Critical Role of Magnesium Ions in DNA Polymerase β's Closing and Active Site Assembly

To dissect the effects of the nucleotide-binding and catalytic metal ions on DNA polymerase mechanisms for DNA repair and synthesis, aside from the chemical reaction, we investigate their roles in the conformational transitions between closed and open states and assembly/disassembly of the active site of polymerase β/DNA complexes before and after the chemical reaction of nucleotide incorporation. Using dynamics simulations, we find that closing before chemical reaction requires both divalent metal ions in the active site while opening after the chemical reaction is triggered by release of the catalytic metal ion. The critical closing is stabilized by the interaction of the incoming nucleotide with conserved catalytic residues (Asp190, Asp192, Asp256) and the two functional magnesium ions; without the catalytic ion, other protein residues (Arg180, Arg183, Gly189) coordinate the incomer's triphosphate group through the nucleotide-binding ion. Because we also note microionic heterogeneity near the active site, Mg2+ and Na+ ions can diffuse into the active site relatively rapidly, we suggest that the binding of the catalytic ion itself is not a rate-limiting conformational or overall step. However, geometric adjustments associated with functional ions and proper positioning in the active site, including subtle but systematic motions of protein side chains (e.g., Arg258), define slow or rate-limiting conformational steps that may guide fidelity mechanisms. These sequential rearrangements are likely sensitively affected when an incorrect nucleotide approaches the active site. Our suggestion that subtle and slow adjustments of the nucleotide-binding and catalytic magnesium ions help guide polymerase selection for the correct nucleotide extends descriptions of polymerase pathways and underscores the importance of the delicate conformational events both before and after the chemical reaction to polymerase efficiency and fidelity mechanisms

Metal Nickel Foam as an Efficient and Stable Electrode for Hydrogen Evolution Reaction in Acidic Electrolyte under Reasonable Overpotentials

Acidic electrolytes are advantageous for water electrolysis in the production of hydrogen as there is a large supply of H⁺ ions in the solution. In this study, with the applied overpotential larger than the equilibrium potential of Ni⁰/Ni²⁺, Ni foam as HER electrode exhibits excellent and stable HER activity with an onset potential of −84 mV (vs RHE), a high current density of 10 mA cm^–2 at −210 mV (vs RHE), and prominent electrochemical durability (longer than 5 days) in acidic electrolyte. The results presented herein may has potential large-scale application in hydrogen energy production

Effects of seed crystal concentration, pH, and stirring rate on ammonium sulfate crystallization under the action of ammonium nitrate

In order to explore the effect of ammonium nitrate on the crystallization of ammonium sulfate mother liquor, this paper selected crystal seed, pH and stirring rate as the influencing factors, and studied the changes of average particle size, morphology and phase structure of ammonium sulfate crystals under the action of ammonium nitrate. When the seed crystal concentration was 1%–2%, the solute growth of the mixed solution could effectively reduce the supersaturation during the evaporation process, and the crystal growth did not generate new crystal nuclei, interfering with the crystallization process. A pH value of 4–5 promotes solvent/crystal surface interaction and crystal surface growth, which is beneficial for obtaining high-quality crystals. At a stirring rate of 200–300 r/min, the nucleation rate and secondary nucleation were improved, which is conducive to solid–liquid separation.</p

N‑Doped Carbon-Wrapped Cobalt Nanoparticles on N‑Doped Graphene Nanosheets for High-Efficiency Hydrogen Production

Development of non-noble-metal catalysts for hydrogen evolution reaction (HER) with both excellent activity and robust stability has remained a key challenge in the past decades. Herein, for the first time, N-doped carbon-wrapped cobalt nanoparticles supported on N-doped graphene nanosheets were prepared by a facile solvothermal procedure and subsequent calcination at controlled temperatures. The electrocatalytic activity for HER was examined in 0.5 M H₂SO₄. Electrochemical measurements showed a small overpotential of only −49 mV with a Tafel slope of 79.3 mV/dec. Theoretical calculations based on density functional theory showed that the catalytically active sites were due to carbon atoms promoted by the entrapped cobalt nanoparticles. The results may offer a new methodology for the preparation of effective catalysts for water splitting technology

Regulated Synthesis of Mo Sheets and Their Derivative MoX Sheets (X: P, S, or C) as Efficient Electrocatalysts for Hydrogen Evolution Reactions

Electrochemical H2 generation from H2O has been focused on the exploration of non-noble metals as well as earth-rich catalysts. In our practical work, we provide a simple cost-efficient fabrication process to prepare large Mo sheets via the controlled equilibrium between sublimation of MoO3 and reduction of H2. Porous MoP sheets were synthesized from the obtained Mo sheets as the Mo source and template which exhibit notable activity in the hydrogen evolution reaction with a low onset potential of −88 mV vs RHE, small Tafel value of 54.5 mV/dec, and strong catalytic stability. With Mo sheets as the universal Mo source and template, MoS2 and Mo2C sheets were synthesized by a similar process, and the corresponding catalytic activities were calculated by density functional theory

Core–Shell Nanocomposites Based on Gold Nanoparticle@Zinc–Iron-Embedded Porous Carbons Derived from Metal–Organic Frameworks as Efficient Dual Catalysts for Oxygen Reduction and Hydrogen Evolution Reactions

Core–shell nanocomposites based on Au nanoparticle@zinc–iron-embedded porous carbons (Au@Zn–Fe–C) derived from metal–organic frameworks were prepared as bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). A single Au nanoparticle of 50–100 nm in diameter was encapsulated within a porous carbon shell embedded with Zn–Fe compounds. The resulting Au@Zn–Fe–C hybrids exhibited apparent catalytic activity for ORR in 0.1 M KOH (with an onset potential of +0.94 V vs RHE, excellent stability and methanol tolerance) and for HER as well, which was evidenced by a low onset potential of −0.08 V vs RHE and a stable current density of 10 mA cm^–2 at only −0.123 V vs RHE in 0.5 M H₂SO₄. The encapsulated Au nanoparticles played an important role in determining the electrocatalytic activity for ORR and HER by promoting electron transfer to the zinc–iron-embedded porous carbon layer, and the electrocatalytic activity was found to vary with both the loading of the gold nanoparticle cores and the thickness of the metal–carbon shells. The experimental results suggested that metal-embedded porous carbons derived from metal–organic frameworks might be viable alternative catalysts for both ORR and HER