Crystal engineering in IUCrJ 2021: interactions, structures, properties

The articles in the chemistry and crystal engineering section of IUCrJ published from 2021 onwards continue to deal with themes like interactions, structure and properties taken in the broadest sense.

Water and 2,2,6,6-tetra­methyl­piperidine: an odd couple make a solid match

Commentary is given on a paper [Butler et al. (2022). IUCrJ, 9, 364–369] reporting the crystallization of two room-temperature liquids, water and 2,2,6,6-tetra­methyl­piperidine, to form a crystalline solid with a water-lined channel potentially capable of proton transport.

Crystal structure of a constitutive active mutant of adenosine A_2A receptor

The structure of constitutive active mutant I92N reveals a hydrophilic network in the transmission-switch region of the adenosine A_2A receptor (A_2AAR). The structure combined with molecular dynamics simulations suggests that the mutant I92N preserves the intermediate state in the presence or removal of an agonist, thus this sheds light on its higher basal activity.

Re-evaluation of protein neutron crystallography with and without X-ray/neutron joint refinement

The crystallographic structure of a bacterial copper amine oxidase was determined solely using neutron diffraction data at 1.72 Å resolution. Although the neutron scattering length densities thus obtained were sufficient to determine the locations of all atoms, including H and D atoms, it was confirmed that joint refinement with high-resolution X-ray diffraction data provided more accurate structural features that were not visible in the structure refined from the neutron data alone.

The benefits of Cu Kβ radiation for the single-crystal X-ray structure determination of crystalline sponges

Copper Kβ radiation offers some advantages over its Kα counterpart that prove very useful for determining crystal structures in metal–organic framework host–guest systems.

Effect of synthesis time on plasmonic properties of Ag dendritic nanoforests

The morphological variation of longer-time synthesized or thicker Ag dendritic nanoforests on Si substrates did not have superior plasmonic properties. The prepared sample achieved the most desirable light-to-heat conversion efficiency and SERS response with an intermediated growth time.

The spontaneous self-assembly of a molecular water pipe in 3D space

When an exact 2:1 ratio of water and 2,2,6,6-tetra­methyl­piperidine is mixed in a sealed vessel at room temperature, the formation of crystals is immediately observed. Single-crystal X-ray and neutron diffraction show that the phenomenon can be described as the spontaneous self-assembly of a 3D water pipe from its components.

Spatiotemporal control of L-phenyl­alanine crystallization in microemulsion: the role of water in mediating molecular self-assembly

In nanoconfinement environments, different types of water trigger different forms of self-assembly of high-quality L-phenyl­alanine crystals through molecular oriented attachment. In addition, it was also found that the formation of L-phenyl­alanine amyloid fibrils is related to free water.

Orthorhombic charge density wave on the tetragonal lattice of EuAl₄

The incommensurate charge density wave of EuAl₄ below T_CDW = 145 K is found to possess orthorhombic symmetry, despite an average crystal structure that remains tetragonal in very good approximation. This finding has ramifications for the interpretation of all physical properties of EuAl₄, in particular, its multiple magnetic transitions.

New ligand-binding sites identified in the crystal structures of β-lactoglobulin complexes with desipramine

New complexes of β-lactoglobulin with several ligand molecules simultaneously bound at different sites are presented and discussed in the context of a systematic classification of all possible binding sites in the lactoglobulin molecule.