A model-guided determination of Δdis G2 ∞ for slightly soluble gases in water using solubility data: From the solvent's freezing point to its critical point

There is continuing interest in the description of the solubility of nonpolar gases in water over a wide range of temperatures. On one hand, the solubility data are used in many fields of science and technology; and on the other hand, simulation and theoretical calculations require experimental data to test their results and predictions. For these reasons it is important to have a means of calculating from the experimental solubility data the Gibbs energy of dissolution of gases (Δdis G 2 ∞ ) and Henry's constant (k H) over all the temperature range of existence of liquid water. Under ambient conditions it is relatively easy to relate Δdis G 2 ∞ and, hence, k H to the solubility data of nonpolar gases. However, this simple procedure becomes increasingly complicated as the temperature approaches the critical temperature of the solvent and it is necessary to make important corrections to obtain the thermodynamic quantities for the dissolution process. This difficulty can be resolved with a procedure that employs a perturbation method applied to a simple model solvent to guide the correct determination of k H and Δdis G 2 ∞ . We describe in this work an iterative calculation procedure whose correctness was validated with a thermodynamic relationship that uses only experimental data, hence it is model-free. Unfortunately this relationship can be applied only to a few systems due to its data requirements. The iterative procedure described in this work can be extended to higher pressures, p≅50 MPa above the solvent's vapor pressure, and also to gases dissolved in nonaqueous solvents.Fil: Alvarez, Jorge. Comisión Nacional de Energía Atómica; ArgentinaFil: Fernandez Prini, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Comisión Nacional de Energía Atómica; Argentin

The solubility of solids in near-critical fluids. Vi. CHI3 in CO2 revisited

The possibility of a complete thermodynamic description of the behaviour of dilute solutions on the basis of the Krichevskii function J = (∂p/∂x)V,T∞, which performs well in the near-critical region, is hampered by its weak temperature dependence. A previous determination of the solubility of CHI3 in near-critical CO2 showed little change in J over a temperature interval of 30 K. Using a high-pressure spectrophotometric technique, we have re-investigated (CHI3 + CO2), covering the temperature range 273 K to 373 K with seven isotherms. The maximum pressure was 25 MPa and, depending on temperature, the density of CO2 studied was between 0.5 mol · dm-3 and 25 mol · dm-3. As the maximum solubility of CHI3 was 1.7 · 10-2 mol · dm-3 (at the highest temperature and pressure), the solutions were sufficiently dilute to be considered in the Henrian range. The solubility data expressed as ln E, where E is the enhancement factor, were successfully fitted (with the exception of the 305.4 K isotherm) to polynomials of the reduced solvent density and of the square root of the reciprocal reduced temperature. The solubility of CHI3 at low fluid densities was used to obtain information about the intermolecular parameters of the solute using the second virial coefficient limiting expression for ln E. The experimental data allowed reliable estimation of the temperature dependence of J in the whole temperature and pressure ranges studied. The 305.4 K isotherm, which is only 0.4 per cent above the critical temperature of CO2, shows a different dependence on the fluid density, and consequently had to be analysed separately. A careful analysis of the experimental errors suggests that the difference is not an artifact, but is due to the near-critical behaviour of the solvent coupled with the solvent-solute intermolecular interactions

Thermodynamics of non-reactive gases dissolved in water at ambient temperature (T≤333 K): an update

The thermodynamics of dissolution of non-reactive gases in water under ambient conditions is of importance for the description of the properties of small hydrophobic solutes, and they are also of interest for environmental assessments. The review published in 1977 by Wilhelm, Battino and Wilcock (Chem. Rev. 77:219-262, 1977) constitutes a milestone in this field. However, a number of new data have been published since then, including both solubility and calorimetric determinations. We have analyzed the new data for 27 binary systems reported in the literature at the time of writing this article. Whenever solubility and calorimetric data both exist they have been fitted together. There are, however, systems for which only one type of new thermodynamic information is available; these systems were also analyzed using procedures that are described in this work.Fil: Alvarez, Jorge L.. Comisión Nacional de Energía Atómica; ArgentinaFil: Fernandez Prini, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin

Inmigrantes y el derecho a la información : Programa 92

Fil: Fernandez Prini, Roberto. Universidad de Buenos Aires; ArgentinaFil: Halpern, Gerardo. Universidad de Buenos Aires; ArgentinaEn esta emisión, contamos con la participación de dos participantes. En primer lugar, Roberto Fernandez Prini, Lic. en Cs. Químicas y Dr. de la UBA, Académico titular de la ANCEFN, nos estuvo hablando sobre el "Ciclo de Difusión Científica: La química moderna y el medio ambiente". Luego, contamos con la visita de Gerardo Halpern, Dr. en Antropología y Lic. en Cs. Comunicación (UBA). El tema de la entrevista fue: "Debates en torno a la ciudadanía y los Derechos Humanos: inmigrantes y el derecho a la información"

Molecular conformation of linear alkane molecules: From gas phase to bulk water through the interface

We studied the behavior of long chain alkanes (LCAs) as they were transferred from gas to bulk water, through the liquid-vapor interface. These systems were studied using umbrella sampling molecular dynamics simulation and we have calculated properties like free energy profiles, molecular orientation, and radius of gyration of the LCA molecules. The results show changes in conformation of the solutes along the path. LCAs adopt pronounced molecular orientations and the larger ones extend appreciably when partially immersed in the interface. In bulk water, their conformations up to dodecane are mainly extended. However, larger alkanes like eicosane present a more stable collapsed conformation as they approach bulk water. We have characterized the more probable configurations in all interface and bulk regions. The results obtained are of interest for the study of biomatter processes requiring the transfer of hydrophobic matter, especially chain-like molecules like LCAs, from gas to bulk aqueous systems through the interface.Fil: Murina, Ezequiel Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Comisión Nacional de Energía Atómica. Gerencia Química. CAC; ArgentinaFil: Fernandez Prini, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Comisión Nacional de Energía Atómica. Gerencia Química. CAC; ArgentinaFil: Pastorino, Claudio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Grupo de Materia Condensada; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Entrance dynamics of CH4 molecules through a methane-water interface

We studied the entrance mechanism of methane molecules into bulk water by Molecular Dynamics simulation over a broad time window. We corroborated that the presence of absorbed methane, under the studied thermodynamic state (298 K and roughly 10 MPa), does not influence the molecular configuration of water interface. Some representative interfacial trajectories were analyzed in detail and we propose an entrance mechanism in which interfacial water is not actively involved in the dissolution process. Finally, we described the Helmholtz Free Energy profile through the interface and obtained the dissolution free energy of methane in water.Fil: Murina, Ezequiel Luis. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pastorino, Claudio. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fernandez Prini, Roberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin

Near-critical and supercritical dilute solutions viewed from macroscopic and molecular-scale perspectives

Partial molar properties of dilute solutes in near-critical solvents exhibit a strong dependence on temperature and density which hinders the description of their behaviour under those conditions. We used the well-behaved Krichevskii function, J = (dp/dx)V,T supra infinity, to describe that region of the thermodynamic space, and have extended its use to ternary solutions (two solutes + one near-critical solvent) successfully. The use of supercritical solvents permits a controlled and continuous exploration of the density dependence of solutes' properties without undergoing phase transitions, hence the availability of a non-diverging property like J to describe the systems is greatly important. We show its application for binary and ternary systems that have been studied and also give some information about the molecular structure of near-critical solutions. This knowledge provides a better understanding about solvation and its dependence on long-range (critical) fluctuations in the presence of intermolecular interactions.Fil: Fernandez Prini, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Japas, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; ArgentinaFil: Marceca, Ernesto José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentin