The structural behaviour of homoleptic xenon difluoride (XeF2) complexes [M(XeF2)6][SbF6]2 (M= Cu, Zn) under varying temperature and pressure has been investigated, aiming to resolve the disordered Jahn-Teller distortions in the copper complex (CuSb). At 200 K, both CuSb and its zinc analogue (ZnSb) crystallize in a layered CdCl2-type structure with the space group R3. Upon cooling below 170 (CuSb) and 160 K (ZnSb), both systems transition to isostructural phases in P1, with CuSb assuming an ordered Jahn-Teller distortion. The transformation is driven by the shortening and optimization of the Xe...F intermolecular contacts, forming stronger and more directional interactions, rather than by Jahn-Teller effects alone. This is supported by the observation of similar transitions in the Jahn-Teller-inactive Zn system. High-pressure experiments up to ∼2.8 GPa at room temperature show the structural stability of the high-symmetry phases, implicating kinetic barriers to further transformation. Additionally, the synthesis and structural characterization of a novel arsenic analogue, [Zn(XeF2)6][AsF6]2 (ZnAs), reveal similar layered motifs but distinct phase behaviour. Symmetry-mode analyses relate all observed phases through distortions of a common CdCl2 aristotype.

In the era of single-particle cryogenic electron microscopy (cryo-EM) and AI-driven protein structure prediction, obtaining high-resolution protein structures, either experimentally or computationally, has become increasingly routine. Yet studying and understanding protein dynamics remains challenging. In single-particle cryo-EM, protein dynamics are most obviously manifested as poor local resolution or disappearing densities in specific regions of a reconstruction. No method is yet available to computationally generate conformational ensembles that fully deconvolute these experimental observations. When dynamics are key to understanding protein function, it is clear to us that introducing new experimental approaches is necessary to close this gap and make sense of invisible densities in single-particle cryo-EM.

Lytic transglycosylases (LTs) play a central role in bacterial cell wall remodeling by cleaving the β-1,4-glycosidic bond in peptidoglycan via a non-hydrolytic mechanism, producing 1,6-anhydroMurNAc termini crucial for recycling and signaling. Among LTs, membrane-bound lytic transglycosylase B (MltB) contributes to peptidoglycan turnover, antibiotic resistance and protein-protein interactions. Despite its importance, the structural basis of MltB function in Acinetobacter baumannii, a multidrug-resistant pathogen, remains unclear. Here, we report the crystal structure of abMltB at 1.79 Å resolution. abMltB adopts a monomeric structure comprising three domains: an N-terminal domain (NTD), a catalytic domain (CD) and a C-terminal domain (CTD). The NTD connects to the CD via a flexible loop that partially occludes the active site, forming a tunnel-like cavity. Comparative analysis with homologous enzymes such as SltB1 and Slt35 reveals conserved catalytic residues, including Glu129 and key aromatic residues, while the CTD in abMltB adopts a distinct orientation. Notably, although calcium ions stabilize related enzymes, no metal binding was observed in abMltB. These findings highlight conserved mechanistic features and unique structural adaptations of abMltB, offering insight into its functional role in A. baumannii and potential as a novel antimicrobial target.

Understanding structure at the atomic scale is fundamental for understanding the functioning and the development of materials with improved properties. Compared with other probes providing atomic resolution, electrons offer the strongest interaction in combination with minimal radiation damage, which makes them an ideal tool for investigating very small and radiation-sensitive samples [Henderson (1995), Q. Rev. Biophys. 28, 171-193]. However, these benefits are often offset by the laborious preparation of nanometre-sized samples that are not visible using a light microscope, and the fact that experiments are largely restricted to ultra-high vacuum [Duyvesteyn et al. (2018), Proc. Natl Acad. Sci. USA 115, 9569-9573; Gruene et al. (2021), Nat. Rev. Chem. 5, 660-668]. Here, we report the successful implementation of MeV electron diffraction for ab initio 3D structure determination of the quasi-2D material muscovite and the quantum material 1T-TaS2 at atomic resolution. By employing ultrashort electron pulses from the REGAE (Relativistic electron gun for atomic exploration) accelerator, we obtained high-quality diffraction datasets suitable for structural refinements based on dynamical scattering theory, enabling precise localization of even hydrogen atoms. The increased penetration depth of MeV electrons significantly expands the applicable thickness range of samples, overcoming previous restrictions associated with traditional electron diffraction. These findings establish MeV electron diffraction as a viable approach for investigating a broad range of materials, including nanostructures and radiation-sensitive compounds, and open up new opportunities for in situ and time-resolved experiments [Chao et al. (2023), Chem. Rev. 123, 8347-8394; Filippetto et al. (2022), Rev. Mod. Phys. 94, 045004].

We demonstrate a grazing-incidence X-ray platform that simultaneously records time-resolved grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GID) from a femtosecond-laser-irradiated gold film above the melting threshold, with picosecond resolution using an X-ray free-electron laser (XFEL). By tuning the X-ray incidence angle, the probe depth is set to tens of nanometres, enabling depth-selective sensitivity to near-surface dynamics. GISAXS resolves ultrafast changes in surface nanomorphology (correlation length, roughness), while GID quantifies subsurface lattice compression, grain orientation, melting and recrystallization. The approach overcomes photon-flux limitations of synchrotron grazing-incidence geometries and provides stringent, time-resolved benchmarks for complex theoretical models of ultrafast laser-matter interaction and warm dense matter. Looking ahead, the same depth-selective methodology is well suited to inertial confinement fusion (ICF): it can visualize buried-interface perturbations and interfacial thermal resistance on micron to sub-micron scales that affect instability seeding and burn propagation.

The paper by Gilski et al. in this issue [IUCrJ (2026), 13, 132-145] focuses on the stereochemical analysis of the catalytic mechanism of asparaginases with the aim of resolving key ambiguities in the mechanism. These enzymes have found truly remarkable therapeutic success in the treatment of childhood leukemias.

The antidiabetic drug chlorpropamide [1-(4-chlorophenyl)sulfonyl-3-propylurea, CPA] has one of the highest numbers of reported polymorphs, making it an excellent model system for studying structural responses to pressure or temperature. The densest polymorph, δ-CPA, was probed by single-crystal X-ray diffraction at both laboratory and synchrotron facilities. A new high-pressure phase with tripled cell parameter b as compared with the ambient pressure phase was discovered. High-brilliance synchrotron sources and fast data collection strategies allowed us to also detect the formation of the intermediate incommensurately modulated phase at 2.37 (5) GPa. The experiments revealed the effect of the pressure-increasing protocol on the structure evolution on hydrostatic compression. The importance and necessity of conducting both laboratory and synchrotron experiments for the same compound when studying solid-state transformations is illustrated. The opportunities provided by synchrotron sources for studying phase transformations are discussed, together with specific characteristics of synchrotron experiments that should not be overlooked.

Time-resolved X-ray crystallography is undergoing a renaissance due to the development of serial crystallography at synchrotron and XFEL beamlines. Crucial to such experiments are efficient and effective methods for uniformly initiating time-dependent processes within microcrystals, such as ligand binding, enzymatic reactions or signalling. A widely applicable approach is the use of photocaged substrates, where the photocage is soaked into the crystal in advance and then activated using a laser pulse to provide uniform initiation of the reaction throughout the crystal. This work characterizes photocage release of nitric oxide and binding of this ligand to two heme protein systems, cytochrome c'-β and dye-decolourizing peroxidase B using a fixed target sample delivery system. Laser parameters for photoactivation are systematically explored, and time-resolved structures over timescales ranging from 100 µs to 1.4 s using synchrotron and XFEL beamlines are described. The effective use of this photocage for time-resolved crystallography is demonstrated and appropriate illumination conditions for such experiments are determined.

Time-resolved neutron scattering has been used to study dynamically polarized protons in tyrosyl-doped bovine liver catalase. While the evolution of proton polarization and its inversion by the method of adiabatic fast passage (AFP) in a standard dynamic nuclear polarization (DNP) system with organic Cr(V) complexes can be well modelled and understood, the experiments with tyrosyl-doped catalase lead us into the world of extremely dilute paramagnets with only about 1017 unpaired electrons per cm3. In this regime, the strength of DNP is comparable to the drift of proton polarization towards its thermal equilibrium of Pe = 0.35% at T = 1 K and B = 3.5 T. Negative DNP, which counteracts this drift, is confined to protons very close to the radical site, typically within 5 Å. In contrast, AFP reverses the polarization of protons at a larger distance from the radical. The contrast of a domain of polarized close protons giving rise to neutron scattering is considerably enhanced by AFP. Moreover, the spread of proton polarization is sensitive to magnetic inhomogeneities, like the iron of the heme of the catalase molecule. In short, polarized neutron scattering from AFP-modulated polarized samples provides an excellent tool for mapping sources and sinks of proton polarization in radical proteins.

Co-crystal structures of a base-excision DNA-repair enzyme (human 8-oxoguanine DNA glycosylase; hOgg1) in complex with a photocaged 8-oxoguanine DNA lesion were determined before and after uncaging via illumination at 2.81 and 2.48 Å resolution, respectively. The structures were carefully reassessed to rapidly expand the target repertoire of light-triggered time-resolved macromolecular crystallography. Late-intermediate cryo-trapping after uncaging revealed the partial accommodation of 8-oxoguanine in the active site with 68% occupancy, which did not induce full active-site adaptation to the catalytic state. Crystal illumination led to a light-dependent loss of diffraction power, likely due to crystal-packing collapse during the very late reaction stages. This work therefore not only demonstrates that hOgg1 is well suited for time-resolved crystallography, but also that such analysis is necessary to determine further steps in its reaction.