Pressure-sensitive Reactions Research Articles

Diffusive effects of hydrogen on pressurized lean turbulent hydrogen-air premixed flames

To understand the turbulence-chemistry interaction of lean hydrogen-air premixed flames at elevated pressures, we conduct a series of high-fidelity direct numerical simulations with detailed chemistry and transport by increasing pressure from 1 up to 7 atm. For a fixed ratio of the root-mean-square turbulent velocity fluctuation to the laminar flame speed, two sets of simulations were conducted: one for a fixed ratio of integral length scale to the laminar flame thickness and the other one for a fixed integral length scale. We observe that the turbulent flame speed and volume-integrated heat release rate (HRR) increase with pressure due to the promoted chemical effects. To elucidate the enhanced chemical effects, we conduct a budget analysis of diffusive transport and reaction rate of hydrogen and examine the conditionally-averaged flame structure. As opposed to the laminar flames, the diffusive effects of hydrogen for turbulent flames are found to increase with pressure in a more non-linear way, which significantly enhances the radical pool generation, leading to abundant H radical that is required for the rate of the pressure-sensitive reaction H + O2(+M) = HO2(+M) to be accelerated at higher pressures. Due to the strong diffusive transport of hydrogen for pressurized turbulence, not only does another small HRR peak emerge upstream, but also the location of the main HRR peak is moved towards the upstream region. Furthermore, the probability density function (PDF) of the flame curvature, computed for the isosurface associated with maximal diffusive transport of hydrogen, shows a clear trend of the PDF peak shifting to larger positive values as pressure increases. Simulations with the inclusion of thermal diffusion are also carried out at atmospheric and elevated pressure conditions to quantify the Soret effect. It is found that the magnitude of the hydrogen diffusion rate is augmented by thermal diffusion, affecting its mass fraction distribution. The mean turbulent flame speed is enhanced by approximately 8% and 7% for the 1 and 7 atm conditions, respectively.

Pressure-sensitive reaction yield of the TePixD blue-light sensor protein.

The effect of pressure on the dissociation reaction of the TePixD decamer was investigated by high-pressure transient grating (TG). The TG signal intensity representing the dissociation reaction of the TePixD decamer significantly decreased by applying a relatively small pressure. On the other hand, the reaction rate increased with increasing pressure. The equilibrium between the pentamer and the decamer was investigated by high-pressure dynamic light scattering. The results indicated that the fraction of the decamer slightly increased in the high-pressure region. From these measurements, it was concluded that the pressure-dependent signal intensity originated from the decrease of the quantum yield of the dissociation reaction of the decamer, indicating that this reaction efficiency is very sensitive to pressure. Using densimetry at high pressures, the compressibility was found to be pressure dependent even in a relatively low pressure range. We attributed the origin of the pressure-sensitive reaction yield to the decrease of compressibility at high pressure. Because the compressibility is related to the volume fluctuation, this observation suggests that the driving force for this reaction is fluctuation of the protein. The relationship between the cavities at the interfaces of the monomer units and the reactivity is also discussed.

Single-Molecule Analysis of the Rotation of F1-ATPase under High Hydrostatic Pressure

F1-ATPase is the water-soluble part of ATP synthase and is an ATP-driven rotary molecular motor that rotates the rotary shaft against the surrounding stator ring, hydrolyzing ATP. Although the mechanochemical coupling mechanism of F1-ATPase has been well studied, the molecular details of individual reaction steps remain unclear. In this study, we conducted a single-molecule rotation assay of F1 from thermophilic bacteria under various pressures from 0.1 to 140 MPa [1, 2]. Even at 140 MPa, F1 actively rotated with regular 120° steps in a counterclockwise direction, showing high conformational stability and retention of native properties. Rotational torque was also not affected. However, high hydrostatic pressure induced a distinct intervening pause at the ATP-binding angles during continuous rotation. The pause was observed under both ATP-limiting and ATP-saturating conditions, suggesting that F1 has two pressure-sensitive reactions, one of which is evidently ATP binding. The rotation assay using a mutant F1(ßE190D) suggested that the other pressure-sensitive reaction occurs at the same angle at which ATP binding occurs. The activation volumes were determined from the pressure dependence of the rate constants to be +100 Å3 and +88 Å3 for ATP binding and the other pressure-sensitive reaction, respectively. These results are discussed in relation to recent single-molecule studies of F1 and pressure-induced protein unfolding. [1] Nishiyama M. and Y. Sowa. 2012. Microscopic Analysis of Bacterial Motility at High Pressure. Biophys. J.102:1872-1880. [2] Okuno D., M. Nishiyama, and H. Noji. 2013. Single-Molecule Analysis of the Rotation of F1-ATPase under High Hydrostatic Pressure. Biophys. J.105:1635-1642.

Pressure-Speed Relationship of the Sodium-Driven Flagellar Motor of Vibrio Alginolyticus

The bacterial flagellar motor is a molecular machine that converts an ion flux to the rotation of a helical flagellar filament. Motor rotation rate and directions can be changed by environmental factors such as temperature, pH, and solvation. Hydrostatic pressure is also an inhibitor of the rotation of flagellar motors [1, 2]. Our previous results indicated that the application of pressure inhibits the rate of ion tranlocation in the mechanochemical energy translation, but the detailed mechanism is still unknown. Here, we characterized the pressure dependence of the rotational speed of sodium-driven flagellar motor in swimming Vibrio alginolyticus cells. The motor in strain NMB136 exclusively rotates in counter-clockwise direction and propells the cell body forward. We monitored the pressure-induced effects on the behavior of the cells that swim freely in solution. The swimming speed exponentially decreased with the increment of pressure. The sodium concentration dependence of the swimming speed at each pressure was well described by a Michaelis-Menten kinetics. The applied pressures decreased the maximum velocity, but increased the Michalis constant. Our results showed that the motor has at least two pressure-sensitive reactions, one of which is the binding process of external sodium ions to the motor. Another is the post-sodium-binding process, suggesting sodium transit and/or its release to inside the cell.[1] Nishiyama M. and Y. Sowa. 2012. Microscopic Analysis of Bacterial Motility at High Pressure. Biophys. J.102:1872-1880.[2] Nishiyama M. et al. 2013. High Hydrostatic Pressure Induces Counterclockwise to Clockwise Reversals of the Escherichia coli Flagellar Motor. J. Bactetiol.195: 1809-1814.

Single-Molecule Analysis of the Rotation of F1-ATPase under High Hydrostatic Pressure

F1-ATPase is the water-soluble part of ATP synthase and is an ATP-driven rotary molecular motor that rotates the rotary shaft against the surrounding stator ring, hydrolyzing ATP. Although the mechanochemical coupling mechanism of F1-ATPase has been well studied, the molecular details of individual reaction steps remain unclear. In this study, we conducted a single-molecule rotation assay of F1 from thermophilic bacteria under various pressures from 0.1 to 140 MPa. Even at 140 MPa, F1 actively rotated with regular 120° steps in a counterclockwise direction, showing high conformational stability and retention of native properties. Rotational torque was also not affected. However, high hydrostatic pressure induced a distinct intervening pause at the ATP-binding angles during continuous rotation. The pause was observed under both ATP-limiting and ATP-saturating conditions, suggesting that F1 has two pressure-sensitive reactions, one of which is evidently ATP binding. The rotation assay using a mutant F1(βE190D) suggested that the other pressure-sensitive reaction occurs at the same angle at which ATP binding occurs. The activation volumes were determined from the pressure dependence of the rate constants to be +100 Å3 and +88 Å3 for ATP binding and the other pressure-sensitive reaction, respectively. These results are discussed in relation to recent single-molecule studies of F1 and pressure-induced protein unfolding.

Petrology of a non-classical Barrovian inverted metamorphic sequence from the western Arunachal Himalaya, India

In this study, we reconstruct the inverted metamorphic sequence in the western Arunachal Himalaya using combined structural and metamorphic analyses of rocks of the Lesser and Greater Himalayan Sequences. Four thrust-bounded stratigraphic units, which from the lower to higher structural heights are (a) the Gondwana rocks and relatively weakly deformed metasediments of the Bomdila Group, (b) the tectonically interleaved sequence of Bomdila gneiss and Bomdila Group, (c) the Dirang Formation and (d) the Se La Group are exposed along the transect, Jira–Rupa–Bomdila–Dirang–Se La Pass. The Main Central thrust, which coincides with intense strain localization and the first appearance of kyanite-grade partial melt is placed at the base of the Se La Group. Five metamorphic zones from garnet through kyanite, kyanite migmatite, kyanite-sillimanite migmatite to K-feldspar-kyanite-sillimanite migmatites are sequentially developed in the metamorphosed low-alumina pelites of Dirang and Se La Group, with increasing structural heights. Three phases of deformation, D 1–D 2–D 3 and two groups of planar structures, S 1 and S 2 are recognized, and S 2 is the most pervasive one. Mineral growths in all these zones are dominantly late-to post-D 2, excepting in some garnet-zone rocks, where syn-D 1 garnet growths are documented. Metamorphic isograds, which are aligned parallel to S 2 were subsequently folded during D 3. The deformation produced plane-non-cylindrical fold along NW–SE axis. In the garnet-zone, peak metamorphism is marked by garnet growth through the reaction biotite + plagioclase → garnet + muscovite. An even earlier phase of syn-D 1 garnet growth occurred in the chlorite stability field with or without epidote. In the kyanite-zone metapelites, kyanite appeared via the pressure-sensitive reaction, garnet + muscovite → kyanite + biotite + quartz. Staurolite was produced in the same rock by retrograde replacement of kyanite following the reaction, garnet + kyanite + H 2O → staurolite + quartz. These reactions depart from the classical kyanite- and staurolite-isograd reactions in low-alumina pelites, encountered in other segments of eastern Himalaya. In the metapelites, just above the kyanite-zone, melting begins in the kyanite field, through water-saturated and water-undersaturated melting of paragonite component in white mica. Leucosomes formed through these reactions are characteristically free of K-feldspar, with sodic plagioclase and quartz as the dominant constituents. With increasing structural height, the melting shifts to water-undersaturated melting of muscovite component of white mica, producing an early K-feldspar + kyanite and later K-feldspar + sillimanite assemblages and granitic leucosomes. Applications of conventional geothermobarometry and average P– T method reveal near isobaric (at P ∼ 8 kbar) increase in peak metamorphic temperatures from 550 °C in the garnet-zone to >700 °C for K-feldspar-kyanite-sillimanite-zone rocks. The findings of near isobaric metamorphic field gradient and by the reconstruction of the reaction history, reveal that the described inverted metamorphic sequence in the western Arunachal Himalaya, deviates from the classical Barrovian-type metamorphism. The tectonic implication of such a metamorphic evolution is discussed.

Counter-clockwise prograde P–T path in collisional orogeny and water subduction at the Precambrian–Cambrian boundary: The ultrahigh-pressure pelitic schist in the Kokchetav massif, northern Kazakhstan

A prograde pressure–temperature ( P–T) path is estimated for pelitic schists from the latest Precambrian Kokchetav ultrahigh-pressure massif, Kazakhstan, using compositional zoning and mineral inclusions in coarse-grained and inclusion-rich garnets. Ti-bearing inclusions are abundant in garnet and display a zonal distribution. Ilmenite occurs in the inner-core, where most of it makes a composite inclusion with rutile, whereas monomineralic rutile occurs in the outer-core to mantle domains. In the rim region both ilmenite and rutile are present, although in small amounts. Application of the ilmenite-garnet thermometer yields a systematic temperature increase towards rim from 500 to 750 °C. The pressure-sensitive reaction: 3 Fe-Ilm (in Ilm) + Ky + 2 Qtz = 3 Rt + Alm (in Grt) yielded pressures of 1.2–1.3 GPa for the outer-core inclusions. A petrogenetic grid in the K 2O–CaO–FeO–MgO–Al 2O 3–SiO 2–H 2O model system was used to estimate the equilibrium compositions of the garnet. The change of the grossular component along the model P–T path expected from the forward modelling is close to the observed compositional profile of the outer-core to rim domains. No constraint is available from thermobarometry in the inner-core; however, the forward modelling of garnet zoning provides information on the early stage of the P–T path during the garnet growth. The estimated P–T path is counter-clockwise in the prograde stage with a steep bend at around 700 °C and 1.2–1.5 GPa. This is similar to the metamorphic P–T gradient of the Kokchetav massif. This result contrasts markedly with the traditional clockwise P–T path in many collisional metamorphic terranes, and is regarded to represent a subduction geotherm at the Precambrian–Cambrian boundary. The P–T path proposed in this study also supports the models for the recovery of the “snowball Earth” from late-Proterozoic glaciation through effect of water in the solid Earth mantle.

Stability of detonations for an idealized condensed-phase model

The stability of travelling wave Chapman–Jouguet and moderately overdriven detonations of Zeldovich–von Neumann–Döring type is formulated for a general system that incorporates the idealized gas and condensed-phase (liquid or solid) detonation models. The general model consists of a two-component mixture with a one-step irreversible reaction between reactant and product. The reaction rate has both temperature and pressure sensitivities and has a variable reaction order. The idealized condensed-phase model assumes a pressure-sensitive reaction rate, a constant-γ caloric equation of state for an ideal fluid, with the isentropic derivative γ=3, and invokes the strong shock limit. A linear stability analysis of the steady, planar, ZND detonation wave for the general model is conducted using a normal-mode approach. An asymptotic analysis of the eigenmode structure at the end of the reaction zone is conducted, and spatial boundedness (closure) conditions formally derived, whose precise form depends on the magnitude of the detonation overdrive and reaction order. A scaling analysis of the transonic flow region for Chapman–Jouguet detonations is also studied to illustrate the validity of the linearization for Chapman–Jouguet detonations. Neutral stability boundaries are calculated for the idealized condensed-phase model for one- and two-dimensional perturbations. Comparisons of the growth rates and frequencies predicted by the normal-mode analysis for an unstable detonation are made with a numerical solution of the reactive Euler equations. The numerical calculations are conducted using a new, high-order algorithm that employs a shock-fitting strategy, an approach that has significant advantages over standard shock-capturing methods for calculating unstable detonations. For the idealized condensed-phase model, nonlinear numerical solutions are also obtained to study the long-time behaviour of one- and two-dimensional unstable Chapman–Jouguet ZND waves.

Fluid-melt-rock interaction in mafic eclogites and coesite-bearing metasediments: Constraints on volatile recycling during subduction

The question as to whether the metasomatizing-slab agent needed to form island-arc magmas is an aqueous fluid or a hydrous melt requires a knowledge of fluid-melt-rock interaction during high-pressure low-temperature metamorphism. In the Western Alps, typical “anhydrous” mafic eclogites (Monviso Massif) and coesite-bearing metasediments (Dora-Maira Massif) have experienced a prograde P- T path characteristic of a mature (cold) subduction zone. Microstructural, petrologic, geochemical and fluid inclusion studies show that fluid flow was limited during eclogite and high-grade blueschist facies metamorphism. Most of the fluids were driven off the rocks at pressures lower than 1 and 1.6 GPa, respectively. With increasing pressure and temperature, the remaining fluid phase was released during crystal plastic flow processes or devolatilisation reactions but retain the host rocks to form veins, partial melts or dense hydrous silicates. Tectonic erosion at modern convergent margins delivers large amounts of terrigenous sediments (KMASH system) in subduction zones. In contrast to the basalt and peridotite systems, the KMASH system is characterized by a wide range of pressure-sensitive reactions which allow the reconstruction of dehydration/hydration depths in the subducted slab. Independently of the thermal structure of subduction zones, terrigenous sediments will begin to melt at pressures < 2 GPa. The melt phase can absorb tremendeous quantities of water and represent major sinks for devolatilisation fluids. Dense hydrous silicates will form in any subducted sediments at all depths. These silicates can store significant amount of water in their structure. In the subducted oceanic crust and upper mantle, heterogeneous distribution of fluids inherited from hydrothermal alteration at mid-ocean ridges will cause contemporaneous dehydration and hydration reactions on a local scale rather than large-scale fluid infiltration in the overlying mantle wedge. The situation where a cold, competent and fluid-rich subducted slab is bounded above by a hot, relatively weak and anhydrous material is likely to act against buoyant rise of devolatilisation fluids by forcing the fluids to flow downwards. At sub-arc depths (50 ± 10 to 80 150 km ) and for any geothermal gradient, continuous internal buffering of volatile activities will retain the fluid phase in the slab. This is in contrast with shallow, sub-forearc depths (20 to 50 ± 10 km), where tectonic vein arrays, localized thrust faults, serpentine diapirs, mud volcanoes and boninite magmas attest to the release of large volume of fluids into the overriding mantle wedge.

Stable isotope geochemistry and phase equilibria of coesite-bearing whiteschists, Dora Maira Massif, western Alps

Peak metamorphic temperatures for the coesite-pyrope-bearing whiteschists from the Dora Maira Massif, western Alps were determined with oxygen isotope thermometry. The δ18O(smow) values of the quartz (after coesite) (δ18O=8.1 to 8.6‰, n=6), phengite (6.2 to 6.4‰, n=3), kyanite (6.1‰, n=2), garnet (5.5 to 5.8‰, n=9), ellenbergerite (6.3‰, n=1) and rutile (3.3 to 3.6‰, n=3) reflect isotopic equilibrium. Temperature estimates based on quartz-garnet-rutile fractionation are 700–750 °C. Minimum pressures are 31–32 kb based on the pressure-sensitive reaction pyrope + coesite = kyanite + enstatite. In order to stabilize pyrope and coesite by the temperature-sensitive dehydration reaction talc+kyanite=pyrope+coesite+H2O, the a(H2O) must be reduced to 0.4–0.75 at 700–750 °C. The reduced a(H2O) cannot be due to dilution by CO2, as pyrope is not stable at X(CO2)>0.02 (T=750 °C; P=30 kb). In the absence of a more exotic fluid diluent (e.g. CH4 or N2), a melt phase is required. Granite solidus temperatures are ∼680 °C/30 kb at a(H2O)=1.0 and are calculated to be ∼70°C higher at a(H2O)=0.7, consistent with this hypothesis. Kyanite-jadeite-quartz bands may represent a relict melt phase. Peak P-T-f(H2O) estimates for the whiteschist are 34±2 kb, 700–750 °C and 0.4–0.75. The oxygen isotope fractionation between quartz (δ18O=11.6‰) and garnet (δ18O=8.7‰) in the surrounding orthognesiss is identical to that in the coesitebearing unit, suggesting that the two units shared a common, final metamorphic history. Hydrogen isotope measurements were made on primary talc and phengite (δD(SMOW)=-27 to-32‰), on secondary talc and chlorite rite after pyrope (δD=-39 to -44‰) and on the surrounding biotite (δD=-64‰) and phengite (δD=-44‰) gneiss. All phases appear to be in nearequilibrium. The very high δD values for the primary hydrous phases is consistent with an initial oceanicderived/connate fluid source. The fluid source for the retrograde talc+chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization. The similar δD, but dissimilar δ18O values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium, but not oxygen isotope equilibrium. The unusual hydrogen and oxygen isotope compositions of the coesite-bearing unit can be explained as the result of metasomatism from slab-derived fluids at depth.

Explosive volcanism and the graphite-oxygen fugacity buffer on the parent asteroid(s) of the ureilite meteorites

The ∼39 ureilite meteorites are in many respects primitive objects. They are highly carbonaceous, averaging ∼3.0 wt% C, mostly as graphite. Yet their consistently coarse-grained textures and plagioclase-depleted compositions imply that they are igneous. Despite diverse mafic-silicate Mg/(Mg + Fe) and pyroxene/olivine ratios, plagioclase is totally absent among ∼35 monomict/unbrecciated ureilites; even among 4 polymict/brecciated ureilites the average Al concentration is only 0.28 ± 0.04 wt%. We suggest that the ureilites are residues from partial melting of graphite-rich source materials, which formed sufficiently deep in a relatively large, low- f(O 2) asteroid (or more likely asteroids) for graphite to be stable even at magmatic T. The Al-rich basaltic magmas that ascended from the residues were nearly quantitatively lost from the asteroid during pyroclastic eruptions. Graphite entrained in the ascending magmas was oxidized by an extremely pressure-sensitive reaction into CO x , the expansion of which into the vacuous environment of the asteroid engendered pyroclastic exit velocities greatly in excess of the asteroid's escape velocity. Carbon would oxidize long before the attainment of magmatic temperatures in small asteroids, but we infer that basalt-dissipative explosive volcanism was common on all C-rich asteroids that were roughly 100–200 km in radius and heated to widespread, deep melting; and most unmetamorphosed chondritic meteorites are C-rich. Based on the ureilites' consistently modest depletions of light rare-earth elements, siderophile elements, and FeNi metal, we infer that the melt fraction was removed mostly by equilibrium, “batch” partial melting. Late-stage ureilite evolution involved an abrupt increase in the cooling rate, implying a drop in environmental temperature, and a slight amount of graphite oxidation, implying a drop in pressure. The simplest model to account for this non sequitur (and for the conversion of some of the graphite into diamonds) is catastrophic impact disruption of the primary asteroid. The remarkably efficient removal of the final traces of melt from the ureilites is difficult to explain by any model, but possibly was caused by thermal migration along steep thermal gradients engendered after the catastrophic disruption.

Rapid initiation in condensed phases through resonant nonlinear acoustics

Experiments indicate that small-scale inhomogeneities have a prominent role in accelerating the global heat-release rate in a variety of condensed-phase liquid and solid materials. In this paper, simplified asymptotic equations are studied that incorporate small-scale inhomogeneities, their interaction with each other, and the interaction of the microstructure with the global reaction scale. A variety of chemical-acoustic resonant mechanisms with the microstructure are developed and documented for both temperature-sensitive and pressure-sensitive reaction rates. It is demonstrated that these specific resonant mechanisms lead to dramatic shortening of the local induction time for regimes of equations of state and chemical reactions appropriate for condensed phases. These mechanisms are completely different than the conventional mechanism of simple thermal explosion of hot spots.

Analysis of the Escherichia coli ribosome-ribosomal subunit equilibrium using pressure-induced dissociation.

Hydrostatic pressure can be used to perturb the ribosome-ribosomal subunit equilibrium. We have used glutaraldehyde fixation and subsequent sucrose gradient analysis to determine the equilibrium concentrations of Escherichia coli 70 S, 50 S, and 30 S particles at pressures from 1 to 1400 atm. This method is shown to be sufficiently rapid and free of interfering ribosomal aggregation artifacts when performed at Mg2+ concentrations below 8 mM. We show directly that the E. coli ribosome is in equilibrium with its subunits and that the pressure-sensitive reaction is appropriately described by the expression: In Kp = ln K0 + (P delta V/RT), where Kp and K0 are the equilibrium constants at pressure P and 1 atm, respectively, and delta V is the change in molecular volume that occurs during the reaction. The method provides values for K0 under different conditions, and the effects of Mg2+ ion can be readily ascertained. K0 and delta V were also estimated by a method of fitting computer-generated sucrose gradient profiles to experimental profiles. Determination of delta H0, delta S0, and delta V0 at 5 mM Mg2+ are presented. The results are discussed in the context of previous thermodynamic studies of the E. coli ribosome.