Simulación molecular de disoluciones de electrolitos

50 páginas.Trabajo de Máster Universitario en Simulación Molecular (2020/21). Directores: Dra. Dña. María Martín Conde ; Dr. D. Carlos Vega de las Heras. En este trabajo, se ha desarrollado un nuevo modelo de potencial basado en cargas escaladas para NaCl. En trabajos anteriores presentamos el modelo Madrid-2019 utilizando una carga de ±0,85 e. En este trabajo en cambio, exploramos diferentes valores de cargas para los iones con el fin de reproducir los valores experimentales de propiedades de transporte que eran sobreestimados con el modelo Madrid-2019 y aún más con modelos de cargas unitarias. Este nuevo modelo de potencial se denominará Madrid-Transport y se trata de un modelo no polarizable para ser utilizado con el modelo de agua TIP4P/2005. Se han empleado cargas de ±0,75 e para los iones Na+ y Cl− para describir con precisión no sólo las densidades sino también las viscosidades y los coeficientes de difusión de disoluciones acuosas de NaCl en todo el intervalo de concentraciones hasta el límite de solubilidad experimental del cloruro sódico. Sin embargo, la disminución de la carga de los iones lleva a una peor descripción de otras propiedades como el descenso crioscópico del hielo, la predicción de la temperatura a la que ocurre el máximo en densidad (a presión atmosférica) o la tensión superficial. Esta última magnitud puede describirse correctamente utilizando una carga de ±0,92 e con un nuevo modelo también desarrollado en este trabajo llamado Madrid-Interfacial.In this work we have developed a new force field based on scaled charges for NaCl. Previously, we have presented the Madrid-2019 model using a charge of ±0.85 e. In this work we explore different values of charge for the ions in order to reproduce several transport properties which were overestimated with Madrid-2019 force field and with unit charge models. This force field named as Madrid-Transport is a nonpolarizable model which can be used with the TIP4P/2005 water model. A charge of ±0.75 e for Na+ and Cl− ions has been employed to describe accurately not only the densities but also the viscosities and diffusion coefficients of NaCl aqueous solutions in all the concentrations interval up to the experimental solubility limit of NaCl. Decreasing the charge of the NaCl gets worse the description of other properties such as the freezing depression of ice, the prediction of temperature of maximum density (at room pressure) or interfacial tension. The last one which can be described properly using a charge of ±0.92 e with a new force field also developed in this work called Madrid-Interfacial

Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation

In this paper, the solubility of methane in water along the 400 bar isobar is determined by computer simulations using the TIP4P/Ice force field for water and a simple LJ model for methane. In particular, the solubility of methane in water when in contact with the gas phase and the solubility of methane in water when in contact with the hydrate has been determined. The solubility of methane in a gas–liquid system decreases as temperature increases. The solubility of methane in a hydrate–liquid system increases with temperature. The two curves intersect at a certain temperature that determines the triple point T3 at a certain pressure. We also determined T3 by the three-phase direct coexistence method. The results of both methods agree, and we suggest 295(2) K as the value of T3 for this system. We also analyzed the impact of curvature on the solubility of methane in water. We found that the presence of curvature increases the solubility in both the gas–liquid and hydrate–liquid systems. The change in chemical potential for the formation of hydrate is evaluated along the isobar using two different thermodynamic routes, obtaining good agreement between them. It is shown that the driving force for hydrate nucleation under experimental conditions is higher than that for the formation of pure ice when compared at the same supercooling. We also show that supersaturation (i.e., concentrations above those of the planar interface) increases the driving force for nucleation dramatically. The effect of bubbles can be equivalent to that of an additional supercooling of about 20 K. Having highly supersaturated homogeneous solutions makes possible the spontaneous formation of the hydrate at temperatures as high as 285 K (i.e., 10K below T3). The crucial role of the concentration of methane for hydrate formation is clearly revealed. Nucleation of the hydrate can be either impossible or easy and fast depending on the concentration of methane which seems to play the leading role in the understanding of the kinetics of hydrate formation

GEHEP 010 study: Prevalence and distribution of hepatitis B virus genotypes in Spain (2000–2016)

[Objective] To study the prevalence and distribution of HBV genotypes in Spain for the period 2000–2016.[Methods] Retrospective study recruiting 2559 patients from 17 hospitals. Distribution of HBV genotypes, as well as sex, age, geographical origin, mode of transmission, HDV-, HIV- and/or HCV-coinfection, and treatment were recorded.[Results] 1924 chronically HBV native Spanish patients have been recruited. Median age was 54 years (IQR: 41–62), 69.6% male, 6.3% HIV-coinfected, 3.1% were HCV-coinfected, 1.7% HDV-co/superinfected. Genotype distribution was: 55.9% D, 33.5% A, 5.6% F, 0.8% G, and 1.9% other genotypes (E, B, H and C). HBV genotype A was closely associated with male sex, sexual transmission, and HIV-coinfection. In contrast, HBV genotype D was associated with female sex and vertical transmission. Different patterns of genotype distribution and diversity were found between different geographical regions. In addition, HBV epidemiological patterns are evolving in Spain, mainly because of immigration. Finally, similar overall rates of treatment success across all HBV genotypes were found.[Conclusions] We present here the most recent data on molecular epidemiology of HBV in Spain (GEHEP010 Study). This study confirms that the HBV genotype distribution in Spain varies based on age, sex, origin, HIV-coinfection, geographical regions and epidemiological groups.This study has been funded in part by the funds of the research project GEHEP-2018-010, granted by the Hepatitis Group of the Spanish Society of Infectious Diseases and Clinical Microbiology (Grupo de Hepatitis de la Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica, GEHEP/SEIMC)

Three phase equilibria of the methane hydrate in NaCl solutions: A simulation study

Depto. de Química FísicaFac. de Ciencias QuímicasTRUEpu

Melting points of water models: Current situation

By using the direct coexistence method, we have calculated the melting points of ice Ih at normal pressure for three recently proposed water models, namely, TIP3P-FB, TIP4P-FB, and TIP4P-D. We obtained Tm = 216 K for TIP3P-FB, Tm = 242 K for TIP4P-FB, and Tm = 247 K for TIP4P-D. We revisited the melting point of TIP4P/2005 and TIP5P obtaining Tm = 250 and 274 K, respectively. We summarize the current situation of the melting point of ice Ih for a number of water models and conclude that no model is yet able to simultaneously reproduce the melting temperature of ice Ih and the temperature of the maximum in density at room pressure. This probably points toward our both still incomplete knowledge of the potential energy surface of water and the necessity of incorporating nuclear quantum effects to describe both properties simultaneously.Depto. de Química FísicaFac. de Ciencias QuímicasTRUEpu

Building a Hofmeister-like series for the maximum in density temperature of aqueous electrolyte solutions.

The temperature of the maximum in density (TMD) at room pressure is experimentally evaluated for aqueous solutions of a set of halides containing F−, Cl−, Br−, I−, Li+, Na+, K+, Rb+, Cs+ and Mg2+ at a 1 m concentration. The measurements were performed by monitoring the density- temperature profiles and tracking the temperature-dependent position of the meniscus, in a capillary glass tube. Adding salts diminishes the TMD of the solutions with respect to pure water, being the magnitude of the change dependent on the nature of the electrolyte. The experimental values of the shift in the TMD can be split into individual ion contributions. From this information we were able to establish a rank of ions (i.e. a Hofmeister-like series) according to their efficiency in shifting down the TMD. The experimental results are also compared to simulation values obtained via Molecular Dynamics using the Madrid-2019 force field that assigns non-integer charges for the ions and is parametrized for the TIP4P/2005 water model. Finally, since the TMD is a fingerprint property of water, we will discuss the impact of ions on this maximum in relation with the way different ions modify the structure of water

Unveiling the reinforcement effects in cottonseed protein/polycaprolactone blend biocomposites

Cottonseed protein (CP) was compounded with polycaprolactone (PCL) in different concentrations by melt blending, and then hot-pressed to prepare CP/PCL blend films. A co-continuous phase is formed when the CP/PCL content is 50/50, and the tensile strength, modulus and toughness are 9, 10, and 63 times greater than that of neat CP film. This remarkable improvement is mainly due to the intrinsic flexibility of long PCL polymer chains, whilst the polymeric crystalline structure can still be formed. Furthermore, 1 wt% of compatibilizing agent — glycidyl methacrylate (GMA) or maleic anhydride (MA), is added to the blends. Measurements from scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) showed the presence of chemically reactive compatibilization between the compatibilizer and CP or PCL phase, and the two phases with strong binding forces are well dispersed. Meanwhile, the compatibilizer can induce the protein secondary structure to unfold, further increasing the physical compatibilization between the protein and polymer chains, which has a noticeable contribution to the blend's mechanical, hydrophobic properties and thermal stability. This work adds new element to the knowledge of compatibilization in terms of optimised interfaces of polymer blends, and provide new insights into fabricating high performance protein derived bioplastics and biocomposites

Innovación sobre la docencia y evaluación del laboratorio de Química Física I

Depto. de Química FísicaFac. de Ciencias QuímicasFALSEsubmitte

CAVITY: Calar Alto Void Integral-field Treasury surveY. I. First public data release

International audienceThe Calar Alto Void Integral-field Treasury surveY (CAVITY) is a legacy project aimed at characterising the population of galaxies inhabiting voids, which are the most under-dense regions of the cosmic web, located in the Local Universe. This paper describes the first public data release (DR1) of CAVITY, comprising science-grade optical data cubes for the initial 100 out of a total of $\sim$300 galaxies in the Local Universe ($0.005 < z < 0.050$). These data were acquired using the integral-field spectrograph PMAS/PPak mounted on the 3.5m telescope at the Calar Alto observatory. The DR1 galaxy sample encompasses diverse characteristics in the color-magnitude space, morphological type, stellar mass, and gas ionisation conditions, providing a rich resource for addressing key questions in galaxy evolution through spatially resolved spectroscopy. The galaxies in this study were observed with the low-resolution V500 set-up, spanning the wavelength range 3745-7500 Å, with a spectral resolution of 6.0 Å (FWHM). Here, we describe the data reduction and characteristics and data structure of the CAVITY datasets essential for their scientific utilisation, highlighting such concerns as vignetting effects, as well as the identification of bad pixels and management of spatially correlated noise. We also provide instructions for accessing the CAVITY datasets and associated ancillary data through the project's dedicated database