Higher hydrogen fractions in dielectric polymers boost self-healing in electrical capacitors.

Electrical capacitors are omnipresent in modern electronic devices, in which they swiftly release large portions of energy on demand. The capacitors may suffer from arc discharges due to local structural heterogeneities in their components and inappropriate exploitation practices. High energies of the arc discharge are transferred as phonons to the electrode and dielectric film, which burn out locally. The dielectric breakdown takes place. The complete burnout leads to the isolation of the failed region and the capacitor's self-healing. The emerging soot can form a semiconducting channel and damage the capacitor. The efficiency of self-healing depends on the dielectric properties of the soot and its amount. We employ reactive molecular dynamics simulations to reveal the regularities of the high-temperature polymer destruction and record by-products emerging during this process. We found the formation of multiple volatile low-molecular compounds and contaminated quantum carbon dots (CQD) designated as soot. The percentage of carbon in soot is higher compared to the polymer. Furthermore, the CQD contains numerous unsaturated C-C bonds and aromatic C6-rings suggesting an enhanced electrical conductivity. The size of the CQD depends on the available volume, i.e., on the spatial scale of the dielectric breakdown. The elemental composition of the soot is unique for each polymer. Polypropylene undergoes the most efficient self-healing thanks to containing a large molar fraction of hydrogen atoms. The results are addressed to the experts in electrical engineering and polymer fine-tuning.

Chemical similarity of dialkyl carbonates and carbon dioxide opens an avenue for novel greenhouse gas scavengers: cheap recycling and low volatility via experiments and simulations.

Global warming linked to the industrial emissions of greenhouse gases may be the end of mankind unless it is adequately and timely handled. To prevent irreversible changes to the climate of the Earth, numerous research groups are striving to develop robust CO2 sorbents. Dialkyl carbonates (DACs) and CO2 exhibit obvious chemical similarities in their structure and properties. The degrees of oxidation of all atoms composing DACs and CO2 are identical resulting in very similar nucleophilicities and electrophilicities of all interaction centers. While both compounds possess relatively high partial atomic charges on their polar moieties, the molecular geometries prevent tight binding of the head groups. The computed DAC-DAC binding energies are ∼40 kJ mol-1, whereas the effect of the alkyl chain length is marginal. The phase transition points and shear viscosities of DACs are very low. We herein hypothesize and numerically rationalize that DACs represent noteworthy physical sorbents for CO2 thanks to the similar sorbent-CO2 and sorbent-sorbent interaction energies. By reporting in silico-derived sorption thermodynamics at various conditions, spectral and structural properties, and experimentally derived CO2 capacities and recyclabilities, we highlight the mutual affinity of DACs and CO2. Indeed, the experimentally determined CO2 sorption capacity of 0.88 mol% (diethyl carbonate) at 278.15 K and 30 bar is competitive. The unprecedentedly low DAC-CO2 binding energies, ∼14 kJ mol-1, suggest a low-cost desorption process and outstanding recyclability of the sorbent. We also note that DACs possessing long alkyl chains (butyl, hexyl, octyl) exhibit negligible volatilities, while preserving the liquid aggregate state over a practically important temperature range. The reported results may foster the development of a new class of CO2 scavengers with possibly quite peculiar characteristics.

Extensively amino-functionalized graphene captures carbon dioxide.

The development of robust carbon dioxide (CO2) scavengers is a challenging but paramount problem of modern humanity. In the present work, we report a prospective CO2 sorbent based on amino-functionalized graphene (FG). Amino-FG retains the favorable physicochemical properties of graphene and acquires the capability of chemically fixing CO2via the carbamic acid formation mechanism. In the present work, we comprehensively investigate CO2 capturing prospects by extensively amino-FG using hybrid density functional theory. We show that up to six amino groups can be grafted, remain stable, and subsequently chemisorb CO2 per benzene ring. Two functional groups above the benzene ring and four such groups below the benzene ring represent a thermodynamically stable molecular configuration in which the number of carbon atoms is equal to the number of functional groups. The thermochemistry of chemisorption is, in general, negatively impacted by the increase in the density of functional groups. However, a less favorable Gibbs free energy is compensated by a several fold higher number of prospective reaction sites. The thermochemistry results are rationalized by considering steric hindrances on the surface of graphene in the context of the states of hybridization and genuine geometries of the amino- and carboxamido functional groups. The functionalization and chemisorption decrease the hydrophobicity of graphene derivatives and, therefore, foster the development of novel and more robust chemical engineering setups.

Ammonium-, phosphonium- and sulfonium-based 2-cyanopyrrolidine ionic liquids for carbon dioxide fixation.

The development of carbon dioxide (CO2) scavengers is an acute problem nowadays because of the global warming problem. Many groups around the globe intensively develop new greenhouse gas scavengers. Room-temperature ionic liquids (RTILs) are seen as a proper starting point to synthesize more environmentally friendly and high-performance sorbents. Aprotic heterocyclic anions (AHA) represent excellent agents for carbon capture and storage technologies. In the present work, we investigate RTILs in which both the weakly coordinating cation and AHA bind CO2. The ammonium-, phosphonium-, and sulfonium-based 2-cyanopyrrolidines were investigated using the state-of-the-art method to describe the thermochemistry of the CO2 fixation reactions. The infrared spectra and electronic and structural properties were simulated at the hybrid density functional level of theory to characterize the reactants and products of the chemisorption reactions. We conclude that the proposed CO2 capturing mechanism is thermodynamically allowed and discuss the difference between different families of RTILs. Quite unusually, the intramolecular electrostatic attraction plays an essential role in stabilizing the zwitterionic products of the CO2 chemisorption. The difference in chemisorption performance between the families of RTILs is linked to sterical hindrances and nucleophilicities of the α- and ß-carbon atoms of the aprotic cations. Our results rationalize previous experimental CO2 sorption measurements (Brennecke et al., 2021).

Enzymes of Polyphosphate Metabolism in Yeast: Properties, Functions, Practical Significance.

Inorganic polyphosphates (polyP) are the linear polymers of orthophosphoric acid varying in the number of phosphate residues linked by the energy-rich phosphoanhydride bonds. PolyP is an essential component in living cells. Knowledge of polyP metabolizing enzymes in eukaryotes is necessary for understanding molecular mechanisms of polyP metabolism in humans and development of new approaches for treating bone and cardiovascular diseases associated with impaired mineral phosphorus metabolism. Yeast cells represent a rational experimental model for this research due to availability of the methods for studying phosphorus metabolism and construction of knockout mutants and strains overexpressing target proteins. Multicomponent system of polyP metabolism in Saccharomyces cerevisiae cells is presented in this review discussing properties, functioning, and practical significance of the enzymes involved in the synthesis and degradation of this important metabolite.

Understanding weakly coordinating anions: tetrakis(pentafluorophenyl)borate paired with inorganic and organic cations.

Efficient design of ionic compounds requires a systematic understanding of cation-anion interactions. Weakening of electrostatic attraction is essential to increase the liquid range of the ionic compound and decrease its melting point. Here, we report simulations of the closest-approach cation-anion distances in a variety of ion pairs containing the tetrakis(pentafluorophenyl)borate (TFPB-) anion. Small alkali cations (Li+, Na+) penetrate the TFPB- core, whereas K+ and larger organic cations do not. In the latter case, the shortest possible distance from the cations to the boron atom of TFPB- ranges from 0.50 nm to 0.63 nm. TFPB- was shown to be substantially rigid, providing a steric hindrance to thermodynamically efficient cation-anion coordination. Our results prove that TFPB- is more efficient for electrostatic charge confinement than the tetraoctylammonium cation, whereas the perfluorophenyl group is more efficient than linear alkyl chains. These simulations will motivate development of TFPB--based ionic liquids with low phase transition points. Graphical Abstract Ionic configuration of the equilibrated "TFPB + K"system.

Sodium-ion electrolytes based on ionic liquids: a role of cation-anion hydrogen bonding.

Recent success of the sodium-ion batteries fosters an academic interest for their investigation. Room-temperature ionic liquids (RTILs) constitute universal solvents providing non-volatility and non-flammability to electrolytes. In the present work, we consider four families of RTILs as prospective solvents for NaBF4 and NaNO3 with an inorganic salt concentration of 25 and 50 mol%. We propose a methodology to rate RTILs according to their solvation capability using parameters of the computed radial distribution functions. Hydrogen bonds between the cations and the anions of RTILs were found to indirectly favor sodium solvation, irrespective of the particular RTIL and its concentration. The best performance was recorded in the case of cholinium nitrate. The reported observations and correlations of ionic structures and properties offer important assistance to an emerging field of sodium-ion batteries. Graphical Abstract Sodium-ion electrolytes.

Solvation of the morpholinium cation in acetonitrile. Effect of an anion.

Ionic liquids (ILs) constitute a fast growing class of compounds finding multiple applications in science and technology. Morpholinium-based ILs (MBILs) and their mixtures with polar molecular co-solvents are interesting as sustainable electrolyte systems for electrochemistry. We investigate local structures of protic and apropic morpholinium cations in acetonitrile (ACN) using semi-empirical molecular dynamics (MD) simulations. An impact of an anion (acetate) on the cation solvation regularities is discussed. Unlike oxygen, nitrogen of the morpholine ring is a strong electrophilic binding center. This site is responsible for the interactions of the cation with the solvent and with the anion. In protic MBILs, the role of nitrogen is delegated to the proton, which is linked to nitrogen. The acetate anion weakens solvation of the cation due to occupation of space near nitrogen or proton. The analysis reveals a favorable solvation of MBILs in ACN, which is a prerequisite for a new high-performance electrolyte system. The reported structural data were validated through point-to-point comparison with the MP2 post-Hartree-Fock theory and density functional theory.

Menadione reduces rotenone-induced cell death in cerebellar granule neurons.

Oxidative stress has been implicated in neuronal death caused by cerebral ischemia or some neurologic disorders. Chemical hypoxia (term defining the simulation by using respiratory inhibitors) chosen as in vitro ischemic model, was induced in primary cultures of rat cerebellar granule neurons by inhibitors of mitochondrial electron transport such as rotenone or paraquat (complex I), 3-nitropropionic acid (3-NPA, complex II), antimycin A (complex III), or sodium azide (complex IV). All compounds caused neuronal death determined by trypan blue staining and MTT-test. On the other hand, neurotoxicity of rotenone and paraquat but not of 3-NPA, antimycin or azide was significantly abolished by menadione (vitamin K3, 2-methyl-1,4-naphthoquinone). This neuroprotective effect of menadione was associated with a decrease of rotenone-induced free radical production.

Exopolyphosphatases of the yeast Saccharomyces cerevisiae.

Separate compartments of the yeast cell possess their own exopolyphosphatases differing from each other in their properties and dependence on culture conditions. The low-molecular-mass exopolyphosphatases of the cytosol, cell envelope, and mitochondrial matrix are encoded by the PPX1 gene, while the high-molecular-mass exopolyphosphatase of the cytosol and those of the vacuoles, mitochondrial membranes, and nuclei are presumably encoded by their own genes. Based on recent works, a preliminary classification of the yeast exopolyphosphatases is proposed.