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The massive technical and computational progress of biomolecular crystallography has generated some adverse side effects. Most crystal structure models, produced by crystallographers or well‐trained structural biologists, constitute useful sources of information, but occasional extreme outliers remind us that the process of structure determination is not fail‐safe. The occurrence of severe errors or gross misinterpretations raises fundamental questions: Why do such aberrations emerge in the first place? How did they evade the sophisticated validation procedures which often produce clear and dire warnings, and why were severe errors not noticed by the depositors themselves, their supervisors, referees and editors? Once detected, what can be done to either correct, improve or eliminate such models? How do incorrect models affect the underlying claims or biomedical hypotheses they were intended, but failed, to support? What is the long‐range effect of the propagation of such errors? And finally, what mechanisms can be envisioned to restore the validity of the scientific record and, if necessary, retract publications that are clearly invalidated by the lack of experimental evidence? We suggest that cognitive bias and flawed epistemology are likely at the root of the problem. By using examples from the published literature and from public repositories such as the Protein Data Bank, we provide case summaries to guide correction or improvement of structural models. When strong claims are unsustainable because of a deficient crystallographic model, removal of such a model and even retraction of the affected publication are necessary to restore the integrity of the scientific record. [ABSTRACT FROM AUTHOR]

A teaching tool is proposed to help beginner students of crystallography understand how crystallographic calculations work. Examples of the most important methods taught in X-ray crystallography courses have been adapted to a one-dimensional hypothetical structure. All calculations can be carried out in class with a scientific calculator or by using a simple spreadsheet. [ABSTRACT FROM AUTHOR]

Beamline X25 at the NSLS is one of the five beamlines dedicated to macromolecular crystallography operated by the Brookhaven National Laboratory Macromolecular Crystallography Research Resource group. This mini-gap insertion-device beamline has seen constant upgrades for the last seven years in order to achieve mini-beam capability down to 20 µm x 20 µm. All major components beginning with the radiation source, and continuing along the beamline and its experimental hutch, have changed to produce a state-ofthe- art facility for the scientific community. [ABSTRACT FROM AUTHOR]

For years, the community working on quasicrystals in many countries in the world was expecting the ultimate recognition of its contribution to the advancement of crystal chemistry, solid-state physics, mathematics, and other fields. Nearly thirty years after the initial discovery, it was finally awarded in October 2011 to Prof. Danny Shechtman by the Nobel Committee for Physics and Chemistry. Many, most often independent, achievements contributed to this success. The purpose of this article is to chronicle the role played by the applications of quasicrystals and related compounds in the development of the field and its financing by governmental institutions as well as private companies. Those applications, potential or realized, have made the field of quasicrystals comprehensible to the general public and to decision makers all over the world, including in Stockholm, in spite of its rather complicated high-dimensional crystallographic background, and in spite of the absolute opposition that a great chemist manifested against it in its infancy. [ABSTRACT FROM AUTHOR]

The article provides information on a study which described the ways in which BluIce was combined with Experimental Physics and Industrial Control System (EPICS) and converted into the Java-based JBluIce. The solutions aimed at streamlining and speeding up operations are described. An overview of the tools that are provided by the open-source control system for facilitating crystallographic experiments is presented. A review of the structure and functionality of EPICS and SSRL BluIce is given.

The article provides information on a study which investigated the polymorphic behavior of a mutant of the α-spectrin SH3 domain by means of two 1.1À resolution structures. The role of the availability of different polymorphic crystals in the determination of the structures in different crystal environments is discussed. Also presented is a study of the effect of the crystal contacts. The origin of polymorphic behaviour in proteins is noted.

The article provides information on a study which identified cinnamic acid derivatives as starting point for potent Pim-1 inhibitors. The fragment binders identified by the study's crystallographic fragment screen with Pim-1 are described. The results of the fragment-screening study are discussed. In addition, the binding modes of the cinnamic acid fragment hits are compared with the optimized-1 compounds originating from the high-throughput screen (HTS) approach.

The article discusses a research study on the multiwavelength anomalous diffraction (MAD) for macromolecular phasing at low resolution. Methodology of the study included crystallization where crystals were soaked in cryo-protectant solution and the single-crystal data sets were indexed then integrated by XDS technology solutions. Conclusions indicated the advantages of improved multi-crystal anomalous data in single anomalous diffraction (SAD) phasing including the ability of MAD to allow substructure determinations not seen in single-crystal data.

The article investigates the through-thickness variations of the crystallographic texture using the real-space and the Laplace-space methods. In utilizing the real-space method, the depth-resolution was achieved by a decoupled z translation of the sample relative to the gauge volume allowing a direct allocation of the measured diffraction signal. On the other hand, the Laplace-space method was used for the measurement of the texture depth distribution by the comparison of higher-order reflections.

The article discusses a birefringence imaging microscopic study of LiTaO3 and LiTaxNb1-xO3 crystals with near-zero birefringence at room temperature. It revealed that periodic self-organized birefringent stripes often formed in directions consistent with the type of cleavage planes in both types of crystal. It also showed that a microscopic strain influences the stabilization of the periodicity of these stripes.

Gallate dioxygenase (DesB) from Sphingobium sp. SYK-6, which belongs to the type II extradiol dioxygenase family, was purified and crystallized using the hanging-drop vapour-diffusion method. Two crystal forms were obtained. The form I crystal belonged to space group C2, with unit-cell parameters a = 136.2, b = 53.6, c = 55.1 Å, β = 112.8°, and diffracted to 1.6 Å resolution. The form II crystal belonged to space group P21, with unit-cell parameters a = 56.2, b = 64.7, c = 116.1 Å, β = 95.1°, and diffracted to 1.9 Å resolution. A molecular-replacement calculation using LigAB as a search model yielded a satisfactory solution for both crystal forms. [ABSTRACT FROM AUTHOR]

The article discusses the use of t-distributions in a probability plot to model real data more realistically. It defines probability plots as a tool in crystallography used to verify how the distribution of errors in a set of observed values visually compares with a general presumed error distribution. It suggests that the use of a Student's t-distribution in analyzing errors by means of a probability plot improves error modeling.

The article discusses the problem of a minimum tetrahedron in a three-dimensional lattice and its solution by lowering the number of bodies admitted by the minimum condition. It points to tetrahedron as the simplest three-dimensional body determined by the smallest possible number of quite arbitrary points. It provides a formula that suggests the possibility of thrice ambiguous minitetrahedra.

The article discusses the relationship of the properties of the hyperspherical harmonics with the analysis of crystallographic orientation information and the orientation distribution functions (ODF). It provides an addition theorem for the hyperspherical harmonics and an exact expressions for the matrices that determine the effect of rotations on the hyperspherical harmonics. It indicates a possible increase in the use of the hypersherical harmonic expansion for the crystallography community and the materials science community as a whole.

The X-ray analysis of (6R,7aS)-6-(tert-butyl-dimethylsilanyl- oxy)-1-hydroxy-2-phenyl-5,6,7,7a-tetrahydropyrrolizin-3-one, C19H27NO3Si, revealed a diffraction pattern which is typical for modulated structures: strong Bragg peaks surrounded by weaker reflections which cannot be indexed with the same three reciprocal lattice vectors that are used to describe the strong peaks. For this class of crystal structures the concept of superspace has been developed which, however, for many crystallographers still constitutes a Gordian Knot. As a possible tool to cut this knot the crystal structure of the above-mentioned tetrahydropyrrolizinone derivative is presented as an illustrative example for handling and describing the modulated structure of a typical pharmaceutical (i.e. molecular) compound. Having established a working knowledge of the concepts and terminology of the superspace approach a concise and detailed description of the complete process of peak indexing, data processing, structure solution and structure interpretation is presented for the incommen- surately modulated crystal structure of the above-mentioned compound. The superspace symmetry applied is P21(α0γ)0; the (incommensurate) q vector components at 100 K are α = 0.1422 (2) and γ = 0.3839 (8). [ABSTRACT FROM AUTHOR]

Chiral amino acids without functional groups in their side chains (hydrophobic amino acids) systematically form crystals with two molecules in the asymmetric unit. In contrast, racemates of the same compounds form crystals with Z′ = 1. The present investigation addresses the origin of this important difference between enantiomeric and racemic crystals. Through a series of ab initio calculations on infinite two-dimensional slabs, derived from crystal structures, as well as calculations on full crystal structures it is shown that it is indeed possible to explain the observed behaviour. Addition- ally, the (not unexpected) observation that amino acids usually form racemates in the solid phase rather than undergoing racemic separation upon crystallization is rationalized on the basis of energy calculations. [ABSTRACT FROM AUTHOR]

The drug benzocaine (ethyl 4-aminobenzoate), commonly used as a local anaesthetic, is a bimorphic solid at room temperature. Form (I) is monoclinic P21/c, while the metastable form (II) is orthorhombic P212121. Three-dimen- sional diffuse X-ray scattering data have been collected for the two forms on the 11-ID-B beamline at the Advanced Photon Source (APS). Both forms show strong and highly structured diffuse scattering. The data have been interpreted and analysed using Monte Carlo (MC) modelling on the basis that the scattering is purely thermal in origin and indicates the presence of highly correlated molecular motions. In both forms (I) and (II) broad diffuse streaks are observed in the 0kl section which indicate strong longitudinal displacement correlations between molecules in the ⟨031⟩ directions, extending over distances of up to 50 Å. Streaks extending between Bragg peaks in the hk0 section normal to [100] correspond to correlated motions of chains of molecules extending along a that are linked by N-H⋯O=C hydrogen bonds and which occur together as coplanar ribbon pairs. The main difference between the two forms is in the dynamical behaviour of the ribbon pairs and in particular how they are able to slide relative to each other. While for form (I) a model involving harmonic springs is able to describe the motion satisfactorily, as simple excursions away from the average structure, there is evidence in form (II) of anharmonic effects that are precursors of a phase transition to a new low- temperature phase, form (III), that was subsequently found. [ABSTRACT FROM AUTHOR]

Examination of the symmetric Hantzsch 1,4-dihydropyridine ester derivatives of the prototypical nifedipine molecule indicates the tendency of this class of molecule to form a common packing motif. Crystal structure analysis of 2,6- dimethyl-i,4-dihydropyridine-3,5-dicarboxylic diesters and analogs reveals that they form extended chains, characterized as the C(6) packing motif, via intermolecular (amine) N-H⋯O=C (C3,C5 carbonyl) hydrogen bonds. In addition, all the prepared derivatives also satisfy the basic structural requirements for their high binding efficiency to the receptor. The reproducible C(6) packing motif observed among these compounds has a use in the design of solid-state materials. [ABSTRACT FROM AUTHOR]

The electron density of monoclinic paracetamol was derived from high-resolution X-ray diffraction at 100 K. The Hansen-Coppens multipole model was used to refine the experimental electron density. The topologies of the electron density and the electrostatic potential were carefully analyzed. Numerical and analytical procedures were used to derive the charges integrated over the atomic basins. The highest charge magnitude (-1.2 e) was found for the N atom of the paracetamol molecule, which is in agreement with the observed nucleophilic attack occurring in the biological media. The electric field generated by the paracetamol molecule was used to calculate the atomic charges using the divergence theorem. This was simultaneously applied to estimate the total electrostatic force exerted on each atom of the molecule by using the Maxwell stress tensor. The interaction electrostatic energy of dimers of paracetamol in the crystal lattice was also estimated. [ABSTRACT FROM AUTHOR]

Reversed-phase chiral high-performance liquid chromatography (HPLC) is a potentially powerful technique for the enantiomeric resolution of racemic mixtures, although the elution order of enantiomers is only relative and it is necessary to fully characterize reference systems for this method to provide absolute configurational information. The enantiomeric resolution of a series of racemic di-spiro cyclotriphos- phazene derivatives, N3P3X2[O(CH2)3NH]2 (X = Cl, Ph, SPh, NHPh, OPh) [(1)-(5), respectively] was carried out by reversed-phase chiral HPLC on a commercially available Pirkle-type chiral stationary phase (R,R)-Whelk-01 using 85:15 (v/v) hexane-thf as the mobile phase. The absolute configurations of the resulting enantiomers of compounds (3) (X = SPh) and (5) (X = OPh) were determined unambiguously by X-ray crystallography. For both (3) and (5) it was found that the SS enantiomer eluted before the RR enantiomer, indicating a convenient method to determine the absolute configurations of enantiomers of this series of cyclophos- phazene derivatives and providing the first set of enantiomeric reference compounds for cyclophosphazene derivatives. These structures demonstrate an interesting anomaly in that the pair of enantiomers of (3) crystallize in enantiomorphically paired space groups whilst, under the same conditions, the solid-state forms of the enantiomers of (5) form structures in Sohncke space groups that are not enantiomorphous. [ABSTRACT FROM AUTHOR]

The title compound, [Ca(C4H4O6)]·4H2O, calcium tartrate tetrahydrate, is a new triclinic centrosymmetric form identified in rat kidney calculus. The crystal structure was determined from powder and single-crystal X-ray diffraction. The four water molecules belong to one square face of the Ca-atom coordination (a square antiprism), the four 0 atoms of the second square face coming from two tartrate anions, building infinite chains alternating Ca atom polyhedra and tartrate anions along a, with the chains cross-linked by a network of hydrogen bonds. [ABSTRACT FROM AUTHOR]

For SiBr4 no crystal structures have been reported yet. In this work the crystal structures of SiBr4 were predicted by global lattice-energy minimizations using force-field methods. Over an energy range of 5 kJ mol-1 above the global minimum ten possible structures were found. Two of these structures were experimentally determined from X-ray synchrotron powder diffraction data: The low-temperature β phase crystallizes in P21/c, the high-temperature a phase in Pa3¯. Temperature- dependant X-ray powder diffraction shows that the phase transition occurs at 168 K. [ABSTRACT FROM AUTHOR]

The crystal structure of Cu2(OH)3Cl has been determined using two natural samples with almost ideal stoichiometry. While one of the samples exhibits a twinned clinoatacamite structure, the other sample is characterized by the appearance of additional weak diffraction maxima at half integer positions of h and k. Structure refinement was carried out with the space group P1¯. The relationship between the triclinic phase, clinoatacamite, paratacamite and the herbertsmithite structure is discussed in terms of symmetry as a function of Cu concentration. [ABSTRACT FROM AUTHOR]

A combinatorial topological analysis is carried out by means of the program package TOPOS4.0 [Blatov (2006), IUCr Comput. Commun. Newsl. 7, 4-38] and the matrix self- assembly is modeled for crystal structures of the ZrZn22 family (space group Fd3¯m, Pearson code cF184), including the compounds with superstructural ordering. A number of strict rules are proposed to model the crystal structures of intermetallics as a network of cluster precursors. According to these rules the self-assembly of the ZrZn22-like structures was considered within the hierarchical scheme: primary polyhedral cluster → zero-dimensional nanocluster precursor → one-dimensional primary chain → two-dimensional microlayer → three-dimensional microframework (three-dimensional supraprecursor). The suprapolyhedral cluster precursor AB2X37 of diameter ∼ 12 Å and volume ∼350 ų consists of three polyhedra (one AX16 of the 4¯3m point symmetry and two regular icosahedra BX12 of the 3¯m point symmetry); the packing of the clusters determines the translations in the resulting crystal structure. A novel topological type of the two-dimensional crystal-forming 4,4-coordinated binodal net AB2, with the Schläfli symbols 3636 and 3366 for nodes A and B, is discovered. It is shown that the ZrZn22 superstructures are formed by substituting some atoms in the cluster precursors. Computer analysis of the CRYSTMET and ICSD databases shows that the cluster AB2X37 occurs in 111 intermetallics belonging to 28 structure types. [ABSTRACT FROM AUTHOR]

The weberite structure (A2B2X7) is an anion-deficient fluorite- related superstructure. Compared with fluorites, the reduction in the number of anions leads to a decrease in the coordination number of the B cations (VI coordination) with respect to the A cations (VIII coordination), thus allowing the accommodation of diverse cations. As a result, weberite compounds have a broad range of chemical and physical properties and great technological potential. This article summarizes the structural features of weberite and describes the structure in several different ways. This is the first time that the stacking vector and stacking angle are used to represent the weberite structure. This paper also discusses the crystallographic relationship between weberite, fluorite and pyrochlore (another fluorite-related structure). The cation sublattices of weberite and pyrochlore are correlated by an axial transformation. It has been shown that the different coordination environment of anions is due to the alternating layering of the AB3 and A3B close-packed cation layers. A stability field of weberite oxides is proposed in terms of the ratio of ionic radius of cations and relative bond ionicity. In addition, a selection of weberite compounds with interesting properties is discussed. [ABSTRACT FROM AUTHOR]

Accurate measurement of photon flux from an X-ray source, a parameter required to calculate the dose absorbed by the sample, is not yet routinely available at macromolecular crystallography beamlines. The development of a model for determining the photon flux incident on pin diodes is described here, and has been tested on the macromolecular crystallography beamlines at both the Swiss Light Source, Villigen, Switzerland, and the Advanced Light Source, Berkeley, USA, at energies between 4 and 18 keV. These experiments have shown that a simple model based on energy deposition in silicon is sufficient for determining the flux incident on high-quality silicon pin diodes. The derivation and validation of this model is presented, and a web-based tool for the use of the macromolecular crystallography and wider synchrotron community is introduced. [ABSTRACT FROM AUTHOR]

We quantitatively evaluated the effects of elevated concentration of ozone (O3) on growth, leaf chemistry, gas exchange, grain yield, and grain quality relative to carbon-filtered air (CF) by means of meta-analysis of published data. Our database consisted of 53 peer-reviewed studies published between 1980 and 2007, taking into account wheat type, O3 fumigation method, rooting environment, O3 concentration ([O3]), developmental stage, and additional treatments such as drought and elevated carbon dioxide concentration ([CO2]). The results suggested that elevated [O3] decreased wheat grain yield by 29% (CI: 24–34%) and aboveground biomass by 18% (CI: 13–24%), where CI is the 95% confidence interval. Even in studies where the [O3] range was between 31 and 59 ppb (average 43 ppb), there was a significant decrease in the grain yield (18%) and biomass (16%) relative to CF. Despite the increase in the grain protein content (6.8%), elevated [O3] significantly decreased the grain protein yield (−18%). Relative to CF, elevated [O3] significantly decreased photosynthetic rates (−20%), Rubisco activity (−19%), stomatal conductance (−22%), and chlorophyll content (−40%). For the whole plant, rising [O3] induced a larger decrease in belowground (−27%) biomass than in aboveground (−18%) biomass. There was no significant response difference between spring wheat and winter wheat. Wheat grown in the field showed larger decreases in leaf photosynthesis parameters than wheat grown in < 5 L pots. Open-top chamber fumigation induced a larger reduction than indoor growth chambers, when plants were exposed to elevated [O3]. The detrimental effect was progressively greater as the average daily [O3] increased, with very few exceptions. The impact of O3 increased with developmental stages, with the largest detrimental impact during grain filling. Both drought and elevated [CO2] significantly ameliorated the detrimental effects of elevated [O3], which could be explained by a significant decrease in O3 uptake resulting from decreased stomatal conductance. [ABSTRACT FROM AUTHOR]

This paper describes a method about the crystal shape control improving the antitumor activity of tumor necrosis factorrelated apoptosisinducing ligand Apo2LTRAIL in a batch cooling suspension crystallization by selecting pH values as a controllable variable. Three shaped TRAIL crystals could be obtained under different pH conditions, among which the hexagonal plate crystals had the highest specific activities against tumor cell line. The relationship among pH values, trimer contents and the specific activities of crystals and the purified TRAIL solutions were investigated. The results showed that different trimer contents resulted from pH altering in crystals and protein solutions is a main reason for their different specific activities. The studies may supply a new method to improve the bioactivity of TRAIL agent during its production and storage. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim [ABSTRACT FROM AUTHOR]

KDP crystals were rapidly grown from solution doped with different Ba2concentrations. The effects of Ba2on the growth rate, morphology and quality of KDP crystals were discussed. Significant changes in shapes and volume of the grown crystals have been observed. During the growth process, defect region expands gradually with the increasing Ba2concentration. Samples were cut from different parts of the asgrown crystals for investigating the optical quality, including transmission spectrum, scattering centers. Through comparison, it is found that the nonuniform distribution of Ba2ions causes remarkable difference in optical quality between prismatic and pyramidal sectors. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim [ABSTRACT FROM AUTHOR]

Larginine hydrochloride monohydrate LAHCl.H2O has been synthesized and single crystals have been grown from its aqueous solution by slow evaporation and slow cooling methods. The solubility of the material was measured at various temperatures and bulk crystals of size 26×13×11 mm3have been grown by optimizing the growth parameters. The grown crystals have been subjected to single crystal XRD studies to confirm the structure and to estimate the lattice parameters. FTIR analysis indicate the mode of vibrations of different molecular groups present in LAHCl and confirm the protonation of guanidyl, amino groups and deprotonation of COOgroups. UVVis transmission spectrum revealed the linear optical properties of the grown crystals with a transparency of 65 over the entire visible range upto 300 nm. Thermal behavior of the grown crystal was investigated from DTA and TGA measurements. Dielectric studies have been carried out on the grown crystals. Kurtz and Perry powder SHG technique confirms the NLO property of the grown crystal. The SHG efficiency of LAHCl was found to be 0.38 with respect to KDP. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim [ABSTRACT FROM AUTHOR]

The article examines the anisotropic shrinkage of injection molded Poly Vinylidene Fluoride (PVDF) samples. The section analyzes the anisotropic shrinkage of injection molded PVDF samples using a thermomechanical model for shrinkage, which can keep into account anisotropy in material properties. The material was injected into a simple rectangular cavity under different holding pressures, and the dimensions of the resulting samples were accurately measured at room temperature 10 minutes after demolding.

Crystallographic orientations of Y–Ba–Cu–O (YBCO) and embedded Y2Ba4CuMO x (M=Nb, Zr, Ag) nanoparticles in bulk, melt-textured YBCO samples are studied by electron backscatter diffraction. Y2BaCuO5 particles exhibit no preferred orientation but have a strong negative influence on the matrix orientation. In contrast, the nanoparticles do not disturb the texture of the YBCO matrix. Depending on the preparation route, a different particle orientation with respect to the matrix is obtained. Untextured nanoparticles are formed by solid-state reaction during the melt process by adding oxides (Nb2O5 or Y2O3) to the precursor powder. Preformed Y2Ba4CuMO x particles added to the precursor in the form of prereacted nanopowder exhibit a dominant single orientation related to the surrounding YBCO matrix. [ABSTRACT FROM AUTHOR]

Interfaces in LaB6–ZrB2 composites directionally solidified by a zone melting process were characterized by transmission electron microscopy (TEM). The nominal crystallographic orientation relationship between the two phases corresponded to a high-symmetry near-coincidence site lattice (NCSL). The small mistilt (2°–5°) from the high-symmetry orientation relationship was shown to result in an increased volume density of coincident sites. Furthermore, the dominant interface facet planes were predicted by the NCSL model. The configurations of interfacial misfit dislocations were analyzed by high-resolution TEM and showed a good agreement with predictions based on the displacement shift complete lattice and secondary original lattice (O2-lattice) models. These analyses suggested that interfaces were relaxed to relatively low-energy configurations. [ABSTRACT FROM AUTHOR]

A sizeable proportion of structures with Z′ = 2 are thought to exhibit pseudosymmetry, but establishing the extent of the deviation from true symmetry is problematic. By considering both the conformational similarity between the independent molecules and the way in which they are related in space, assessment of the pseudosymmetry of a structure becomes possible. A method of matching two groups of atoms where both these factors are quantified using CRYSTALS [Betteridge, Carruthers, Cooper, Prout & Watkin (2003). J. Appl. Cryst. 36, 1487] is described. [ABSTRACT FROM AUTHOR]

The structure of a newly crystallized form of the copper-dependent amine oxidase from pea seedlings has been refined at a resolution of 2.2 Å to a final R factor of 0.181. The structure (form II) was originally discovered during a study of xenon binding to copper-dependent amine oxidases as a probe for dioxygen-binding sites [Duff et al. (2004), J. Mol. Biol. 344, 599–607]. The form II crystals belong to space group P21, with two dimers in the asymmetric unit. The overall structure is very similar to the crystals of form I in space group P212121 with a dimer in the asymmetric unit [Kumar et al. (1996), Structure, 4, 943–955]. In form I the last three residues (644–647) observable in the two subunits were apparently splayed apart. It was noted that the absence of a disulfide bond between the Cys647 residues of the two subunits was inconsistent with chemical evidence for the absence of free sulfhydryl groups. In both of the crystallographically independent dimers of form II the two subunits are clearly joined by a disulfide bridge between the C-terminal cysteine residues. This is only possible if the two polypeptide chains in the dimer adopt different conformations near the C-terminus so that the twofold symmetry is lost. A proline residue (645) two residues before the cysteine has a cis conformation in one chain and a trans conformation in the other. As a result, the disulfide bond lies more than 5 Å from the twofold axis. The loss of local twofold symmetry in form II can be explained by intermolecular contacts, which provide an asymmetric environment. [ABSTRACT FROM AUTHOR]

A recent study by high-resolution neutron powder diffraction provided accurate crystallographic information for the newly developed ferromagnetic shape memory alloy 53 at.%Ni–25 at.%Mn–22 at.%Ga. This made it possible to study by high-resolution electron backscatter diffraction the local microstructures and the twinning relationships between martensitic variants. The twin interfaces were also investigated and they are found to be coherent on the {112} planes. [ABSTRACT FROM AUTHOR]

The wide-angle scattering of X-rays (WAXS) by anisotropic powders of nano-layered crystallites (nano-stacks) is addressed. Assuming that the orientation distribution probability function f of the nano-stacks only depends on the deviation of the crystallites' orientation from a fixed reference direction, a relation providing f from the dependence of a given diffraction peak's amplitude on the azimuthal angle is derived. The method is applied to two systems of sodium fluorohectorite (NaFH) clay particles, using synchrotron radiation and a WAXS setup with a two-dimensional detector. In the first system, which consists of dry-pressed NaFH samples, the orientation distribution probability function corresponds to a classical uniaxial nematic order. The second system is observed in bundles of polarized NaFH particles in silicon oil; in this case, the nano-stacks have their directors, on average, in a plane normal to the reference direction, and f is a function of the angle between a nano-stack's director and that of the plane. In both cases, a suitable Maier–Saupe function is obtained for the distributions, and the reference direction is determined with respect to the laboratory frame. The method only requires one scattering image. Consistency can be checked by determining the orientation distribution from several diffraction peaks independently. [ABSTRACT FROM AUTHOR]

The volcanic exhalation product chlorartinite, [Mg2(CO3)(H2O)(OH)]Cl·H2O, has recently been found to be a minor, and in some samples a major, component of magnesia floors for industrial use. In order to be able to perform quantitative phase analysis using the Rietveld method, its crystal structure was determined from high-resolution synchrotron powder diffraction data by the global optimization technique of simulated annealing and Rietveld refinement. The final Rp and Rwp values are 5.23% and 6.56%, respectively. Chlorartinite crystallizes in the rhombohedral space group R3 c (No. 161), with a = 23.14422 (16) Å, c = 7.22333 (5) Å, V = 3350.84 (5) Å3, Z = 18. The building units of chlorartinite consist of MgO6 octahedra forming 15-membered puckered rings which are interconnected by CO3 triangular moieties. The rings are stacked to form a honeycomb-like three-dimensional framework structure with large isolated channels. Within the channels, free chlorine atoms and disordered water molecules are located. [ABSTRACT FROM AUTHOR]

SXD, the single-crystal diffractometer at the ISIS spallation neutron source, uses an array of two-dimensional position-sensitive detectors and the neutron time-of-flight technique to measure diffraction data throughout very large volumes of reciprocal space for each fixed orientation of a single-crystal sample. This paper describes SXD in detail, following major improvements to the instrument. Particular emphasis is placed on the range of science possible, using recent results as examples, and the opportunities for future experiments. [ABSTRACT FROM AUTHOR]

The crystal structure of monoclinic KLu(WO4)2 (KLuW) crystals was determined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters were a = 10.576 (7), b = 10.214 (7), c = 7.487 (2) Å, β = 130.68 (4)°, with Z = 4, in space group C2/ c. The unit-cell parameters of KLu1− xYb x(WO4)2 were determined in relation to Yb concentration. Vickers micro-indentations were used to study the microhardness of KLuW. The linear thermal expansion tensor was determined and the principal axis with maximum thermal expansion ( = 16.72 × 10−6 K−1), , was located 13.51° from the c axis. The room-temperature optical tensor was studied in the near-infrared (NIR) and visible range. The principal optical axis with maximum refractive index ( ng = 2.113), Ng, was located 18.5° from the c axis at 632.8 nm. Undoped and ytterbium-doped KLuW crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, { }, {010} and {310} faces that basically constitue the habit of the KLuW crystals. [ABSTRACT FROM AUTHOR]

The Box Model of crystal packing describes unit cells in terms of a limited number of arrangements of molecular building blocks. An analysis of Z′≤ 1 structures has shown that cell dimensions are related to molecular dimensions in a systematic way and that the spatial arrangement of molecules in crystal structures is very similar, irrespective of Z or space group. In this paper it is shown that the spatial arrangement of molecules in Z′ = 2 structures are, within the context of the Box Model, very similar to that found for Z′≤ 1 structures. The absence of crystallographic symmetry does not appear to affect correlations between molecular dimensions and cell dimensions, or between the packing patterns and the positions of molecules in the unit cell, established from the analysis of Z′≤ 1 structures. The preference shown by Z′ = 2 structures for low surface-area packing patterns and the observation that strong energetic interactions are most often found between the large faces of the independent molecules reaffirms the importance of molecular shape in crystal packing. [ABSTRACT FROM AUTHOR]

The crystal structure of monoclinic KLu(WO4)2 (KLuW) crystals was determined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters were a = 10.576 (7), b = 10.214 (7), c = 7.487 (2) Å, β = 130.68 (4)°, with Z = 4, in space group C2/ c. The unit-cell parameters of KLu1− xYb x(WO4)2 were determined in relation to Yb concentration. Vickers micro-indentations were used to study the microhardness of KLuW. The linear thermal expansion tensor was determined and the principal axis with maximum thermal expansion ( = 16.72 × 10−6 K−1), , was located 13.51° from the c axis. The room-temperature optical tensor was studied in the near-infrared (NIR) and visible range. The principal optical axis with maximum refractive index ( ng = 2.113), Ng, was located 18.5° from the c axis at 632.8 nm. Undoped and ytterbium-doped KLuW crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, { }, {010} and {310} faces that basically constitue the habit of the KLuW crystals. [ABSTRACT FROM AUTHOR]

In this article, a number of the results relevant to the concept of sublattices of a basic crystallographic lattice are reviewed, emphasizing particularly previously unpublished work on the algebraic aspects. A three-dimensional geometric lattice L can be considered as an infinite Abelian group under addition. A sublattice S of L, which is also three-dimensional, is a subgroup of L such that the finite quotient group, is an Abelian group of order the index of S in L. The sublattice itself in its standard form is represented by an upper triangular matrix. The index of the sublattice is given by the determinant of this matrix. It is first noted that a sublattice described by an arbitrary basis set in L may be converted to this standard form. Next the sublattice is expressed as the intersection of a set of sublattices of individual index a power of a distinct prime, i.e. where p1, p2 etc. are prime numbers and is the Euclidean factorization of n. This decomposition is important because it corresponds to the Sylow decomposition of the corresponding quotient group It is also useful to be able to carry out two commutative binary operations on sublattices of L; these are to find their common sublattice of lowest index in L, which is their intersection and their common superlattice of highest index in L, given by where <> indicates the span of the sublattices. [ABSTRACT FROM AUTHOR]

The structure of the coincidence symmetry group of an arbitrary -dimensional lattice in the -dimensional Euclidean space is considered by describing a set of generators. Particular attention is given to the coincidence isometry subgroup (the subgroup formed by those coincidence symmetries that are elements of the orthogonal group). Conditions under which the coincidence isometry group can be generated by reflections defined by vectors of the lattice are discussed and an algorithm to decompose an arbitrary element of the coincidence isometry group in terms of reflections defined by vectors of the lattice is given. [ABSTRACT FROM AUTHOR]

Quartz aggregates that formed by coalescence of quartz crystals in the magma or in hydrothermal solution are considered. If the individuals have rhombohedral faces in contact, there will be two special cases: parallel intergrowths and intergrowths that agree in orientation and contact plane with Esterel twins grown from a twinned nucleus. For all other known cases, i.e. when the relative orientation satisfies the Japan, Sardinian, Tiflis, Zyndel-A or Samshvildo law, both individuals have exactly coinciding short symmetry translations in only one direction in the contact plane (monoperiodic twins). If a rhombohedral face is in contact with a prism face, monoperiodic twins will occur if the relative orientation satisfies the Zinnwald, Disentis or a proposed hypothetic law. The orientation of the two lattices can be expressed by a 180° rotation about an axis with low indices independent of c/ a in the case of the Esterel, Japan and Sardinian laws. The same is true for the Tiflis and Zyndel-A laws only if they are redefined, and not at all in the case of the Samshvildo, Zinnwald, Disentis and hypothetic laws. When the two individuals have rhombohedral faces in contact, there will even be exact two-dimensional coincidence (multiplicity σ) in the contact plane and exact three-dimensional coincidence (multiplicity Σ) in space if the square of the axial ratio c/ a is rational. Indications are found that (despite their high values) these multiplicities may be related to the frequency of occurrence of intergrowths in low- and high-quartz. [ABSTRACT FROM AUTHOR]

The system of Hermann–Mauguin symbols for space and subperiodic Euclidean groups in two and three dimensions is extended to groups with continuous and semicontinuous translation subgroups (lattices). An interpretation of these symbols is proposed in which each symbol defines a quite specific Euclidean group with reference to a crystallographic basis, including the location of the group in space. Symbols of subperiodic (layer and rod) groups are strongly correlated with symbols of decomposable space groups on the basis of the factorization theorem. Introduction of groups with continuous and semicon­tinuous lattices is connected with a proposal for several new terms that describe the properties of these groups and with a proposal to amend the meaning of space groups and of crystallographic groups. Charts of plane, layer and space groups describe variants of these groups with the same reducible point group but various types of lattices. Examples of such charts are given for plane, layer and space groups to illustrate the unification principle for groups with decomposable lattices. [ABSTRACT FROM AUTHOR]

This article is a roadmap to a systematic calculation and tabulation of tensorial covariants for the point groups of material physics. The following are the essential steps in the described approach to tensor calculus. (i) An exact specification of the considered point groups by their embellished Hermann–Mauguin and Schoenflies symbols. (ii) Introduction of oriented Laue classes of magnetic point groups. (iii) An exact specification of matrix ireps (irreducible representations). (iv) Introduction of so-called typical (standard) bases and variables – typical invariants, relative invariants or components of the typical covariants. (v) Introduction of Clebsch–Gordan products of the typical variables. (vi) Calculation of tensorial covariants of ascending ranks with consecutive use of tables of Clebsch–Gordan products. (vii) Opechowski's magic relations between tensorial decompositions. These steps are illustrated for groups of the tetragonal oriented Laue class D4 z− 4 z2 x2 xy of magnetic point groups and for tensors up to fourth rank. [ABSTRACT FROM AUTHOR]

The theory of domain states is reviewed as a prerequisite for consideration of tensorial distinction of domain states. It is then shown that the parameters of the first domain in a ferroic phase transition from a set of isomorphic groups of the same oriented Laue class can be systematically and suitably represented in terms of typical variables. On replacing these variables by actual tensor components according to the previous paper [Kopský (2006), Acta Cryst. A 62, ], we can reveal the tensorial parameters associated with each particular symmetry descent. Parameters are distinguished by the ireps to which they belong and this can be used to determine which of them are the principal parameters that distinguish all domain states, in contrast to secondary parameters which are common to several domain states. In general, the parameters are expressed as the covariant components of the tensors. A general procedure is described which is designed to transform the results to Cartesian components. It consists of two parts: the first, called the labelling of covariants, and its inverse, called the conversion equations. Transformation of parameters from the first domain state to other states is now reduced to irreducible subspaces whose maximal dimension is three in contrast with higher dimensions of tensor spaces. With this method, we can explicitly calculate tensor parameters for all domain states. To find the distinction of pairs of domain states, it is suitable to use the concept of the twinning group which is briefly described. [ABSTRACT FROM AUTHOR]

The Bilbao Crystallographic Server is a web site with crystallographic programs and databases freely available on-line ( ). The server gives access to general information related to crystallographic symmetry groups (generators, general and special positions, maximal subgroups, Brillouin zones etc.). Apart from the simple tools for retrieving the stored data, there are programs for the analysis of group–subgroup relations between space groups (subgroups and supergroups, Wyckoff-position splitting schemes etc.). There are also software packages studying specific problems of solid-state physics, structural chemistry and crystallography. This article reports on the programs treating representations of point and space groups. There are tools for the construction of irreducible representations, for the study of the correlations between representations of group–subgroup pairs of space groups and for the decompositions of Kronecker products of representations. [ABSTRACT FROM AUTHOR]