Journal of Applied Crystallography最新文献

A comprehensive analysis of Bi₂O₂CO₃ nanosheets, which were synthesized using nanosecond-pulsed discharges in water between bismuth electrodes, was conducted in order to investigate the crystallographic features of this material. Electron diffraction, X-ray diffraction and electron energy-loss spectrometry techniques revealed the presence of a stoichiometric tetragonal Bi₂O₂CO₃ structure, labelled BOC in this study. It crystallizes in the body-centred tetragonal Bravais lattice and belongs to the I4/mmm space group (No. 139), with the following lattice parameters: a = 3.91, c = 13.77 Å. The nanosheets adopt square shapes. This shape is dictated by the symmetry elements of its point group (4/mmm) under the prevailing local conditions. From the energetic point of view, this shape, dictated by the 4/m2/m2/m point group and therefore a pinacoid, corresponds to an absolute extremum, an indicator of the stability of these BOC nanosheets. Most nanosheets are crossed by equal-inclination fringes or bend contours. These bend contours reflect the fact that the BOC nanosheets contain crystal defects and/or are so thin that they bend elastically, leading to rotation of the lattice planes towards the diffracting Bragg position. The diffraction patterns corresponding to bend contours intersecting along the [001] zone axis have been studied in detail. Extra reflections are superimposed on the diffraction pattern of the BOC crystallographic structure. These extra reflections are essentially attributed to two phenomena: multiple diffraction and local disorder–order transformations of the BOC crystal structure, passing from a body-centred tetragonal to a primitive Bravais lattice. A mechanism related to the ledge mechanism (kinks and jogs), explaining the formation of nanosheets in a metallic matrix, has been adapted and proposed for the formation of BOC nanosheets in water. When the nanosheets are removed from the water, they become carbonated once in the air, leading to the formation of BOC that inherits the nanosheet morphology.

For membrane proteins, ab initio modelling based on a single curve of small-angle X-ray scattering (SAXS) is precluded by the presence of detergent molecules bound to the hydrophobic region of the protein. MEMPROT was developed for the modelling of protein–detergent complexes based on the SAXS curve of the complex, and on an a priori representation of the detergent corona by an elliptical semi-torus surrounding the protein. In previous studies, MEMPROT has succeeded in modelling several membrane proteins solubilized in n-dodecyl-β-maltopyranoside (DDM). However, it has never been tested on proteins solubilized in other detergents. To understand whether the geometrical shape currently parametrized in MEMPROT could be applied to a broader catalogue of protein–detergent complexes, here, MEMPROT was used to model the detergent corona around the multi-hydrophobic substrate transporter from Bacillus halodurans solubilized in four different detergents, namely DDM, n-decyl-β-maltopyranoside (DM), 4-cyclohexyl-1-butyl-β-d-maltoside (Cymal4) and decyl-maltose-neopentyl-glycol (DMNG). The study indicates a significant variation in detergent shapes, depending on the type of detergent. The modelling results suggest that the elliptical semi-torus with a circular closure is an excellent approximation for long-tailed detergents (DDM and DM) but leads to a slightly poorer agreement with the data for DMNG and Cymal4, which have a shorter hydrophobic tail, smaller than the half-width of the protein hydrophobic region. Here, for the latter, it is hypothesized that a corona with a flatter closure would be a better shape descriptor.

A multi-technique analysis was used to investigate how the orientation of single-crystal Si wafer surfaces affects the size, shape and orientation of NiSi₂ nanocrystals grown within the wafers through the thermal diffusion of Ni atoms from a nickel-doped thin film deposited on the surface. Nickel-doped thin films were prepared on silicon wafers with three distinct crystallographic orientations, [001], [110] and [111]. Three sets of samples were then annealed at 500, 600 and 700°C for 2 h. Regardless of crystallographic orientation or annealing temperature, NiSi₂ nanoplates with a nearly hexagonal shape grew close to the external surface of the wafers, aligning their larger surfaces parallel to one of the planes of the Si{111} crystallographic form. The crystallographic orientation and annealing temperature in the 500–700°C range did not significantly affect the final values of the average diameter and thickness of the nanoplates. However, significant differences were noted in the number of nanoplates formed in Si wafers with different crystallographic orientations. The results indicate that these observed differences are correlated with the number of pre-existing defects in the wafers that influence the heterogeneous nucleation process. In addition, the average size and size dispersion were determined for pores at the surface of the Si wafers formed due to the etching process used for native oxide removal.

The workshop titled `X-ray-based technologies in emerging fuel cell research', organized by Vivian Stojanoff from Brookhaven National Laboratory (BNL) and Narayanasami Sukumar from Cornell University/Advanced Photon Source-Northeastern Collaborative Access Team, was a notable segment of the National Synchrotron Light Source II and Center for Functional Nanomaterials Users' Meeting held 13–17 May 2024. This one-day event, on 13 May 2024, at BNL in New York, aimed to bring together researchers, beamline scientists, management and developers to propel fuel cell technology forward using model systems inspired by natural photosynthesis and redox enzymes. This summary encapsulates the key discussions, advancements and future implications of the workshop.