scholarly journals Behavior and properties of water in silicate melts under deep mantle conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bijaya B. Karki ◽  
Dipta B. Ghosh ◽  
Shun-ichiro Karato
Keyword(s):  
Electrical Conductivity ◽  
Molar Volume ◽  
Water Solution ◽  
Pure Water ◽  
Electrical Conductance ◽  
Water Structure ◽  
Bulk Water ◽  
Silicate Melts ◽  
Pressure Regime ◽  
Low Pressures

AbstractWater (H2O) as one of the most abundant fluids present in Earth plays crucial role in the generation and transport of magmas in the interior. Though hydrous silicate melts have been studied extensively, the experimental data are confined to relatively low pressures and the computational results are still rare. Moreover, these studies imply large differences in the way water influences the physical properties of silicate magmas, such as density and electrical conductivity. Here, we investigate the equation of state, speciation, and transport properties of water dissolved in Mg1−xFexSiO3 and Mg2(1−x)Fe2xSiO4 melts (for x = 0 and 0.25) as well as in its bulk (pure) fluid state over the entire mantle pressure regime at 2000–4000 K using first-principles molecular dynamics. The simulation results allow us to constrain the partial molar volume of the water component in melts along with the molar volume of pure water. The predicted volume of silicate melt + water solution is negative at low pressures and becomes almost zero above 15 GPa. Consequently, the hydrous component tends to lower the melt density to similar extent over much of the mantle pressure regime irrespective of composition. Our results also show that hydrogen diffuses fast in silicate melts and enhances the melt electrical conductivity in a way that differs from electrical conduction in the bulk water. The speciation of the water component varies considerably from the bulk water structure as well. Water is dissolved in melts mostly as hydroxyls at low pressure and as –O–H–O–, –O–H–O–H– and other extended species with increasing pressure. On the other hand, the pure water behaves as a molecular fluid below 15 GPa, gradually becoming a dissociated fluid with further compression. On the basis of modeled density and conductivity results, we suggest that partial melts containing a few percent of water may be gravitationally trapped both above and below the upper mantle-transition region. Moreover, such hydrous melts can give rise to detectable electrical conductance by means of electromagnetic sounding observations.

scholarly journals Behavior and properties of water in silicate melts under deep mantle conditions

2021 ◽  
Author(s):  
Bijaya Karki ◽  
Dipta B. Ghosh ◽  
Shun-ichiro Karato
Keyword(s):  
Electrical Conductivity ◽  
Molar Volume ◽  
Water Solution ◽  
Pure Water ◽  
Electrical Conductance ◽  
Bulk Water ◽  
Silicate Melts ◽  
Ideal Mixing ◽  
Pressure Regime ◽  
Low Pressures

Abstract Water (H2O) as one of the most abundant fluids present in Earth plays crucial role in the generation and transport of magmas in the interior. Though hydrous silicate melts have been studied extensively, the experimental data are confined to relatively low pressures and the computational results are still rare. Moreover, these studies imply large differences in the way water influences the physical properties of silicate magmas, such as density and electrical conductivity. Here, we invesigate the equation of state, speciation, and transport properties of water dissolved in Mg1 − xFexSiO3 and Mg2(1−x)Fe2xSiO4 melts (for x = 0 and 0.25) as well as in its bulk (pure) fluid state over the entire mantle pressure regime at 2000 to 4000 K using first-principles molecular dynamics. The simulation results allow us to constrain the partial molar volume of the water component in melts along with the molar volume of pure water. The predicted volume of silicate melt + water solution is negative at low pressures but becomes zero above 15 GPa implying ideal mixing at higher pressures. Consequently, the hydrous component tends to lower the melt density to similar extent over much of the mantle pressure regime irrespective of composition. Our results also show that hydrogen diffuses fast in silicate melts and enhances the melt electrical conductivity in a way that differs from electrical conduction in the bulk water. The speciation of the water component varies considerably from the bulk water structure as well. Water is dissolved in melts mostly as hydroxyls at low pressure and as -O-H-O-, -O-H-O-H- and other extended species with increasing pressure. On the other hand, the pure water behaves as a molecular fluid below 15 GPa, gradually becoming a dissociated fluid with further compression. On the basis of modeled density and conductivity results, we suggest that partial melts containing a few percent of water may be gravitationally trapped both above and below the upper mantle-transition region. Moreover, such hydrous melts can give rise to detectable electrical conductance by means of electromagnetic sounding observations.

Association of Graft Copolymers of Alkyl Methacrylates with α-Methyl-ω-hydroxy-poly(oxyethylene) ethacrylates

1995 ◽  
Vol 60 (11) ◽  
pp. 1971-1985 ◽  
Author(s):  
Čestmír Koňák ◽  
Zdeněk Tuzar ◽  
Pavla Kopečková ◽  
Joseph D. Andrade ◽  
Jindřich Kopeček
Keyword(s):  
Light Scattering ◽  
Graft Copolymers ◽  
Water Solution ◽  
Pure Water ◽  
Solution Properties ◽  
Monomer Composition ◽  
Special Procedure ◽  
Methyl Cellosolve ◽  
Hexyl Methacrylate ◽  
Alkyl Methacrylates

Solution properties of the statistical copolymers of alkyl methacrylates (AMA) with α-methyl-ω-hydroxy-poly(oxyethylene) methacrylates (MPOEMA) (nonionic polysoaps) were studied using static and dynamic ligh scattering as a function of monomer composition and concentration in aqueous and methyl cellosolve solutions. The solubility of the copolymers in water was found to be dependent on molar contant of AMA. While copolymers with low content of hexyl methacrylate (HMA) (0 and 20 mole %) were directly soluble in water, forming true solutions with a low content of large swollen aggregates, copolymers with a higher content of HMA or lauryl methacrylate (LMA) were not directly dispersable in water. A special procedure, the stepwise dialysis from methyl cellosolve solutions against water, had to be used to prepare them in the pseudomicellar form. The copolymers were directly soluble in methyl cellosolve and its water solution containing up to 60 vol.% of water. Nevertheless, the light scattering experiments were dominated by light scattering of swollen particles of aggregated copolymer molecules. The copolymers were not soluble in the mixtures containing 70-100 vol.% of water. Paramaters of aggregates in the mixture with 60 vol.% of water and in pure water were found to be very similar.

scholarly journals Testing for ion-mediated enhancement of the hydraulic conductance of the leaf xylem in diverse angiosperms

2017 ◽  
Vol 4 ◽  
pp. e004 ◽  
Author(s):  
Christine Scoffoni ◽  
Grace John ◽  
Herve Cochard ◽  
Lawren Sack
Keyword(s):  
Water Solution ◽  
Pure Water ◽  
Xylem Sap ◽  
Hydraulic Conductance ◽  
Membrane Pores ◽  
Whole Plant ◽  
Pit Membrane ◽  
Major Bottleneck ◽  
The Difference ◽  
Xylem Conduits

Replacing ultra-pure water solution with ion solution closer to the composition of natural xylem sap increases stem hydraulic conductance by up to 58%, likely due to changes in electroviscosity in the pit membrane pores. This effect has been proposed to contribute to the control of plant hydraulic and stomatal conductance and potentially to influence on carbon balance during dehydration. However, this effect has never been directly tested for leaf xylem, which constitutes a major bottleneck in the whole plant. We tested for an ion-mediated increase in the hydraulic conductance of the leaf xylem (Kx) for seven species diverse in phylogeny and drought tolerance. Across species, no significant changes in Kx were observed between 0 and 15 mM KCl. We further tested for an effect of ion solution during measurements of Kx vulnerability to dehydration in Quercus agrifolia and found no significant impact. These results for leaf xylem contrast with the often strong ion effect reported for stems, and we suggest several hypotheses to account for the difference, relating to the structure of xylem conduits across vein orders, and the ultrastructure of leaf xylem pores. A negligible ion response in leaves would weaken xylem sap ion-mediated control of plant hydraulic conductance, facilitating modeling of whole plant hydraulic behavior and its influence on productivity.

scholarly journals Protein Denaturation Zero Entropy Temperature, and the Structure of Water Around Hydrophobic and Amphiphilic Solutes

2020 ◽  
Author(s):  
kazimieras Tamoliūnas ◽  
Nuno Galamba
Keyword(s):  
Protein Denaturation ◽  
Structural Information ◽  
Pure Water ◽  
Hydrophobic Effect ◽  
Hydrophobic Hydration ◽  
Bulk Water ◽  
Solvent Accessible Surface Area ◽  
Effect Of Temperature ◽  
Structure Of Water ◽  
Zero Entropy

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 in sight on the singular behavior of water concerning the zero entropy temperature TS and entropic convergence also observed upon protein denaturation. We show that, similar to hydrocarbons and proteins, polar amphiphilic solutes exhibit a TS, although strongly dependent upon 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. However, 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, consistent with IT assumptions. The source of the differences between Kauzmann's "hydrocarbon model" on protein denaturation and hydrophobic hydration is also discussed with relatively large amphiphilic hydrocarbons displaying a more similar behavior to globular proteins, than aliphatic hydrocarbons.<br>

scholarly journals Thermodynamic Study of the Solubility of Naproxen in Some 2-Propanol + Water Mixtures

2016 ◽  
Vol 12 (1) ◽  
pp. 48-55 ◽  
Author(s):  
Diego Iván Caviedes Rubio ◽  
Gerson Andrés Rodríguez Rodríguez ◽  
Daniel Ricardo Delgado
Keyword(s):  
Gibbs Energy ◽  
Volume Fraction ◽  
Pure Water ◽  
Water Structure ◽  
Negative Slope ◽  
Driving Mechanism ◽  
Linear Plot ◽  
Enthalpy And Entropy ◽  
The Mean ◽  
Rich Mixtures

The equilibrium solubilities of the anti-inflammatory drug naproxen (NPX) in 2-propanol + water mixtures were determined at several temperatures from 298.15 to 313.15 K. The Gibbs energy, enthalpy, and entropy of solution and of mixing were obtained from these solubility data. The solubility was maximal in φ1 = 0.90 and very low in pure water at all the temperatures studied. A non-linear plot of ∆solnH° vs. ∆solnG° with negative slope from pure water up to 0.20 in volume fraction of 2-propanol and positive beyond this composition up pure 2-propanol was obtained at the mean temperature, 305.55 K. Accordingly, the driving mechanism for NPX solubility in the water-rich mixtures was the entropy, probably due to water-structure loss around non-polar moieties of the drug and for the 2-propanol-rich mixtures it was the enthalpy, probably due to its better solvation of the drug.

Pure Water Structure and Hydration Forces for Protein Folding

2002 ◽  
pp. 403-416
Author(s):  
Teresa Head-Gordon ◽  
Greg Hura ◽  
Jon M. Sorenson ◽  
Robert M. Glaeser
Keyword(s):  
Protein Folding ◽  
Pure Water ◽  
Water Structure ◽  
Hydration Forces

Hydrometallurgical thermodynamics. I. Effect of sulfate ion-pairing and ion-solvation on the copper-iron redox equilibrium in aqueous acetonitrile

1983 ◽  
Vol 36 (9) ◽  
pp. 1687 ◽  
Author(s):  
BW Clare ◽  
P Singh ◽  
P Mangano ◽  
AJ Parker ◽  
DM Muir
Keyword(s):  
Water Solution ◽  
Pure Water ◽  
Ion Pairing ◽  
Ion Solvation ◽  
Sulfate Ion ◽  
Redox Equilibrium ◽  
Small Shift ◽  
Enthalpy Changes ◽  
The Right ◽  
Iron Redox

The copper-iron redox equilibrium is shifted to the right CuII+FeII↔CuI+FeIII by strong ion-pairing of sulfate ion with FeIII and by specific solvation of CuI with acetonitrile. The equilibrium constant has been measured by direct e.m.f. and spectroscopic methods between pH 0-2 and found to be about 107 higher for practical solutions of sulfates in acetonitrile/water than that calculated for perchlorates in pure water. Enthalpies and free energies of transfer of these ions from water to acetonitrile/water show that the shift in equilibrium to Cul+FeIII in acetonitrile/water solution is strongly favoured by enthalpy changes associated with copper(I)-acetonitrile ion-solvation. Ion-pairing of sulfate ion with iron(III) results in an increase in entropy and a small shift of the equilibrium to the right.

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