Low-density Water Research Articles

Protein Denaturation, Zero Entropy Temperature, and the Structure of Water around Hydrophobic and Amphiphilic Solutes.

The hydrophobic effect plays a key role in many chemical and biological processes, including protein folding. Nonetheless, a comprehensive picture of the effect of temperature on hydrophobic hydration and protein denaturation remains elusive. Here, we study the effect of temperature on the hydration of model hydrophobic and amphiphilic solutes, through molecular dynamics, aiming at getting insight on the singular behavior of water, concerning the zero-entropy temperature, TS, and entropy convergence, TS*, also observed for some proteins, upon denaturation. We show that, similar to hydrocarbons, polar amphiphilic solutes exhibit a TS, although strongly dependent on solute-water interactions, opposite to hydrocarbons. Further, the temperature dependence of the hydration entropy, normalized by the solvent accessible surface area, is shown to be nearly solute size independent for hydrophobic but not for amphiphilic solutes, for similar reasons. These results are further discussed in the light of information theory (IT) and the structure of water around hydrophobic groups. The latter shows that the tetrahedral enhancement of some water molecules around hydrophobic groups, associated with the reduction of water defects, leads to the strengthening of the weakest hydrogen bonds, relative to bulk water. In addition, a larger tetrahedrality is found in low density water populations, demonstrating that pure water has encoded structural information, similar to that associated with hydrophobic hydration. The reversal of the hydration entropy dependence on the solute size, above TS*, is also analyzed and shown to be associated with a greater loss of water molecules exhibiting enhanced orientational order, in the coordination sphere of large solutes. Finally, the source of the differences between Kauzmann's "hydrocarbon model" on protein denaturation and hydrophobic hydration is discussed, with relatively large amphiphilic hydrocarbons seemingly displaying a more similar behavior to some globular proteins than aliphatic hydrocarbons.

The dose response of high-resolution diode-type detectors and the role of their structural components in strong magnetic field.

This study aims to investigate the dose response of diode-type detectors in the presence of strong magnetic field and to understand the underlying mechanisms leading to the observed magnetic field dependence by close examinations on the role of the detector's design. Three clinical diode-type detectors (PTW microSilicon type 60023, PTW microDiamond type 60019, and IBA Razor diode) have been studied. Measurements were performed at the linear accelerator experimental facility of the German National Metrology Institute (PTB, Braunschweig) with electromagnets up to 1.4T to obtain the magnetic field correction factors . The experimental results were compared to Monte Carlo simulations. Stepwise modifications of the detectors' models were performed to characterize the contributions of the structural components toward the magnetic field-dependent dose response. Additionally, systematic Monte Carlo study was conducted to elucidate the influence of the structural layers with varying density located above and beneath the detector's sensitive volume. The dose response of all investigated detectors decreases with magnetic field. As a result, the associated factors increase by approximately 10% for the PTW detectors, and by 5% for the IBA Razor diode at 1.5T. The sensitive volume itself was shown to cause negligible effect but the diode substrate with enhanced density situated directly below the sensitive volume contributes strongest to the observed magnetic field dependence. Systematic simulations revealed that increases with magnetic field if the density of the structural layer located beneath the sensitive volume is higher than that of normal water (>1g/cm3 ). In the case where the layer consists of low-density water (1.2mg/cm3 ), decreases with the magnetic field strength. On the contrary , if the structural layer with varying density is situated above the sensitive volume, the reversed effect could be observed. The experimental and Monte Carlo results demonstrated that the dose response of the investigated diode-type detectors decreases in magnetic field. This observation can be generally attributed to the common construction of diode-type detectors, where structural components with enhanced density, for example the diode substrate, are situated below the sensitive volume. The results provide deeper insights into the behavior of clinical diode detectors when used in strong magnetic field.

Warm Spiral Streamers over Gulf Stream Warm-Core Rings

AbstractThis study examines the generation of warm spiral structures (referred to as spiral streamers here) over Gulf Stream warm-core rings. Satellite sea surface temperature imagery shows spiral streamers forming after warmer water from the Gulf Stream or newly formed warm-core rings impinges onto old warm-core rings and then intrudes into the old rings. Field measurements in April 2018 capture the vertical structure of a warm spiral streamer as a shallow lens of low-density water winding over an old ring. Observations also show subduction on both sides of the spiral streamer, which carries surface waters downward. Idealized numerical model simulations initialized with observed water-mass densities reproduce spiral streamers over warm-core rings and reveal that their formation is a nonlinear submesoscale process forced by mesoscale dynamics. The negative density anomaly of the intruding water causes a density front at the interface between the intruding water and surface ring water, which, through thermal wind balance, drives a local anticyclonic flow. The pressure gradient and momentum advection of the local interfacial flow push the intruding water toward the ring center. The large-scale anticyclonic flow of the ring and the radial motion of the intruding water together form the spiral streamer. The observed subduction on both sides of the spiral streamer is part of the secondary cross-streamer circulation resulting from frontogenesis on the stretching streamer edges. The surface divergence of the secondary circulation pushes the side edges of the streamer away from each other, widens the warm spiral on the surface, and thus enhances its surface signal.

Topographic, soil, and climate drivers of drought sensitivity in forests and shrublands of the Pacific Northwest, USA

Climate change is anticipated to increase the frequency and intensity of droughts, with major impacts to ecosystems globally. Broad-scale assessments of vegetation responses to drought are needed to anticipate, manage, and potentially mitigate climate-change effects on ecosystems. We quantified the drought sensitivity of vegetation in the Pacific Northwest, USA, as the percent reduction in vegetation greenness under droughts relative to baseline moisture conditions. At a regional scale, shrub-steppe ecosystems—with drier climates and lower biomass—showed greater drought sensitivity than conifer forests. However, variability in drought sensitivity was considerable within biomes and within ecosystems and was mediated by landscape topography, climate, and soil characteristics. Drought sensitivity was generally greater in areas with higher elevation, drier climate, and greater soil bulk density. Ecosystems with high drought sensitivity included dry forests along ecotones to shrublands, Rocky Mountain subalpine forests, and cold upland sagebrush communities. In forests, valley bottoms and areas with low soil bulk density and high soil available water capacity showed reduced drought sensitivity, suggesting their potential as drought refugia. These regional-scale drought-sensitivity patterns discerned from remote sensing can complement plot-scale studies of plant physiological responses to drought to help inform climate-adaptation planning as drought conditions intensify.

Correlation and prediction of thermodynamic properties of dilute solutes in water up to high T and P. III. Polar and aromatic solutes H2S, C6H6, C7H8, CH3SH, SO2, HCN, acetone, NH3, CH3NH2, CH3OH, C2H5OH, phenol

Fugacity coefficients of twelve polar or aromatic species at infinite dilution in water (H2S, benzene C6H6, toluene C7H8, methanethiol CH3SH, SO2, HCN, acetone (CH3)2CO, NH3, methylamine CH3NH2, methanol CH3OH, ethanol C2H5OH and phenol C6H5OH) have been evaluated from ambient conditions (298 K, 0.1 MPa) to high temperatures (up to 2000 K) and water densities (up to 1500 kg m–3). The approach is based on a correlation developed for the function, A12∞=V2∞/κTRT, and includes known constraints: second virial coefficients at low water densities, hard sphere behavior at high water densities, near–critical principles, and corresponding–states relations. A comparison with literature data at subcritical (Henry's and vapor–liquid distribution constants) and supercritical temperatures (fugacity coefficients) is made.

Molecular dynamics study of grain boundaries and triple junctions in ice.

We perform classical molecular dynamics simulations of polycrystalline ice at 250 K using the TIP4P/Ice model. The structures of polycrystalline ice are prepared by growing ice particles in supercooled water. An order parameter developed recently is used to characterize local structures in terms of the liquid-liquid phase transition scenario. It is shown that the grain boundaries and triple junctions in ice are structurally similar to low-density liquid water in which most water molecules form four hydrogen bonds and the O-O-O angles deviate from the tetrahedral angle of 109.47°. The thickness of the grain boundaries is ∼1 nm. The diffusion coefficient of water molecules along the grain boundaries calculated in this study, 5.0 × 10-13 m2 s-1, is in good agreement with experimental data. The diffusion along the triple junctions is 3.4 times faster than that along the grain boundaries. We model the grain size dependence of diffusivity of water molecules in polycrystalline ice using the simulation results and find that the impact of the grain boundaries and the triple junctions on the diffusivity is negligible for typical polycrystalline ice samples having grain sizes of the order of millimeters. We also demonstrate that the properties of the grain boundaries are quite different from those of the ice/vapor interface at the same temperature: the quasi-liquid layer at the ice/vapor interface is similar to high-density liquid water and the diffusion coefficient along the ice/vapor interface is two orders of magnitude larger than that along the grain boundaries.

Analytical Determination of the Nucleation-Prone, Low-Density Fraction of Subcooled Water.

Subcooled water is the primordial matrix for ice embryo formation by homogeneous and heterogeneous nucleation. The knowledge of the specific Gibbs free energy and other thermodynamic quantities of subcooled water is one of the basic prerequisites of the theoretical analysis of ice crystallization in terms of classical nucleation theory. The most advanced equation of state of subcooled water is the IAPWS G12-15 formulation. The determination of the thermodynamic quantities of subcooled water on the basis of this equation of state requires the iterative determination of the fraction of low-density water in the two-state mixture of low-density and high-density subcooled water from a transcendental equation. For applications such as microscopic nucleation simulation models requiring highly frequent calls of the IAPWS G12-15 calculus, a new two-step predictor-corrector method for the approximative determination of the low-density water fraction has been developed. The new solution method allows a sufficiently accurate determination of the specific Gibbs energy and of all other thermodynamic quantities of subcooled water at given pressure and temperature, such as specific volume and mass density, specific entropy, isothermal compressibility, thermal expansion coefficient, specific isobaric and isochoric heat capacities, and speed of sound. The misfit of this new approximate analytical solution against the exact numerical solution was demonstrated to be smaller than or equal to the misprediction of the original IAPWS G12-15 formulation with respect to experimental values.

Preparation of glass shell fly ash-clay based lightweight aggregate with low water absorption by using sodium carbonate solution as binder

Fly ash-clay based lightweight aggregates with low density and low water absorption were prepared using sodium carbonate solution as binder and coke particles as pore-forming agent. The addition of 60 wt% coke particles to the initial formula of only fly ash and clay could form the porous structure and effectively lower the apparent density. The apparent density, water absorption and strength of the aggregates at different conditions including mass concentration and sintering temperature were tested. It was found that the mass concentration 10 wt% of the sodium carbonate solution was the best concentration to form the completely glassy shell at 1220 °C. And the glassy shell could significantly lower the water absorption from 22.97% to 8.84%. Then the glassy shell aggregates with low density (1.22 g/cm3 apparent density), 8.84% water absorption and particle strength (4.25 MPa) were obtained. All the properties meet the national standards of GB/T 17431. Therefore, using sodium carbonate solution to replace water as the binder by spraying in the forming process is a simple and applicable way to lower the water absorption of aggregates in the industrial production of lightweight aggregates. At the same time, the production of aggregates using solid waste fly ash as a raw material can effectively reduce production costs.

Correlation and prediction of thermodynamic properties of dilute solutes in water up to high T and P. II. Normal fluids CO2, C2H4, C2H6, C3H8, n-C4H10, i-C4H10, functional groups CH3 and CH2

Fugacity coefficients of dilute aqueous solutions of six species belonging to normal fluids (CO2, C2H4, C2H6, C3H8, n-C4H10, i-C4H10) as well as functional groups CH3 and CH2 have been evaluated from ambient conditions (298 K, 0.1 MPa) to high temperatures (up to 2000 K) and water densities (up to 1500 kg m−3). The basis of the approach is a correlation developed for the function, A12∞=V2∞/κTRT, that includes known constraints: second virial coefficients at low water densities, hard sphere behavior at high water densities, near-critical principles, and corresponding-states relations. A comparison with literature data at subcritical (Henry's and vapor-liquid distribution constants) and supercritical temperatures (fugacity coefficients) is made. For aqueous CO2, the agreement with literature data is generally satisfactory. It is shown that for other solutes existing disagreements can be traced mostly to the values of the second cross virial coefficients employed in the literature models, suggesting the room for improvement of existing recommendations.

Transfer of water molecules in presence of low density water vapor

Problems of molecular transfer in gas environment are considered with assumption that part of water molecules may change their properties to provide transfer process. This change consists in increase of dimension of vector space, which used to describe transfer process, from 3 to 4. Other cases of extending of dimension of vector space are particular considered. At first, relations between affine group and Markov chain is considered. An action of Markov chain matrix as affine matrix is analyzed with result that point with coordinate number equal 1 is fixed point on straight line.

Enhanced nitrogen removal of aerobic denitrifier using extracellular algal organic matter as carbon source: application to actual reservoir water.

Man-made organic matter acting as carbon source for oligotrophic aerobic denitrification has been studied extensively, while less attention has been paid to the actual organic matter derived from drinking water reservoir. In this study, the effect of extracellular organic matter (EOM) released from Microcystis aeruginosa and Chlorella sp. and organic matter in actual reservoir water on aerobic denitrification performance of Acinetobacter johnsonii strain WGX-9 has been investigated, by measuring nitrogen removal and determining changes in the properties of organic matter. Results indicated that the Acinetobacter johnsonii strain WGX-9 showed effective nitrogen removal efficiency when cultural conditions were low C/N of 5, pH of 5-11, and low temperature of 8°C. The nitrate removal efficiency with EOM as the sole carbon source was relatively higher than that with intracellular organic matter or natural organic matter as the sole carbon source. This is probably due to that EOM exerts a lower molecular weight and better ability of donating electrons. Besides, the findings can elucidate that nitrate and total organic matter removal efficiency with actual high-density algal water as the carbon source was higher than that with actual low-density algal water as the carbon source. This was attributed to that more EOM was released in high-density algal water, which highlighted the aerobic denitrification performance of Acinetobacter johnsonii strain WGX-9. This study will provide a reference for the application of aerobic denitrifier in drinking water reservoirs.

Pressure Effects on Water Dynamics by Time-Resolved Optical Kerr Effect.

Despite water being the most common and most widely studied substance in the world, it still presents unknown aspects. In particular, water shows several thermodynamic and dynamical anomalies in the liquid and supercooled metastable phases, and the natures of these phases are still hotly debated. Here, we report measurements of water using the optical Kerr effect as a function of pressure along two isotherms, at 273 K from 0.1 to 750 MPa and at 297 K from 0.1 to 1350 MPa, reaching the supercooled metastable phase. The structural relaxation and the low frequency vibrational dynamics of water show a peculiar pressure dependence similar to that of other dynamical properties. The data analysis suggests the presence in the water phase diagram of a crossover area that divides two regions characterized by different dynamic regimes, which appear to be related to two liquid forms, one dominated by the high density water and the other by the low density water.

Properties of silicon manganese slag as an aggregate for concrete depending on cooling conditions

When molten silicon manganese slag contacts with water, it is cooled down rapidly with much water vapor and to be a rock masses like as volcano rock. This porous rock may be used as a lightweight aggregate. In this study, we have tried to evaluate engineering properties of this material to use for construction fields. In the view point of engineering properties, such as low density and low water absorption, regular shape the aggregate cooled by air–water is comparatively superior to other cooling condition. Depending on the ratio of air to water, the size of the pore in aggregate is found to change, and the higher the ratio of water, the higher the average pore size. The effect of pore size and pore volume has a direct effect on mortar, and the dry shrinkage is low in mortar using air–water mixed rapidly cooled aggregates. In mortar engineering properties, the mortar replacing air–water mixed rapid cooled aggregate shows comparatively proper properties, such as unit weight of 1682 kg/3 and compressive strength of 22.9 MPa, which means that this lightweight aggregate has the possibility as a structural lightweight aggregate.

Recrystallization of fine-crystalline barium titanate in low-density water medium

Fine-crystalline barium titanate was synthesized from a mixture of barium hydroxide monohydrate and titanium dioxide in water vapor medium at 200 °C and 1.55 MPa and subsequently treated in subcritical vapor and supercritical water at 200−400 °C and 1.55-26.3 MPa. Recrystallization of synthesized powder led to an increase in average crystal size and to tetragonal distortion of BaTiO3 structure. Formation of highly tetragonal BaTiO3 was observed after the treatment in supercritical water at 400 °C, 26.3 MPa. Treatment of BaTiO3 crystals in water vapor and supercritical water made for elimination of structural defects and for changes in the morphology and dispersion composition of the powder. The results are of importance for effective production of barium titanate powder of different dispersion as raw material for ferroelectric ceramics.

Structural and Thermophysical Anomalies of Liquid Water: A Tale of Molecules in the Instantaneous Low- and High-Density Regions.

Water is believed to be a heterogeneous liquid comprising multiple density regions that arise because of the presence of interstitial molecules and can be differentiated by their structure as well as the existence of hydrogen-bonded pairs with varying strengths. First-principles molecular dynamics studies were performed at six different temperatures to investigate the effect of temperature on the thermophysical, structure, dynamics, and vibrational spectral properties of the water molecules using dispersion-corrected density functional theory. The variation of properties like density, cohesive energy, and compressibility with a change in temperature produces a trend that matches with the experiments and resembles the experimentally observed anomalous behavior. We explore the possibility of explaining the trends in calculated properties by analyzing the structure and dynamics of the water molecules in terms of instantaneous low- and instantaneous high-density regions that are found during the simulation time. The dynamics of these two types of water molecules were studied by calculating the lifetime from the proposed autocorrelation functions. The lifetime of formation of instantaneous low-density water is found to decrease with an increase in temperature, whereas the lifetime of instantaneous high-density water is found to be maximum at 298 K among all the considered temperatures. The presence of more interstitial water molecules is observed at this temperature. The signature of these water molecules is found in the radial distribution function, spatial distribution function, void distribution, configurational space, orientational dynamics, and spectral diffusion calculations. It is also found that around 298 K, these water molecules are present distinctively that mix up with the first and second solvation shells with the rise of the temperature. The outlook of the reported results can be extended to other thermodynamic conditions to explain some of the anomalous properties, which can be related to the presence of the interstitial molecules in water.

Enhancement of water droplet evaporation rate by application of low frequency acoustic field

Evaporation rates of low-density water aerosols in a cylindrical acoustic resonator were investigated experimentally, motivated by the potential use of water droplet aerosols in two-phase thermoacoustic devices. Measurements of water aerosol evaporation rates were conducted using a novel direct visualization method combining mass balance quantification based on the light scattering from water droplets and two-dimensional PIV measurements with the droplets acting as the flow visualization particles. Water droplet aerosol evaporation was monitored at a location between the resonator pressure and velocity anti-nodes, while being subjected to a low frequency (110 Hz) acoustic standing wave with various acoustic pressure amplitude (APA) values. Application of the acoustic field was found to significantly increase water droplet evaporation rates, exhibiting a linear dependency on the applied APA in the range 600 Pa < APA < 1720 Pa Normalization of the obtained results using a simple dimensional model enabled the identification of the main governing parameters controlling droplet evaporation rates. These were found to be the known Reynolds number based on relative droplet motion, the newly introduced acoustic drive ratio, and droplet-to-air temperature difference over air water vapor concentration ratio. In addition, significant variations in the acoustic intensity, detected during the experiments, were shown to be a useful marker for measurements of droplet evaporation rate.

A folded ice monolayer.

A highly stable ice monolayer with folded structural motifs is predicted by means of a novel tiling method augmented with ab initio calculations. This ice monolayer has every two neighboring water hexamers connected by a water square yet folded into two distinct planes, and is thus coined as a folded ice model. It is in the ground state in a range of water densities from 0.08 to 0.12 Å-2, with a stronger energy preference at a lower water density. Its stability shown by ab initio molecular dynamics simulations can sustain up to a temperature of 100 K. The tiling method also enables the prediction of a family of considerably stable ice monolayers with a variety of puckered structures. These results enrich our knowledge of low-dimensional water structures and pave a way to explore more exotic ice nanostructures under confinements.

Preventing damage to floating foils caused by Rayleigh-Taylor instabilities

An evaporated metal foil target is often produced on a layer of water-soluble parting agent previously applied to a massive substrate. The foil is then floated onto a water surface by immersing the substrate into a water bath. and is picked up later if the foil survives. During the foil's release, a significant fraction of the dissolved parting agent may remain close to the floating foil, as a "heavy" thin layer of solution having higher density than water. This layer of parting agent solution and the lower-density water bath below it form a gravitationally unstable configuration known as a Rayleigh-Taylor instability. If the foil is sufficiently thin, its mass and elastic properties can be ignored, and the motion of the liquids is determined by only the liquids' properties. This system can spontaneously adjust itself toward stability in several ways, one of which involves rotating a cylindrical liquid cell having a horizontal axis, and its cylindrical surface tangent to the surface. This motion moves part of the heavy layer from the top surface downward. The target maker detects this occurrence by the motions of the foil floating on the top of the bath; if the foil is frail, these motions may result in the crumpling, wrinkling, or tearing of the foil. We have observed such behavior with aluminum foils having thickness of 37 nm and diameter of 920 mm on NaCl parting agent, and have successfully implemented methods to prevent such damage.

Highly recyclable and super-tough hydrogel mediated by dual-functional TiO2 nanoparticles toward efficient photodegradation of organic water pollutants

A novel photocatalytic hydrogel was prepared by loading TiO2 nanoparticles (TiO2 NPs) onto the surface of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized chitin nanofibers (TOCNs), which were further incorporated into the polyacrylamide (PAM) matrix. The resultant hydrogel exhibited a macro-porous structure with a low density (~1.45 g/cm3) and high water content (~80%). The well-dispersed TiO2 NPs not only acted as a crosslinking agent for bridging the three-dimensional porous network structure, but also endowed the hydrogel with good catalytic activity. After the introduction of TiO2 accounting for 10 wt% of the hydrogel mass, the hydrogels showed compressive strength of 1.46 MPa at 70% strain, tensile stress of 316 kPa, tensile strain of 310%, toughness of 47.25 kJ/m3 and fatigue resistance. Compared with neat TOCN-PAM hydrogel, the uniaxial compressive and tensile strengths of the TiO2-TOCN-PAM10 hydrogel increased 6.35-fold and 3.70-fold, respectively. Furthermore, the removal of methyl orange (MO) was attributed to the synergistic effect of the adsorption and photocatalytic degradation of the hydrogels. The hydrogels adsorbed up to 8.5% of MO after 150 min of adsorption and a photocatalytic degradation rate of 97.3% achieved after 90 min of UV irradiation at pH = 2. Especially, the TiO2-TOCN-PAM10 hydrogel exhibited excellent recycling performance: its MO removal efficiency was around 96% even after 10 reuse cycles. The as-prepared hydrogels, with characteristics of excellent stretchability, photocatalytic activity and recyclability, are expected to be used in alleviating organic pollutants in practical wastewater treatments.

A molecular simulation demonstrates proteins re-folding at extremely low temperatures

Low water density may be the culprit behind unusual protein refolding at temperatures 55K below the freezing temperature of water.