Self-Consistent Implementation of a Solvation Free Energy Framework to Predict the Salt Solubilities of Six Alkali Halides.

To assess the salt solubilities of six alkali halides in aqueous systems, we proposed a thermodynamic cycle and an efficient molecular modeling methodology. The Gibbs free energy changes for vaporization, dissociation, and dissolution were calculated using the experimental data of ionic thermodynamic properties obtained from the NBS tables. Additionally, the Marcus' and Tissandier's solvation free energy data for Li+, Na+, K+, Cl-, and Br- ions were compared with the conventional solvation free energies by substituting into our self-consistent thermodynamic cycle. Furthermore, Tissandier's absolute solvation free energy data were used as the training set to refit the Lennard-Jones parameters of OPLS-AA force field for ions. To predict salt solubilities, an assumption of a pseudo-solvent was proposed to characterize the coupling work of a solute with its environment from infinitely diluted to saturated solutions, indicating that the Gibbs energy change of solvation process is a function of ionic strength. Following the self-consistency of the cycle, the newly derived formulas were used to determine the salt solubilities by interpolating the intersection of Gibbs free energy of dissolution and the zero free energy line. The refined ion parameters can also predict the structure and thermodynamic properties of aqueous electrolyte solutions, such as densities, pair correlation functions, hydration numbers, mean activity coefficients, vapor pressures, and the radial dependences of the net charge at 298.15 K and 1 bar. Our method can be used to characterize the solid-liquid equilibria of ions or charged particles in aqueous systems. Furthermore, for highly concentrated strong electrolyte systems, it is essential to introduce accurate water models and polarizable force fields.

Catalytic Descriptor Exploration for Ru-Based Fischer-Tropsch Catalysts: Effect of Chlorine and Sulfur Addition.

As an important factor in the design of catalysts, catalytic descriptor exploration has emerged as a novel frontier in heterogeneous catalysis. Here, the underlying structure-activity relationships of Ru-based catalysts are theoretically studied to shed light on this area. Calculations of different competing reaction paths suggest that the HCO*-mediated path─because of two synergistic active sites─is more favorable than others. In addition, compared to unadulterated Ru catalysts, the presence of Cl enhances the hydrocarbon production, whereas the presence of S decreases it. After a systematic examination of a series of structure-activity relationships (42 in total), we found that both charge transfer and average charge difference of active Ru atoms are good descriptors for the binding stability of reactants. However, for reactivity the Gibbs free energy of the reactants performs better. More interestingly, due to the quite different catalytic processes of the dissociation and hydrogenation steps, their correlations have opposite slopes.

Recent Advances in Mechanochromism of Metal-Organic Compounds.

Smart luminescent materials, which can respond to the changing of external environment (light, electricity, force, temperature, etc.), have always been one of the research hotspots. Mechanochromism refers to the materials whose emission color or intensity can be altered under the stimulation of external mechanical force. This kind of smart materials have been widely used in data storage, information encryption and sensors due to its simple operation, obvious and rapid response. The introduction of metal atoms in metal-organic compounds brings about fascinating metalophilic interactions and results in more interesting and surprising mechanochromic behaviors. In this mini-review, recent advances in mechanochromism of metal-organic compounds, including mono-, di-, multinuclear metal-organic complexes and metallic clusters are summarized. Varies mechanisms are discussed and some design strategies for metal-organic compounds with mechanochromism are also presented.

Theoretical investigation on the reaction mechanism and kinetics of a Criegee intermediate with ethylene and acetylene.

The detailed reaction mechanism of the Criegee intermediate CH2OO with ethylene and acetylene has been investigated by using the HL//M06-2X/AUG-cc-pVTZ method. The 1,3-cycloaddition of CH2OO to the unsaturated bond of ethylene or acetylene forms a five-membered ring adduct. For the reaction of CH2OO with ethylene, the subsequent ring-opening, H-shift isomerization and decomposition result in the formation of ethenol + HCHO and acetaldehyde + HCHO, and for the reaction of CH2OO with acetylene, the adduct proceeds via ring-opening and H-shift isomerization forming malonaldehyde. The calculated overall rate constant increases in the temperature range of 200-500 K, and at 298 K, it is 3.91 × 10-15 cm3 molecule-1 s-1 for the CH2OO + C2H4 reaction and 1.27 × 10-16 cm3 molecule-1 s-1 for the CH2OO + C2H2 reaction. The product branching ratio of the CH2OO + C2H4 reaction is pressure dependent, and the adduct tends to decompose to ethenol + HCHO and acetaldehyde + HCHO at lower pressures and higher temperatures. For the CH2OO + C2H2 reaction, the adduct isomerizes completely to malonaldehyde in the temperature range of 200-500 K and the pressure range of 100-1000 Torr.