Lattice-Energy Calculations on Organometallic Compounds

Lattice-energy calculations in the atom-atom approach have been performed for five organometallic com­ pounds of previously determined crystal structure. Minimization of energy in terms of positional, orienta­ tional, torsional and cell parameters gave satisfactory results. Computation of energy as a function of torsion angle gave two-dimensional cross sections which o108-7681/88/030259-04$03.00 present minimum-energy conformations at maximum deviations of 10° from the experimental conforma­ tions

On the volumetric properties of 2-hydroxy ethylammonium formate ionic liquid under high-pressures: Measurement and molecular dynamics

This work aims to report not only the new measurement for densities of 2-hydroxy ethylammonium formate (2-HEAF) ionic liquid under high-pressures but also molecular dynamics considerations of nanoscopic characterization for physicochemical properties in the pressure range studied. High-pressure densities of 2-HEAF showed smooth trends with temperature and pressure variations. Measurements were carried out at temperatures T = (298.15 to 333.15) K and at pressures P = (0.1 to 40) MPa. The high-pressure densities of 2-HEAF have also been correlated by the use of Tait equation with AARD equal to 0.031% and the mechanical coefficients including the isothermal compressibility, isobaric expansivity and thermal pressure were estimated. Molecular dynamics simulations were carried out in the same pressure – temperature range as the experimental study. Force field was validated against experimental results and the microscopic structure was analyzed in terms of intermolecular interactions and their evolution with temperature and pressure.Iran National Science Foundation for supporting this project via the grant number (INSF-96000966

Tuning the properties of ionic liquids by mixing with organic solvents: The case of 1-butyl-3-methylimidazolium glutamate with alkanols

Binary liquid mixtures of 1-butyl-3-methylimidazolium glutamate acid ([bmim][glu]) with alkanols (1-propanol, isobutanol and 1,2-propanediol) are studied in the full composition range as a function of temperature using a combined experimental and computational chemistry approach. Experimental thermophysical information as well as derived excess and mixing properties allowed to characterize these complex liquid mixtures in terms of deviation from ideality as well their relationships with the developed intermolecular forces and changes with the type of considered alkanols. Theoretical studies using quantum chemistry and classical molecular dynamics simulations provided nanoscopic characterization on the studied fluids, with particular attention to the extension and nature of hydrogen bonding and its effects on molecular arrangements and mixed fluids’ properties. The reported study provides a micro and macroscopic characterization of the considered aminoacid-based ionic liquid mixtures, thus contributing to the knowledge of sustainable ionic liquid systems mixed with organic solvents for fine tuning properties and developing task specific applications.Shiraz University of Technology and Ministerio de Ciencia, Innovación y Universidades (Spain, project RTI2018-101987-B-I00)

Insights on biodiesel blends with alkanol solvents

Thermophysical properties of mixtures of fatty acid esters with alkanols were measured in the whole composition range as a function of temperature for understanding features of biodiesel blends. Excess and mixing properties calculated from experimental measurements allowed to quantify and analyze the intermolecular forces in the considered systems. Likewise, molecular modelling studies using quantum chemistry and classical molecular dynamics simulations led to a detailed characterization of these systems at the nanoscopic level. The nature of hydrogen bonding in these liquid mixtures was particularly analyzed from macroscopic properties and theoretical modelling results. The reported experimental and computational study allowed to infer the relationships between the intermolecular forces and additional microscopic features and the mixtures macroscopic properties, which are relevant for the development and characterization of biodiesels. The non-ideality behavior of the studied systems shows relevant changes in hydrogen bonding structuring upon mixing, with the fatty acid esters largely disrupting the alcohols self-association, although ester – alcohol hydrogen bonding is developed, this type of interactions is remarkably weaker than those for alcohols. Therefore, the studied biodiesel blends macroscopic properties may be tuned and controlled through the amount of alcohols in the mixtures and rooted on its effect on hydrogen bonding.Shiraz University of Technology (Iran), Junta de Castilla y León (Spain, project BU094G18) and Ministerio de Ciencia, Innovación y Universidades (Spain, project RTI2018-101987-B-I00) for supporting this project. We also acknowledge SCAYLE (Supercomputación Castilla y León, Spain) for providing supercomputing facilities

The star formation history of the Local Group dwarf elliptical galaxy NGC 185: II. Gradients in the stellar population

The star formation history of the dE NGC 185, together with its spatial variations, has been investigated using new ground-based $H_\alpha$ and $BVI$ photometry, and synthetic color--magnitude diagrams (CMDs). We find that the bulk of the stars were formed in NGC 185 at an early epoch of its evolution. After that, the star formation proceeded at a low rate until the recent past, the age of the most recent traces of star formation activity detected in the galaxy being some 100 Myr. The star formation rate, $\psi(t)$ for old and intermediate ages shows a gradient in the sense of taking smaller values for higher galactocentric radii. Moreover, recent star formation is detected in the central $150 \times 90$ pc$^2$ only, where the youngest, 100 Myr old population is found. The luminous blue {\it stars} discovered by Baade (1951) in the center of NGC 185 are discussed using new CCD images in $B$ and Baade's original photographic plates, reaching the conclusion that most of them are in fact star clusters. A consistent picture arises in which the gas observed in the central region of NGC 185 would have an internal origin. The rate at which evolved stars return gas to the ISM is enough to seed the recent star formation observed in the center of the galaxy and the SN rate is probably low enough to allow the galaxy to retain the gas not used in the new stellar generations.Comment: 34 pages, 17 figures, 5 Tables, to be published in AJ October 9

Gas solubility and rheological behavior study of betaine and alanine based natural deep eutectic solvents (NADES)

Natural deep eutectic solvent (NADES) produced herein this work by mixing betaine and alanine with lactic acid and malic acid with 1:1 M mixing ratios. Thermophysical properties including water content, thermal stability, density and gas solubility of CO2 and N2 were experimented at different isotherms for wide pressures range up to 50 bars. Moreover, detailed rheological experiments were conducted on the studied materials to obtain viscosity and deduce the dynamic flow behavior. A pressure driven physisorption mechanism was observed for the studied systems. Betaine based NADES materials showed superior carbon dioxide and nitrogen solubility when they are mixed with lactic acid. On the other hand, the rheological experimental results show shear-thinning effect in which the η is decreasing with shear rate at all temperatures. Low viscosity profiles NADES assure the less mass transfer resistance for lactic acid based NADES systems and it also confirmed that the high CO2 and N2 solubility for lactic acid based NADES samples.NPRP grant # 6-330-2-140 from the Qatar National Research Fund (a member of Qatar Foundation) and by Ministerio de Economía y Competitividad (Spain, project CTQ2013-40476-R)

The Resolved Stellar Halo of NGC 253

We have obtained Magellan/IMACS and HST/ACS imaging data that resolve red giant branch stars in the stellar halo of the starburst galaxy NGC 253. The HST data cover a small area, and allow us to accurately interpret the ground-based data, which cover 30% of the halo to a distance of 30 kpc, allowing us to make detailed quantitative measurements of the global properties and structure of a stellar halo outside of the Local Group. The geometry of the halo is significantly flattened in the same sense as the disk, with a projected axis ratio of b/a ~ 0.35 +/- 0.1. The total stellar mass of the halo is estimated to be M_halo ~ 2.5 +/- 1.5 x 10^9 M_sun, or 6% of the total stellar mass of the galaxy, and has a projected radial dependence that follows a power law of index -2.8 +/- 0.6, corresponding to a three-dimensional power law index of ~ -4. The total luminosity and profile shape that we measure for NGC 253 are somewhat larger and steeper than the equivalent values for the Milky Way and M31, but are well within the scatter of model predictions for the properties of stellar halos built up in a cosmological context. Structure within the halo is seen at a variety of scales: there is small kpc-scale density variation and a large shelf-like feature near the middle of the field. The techniques that have been developed will be essential for quantitatively comparing our upcoming larger sample of observed stellar halos to models of halo formation.Comment: ApJ, in press. Version with full resolution figures available at http://www.astro.lsa.umich.edu/~jbailin/papers/bailin_n253halo.pd