Tetragonal Crystals Research Articles

Solving protein nanocrystals by cryo-EM diffraction: multiple scattering artifacts.

The maximum thickness permissible within the single-scattering approximation for the determination of the structure of perfectly ordered protein microcrystals by transmission electron diffraction is estimated for tetragonal hen-egg lysozyme protein crystals using several approaches. Multislice simulations are performed for many diffraction conditions and beam energies to determine the validity domain of the required single-scattering approximation and hence the limit on crystal thickness. The effects of erroneous experimental structure factor amplitudes on the charge density map for lysozyme are noted and their threshold limits calculated. The maximum thickness of lysozyme permissible under the single-scattering approximation is also estimated using R-factor analysis. Successful reconstruction of density maps is found to result mainly from the use of the phase information provided by modeling based on the protein data base through molecular replacement (MR), which dominates the effect of poor quality electron diffraction data at thicknesses larger than about 200 Å. For perfectly ordered protein nanocrystals, a maximum thickness of about 1000 Å is predicted at 200 keV if MR can be used, using R-factor analysis performed over a subset of the simulated diffracted beams. The effects of crystal bending, mosaicity (which has recently been directly imaged by cryo-EM) and secondary scattering are discussed. Structure-independent tests for single-scattering and new microfluidic methods for growing and sorting nanocrystals by size are reviewed.

Preparation, characterization of superacid SO4 2−/ZrO2-SiO2 and its activity on catalytic synthesis of methyl p-nitrobenzoate

Solid superacid SO42−/ZrO2-SiO2 was prepared by dip-impregnation method, and its catalytic activity was tested with esterification of p-nitrobenzoic acid and methanol. The optimum conditions were also found, that is, the molar ratio between silica and zirconia was 10:1, the calcination temperature was 550 °C and the soaked consistency of H2SO4 was 1.0 mol·L−1. Under the conditions that the ratio of methanol to acid(mL/g) was 12:1, the amount of catalyst was 0.5 g, the reaction time was 5 h and the stirring speed was 800 r·min−1, the yield of methyl p-nitrobenzoate could reach up to 90.5%. Then the characterizations of cataslyst, including the acidity and types of acidic centers, specific surface area and surface structure was respectively examined by Hammett indicator, in-situ pyridine IR, BET method, FT-IR(KBr), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results showed that the catalyst SO42−/ZrO2-SiO2 was superacid with high specific surface area due to Ho<-12.70. It contained acidic sites of Lewis and Brψnsted, and its surface structure changed after esterification. The zirconia crystal was mainly tetragonal and silica crystal was not found.

Effect of hydrothermal degradation on three types of zirconias for dental application

Concern has been expressed with regard to hydrothermal aging of yttria-stabilized tetragonal zirconia polycrystalline. The purpose of this study was to assess the accelerated aging characteristics of a new yttria-stabilized tetragonal zirconia polycrystalline material and 2 commercially available yttria-stabilized tetragonal zirconia polycrystalline materials by exposing specimens to hydrothermal treatments in steam at 134°C, 0.2 MPa, and at 180°C, 1.0 MPa. Thin bars of zirconia: Prettau, Zirprime, and a new zirconia, ZirTough, n = 55 for each brand (22 × 3 × 0.2 mm) were cut and ground from blocks sintered according to the manufacturer's specifications. The control specimens for each group were evaluated in the nonaged condition, and their chemical composition was measured with energy dispersive spectroscopy. The experimental specimens were artificially aged under standard autoclave sterilization conditions, 134°C at 0.2 MPa (n = 5 per group at 5, 50, 100, 150, and 200 hours), and under standard industrial ceramic aging conditions, 180°C at 1.0 MPa (n = 5 per group at 8, 16, 24, and 48 hours). The tetragonal to monoclinic transformation was measured by using x-ray diffraction for all groups. Flexural strength was measured with a 4-point bend test (ASTM 1161-B) for all the groups, and the fracture surfaces were examined with scanning electron microscopy. The data were analyzed as a function of aging time. To test for an aging effect on the flexural strength and the monoclinic-tetragonal ratio, a 1-way ANOVA (with heteroscedasticity-consistent standard errors) was used to test for a general time effect. For the analyses of the monoclinic-tetragonal ratio, the same specimens were used at 0 hours and after aging, and the data were analyzed with an ANOVA for an incomplete block design. The relationship between flexural strength and monoclinic-tetragonal ratio was assessed with the Spearman rank correlation coefficient based on the average value at each aging. After 200 hours at 134°C and 0.2 MPa, the flexural strength decreased from a mean (standard deviation) of 1328 ± 89.9 MPa to all fractured during aging for Prettau (P < .001); 1041 ± 130 to 779 ± 137 MPa for Zirprime (P = .<.001) and 1436 ± 136 to 1243 ± 101 MPa for ZirTough (P = .017). After 200 hours at 134°C and 0.2 MPa, a portion of the tetragonal crystals transformed to the monoclinic phase in all specimens. The mean (standard deviation) monoclinic phase fraction increased from 3.08% ± 0.28% to 78.8% ± 2.0% for Prettau, 1.95% ± 0.48% to 74.8% ± 0.52% for Zirprime, and 12.4% ± 0.60% to 31.4% ± 4.4% for ZirTough (all P < .001). After 16 hours at 180°C and 1.0 MPa, all Prettau specimens had spontaneously fractured during aging. The Zirprime and ZirTough specimens were intact after 48 hours at 180°C and 1.0 MPa, and the mean (standard deviation) flexural strength had decreased from 1041 ± 130 MPa to 595 ± 88.4 MPa for Zirprime and 1436 ± 136 MPa to 1068 ± 76.8 MPa for ZirTough (all P < .001). The mean (standard deviation) monoclinic phase fraction increased from 3.08% ± 0.28% to 79.0% ± 0.13% for Prettau, from 1.95% ± 0.48% to 68.1% ± 4.4%, for Zirprime, and from 12.4% ± 0.60% to 39.5% ± 5.56% for ZirTough (all P<.001). The flexural strength decreased with an increase in the monoclinic phase for all the groups (Spearman rank correlation coefficients, -0.71 to -1.0). Scanning electron microscope micrographs revealed a transformed layer on the fracture surfaces. The decrease in flexural strength was related to the increase in monoclinic phase from long-term degradation. Hydrothermal aging of zirconia caused a statistically significant decrease in flexural strength of thin bars of zirconia, which was the result of the transformation from tetragonal to monoclinic crystal structure. ZirTough exhibited the least decrease in strength and smallest amount of monoclinic phase after aging.

Control of Subgrain Formation in Protein Crystals by the Application of an External Electric Field

X-ray diffraction rocking-curve measurements were performed on tetragonal hen egg white (HEW) lysozyme crystals grown with and without the application of an external alternating current (AC) electric field. Analysis of the full width at half-maximum (fwhm) of the rocking curves indicated that misorientation between subgrains, |θ – φ|, and local strain, ⟨e⟩, in the crystals contributed to the broadening of the experimentally determined rocking curves for the tetragonal HEW lysozyme crystals. In particular, the data suggested that imperfections in tetragonal HEW lysozyme crystals are predominantly caused by misorientation between subgrains. Moreover, it was determined that improvements in the quality of tetragonal HEW lysozyme crystals, as assessed by a decrease in the misorientation between subgrains, can be achieved by imposing a 1 MHz electric field during crystal growth. This paper also discusses the origin of subgrain misorientation in light of the incorporation of impurities into protein crystals.

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.

Effect of temperature on the region of residual rays of CdP2 and ZnP2 single crystals

The technology of growing tetragonal ZnP2 and CdP2 single crystals has been presented. The dielectric permittivity dispersion of tetragonal zinc and cadmium diphosphides in the region of residual rays has been studied, and its dependence on temperature has been scrutinized.

Carboplatin binding to histidine.

Carboplatin is a second-generation platinum anticancer agent used for the treatment of a variety of cancers. Previous X-ray crystallographic studies of carboplatin binding to histidine (in hen egg-white lysozyme; HEWL) showed the partial conversion of carboplatin to cisplatin owing to the high NaCl concentration used in the crystallization conditions. HEWL co-crystallizations with carboplatin in NaBr conditions have now been carried out to confirm whether carboplatin converts to the bromine form and whether this takes place in a similar way to the partial conversion of carboplatin to cisplatin observed previously in NaCl conditions. Here, it is reported that a partial chemical transformation takes place but to a transplatin form. Thus, to attempt to resolve purely carboplatin binding at histidine, this study utilized co-crystallization of HEWL with carboplatin without NaCl to eliminate the partial chemical conversion of carboplatin. Tetragonal HEWL crystals co-crystallized with carboplatin were successfully obtained in four different conditions, each at a different pH value. The structural results obtained show carboplatin bound to either one or both of the N atoms of His15 of HEWL, and this particular variation was dependent on the concentration of anions in the crystallization mixture and the elapsed time, as well as the pH used. The structural details of the bound carboplatin molecule also differed between them. Overall, the most detailed crystal structure showed the majority of the carboplatin atoms bound to the platinum centre; however, the four-carbon ring structure of the cyclobutanedicarboxylate moiety (CBDC) remained elusive. The potential impact of the results for the administration of carboplatin as an anticancer agent are described.

Lifshitz transition and metamagnetism: Thermoelectric studies ofCeRu2Si2

We report field and temperature dependent measurements of the thermoelectric power (TEP) across the pseudo-metamagnetic transition (MMT) in CeRu$_2$Si$_2$. We applied the thermoelectric gradient parallel and perpendicular to the field along the c axis of the tetragonal crystal which is the easy magnetization axis. At the MMT at H$_m$=7.8 T, a strong anomaly in the TEP is observed for both configurations with opposite signs. The anomaly at Hm becomes a cascade of anomalies at very low temperature which seems to be a generic feature of the TEP at a change in the topology of the Fermi surface (FS) in heavy Fermion multiband systems. Simultaneously, quantum oscillations in the magnetic field dependence of the TEP are observed for both configurations below and above the MMT.

Microstructure study on selective laser melting yttria stabilized zirconia ceramic with near IR fiber laser

Purpose– The purpose of this paper is to explore selective laser melting of yttria-stabilized zirconia (YSZ) ceramic by a 1 μm wavelength fibre laser; investigate the influence of different laser powers and different scanning velocities on the microstructure, the relative density, the deformation of ceramic sample and the micro-hardness; and analyze the crystal structure transformation during the fabrication.Design/methodology/approach– During the fabrication, the 5 mm × 5 mm × 5 mm YSZ ceramic samples are fabricated by rapid prototyping (RP) machine MCP Realizer SLM 250; density and microscopic photographs show the ceramic melting situation. The density of cubic sample with different laser powers and different scanning velocities is measured by Archimedes method. The microstructure of samples and powder is observed by SEM. The micro-hardness is measured by the Vickers micro-hardness equipment, and the crystal structure transition is studied by XRD.Findings– It is possible to melt YSZ powder completely with near-IR fibre laser, and the relative density of 5 mm × 5 mm × 5 mm cubic sample is 88 per cent, and the micro-hardness could reach 1,209 ± 262 HV500. The influence of laser power on the volume deformation is more sensitive than the scanning speed at the same energy density. The small pores and the obvious orderly cracks can be observed in the cross-section of sample; the uneven distribution of laser energy input is the main reason of the formation of orderly cracks. The transformation from monoclinic and cubic crystal to tetragonal crystal occurred during the melting process. Heat treatment (1400°C for 30 min) cannot significantly improve the density of the sample, but it can restore the colour of ceramic.Research limitations/implications– Particularly serious due to the deformation of the ceramic material, the authors cannot prepare a large ceramic sample and measure its macroscopic mechanical properties.Originality/value– This paper describes the manufacture of YSZ ceramic sample by SLM technology with a 1 μm wavelength fibre laser, and preliminary studies show the microscopic structure, distribution of laser parameters and crystal transformation.

Thermal stresses in the laser disc from a tetragonal c-cut crystal

Analytical expressions for thermal stresses and strains, as well as displacements, are obtained for the laser disc from a tetragonal crystal cut along the [001] axis under plane stress approximation, for the first time, to our knowledge. This study illustrates that, in polar coordinates, the normal stresses, σr and σθ, are angular independent, while the shear one τrθ is zero. The thermal strains, εr and εθ, and displacements, u and υ, depend on both radial and tangential coordinates; this dependence has the shape of a four-leaf rose. For considered crystal cutting with isotropic in-plane thermal expansion, the displacements are not pure radial (υ≠0). The values of stresses, strains and displacements are calculated for the disc from a c-cut yttrium vanadate laser crystal, Nd:YVO4. The thermal fracture issues are analyzed for this crystal.

Visualizing soaking process of protein crystal

Time-resolved visualization of the soaking process of tetragonal lysozyme crystal was performed by synchrotron radiation microtomography. Mother liquor containing hexachloroplatinate was introduced into a capillary bearing lysozyme crystals to visualize crystals undergoing soaking. The platinum distribution was first observed in the superficial layer of crystal and then gradually penetrated into the crystal core. The crystal structure of the platinum derivative in each soaking period was determined by time-resolved crystallography. A total of five platinum sites were identified in Bijvoet difference maps. These sites were classified into two groups on the basis of the time dependence of electron density development. A soaking process model consisting of binding-rate-driven and equilibrium-driven layers is proposed to describe the results. This study suggests that the structures of soaked crystals vary depending on the crystal position from which diffractions were taken.

Oxygen Electrocatalysis on High-Surface Area at Non-Pt Modified Carbon Catalysts

Although a Pt/C electrocatalyst is the most widely used cathode material, there is a great interest in the development of more active catalysts for the oxygen electroreduction reaction (ORR). Promising results have been achieved by alloying Pt with non-noble metals [1]. In order to lower the cost of cathode catalysts, employing bi-metallic catalysts that combine platinum with other less expensive metals are under investigation [2,3].The main aim of this work is to extend the previous study in order to characterize the ORR kinetics on non-Pt and Fe-Pt nanoparticles in alkaline media (0.1M KOH solution) using crystallographically and structurally different carbon supports.The novel non-conventional micro-mesoporous carbide derived carbon powder, synthesized from molybdenum carbide (Mo2C) at 750°C using the high-temperature chlorination method, and carbon aerogel (CAG) have been used as electrocatalyst supports for oxygen electroreduction. For comparison, the commercially available VulcanXC72® has been used. XRD, XRF and SEM methods were applied for structural and electronic characterization of the materials. Gas adsorption data at liquid nitrogen temperature were used for the porosity analysis of the materials under discussion (Table).XRD patterns of the electrode materials were recorded on a Bruker D8 diffractometer (Bruker Corp.) employing CuKα radiation with a step size of 0.01° and counting time of 2 s using a position sensitive LynxEye detector. The diffraction spectrums were recorded at 25 °C.XRD patterns of the obtained catalysts show the characteristic peaks (2q = 24.5o) of carbon supports (presented in Figure). Analysis shows that the Fe-Pt nanoclusters have been deposited mainly as the face-centered cubic and face-centered tetragonal internal crystals at all carbon supports studied. The metal particles were distributed uniformly on the carbon supports. Both C(Mo2C) and CAG based catalysts are practically amorphous. However, there is a small amount of graphitic structure in all materials as well [4]. The RDE measurements were carried out in a three-electrode electrochemical cell. Several important reaction parameters, such as the number of electrons involved in the ORR, Tafel slopes, and the kinetic rate constant for the ORR, were obtained [5-9].Potentials were measured against Hg|HgO|0.1M KOH reference electrode. RDE data were measured at rotation rates from 0 to 3000 rpm (v=10 mV∙s-1) and in the region of potentials from +0.21 to -0.75 V vs. Hg|HgO|0.1M KOH. CVs were measured at potential scan rates (v mV/s) 5, 10, 20, 30, 50, 70, 100, 150 and 200, in both Ar and O2 saturated solutions. The solutions were saturated with Ar or O2, respectively, between measuring of each voltammogram. Acknowledgements: This work was supported by the Estonian Centre of Excellence in Science Project TK117T "High-technology Materials for Sustainable Development", the Estonian Energy Technology Program project SLOKT 10209T, the Materials Technology project SLOKT12180T.

Protein Crystal Staining for Second Harmonic Generation Imaging

Recently, second harmonic generation (SHG) microscopy has become a useful tool in the field of structural biology for the detection of protein crystals. SHG, or the frequency doubling of light, is a process specific to crystalline media lacking inversion centers. Through theoretical models and experimental data, it is estimated that ~84% of the known protein crystal structures give detectable SHG signal using current SHG microscopy instrumentation. Extending this coverage could be extremely useful to structural biologists who routinely screen entire 96 well plates, with hundreds of crystallization conditions, in search of diffraction-quality protein crystals. A series of SHG active dyes, including Malachite Green (MG) and trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DMI) were investigated to assess their ability to enhance the nonlinear optical (NLO) response across a broad range of protein crystals with varying degrees of inherent SHG activity. MG and DMI were shown to enhance the SHG activity of tetragonal (P43212) lysozyme crystals, a protein that typically generates little to no SHG signal. SHG enhancements for lysozyme of approximately 16000x and 20x were achieved by intercalation of MG and DMI, respectively. These results are consistent with predictions based on the differences in symmetry and structure for the two dyes. The kinetics of the dye intercalation and uptake were investigated with SHG time-lapse images taken of a lysozyme crystal after the addition of MG dye into the crystallization well. Kinetic results indicate that an increase in SHG activity becomes easily noticeable within minutes of exposure to the dyes. These results show a significant progress towards increasing the coverage of SHG microscopy for protein crystal detection.

Thermal behavior and phase transformation of ZrO2–10%SiO2 precursor powder prepared by a co-precipitation route without adding stability agent

Thermal behavior and phase transformation of ZrO2–10%SiO2 precursor powder prepared by a co-precipitation route without adding stability agent has been studied using different thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), high-resolution TEM (HRTEM) and energy-dispersive X-ray spectrometer (EDS). The TG results show that four weight loss regions were from 298 to 443K, 443 to 743K, 743 to 793K and 793 to 1400K. The DTA result shows that the ZrO2 freeze-dried precursor powders crystallization at 1014K. The activation energy of 993.7kJ/mol was obtained for tetragonal ZrO2 crystallization using a non-isothermal process. The XRD result shows that only a single phase of tetragonal ZrO2 appears when the freeze-dried precursor powders after calcination between 1173 and 1373K for 2h. Moreover, when calcined at 1473K for 2h, the phase transformation from tetragonal ZrO2 fully converted to monoclinic ZrO2 occurred.

Spatiotemporal development of soaked protein crystal.

Crystal soaking is widely performed in biological crystallography. This paper reports time-resolved X-ray crystallographic and microtomographic analyses of tetragonal crystals of chicken egg-white lysozyme soaked in mother liquor containing potassium hexachloroplatinate. The microtomographic analysis showed that X-ray attenuation spread from the superficial layer of the crystal and then to the crystal core. The crystallographic analyses indicated that platinum sites can be classified into two groups from the temporal development of the electron densities. A soaking process consisting of binding-rate-driven and equilibrium-driven layers is proposed to describe these results. This study suggests that the composition of chemical and structural species resulting from the soaking process varies depending on the position in the crystal.

In-situ observation of domain wall motion in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Various domain structures, including wave-like domains, mixed needle-like and laminar domains, typical embedded 90° and 180° domains, have been observed in unpoled rhombohedral, monoclinic, and tetragonal Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) crystals by polarizing light microscope; while in poled tetragonal crystals, the parallel 180° domains were reversed and only vertical 90° domain walls were observed. For 0.24PIN-0.42PMN-0.34PT crystals with morphotropic phase boundary composition, the domain wall motion was in-situ observed as a function of applied electric field along crystallographic [100] direction. With increasing the electric field from 0 to 12 kV/cm, the rhombohedral (R) domains were found to change to monoclinic (M) domains and then to tetragonal (T) domains. The electric field-induced phase transition was also confirmed by X-ray diffraction and the temperature-dependent dielectric behavior.

Tetragonal SrGdGa3O7 and SrLaGa3O7—novel SRS-active crystals

We report on the first observation of stimulated Raman scattering (SRS) effects in tetragonal crystals of SrGdGa3O7 and SrLaGa3O7, known as host crystals for Ln3+-lasant ions. All recorded Raman-induced spectral lines were identified and attributed to the promoting χ(3)-vibrational modes of these gallates. Steady-state Raman gain coefficients for first Stokes generation were estimated. A short review of known simultaneous SRS- and Ln3+-laser active melilite-type crystals is given as well.

Purification of Lysozyme from Protein Mixtures by Solvent‐Freeze‐Out Technology

AbstractThe purification of hen egg white lysozyme from a lysozyme/crude extract mixture was carried out by the solvent‐freeze‐out (SFO) technology on the laboratory scale. Compared to previous works, this investigation focuses on the crystallization of lysozyme from a complicated system. The crystallization conditions were determined by screening tests. Based on these results, the crystallization process was performed in basic buffer solution in which the formation of tetragonal lysozyme crystals is considered to be difficult. The protein composition and purity of the crystals were evaluated by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. The enzymatic activity was also measured by the use of a spectrophotometer. The results show that lysozyme retained its original enzyme activity.

Effect of lithium chloride on crystallization process of neodymium disilicate

Tetragonal neodymium disilicate (i.e., Nd2Si2O7) powder was synthesized in the absence and presence of 5wt% lithium chloride (i.e., LiCl) as a mineralizer by sol–gel method and subsequent thermal treatment process. The effect of LiCl on the crystallization process of the synthesized xerogel was investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The crystallization kinetic was analyzed at different heating rates (i.e., 2, 5, 10 and 20K/min) by a non-isothermal differential thermal analysis method. The activation energies of the tetragonal Nd2Si2O7 crystallization calculated by the Kissinger and the Ligero methods are 673kJ/mol for the xerogel without LiCl and 586kJ/mol for the xerogel with 5wt% LiCl. In addition, the crystallization mechanism was also discussed, indicating that the crystallization mechanism of the tetragonal Nd2Si2O7 changes from bulk and homogeneous to two-dimension crystallization in the presence of 5wt% LiCl.

Thermally Activated Exciton Dissociation and Recombination Control the Carrier Dynamics in Organometal Halide Perovskite.

Solar cells based on organometal halide perovskites have seen rapidly increasing efficiencies, now exceeding 15%. Despite this progress, there is still limited knowledge on the fundamental photophysics. Here we use microwave photoconductance and photoluminescence measurements to investigate the temperature dependence of the carrier generation, mobility, and recombination in (CH3NH3)PbI3. At temperatures maintaining the tetragonal crystal phase of the perovskite, we find an exciton binding energy of about 32 meV, leading to a temperature-dependent yield of highly mobile (6.2 cm(2)/(V s) at 300 K) charge carriers. At higher laser intensities, second-order recombination with a rate constant of γ = 13 × 10(-10) cm(3) s(-1) becomes apparent. Reducing the temperature results in increasing charge carrier mobilities following a T(-1.6) dependence, which we attribute to a reduction in phonon scattering (Σμ = 16 cm(2)/(V s) at 165 K). Despite the fact that Σμ increases, γ diminishes with a factor six, implying that charge recombination in (CH3NH3)PbI3 is temperature activated. The results underline the importance of the perovskite crystal structure, the exciton binding energy, and the activation energy for recombination as key factors in optimizing new perovskite materials.