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IUCr Congress collection
Celebrating the 75th Anniversary of the IUCr
The triennial congresses of the IUCr are the major international scientific meetings for structural scientists worldwide. This virtual issue presents a collection of articles covering research reported at the 26th IUCr Congress and articles celebrating the 75th Anniversary of the IUCr. The 26th Congress was held in Melbourne, Australia from 22 to 29 August 2023. Articles will be added to the collection during 2023 and 2024.
editorial
The International Union of Crystallography (IUCr) and its journals are celebrating their 75th anniversary. In this editorial, some of the publication achievements are highlighted and prospects for the future reviewed in an emerging open-access world.
lead articles
This article reviews phase evaluation in macromolecular crystallography. It accompanies the 2023 Ewald Prize lecture at the 26th IUCr Congress, paying tribute to Paul Ewald's far-reaching influence.
topical reviews
Formate dehydrogenases (FDHs) catalyze the two-electron oxidation of formate to carbon dioxide. This article presents recent progress in the structural analysis of FDHs together with their potential biotechnological applications.
Photosystem II is the enzyme responsible for generating nearly all the oxygen in the atmosphere. Room-temperature time-resolved crystallography and spectroscopy measurements at X-ray free-electron lasers help to elucidate the sequence of events in the water oxidation reaction of photosystem II leading to the formation of dioxygen from two molecules of water.
Diffuse X-ray scattering is used to characterize the time dependence of the liquid phase emerging from femtosecond laser-induced melting of polycrystalline gold thin films using an XFEL. Its structure factor and partial pair distribution function confirm the liquid origin of the diffuse scattering. The liquid fraction increases with a characteristic rise-time of 13 ps.
Interoperability of scientific data within crystallography has been achieved to a high level by the adoption of standard exchange formats and protocols. Extending such interoperability across other disciplines is a goal of the International Science Council Committee CODATA, to which the IUCr has been a leading contributor. Our article combines a description of the importance of interoperability for addressing grand challenges with a desire to stimulate the crystallographic community to continue exploring this topic.
research articles
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A binding approach based on electronic force density fields was used to describe the structures of the molecule, dimer and crystal of a uracil derivative. Transferable multipole pseudo-atoms were successfully used to reconstruct the inner-crystal electronic force density fields.
CCDC reference: 2259862
Open 
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AlphaFold predictions can be used both as a starting point for structure determination and as a method of model optimization. The Phenix PredictAndBuild tool automates iterative prediction and model building, yielding a density map and model starting with sequence information and crystallographic data.
This contribution outlines how to obtain perfect precise colorings of tilings, and illustrates this by obtaining perfect precise colorings of some families of k-valent semiregular planar tilings with k colors.
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Advances in X-ray hardware and software have revolutionized crystallography: now crystal structures can be routinely solved first, with publication-quality datasets collected second. This same approach now allows multi-grain crystallography to be completed in the laboratory with Cu Kα X-rays.
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All the possibilities for permissible (mismatch-free) walls between monoclinic domains of pseudocubic ferroic perovskites are analyzed. Analytical expressions are derived for the orientation of such walls, the orientation relationship between the lattice vectors and the separation between Bragg peaks diffracted from matched domains.
Open access
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X-ray absorption spectroscopy (XAS) measurements of N-truncated amyloid-β samples were corrected for systematic effects such as dead time, detector efficiencies, monochromator glitches, self-absorption, radiation damage and noise at higher wavenumbers k, permitting hypothesis testing in structural refinements. A new protocol was developed using extended X-ray absorption fine structure data analysis for monitoring radiation damage in real time and post-analysis.
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A dipropyl-substituted isoindigo derivative has three polymorphs with different molecular conformations and arrangements.
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A single-particle structure determination pipeline is implemented in the open-source software xFrame, which includes methods for determining rotational invariants from X-ray scattering patterns and performing structure reconstructions by iterative phasing of rotational invariants.
Open access
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A simple symmetric 2D scan using a point focus beam was used to determine the fibre axis of fibre-textured satin spar samples. A geometric explanation of the `wing' feature formed by the diffraction spots in 2D scans helps to visualize the nature of the reciprocal layers of the fibre-textured samples through wide-range reciprocal space mapping.
teaching and education
Open access
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Most introductions to the topic of crystallography only occur during tertiary education, which presents a challenge to communicating it to wider groups. This work describes a simple activity targeted at classroom and community audiences to demonstrate crystal structure(s) and the wider impact of crystallography.
computer programs
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A program has been developed to assist researchers interested in bending crystals to evaluate crystal deformation from a single optical image.
letters to the editor
Open access
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The formal launch of Protein Data Bank China (PDBc) is announced, and the history of the wwPDB, recently established mechanisms for adding new wwPDB data centers and the processes developed to bring PDBc into the partnership are described.
