Délégation Alpes

Controlling the oxidation state of redox-active ligands during the assembly of Porous Coordination Polymers (PCPs) is a key challenge toward the design of electronically functional frameworks.Herein, we report a galvanostatic solvothermal strategy that enables the in situ electrochemical generation of an open-shell gold(III) bis(dithiolene) ligand during the formation of the network.The reduced tetrabenzoate-functionalized precursor undergoes anodic oxidation under constant current conditions, allowing precise control of the ligand's electronic state during the assembly of the framework.Magnetic measurements reveal regular S = 1/2 antiferromagnetic chains arising from one unpaired electron per Au(III)-dithiolene unit, in agreement with band structure calculations.While the room-temperature conductivity is comparable to that of closed-shell analogues, the charge transport proceeds through a Mott-insulating regime rather than a band-gap-activated mechanism, in agreement with band structure calculations.This electrochemical programming approach provides a general route to open-shell PCPs with electronically correlated ground states.

The authors report a combination of multimodal scanning three‐dimensional X‐ray diffraction (S3DXRD), X‐ray diffraction computed tomography (XRD‐CT), and X‐ray fluorescence computed tomography (XRF‐CT) used for the first time to provide multiscale (spanning the size regime 0.15–500 µm) insight into the aging of a CeO 2 ZrO 2 solid solution known to exhibit outstanding reversible oxygen storage capacity (OSC). The authors show that using nanobeams is necessary to map in detail the distribution of elements and crystalline phases. In particular, the latter information is derived from two imaging methodologies to capture the diffraction signal originating from single crystals and powder‐averaged crystallites, respectively. Ultimately, a decrease in relative OSC by 25% in the aged material could be correlated with a transformation of the cation‐ordered pyrochlore Ce 2 Zr 2 O 7 phase to the cation‐disordered CeO 2 ZrO 2 fluorite structure. This is manifested as a loss in homogeneity of Ce and Zr distribution of the cation‐ordered pyrochlore seen by nanoXRF‐CT. The diffraction signal in both the S3DXRD and XRD‐CT provides evidence that the solid‐state transformation between the phases preferentially takes place at the periphery of the catalyst particle, resulting in a pyrochlore‐rich core and fluorite on the surface and accompanied by significant sintering.

Abstract The reaction processes in Li‐ion batteries can be highly heterogeneous at the electrode scale, leading to local deviations in the lithium content or local degradation phenomena. To access the distribution of lithiated phases throughout a high energy density silicon‐graphite composite anode, correlative operando SAXS and WAXS tomography are applied. In‐plane and out‐of‐plane inhomogeneities are resolved during cycling at moderate rates, as well as during relaxation steps performed at open circuit voltage at given states of charge. Lithium concentration gradients in the silicon phase are formed during cycling, with regions close to the current collector being less lithiated when charging. In relaxing conditions, the multi‐phase and multi‐scale heterogeneities vanish to equilibrate the chemical potential. In particular, Li‐poor silicon regions pump lithium ions from both lithiated graphite and Li‐rich silicon regions. This charge redistribution between active materials is governed by distinct potential homogenization throughout the electrode and hysteretic behaviors. Such intrinsic concentration gradients and out‐of‐equilibrium charge dynamics, which depend on electrode and cell state of charge, must be considered to model the durability of high capacity Li‐ion batteries.

Abstract Organothiol monolayers on metal substrates (Au, Ag, Cu) and their use in a wide variety of applications have been extensively studied. Here, the growth of layers of organothiols directly onto muscovite mica is demonstrated using a simple procedure. Atomic force microscopy, surface X‐ray diffraction, and vibrational sum‐frequency generation IR spectroscopy studies revealed that organothiols with various functional endgroups could be self‐assembled into (water) stable and adaptable ultra‐flat organothiol monolayers over homogenous areas as large as 1 cm2. The strength of the mica–organothiol interactions could be tuned by exchanging the potassium surface ions for copper ions. Several of these organothiol monolayers were subsequently used as a template for calcite growth.

Ribonucleotide reductase (RNR) is the enzyme that converts ribonucleotides to corresponding deoxyribonucleotides. The mammalian R2 subunit of the enzyme complex reacts with ferrous iron and dioxygen to generate a diferric iron‐oxygen cluster and a tyrosyl radical that is essential for enzymatic activity. A p53 induced isoform of the R2 subunit (p53R2) is proposed to be involved in the production of deoxyribonucleotides during DNA repair. The human and murine p53R2 proteins have been studied by electron paramagnetic resonance (EPR), Mössbauer spectroscopy, magnetic circular dichroism (MCD) and CD, as previously published for mouse R2. While the studies of the active diferric iron‐oxygen cluster and the tyrosyl radical (also hydrogen binding to the tyrosyl radical) together with the mixed valent form (Fe(II)‐Fe(III) cluster) shows little or no variation between the mouse R2 and p53R2 subunits, the MCD and X‐band integer spin EPR studies reveals a difference between diferrous forms. In addition no cooperative binding of Fe(II) or Co(II) is seen for p53R2. The mouse Co(II)Co(II) R2 form has a S= 3 ground state. The diferrous form has a S=2 ground state, with one positive and one negative zero field splitting. In its active form R2 is in complex with another subunit R1, no differences is observed in the interaction of R1 with either mouse R2 or p53R2.

K+ production far below the free nucleon-nucleon threshold has been investigated in collisions of 36Ar on 12C, natTi, and 181Ta targets at an incident energy of 92 MeV per nucleon. The cross sections for K+ production have been inferred from the observed muon decays of positive kaons. The results are discussed in the framework of a participant-spectator model and are compared to proton induced K+ production and to subthreshold pion production experiments.