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Crystal structure and thermal expansion of a CsCe{sub 2}Cl{sub 7} scintillator
We used single-crystal X-ray diffraction data to determine crystal structure of CsCe{sub 2}Cl{sub 7}. It crystallizes in a P112{sub 1}/b space group with a=19.352(1) Å, b=19.352(1) Å, c=14.838(1) Å, γ=119.87(2)°, and V=4818.6(5) Å{sup 3}. Differential scanning calorimetry measurements combined with the structural evolution of CsCe{sub 2}Cl{sub 7} via X-ray diffractometry over a temperature range from room temperature to the melting point indicates no obvious intermediate solid–solid phase transitions. The anisotropy in the average linear coefficient of thermal expansion of the a axis (21.3×10{sup –6}/°C) with respect to the b and c axes (27.0×10{sup –6}/°C) was determined through lattice parameter refinement of the temperature dependent diffraction patterns. These findings suggest that the reported cracking behavior during melt growth of CsCe{sub 2}Cl{sub 7} bulk crystals using conventional Bridgman and Czochralski techniques may be largely attributed to the anisotropy in thermal expansion. - Graphical abstract: Three-dimensional quadric surface of thermal expansion coefficient of CsCe{sub 2}Cl{sub 7} at room temperature (sphere – isotropic) and near melting point (ellipsoid – anisotropic). - Highlights: • Crystal structure of CsCe{sub 2}Cl{sub 7} was solved through X-ray diffraction. • Linear coefficients of thermal expansion were determined from in-situ XRD in 25–650 °C. • Anisotropy of the a axis with respect to b and c axes (21.3 vs 27.0×10{sup –6}/°C) was found. • No solid–solid phase transitions were observed via XRD and thermal analysis.
Type I antiferromagnetic order in Ba 2 LuReO 6 : Exploring the role of structural distortions in double perovskites containing 5d 2 ions
Abstract not provided
Structural integrity--Searching the key factor to suppress the voltage fade of Li-rich layered cathode materials through 3D X-ray imaging and spectroscopy techniques
Li-rich layered materials are important cathode compounds used in commercial lithium ion batteries, which, however, suffers from some drawbacks including the so-called voltage fade upon electrochemical cycling. Here, our study employs novel transmission X-ray microscopy to investigate the electrochemical reaction induced morphological and chemical changes in the Li-rich Li 2 Ru 0.5 Mn 0.5 O 3 cathode particles at the meso to nano scale. We performed combined X-ray spectroscopy, diffraction and microscopy experiments to systematically study this cathode material's evolution upon cycling as well as to establish a comprehensive understanding of the structural origin of capacity fade through 2D and 3D fine length scale morphology and heterogeneity change of this material. This work suggests that atomic manipulation (e.g. doping, substitution etc.) or nano engineering (e.g. nano-sizing, heterogeneous structure) are important strategies to mitigate the internal strain and defects induced by extensive lithium insertion/extraction. It also shows that maintaining the structural integrity is the key in designing and synthesizing lithium-rich layered materials with better cycle stability.
Structural stability of REE-PO[subscript 4] (REE = Sm,Tb) under swift heavy ion irradiation
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Structure-function relationships in photosynthetic membranes: Challenges and emerging fields
Not provided.
Structure and Misfolding of the Flexible Tripartite Coiled-Coil Domain of Glaucoma-Associated Myocilin
Not Available
Two Active Site Divalent Ions in the Crystal Structure of the Hammerhead Ribozyme Bound to a Transition State Analogue
Abstract not provided
Structural Basis of Tryptophan Reverse N-Prenylation Catalyzed by CymD
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Sequence Modulates Polypeptoid Hydration Water Structure and Dynamics
We use molecular dynamics simulations to investigate the effect of polypeptoid sequence on the structure and dynamics of its hydration waters. Polypeptoids provide an excellent platform to study small-molecule hydration in disordered polymers, as they can be precisely synthesized with a variety of sidechain chemistries. We examine water behavior near a set of peptoid oligomers in which the number and placement of nonpolar versus polar sidechains are systematically varied. To do this, we leverage a new computational workflow enabling accurate sampling of polypeptoid conformations. We find that the hydration waters are less dense, are more tetrahedral, and have slower dynamics compared to bulk water. The magnitude of these shifts increases with the number of nonpolar groups. Here, we also find that shifts in the water structure and dynamics are strongly correlated, suggesting that experimental insight into the dynamics of hydration water obtained by Overhauser dynamic nuclear polarization (ODNP) also contains information about water structural properties. We then demonstrate the ability of ODNP to probe site-specific dynamics of hydration water near these model peptoid systems.
Thermodynamics, Kinetics and Structural Evolution of ε-LiVOPO 4 over Multiple Lithium Intercalation
ε -Li x VOPO 4 is a promising multi-electron cathode for rechargeable lithium-ion bat- teries that has an extremely high theoretical capacity of 318 mAh/g. In this w ork, we demonstrate the stable cycling of more than one Li in solid-state-syn thesized ε - LiVOPO 4 over more than 20 cycles for the first time. Using a combination of densit y functional theory (DFT) calculations, X-ray pair distribution funct ion (PDF) analy- sis and X-ray Absorption Near Edge Structure (XANES) measurements, we pre sent a comprehensive analysis of the thermodynamics, kinetics and stru ctural evolution of ε -Li x VOPO 4 over the entire lithiation range. We identify two intermediate ph ases at x = 1 . 5 and 1.75 in the low-voltage regime using DFT calculations, and the comput ed and electrochemically measured voltage profiles are in excellent agree ment. Operando PDF techniques show a reversible hysteretic change in the short ( < 2° A) V-O bond lengths coupled with an irreversible extension of the long V-O bond ( > 2.4 °A) dur- ing low-voltage cycling. These observations are confirmed with EXAFS spe ctra. We identify hydrogen intercalation from the electrolyte decomposition as a likely explana- tion for the ~ 2 . 4°A V-O bond and its irreversible extension. In terms of electronic conductivity, we find Li x VOPO 4 to be a large band gap insulator across the entire lithiation range, and calculated small polaron migration barriers are similar to those of the olivine LiMPO 4 cathodes. Finally, we demonstrate that ε -LiVOPO 4 is likely to be a one-dimensional diffuser using climbing-image nudged elastic ban d calculations. These results highlight the importance of nano-sizing and carbon coating in achieving good electrochemical performance in this material.
YCrWO 6 : Polar and Magnetic Oxide with CaTa 2 O 6 -Related Structure
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Novel Strategy To Analyze Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Data of Biomass Pyrolysis Oil for Oligomeric Structure Assignment
Among the most prominent challenges for the analysis of biomass pyrolysis products is the characterization of the abundant oligomer fraction of bio-oil. This fraction is principally made up of pyrolytic lignins and dehydrated, highly modified sugar oligomers, called humins, in liquid phase. An emerging technique for analysis of this oligomer fraction is high-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), which allows for accurate determination of C x H y O z formulae for detected oligomers. Additionally, using simple dehydration and fragmentation reaction schemes, similar formulae can be developed from cellulose-, hemicellulose- and lignin-derived oligomers, which are primary depolymerization products. In this paper, FT-ICR MS analysis is coupled with combinatoric dehydration and fragmentation modeling in order to match experimentally detected bio-oil oligomers with hypothetical pathways for their formation during pyrolysis. In this way, we present a novel strategy by which oligomeric structures can be proposed for bio-oils. Using this approach, it becomes possible to advance the understanding of both the molecular structures comprising the bio-oil oligomer fraction and the pathways by which these structures form during biomass pyrolysis reactions.
Temperature Homogeneity under Selective and Localized Microwave Heating in Structured Flow Reactors
Selective heating of different phases of multiphase systems via microwaves can result in energy savings and suppression of side reactions. However, materials properties and operating conditions that maximize temperature gradients are poorly understood. Here we utilize computational fluid dynamics (CFD) computations and temperature measurements in structured flow reactors (monoliths) in a monomodal microwave cavity to assess the temperature difference between the walls and the fluid and develop a simple lumped model to estimate when temperature gradients exist. We also explore the material’s thermal and electrical properties of structured reactors for isothermal catalyst conditions. We propose that CFD simulations can be used as a nonintrusive, predictive tool of temperature homogeneity. Importantly, we demonstrate that localized heating in the bed under several conditions rather than selective heating is responsible for the selectivity enhancement. Furthermore, our results indicate that structured beds made of high thermal conductivity materials avoid arcing and enable temperature homogeneity and low electrical conductivity materials allow microwaves to penetrate the domain.
Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling
Herein, we report the synthesis and structural characterization of K8[(CO3)3Pu]2(µ-η2-η2-O2)2•12H2O. This is the second plutonium-containing addition to the previously studied alkali metal peroxo-carbonate series M8[(CO3)3A]2(µ-η2-η2-O2)2•xH2O (M = alkali metal; A = Ce or Pu; x = 8, 10, 12 or 18), for which only the M = Na analog has been previously reported when A = Pu. The previously reported crystal structure for Na8[(CO3)3Pu]2(µ-η2-η2-O2)2•12H2O is not isomorphous with its known Ce analogue. However, a new synthetic route to these M8[(CO3)3A]2(µ-η2-η2-O2)2•12H2O complexes, described below, has produced crystals of Na8[(CO3)3Ce]2(µ-η2-η2-O2)2•12H2O that are isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M8[(CO3)3Ce]2(µ-η2-η2-O2)2•xH2O have also been synthesized for systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy and density functional theory (DFT) calculations. The cerium salts in particular demonstrate subtle differences in the peroxide bond lengths which correlate to Raman shifts for the peroxide Op–Op stretch (Op = the oxygen atoms of the peroxide bridges) with each of the cations studied: Na+ (1.492(3) Å /847 cm-1), Rb+ (1.471(1) Å /854 cm-1), Cs+ (1.474(1) Å /859 cm-1), and K+ (1.468(6) Å, 870 cm-1). The trends observed in the M–Op and Op–Op bond distances appear to relate to supermolecular interactions between the neighboring cations.
Structural and Functional Characterization of the Hazelnut Allergen Cor a 8
Abstract not provided
Ultrafast X-ray Absorption Near Edge Structure Reveals Ballistic Excited State Structural Dynamics
Here, polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation. Excitation of vitamin B 12 , cyanocobalamin (CNCbl), in the αβ-band at 550 nm and the γ-band at 365 nm was used to uniquely resolve axial and equatorial contributions to the excited state dynamics. The structural evolution of the excited molecule is best described by a coherent ballistic trajectory on the excited state potential energy surface. Prompt expansion of the Co cavity by ca. 0.03 Å is followed by significant elongation of the axial bonds (>0.25 Å) over the first 190 fs. Subsequent contraction of the Co cavity in both axial and equatorial directions results in the relaxed S 1 excited state structure within 500 fs of excitation.