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The competition between E2 and SN2 reactions is essential in organic chemistry. In this paper, the reaction mechanism of F− + CH3CH2Cl is investigated utilizing direct dynamics simulations, and unravel how the collision energy (Ecoll) and the leaving group affect the competition between SN2 and E2 in the F− + CH3CH2Y (Y = Cl and Br) reactions. Simulation results for F− + CH3CH2Cl reaction show that the anti-E2 channel is dominant, but with the increase of Ecoll from 0.04 to 1.9 eV the branching ratio of the anti-E2 pathway significantly decreases by 21%, and the SN2 pathway becomes more important. A transition from indirect to direct reaction has been revealed when Ecoll is increased from 0.04 to 1.90 eV. At lower Ecoll, a large ratio of indirect events occurs via a long-lived hydrogen-bonded complex, and as the collision energy is increased, the lifetimes of the hydrogen-bonded complexes are shortened, due to an initial faster relative velocity. The simulation results of F− + CH3CH2Cl are further compared with the F− + CH3CH2Br reaction at Ecoll of 0.04 eV. Changing the leaving group from Cl to Br drastically suppresses the indirect events of anti-E2 with a branching ratio decreasing from 0.46 to 0.36 due to the mass effect, and promotes direct rebound mechanism resulting from a looser transition state geometry caused by varied electronegativity. [ABSTRACT FROM AUTHOR]

Direct dynamic simulations have been employed to investigate the OH− + CH3Cl reaction with the chosen B3LYP/aug-cc-pVDZ method. The calculated rate coefficient for the bimolecular nucleophilic substitution reaction (SN2), 1.0 × 10−9 cm3 mol−1 s−1 at 300 K, agrees well with the experimental result of (1.3–1.6) × 10−9 cm3 mol−1 s−1. The simulations reveal that the majority of the SN2 reactions are temporarily trapped in the hydrogen-bonded complex at Ecoll = 0.89 kcal mol−1. Importantly, the influences of the leaving group and nucleophile have been discussed by comparisons of X− + CH3Y (X = F, OH; Y = Cl, I) reactions. For the X = F− reactions, the reaction probability of SN2 increases along the increased leaving group ability Cl < I, suggesting that the thermodynamic factor plays a key role. The indirect mechanisms were found to be dominant for both reactions. In contrast, for X = OH−, the fraction of SN2 drops with the enhanced leaving group ability. In particular, a dramatic transition occurs for the dominant atomic reaction mechanisms, i.e., from complex-mediated indirect to direct, implying an interesting contest between the leaving group and the nucleophile and the importance of the dynamic factors, i.e., the dipole moment, steric hindrance, and electronegativity. [ABSTRACT FROM AUTHOR]

Layered transition metal dichalcogenide rhenium selenide (ReSe2) has attracted great attention as an electrocatalyst for the hydrogen evolution reaction (HER) due to its excellent stability and sufficient active sites. However, ReSe2 has intrinsically poor conductivity, which leads to the insufficient utilization of electrocatalytic active sites. Herein, we designed the regulation of the electronic band structure by W replacement in ReSe2 nanosheets to greatly improve the conductivity. The Re0.7W0.3Se2 exhibits an overpotential of 141 mV at 10 mA cm−2 and a Tafel slope of 65.3 mV dec−1, superior to that of the original ReSe2 and WSe2. This work aims to provide a feasible strategy to promote the HER activity of ReSe2. [ABSTRACT FROM AUTHOR]

Since the commercialization of the graphite anode by Sony in 1991, extensive research findings have demonstrated that carbon-based materials are promising candidates for lithium-ion batteries (LIBs) and "post lithium-ion batteries," sodium-ion batteries (SIBs)/potassium-ion batteries (PIBs). These three alkali-ion batteries consist of similar components and electrochemical reaction mechanisms in carbon materials, while some significant difference proved to exist in their electrochemical storage behaviors. This review presents a comprehensive comparison of Li+/Na+/K+ storage behavior in carbon anode materials (graphite, graphene, soft carbon and hard carbon) in view of the possible storage mechanism and favorable strategies to enhance their electrochemical performance. Hence, a better understanding of the relationship between the structure, charge storage mechanism and electrochemical behavior of carbon materials is provided. Finally, critical issues and perspectives are discussed to demonstrate prospective research directions for carbon anode materials in these alkali metal-ion batteries. [ABSTRACT FROM AUTHOR]

Proton transfer between HOCO+ and CO produces the formyl cation HCO+ and isoformyl cation HOC+ isomers initiating multiple astrochemical reaction networks. Here, the direct chemical dynamics simulations are performed to uncover the underlying atomistic dynamics of the above reaction. The simulations reproduce the measured product energy and scattering angle distributions and reveal that the reaction proceeds predominantly through a direct stripping mechanism which results in the prominent forward scattering observed in experiments. The reaction dynamics show propensity for the HCO+ product even at a collision energy larger than the threshold for HOC+ formation. This is a consequence of the larger opacity and impact parameter range for HCO+. In accordance with the revealed direct mechanistic feature, the reaction can be controlled by orienting the reactants into a reactive H–C orientation that also favors HCO+ formation. Considering the lack of equilibrated reactant complexes and the on the fly migration of the proton, the CO2-catalyzed isomerization is assumed to have insignificant impact on the isomer ratios. This work provides insights of dynamical effects besides energetics into the interesting finding of strongly suppressed formation of the metastable isoformyl cation for related proton transfer reactions in the measurements. [ABSTRACT FROM AUTHOR]

Both endogenous and externally applied electrical stimulation can affect a wide range of cellular functions, including growth, migration, differentiation and division. Among those effects, the electrical field (EF)-directed cell migration, also known as electrotaxis, has received broad attention because it holds great potential in facilitating clinical wound healing. Electrotaxis experiment is conventionally conducted in centimetre-sized flow chambers built in Petri dishes. Despite the recent efforts to adapt microfluidics for electrotaxis studies, the current electrotaxis experimental setup is still cumbersome due to the needs of an external power supply and EF controlling/monitoring systems. There is also a lack of parallel experimental systems for high-throughput electrotaxis studies. In this paper, we present a first independently operable microfluidic platform for high-throughput electrotaxis studies, integrating all functional components for cell migration under EF stimulation (except microscopy) on a compact footprint (the same as a credit card), referred to as ElectroTaxis-on-a-Chip (ETC). Inspired by the R–2R resistor ladder topology in digital signal processing, we develop a systematic approach to design an infinitely expandable microfluidic generator of EF gradients for high-throughput and quantitative studies of EF-directed cell migration. Furthermore, a vacuum-assisted assembly method is utilized to allow direct and reversible attachment of our device to existing cell culture media on biological surfaces, which separates the cell culture and device preparation/fabrication steps. We have demonstrated that our ETC platform is capable of screening human cornea epithelial cell migration under the stimulation of an EF gradient spanning over three orders of magnitude. The screening results lead to the identification of the EF-sensitive range of that cell type, which can provide valuable guidance to the clinical application of EF-facilitated wound healing. [ABSTRACT FROM AUTHOR]

The competition between E2 and S N 2 reactions is essential in organic chemistry. In this paper, the reaction mechanism of F - + CH 3 CH 2 Cl is investigated utilizing direct dynamics simulations, and unravel how the collision energy ( E coll ) and the leaving group affect the competition between S N 2 and E2 in the F - + CH 3 CH 2 Y (Y = Cl and Br) reactions. Simulation results for F - + CH 3 CH 2 Cl reaction show that the anti -E2 channel is dominant, but with the increase of E coll from 0.04 to 1.9 eV the branching ratio of the anti -E2 pathway significantly decreases by 21%, and the S N 2 pathway becomes more important. A transition from indirect to direct reaction has been revealed when E coll is increased from 0.04 to 1.90 eV. At lower E coll , a large ratio of indirect events occurs via a long-lived hydrogen-bonded complex, and as the collision energy is increased, the lifetimes of the hydrogen-bonded complexes are shortened, due to an initial faster relative velocity. The simulation results of F - + CH 3 CH 2 Cl are further compared with the F - + CH 3 CH 2 Br reaction at E coll of 0.04 eV. Changing the leaving group from Cl to Br drastically suppresses the indirect events of anti -E2 with a branching ratio decreasing from 0.46 to 0.36 due to the mass effect, and promotes direct rebound mechanism resulting from a looser transition state geometry caused by varied electronegativity.

Layered transition metal dichalcogenide rhenium selenide (ReSe 2 ) has attracted great attention as an electrocatalyst for the hydrogen evolution reaction (HER) due to its excellent stability and sufficient active sites. However, ReSe 2 has intrinsically poor conductivity, which leads to the insufficient utilization of electrocatalytic active sites. Herein, we designed the regulation of the electronic band structure by W replacement in ReSe 2 nanosheets to greatly improve the conductivity. The Re 0.7 W 0.3 Se 2 exhibits an overpotential of 141 mV at 10 mA cm -2 and a Tafel slope of 65.3 mV dec -1 , superior to that of the original ReSe 2 and WSe 2 . This work aims to provide a feasible strategy to promote the HER activity of ReSe 2 .

The advent of biological micro-patterning techniques has given new impetus to many areas of biological research, including quantitative biochemical analysis, tissue engineering, biosensing, and regenerative medicine. Derived from photolithography or soft lithography, current bio-patterning approaches have yet to completely address the needs of out-of-cleanroom, universal applicability, high feature resolution, as well as multi-object placement, though many have shown great promise to precisely pattern one specific biomaterial. In this paper, we present a novel versatile biological lithography technique to achieve integrated multi-object patterning with high feature resolution and high adaptability to various biomaterials, referred to as stereomask lithography (SML). Successive patterning of multiple objects is enabled by using unique three-dimensional masks (i.e., the stereomasks), which lay out current micropatterns while protecting pre-existing biological features on the substrate. Furthermore, high-precision reversible alignment among multiple bio-objects is achieved by adopting a peg-in-hole design between the substrate and stereomasks. We demonstrate that the SML technique is capable of constructing a complex biological microenvironment with various bio-functional components at the single-cell resolution, which to the best of our knowledge has not been realized before.

In this paper, we present a novel rapid-prototyping process for out-of-cleanroom microfabrication of three-dimensional multilayer microfluidic structures with a 10 microm resolution, referred to as the Direct Projection on Dry-film Photoresist (DP(2)). A commercially available digital projector is customized to function as a direct mask generation and photo exposure system, while easy-processing photosensitive dry films are used as the microfluidic constructs. Multilayer alignments among maskless-patterned layers are reliably achieved by using a Software Alignment technique with less than 10 microm precision, which eliminates the use of mechanical travelling stage. The bonding between different layers of dry film, simply enabled by a plasma-assisted thermal lamination, offers an easy implementation for suspended multilayer microstructures. Development of a complex microfluidic chip from computer layout can thus be accomplished within an hour in a regular chemical or biological lab environment using this approach.

With the major advances in soft lithography and polymer materials, use of microfluidic devices has attracted tremendous attention recently. A simple and fast micromachining process is highly in demand to prototype such a device efficiently and economically. In this paper, we first reported an out-of-cleanroom printing-based integrated microfabrication process, referred to as the lab-on-a-print (LOP), for rapid-prototyping three-dimensional microfluidics. Using this lab-on-a-print process, we demonstrated the potential to accomplish an entire design-to-fabrication cycle within an hour, including about 70 microm resolution of direct-lithography patterning, well-controlled polyimide wet etching, three-dimensional pattern alignment and multilayer wax thermal-fusion packaging. A microfluidic gradient generator was prepared and tested for validation of the lab-on-a-print microfabrication process.