Full Crystal Structure Research Articles

Structure and Chemical Analysis of Major Specialized Metabolites Produced by the Lichen Evernia prunastri.

We performed comparative profiling of four specialized metabolites in the lichen Evernia prunastri, collected at three different geographic locations, California and Maine, USA, and Yoshkar Ola, Mari El, Russia. Among the compounds produced at high concentrations that were identified in all three specimens, evernic acid, usnic acid, lecanoric acid and chloroatranorin, evernic acid was the most abundant. Two depsidones, salazinic acid and physodic acid, were detected in the Yoshkar-Ola collection only. The crystalline structure of evernic acid (2-hydroxy-4-[(2-hydroxy-4-methoxy-6-methylbenzoyl)oxy]-6-methylbenzoate) (hmb) revealed two crystallographically and conformationally distinct hmb anions, along with two monovalent sodium atoms. One hmb moiety contained an exotetradentate binding mode to sodium, whereas the other exhibited an exohexadentate binding mode to sodium. Embedded edge-sharing {Na2 O8 }n sodium-oxygen chains connected the hmb anions into the full three-dimensional crystal structure of the title compound. The crystal used for single-crystal X-ray diffraction exhibited non-merohedral twinning. The data suggest the importance of the acetyl-polymalonyl pathway products to processes of maintaining integrity of the lichen holobiont community.

Periodic density functional theory study of the Raman spectrum of the hydrated uranyl oxyhydroxide mineral becquerelite

Raman spectroscopy is one of the main analytic techniques used to identify uranyl-containing minerals. However, the assignment of the Raman spectra of these minerals is usually performed by using empirical arguments leading to unreliable assignments. In this paper, the Raman spectrum of the hydrated uranyl oxyhydroxide mineral becquerelite, $${\text{Ca}}\left( {{\text{UO}}_{2} } \right)_{6} {\text{O}}_{4} \left( {\text{OH}} \right)_{6} \cdot 8{\text{H}}_{2} {\text{O}}$$ , was studied by means of rigorous theoretical solid-state calculations. The computations were carried out using periodic density functional theory with plane waves and pseudopotentials. The theoretical determination of this Raman spectrum was possible due to the previous development of a high-quality norm-conserving relativistic pseudopotential specific for the uranium atom and the recent optimization of the full crystal structure of this mineral, including the position of all hydrogen atoms in the corresponding unit cell. These two pieces of knowledge were formerly used in order to study the structural, mechanical, and thermodynamic properties of this mineral, but due to the very large size of the unit cell, the determination of the vibrational spectra was not possible. The corresponding results for the Raman spectrum, resulting from an intensive computational work, are reported here. The calculated Raman spectrum was compared with the experimental spectrum, and the results were found to be in very good agreement. Therefore, a normal mode analysis of the theoretical spectra was performed to assign the main bands of the Raman spectrum. This assignment improved significantly the current empirical assignment of the bands of the Raman spectrum of becquerelite mineral.

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite.

The full crystal structure of the copper-uranyl tetrahydroxide mineral (vandenbrandeite), including the positions of the hydrogen atoms, is established by the first time from X-ray diffraction data taken from a natural crystal sample from the Musonoi Mine, Katanga Province, Democratic Republic of Congo. The structure is verified using first-principles solid-state methods. From the optimized structure, the mechanical and dynamical stability of vandenbrandeite is studied and a rich set of mechanical properties are determined. The Raman spectrum is recorded from the natural sample and determined theoretically. Since both spectra have a high-degree of consistence, all spectral bands are rigorously assigned using a theoretical normal-coordinate analysis. Two bands in the Raman spectra, located at 2327 and 1604 cm−1, are recognized as overtones and a band at 1554 cm−1 is identified as a combination band. The fundamental thermodynamic functions of vandenbrandeite are computed as a function of temperature using phonon calculations. These properties, unknown so far, are key-parameters for the performance-assessment of geological repositories for storage of radioactive nuclear waste and for understanding the paragenetic sequence of minerals arising from the corrosion of uranium deposits. The thermodynamic functions are used here to determine the thermodynamic properties of formation of vandenbrandeite in terms of the elements and the Gibbs free-energies and reaction constants for a series of reactions involving vandenbrandeite and a representative subset of the most important secondary phases of spent nuclear fuel. Finally, from the thermodynamic data of these reactions, the relative stability of vandenbrandeite with respect to these phases as a function of temperature and in the presence of hydrogen peroxide is evaluated. Vandenbrandeite is shown to be highly stable under the simultaneous presence of water and hydrogen peroxide.

Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography.

A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR, and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, whereas thermally activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature 13 C NMR data reveal evidence for solid-state dynamics, which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen bond involving the pyridine ring and an adjacent imine carbon, which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.

Indexing of grazing-incidence X-ray diffraction patterns: the case of fibre-textured thin films.

Crystal structure solutions from thin films are often performed by grazing-incidence X-ray diffraction (GIXD) experiments. In particular, on isotropic substrates the thin film crystallites grow in a fibre texture showing a well defined crystallographic plane oriented parallel to the substrate surface with random in-plane order of the microcrystallites forming the film. In the present work, analytical mathematical expressions are derived for indexing experimental diffraction patterns, a highly challenging task which hitherto mainly relied on trial-and-error approaches. The six lattice constants a, b, c, α, β and γ of the crystallographic unit cell are thereby determined, as well as the rotation parameters due to the unknown preferred orientation of the crystals with respect to the substrate surface. The mathematical analysis exploits a combination of GIXD data and information acquired by the specular X-ray diffraction. The presence of a sole specular diffraction peak series reveals fibre-textured growth with a crystallographic plane parallel to the substrate, which allows establishment of the Miller indices u, v and w as the rotation parameters. Mathematical expressions are derived which reduce the system of unknown parameters from the three- to the two-dimensional space. Thus, in the first part of the indexing routine, the integers u and v as well as the Laue indices h and k of the experimentally observed diffraction peaks are assigned by systematically varying the integer variables, and by calculating the three lattice parameters a, b and γ. Because of the symmetry of the derived equations, determining the missing parameters then becomes feasible: (i) w of the surface parallel plane, (ii) the Laue indices l of the diffraction peak and (iii) analogously the lattice constants c, α and ß. In a subsequent step, the reduced unit-cell geometry can be identified. Finally, the methodology is demonstrated by application to an example, indexing the diffraction pattern of a thin film of the organic semiconductor pentacenequinone grown on the (0001) surface of highly oriented pyrolytic graphite. The preferred orientation of the crystallites, the lattice constants of the triclinic unit cell and finally, by molecular modelling, the full crystal structure solution of the as-yet-unknown polymorph of pentacenequinone are determined.

Selectively Modulating Conformational States of USP7 Catalytic Domain for Activation

Ubiquitin-specific protease 7 (USP7) deubiquitinase activity is controlled by a number of regulatory factors, including stimulation by intramolecular accessory domains. Alone, the USP7 catalytic domain (USP7cd) shows limited activity and apo USP7cd crystal structures reveal a disrupted catalytic triad. By contrast, ubiquitin-conjugated USP7cd structures demonstrate the canonical cysteine protease active-site geometry; however, the structural features of the USP7cd that stabilize the inactive conformation and the mechanism of transition between inactive and active states remain unclear. Here we use comparative structural analyses, molecular dynamics simulations, and in silico sequence re-engineering via directed sampling by RosettaDesign toidentify key molecular determinants of USP7cd activation and successfully engineer USP7cd for improved activity. Full kinetic analysis and multiple X-ray crystal structures of our designs indicate that electrostatic interactions in the distal "switching loop" region and local packing in the hydrophobic core mediate subtle but significant conformational changes that modulate USP7cd activation.

Crystal Structure, Stability, and Physical Properties of Metastable Electron-Poor Narrow-Gap AlGe Semiconductor.

We report for the first time the full crystal structure, the electronic structure, the lattice dynamics, and the elastic constants of metastable monoclinic AlGe. In addition to ultrarapid cooling techniques such as melt spinning, we show the possibility of obtaining monoclinic AlGe by water-quenching in a quartz tube. Monoclinic AlGe and rhombohedral Al6Ge5 are competing phases with similar stability since they both begin to decompose above 230 °C. The crystal structure and electronic bonding of monoclinic AlGe are similar to those of ZnSb and comply with its 3.5 valence electrons per atom: besides classical two electron-two center Al-Ge and Ge-Ge covalent bonds, Al2Ge2 parallelogram rings are formed by uncommon multicenter bonds. Monoclinic AlGe could be used in various applications since it is found theoretically to be an electron-poor semiconductor with a narrow indirect energy bandgap of about 0.5 eV. The lattice dynamics calculations show the presence of low energy optical phonons, which should lead to a low thermal conductivity.

Verbeekite, the Long-Unknown Crystal Structure of Monoclinic PdSe2

Verbeekite, a monoclinic polymorph of PdSe2, was reported for the first time in 2002 by Roberts et al. The mineral has been discovered in the Musonoi Cu-Co-Mn-U mine, Democratic Republic of Congo, and was named after Dr. Théodore Verbeek, the first geoscientist who studied the palladium mineralization there (1955-1967). Until today, the crystal structure of this very rare mineral has been unknown. By syntheses via multianvil high-pressure/high-temperature methods at 11.5 GPa and 1300 °C, synthetic verbeekite could be obtained in a high degree of purity and comparatively good crystal quality, which made it possible to determine the full crystal structure for PdSe2 verbeekite from single-crystal X-ray diffractometer data: I2/a, a = 671.0(2) pm, b = 415.42(8) pm, c = 891.4(2) pm, β = 92.42(3)°, V = 248.24(4) Å3, R1 = 0.0368, wR2 = 0.0907 (all data). In contrast to layered PdS2-type PdSe2, verbeekite exhibits a novel crystal structure type of dichalcogenides of the platinum-group metals with (Se2)2- dimer anions connecting the layers. The possibility of different arrangements of the characteristic (Se2)2- dumbbells is the reason for the various polymorphs of the dichalcogenides, with now five known PdSe2 representatives.

Single-crystal X-ray diffraction and NMR crystallography of a 1:1 cocrystal of dithianon and pyrimethanil.

A single-crystal X-ray diffraction structure of a 1:1 cocrystal of two fungicides, namely dithianon (DI) and pyrimethanil (PM), is reported [systematic name: 5,10-dioxo-5H,10H-naphtho[2,3-b][1,4]dithiine-2,3-dicarbonitrile-4,6-dimethyl-N-phenylpyrimidin-2-amine (1/1), C14H4N2O2S2·C12H13N2]. Following an NMR crystallography approach, experimental solid-state magic angle spinning (MAS) NMR spectra are presented together with GIPAW (gauge-including projector augmented wave) calculations of NMR chemical shieldings. Specifically, experimental 1H and 13C chemical shifts are determined from two-dimensional 1H-13C MAS NMR correlation spectra recorded with short and longer contact times so as to probe one-bond C-H connectivities and longer-range C...H proximities, whereas H...H proximities are identified in a 1H double-quantum (DQ) MAS NMR spectrum. The performing of separate GIPAW calculations for the full periodic crystal structure and for isolated molecules allows the determination of the change in chemical shift upon going from an isolated molecule to the full crystal structure. For the 1H NMR chemical shifts, changes of 3.6 and 2.0 ppm correspond to intermolecular N-H...O and C-H...O hydrogen bonding, while changes of -2.7 and -1.5 ppm are due to ring current effects associated with C-H...π interactions. Even though there is a close intermolecular S...O distance of 3.10 Å, it is of note that the molecule-to-crystal chemical shifts for the involved sulfur or oxygen nuclei are small.

Simulations of Bama in a Native Outer-Membrane Model and Energetics of Lateral Opening

Gram-negative bacteria possess two cell membranes. The outer membrane is host to almost exclusively β-barrel transmembrane proteins. The β-barrel assembly machinery (BAM) is a five-protein complex responsible for the insertion and assembly of outer membrane β-barrel proteins. The first crystal structures of the transmembrane β-barrel domain of BamA were released in 2013. In these initial crystal structures, the BamA β-barrel possessed a weak interface between its first (1) and last (16) β strands, which led to strand separation within 1 μs in our equilibrium simulations. This strand separation has been proposed to act as a lateral gate for substrate passage into the membrane. In addition, a hydrophobic mismatch near the barrel seam was shown to destabilize the membrane, potentially acting to aid integration of the substrate. Furthermore, full BAM complex crystal structures were recently released, showing accessory proteins rallying around this putative insertion region using the periplasmic domains of BamA as a scaffold. In order to address remaining questions surrounding the role that BamA plays in the insertion and assembly process, we have carried out additional equilibrium simulations of BamA in several membrane bilayers. We also performed a calculation of energetic landscapes associated with lateral gate formation under various conditions. These calculations reveal a lower energetic barrier to strand separation for BamA as compared to FhaC, a member of the same (Omp85) family. They also reveal a significant role played by the C-terminal kink feature in modulating the barrier to strand separation. Finally, equilibrium simulations of NgBamA demonstrate lateral gate opening at 340K in a native lipopolysaccharide bilayer for the first time.

Dynamic versus Static Character of the Magnetic Jahn-Teller Effect: Magnetostructural Studies of [Fe3O(O2CPh)6(py)3]ClO4·py.

Complex [Fe3O(O2CPh)6(py)3]ClO4·py (1) crystallizes in the hexagonal P63/m space group, and its cation exhibits a crystallographically imposed D3h symmetry due to a C3 axis passing through the oxide of its {Fe3O}7+ core. Single-crystal unit-cell studies carried out with synchrotron radiation confirmed that this symmetry is retained down to 4.5 K; a full crystal structure determination carried out at 90 K resolved the previously reported disorder of the perchlorate anion. Magnetic susceptibility and electron paramagnetic resonance (EPR) data for complex 1 were interpreted with a model considering the retention of the threefold crystallographic symmetry while predicting a lowering of the magnetic symmetry. This model considered the effects of atomic vibrations of the central oxide on the magnetic properties of the complex by incorporating these movements into the spin Hamiltonian through angular overlap considerations of the atomic orbitals; no ad hoc magnetic Jahn-Teller effect was considered. The derived magnetostructural correlations achieved an improvement in the interpretation of the magnetic susceptibility data using the same number of free variables. They also improved the simulations of the EPR data, which exhibit a complicated set of at least five axial resonances; improved simulations were achieved using only two spectral components. Due to the thermal effects on the oxide vibrations, the model predicts a temperature dependence of the magnetic coupling J, which should not be viewed as a constant but as a variable.

Antisoma Application: A Fully Integrated V-Like Antibodies Platform

Antibodies, also called immunoglobulins, are large Y-shaped proteins which are produced and used by the immune system in order to identify and neutralize foreign substances called antigens. The study and research of antibodies is a critical issue in science and has led in remarkable results with medical applications such as diseases diagnosis, therapies and antibodies related drugs. Due to the importance of antibodies, a comprehensive database of full length protein sequences or crystal structures of immunoglobulin (IG) and T cell receptor (TR) V-like protein sequences from human and other vertebrate species has been created. In this article, we study in detail the unique numbering system for immunoglobulins of IMGT, we correlate the database antibody entries and we provide a more in detailed approach into the data. Finally, due to the deviation of the expected from the real data, a user friendly application has been created. This powerful and flexible tool manipulates the antibodies V-like protein sequences with the approach described below and gives the opportunity to the user to extract and study the results and its physicochemical properties. The need for new therapeutic targets and the development of more potent drugs is enormous, despite the efforts and the investments all these years for the development of novel next generation drugs, the discovery and the characterization of new therapeutic targets using immunoglobulins or antibodies. The final outcome from this project will support the development of novel therapies. Antisoma can be freely downloaded from http://www.dimvl.com/antisoma.

Further Insights in the Binding Mode of Selective Inhibitors to Human PDE4D Enzyme Combining Docking and Molecular Dynamics.

Alzheimer′s disease has recently emerged as a possible field of application for PDE4D inhibitors (PDE4DIs). The great structure similarity among the various PDE4 isoforms and, furthermore, the lack of the full length crystal structure of the enzyme, impaired the rational design of new selective PDE4DIs. In this paper, with the aim of exploring new insights into the PDE4D binding, we tackled the problem by performing a computational study based on docking simulations combined with molecular dynamics (D‐MD). Our work uniquely identified the binding mode and the key residues involved in the interaction with a number of in‐house catechol iminoether derivatives, acting as PDE4DIs. Moreover, the new binding mode was tested using a series of analogues previously reported by us and it was used to confirm their key structural features to allow PDE4D inhibition. The binding model disclosed within the current computational study may prove to be useful to further advance the design and synthesis of novel, more potent and selective, PDE4D inhibitors.

Editorial: The Physiology and Pharmacology of Leucine-rich Repeat GPCRs.

Editorial: The Physiology and Pharmacology of Leucine-rich Repeat GPCRs.

The discovery of IgE 50 years later

In 1906, Von Pirquet1 used the term supersensitivity without immunity to describe (1) symptoms of inhalant allergy, (2) positive immediate skin test results, and (3) the fact that the results of other tests of immunity were not positive in these patients. The other tests he referred to were precipitin tests and complement fixation. Thus, he opened up the question of serum tests for supersensitivity. In 1919, Ramirez2 reported that a patient who had received a blood transfusion from a horse allergic donor became allergic to horse dander. At this point, Prausnitz and Kustner3 set out to investigate whether the serum of allergic individuals contained a factor or factors that could sensitize the skin. In 1921, they reported that the local injection of serum from a fish allergic individual, Kustner, to an individual who was only allergic to pollen, Prausnitz, would transfer specific sensitivity.3 This transfer of sensitivity came to be known as the P-K test and was used widely to study sensitivity not only to common allergens but also to extracts as diverse as those obtained from schistosomes.4,5 Furthermore, in New York, Cooke et al6 identified that there were other antibodies in the serum that increased during desensitization treatment and could block the skin-sensitizing activity. By the 1950s, it was clear that the transferred sensitivity was specific, that it could be diluted extensively, and that the skin remained locally sensitive for days if not weeks after the injection of serum.7,8 It was also already clear that the ability to sensitize the skin was lost after moderate heating of the serum.7 Several studies had also been reported on the physical properties of P-K activity. Indeed, Heimlich et al9 at Cal Tech reported on the sedimentation properties of skin-sensitizing antibodies in 1960. However, the studies before 1964 had not succeeded in defining the nature of these antibodies.

Terahertz Spectroscopy and Solid-State Density Functional Theory Calculations of Cyanobenzaldehyde Isomers.

Spectral signatures in the terahertz (THz) frequency region are mainly due to bulk vibrations of the molecules. These resonances are highly sensitive to the relative position of atoms in a molecule as well as the crystal packing arrangement. To understand the variation of THz resonances, THz spectra (2-10 THz) of three structural isomers: 2-, 3-, and 4-cyanobenzaldehyde have been studied. THz spectra obtained from Fourier transform infrared (FTIR) spectrometry of these isomers show that the resonances are distinctly different especially below 5 THz. For understanding the intermolecular interactions due to hydrogen bonds, four molecule cluster simulations of each of the isomers have been carried out using the B3LYP density functional with the 6-31G(d,p) basis set in Gaussian09 software and the compliance constants are obtained. However, to understand the exact reason behind the observed resonances, simulation of each isomer considering the full crystal structure is essential. The crystal structure of each isomer has been determined using X-ray diffraction (XRD) analysis for carrying out crystal structure simulations. Density functional theory (DFT) simulations using CRYSTAL14 software, utilizing the hybrid density functional B3LYP, have been carried out to understand the vibrational modes. The bond lengths and bond angles from the optimized structures are compared with the XRD results in terms of root-mean-square-deviation (RMSD) values. Very low RMSD values confirm the overall accuracy of the results. The simulations are able to predict most of the spectral features exhibited by the isomers. The results show that low frequency modes (<3 THz) are mediated through hydrogen bonds and are dominated by intermolecular vibrations.

Structural Studies of the HIV-1 Integrase Protein: Compound Screening and Characterization of a DNA-Binding Inhibitor.

Understanding the HIV integrase protein and mechanisms of resistance to HIV integrase inhibitors is complicated by the lack of a full length HIV integrase crystal structure. Moreover, a lentiviral integrase structure with co-crystallised DNA has not been described. For these reasons, we have developed a structural method that utilizes free software to create quaternary HIV integrase homology models, based partially on available full-length prototype foamy virus integrase structures as well as several structures of truncated HIV integrase. We have tested the utility of these models in screening of small anti-integrase compounds using randomly selected molecules from the ZINC database as well as a well characterized IN:DNA binding inhibitor, FZ41, and a putative IN:DNA binding inhibitor, HDS1. Docking studies showed that the ZINC compounds that had the best binding energies bound at the IN:IN dimer interface and that the FZ41 and HDS1 compounds docked at approximately the same location in integrase, i.e. behind the DNA binding domain, although there is some overlap with the IN:IN dimer interface to which the ZINC compounds bind. Thus, we have revealed two possible locations in integrase that could potentially be targeted by allosteric integrase inhibitors, that are distinct from the binding sites of other allosteric molecules such as LEDGF inhibitors. Virological and biochemical studies confirmed that HDS1 and FZ41 share a similar activity profile and that both can inhibit each of integrase and reverse transcriptase activities. The inhibitory mechanism of HDS1 for HIV integrase seems to be at the DNA binding step and not at either of the strand transfer or 3' processing steps of the integrase reaction. Furthermore, HDS1 does not directly interact with DNA. The modeling and docking methodology described here will be useful for future screening of integrase inhibitors as well as for the generation of models for the study of integrase drug resistance.

Molecular dynamics simulation studies of the wild type and E92Q/N155H mutant of Elvitegravir-resistance HIV-1 integrase.

Although Elvitegravir (EVG) is a newly developed antiretrovirals drug to treat the acquired immunodeficiency syndrome (AIDS), drug resistance has already been found in clinic, such as E92Q/N155H and Q148H/G140S. Several structural investigations have already been reported to reveal the molecular mechanism of the drug resistance. As full length crystal structure for HIV-1 integrase is still unsolved, we herein use the crystal structure of the full length prototype foamy virus (PFV) in complex with virus DNA and inhibitor Elvitegravir as a template to construct the wild type and E92Q/N155H mutant system of HIV-1 integrase. Molecular dynamic simulations was used to revel the binding mode and the drug resistance of the EVG ligand in E92Q/N155H. Several important interactions were discovered between the mutated residues and the residues in the active site of the E92Q/N155H double mutant pattern, and cross correlation and clustering methods were used for detailed analysis. The results from the MD simulation studies will be used to guide the experimental efforts of developing novel inhibitors against drug-resistant HIV integrase mutants.

Molecular dynamics simulation studies of the wild type and E92Q/N155H mutant of Elvitegravir-resistance HIV-1 integrase.

Although Elvitegravir (EVG) is a newly developed antiretrovirals drug to treat the acquired immunodeficiency syndrome (AIDS), drug resistance has already been found in clinic, such as E92Q/N155H and Q148H/G140S. Several structural investigations have already been reported to reveal the molecular mechanism of the drug resistance. As full length crystal structure for HIV-1 integrase is still unsolved, we herein use the crystal structure of the full length prototype foamy virus (PFV) in complex with virus DNA and inhibitor Elvitegravir as a template to construct the wild type and E92Q/N155H mutant system of HIV-1 integrase. Molecular dynamic simulations was used to revel the binding mode and the drug resistance of the EVG ligand in E92Q/N155H. Several important interactions were discovered between the mutated residues and the residues in the active site of the E92Q/N155H double mutant pattern, and cross correlation and clustering methods were used for detailed analysis. The results from the MD simulation studies will be used to guide the experimental efforts of developing novel inhibitors against drug-resistant HIV integrase mutants.

Nuclear and magnetic supercells in the multiferroic candidate: Pb3TeMn3P2O14

The dugganites, Te6+-containing members of the langasite series, have attracted recent interest due to their complex low-temperature magnetic unit cells, magnetodielectric, and potentially multiferroic properties. For Pb2+-containing dugganites, a large monoclinic supercell was reported and was found to have a profound effect on the low temperature magnetism and spin excitation spectra. Pb3TeMn3P2O14 is another dugganite previously shown to distort away from the canonical P321 langasite unit cell, although this supercell was never fully solved. Here we report the full crystal and magnetic structure solution of Pb3TeMn3P2O14 using synchrotron x-ray and neutron diffraction data: a large trigonal supercell is observed in this material, which is believed to be the first supercell of its kind in the langasite family. Here, the magnetic structure, high-magnetic field behavior, and dielectric properties of Pb3TeMn3P2O14 are presented. In addition to showing weak magnetoelectric behavior similar to other langasites, it was found that a phase transition occurs at 3T near the antiferromagnetic transition temperature.