High-pressure Shifts Research Articles

Pushed to extremes: distinct effects of high temperature versus pressure on the structure of STEP

Protein function hinges on small shifts of three-dimensional structure. Elevating temperature or pressure may provide experimentally accessible insights into such shifts, but the effects of these distinct perturbations on protein structures have not been compared in atomic detail. To quantitatively explore these two axes, we report the first pair of structures at physiological temperature versus. high pressure for the same protein, STEP (PTPN5). We show that these perturbations have distinct and surprising effects on protein volume, patterns of ordered solvent, and local backbone and side-chain conformations. This includes interactions between key catalytic loops only at physiological temperature, and a distinct conformational ensemble for another active-site loop only at high pressure. Strikingly, in torsional space, physiological temperature shifts STEP toward previously reported active-like states, while high pressure shifts it toward a previously uncharted region. Altogether, our work indicates that temperature and pressure are complementary, powerful, fundamental macromolecular perturbations.

Hydraulic Fracture Propagation in Fractured Rock Mass

According to fracture mechanics theory, the initial cracking law and wing crack propagation model of compression shear rock cracks subjected to hydraulic pressure and far field stresses are discussed. The results of the theoretical study show that crack initiation strength is inversely related to hydraulic pressure, that hydraulic pressure aggravates the wing crack’s growth, and that the wing crack’s behavior under high hydraulic pressure shifts from stable to unstable expansion. The confining pressure is proportional to the rock mass strength, the wing crack’s stress intensity factor drops as the remote field stress σ3 increases, and the wing crack tends to expand stably. As the crack angle increases, the cracking strength reduces at first, then increases. At the same time, damage fracture mechanics models are established for the occurrence of wing crack-wing crack failure, wing crack-shear crack failure, wing crack-shear crack-wing crack failure, and shear crack-shear crack failure in the compression-shear crack bridge under far-field stress and hydraulic pressure. The link between hydraulic pressure, confining pressure, fracture angle, stress intensity factor, and compression-shear factor λ12 is also clarified. The value of the stress intensity factor increases when the hydraulic pressure decreases, the confining pressure increases, and the crack angle increases, whereas the compression-shear factor decreases. This study lays the groundwork for a quantitative assessment of fractured rock mass destruction under hydraulic pressure.

Pressure overload changes mesenteric afferent nerve responses in a stress-dependent way in a fasting rat model.

It is well known that overload changes the mechanical properties of biological tissues and fasting changes the responsiveness of intestinal afferents. This study aimed to characterize the effect of overload on mechanosensitivity in mesenteric afferent nerves in normal and fasted Sprague-Dawley rats. Food was restricted for 7days in the Fasting group. Jejunal whole afferent nerve firing was recorded during three distensions, i.e., ramp distension to 80cmH2O luminal pressure (D1), sustained distension to 120cmH2O for 2min (D2), and again to 80cmH2O (D3). Multiunit afferent recordings were separated into low-threshold (LT) and wide-dynamic-range (WDR) single-unit activity for D1 and D3. Intestinal deformation (strain), distension load (stress), and firing frequency of mesenteric afferent nerve bundles [spike rate increase ratio (SRIR)] were compared at 20cmH2O and 40cmH2O and maximum pressure levels among distensions and groups. SRIR and stress changes showed the same pattern in all distensions. The SRIR and stress were larger in the Fasting group compared to the Control group (P < 0.01). SRIR was lower in D3 compared to D1 in controls (P < 0.05) and fasting rats (P < 0.01). Total single units and LT were significantly lower in Fasting group than in Controls at D3. LT was significantly higher in D3 than in D1 in Controls. Furthermore, correlation was found between SRIR with stress (R = 0.653, P < 0.001). In conclusion, overload decreased afferent mechanosensitivity in a stress-dependent way and was most pronounced in fasting rats. Fasting shifts LT to WDR and high pressure shifts WDR to LT in response to mechanical stimulation.

Non-isothermal crystallization behavior and kinetics of isotactic polypropylene/ethylene-octene blends. Part I: Crystallization behavior

The non-isothermal crystallization behavior of isotactic polypropylene/ethylene-octene blends under atmospheric pressure and high pressure has been systematically investigated by differential scanning calorimetry (DSC) and PVT. The apparent incubation period (∆ t i) and the apparent total crystallization period (∆ t c) were used to characterize the crystallization behavior of the blends. At low POE content, the addition of POE decreases the ∆ t i and ∆ t c of PP in blends; however, at high POE content, the addition of POE decreases the mobility of PP segments and increases ∆ t i and ∆ t c of PP in blends. The pressure dependence of the crystallization temperature of PP/POE blends shows a linear relationship. The melting temperature of blends crystallized under high pressure is significantly lower than that under atmospheric pressure. With increasing POE content, the melting peak of blends crystallized under high pressure shifts toward higher temperature, in contrast to that under atmospheric pressure.

Theoretical studies of local structure and high-pressure shifts of the spin–orbit levels of Co 2+ in KZnF 3

The local crystal structure of a Co 2+ dopant ion in KZnF 3 has been determined on the basis of the experimental optical spectra, electron paramagnetic resonance parameter g, the approximately equivalent molecular orbital model, and the μ kα model. The results show that when a Co 2+ ion occupies a Zn 2+ site, the bond length changes by about 6%. Using the experimental high-pressure shifts of the spin–orbit levels, the state equation and the pressure dependence of the g-factor are obtained. The good agreement between theory and experimental findings shows that the method is reasonable. The state equation and the pressure dependence of the g-factor await further experimental tests.

Hydrostatic pressure effects on spectral hole burning in a Shpol’skii system

Hydrostatic-pressure effects on persistent spectral holes in a polycrystalline solid solution of chlorin (Chl) in n-octane (C8:Chl, a Shpol’skii system) at 4.2 K were studied at high-pressure [up to 8.4 kbars (1 kbar = 750.06 kTorr)] isobaric (burning and recording at the same pressure) conditions as well as in low-pressure (21–39 bars) nonisobaric (burning and recording at different pressures) experiments. A significant decrease of the hole width was seen at high pressures, with the FWHM of holes in the 15 730-cm−1 line being 130 and 45 MHz at 1 bar and 5.5 kbars, respectively. The latter value approaches the normal-pressure lifetime limit of 40 MHz. A pressure-induced site-dependent instability of spectral holes was found at pressures above 5.5 kbars. High-pressure shifts of Shpol’skii lines and low-pressure hole shifts gave the same pressure coefficient, −4.8 cm−1/kbar, for the S1 ← S0 (0–0) transition energy. This coefficient yielded the value of 13.2 Mbars−1 for the local compressibility. Reversible non-Gaussian non-area-conserving hole broadening was observed in nonisobaric low-pressure experiments.

Pressure dependence of the magnetic susceptibility of YBa 2Cu 3O 6.9 doped by Fe, Ni and Zn

We report measurements of the susceptibility under applied hydrostatic pressure for samples of YBa 2Cu 3O 6.9 with up to 10 at.% substitution of Fe, Ni and Zn for Cu. We find a very large shift of the superconducting transition temperature T c for samples with higher concentrations of Fe and Zn. The numerical values for dln T c/d p range up to 1.2×10 −2/kbar. The anomalously high pressure shifts of T c are found to correlate with very inhomogeneous superconducting ground states. The results indicate that the main positive contribution to d T c/d p for these inhomogeneous superconductors is due to a delocalization of charge carriers under applied hydrostatic pressure.

Pressure-induced spin-state isomerizations in weakly tetragonal Nickel(II) complexes with diethylthiourea

The ability of high pressure to influence spin-state equilibria in (Ni(detu){sub 4}X{sub 2}) (detu = N,N{prime}-diethylthiourea; X = Cl, Br, I) is demonstrated. The complexes are six-coordinate and weakly tetragonal. An equilibrium between singlet and triplet isomers is present. High-pressure shifts the equilibrium toward the triplet isomer in each complex. The equilibria are monitored spectroscopically. The results represent the first examples of low-spin to high-spin conversion via pressure-induced changes in molecular geometry.

On determining the state equation of NiX2from the high-pressure spectra shifts and the μkα model

It is shown that the high-pressure state equation and the alpha -P correlation of NiX2 (X=F, Cl, Br or I) determined by Zhao and Du (1986) from the pressure spectra shifts of NiCl2 and NiBr2 based on their mu k alpha model and fitting procedure are not supported by a great many theoretical analyses and experimental facts, and the pressure behaviours of NiF2 and NiI2 predicted by them, using the above state equation and the alpha -P correlation, are also doubtful. Thus both the mu k alpha model and their fitting procedure may be held to be faulty and unreliable. Hence, the conclusions based on this model should be rejected.

Determination of the state equation of NiX2from the high-pressure spectra shifts

The high-pressure state equation and alpha -P correlation of NiX2(X identical to F, Cl, Br, or I) are determined from the pressure spectra shifts of NiCl2 and NiBr2 based on the mu kappa alpha model. By using the state equation and alpha -P correlation the pressure behaviours of NiF2 and NiI2 are predicted.