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We have developed a machine learning (ML)-assisted Hybrid ReaxFF simulation method ("Hybrid/Reax"), which alternates reactive and non-reactive molecular dynamics simulations with the assistance of ML models to simulate phenomena that require longer time scales and/or larger systems than are typically accessible to ReaxFF. Hybrid/Reax uses a specialized tracking tool during the reactive simulations to further accelerate chemical reactions. Non-reactive simulations are used to equilibrate the system after the reactive simulation stage. ML models are used between reactive and non-reactive stages to predict non-reactive force field parameters of the system based on the updated bond topology. Hybrid/Reax simulation cycles can be continued until the desired chemical reactions are observed. As a case study, this method was used to study the cross-linking of a polyethylene (PE) matrix analogue (decane) with the cross-linking agent dicumyl peroxide (DCP). We were able to run relatively long simulations [>20 million molecular dynamics (MD) steps] on a small test system (4660 atoms) to simulate cross-linking reactions of PE in the presence of DCP. Starting with 80 PE molecules, more than half of them cross-linked by the end of the Hybrid/Reax cycles on a single Xeon processor in under 48 h. This simulation would take approximately 1 month if run with pure ReaxFF MD on the same machine.

Distributed H2 generation coupled with CO2 capture has the potential to deliver clean fuel for transportation purposes, especially in remote communities. Here we present a novel potassium doped Ni-Pt/alumina catalyst which shows remarkable activity and stability for oxidative steam reforming of multiple fuels. At an optimum potassium loading of 5 wt%, the catalyst was found to be stable for at least 42 h time-on-stream, with frequent start-up and shut-down. The catalyst provided nearly identical conversions of methanol, gasoline and diesel, H2 yield and production rates, demonstrating the flexibility of this catalyst for different feedstocks. Potassium doping in the alumina matrix created higher pore surface area, stabilized the Ni ensemble from sintering at high temperatures and prevented nucleation of coke on the Ni surface, making it coke resistant. A K-Al-Si-O type species that formed during the support synthesis along with presence of Pt species on the surface are believed to be the reasons for the stability of catalyst.

The epoxidation of ethylene-propylene-diene rubber (EPDM) with 5-ethylidene-2-norbornene (ENB) as the diene to epoxidized EPDM (eEPDM) creates additional routes to cross-linking and reactive blending, as well as increasing the polarity and thereby the adhesion to polar materials, e.g., mineral fillers such as silica. The low solubility of apolar, high molecular weight polymers in the polar solvents constrains the catalytic method for epoxidation that can be applied. Here we have applied an in situ prepared catalyst comprising a manganese(ii) salt, sodium picolinate and a ketone to the epoxidation of EPDM rubber with hydrogen peroxide (H2O2) as the oxidant in a solvent mixture, that balances the need for polymer and catalyst/oxidant miscibility and solubility. Specifically, a mixture of cyclohexane and cyclohexanone is used, where cyclohexanone functions as a co-solvent as well as the ketone reagent. Reaction progress was monitored off-line through a combination of Raman and ATR-FTIR spectroscopies, which revealed that the reaction profile and the dependence on the composition of the catalyst are similar to those observed with low molar mass alkene substrates, under similar reaction conditions. The combination of spectroscopies offers a reliable method for off-line reaction monitoring of both the extent of the conversion of unsaturation (Raman) and the extent of epoxidation (FTIR) as well as determining side reactions, such as epoxide ring opening and further, aerobic oxidation. The epoxidation of EPDM described, in contrast to currently available methods, uses a non-scarce manganese catalyst and H2O2, and avoids side reactions, such as those that can occur with peracids.

The molecular structure of nanothreads produced by the slow compression of 13C4-furan was studied by advanced solid-state NMR. Spectral editing showed that >95% of carbon atoms were bonded to one hydrogen (C-H) and that there were 2-4% CH2, 0.6% C═O, and

Reactive organic fluid–mineral interactions at elevated temperatures contribute to the evolution of planetary matter. One of the less studied but important transformations in this regard involves t...

In this work, reaction pathways for the oxidation of methane, ethane, and ethylene with CuO was obtained by ReaxFF Molecular Dynamics (MD) simulations between temperatures of 1000 K and 2000 K. Experiments in a fixed-bed flow reactor were preformed with methane, ethane, and ethylene at temperatures ranging from 500 K to 1000 K with time-dependent species measurements from an Electron-Ionization Molecular Beam Mass Spectrometer (MBMS), and species validation with Gas Chromatography (GC) for detection of complete and intermediate combustion products. The MBMS and GC allow for the detection of oxygenated species and larger species produced from radical reformation. The simulation and experiment agree on the production of such species as CH 3 CHO, CH 2 O, CO, and H 2 O, which allow for the creation of simple C1 and C2 reaction pathways, which can be used in kinetic models of C2 species and larger fuels such as biofuels, which inherently depend on C1 and C2 kinetics and reaction pathway. The simulation and experiment disagree on the formation of C 2 H 2 , CH 3 OH, and CO 2 , with large amounts of C 2 H 2 being measured in the ethylene oxidation simulations and CH 3 OH being formed in methane oxidation simulations, while neither species were experimentally found. In the case of CO 2 , large amounts of CO 2 are rapidly produced in experiments with C2 fuels at 800 K, while little-to-no CO 2 was observed in simulations. This is believed to be resulting from the extremely short timescale of the simulations, preventing total oxidation of the fuel. The differences in products produced between simulation and experiment allow for the potential to modify the ReaxFF potential functions to more accurately model the experimental products of Cu–H–O–C reaction kinetics.

Two NNN pincer complexes of Cu(ii) and Ni(ii) with BPIMe- [BPIMe- = 1,3-bis((6-methylpyridin-2-yl)imino)isoindolin-2-ide] have been prepared and characterized structurally, spectroscopically, and electrochemically. The single crystal structures of the two complexes confirmed their distorted trigonal bipyramidal geometry attained by three equatorial N-atoms from the ligand and two axially positioned water molecules to give [Cu(BPIMe)(H2O)2]ClO4 and [Ni(BPIMe)(H2O)2]ClO4. Electrochemical studies of Cu(ii) and Ni(ii) complexes have been performed in acetonitrile to identify metal-based and ligand-based redox activity. When subjected to a saturated CO2 atmosphere, both complexes displayed catalytic activity for the reduction of CO2 with the Cu(ii) complex displaying higher activity than the Ni(ii) analogue. However, both complexes were shown to decompose into catalytically active heterogeneous materials on the electrode surface over extended reductive electrolysis periods. Surface analysis of these materials using energy dispersive spectroscopy as well as their physical appearance suggests the reductive deposition of copper and nickel metal on the electrode surface. Electrocatalysis and decomposition are proposed to be triggered by ligand reduction, where complex stability is believed to be tied to fluxional ligand coordination in the reduced state.

To understand the mechanisms responsible for thermal decomposition of a Zr-MOF (MIL-140C), we perform atomistic-scale molecular dynamics (MD) simulations and discuss the simulation data in comparison with the TEM images obtained for the decomposed Zr-MOF. First, we introduce the ReaxFF parameters suitable for the Zr/C/H/O chemistry and then apply them to investigate the thermal stability and morphological changes in the MIL-140C during heating. Based on the performed simulations we propose an atomic mechanism for the collapse of the MIL-140C and the molecular pathways for carbon monoxide formation, the main product of the MIL-140C thermal degradation. We also determine that the oxidation state of the ZrOx clusters, evolved due to the thermal degradation, approximates the tetragonal phase of ZrO2. Both simulations and experiments show a distribution of very small ZrOx clusters embedded in the disrupted organic sheet that could contribute to the unusual high catalytic activity of the decomposed MIL-140C.

The prevalence of diabetic metabolic derangement (DMetD) has increased dramatically over the last decades. Although there is increasing evidence that DMetD is associated with cardiac dysfunction, the early DMetD-induced myocardial alterations remain incompletely understood. Here, we studied early DMetD-related cardiac changes in a clinically relevant large animal model. DMetD was established in adult male Göttingen miniswine by streptozotocin injections and a high-fat, high-sugar diet, while control animals remained on normal pig chow. Five months later left ventricular (LV) function was assessed by echocardiography and hemodynamic measurements, followed by comprehensive biochemical, molecular and histological analyses. Robust DMetD developed, evidenced by hyperglycemia, hypercholesterolemia and hypertriglyceridemia. DMetD resulted in altered LV nitroso-redox balance, increased superoxide production—principally due to endothelial nitric oxide synthase (eNOS) uncoupling—reduced nitric oxide (NO) production, alterations in myocardial gene-expression—particularly genes related to glucose and fatty acid metabolism—and mitochondrial dysfunction. These abnormalities were accompanied by increased passive force of isolated cardiomyocytes, and impaired LV diastolic function, evidenced by reduced LV peak untwist velocity and increased E/e′. However, LV weight, volume, collagen content, and cardiomyocyte cross-sectional area were unchanged at this stage of DMetD. In conclusion, DMetD, in a clinically relevant large-animal model results in myocardial oxidative stress, eNOS uncoupling and reduced NO production, together with an altered metabolic gene expression profile and mitochondrial dysfunction. These molecular alterations are associated with stiffening of the cardiomyocytes and early diastolic dysfunction before any structural cardiac remodeling occurs. Therapies should be directed to ameliorate these early DMetD-induced myocardial changes to prevent the development of overt cardiac failure.

Metallic anodes (lithium, sodium, and zinc) are attractive for rechargeable battery technologies but are plagued by an unfavorable metal–electrolyte interface that leads to nonuniform metal deposition and an unstable solid–electrolyte interphase (SEI). Here we report the use of electrochemically labile molecules to regulate the electrochemical interface and guide even lithium deposition and a stable SEI. The molecule, benzenesulfonyl fluoride, was bonded to the surface of a reduced graphene oxide aerogel. During metal deposition, this labile molecule not only generates a metal-coordinating benzenesulfonate anion that guides homogeneous metal deposition but also contributes lithium fluoride to the SEI to improve Li surface passivation. Consequently, high-efficiency lithium deposition with a low nucleation overpotential was achieved at a high current density of 6.0 mA cm(−2). A Li|LiCoO(2) cell had a capacity retention of 85.3% after 400 cycles, and the cell also tolerated low-temperature (−10 °C) operation without additional capacity fading. This strategy was applied to sodium and zinc anodes as well.

In this paper, we present the formation of reversible covalently cross-linked networks in ethylene propylene rubber with grafted anthracene groups (EPM-g-AN) based on the principles of photoinduced anthracene dimerization. First, an industrial-grade EPM rubber grafted with maleic anhydride functional groups (EPM-g-MA) was modified with 9-anthracenemethanol. By irradiating EPM-g-AN with UV light (365 nm), the anthracene moieties dimerize via [4 + 4]cycloaddition, forming a covalent network. The network cleavage proceeds at high temperatures (>170 °C), even if with considerable (chemical) degradation. Furthermore, one of the degradation routes has been identified by 1H NMR to occur via the ester bond cleavage releasing 9-anthracenemethanol. Nevertheless, the reversibility of cross-linking has been achieved by performing the reverse reaction in decalin. The UV-vis spectroscopy clearly shows that the de-cross-linking process in these conditions is due to the anthracene dimer cleavage. Although the recovery in mechanical properties upon recycling is yet to be optimized, the disclosed results pave the way toward the use of anthracene chemistry in thermally reversible networks with possible industrial perspective applications.

To clarify the chemical mechanical polishing (CMP) mechanism of Cu in aqueous hydrogen peroxide and glycine, we developed a ReaxFF reactive force field to describe the interaction between Cu, slurr...

Molecular dynamics (MD) studies of graphene growth at atomistic level can provide valuable insight for understanding its growth mechanism, which is helpful to optimize the growth conditions for syn...

The decomposition of methylcyclohexane (MCH) containing suspended functionalized graphene sheets (FGS) was studied using a high-pressure flow reactor, under supercritical conditions over the temperature range of 780 – 825 K at a constant pressure of 4.72 MPa. Experiments showed both fuel conversion rates and C1-C2 product yields were increased by 43.3% and 62.1%, respectively, with the addition of 50 ppmw of FGS at 820 K. The reaction mechanisms between hydrocarbon and FGS were computationally investigated using reactive molecular dynamics (MD) with ReaxFF force fields at the temperatures of 1700, 1800, and 1900 K. The MD simulations revealed that oxygen-containing functional groups attached to the FGS plays an important role in catalyzing the decomposition of the fuel. Heterogeneous dehydrogenation of MCH into a C7H13 radical intermediate led to formation of secondary and tertiary radicals, such as H, CH3, and C2H5, during early extents of reaction promoting additional fuel-consuming steps, including H-abstraction and hydrogenation.

A fully interactive Cu/C/H/O reactive force field (ReaxFF) was developed for the Cu-metal surface catalysis system following three steps: (1) re-optimization of the Cu force field by an extended tr...

Blends of polyacrylonitrile (PAN) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) as precursors may offer an opportunity to reduce the cost of carbon fiber (CF) production. The all-carbon ring formations and volatile gas production during the heating and carbonization for 9 PAN/PBO blend precursors with varying mixing ratios are studied via the ReaxFF reactive molecular dynamics simulations. Evolutions of oxygen-containing (O-containing) and nitrogen-containing (N-containing) groups are detailed, in order to reveal the reaction mechanisms of the O and N-based CF precursors. Particularly, the O-containing groups are identified to be more efficient for initiating the carbonization, whereas N-containing groups are far longer retained in the graphitic materials and play a key role in capturing and converting carbon radical species into the graphitic networks. Additionally, the PAN/PBO blend precursor with a mole ratio of 1:1 is compared with the pre-oxidized PAN, PAN, and PBO. It is found that the PAN/PBO blends could be a promising alternative for the cost-effective PAN-based CF precursors, since they can decrease the cost of the CF production by means of: (a) eliminating the pre-oxidation process, (b) having considerable all-carbon ring formations within a short period, and (c) having a relatively fast conversion rate, reaching 95% 6-membered carbon ring formation.

Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are 'half van der Waals' metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.

Highly viscous bioinks offer great advantages for the three-dimensional fabrication of cell-laden constructs by microextrusion printing. However, no standardised method of mixing a high viscosity biomaterial ink and a cell suspension has been established so far, leading to non-reproducible printing results. A novel method for the homogeneous and reproducible mixing of the two components using a mixing unit connecting two syringes is developed and investigated. Several static mixing units, based on established mixing designs, were adapted and their functionality was determined by analysing specific features of the resulting bioink. As a model system, we selected a highly viscous ink consisting of fresh frozen human blood plasma, alginate, and methylcellulose, and a cell suspension containing immortalized human mesenchymal stem cells. This bioink is crosslinked after fabrication. A pre-crosslinked gellan gum-based bioink providing a different extrusion behaviour was introduced to validate the conclusions drawn from the model system. For characterisation, bioink from different zones within the mixing device was analysed by measurement of its viscosity, shape fidelity after printing and visual homogeneity. When taking all three parameters into account, a comprehensive and reliable comparison of the mixing quality was possible. In comparison to the established method of manual mixing inside a beaker using a spatula, a significantly higher proportion of viable cells was detected directly after mixing and plotting for both bioinks when the mixing unit was used. A screw-like mixing unit, termed “HighVisc”, was found to result in a homogenous bioink after a low number of mixing cycles while achieving high cell viability rates.

A new ReaxFF reactive force field has been developed for metal carbonate systems including Na+, Ca2+, and Mg2+ cations and the CO32- anion. This force field is fully transferable with previous ReaxFF water and water/electrolyte descriptions. The Me-O-C three-body valence angle parameters and Me-C non-reactive parameters of the force field have been optimized against quantum mechanical calculations including equations of states, heats of formation, heats of reaction, angle distortions and vibrational frequencies. The new metal carbonate force field has been validated using molecular dynamics simulations to study solvation and reactivity of metal and carbonate ions in water at 300 K and 700 K. The coordination radius and self-diffusion coefficient show good consistency with existing experiments and simulations results. The angular distribution analysis explains the structural preference of carbonate ions to form carbonates and bicarbonates, where Na+ predominantly forms carbonates due to lesser angular strain, while Ca2+ and Mg2+ prefer to form bicarbonates monodentate in nature. Residence time distribution analyses on different systems reveal the role of ions in accelerating and decelerating dynamics of water and carbonate ions under different thermodynamic conditions. The formation and dissolution of bicarbonates and carbonates in the solution were explored on the basis of protonation capability in different systems. The nucleation phenomenon of metal carbonates at ambient and supercritical conditions is explained from the perspective of clusters formation over time: Ca2+ ions can form prenucleation clusters at ambient temperature but shows a saturation with temperature, whereas Na+ and Mg2+ ions show rapid increase in cluster size and amount upon increasing time and temperature.

Energy storage is a vital aspect for the successful implementation of renewable energy resources on a global scale. Herein, we investigated the redox cycle of nickel dithiocarbamates for potential use as catholytes in non-aqueous redox flow batteries. The unique redox cycle of nickel dithiocarbamates (Ni(dtc)2) offers the ability to better understand these reactions by displaying 2e- chemistry upon oxidation from Ni(II) → Ni(IV) but 1e- chemistry upon reduction from Ni(IV) → Ni(III) → Ni(II). The underlying reasons for this cycle lie in the structural changes that occur between four-coordinate Ni(dtc)2 and six-coordinate [Ni(dtc)3]+. Cyclic voltammetry and spectroscopic experiments show that these 1e- and 2e- pathways can be controlled by the addition of ancillary ligands such as pyridine derivatives and Lewis acids such as Zn(II). Specifically, the addition of different pyridine based ancillary N-donor ligands (L) to the electrolyte solution results in 1e- oxidation producing a mixture of five-coordinate [Ni(dtc)2L]+ and six-coordinate [Ni(dtc)2(L)2]+ intermediate species which decay to [Ni(dtc)3]+ by parallel pathways. The equilibrium constants for L coordination were determined and found to increase with larger pKa values of the pyridine base. On the reduction side, the addition of Zn(II) to the electrolyte is shown to consolidate the two 1e- reduction peaks into a single 2e- reduction where [Ni(dtc)3]+ is reduced directly to Ni(dtc)2. This enhancement is believed to be due to chemical assistance in removing a dtc- ligand from a Ni(dtc)3 intermediate, allowing for easier reduction to Ni(dtc)2. Around 80% columbic efficiency obtained when Ni(dtc)2 was used as catholyte in the chrono potentiometric (CP) H cell experiment in presence of 24 mM Zn2+ ion.

The phase behavior of ethylene/propylene(/diene) (EP(D)M) co- (and ter-)polymers characterized by ethylene content in the range 64–78 wt%, and comparatively low level of crystallinity, in the range 1–15%, is analyzed during stretching, through collection of wide angle X-ray scattering data. All samples experience crystallization by effect of stretching, but whereas for the samples with ethylene content ≥71% crystallinity starts increasing already after yielding, the nearly amorphous sample, with 64 wt% ethylene content, experiences crystallization only at strain above a threshold (≈170%). In all cases, a high degree of orientation of the amorphous phase is achieved already at low deformations. It is shown that for the samples with high ethylene content, the pre-existing crystals undergo initial fragmentation and/or mechanical melting at low deformations, and successive oriented recrystallization at higher deformations. The role of oriented amorphous phase, along with the role of pre-existing crystals as nuclei able to foster further crystallization is highlighted.

Diels-Alder chemistry has been used for the thermoreversible cross-linking of furan-functionalized ethylene/propylene (EPM) and ethylene/vinyl acetate (EVM) rubbers. Both furan-functionalized elastomers were successfully cross-linked with bismaleimide to yield products with a similar cross-link density. NMR relaxometry and SAXS measurements both show that the apolar EPM-g-furan precursor contains phase-separated polar clusters and that cross-linking with polar bismaleimide occurs in these clusters. The heterogeneously cross-linked network of EPM-g-furan contrasts with the homogeneous network in the polar EVM-g-furan. The heterogeneous character of the cross-links in EPM-g-furan results in a relatively high Youngs modulus, whereas the more uniform cross-linking in EVM-g-furan results in a higher tensile strength and elongation at break.

Understanding the effects of water on the mechanical properties of silica glass is important for many applications of silicate glasses. In this study, the effects of water on both elastic and plastic properties of pure silica glass are investigated. The introduction of molecular water leads to an increase of Young's modulus of silica glass at low water content, while hydroxyl exhibits an opposite effect. While hydroxyl groups decrease both strength and fracture toughness of the glass via destructing the silica network connectivity, molecular water undermines these properties by effectively driving the silica network to a “strained” configuration in absence of external stress. The water effect can be characterized in terms of the change of Si-O bond length and Si-O-Si bond angle. The plateau in the stress-strain curves of silica with the existence of molecular water in compact tension is associated with the Si-O bond breaking followed by formation of silanol groups. Moreover, the introduction of molecular water lowers the critical tensile stress where the plateau occurs.

The presence of leachable ions in multicomponent silicate glasses complicates the understanding of their surface structure and chemistry under a humid or aqueous environment, in particular when com...

Parallel reactive molecular dynamics simulations were used to statistically analyze chemical reactions between tri-cresyl phosphate (TCP) and an amorphous iron oxide surface. To accurately model this system, a new parameter set for Fe/P/O interactions within the ReaxFF framework was developed. Using the new parameter set, 100 parallel simulations of a single TCP molecule on an amorphous iron oxide surface were run to capture multiple possible reactions at temperatures ranging from 300 to 700 K. The frequency of TCP–surface reactions for each atom type and each unique reaction site on the TCP was analyzed across the range of temperatures. Finally, the composition of the material chemisorbed to the surface was determined and analyzed in the context of previously reported experimental measurements of TCP films in oxygen-deficient environments. The results are specifically relevant to TCP, but the parallel reactive simulation approach and statistical analysis of reaction sites can be applied more generally to...

Ferroelectric materials such as barium titanate (BaTiO3) have a wide range of applications in nano scale electronic devices due to their outstanding properties. In this study, we developed an easily extendable atomistic ReaxFF reactive force field for BaTiO3 that can capture both its field- and temperature-induced ferroelectric hysteresis and corresponding changes due to surface chemistry and bulk defects. Using our force field, we were able to reproduce and explain a number of experimental observations: (1) the existence of a critical thickness of 4.8 nm below which ferroelectricity vanishes in BaTiO3; (2) migration and clustering of oxygen vacancies (OVs) in BaTiO3 and a reduction in the polarization and the Curie temperature due to the OVs; (3) domain wall interaction with the surface chemistry to influence the ferroelectric switching and polarization magnitude. This new computational tool opens up a wide range of possibilities for making predictions for realistic ferroelectric interfaces in energy-conversion, electronic and neuromorphic systems.

In the present study, the ReaxFF reactive molecular dynamics simulation method was applied to investigate the effect of a small nickel cluster (Ni13) on the formation of nascent soot from polycyclic aromatic hydrocarbon (PAH) precursors. A series of NVT simulations was performed for systems of a Ni13 cluster and various PAH monomers, namely, naphthalene, anthracene, pyrene, coronene, ovalene, and circumcoronene, at temperatures from 400 to 2500 K. At low temperatures, the PAHs form soot particles via binding and stacking around nickel clusters. Larger soot particles are formed due to the early initiation of clustering provided by nickel compared to those observed in homogenous PAH systems. At 1200-1600 K, the PAH monomers show a chemisorption tendency onto the nickel surface, which results in incipient soot particles. Chemical nucleation was observed at 2000 K where nickel-assisted dehydrogenation and chemisorption of PAH led to the growth of stable soot particles, which did not occur in the absence of Ni-clusters. At a high temperature (2500 K), nickel significantly accelerates the ring-opening and graphitization of PAH molecules and increases the size of the fullerene-type soot as compared to that of homogenous systems.

Molten hydroxides, often used for crystal growth and nanoparticle synthesis, have recently been applied for the single step densification of several inorganic materials under moderate uniaxial pressures and 1000 °C below their usual sintering temperatures. The latter approach, termed cold sintering process (CSP), is a mechanochemically driven process that enables the densification of inorganic materials through a dissolution-precipitation creep mechanism. In this study, we report the main densification mechanisms of BaTiO3 in a NaOH-KOH eutectic mixture. A chemical insight at the atomistic level, investigated by ReaxFF molecular dynamics simulations, offers plausible ionic complex formation scenarios and reactions at the BaTiO3/molten hydroxide interface, enabling the dissolution-precipitation reactions and the subsequent cold sintering of BaTiO3.

Cross-linked polyethylene (XLPE) has been recognized as an outstanding insulator for high-voltage power cables due to its favorable structural integrity at high temperature, low moisture sensitivity, chemical resistance, and low rates of failure due to aging. However, the roles of by-products and amorphous regions generated during the XLPE production are not clearly known at the atomistic scale. In this study, we present an eReaxFF-based molecular dynamics simulation framework with an explicit electron description verified against density functional theory data to investigate the roles of XLPE by-products and processing variables such as density and voids on the time to dielectric breakdown (TDDB) of polyethylene (PE). Our simulation results indicate that an increase in density of PE increases the TDDB; however, adding a by-product with positive electron affinity such as acetophenone can reduce the TDDB. Furthermore, during the electrical breakdown in PE, electrons tend to migrate through voids when transferring from the anode to cathode. In comparison with neutral acetophenone, we find that the acetophenone radical anion can significantly reduce the energy barrier and the reaction energy of secondary chemical reactions.

The ReaxFF method has been successfully applied to study a wide range of chemistries in the fields of materials and biomolecular science, e.g., hydrocarbons, metal/metal oxides, combustion, catalysis, atomic layer deposition, DNA oxidation, and hydrolysis. In this work, we focus on current and potential future applications of ReaxFF to biological systems using various ReaxFF force field parameterizations specifically developed for the study of common reactive processes in biochemistry, including (1) RNA/DNA cleavage, (2) protonation/deprotonation of imidazole-Zn-ligand complexes, and (3) Cu-catalyzed and noncatalyzed peptide bond hydrolysis. First, ReaxFF reproduced the cleavage mechanism for phosphodiester linkage of RNA and DNA with the atomic level picture. Cleaving RNA yields a 2′-OH,3′-phosphate and a 5′-OH nucleoside via 3′,5′-cyclic phosphate intermediate. Also, due to the absence of a 2′-hydroxyl group in DNA, DNA is cleaved by the nucleophilic attack of water on the phosphorus center, producing a 5′-OH nucleoside and a nucleotide. Second, the interactions between Zn(II) metal and various ligands were successfully compared between ReaxFF and the earlier DFT work, which the ligand dissociation energies and proton affinities are systematically examined in Zn-ligand (L) complexes (L = NH2, NH3, NHCH2, NCH2, and NCH2CH3 functional groups, imidazole, and H2O). Using this force field, we performed a reactive MD simulation for the formation of Zn(Im)n(H2O)m in aqueous at 300 K. The results show that the mixed ligand Zn(Im)n(H2O)m complexes are allowed to have various coordination numbers, due to the dynamic nature of Zn(II) coordination. One of the common and important ligands in metalloprotein is imidazole in a histidine residue. The role of imidazole as a proton donor and acceptor is very essential for the proton transfer occurring at enzyme active sites. We showed that ReaxFF can describe the pH-dependent protonation state of imidazole by investigating the energy barriers for the protonation and performing a reactive MD simulation for the formation of imidazolium cations at low pH. Finally, we compared ReaxFF results for catalyzed and uncatalyzed peptide bond hydrolysis mechanisms. It is found that the transition state is stabilized significantly by the formation of a Cu(II)-complex. The ReaxFF potential energy profiles along the reaction pathway for both catalyzed and uncatalyzed hydrolysis reactions are in excellent agreement with the DFT. The role of imidazole as a bridge for the proton transfer and its biological significance in the Ser-His-Asp catalytic triad were further discussed.

Hybrid swell packers are rubber products capable of swelling in (saline) water and hydrocarbon oils, by exploiting the hydrocarbon diffusion properties of an nonpolar elastomer with the osmotic swelling of a water absorbent (WA). In this study, a variety of modified natural and synthetic WAs and mixtures thereof have been screened in a rubber compound with respect to swelling in decalin, demineralized, and saline water, respectively. We aimed at achieving high and fast swelling in all used media. Mixing of the various WAs in an ethylene/propylene/diene monomer (EPDM)/carbon black masterbatch at an addition level of 75 phr did not pose any problems, although it was found that the WAs did affect the sulfur vulcanization. Decalin swelling of the vulcanizates is very fast, reaching high equilibrium swelling within 1.5 days. Swelling in demineralized or saline water is much slower, with up to 300% swelling in water and up to 100% swelling in saline water. Significant leaching of the organic WA from the EPDM vulcanizates to the water phase occurs. Some combinations of WAs show synergetic effects for swelling in water. To our knowledge, such a systematic study of hybrid swelling elastomers constitutes a novelty in the open literature., This work was funded by National Funds through FCT - Portuguese Foundation for Science and Technology, Reference PEst-C/CTM/LA0025/2013.

BackgroundThe production of methane by methanogens is dependent on numerous iron-sulfur (Fe-S) cluster proteins; yet, the machinery involved in Fe-S cluster biogenesis in methanogens remains largely unknown. Methanogen genomes encode uncharacterized homologs of the core components of the ISC (IscS and IscU) and SUF (SufBC) Fe-S cluster biogenesis systems found in bacteria and eukaryotes.Methanosarcina acetivoranscontains threeiscSUand twosufCBgene clusters. Here, we report genetic and biochemical characterization ofM. acetivorans iscSU2.ResultsPurified IscS2 exhibited pyridoxal 5′- phosphate-dependent release of sulfur from L-cysteine. Incubation of purified IscU2 with IscS2, cysteine, and iron (Fe2+) resulted in the formation of [4Fe-4S] clusters in IscU2. IscU2 transferred a [4Fe-4S] cluster to purifiedM. acetivoransapo-aconitase. IscU2 also restored the aconitase activity in air-exposedM. acetivoranscell lysate. These biochemical results demonstrate that IscS2 is a cysteine desulfurase and that IscU2 is a Fe-S cluster scaffold.M. acetivoransstrain DJL60 deleted ofiscSU2was generated to ascertain the in vivo importance of IscSU2. Strain DJL60 had Fe-S cluster content and growth similar to the parent strain but lower cysteine desulfurase activity. Strain DJL60 also had lower intracellular persulfide content compared to the parent strain when cysteine was an exogenous sulfur source, linking IscSU2 to sulfur metabolism.ConclusionsThis study establishes thatM. acetivoranscontains functional IscS and IscU, the core components of the ISC Fe-S cluster biogenesis system and provides the first evidence that ISC operates in methanogens.

Treatment of multidrug-resistant Gram-negative bacterial pathogens represents a critical clinical need. Here, we report a novel γ-lactam pyrazolidinone that targets penicillin-binding proteins (PBPs) and incorporates a siderophore moiety to facilitate uptake into the periplasm. The MIC values of γ-lactam YU253434, 1, are reported along with the finding that 1 is resistant to hydrolysis by all four classes of β-lactamases. The druglike characteristics and mouse PK data are described along with the X-ray crystal structure of 1 binding to its target PBP3.

Sooting tendencies of a series of nitrogen-containing hydrocarbons (NHCs) have been recently characterized experimentally using the yield sooting index (YSI) methodology. This work aims to identify soot-relevant reaction pathways for three selected C6H15N amines, namely, dipropylamine (DPA), diisopropylamine (DIPA), and 3,3-dimethylbutylamine (DMBA) using ReaxFF molecular dynamics (MD) simulations and quantum mechanical (QM) calculations and to interpret the experimentally observed trends. ReaxFF MD simulations are performed to determine the important intermediate species and radicals involved in the fuel decomposition and soot formation processes. QM calculations are employed to extensively search for chemical reactions involving these species and radicals based on the ReaxFF MD results and also to quantitatively characterize the potential energy surfaces. Specifically, ReaxFF simulations are carried out in the NVT ensemble at 1400, 1600, and 1800 K, where soot has been identified to form in the YSI experiment. These simulations account for the interactions among test fuel molecules and pre-existing radicals and intermediate species generated from rich methane combustion, using a recently proposed simulation framework. ReaxFF simulations predict that the reactivity of the amines decrease in the order DIPA > DPA > DMBA, independent of temperature. Both QM calculations and ReaxFF simulations predict that C2H4, C3H6, and C4H8 are the main nonaromatic soot precursors formed during the decomposition of DPA, DIPA, and DMBA, respectively, and the associated reaction pathways are identified for each amine. Both theoretical methods predict that sooting tendency increases in the order DPA, DIPA, and DMBA, consistent with the experimentally measured trend in YSI. This work demonstrates that sooting tendencies and soot-relevant reaction pathways of fuels with unknown chemical kinetics can be identified efficiently through combined ReaxFF and QM simulations. Overall, predictions from ReaxFF simulations and QM calculations are consistent, in terms of fuel reactivity, major intermediates, and major nonaromatic soot precursors.

One of the challenges for the clinical translation of RNA interference (RNAi)-based therapies concerns the deposition of therapeutically effective doses of the nucleic acids, like siRNA, at a local tissue level without severe off-target effects. To address this issue, hydrogels can be used as matrices for the local and sustained release of the siRNA cargo. In this study, the formation of polyplexes based on siRNA and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA)-based polymers was investigated, followed by their loading in a thermosensitive hydrogel to promote local siRNA release. A multifunctional NPD triblock copolymer consisting of a thermosensitive poly(N-isopropylacrylamide) (PNIPAM, N), a hydrophilic poly(ethylene glycol) (PEG, P), and a cationic PDMAEMA (D) block was used to study the binding properties with siRNA taking the non-thermosensitive PD polymer as control. For both polymers, small polyplexes with sizes ranging from 10-20 nm were formed in aqueous solution (HBS buffer, 20 mM HEPES, 150 mM NaCl, pH 7.4) when prepared at a N/P charge ratio of 5 or higher. Formulating the siRNA into NPD or PD polyplexes before loading into the thermosensitive PNIPAM-PEG-PNIPAM hydrogel resulted in a more controlled and sustained release compared to free siRNA release from the hydrogel. The polyplexes were released for 128 hours in HBS, when changing the release medium twice a day, while free siRNA was completely released within 50 hours with already 40% being released after changing the release medium just once. The release of the polyplexes was dependent on the dissolution rate of the hydrogel matrix. Moreover, intact polyplexes were released from the hydrogels with a similar size as before loading, suggesting that the hydrogel material did not compromise the polyplex stability. Finally, it was shown that the released polyplexes were still biologically active and transfected FaDu cells, which was observed by siRNA-induced luciferase silencing in vitro. This study shows the development of an injectable thermosensitive hydrogel to promote local and sustained release of siRNA, which can potentially be used to deliver siRNA for various applications, such as the treatment of tumors.

Extensive application of coronary intravascular procedures has led to the increased need of understanding the injury inflicted to the coronary arterial wall. We aimed to investigate acute and prolonged coronary endothelial injury as a result of guidewire use, repeated intravascular imaging and stenting. These interventions were performed in swine (N = 37) and injury was assessed per coronary segment (n = 81) using an Evans Blue dye-exclusion-test. Scanning electron microscopy and light microscopy were then used to visualize the extent and nature of acute (

International audience; While shale gas has become a major source of energy, a more sustainable recovery requires better understanding of the gas/kerogen matrix interactions. Here we use replica exchange molecular dynamics to investigate the geological conversion of two important classes of gas-forming constituents of terrestrial organic matter: lignin and cellulose. In agreement with results from pyrolysis experiments, we show that lignin 1 produces twice as much kerogen and five times more methane than cellulose. In addition , while ex-cellulose kerogen is relatively stiff and almost non porous, ex-lignin kerogen, despite having very similar composition and bonding, is an order of magnitude more compliant due to the presence of large micropores. The obtained results can potentially improve the nanoscale brick of bottom-up models of shale gas recovery.

Plazomicin was tested against 697 recently acquired carbapenem-resistant Klebsiella pneumoniae isolates from the Great Lakes region of the United States. Plazomicin MIC 50 and MIC 90 values were 0.25 and 1 mg/liter, respectively; 680 isolates (97.6%) were susceptible (MICs of ≤2 mg/liter), 9 (1.3%) intermediate (MICs of 4 mg/liter), and 8 (1.1%) resistant (MICs of >32 mg/liter). Resistance was associated with rmtF -, rmtB -, or armA -encoded 16S rRNA methyltransferases in all except 1 isolate.

Erythritol tetranitrate (ETN) was prepared independently by two research groups from the USA and the Netherlands. The partially nitrated impurities present in ETN were studied using liquid chromatography-mass spectrometry to address the ultimate challenge in forensic explosives investigations, i.e., providing chemical and tactical information on the production and origin of the explosive material found at a crime scene. Accurate quantification of the tri-nitrated byproduct erythritol trinitrate (ETriN) was achieved by in-lab production of an ETriN standard and using custom-made standards of the two isomers of ETriN (1,2,3-ETriN and 1,2,4-ETriN). Large differences in levels of ETriN were observed between the two sample sets showing that, even when similar synthesis routes are employed, batches from different production locations can contain different impurity profiles. In one of the sample sets the ratios of the lesser partially nitrated impurities, EDiN and EMN, in the ETN samples could be determined. The impurity profiles enable prediction of post-synthesis work-up steps by reduction of the level of partially nitrated products upon recrystallization. However, impurity analysis does not enable predictions with respect to raw material or synthesis route used. Nonetheless, characteristic impurity profiles obtained can be used in forensic casework to differentiate or link ETN samples. However, forensic interpretation can be complicated by acid catalyzed degradation which can cause changes in impurity levels over time. The high food-grade quality of the erythritol precursor materials did not provide other impurity markers using the LC-MS methods in this study. To expand our framework of chemical attribution a follow-up study will be reported that focuses on stable isotope analysis of ETN and its precursor materials that potentially allow predictions for forensic explosives intelligence. © 2019 Elsevier B.V. Chemicals / CAS erythritol, 149-32-6, 7541-59-5; erythrityl tetranitrate, 7297-25-8

Monolayer metal oxides (MMOs) can provide tunable chemical properties dictated by choice of the support and coating metal oxide. Experimental discovery of (meta)stable coating/support combinations ...

Instantaneous adhesion between different materials is a requirement for several applications ranging from electronics to biomedicine. Approaches such as surface patterning, chemical cross-linking, surface modification, and chemical synthesis have been adopted to generate temporary adhesion between various materials and surfaces. Because of the lack of curing times, temporary adhesives are instantaneous, a useful property for specific applications that need quick bonding. However, to this day, temporary adhesives have been mainly demonstrated under dry conditions and do not work well in submerged or humid environments. Furthermore, most rely on chemical bonds resulting from strong interactions with the substrate such as acrylate based. This work demonstrates the synthesis of a universal amphibious adhesive solely by combining solid polytetrafluoroethylene (PTFE) and liquid polydimethylsiloxane (PDMS) polymers. While the dipole-dipole interactions are induced by a large electronegativity difference between fluorine atoms in PTFE and hydrogen atoms in PDMS, strong surface wetting allows the proposed adhesive to fully coat both substrates and PTFE particles, thereby maximizing the interfacial chemistry. The two-phase solid-liquid polymer system displays adhesive characteristics applicable both in air and water, and enables joining of a wide range of similar and dissimilar materials (glasses, metals, ceramics, papers, and biomaterials). The adhesive exhibits excellent mechanical properties for the joints between various surfaces as observed in lap shear testing, T-peel testing, and tensile testing. The proposed biocompatible adhesive can also be reused multiple times in different dry and wet environments. Additionally, we have developed a new reactive force field parameterization and used it in our molecular dynamics simulations to validate the adhesive nature of the mixed polymer system with different surfaces. This simple amphibious adhesive could meet the need for a universal glue that performs well with a number of materials for a wide range of conditions., by Chandra Sekhar Tiwary et al.

In the Netherlands, the illegal use of powerful flash bangers is popular and as a result these items are frequently encountered in forensic casework. In collaboration with the Dutch police a representative sample set of the most frequently confiscated flash bangers, the Cobra 6 and Cobra 6 2G, has previously been collected also including imitation items. Classification of the different flash bangers was performed by analysing the pyrotechnic charge using capillary electrophoresis (CE) with indirect UV-detection. Two rapid CE methods were used to determine the anions and cations present in the pyrotechnic mixtures. Black and flash powders were easily distinguishable based on their main inorganic compositions,i.e., KNO3and KClO4, respectively. Differentiation of flash powders from the commercial and imitation pyrotechnic items was achieved by the identification of Ca2+and Mg2+cation traces in the imitation flash banger powders. Quantitative CE results were used to explore the possibilities to differentiate seized sets of flash bangers but this proved to be difficult for commercial items due to lack of impurities and uniform production processes. In addition, inherent inhomogeneity of the powders and incomplete sample extraction yielded a relative high measurement uncertainty within a set. For the imitation items potential for set-based differentiation was observed. Although the number of seized imitation sets was limited, a first step has been taken to classify pyrotechnic mixtures to provide additional information and intelligence in forensic casework of flash bangers.

Monolayer metal oxide coatings on metal oxide supports have the possibility of tuning the surface chemical properties of the coated systems. However, the (meta)stability of these structures makes experimental discovery challenging. A computational approach can help to determine properties that make a coating/substrate system stable and evaluate the stability of a variety of combinations. Herein, we use density functional theory (DFT) to study the stability of monolayer transitional metal oxides over different facets of anatase, brookite, and rutile phase of TiO2. We find that coatings that have a stable polymorph matching that of the support, as well as substrates with higher surface energies, are more likely to form monolayer-coated systems. DFT calculations recommend a number of coating/TiO2 surface facet combinations that may be stable. Despite these predictive observations, we did not find a significant correlation between monolayer stability and a single atomic, surface, or structural property of the...

Exposure of sulfonated poly(ether etherketone), SPEEK, in aqueous solutions to 350 nm photons induced reduction of CHCl3 to CH2Cl2 and chloride ions in the presence of HCO2H/HCO2– buffers or poly(v...

We present the development of a ReaxFF reactive force field for Na/Si/O/H interactions, which enables reactive molecular dynamics simulation of the sodium silicate–water interfaces. The force field parameters were fitted against various quantum mechanical calculations, including equations of state of different NaSiOx crystalline phases, energy barriers of a sodium cation’s transport within the sodium silicate crystal structure, interactions between the hydroxylated silica surface and sodium cation–water systems, and dissociation energies of [NaOH–n(H2O)] (n = 1–6) clusters. After the optimization process, we validated the force field capability through calculating the structures of sodium silicate crystals and glasses and transport properties of sodium ions and protons within the amorphous structures. The force field was also applied to validate the dissociation behavior of sodium hydroxides within the bulk water. Our results with the developed force field are relevant to detailed chemical dissolution mec...

Model compounds anthracene, sucrose, anthanthrone, anthrone and fluorene were carbonized at 500 °C and subsequently heat treated at 2600 °C. The majority of initial oxygen content was lost during low temperature carbonization. The intermediate species formed after oxygen evolution dictated the resulting carbon skeleton and thus the graphitizability. Anthracene and sucrose were selected as model graphitizing and non-graphitizing compounds based on historical precedence. Carbonization of anthanthrone resulted in a graphitizable coke, whereas anthrone yielded a non-graphitizable char. It is proposed that CO loss from anthanthrone results in the formation of perylene, where CO loss from anthrone produces fluorene. An obvious resemblance was observed in structure between heat treated sucrose and anthrone char as compared to heated treated char embedded with 5 membered rings via carbonization of fluorene. Thus, providing evidence that 5 membered rings are present in the virgin chars and are the cause of non-graphitizability. Polarized light microscopy was employed to measure the extent of mesophase development after carbonization. Transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy were used to characterize the material before and after annealing.

A series of compounds based on peroxide-cured ethylene–propylene–diene monomer rubber (EPDM) was prepared with varying amounts of paraffinic process oil, such as Sunpar 2280, squalane, and dodecane. The cross-linked network composition of EPDM vulcanizates, which correlated directly with the structure and the concentration of process oils, was successfully carried out by either an exponential or a linear fitting procedure. It was found that an increase in process oil concentration caused a decrease in total cross-link density, which could be quantitatively divided into the effect of dilution and chemical effect of oil, represented as a linear and an exponential function of process oil concentration, respectively. Experimental results indicated that whether dilution effect or chemical effect, the addition of Sunpar 2280 affected the decrease of cross-link densities of EPDM vulcanizates most obviously, followed by squalane, and then dodecane, which was the weakest. On the other hand, at lower squalane loading, the chemical effect of squalane dominated the decrease of cross-link density of peroxide-cured EPDMs compared with the dilution effect of oils. Gel permeation chromatography spectra confirmed squalane could consume the free radicals derived from peroxide, forming dimers and trimers, and the variation of squalane content did not affect the activation energy of the cross-linking reaction calculated based on the Kissinger method. The cross-linking efficiency of peroxide and physical entanglement density both linearly decreased with the increase of squalane content.

It is demonstrated that the concept of thermoreversible cross-linking of functionalized maleic anhydride grafted ethylene–propylene (EPM-g-MA) rubber using Diels–Alder chemistry is limited neither to laboratory scale using a solvent route nor to gum rubber. The use of an internal mixer is the first step toward an industrial process, since it greatly reduces the processing time and allows for a solventless process for the furan-functionalization and subsequent bismaleimide cross-linking of EPM rubber. Practical rubber compounds were prepared by mixing thermoreversibly cross-linked EPM with carbon black and mineral oil in the same batch mixer. This resulted in reinforcement of the rubber without affecting the thermoreversible character of the cross-linking. The pendant furan groups of the (non)cross-linked EPM-g-furan interact with the carbon black filler. Finally, crystalline EPM rubber compounds were prepared, which show excellent material properties and property retention over multiple reprocessing cycles.