Effect of glycerol on the pressure dissociation of tetrameric LDH using high-pressure native PAGE velocity method.

IntroductionIncited by the possibility of room-temperature superconductors in superhydrides, numerous them have been synthesized using a diamond anvil cell under high pressures up to several hundred GPa. Although palladium has widely researched for a long time as a prototype hydrogen-absorbing metal, the palladium superhydrides has not yet been obtained under such high pressures. A recent theorical calculation has predicted that the palladium superhydrides (e.g., PdH10) may be synthesized by combing electrolysis and high pressure1), but it is not certain whether it can be achieved. In this study, we attempted to synthesize the palladium superhydrides by using electrolytic hydrogen charging under high pressures, and subsequently applied protective coatings to suppress the hydrogen desorption from the palladium hydrides at ambient pressure.ExperimentalFigure shows a schematic illustration of the high-pressure apparatus. The high-pressure apparatus can apply the pressure of up to 400 MPa to the electrolyte in the electrolytic cell by pumping water into a sealed high-pressure vessel using a plunger pump and pressure multipliers. A cold-rolled palladium foil of 30 ~ 40 μm in thickness was used as a cathode, and a zinc plate was utilized as a soluble anode. Hydrogen was electrochemically loaded into the palladium foil at 0 V vs. Zn in an electrolyte consisting of 0.1 mol dm-3 sulfuric acid and 4.6 mmol dm-3 zinc sulfate under various pressures for 6 hours. Subsequently, the palladium foil was coated with the zinc film at constant current density 25 mA cm-2 for 120 seconds under the high pressure. The specimen was removed from the electrolytic cell in the high-pressure vessel at ambient pressure, and the hydrogen concentration of the palladium hydride PdH x was determined by thermal desorption spectroscopy. Structural analysis was conducted using X-ray diffraction and scanning electron microscopy.Results and discussionA number of bubbles were observed on the palladium foil surface during the electrolytic charging at ambient pressure. On the other hand, no bubbles were observed at 300 MPa. The zinc film with approximately 1.4 μm thick was coated on the PdH x surface after the electrolytic hydrogen charging. The hydrogen concentration of the PdH x was approximately x = 0.7 immediately after synthesis, which decreased to x = 0.2 without the zinc coating. On the other hand, the hydrogen concentration of the PdH x was maintained at least 1 week with the zinc coating. This result indicates that the zinc film acts as a barrier to hydrogen desorption from PdH x , and suggests that if the palladium superhydrides could be synthesized by electrolytic hydrogen charging under high pressure, it could be taken out to ambient pressure while maintaining its concentration.Reference1) W. Guan, R. J. Hemley, and V. Viswanathan, PNAS, 118, e2110470118 (2021) Figure 1

The contribution of heterotropic effectors to hemoglobin allostery is still not completely understood. With the recently proposed global allostery model, this question acquires crucial significance, because it relates tertiary conformational changes to effector binding in both the R- and T-states. In this context, an important question is how far the induced conformational changes propagate from the binding site(s) of the allosteric effectors. We present a study in which we monitored the interdimeric interface when the effectors such as Cl-, 2,3-diphosphoglycerate, inositol hexaphosphate, and bezafibrate were bound. We studied oxy-Hb and a hybrid form (alphaFeO2)2-(betaZn)2 as the T-state analogue by monitoring heme absorption and Trp intrinsic fluorescence under hydrostatic pressure. We observed a pressure-dependent change in the intrinsic fluorescence, which we attribute to a pressure-induced tetramer to dimer transition with characteristic pressures in the 70-200-megapascal range. The transition is sensitive to the binding of allosteric effectors. We fitted the data with a simple model for the tetramer-dimer transition and determined the dissociation constants at atmospheric pressure. In the R-state, we observed a stabilizing effect by the allosteric effectors, although in the T-analogue a stronger destabilizing effect was seen. The order of efficiency was the same in both states, but with the opposite trend as inositol hexaphosphate > 2,3-diphosphoglycerate > Cl-. We detected intrinsic fluorescence from bound bezafibrate that introduced uncertainty in the comparison with other effectors. The results support the global allostery model by showing that conformational changes propagate from the effector binding site to the interdimeric interfaces in both quaternary states.

The lactate dehydrogenases (LDHs) in hagfish have been estimated to be the prototype of those in higher vertebrates. The effects of high hydrostatic pressure from 0.1 to 100 MPa on LDH activities from three hagfishes were examined. The LDH activities of Eptatretus burgeri, living at 45–60 m, were completely lost at 5 MPa. In contrast, LDH-A and -B in Eptatretus okinoseanus maintained 70% of their activities even at 100 MPa. These results show that the deeper the habitat, the higher the tolerance to pressure. To elucidate the molecular mechanisms for adaptation to high pressure, we compared the amino acid sequences and three-dimensional structures of LDHs in these hagfish. There were differences in six amino acids (6, 10, 20, 156, 269, and 341). These amino acidresidues are likely to contribute to the stability of the E. okinoseanus LDH under high-pressure conditions. The amino acids responsible for the pressure tolerance of hagfish are the same in both human and hagfish LDHs, and one substitution that occurred as an adaptation during evolution is coincident with that observed in a human disease. Mutation of these amino acids can cause anomalies that may be implicated in the development of human diseases.

High-pressure methods have become an interesting tool of investigation of structural stability of proteins. They are used to study protein unfolding, but dissociation of oligomeric proteins can be addressed this way, too. HIV-1 protease, although an interesting object of biophysical experiments, has not been studied at high pressure yet. In this study HIV-1 protease is investigated by high pressure (up to 600 MPa) fluorescence spectroscopy of either the inherent tryptophan residues or external 8-anilino-1-naphtalenesulfonic acid at 25°C. A fast concentration-dependent structural transition is detected that corresponds to the dimer-monomer equilibrium. This transition is followed by a slow concentration independent transition that can be assigned to the monomer unfolding. In the presence of a tight-binding inhibitor none of these transitions are observed, which confirms the stabilizing effect of inhibitor. High-pressure enzyme kinetics (up to 350 MPa) also reveals the stabilizing effect of substrate. Unfolding of the protease can thus proceed only from the monomeric state after dimer dissociation and is unfavourable at atmospheric pressure. Dimer-destabilizing effect of high pressure is caused by negative volume change of dimer dissociation of −32.5 mL/mol. It helps us to determine the atmospheric pressure dimerization constant of 0.92 μM. High-pressure methods thus enable the investigation of structural phenomena that are difficult or impossible to measure at atmospheric pressure.

The double perovskite Sr2FeMoO6 has been prepared in polycrystalline form by high-pressure methods, starting from aprecursor developed via a citrate technique, containing an elevated degree ofanti-site disordering. The application of high external pressure (2 GPa) toSr2FeMoO6 promotes the long distance Fe/Mo cationic order, due to the smaller lattice volume of theordered sample. Both the disordered perovskite obtained at ambient pressure and thesample synthesized under high-pressure methods have been characterized by means of x-raydiffraction, neutron powder diffraction and magnetic measurements. The magneticproperties of the two oxides have been compared; the specimen prepared under highpressure not only presents an improved cationic ordering, but also displays a superiorsaturation magnetization and a sharpener ferromagnetic transition at a significantly hightemperature of 430 K.

Olive wastewater (OMW) is an important environmental problem due to the high phenol level and contains organic substances such as sugars, organic acids, polyalcohols, pectins, colloids, tannins, and lipids. Removing OMW is difficult because of the high concentrations of chemical oxygen demand (COD), biochemical oxygen demand, and phenolic compounds. In this study, we concentrated on the degradation of OMW to solve this problem. The degradation of OMW at high pressure and temperature (with H2O2 and without H2O2), at room temperature and atmospheric pressure with H2O2, at room temperature and atmospheric pressure with O3, and with ultrasound-assisted ozonation, was investigated by means of COD, phenolic compounds, and sulfur analyses. The results showed that the method of high pressure and temperature with H2O2 was the most successful. H2O2 at high pressure (O2) and temperature removed 89.2% of COD, 91.5% of phenolic compounds, and color of OMW. With this result, we showed that the use of O2 atmosphere instead of N2 is important for degradation and also especially for color removing. In addition, the antioxidant property of OMW was also examined. Fourier-transform infrared spectroscopy of the extracts revealed vibration bands corresponding to acid, alcohol, and ketone groups. The results showed that high pressure and temperature treatment is very effective for removing phenolic compounds from olive oil wastewater. In addition, 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging potential of OMW in the Cukurova area of Turkey was studied and the IC50 value of OMW was determined to be 118 µg/mL.

Crystallization and characterization of Pb 2Nb 2O 7 thin films prepared at high pressure and low temperature

The molecular crystal structure and the molecular dissociation of iodine, bromine, and chlorine under high pressure have been studied using the pseudopotential plane-wave method with both local-density approximated (LDA) and the generalized gradient approximated (GGA) exchange-correlation functionals. Although the generalized gradient approximation overestimates the interlayer distance, it describes the geometry parameters within the molecular plane much better than the local-density approximation. In contrast to the usual geometry optimization for isolated molecules, the local-density approximation largely overestimates the bond lengths of the halogen molecules in the molecular crystal. The GGA dissociation pressures are in good agreement with the experimental values whereas the LDA dissociation pressures are lower than the experimental values. The gap closures for the three elements are observed before the dissociation pressure. The scaled parameters are universal for all three halogens in the molecular phase and at the transition points. Therefore a universal equation of state can be obtained and the dissociation pressures can be well estimated from the scaled volume at ambient pressure.

Fitness of enzyme binding sites for their physical environment: Coenzyme and substrate binding sites of M4 lactate dehydrogenases

All in an engineer’s life

Equilibria of oligomeric proteins under high pressure – A theoretical description

A new method of synthesis for thermoelectric materials: HPHT

Molecular Basis of Allosteric Activation of Bacterial L-Lactate Dehydrogenase

Molecular Basis of Allosteric Activation of Bacterial l-Lactate Dehydrogenase

High temperature cuprate superconductors are the only materials that have a T c higher than liquid nitrogen temperature at ambient condition so far. The comprehensive study of cuprate superconductors was selected as one of the 125 unsolved most challenging scientific issues published on Science . It triggers huge innovative scientific inquiry as well as of important application prospects. Heavy metal elements such as Rare-Earth, Bi, Tl and Hg etc are usually induced to stabilize the basic cystal structure in synthesis of the cuprate superconductors, which are classified as Y based system, Bi based sytem, Tl based system, respectively. As these heavy metal elements are usually expensive, volatile, or toxic, to develop new superconducting materials with simple and environmental friendly compositions but with T c above liquid nitrogen temperature, is a great challenge in superconductor material research. In this paper, we primarily focus on the author’s research to briefly introduce the Cu12( n −1) n (i. e., Cu homologous series) cuprate superconductors that are synthesized using high pressure method. The “Cu homologous series” superconductors comprise only copper and alkaline oxides, which are the simplest reagents that are necessary to form high T c cuprates as well as envioramental friendly compositions. The compounds can be synthesized only at high pressure high temperature and can be very stable at ambient pressure like artificial diamond. The properties measured in this paper are all measured at ambient pressure. “Cu homologous series” superconductors own a special crystal structure of a perovskite type charge reservoir layer, which presents a strong interlayer coupling, and exhibit excellent superconductivity properties at high temperature region. The advantages of the “Cu homologous series” superconductors include: (1) high T c above 120 K at ambient pressure, near Hg1223 that has the highest T c in cuprates; (2) excellent critical current densities at liquid nitrogen temperature, which are superior to Bi cuprate homologous superconductors and are comparable to the classical Y123 based system that are the best in terms of comprehensive properties; (3) containing alkaline earth copper oxides only but stable in air condition.