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We measured the solid–liquid–vapor (SLV) equilibrium of binary mixtures during experiments that alternated between cooling the mixture and injecting the more-volatile component into the sample chamber; thus, the composition of the mixture changed (non-isoplethic) throughout the experiment. Four binary mixtures were used in the experiments to represent mixtures with miscible solid phases (N2/CO) and barely miscible solid solutions (N2/C2H6), as well as mixtures with intermediate solid miscibility (N2/CH4 and CO/CH4). We measured new SLV pressure data for the binary mixtures, except for N2/CH4, which are also available in the literature for verification in this work. While these mixtures are of great interest in planetary science and cryogenics, the resulting pressure data are also needed for modeling purposes. We found the results for N2/CH4 to be consistent with the literature. The resulting new SLV curve for CO/CH4 shows similarities to N2/CH4. Both have two density inversion points (bracketing the temperature range where the solid floats). This result is important for places such as Pluto, Triton, and Titan, where these mixtures exist in vapor, liquid, and solid phases. Based on our experiments, the presence of a eutectic is unlikely for the N2/CH4 and CO/CH4 systems. An azeotrope with or without a peritectic is likely, but further investigations are needed to confirm. The N2/CO system does not have a density inversion point, as the ice always sinks in its liquid. For N2/C2H6, new SLV pressure data were measured near each triple point of the pure components. [ABSTRACT FROM AUTHOR]

Using nonequilibrium switching simulations to determine the free-energy difference between two thermodynamic states has gained tremendous popularity since Jarzynski’s identity was proposed. The efficiency of a nonequilibrium switching simulation depends on the switching function. A well selected switching function can significantly minimize the associated dissipative work and reduce the computational cost of nonequilibrium free-energy simulations. In this paper, a method for estimating an efficient switching function during a nonequilibrium free-energy simulation is presented. The switching rate depends on the fluctuation of the fictitious force and a relaxation time. This method is similar to a prior method described by de Koning [J. Chem. Phys. 122, 104106 (2005)], except in our approach the switching rate is determined on-the-fly without the need for trial pulls. Our method can be easily incorporated into any existing implementation of the nonequilibrium switching method. The on-the-fly approach was used to determine the transformation free energy between two types of Einstein crystals and the isothermal free energy of expansion of a van der Waals gas. For both of the test cases, our on-the-fly method is found to provide a switching function much more superior than the standard one. [ABSTRACT FROM AUTHOR]

The article discusses a new electrostatic switching procedure, which is used for the systematic generation of high-quality ice samples at several different temperatures. Though the procedure proves to be highly useful, it seems to reflect smaller error bars at lower temperatures.

The effects of sustained mutational loading during multigenerational propagations, appearance of apparent single- and perhaps multiple-locus phenotypes and an overall trend toward decreased fitness are demonstrated. Analyses of insertion /deletion mutation at six repeat-sequence loci showed each Atmsh2-1 line to have evolved its own fingerprint the results of as many as 10 microsatellite mutations in a single line.

The A. aeolicus intrinsically disordered protein FlgM has four well-defined α-helices when bound to σ28, but in water FlgM undergoes a change in tertiary structure. In this work, we investigate the structure of FlgM in aqueous solutions of the ionic liquid [C4mpy][Tf2N]. We find that FlgM is induced to fold by the addition of the ionic liquid, achieving average α-helicity values similar to the bound state. Analysis of secondary structure reveals significant similarity with the bound state, but the tertiary structure is found to be more compact. Interestingly, the ionic liquid is not homogeneously dispersed in the water, but instead aggregates near the protein. Separate simulations of aqueous ionic liquid do not show ion clustering, which suggests that FlgM stabilizes ionic liquid aggregation. [ABSTRACT FROM AUTHOR]

This study focuses on understandingthe relative effects of ammoniumsubstituent groups (we primarily consider tetramethylammonium, benzyltrimethylammonium,and tetraethylammonium cations) and anion species (OH–, HCO3–, CO32–, Cl–, and F–) on ion transportby combining experimental and computational approaches. We characterizetransport experimentally using ionic conductivity and self-diffusioncoefficients measured from NMR. These experimental results are interpretedusing simulation methods to describe the transport of these cationsand anions considering the effects of the counterion. It is particularlynoteworthy that we directly probe cation and anion diffusion withpulsed gradient stimulated echo NMR and molecular dynamics simulations,corroborating these methods and providing a direct link between atomic-resolutionsimulations and macroscale experiments. By pairing diffusion measurementsand simulations with residence times, we were able to understand theinterplay between short-time and long-time dynamics with ionic conductivity.With experiment, we determined that solutions of benzyltrimethylammoniumhydroxide have the highest ionic conductivity (0.26 S/cm at 65 °C),which appears to be due to differences for the ions in long-time diffusionand short-time water caging. We also examined the effect of CO2on ionic conductivity in ammonium hydroxide solutions. CO2readily reacts with OH–to form HCO–3and is found to lower the solution ionicconductivity by almost 50%. [ABSTRACT FROM AUTHOR]

The A. aeolicus intrinsically disordered protein FlgM has four well-defined α-helices when bound to σ28, but in water FlgM undergoes a change in tertiary structure. In this work, we investigate the structure of FlgM in aqueous solutions of the ionic liquid [C4mpy][Tf2N]. We find that FlgM is induced to fold by the addition of the ionic liquid, achieving average α-helicity values similar to the bound state. Analysis of secondary structure reveals significant similarity with the bound state, but the tertiary structure is found to be more compact. Interestingly, the ionic liquid is not homogeneously dispersed in the water, but instead aggregates near the protein. Separate simulations of aqueous ionic liquid do not show ion clustering, which suggests that FlgM stabilizes ionic liquid aggregation.