151 research outputs found
Chains of Cobalt Doped Magnetosomes Extracted from AMB-1 Magnetotactic Bacteria for Application in AMF hyperthermia
International audienceWe report themagnetic properties and heating efficiency of cobalt doped chains of magnetosomes extracted frommagnetotactic bacteria for applications in alternativemagnetic field cancer therapy. The changes of the magnetic properties of the chains of magnetosomes observed in the presence of cobalt are characterized by an enhancement of the magnetocrystalline anisotropy from Keff ⌠12 KJ/m3 in the absence of cobalt up to Keff ⌠104 KJ/m3 in the presence of cobalt. We show that these changes are only observed for the magnetosomes organized in chains. Furthermore, the SAR of the extracted chains of magnetosomes mixed in solution and exposed to an oscillating magnetic field of field amplitude 80 mT and frequency 183 kHz is shown to increase fromâŒ400W/gFe for the undoped chains ofmagnetosomes up to âŒ500 W/gFe for the cobalt doped chains of magnetosomes
Rearrangement of the structure during nucleation of a cordierite glass doped with TiO2
Ordering of disordered materials occurs during the activated process of nucleation that requires the formation of critical clusters that have to surmount a thermodynamic barrier. The characterization of these clusters is experimentally challenging but mandatory to improve nucleation theory. In this paper, the nucleation of a magnesium aluminosilicate glass containing the nucleating oxide TiO2 is investigated using neutron scattering with Ti isotopic substitution and 27Al NMR. We identified the structural changes induced by the formation of crystals around Ti atoms and evidenced important structural reorganization of the glassy matrix
LES NANOPARTICULES: QUELS RISQUES EN SEINE ?
32 pInternational audienceL'obtention de nanoparticules (NPs) manufacturĂ©es et les propriĂ©tĂ©s physico-chimiques spĂ©cifiques qu'elles prĂ©sentent autorisent aujourd'hui des applications de plus en plus nombreuses et innovantes. La quantitĂ© de nanoparticules manufacturĂ©es mises sur le marchĂ© est en constante augmentation et elles sont aujourd'hui prĂ©sentes dans de nombreux produits de consommation courante. Cela alimente un dĂ©bat croissant sur les coĂ»ts environnementaux et sociĂ©taux qui pourraient dĂ©passer les bĂ©nĂ©fices escomptĂ©s par l'utilisation des nanotechnologies en gĂ©nĂ©ral et des nanomatĂ©riaux ou nanoparticules (i.e. taille < 100 nm) en particulier. Elles sont devenues un enjeu majeur de santĂ© publique du point de vue de la toxicitĂ© potentielle qu'elles pourraient engendrer dans les Ă©cosystĂšmes. Les nanoparticules peuvent en effet prĂ©senter un risque Ă©cotoxicologique (dispersion et dĂ©gradation dans l'environnement) et un risque en termes de santĂ© humaine (exposition au poste de travail par exemple). Il est donc nĂ©cessaire d'Ă©valuer la persistance, le devenir et l'impact de ces nouveaux polluants sur les Ă©cosystĂšmes et sur la qualitĂ© des ressources naturelles (eaux, cultures, etc...). Dans ce contexte, l'objectif de cette Ă©tude Ă©tait de mieux cerner l'Ă©tat physique et chimique des NPs dans des concentrations reprĂ©sentatives des niveaux de toxicitĂ© observĂ©s et dans des conditions proches de celles des milieux naturels. Elle s'est focalisĂ©e sur l'eau de Seine, reprĂ©sentative des eaux naturelles de surface qui sont un des vecteurs principaux de la dispersion de ces NPs manufacturĂ©es. Les NPs Ă©tudiĂ©es ici sont produites en grande quantitĂ© et largement utilisĂ©es dans diffĂ©rents domaines industriels : il s'agit de NPs d'oxydes de zinc (ZnO) et de dioxyde de titane (TiO2). L'analyse des NPs de ZnO par XPS a mis en Ă©vidence l'existence d'un cĆur de ZnO et d'un coquille de Zn(OH)2 en surface. ParallĂšlement, des NPs enrobĂ©es ont Ă©tĂ© Ă©tudiĂ©es et caractĂ©risĂ©es, afin de mettre en Ă©vidence le rĂŽle de l'enrobage organique sur la solubilitĂ© des NPs. Les expĂ©riences de mesures de solubilitĂ© des nanoparticules manufacturĂ©es en milieu naturel ont Ă©tĂ© rĂ©alisĂ©es par utilisation combinĂ©e des techniques de DMT et d'UF, associĂ©e Ă des calculs thermodynamiques. Il s'avĂšre que la forme nanoparticulaire du TiO2 n'est pas davantage soluble que ses homologues microparticulaire ou macroparticulaire. A l'inverse, une fraction non nĂ©gligeable des nanoparticules d'oxydes de zinc est rapidement dissoute dans l'eau de Seine. Puis les NPs sont "piĂ©gĂ©es" dans des phases secondaires carbonatĂ©es, ce qui peut signifier leur isolement par rapport au milieu et donc l'arrĂȘt des rĂ©actions impliquant les NPs, soit une forme de passivation des nanoparticules. Le comportement des NPs dans le milieu est donc en grande partie contrĂŽlĂ© par la couche directement Ă leur surface (GĂ©labert et al., 2014; Sivry et al., 2014) : la couche d'hydroxydes de zinc contrĂŽle le Ks apparent, l'enrobage organique augmente la vitesse et le taux de dissolution des NPs et, enfin, la formation d'une gangue carbonatĂ©e emprisonne les NPs et provoque potentiellement leur passivation
Recombinant human activated protein C improves endotoxemia-induced endothelial dysfunction: a blood-free model in isolated mouse arteries
Recombinant human activated protein C (rhAPC) is one of the treatment panels for improving vascular dysfunction in septic patients. In a previous study, we reported that rhAPC treatment in rat endotoxemia improved vascular reactivity, although the mechanisms involved are still under debate. In the present study, we hypothesized that rhAPC may improve arterial dysfunction through its nonanticoagulant properties. Ten hours after injection of LPS in mice (50 mg/kg ip), aortic rings and mesenteric arteries were isolated and incubated with or without rhAPC for 12 h. Aortic rings were mounted in a myograph, after which arterial contractility and endothelium-dependent relaxation were measured in the presence or absence of nitric oxide synthase or cyclooxygenase inhibitors. Flow (shear stress)-mediated dilation with or without the above inhibitors was also measured in mesenteric resistance arteries. Protein expression was assessed by Western blotting. Lipopolysaccharide (LPS) reduced aortic contractility to KCl and phenylephrine as well as dilation to acetylcholine. LPS also reduced flow-mediated dilation in mesenteric arteries. In rhAPC-treated aorta and mesenteric arteries, contractility and endothelial responsiveness to vasodilator drug and shear stress were improved. rhAPC treatment also improved LPS-induced endothelial dysfunction; this effect was associated with an increase in the phosphorylated form of endothelial nitric oxide synthase and protein kinase B as well as cyclooxygenase vasodilatory pathways, thus suggesting that these pathways, together with the decrease in nuclear factor-ÎșB activation and inducible nitric oxide synthase expression in the vascular wall, are implicated in the endothelial effect of rhAPC. In conclusion, ex vivo application of rhAPC improves arterial contractility and endothelial dysfunction resulting from endotoxemia in mice. This finding provides important insights into the mechanism underlying rhAPC-induced improvements on arterial dysfunction during septic shock
Experimental investigation of the stability of Fe-rich carbonates in the lower mantle
International audienceThe fate of carbonates in the Earth's mantle plays a key role in the geodynamical carbon cycle. Although iron is a major component of the Earth's lower mantle, the stability of Fe-bearing carbonates has rarely been studied. Here we present experimental results on the stability of Fe-rich carbonates at pressures ranging from 40 to 105 GPa and temperatures of 1450-3600 K, corresponding to depths within the Earth's lower mantle of about 1000-2400 km. Samples of iron oxides and iron-magnesium oxides were loaded into CO2 gas and laser heated in a diamond-anvil cell. The nature of crystalline run products was determined in situ by X-ray diffraction, and the recovered samples were studied by analytical transmission electron microscopy and scanning transmission X-ray microscopy. We show that Fe-(II) is systematically involved in redox reactions with CO2 yielding to Fe-(III)-bearing phases and diamonds. We also report a new Fe-(III)-bearing high-pressure phase resulting from the transformation of FeCO3 at pressures exceeding 40 GPa. The presence of both diamonds and an oxidized C-bearing phase suggests that oxidized and reduced forms of carbon might coexist in the deep mantle. Finally, the observed reactions potentially provide a new mechanism for diamond formation at great depth
Elongated magnetite nanoparticle formation from a solid ferrous precursor in a magnetotactic bacterium
Magnetotactic bacteria are aquatic microorganisms that intracellularly mineralize ferrimagnetic nanoparticles enabling the cells to align with the geomagnetic field. The bacteria produce a magnetic mineral of species-specific phase (magnetite Fe(II)Fe(III)2O4 or greigite Fe(II)Fe(III)2S4), size, morphology and particle assembly. Several species produce crystals of unusual elongated particle shapes, which break the symmetry of the thermodynamically favoured isometric morphology. Such morphologies are thought to affect domain size and orientation of the internal magnetization. Therefore, they are interesting study objects to develop new synthetic strategies for the morphological control of nanoparticles. We investigate the formation of such irregularly shaped nanomagnets in the species Desulfovibrio magneticus RS-1. In contrast to previously described organisms, this bacterium accumulates iron predominantly as Fe(II) rather than Fe(III) consistent with an alternative oxidative biomineralization route. Further, using high-resolution electron microscopy, we observe an epitaxial relationship between precursor and the final mineral phase supporting the notion of a solid-state transformation pathway. The precursor is likely a green rust previously thought to convert to magnetite only by dissolution and re-precipitation. Our findings represent a novel observation in the interconversion of iron (oxyhydr)oxide materials and suggest that solid-state growth processes could be required to produce irregularly shaped, elongated magnetite nanocrystals
Cerebrovascular dysfunction and microcirculation rarefaction precede white matter lesions in a mouse genetic model of cerebral ischemic small vessel disease
Cerebral ischemic small vessel disease (SVD) is the leading cause of vascular dementia and a major contributor to stroke in humans. Dominant mutations in NOTCH3 cause cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a genetic archetype of cerebral ischemic SVD. Progress toward understanding the pathogenesis of this disease and developing effective therapies has been hampered by the lack of a good animal model. Here, we report the development of a mouse model for CADASIL via the introduction of a CADASIL-causing Notch3 point mutation into a large P1-derived artificial chromosome (PAC). In vivo expression of the mutated PAC transgene in the mouse reproduced the endogenous Notch3 expression pattern and main pathological features of CADASIL, including Notch3 extracellular domain aggregates and granular osmiophilic material (GOM) deposits in brain vessels, progressive white matter damage, and reduced cerebral blood flow. Mutant mice displayed attenuated myogenic responses and reduced caliber of brain arteries as well as impaired cerebrovascular autoregulation and functional hyperemia. Further, we identified a substantial reduction of white matter capillary density. These neuropathological changes occurred in the absence of either histologically detectable alterations in cerebral artery structure or blood-brain barrier breakdown. These studies provide in vivo evidence for cerebrovascular dysfunction and microcirculatory failure as key contributors to hypoperfusion and white matter damage in this genetic model of ischemic SVD
Biomineralization of amorphous Fe-, Mn- and Si-rich mineral phases by cyanobacteria under oxic and alkaline conditions
Iron and manganese are poorly soluble elements in oxic and alkaline solutions, whereas they are much more soluble under anoxic conditions. As a
result, the formation of authigenic mineral phases rich in Fe and/or Mn has traditionally been viewed as diagnostic of global or local
anoxic conditions. Here we reveal that some specific cyanobacteria of very small size (<â2â”m, i.e., picocyanobacteria) can
biomineralize abundant, authigenic Fe(III)-, Mn(IV)- and Si-rich amorphous phases under oxic conditions in an alkaline lake in
Mexico. The resulting biominerals cluster as small globules arranged as rings around the division septum of cyanobacterial cells. These rings are
enveloped within an organic, likely polysaccharidic envelope and are partially preserved, at least morphologically, upon sedimentation. Based on
their 16S rDNA sequence, these cyanobacteria were affiliated with the Synechococcales order. The high Fe and Mn enrichment of the
biominerals questions the systematic inference of anoxic conditions based on their detection. Moreover, this process scavenges iron from the water
column, an overlooked biological contribution to the Fe cycle. Finally, it reveals a new case of controlled biomineralization of
Si-rich phases by bacteria.</p
Regulation of seed germination and seedling growth by an Arabidopsis phytocystatin isoform, AtCYS6
Phytocystatins are cysteine proteinase inhibitors in plants that are implicated in the endogenous regulation of protein turnover and defense mechanisms against insects and pathogens. A cDNA encoding a phytocystatin called AtCYS6 (Arabidopsis thaliana phytocystatin6) has been isolated. We show that AtCYS6 is highly expressed in dry seeds and seedlings and that it also accumulates in flowers. The persistence of AtCYS6 protein expression in seedlings was promoted by abscisic acid (ABA), a seed germination and post-germination inhibitory phytohormone. This finding was made in transgenic plants bearing an AtCYS6 promoterâÎČ-glucuronidase (GUS) reporter construct, where we found that expression from the AtCYS6 promoter persisted after ABA treatment but was reduced under control conditions and by gibberellin4+7 (GA4+7) treatment during the germination and post-germinative periods. In addition, constitutive over-expression of AtCYS6 retarded germination and seedling growth, whereas these were enhanced in an AtCYS6 knock-out mutant (cys6-2). Additionally, cysteine proteinase activities stored in seeds were inhibited by AtCYS6 in transgenic Arabidopsis. From these data, we propose that AtCYS6 expression is enhanced by the germination inhibitory phytohormone ABA and that it participates in the control of germination rate and seedling growth by inhibiting the activity of stored cysteine proteinases
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