A New Density Model of Quartz Solubility in H2O-CO2-NaCl Ternary Systems up to High Temperatures and High Pressures

A novel density model for computing quartz solubility in H2O-CO2-NaCl hydrothermal fluids applicable to wide ranges of temperature and pressure is proposed. Based on the models of Akinfiev and Diamond (2009) and Wei et al. (2012), the effective partial molar volume of water ( V H 2 O ∗ ) is replaced by the partial molar volume of water ( V ¯ H 2 O ) by implementing an empirical correction, and water molar fraction ( x H 2 O ) is modified with water activity ( a H 2 O ), in addition to a series of changes to the model coefficient forms. The absolute values of averaged relative deviation of this model compared to the experimental data sets in pure water, H2O-CO2, and H2O-NaCl solutions are 5.74%, 6.69%, and 7.09%, respectively, which are better than existing models in the literature. The model can be reliably used for computing quartz solubilities in pure water from 0°C to 1000°C, from 0 bar to 20,000 bar, and in CO2- and/or NaCl-bearing solutions from 0°C to 1000°C, from 0 bar to 10,000 bar (with slightly lower accuracy at 5000-10,000 bar in H2O-NaCl systems) in the single liquid region. Moreover, the trends and overall ranges of this model may probably be more accurate in the H2O-CO2-NaCl fluid mixtures compared to the limited experimental data. In addition, a bisection algorithm for deriving the isopleths of quartz solubilities based on this new model is first proposed, and application perspectives are discussed for various geologic settings including subduction zone, lower crust-upper mantle, migmatite, pegmatite, porphyry, and orogenic deposits.

How internal cavities destabilize a protein

Although many proteins possess a distinct folded structure lying at a minimum in a funneled free energy landscape, thermal energy causes any protein to continuously access lowly populated excited states. The existence of excited states is an integral part of biological function. Although transitions into the excited states may lead to protein misfolding and aggregation, little structural information is currently available for them. Here, we show how NMR spectroscopy, coupled with pressure perturbation, brings these elusive species to light. As pressure acts to favor states with lower partial molar volume, NMR follows the ensuing change in the equilibrium spectroscopically, with residue-specific resolution. For T4 lysozyme L99A, relaxation dispersion NMR was used to follow the increase in population of a previously identified “invisible” folded state with pressure, as this is driven by the reduction in cavity volume by the flipping-in of a surface aromatic group. Furthermore, multiple partly disordered excited states were detected at equilibrium using pressure-dependent H/D exchange NMR spectroscopy. Here, unfolding reduced partial molar volume by the removal of empty internal cavities and packing imperfections through subglobal and global unfolding. A close correspondence was found for the distinct pressure sensitivities of various parts of the protein and the amount of internal cavity volume that was lost in each unfolding event. The free energies and populations of excited states allowed us to determine the energetic penalty of empty internal protein cavities to be 36 cal⋅Å−3.

A Comparative Study of Molecular Interactions of Three Tetracycline Derivatives with Aqueous β-Cyclodextrin Solution at Different Temperatures

A comparative study of complexation behaviour of three tetracycline derivatives viz. doxycycline hydrochloride, oxytetracycline hydrochloride and minocycline hydrochloride with β-cyclodextrin (β-CD) has been done with the help of various thermodynamic and spectroscopic methods. Density (ρ) and conductivity measurements have been carried out for binary drug/water and ternary drug/water/(β-CD) systems at three different temperature viz. 305.15, 310.15 and 315.15 K. The interactions of these tetracycline derivatives with β-cyclodextrin in aqueous solutions are further studied by means of fluorescence spectroscopy and UV-visible spectroscopy. From the measured density (ρ) data, partial molar volume (Φ°ν), partial molar volume expansibility (ϕ°e), Hepler′s constant (∂2ϕ°ν / ∂T2)P and partial molar volume of transfer (Δϕ°ν) have been obtained. From the conductance studies, the energetically favourable interactions are interpreted in the form of free energy change (ΔG) and the apparent association constant (Ka) was estimated from the fluorescence data.

Effect of 1-Octyl-3-Methylimidazolium Salicylate as an Active Pharmaceutical Ingredient (API-IL) on the Thermodynamic Behavior of Aqueous Glycine Solutions at T= 298.15 K

Background: The thermophysical properties of 1-octyl-3-methylimidazolium salicylate as an active pharmaceutical ingredient based on ionic liquid have been investigated in the presence of aqueous solutions of glycine. Therefore, the scope of this article was to determine these properties by measuring the densities, speeds of sound, viscosities, electrical conductances and refractive indices for ternary (glycine + 1-octyl-3-methylimidazolium salicylate + water) soloutions at T = 298.15 K. Methods: A commercial density and speed of sound measurement apparatus was used to measure the density and speed of sound data. Viscosities, electrical conductivities and refractive indices of the studied solutions were measured using digital viscometer, conductivity meter and refractometer, respectively. Results: Variety of properties such as partial molar volume of transfer ∆traV0ϕ, partial molar isentropic compressibility of transfer ∆traK0ϕ, viscosity B-coefficients of transfer ∆traB, ion association constants (KA) and molar refraction RD were determined to investigate the solute-solute and solute-solvent interactions in these systems. Conclusion: The positive values of transfer properties including partial molar volume of transfer (∆traV0ϕ), partial molar isentropic compressibility of transfer (∆traK0ϕ), and viscosity B-coefficients of transfer (∆traB) indicated that in these systems, the ion-polar and polar-polar interactions are dominant. The calculated hydration number showed that dehydration of glycine occurs in presence of this ionic liquid.

Cyclodextrins in Parkinson’s Disease

: Parkinson’s disease is a movement disorder characterized by a progressive degeneration of dopaminergic neurons that has been object of study by the scientific community through the last decades. However, nowadays there is still no treatment to cure it, although there are drugs available, with limited efficacy, to relieve the symptoms or replenish the cells with dopamine to supply the lack of dopaminergic neurons. This work was structured in two parts. In the first one, binary aqueous solutions of L-dopa and cyclodextrins were studied. In the second part, ternary aqueous solutions of L-dopa were studied with each of the selected cyclodextrins. In all cases, thermodynamic properties (density, partial molar volume and thermodynamic transfer functions for temperatures between 294.15 ± 0.01 K and 312.15 ± 0.01 K) and transport properties (mutual diffusion coefficients, viscosity, transfer viscosity at 298.15 ± 0.01 K and 310.15 ± 0.01 K) were studied. Using theoretical models to adjust the experimental data obtained for the diffusion coefficients and for the apparent molar volumes, in the ternary aqueous solutions, it was possible to estimate the values to the L-dopa-cyclodextrin association constant. For the aqueous ternary solutes, the partial molar volume of transfer of levodopa in the presence of the cyclodextrins, the partial molar expansibility at infinite dilution and from this, the Hepler constant, were determined. Also, the values of Gibbs free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) were determined. From the obtained information, it was possible to characterize the molecular interactions, as well as to identify some structural characteristics of the controlled drug delivery systems under study and to estimate the influence of the cyclodextrin substituent groups, and, also, the temperature effect in the interaction levodopa-cyclodextrin. It is our intent to attain information about the mechanism of possible new systems for controlled drug delivery systems, throughout an alternative perspective, which could allow to increase its effectiveness in the Parkinson’s treatment.

Partial Molar Volume of NaCl and CsCl in Mixtures of Water and Methanol by Experiment and Molecular Simulation

Densities of solutions of NaCl and CsCl in mixtures of water and methanolare determined by experiment and molecular dynamics simulation. Both experimentsand simulations cover the concentration range up to the solubilitylimit of the salt in the temperature range 288.15 ? T / K ? 318.15 at ambientpressure. Non-polarizable molecular models from the literature are usedfor the ions and solvents. The partial molar volume of the salts at in?nitedilution in the mixed solvent is determined from an empirical correlation ofthe data. The mixed solvent e?ects on the density and the partial molarvolumes of the salts are well predicted by the molecular models.