Recherche sur le Covid-19

An international team of scientists from the Paul Scherrer Institute and members of the LeadXpro and Heptares pharmaceutical companies led by Karol Nass (Alvra group, SwissFEL) demonstrated a significant advancement in de novo protein structure determination at X-ray free-electron lasers. Their article, published recently in IUCrJ (DOI: 10.1107/S2052252520011379), describes structure determination of a membrane protein and an important drug target (A_2A adenosine receptor) by native single-wavelength anomalous diffraction (native-SAD) at SwissFEL with up to ten fold reduction in the required number of indexed images.

After the joint position paper published as a pre-release in July, in which the Analytical Research Infrastructures of Europe (ARIE) presented their plan to tackle HE Missions,  the ARIE enhanced its cross-border, multidisciplinary collaboration to offer Europe a strong and valid weapon against the present COVID-19 challenge and other potential viral and microbial threats.

Excitation of coherent phonons using light is an emerging approach for investigating condensed matter physics. It has the potential not only to reveal the dynamics of collective lattice vibrations but also to tailor them for the ultrafast control over the electronic, magnetic, and structural properties in solids. The optical phonons, in most solids, lie primarily in the spectral region between 1 and 10 THz. Unlike conventional laser sources, coherent radiation at these frequencies allows us to study time-resolved lattice displacements with only minor deposition of heat or generation of hot electrons. However, the available high-field terahertz sources, with their quasi-single cycle temporal shape and broadband spectrum, cannot be used to excite the individual phonon modes. By contrast, the challenge of understanding the transient dynamics of low-energy excitations calls for novel sources of narrow-band terahertz radiation at high intensities that can be tuned to the individual phonon resonances. Moreover, with strong enough fields tuned precisely to a phonon resonance, non-linearities in the material can be targeted and potentially exploited.

The results from the very first user experiment at SwissFEL have just been published in the Proceedings of the National Academy of Sciences (PNAS). The measurements probed the electron transport properties of the cytochrome c protein, which is found in cellular mitochondria. The measurements show that when the Fe atom at the centre of the protein undergoes electronic excitation, for example when it gains or loses and electron, the  active centre of the protein undergoes a doming structural rearrangement. This result raises interesting questions about how this structural change is involved in the electron transfer properties of cytochrome c.

Magnesium rich calcites are important functional biominerals. For example, they can be found in protective shells or eye lenses. Natural organism provide a surprisingly high degree of control on the amount of magnesium incorporation into calcites by yet not well understood mechanisms. Understanding such control mechanism is important when designing bio inspired functional materials. Here we systematically explore the impact of thermodynamic parameters on the degree of magnesium incorporation into calcite. In particular, we identify the thermodynamic conditions, where very high magnesium rich calcites (50% Mg/50% Ca) forms under ambient conditions of temperature and pressure. This is an important finding for geochemistry: Very high magnesium rich calcite is believed to be the precursor for dolomite. Despite its frequent occurrence in nature, its unknown formation pathway remains one of the big mysteries in geochemistry.

Calcium carbonates are key materials to biomineralization, they are frequently used in industrial applications and also for carbon capture technologies. Finally, they serve as an important model system to test novel nucleation theories.  Calcium carbonate crystalizes in a multi-step process, where amorphous calcium carbonate (ACC) is the most important precursor in the crystallization process. Existing synthesis protocols generate ACC of different stability and purity.  To improve our mechanistic understanding of carbonate crystallization, reactivity and polymorph formation, the reproducible synthesis of clean and stable ACC is an important, and yet unresolved step. Here we use the fast reaction of CO2 with calcium hydroxide in airborne aerosols to reproducibly create pure and stable ACC, which may serve as a well-defined starting material for further chemical processing.

Magnesium rich calcites are important functional biominerals. For example, they can be found in protective shells or eye lenses. Natural organism provide a surprisingly high degree of control on the amount of magnesium incorporation into calcites by yet not well understood mechanisms. Understanding such control mechanism is important when designing bio inspired functional materials. Here we systematically explore the impact of thermodynamic parameters on the degree of magnesium incorporation into calcite. In particular, we identify the thermodynamic conditions, where very high magnesium rich calcites (50% Mg/50% Ca) forms under ambient conditions of temperature and pressure. This is an important finding for geochemistry: Very high magnesium rich calcite is believed to be the precursor for dolomite. Despite its frequent occurrence in nature, its unknown formation pathway remains one of the big mysteries in geochemistry.

Calcium carbonates are key materials to biomineralization, they are frequently used in industrial applications and also for carbon capture technologies. Finally, they serve as an important model system to test novel nucleation theories.  Calcium carbonate crystalizes in a multi-step process, where amorphous calcium carbonate (ACC) is the most important precursor in the crystallization process. Existing synthesis protocols generate ACC of different stability and purity.  To improve our mechanistic understanding of carbonate crystallization, reactivity and polymorph formation, the reproducible synthesis of clean and stable ACC is an important, and yet unresolved step. Here we use the fast reaction of CO2 with calcium hydroxide in airborne aerosols to reproducibly create pure and stable ACC, which may serve as a well-defined starting material for further chemical processing.

We study the gas diffusion in still liquids under gas high pressures. We demonstrate that the pressure-induced gas diffusion, liquid swelling and the liquid surface tension can be measured simultaneously in a one-pot experiment. The measurements are performed using the high-resolution neutron imaging in a non-tactile way. A major advantage of this new method is that the determination of surface tension necessitate no assumptions imposed on the properties of the liquid.

Long-wavelength pulses from the Swiss X-ray free-electron laser (XFEL) have been used for de novo protein structure determination by native single-wavelength anomalous diffraction (native-SAD) phasing of serial femtosecond crystallography (SFX) data.

We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-1/2 system: Y₂CuTiO₆. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale (-θ_CW) of ∼134 K. 

We generate frequency-tunable narrow-band intense fields in the terahertz (THz) range by optical rectification of a temporally modulated near-infrared laser pumping a nonlinear organic crystal.

A fundamental understanding of the active sites in technical CoMo/ Al₂O₃ catalysts is crucial to improve the production of clean transportation fuels by hydrodesulfurization (HDS), which removes sulfur from fossil fuels. Sulfur dioxide, resulting from fossil fuel combustion, is one of the main causes for acid rain. In situ X-ray spectroscopic experiments at the SuperXAS beamline of the SLS provided insight in the structure and number of active sites (“Co−Mo−S”) in sulfided CoMo/ Al₂O₃ catalysts. When the Co to Mo ratio is less than 0.1, cobalt forms isolated sites on the MoS₂ phase, where the cobalt promoter atoms are in centrosymmetric octahedral coordination with six-sulfur ligands.

We report muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system La_2−xBa_xCuO₄ with x = 0.115. An extremely low uniaxial stress of ∼0.1 GPa induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from ∼10 to 32 K.