Solvation structure and dynamics of Li and LiO2 and their transformation in non-aqueous organic electrolyte solvents from first-principles simulations

Density functional theory calculations together with ab initio molecular dynamics (AIMD) simulations have been used to study the solvation, diffusion and transformation of Li+ and LiO2 upon O2 reduction in three organic electrolytes. These processes are critical for the performance of Li-air batteries. Apart from studying the structure of the solvation shells in detail, AIMD simulations have been used to derive the diffusivity and together with the Blue Moon ensemble approach to explore LiO2 formation from Li+ and O2- and the subsequent disproportionation of 2LiO2 into Li2O2 + O2. By comparing the results of the simulations to gas phase calculations the impact of electrolytes on these reactions is assessed which turns out to be more pronounced for the ionic species involved in these reactions.

Surface Activity and Efficiency of Cat-Anionic Surfactant Mixtures

The surface activity of surfactant mixtures is critically analyzed. Cat-anionic systems, in which two ionic species are mixed in non-stoichiometric ratios, are considered. With respect to the solution behavior, where a substantial decrease of cmc is met compared to the pure components, a moderate effect on surface tension, γ, occurs. Compared to the pure species, the decrease of surface tension for such mixtures is not significant, and no clear dependence on the mole fraction anionic/cationic is met. The surface tension is grossly constant in the whole concentration range. Conversely, the interaction parameter for surfaces, βsurf (calculated by the regular solution theory), is more negative than that for micelle formation, βmic. This fact suggests that the desolvation of polar heads of the two species at interfaces is largely different. Very presumably, the underlying rationale finds origin in the sizes and solvation of both polar head groups.

Steric Effects on Electroosmotic Nano-Thrusters under High Zeta Potentials

Here, space electroosmotic thrusters in a rigid nanochannel with high wall zeta potentials are investigated numerically, for the first time, considering the effect of finite size of the ionic species. The effect, which is called a steric effect, is often neglected in research about micro/nano thrusters. However, it has vital influences on the electric potential and flow velocity in electric double layers, so that the thruster performances generated by the fluid motion are further affected. These performances, including thrust, specific impulse, thruster efficiency, and the thrust-to-power ratio, are described by using numerical algorithms, after obtaining the electric potential and velocity distributions under high wall zeta potentials ranging from −25.7 mV to −128.5 mV. As expected, the zeta potential can promote the development of thruster performances so as to satisfy the requirement of space missions. Moreover, for real situation with consideration of the steric effect, the thruster thrust and efficiency significantly decrease to 5–30 micro Newtons and 80–90%, respectively, but the thrust-to-power ratio is opposite, and expends a short specific impulse of about 50–110 s.

Correlation between Ion Composition of Oligomineral Water and Calcium Oxalate Crystal Formation

The ion content of drinking water might be associated with urinary stone formation, representing a keystone of conservative nephrolithiasis management. However, the effects of specific ions on calcium oxalate crystal formation and their mechanism of action are still highly controversial. We report an investigation of the effects of oligomineral waters with similar total salt amount but different ion composition on calcium oxalate (CaOx) precipitation in vitro, combining gravimetric and microscopic assays. The results suggest that the “collective” physicochemical properties of the aqueous medium, deriving from the ion combination rather than from a single ionic species, are of importance. Particularly, the ability of ions to strengthen/weaken the aqueous medium structure determines an increase/decrease in the interfacial energy, modulating the formation and growth of CaOx crystals.

Gas-phase Modeling of the Cometary Coma of Interstellar Comet 2I/Borisov

Comet 2I/Borisov is the first interstellar comet observed in the solar system, providing a unique opportunity to understand the physical conditions that prevailed in a distant unknown planetary system. Observations of the comet show that the CO/H2O ratio is higher than that observed in solar system comets at a heliocentric distance r h < 2.5 au. We aim to study the gas-phase coma of comet 2I/Borisov using a multifluid chemical-hydrodynamical model. The gas-phase model includes a host of chemical reactions, with the neutrals, ions, and electrons treated as three separate fluids. Energy exchange between the three fluids due to elastic and inelastic scattering and radiative losses are also considered. Our model results show that in the region of the coma beyond ∼100 km of the nucleus, e−−CO inelastic collisions leading to vibrational excitation of CO causes a loss of energy from the electron fluid. We find a high abundance of CO+ and HCO+ ions, and we show how these two ions affect the creation/destruction rates of other ions such as H2O+, H3O+, N-bearing ions, and large organic ions. We find that the presence of CO leads to a higher abundance of large organic ions and neutrals such as CH 3 OH 2 + , CH 3 OCH 4 + , and CH3OCH3, as compared to a typical H2O-rich solar system comet. We conclude that the presence of a large amount of CO in the coma of comet 2I/Borisov, combined with a low production rate, affects the coma temperature profile and flux of major ionic species significantly.

Capture and Activation of Carbon Dioxide Using Guanidine Superbases

<p>Due to its abundance and low-cost, carbon dioxide is a desirable C₁-building block within organic transformations. However, the thermodynamic and kinetic stability of CO₂ often necessitates preliminary activation before it can be inserted into organic molecules. This prompts the need for compounds that can effectively promote the activation of CO₂. This research investigates the capture and activation of carbon dioxide using a class of superbases that incorporate the bicyclic guanidine unit, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (hppH, 1). A series of compounds containing multiple hpp-units assembled around a phenyl ring scaffold were synthesized and investigated in the functionalization of CO₂. The work presented in this study has demonstrated the ability of protonated superbasic hppH derivatives to efficiently and effectively capture and activate carbon dioxide from ambient air to form the corresponding guanidinium bicarbonate salts. A series of optimization reactions was carried out, and showed that addition of substoichiometric concentrations of a proton source activates these guanidine compounds to their fully protonated cationic forms, and results in CO₂ capture through bicarbonate formation. A series of protonation studies were employed to fully characterize the cationic species. The tetraphenylborate and hydrochloride guanidinium salts were synthesized, isolated, and characterized by ¹H NMR and ¹³C NMR spectroscopic analysis. Molecular structures of relevant crystals were obtained through single crystal X-ray diffraction. These structures revealed a complex hydrogen-bonding network within these ionic species, and showed efficient delocalization of the formal positive charge within the protonated guanidinium units. The guanidine superbases were implemented in a series of reactions attempting the functionalization of CO₂ and an alcohol to form corresponding alkylcarbonate products. However, the synthesis of these carbonate products was not achieved under the reaction conditions employed. This lack of success has been attributed to the hygroscopic nature of this class of compounds, resulting in the preferential capture of ambient water.</p>

Capture and Activation of Carbon Dioxide Using Guanidine Superbases

<p>Due to its abundance and low-cost, carbon dioxide is a desirable C₁-building block within organic transformations. However, the thermodynamic and kinetic stability of CO₂ often necessitates preliminary activation before it can be inserted into organic molecules. This prompts the need for compounds that can effectively promote the activation of CO₂. This research investigates the capture and activation of carbon dioxide using a class of superbases that incorporate the bicyclic guanidine unit, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (hppH, 1). A series of compounds containing multiple hpp-units assembled around a phenyl ring scaffold were synthesized and investigated in the functionalization of CO₂. The work presented in this study has demonstrated the ability of protonated superbasic hppH derivatives to efficiently and effectively capture and activate carbon dioxide from ambient air to form the corresponding guanidinium bicarbonate salts. A series of optimization reactions was carried out, and showed that addition of substoichiometric concentrations of a proton source activates these guanidine compounds to their fully protonated cationic forms, and results in CO₂ capture through bicarbonate formation. A series of protonation studies were employed to fully characterize the cationic species. The tetraphenylborate and hydrochloride guanidinium salts were synthesized, isolated, and characterized by ¹H NMR and ¹³C NMR spectroscopic analysis. Molecular structures of relevant crystals were obtained through single crystal X-ray diffraction. These structures revealed a complex hydrogen-bonding network within these ionic species, and showed efficient delocalization of the formal positive charge within the protonated guanidinium units. The guanidine superbases were implemented in a series of reactions attempting the functionalization of CO₂ and an alcohol to form corresponding alkylcarbonate products. However, the synthesis of these carbonate products was not achieved under the reaction conditions employed. This lack of success has been attributed to the hygroscopic nature of this class of compounds, resulting in the preferential capture of ambient water.</p>

Propagating wave in a fluid by coherent motion of 2D colloids

Just like in living organisms, if precise coherent operation of tiny movable components is possible, one may generate a macroscopic mechanical motion. Here we report that ~1010 pieces of colloidally dispersed nanosheets in aqueous media can be made to operate coherently to generate a propagating macroscopic wave under a non-equilibrium state. The nanosheets are initially forced to adopt a monodomain cofacial geometry with a large and uniform plane-to-plane distance of ~420 nm, where they are strongly correlated by competitive electrostatic repulsion and van der Waals attraction. When the electrostatic repulsion is progressively attenuated by the addition of ionic species, the nanosheets sequentially undergo coherent motions, generating a propagating wave. This elaborate wave in time and space can transport microparticles over a long distance in uniform direction and velocity. The present discovery may provide a general principle for the design of macroscopically movable devices from huge numbers of tiny components.

Albumin–Hyaluronan Interactions: Influence of Ionic Composition Probed by Molecular Dynamics

The lubrication mechanism in synovial fluid and joints is not yet fully understood. Nevertheless, intermolecular interactions between various neutral and ionic species including large macromolecular systems and simple inorganic ions are the key to understanding the excellent lubrication performance. An important tool for characterizing the intermolecular forces and their structural consequences is molecular dynamics. Albumin is one of the major components in synovial fluid. Its electrostatic properties, including the ability to form molecular complexes, are closely related to pH, solvation, and the presence of ions. In the context of synovial fluid, it is relevant to describe the possible interactions between albumin and hyaluronate, taking into account solution composition effects. In this study, the influence of Na+, Mg2+, and Ca2+ ions on human serum albumin–hyaluronan interactions were examined using molecular dynamics tools. It was established that the presence of divalent cations, and especially Ca2+, contributes mostly to the increase of the affinity between hyaluronan and albumin, which is associated with charge compensation in negatively charged hyaluronan and albumin. Furthermore, the most probable binding sites were structurally and energetically characterized. The indicated moieties exhibit a locally positive charge which enables hyaluronate binding (direct and water mediated).