This is a review of atomic pair distribution function (PDF) analysis as applied to the study of molecular materials. The PDF method is a powerful approach to study short- and intermediate-range order ...in materials on the nanoscale. It may be obtained from total scattering measurements using X-rays, neutrons, or electrons, and it provides structural details when defects, disorder, or structural ambiguities obscure their elucidation directly in reciprocal space. While its uses in the study of inorganic crystals, glasses, and nanomaterials have been recently highlighted, significant progress has also been made in its application to molecular materials such as carbons, pharmaceuticals, polymers, liquids, coordination compounds, composites, and more. Here, an overview of applications toward a wide variety of molecular compounds (organic and inorganic) and systems with molecular components is presented. We then present pedagogical descriptions and tips for further implementation. Successful utilization of the method requires an interdisciplinary consolidation of material preparation, high quality scattering experimentation, data processing, model formulation, and attentive scrutiny of the results. It is hoped that this article will provide a useful reference to practitioners for PDF applications in a wide realm of molecular sciences, and help new practitioners to get started with this technique.
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The discovery of high-temperature superconductivity in a layered iron arsenide has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the ...chemical composition of the spacer layer between adjacent anionic iron arsenide layers. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li(+), Na(+), K(+), Ba(2+)) or PbO- or perovskite-type oxide layers, and also in Fe(1.01)Se (ref. 8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Li(x)(NH(2))(y)(NH(3))(1-y)Fe(2)Se(2) (x~0.6; y~0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1) K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family.
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Trivalent lanthanide ions offer remarkable opportunities in the design of bioimaging agents: this review presents an accessible discussion of their application in both optical and magnetic resonance ...imaging. Aspects of molecular design, control over key physical properties and biological compatibility are discussed in this context, together with developments and opportunities as responsive probes and in multimodal imaging.
This review presents an accessible discussion of the application of trivalent lanthanide ions in both optical and magnetic resonance imaging.
DNA double-strand breaks (DSBs) are highly toxic lesions that can drive genetic instability. To preserve genome integrity, organisms have evolved several DSB repair mechanisms, of which nonhomologous ...end-joining (NHEJ) and homologous recombination (HR) represent the two most prominent. It has recently become apparent that multiple layers of regulation exist to ensure these repair pathways are accurate and restricted to the appropriate cellular contexts. Such regulation is crucial, as failure to properly execute DSB repair is known to accelerate tumorigenesis and is associated with several human genetic syndromes. Here, we review recent insights into the mechanisms that influence the choice between competing DSB repair pathways, how this is regulated during the cell cycle, and how imbalances in this equilibrium result in genome instability.
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Patients with pulmonary arterial hypertension were randomly assigned to receive sotatercept at a dose of 0.3 mg per kilogram or 0.7 mg per kilogram or placebo, in addition to standard therapy. At 24 ...weeks, both sotatercept groups had a greater reduction in pulmonary vascular resistance than the placebo group.
Cubic energy materials such as thermoelectrics or hybrid perovskite materials are often understood to be highly disordered
. In GeTe and related IV-VI compounds, this is thought to provide the low ...thermal conductivities needed for thermoelectric applications
. Since conventional crystallography cannot distinguish between static disorder and atomic motions, we develop the energy-resolved variable-shutter pair distribution function technique. This collects structural snapshots with varying exposure times, on timescales relevant for atomic motions. In disagreement with previous interpretations
, we find the time-averaged structure of GeTe to be crystalline at all temperatures, but with anisotropic anharmonic dynamics at higher temperatures that resemble static disorder at fast shutter speeds, with correlated ferroelectric fluctuations along the
direction. We show that this anisotropy naturally emerges from a Ginzburg-Landau model that couples polarization fluctuations through long-range elastic interactions
. By accessing time-dependent atomic correlations in energy materials, we resolve the long-standing disagreement between local and average structure probes
and show that spontaneous anisotropy is ubiquitous in cubic IV-VI materials.
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Electrodeposited manganese oxide films (MnOx) are promising stable oxygen evolution catalysts. They are able to catalyze the oxygen evolution reaction in acidic solutions but with only modest ...activity when prepared by constant anodic potential deposition. We now show that the performance of these catalysts is improved when they are “activated” by potential cycling protocols, as measured by Tafel analysis (where lower slope is better): upon activation the Tafel slope decreases from ∼120 to ∼70 mV/decade in neutral conditions and from ∼650 to ∼90 mV/decade in acidic solutions. Electrochemical, spectroscopic, and structural methods were employed to study the activation process and support a mechanism where the original birnessite-like MnOx (δ-MnO2) undergoes a phase change, induced by comproportionation with cathodically generated Mn(OH)2, to a hausmannite-like intermediate (α-Mn3O4). Subsequent anodic conditioning from voltage cycling or water oxidation produces a disordered birnessite-like phase, which is highly active for oxygen evolution. At pH 2.5, the current density of activated MnOx (at an overpotential of 600 mV) is 2 orders of magnitude higher than that of the original MnOx and begins to approach that of Ru and Ir oxides in acid.
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