Crystal engineering in IUCrJ: from `the' crystal structure to `a' crystal structure

What is `structure' in the context of a molecular solid?

Towards a better understanding and improved refinement of disordered crystal structures

The new approach of Dittrich [IUCrJ (2021). 8, 305–318] towards describing, understanding and modelling disorders is discussed.

Increasing complexity: structural equivalence and combinatorial approaches to preparation of high order cocrystals

An algorithmic strategy to design stoichiometric quaternary and solid-solution quinary solids is described. The strategy involves recognition of structural inequivalences to generate ternary and quaternary cocrystals which can then be extended to five-component solid solutions through matching of suitable interactions.

Functionalization of the BCL6 BTB domain into a noncovalent crystallization chaperone

The BCL6 BTB domain has been adapted to form a promiscuous assembly block as a basis for affinity-capture crystallography.

Use of additives to regulate solute aggregation and direct conformational polymorph nucleation of pimelic acid

The interference of solute self-assembly caused by the interactions between pimelic acid and a series of homologous additives is closely related to the ability to induce the form II compound with similar packing but a different conformation to that of form I. The novel use of additives demonstrates the direct link between solute aggregation in solution and molecular conformation in crystals.

Insights into the structure of mature streptavidin C1 from Streptomyces cinnamonensis reveal the self-binding of the extension C-terminal peptide to biotin-binding sites

The structural analysis of mature streptavidin C1 from S. cinnamonensis is reported.

Quaternary and quinary molecular solids based on structural inequivalence and combinatorial approaches: 2-nitro­resorcinol and 4,6-di­chloro­resorcinol

Stoichiometric ternary and quaternary, and nonstoichiometric quinary molecular solids were engineered based on structural inequivalence and combinatorial approaches from 2-nitroresorcinol. A total of 32 binary, ternary, quaternary and quinary solids were characterized. The great difficulty in obtaining such solids is that crystallization must occur in a single step from precursors in solution, with multistep sequences, as are typical in solution syntheses, not being possible in most situations.

Devitrification reduces beam-induced movement in cryo-EM

Controlled devitrification of vitreous samples for high-resolution single-particle cryo-EM reduces beam-induced motion in the critical early frames of a movie stack by a factor of approximately four.

Competitive cocrystallization and its application in the separation of flavonoids

Competitive cocrystallization provides a green chemical method for flavonoid separation with fewer steps and lower energy consumption than the traditional organic solvent extraction method.

Nitro­sonium nitrate (NO⁺NO₃⁻) structure solution using in situ single-crystal X-ray diffraction in a diamond anvil cell

The crystal structure of nitro­sonium nitrate (NO⁺NO₃⁻) is determined by synchrotron single-crystal X-ray diffraction at pressures of 7.0 and 37.0 GPa – resolving a long-standing controversy. Remarkably, the oxygen atom of the NO⁺ unit is determined to be positively charged, a rare occurrence when in the presence of a less-electronegative element.

Coherent crystal branches: the impact of tetragonal symmetry on the 2D confined polymer nanostructure

The impact of tetragonal crystal symmetry on the two-dimensional (2D) confined polymer nanostructure is demonstrated. Our research shows that this chain packing defect in the tetragonal cell can be controlled to develop along the rod long axis in 2D confinement.

REGALS: a general method to deconvolve X-ray scattering data from evolving mixtures

A method is introduced to deconvolve SAXS datasets from evolving mixtures, such as those produced by time-resolved, temperature jump, ligand titration and chromatography-coupled setups. The method incorporates general restraints using regularized alternating least squares (REGALS), enabling physically meaningful deconvolution without the need for a hard physicochemical or structural model.

Crystallographic models of SARS-CoV-2 3CL^pro: in-depth assessment of structure quality and validation

Over 100 models of SARS-CoV-2 3CL^pro, a major drug-design target for COVID-19, have been carefully validated and assembled in a dedicated database. Their comparative analysis provides lessons for similar medically oriented efforts and for structural biology in general.

Whole pair distribution function modeling: the bridging of Bragg and Debye scattering theories

The whole pair distribution function modeling method is introduced to overcome the distinction between Bragg and Debye theories in analysis of powder-scattering data. Models based on Bragg's law are used to facilitate the computation of a whole pair distribution function followed by the solution of the Debye scattering equation.

Theoretical and experimental investigation of protein crystal nucleation in pores and crevices

Using a theoretical method which employs equilibration between the cohesive and destructive energies of a crystal, it is shown that protein layers of monomolecular thickness formed in pores can grow into macroscopic crystals. Experimental studies, stimulated from theoretical considerations, widen the palette of porous materials that can promote protein crystallization.

Structures of the germline-specific Deadhead and thioredoxin T proteins from Drosophila melanogaster reveal unique features among thioredoxins

The first structures of the Drosophila germline-specific thioredoxins Deadhead (Dhd) and thioredoxin T (TrxT), which present unusual properties with respect to canonical Trxs, are reported. Dhd is highly positively charged, which facilitates nonspecific DNA binding to promote chromatin remodeling. TrxT contains a C-terminal extension, which is mostly unstructured and highly flexible, that modulates the redox activity of the protein. These structures will facilitate the virtual screening of small-molecule ligands and protein partners.

Electronic structure of Schiff-base peroxo{2,2′-[1,2-phenyl­enebis(nitrilo­methanylyl­idene)]bis­(6-meth­oxy­phenolato)}titanium(IV) monohydrate: a possible model structure of the reaction center for the theoretical study of hemoglobin

The experimental electron-density distribution in a titanium peroxo complex has been studied and compared with theoretical results.

On modelling disordered crystal structures through restraints from molecule-in-cluster computations, and distinguishing static and dynamic disorder

Restraints extracted from molecule-in-cluster optimizations of separate disorder components permit improved least-squares modelling of experimental crystal structures, and considering energy barriers alongside enthalpy differences further enables the distinguishing of disorder into static and dynamic.

Manganese-doping enhanced local heterogeneity and piezoelectric properties in potassium tantalate niobate single crystals

A large enhancement (118%) of electric field-induced strain of KTa_1−xNb_xO₃ is achieved by Mn doping. The intensified local heterogeneity and modified structural features yielded by Mn dopants are demonstrated to be responsible for improved piezoelectricity. The role of Mn doping in local structures and properties of KTa_1−xNb_xO₃ crystals is revealed, providing a basis for material design and performance optimization.

Comment on the article Structure and mechanism of copper–carbonic anhydrase II: a nitrite reductase

The paper discusses a recent paper [Andring et al. (2020). IUCrJ, 7, 287–293] on the nitrite reductase and nitrous anhydrase activity of carbonic anhydrase.

Structure and mechanism of copper–carbonic anhydrase II: a nitrite reductase. Corrigendum

Corrigendum to the article by Andring et al. [IUCrJ, (2020), 7, 287–293].

Shock-synthesized quasicrystals. Corrigendum

Corrigendum to the article by Németh [IUCrJ, (2020), 7, 368–369].