Acta crystallographica Section B, Structural science, crystal engineering and materials最新文献

Crystallization induced by lithobiont microbial communities (fungi, bacteria, lichens) has received great attention in science and beyond. The studies discussed here focus on the mechanisms and factors of microbial biomineralization. The multilevel modelling approach, which made it possible to solve this interdisciplinary problem, is highlighted. The effect of chemical composition of biofilms, including acidity of the medium and cation oxidation degree, on oxalate formation is discussed. The variants of interaction between biofilm components and growing oxalate crystals are addressed. Particular attention is paid to the effect of metabolism of fungi, bacteria and their associations on carbonate and oxalate crystallization under various trophic conditions and the transitions between them. The possibility of applying the identified patterns to reveal the role of fungi and bacteria in the oxalate-carbonate pathway and in biotechnologies is considered.

Two new crystals of amantadinium salts were obtained from fenamic and tolfenamic acid. The salt of fenamic acid is a model compound for interaction analysis, while amantadinium tolfenamate is a composition of a drug used in the treatment of symptoms of Parkinsonism and as a nonsteroidal anti-inflammatory drug. The crystal structures were studied and a theoretical analysis of the hydrogen bonds and weak interactions was carried out using quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) methods.

The online software server SARAh-webRepresentational Analysis is introduced. It replaces the previous Windows-versions of SARAh-Representational analysis and SARAh-Refine, and related theory. The new suite of web apps carries out a range representational analysis calculations, including those based on the works of Kovalev, Bertaut, Izyumov, Bradley, Cracknell, Birman and Landau, for magnetic structures and electronic properties within frameworks based on the crystallographic space groups and point groups. Irreducible representations are sourced from the works of Kovalev, tabulated and computations are carried out on a server using Mathematica.

The search for a Kitaev quantum spin liquid in crystalline magnetic materials has fueled intense interest in the two-dimensional honeycomb systems. Many promising candidate Kitaev systems are characterized by a long-range-ordered magnetic structure with an antiferromagnetic zigzag-type order, where the static moments form alternating ferromagnetic chains. Recent experiments on high-quality single crystals uncovered the existence of intriguing multi-k magnetic structures, which evolved from zigzag structures. Those discoveries have sparked new theoretical developments and amplified interest in these materials. We present an overview of the honeycomb materials known to display this type of magnetic structure and provide detailed crystallographic information for the possible single- and multi-k variants.

A microporous zincophosphate with the idealized formula Na₅Zn[Zn(PO₄)₃] was obtained through high-temperature hydrothermal synthesis and characterized by scanning electron microscopy, microprobe analysis and X-ray diffraction. The orthorhombic compound, which crystallizes in non-centrosymmetric space group Pna2₁ with unit-cell parameters a = 12.9901 (2), b = 16.2647 (3), c = 5.2158 (1) Å and Z = 4, is characterized by a new structure type. Each ZnO₄ tetrahedron shares all O atoms with four phosphate tetrahedra to form groups of five polyhedra, that are further linked via oxygen-bridging contacts of Zn- and P-centered tetrahedra in chains aligned in the c-axis direction. These one-periodic structural fragments [Zn(PO₄)₃]^7- define the prismatic habitus of the crystals. The negatively charged zincophosphate chains are balanced by Na⁺ cations, disposed in an open space between the chains, and somewhat `diluted' with Zn²⁺, Ca²⁺ and Mn²⁺ ions as impurities. A rare case of the Na/Zn occupation of one structural site was found in the structure. Theoretical calculations of possible pathways of alkali metal ion migration through the structure and activation energies revealed that the Li-substituted counterpart Li₅Zn[Zn(PO₄)₃] can be considered as a potential solid electrolyte.

All crystal structures containing nitrate ions, water molecules and one of the rare earth (RE) metal atoms (La-Lu, Y, Sc) were extracted from the Inorganic Crystal Structure Database. The composition of the identified compounds is analyzed in terms of the number of coordinated and uncoordinated water molecules and nitrate ions. Among the resulting compounds, several isotypic and morphotropic series are observed. The structures were analyzed within the stereoatomic model of crystal structures. Coordination numbers of RE metals are calculated using the method of intersecting spheres. The variation of RE-O distances is analyzed over the entire series of metal atoms. Coordination modes of both nitrate ions and water molecules are established. Combinatorial topological types of Voronoi-Dirichlet polyhedra of rare earth metal atoms as coordination centers in the studied compounds are calculated.

We present an approach to reduce this computational cost substantially, based on the partitioning of the molecule into geometrically separated torsional groups, with the dependence of the intramolecular energy and atomic point charges and dependent degrees of freedom on molecular conformation being computed as a linear combination of the contributions of these groups. This can lead to large savings in computational cost without a significant impact on accuracy, as demonstrated in the cases of N-acetyl-para-aminophenol (paracetamol) and methyl 4-hydroxybenzoate (methyl paraben). The approach is also applied successfully to two larger molecules, benzyl [4-(4-methyl-5-[(4-methylphenyl)sulfonyl]-1,3-thiazol-2-yl)phenyl]carbamate (molecule XX from the fifth CSP blind test) and (2S)-2-[4-(3-fluorobenzyloxy)benzylamino]propionamide (safinamide), for which we conduct the first reported CSP study. In both cases, the use of torsional groups results in over 99% reduction in computational cost, which enables the generation of an initial CSP landscape with high-quality structures found within the standard cutoff of 20 kJ mol^-1 for progression to refinement.

The magnetic structures of the Ho-based i-MAX phase (Mo_2/3Ho_1/3)₂GaC were studied with neutron powder diffraction at low temperature. (Mo_2/3Ho_1/3)₂GaC crystallizes in the orthorhombic space group Cmcm. The material undergoes two successive antiferromagnetic transitions at T_N1 = 10 K and T_N2 = 7.2 K. The magnetic structure below T_N1 is incommensurate with the propagation vector k₁ = (0, k_y, 0) with k_y = 0.696 (1) at 9 K. For the analysis of the magnetic structure, a group-theoretical approach based on the space group of the nuclear structure and its subgroups was employed. A model in the (3+1)D superspace group Cmcm.1'(0β0)s0ss yielded the most accurate results in neutron powder diffraction refinements. The determined structure was found to be an incommensurate longitudinal amplitude-modulated magnetic structure. Below T_N2, additional magnetic satellites develop. They could be indexed by a propagation vector k₂ = (τ_x, 0, 0) with the τ_x value increasing below T_N2 until it stabilizes at approximately 3 K at 0.075. A magnetic structure determination considering two propagation vectors k₁ and k₂ was carried out using the superspace formalism by building the corresponding (3+2)D model. The determination was based on the observation that the additional magnetic peaks emerge exclusively in the vicinity of the incommensurate magnetic peaks with propagation vector k₁, and not in the vicinity of nuclear peaks. This indicates that only mixed-index reflections were observed, and not reflections purely related to k₂. The magnetic superspace group (MSSG) that was determined is Amma.1' (0,β,0)00s0 (0,0,γ)ss0s. The structure can be described as a longitudinal amplitude-modulated structure, which itself is amplitude-modulated in a perpendicular direction. This represents a very unusual case of a 2-k magnetic structure with no symmetry relation between the propagation vectors.

High-pressure and low-temperature structural changes in the ferroelectric phase of (R)-3-quinuclidinol are analysed. The changes in unit-cell volume and parameters are continuous both on cooling and under increasing pressure. The anisotropy of the structural strain, however, is found to be different. At high pressures, the shortest possible distances for H...H contacts are achieved. Since the deformation along the polarization axis can be related to spontaneous polarization, different piezoelectric responses may be expected on cooling and under hydrostatic compression.

Drug polymorphism attracts considerable interest within the pharmaceutical field. Herein, we investigate the impact of low-concentration poly(ethylene oxide) (PEO) on the crystal growth of carbamazepine (CBZ) polymorphs in the glassy state. The addition of 3%(w/w) PEO increases 5.3-fold the bulk crystal growth rates of CBZ form III and 36.7-fold of form IV at 40°C (T_g -11°C). However, the same content of PEO exhibits a negligible effect on the bulk crystal growth of form I. In addition, the effects of PEO on the crystal growth of the CBZ polymorph at the free surface are also explored. In the presence of 3%(w/w) PEO, surface growth rates of forms III and IV of CBZ are accelerated by 4.7-fold and 3.1-fold, respectively. For comparison, the same content of PEO exhibits an unexpected inhibitory effect on the surface growth rates of form I. Molecular-dynamic simulations attribute these polymorph-dependent effects of PEO mainly to the polymer enrichment at the interface and different crystal surface polymer interactions. This study is relevant for understanding the crystallization of amorphous pharmaceutical solids containing polymorphic drugs.