenic donor in a GaAs spherical quantum dot in the Ga_1−xAl_xAs matrix are presented assuming parabolic confinement. Effects of hydrostatic pressure and electric field are discussed on the results obtained using a variational method. Effects of the spatial variation of the dielectric screening and the effective mass mismatch are also investigated. Our results show that (i) the ionization energy decreases with dot size, with the screening function giving uniformly larger values for dots which are less than about 25 nm, (ii) the hydrostatic pressure increases the donor ionization energy such that the variation is larger for a smaller dot, and (iii) the ionization energy decreases in an electric field. All the calculations have been carried out with finite barriers and good agreement is obtained with the results available in the literature in limiting cases.     

Bestimmung des Schmelzpunktes von die W?rme schlecht leitenden K?rpern

Ohne Zusammenfassung     

Mise en évidence de CaF2e4O6 et détermination des structures cristallines des ferrites de calcium CaFe2+nO4+n(n = 1, 2, 3): nouvel exemple d'intercroissance

The synthesis of a new calcium ferrite CaFe₄O₆ has been carried out at 1125°C under a controlled atmosphere of H₂H₂O. The existence of this compound modifies a part of the diagram FeCaO. The crystal structures of the ferrites CaFe_2+nO_4+n (n = 1, 2, 3) have been resolved on a series of single crystals; these ferrites crystallize in the orthorhombic system, space group Cmcm, with the average parameters a = 3.04 Å, b = 10 Å, c = 10 + 2.65 nÅ. The three structures derive from each other through an intergrowth process, in the direction of the c axis, with CaFe₂O₄ blocks between the FeO blocks. The coordination of the iron atoms is slightly changed by the nature of the neighboring blocks during stacking.     

Study of the (3He,d) reactions on 58, 60Ni and 56Fe near the Coulomb barrier

Using spectroscopic information gained by earlier measurements of the proton bound states populated by stripping reactions, (³He, d) reactions on ^{58, 60}Ni and ⁵⁶Fe targets are studied at energies near the Coulomb barrier and evaluation is made of the vertex function . This value is then used to determine spectroscopic factors for low-lying states in ⁵⁷Co.     

Fe3PO7, Un cas de coordinence 5 du fer trivalent,etude structurale et magnetique

The structure of Fe₃PO₇ is established from a single crystal. The cell is trigonal R3m, with, in hexagonal reference a = 8,006(5), c = 6,863(5)Å, Z = 3. The structure is determined with the direct method and refined to R = 0,027. The PO₄ tetraedra are isolated; the iron atoms are in a five coordinated site constituted of trigonal bipyramids sharing 2 edges and forming groups of 3 hexaedra; through these shared edges the iron atoms are at 3.13 Å a distance rather short which brings a repulsion causing the off centering of the cation along the pseudo axis of the bipyramid. The magnetic measurements and the Mössbauer spectroscopy show antiferromagnetism behaviour and, in the paramagnetic state, outstanding parameters (μ = 6.45 μ_B, θ_p = ?1707 K) recalling however Ca₂Fe₂O₅ or LaFeO₃. The Mössbauer spectroscopy gives, at room temperature, parameters classical for trivalent iron; through cooling, it points to a magnetic transition temperature of 160 ± 3 K below which the spectrum displays at least 2 hyperfine patterns. The magnetic interactions are discussed.     

P1 approximation,MDA and IDA for the simulation of radiative transfer in a 3D geometry for an absorbing scattering medium

A numerical study has been conducted using the differential approximation and two modified versions of this method, known as MDA and IDA. The methods have been applied on a 3D geometry containing a participating, absorbing, emitting and anisotropically scattering medium. Comparisons have been carried out with some cases of the literature. It has been observed that the IDA can significantly improve the solution, where the classical P1 approximation is not able to reproduce accurately the actual flux or flux divergence in some of studied configurations. The MDA does not really improve the solution in the purely absorbing cases and when radiation is mainly coming from the medium. In other situations (scattering media, relevant influence of the boundaries), the MDA is more accurate than the P1 but the IDA still performs better, with uncertainties around a few percents for the literature cases studied in the present work.     

Effects of maternal exposure to extract of Trichilia catigua on antibody production in the offspring of Wistar rats

It was evaluated the effects of maternal treatment with the Trichilia catigua (ExTc) crude extract on the antibodies’ production by their offspring. Female rats received ExTc or saline from the first day of pregnancy until the twenty-first day after the birth of the pups, when the pups were weaned. All pups were inoculated with two doses of 50 μg of IgY diluted in aluminium hydroxide/PBS on days 26 and 40 of life. Antibody levels were analysed by ELISA. Our results show an increase in levels of IgG1 and IgG2a anti-IgY in female offspring of mothers treated with ExTc compared to female offspring of untreated mothers. Furthermore, ExTc treatment suppressed the production of IgG2a anti-IgY antibodies in males. The data show that maternal exposure to ExTc can modulate the production of antibodies in the offspring.