Properties and suspension stability of dendronized iron oxide nanoparticles for MRI applications

Functionalized iron oxide nanoparticles have attracted an increasing interest in the last 10 years as contrast agents for MRI. One challenge is to obtain homogeneous and stable aqueous suspensions of iron oxide nanoparticles without aggregates. Iron oxide nanoparticles with sizes around 10 nm were synthesized by two methods: the particle size distribution in water suspension of iron oxide nanoparticles synthesized by the co-precipitation method was improved by a process involving two steps of ligand exchange and phase transfer and was compared with that of iron oxide nanoparticles synthesized by thermal decomposition and functionalized by the same dendritic molecule. The saturation magnetization of dendronized nanoparticles synthesized by thermal decomposition was lower than that of nanoparticles synthesized by co-precipitation. The r(2) relaxivity values were shown to decrease with the agglomeration state in suspension and high r(2) values and r(2)/r(1) ratios were obtained with nanoparticles synthesized by co-precipitation by comparison with those of commercial products. Dendronized iron oxide nanoparticles thus have potential properties as contrast agent. Copyright (C) 2010 John Wiley & Sons, Ltd

What does the structure-function relationship of the HIV-1 Tat protein teach us about developing an AIDS vaccine?

The human immunodeficiency virus type 1 (HIV-1) trans-activator of transcription protein Tat is an important factor in viral pathogenesis. In addition to its function as the key trans-activator of viral transcription, Tat is also secreted by the infected cell and taken up by neighboring cells where it has an effect both on infected and uninfected cells. In this review we will focus on the relationship between the structure of the Tat protein and its function as a secreted factor. To this end we will summarize some of the exogenous functions of Tat that have been implicated in HIV-1 pathogenesis and the impact of structural variations and viral subtype variants of Tat on those functions. Finally, since in some patients the presence of Tat-specific antibodies or CTL frequencies are associated with slow or non-progression to AIDS, we will also discuss the role of Tat as a potential vaccine candidate, the advances made in this field, and the importance of using a Tat protein capable of eliciting a protective or therapeutic immune response to viral challenge

Metal-Spinel Composites (M0xFe01-x)α-(MyFe3-y)1-α with M=Co, Ni Synthesis and Physical Properties

Composite materials made up of cobalt-iron alloy (or nickel -iron alloy) and Co (or Ni) doped magnetite are synthesized in an aqueous media. The procedure employed is a low temperature reaction in alkaline KOH solution which involves the disproportionation of Fe(II) into Fe0 and Fe(III) and a reduction of Co(II) or Ni(II). The composition of the final product depends on the initial and final concentrations of reagents and KOH. Pure cobalt - containing composites are obtained in a narrow range of KOH concentration. The metallic phases have the α-Fe (b.c.c. structure) or α-Mn structure, and the lattice parameter of the cobalt - containing magnetite lies between 8.396(2)Å and 8.405(2)Å. Nickel - containing composites without hydroxides are obtained for higher KOH concentrations, 14-15 mol/liter. For lower and higher KOH concentration, hydroxides or amorphous phases precipitate. The coercive field increases when [Co]/[Fe] increases

New metallic iron / manganese-zinc ferrite nanocomposites prepared by hydrothermal microwave synthesis

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Novel metallic iron/manganese-zinc ferrite nanocomposites prepared by microwave hydrothermal flash synthesis

8 Caillot, T. Pourroy, G. Stuerga, D.Metallic iron (alpha-Fe)/manganese-zinc ferrite (Fe3-x-yMnxZnyO4) nanocomposites have been successfully synthesized for the first time using microwave hydrothermal treatment of alcoholic solutions of chloride precursors and sodium ethoxide. This new type of nanocomposites, never obtained by conventional synthesis, can now be produced in a short period (e.g. 15s). The powders were characterized by X-ray diffraction, transmission electron microscopy and magnetic properties were measured. In most cases, three classes of crystallites were observed; one of them is composed of grains of about 100 nm in size where the metal is inserted into the oxide. For all samples, 20% of metallic iron was routinely obtained using the microwave flash synthesis. Consequently, the microwave heating appears to provide an efficient source of energy in producing metallic iron nanoparticles protected against oxidation by an oxide matrix. (c) 2010 Elsevier B.V. All rights reserved

Study of metal-ferrite composites: complementary use of

The complementarity between 57Fe Mössbauer spectrometry and classical methods of powder characterizations is pointed out for determining the formula of metal-ferrite composites (Fe$_p^0$Co$_{1-p}^0$)a(CoxFe$_{3-x-t}$ $\square_t$O4). It is shown that X-ray diffraction is essential to determine the composition of the metal, while TG measurements in air give an approximate value for the metal ratio. In-field spectrometry is expected as the most suitable tool to determine the Fe sites occupancy, although the complex hyperfine structure might originate some misfits. The composites formulae were therefore determined by selecting the set of refined Mössbauer parameters that were in best agreement with the TG measurements. Magnetic measurements prove the validity of such an approach

Optical properties of Co2+-doped silica gel monoliths

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