Structural Changes in the Local Environment of Uranium Atoms in the Three Phases of U₄O₉

The crystal structure of U₄O₉ remains an enigma because of its differences with U⁴⁺ and U⁵⁺ coordination polyhedral mixtures, as shown in the XANES experimental results. To better understand this crystal structure, its diffraction pattern was measured at seven different temperatures using neutron diffraction before being independently refined by Rietveld’s method and pair distribution function analysis. The O cuboctahedrona structural element consisting of 13 oxygen atomsis a specific feature of the U₄O₉ crystal structure. The volume of the cuboctahedron decreases when the temperature increases, whereas the overall volume of the crystal cell increases. This feature can be correlated with the two U₄O₉ phase transitions that induce sharp changes in the cuboctahedron geometry, suggesting that this structural element has internal dynamics. In particular, these structural modifications in the γ phase suggest that the high-temperature phase can be described as a mixture of U⁴⁺ and U⁵⁺ coordination polyhedra, the latter having U–O distances shorter than 2.2 Å, that are absent in the former. These changes in uranium polyhedra as a function of temperature are tentatively interpreted using steric arguments. They also raise the question of charge localization on the different U ion sites in the low-temperature phases of U₄O₉

Structural Changes in the Local Environment of Uranium Atoms in the Three Phases of U₄O₉

The crystal structure of U₄O₉ remains an enigma because of its differences with U⁴⁺ and U⁵⁺ coordination polyhedral mixtures, as shown in the XANES experimental results. To better understand this crystal structure, its diffraction pattern was measured at seven different temperatures using neutron diffraction before being independently refined by Rietveld’s method and pair distribution function analysis. The O cuboctahedrona structural element consisting of 13 oxygen atomsis a specific feature of the U₄O₉ crystal structure. The volume of the cuboctahedron decreases when the temperature increases, whereas the overall volume of the crystal cell increases. This feature can be correlated with the two U₄O₉ phase transitions that induce sharp changes in the cuboctahedron geometry, suggesting that this structural element has internal dynamics. In particular, these structural modifications in the γ phase suggest that the high-temperature phase can be described as a mixture of U⁴⁺ and U⁵⁺ coordination polyhedra, the latter having U–O distances shorter than 2.2 Å, that are absent in the former. These changes in uranium polyhedra as a function of temperature are tentatively interpreted using steric arguments. They also raise the question of charge localization on the different U ion sites in the low-temperature phases of U₄O₉

Electron Transfer at Oxide/Water Interfaces Induced by Ionizing Radiation

The electron transfer from oxide into water is studied in nanoparticle suspensions of various oxides (SiO₂, ZnO, Al₂O₃, Nd₂O₃, Sm₂O₃, and Er₂O₃) by means of pulse and γ radiolysis. The time-resolved and steady-state investigations of the present study demonstrate independently that whatever the band gap and the electron affinity of the oxide, the electron transfer always takes place in these nanometric systems: Irradiation generates hot electrons which have enough energy to cross the semiconductor–liquid interface. Moreover, picosecond measurements evidence that the spectrum of the solvated electron is the same as in water. Lastly, the decay of the solvated electron is similar on the picosecond to nanosecond time scale in water and in these suspensions, but it is clearly different on the nanosecond to microsecond time scale

Dynamics of Water Confined in Clay Minerals

Ultrafast infrared spectroscopy of the O–D stretching mode of dilute HOD in H₂O probes the local environment and the hydrogen bond network of confined water. The dynamics of water molecules confined in the interlayer space of montmorillonites (Mt) and in interaction with two types of cations (Li⁺ and Ca²⁺) but also with the negatively charged siloxane surface are studied. The results evidence that the OD vibrational dynamics is significantly slowed down in confined media: it goes from 1.7 ps in neat water to 2.6 ps in the case of Li⁺ cations with two water pseudolayers (2.2–2.3 ps in the case of Ca²⁺ cations) and to 4.7 ps in the case of Li⁺ cations with one water pseudolayer. No significant difference between the two cations is noticed. In this 2D confined geometry (the interlayer space being about 0.6 nm for two water pseudolayers), the relaxation time constants obtained are comparable to the ones measured in analogous concentrated salt solutions. Nevertheless, and in strong opposition to the observations performed in the liquid phase, anisotropy experiments evidence the absence of rotational motions on a 5 ps time scale, proving that the hydrogen bond network in the interlayer space of the clay mineral is locked at this time scale

DataSheet1_Combining metal nanoparticles and nanobodies to boost the biomedical imaging in neurodegenerative diseases.docx

Introduction: In the study of neurodegenerative diseases, the possibility to follow the fate of specific cells or molecules within the whole body would be a milestone to better understand the complex evolution of disease mechanisms and to monitor the effects of therapies. The techniques available today do not allow the visualization of disease-relevant cells within the whole tridimensional biological context at high spatial resolution.Methods: Here we show the results from the first validation steps of a novel approach: by combining the conjugate nanobodies anti-glial fibrillary acidic protein (GFAP) and metal-nanoparticles (i.e. 2 nm gold NP) with X-ray phase contrast tomography (XPCT) we would be able to obtain a tridimensional visualization and identification of cells of interest together with the surrounding tissue and the vascular and neuronal networks.Results: By exploiting the X-ray attenuation properties of metal nanoparticles and the specific targeting capabilities of nanobodies, we could give XPCT the specificity it presently lacks, making it no longer a pure morphological but a molecular and targeted imaging technique. In our case, we synthesized and characterized Gold-NP/GFAP nanobody to target the astrocytes of mouse brain.Discussion: The results of the first tests presented in this paper have provided us with information on the feasibility of the approach, encouraging us to carry out further experiments in order to achieve the ultimate goal of setting up this new imaging technique.</p