Les sous-produits industriels dans l'alimentation animale

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Mastocytosis in mice expressing human Kit receptor with the activating Asp816Val mutation

Mastocytosis is a rare neoplastic disease characterized by a pathologic accumulation of tissue mast cells (MCs). Mastocytosis is often associated with a somatic point mutation in the Kit protooncogene leading to an Asp/Val substitution at position 816 in the kinase domain of this receptor. The contribution of this mutation to mastocytosis development remains unclear. In addition, the clinical heterogeneity presented by mastocytosis patients carrying the same mutation is unexplained. We report that a disease with striking similarities to human mastocytosis develops spontaneously in transgenic mice expressing the human Asp816Val mutant Kit protooncogene specifically in MCs. This disease is characterized by clinical signs ranging from a localized and indolent MC hyperplasia to an invasive MC tumor. In addition, bone marrow–derived MCs from transgenic animals can be maintained in culture for >24 mo and acquire growth factor independency for proliferation. These results demonstrate a causal link in vivo between the Asp816Val Kit mutation and MC neoplasia and suggest a basis for the clinical heterogeneity of human mastocytosis

Des possibilités d'emploi du sperme de taureau transporté de France pour l'insémination artificielle dans les territoires d'Outre-mer

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Theoretical investigation of the electronic structure of Fe(II) complexes at spin-state transitions

The electronic structure relevant to low spin (LS)high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+(1) (tz=1H-tetrazole), [Fe(bipy)3]2+(2) (bipy=2,2’-bipyridine) and [Fe(terpy)2]2+ (3) (terpy=2,2’:6’,2’’-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT) and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS-HS states (ΔEHL) applying the above methods, and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy)2]2+ were computed both at the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet-triplet and triplet-quintet states are separated along different coordinates, i.e. different vibration modes. Our results confirm that in contrast to the case of complexes with mono- and bidentate ligands, the singlet-quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration coordinate

Temperature- and Light-Induced Spin Crossover Observed by X-ray Spectroscopy on Isolated Fe(II) Complexes on Gold

Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur

Crystallographic elucidation of purely structural, thermal and light-induced spin transitions in an iron(ii) binuclear complex

The intricate phase diagram of the binuclear iron(ii) spin-crossover complex [{Fe(3-bpp)(NCS)2}2(4,4�-bypiridine)] ·2CH3OH where 3-bpp is 2,6-bis(pyrazol-3-yl)pyridine has been investigated by variable temperature single crystal X-ray diffraction including a study into the effect of photo-irradiation. This sample is known to exhibit an incomplete spin transition at low temperature. At room temperature, in phase I, iron ions are all crystallographically equivalent, adopting the high spin state (HS). X-Ray structural investigation has revealed two phase transitions in the range (300-30 K). The first transition (T�161 K) leading to phase II is of a purely structural nature and corresponds to a break in symmetry as a result of a twist of the two rings of 4,4�-bipyridine; the two iron sites of the binuclear unit becoming crystallographically independent but remaining all HS. The second structural transition corresponds to the spin crossover, one of the two Fe(ii) ions of the binuclear complex being in the low spin state (LS) in phase III. The crystal structure shows an ordered HS-LS crystal packing where HS and LS sites are clearly identified and not randomly distributed in the metal ion sites as often observed. Moreover, light irradiation of single crystals in phase III at 30 K, leading to phase III*, induces a light-induced spin-state trapping (LIESST) effect corresponding to the full conversion of all the iron sites to HS. The crystal packing in phase III* is closer to that of phase III than to those observed in the other HS phases, I and II. This reveals an unusual differentiation between the thermal and light-induced HS states. A deeper analysis of the structural properties first demonstrates the key role of the bipyridine bridge in the peculiar preliminary pure structural transition shown by the title compound. Elsewhere, it also shows that the molecular packing is strongly dependent on the nature of the external perturbation contrary to the iron coordination sphere geometry that appears to be only dependent on the spin state. Moreover, in the HS phase II, the distortion of the iron sites that will subsequently undergo a spin crossover demonstrates some differences with the distortion of the iron sites that remain HS. The predominant role of the iron environment distortion in the spin crossover phenomenon is thus clearly evidenced. © 2010 The Royal Society of Chemistry

Structure, magnetism and photomagnetism of mixed-ligand tris(pyrazolyl)methane iron(II) spin crossover compounds

A range of bis-facial tridentate chelate complexes of type [Fe((R-pz)3CH)((3,5-Me2pz)3CH)](BF4)2 has been characterised that contain two different tris-pyrazolylmethane ligands, with variations in R being H (complex 1 crystallised as polymorphs 1a and 1b) and 4-Me (2), as well as R = H with a CH2OH arm off the methane carbon (3). A tris(pyridyl)methane analogue is also described (4). The tris(3,5-dimethylpyrazolyl)methane co-ligand (3,5-Me2pz), and the BF4– counterion, are constant throughout. The spin-crossover properties of these Fe(II) d6 compounds have been probed in detail by variable temperature magnetic, Mössbauer spectral and crystallographic methods. The effects of distortions from octahedral symmetry around the Fe(II) centres, of crystal solvate molecules (1.5 MeCN in 2 and 2 MeCN in 3) and of supramolecular/crystal packing, are discussed. In the case of 1, subtle twisting of pyrazole rings occurs, as a function of temperature, that has a greater effect upon the relative positions of the Fe(II) chelate molecules in polymorph 1b than in polymorph 1a; this is thought to drive the cooperativity differences observed in the magnetism of the polymorphs..