Journal of Chemical Sciences最新文献

The methane emission from natural sources cannot be stopped and it makes the global warming situation worse. Hope lies in its catalytic conversion into useful ‘syngas’ in the presence of oxygen and this reaction is partial oxidation of methane (POM). A mordenite-type molecular sieve having silica-alumina ratio 20 (abbreviated as CBV20A) is investigated herein to stabilize the active sites Ni at their cages and charge compensation sites. The promotion role of ceria over 5Ni/ CBV20A is further investigated to improve the catalytic performance towards POM. The catalyst’s texture property, crystallinity, polarizability, adsorption-desorption-oxidation and topology are studied by surface area-porosity, X-ray diffraction study, Raman spectroscopy, temperature programmed techniques and transmission electron microscopy respectively. The metal-support interaction is enhanced by the periodic exposure of hydrogen and oxygen during POM over the current catalyst system. Upon promotional addition of 2wt% ceria over Ni/CBV20A, the concentration of active sites are growing, the weak metal-support interaction diminished and strong metal-support established. The surface area and pore volume of this catalyst is also greater than those of the rest of the catalyst. The improved reduction profile and surface texture property turns 2 wt.% ceria promoted 5Ni/ CBV20A catalyst best towards POM reaction. It catalyzes POM gas feed composed of 50% CH₄, 25% O_2, and 25% N₂ (total space velocity14400 mL/h/g_cat) most effectively and achieves 62% H₂ yield with H₂/CO ratio of 2.5 during 230 min time on stream and ~60% H₂ yield with H₂/CO ratio of 2.4 during 22 h time on stream at 650 °C. High catalytic activity and the generation of hydrogen-rich syngas demonstrate the potential of Ni-based catalysts supported on a molecular sieve with a Ce promoter for POM.

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We present a benchmarking study to determine the optimal frequency, m of Monte Carlo (MC) steps to attempt changes in the protonation states of titratable sidechains of amino acid residues in constant pH molecular dynamics (CpHMD) simulations. The enzyme, human carbonic anhydrase (HCA) II, having a total of 72 titratable amino acid sidechains, has been used as the template. Along the CpHMD trajectories with (200 le m le 500) at pH 7.8, HCA II in water is found to exhibit stable structures with equilibrium fluctuations attributed mainly to the loops and turns exposed to the solvent. While the MC sampling step of CpHMD simulations involved all the titratable sites, the present work focuses primarily on the sidechain of catalytically important His-64 due to its well-known role in proton transfer in terms of two major sidechain orientations. The distribution of water molecules around the outward sidechain conformation of His-64 is found to be more sensitive to the choice of m than that around the Zn(II) ion deep inside the active site cavity. The underlying free energy and dynamics of the His-64 sidechain also showed a strong dependence on m. In both cases, an optimal convergence is observed for (m = 400)–500 where the fraction of protonated and neutral tautomers of His-64 sidechain accurately reproduce the results derived from a long-timescale CpH-REMD simulation and experimentally determined values of (pK_a).

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synopsis An optimal frequency, m of 400-500 of Monte Carlo steps is reported to attempt changes in protonation states of titratable amino acid sidechains in constant-pH MD simulations by comparing against NMR results. The choice of m on stable conformations of His-64 sidechain of human carbonic anhydrase II is also highlighted.

A novel azobenzene and quinoline amide based organogelator G1 was synthesized and characterized, the gelator formed stable organogels in 9 out of the 18 kinds of tested solvents. The G1-ethanol gel presents remarkable gelation properties, with the critical gelation concentrations 5.9 mg·mL^–1 and the gel-sol phase transition temperature at 72 °C. It was seen that the hydrogen bonding, π–π stacking, and van der Waals forces play crucial roles in the gelling process. Specifically, the G1-ethanol gel demonstrated outstanding reversibility in its gel↔sol state transitions induced by thermal, photo, and ionic stimuli, which attributed to the weak intermolecular forces and the trans-cis isomerization of azobenzene moieties within the gelator. The ion recognition characteristics of the G1-ethanol gel for Zn²⁺, Fe³⁺ and Sn²⁺ were investigated, the gel transformed into a transparent light yellow solution upon the addition of Sn²⁺.

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The gelator G1 exhibits trans-cis photoisomerization under alternating irradiation of UV and visible light, while reversible thermal gel-sol transition is achieved via weak intermolecular interactions. The G1-ethanol gel exhibits prominent response to Zn²⁺, Fe³⁺ and Sn²⁺. Notably, the addition of Sn²⁺ leads to a marked gel-to-sol transition, whereby the original gel disassembles into a light yellow transparent solution.

Amide bond formation is one of the most fundamental transformations in organic synthesis, yet its sustainable implementation still relies on stoichiometric coupling reagents, poor atom economy, and waste generation. In a recent study, Lee and co-workers found an alternative for the direct activation of carboxylic acids by utilizing dichloromethane as a coupling reagent. This methodology enables efficient amide synthesis without relying on conventional activating agents. Mechanistic investigations reveal the crucial participation of dichloromethane in generating the reactive intermediates responsible for amide bond formation.

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Dichloromethane, traditionally regarded as an inert solvent, is reappraised as a hidden coupling reagent that activates carboxylic acids for efficient direct amide synthesis. The broad applicability of the approach was demonstrated through 111 examples involving diverse carboxylic acids and amines, underscoring its versatility for amide bond formation.

A Ga-substituted ZSM-5 zeolite was successfully synthesized via a hydrothermal synthesis method, and its catalytic performance and physicochemical properties in propane aromatization were systematically investigated. Comprehensive characterizations including XRD, SEM, ICP-AES, IR, NH₃-TPD, XPS, N₂ adsorption-desorption and TG analyses revealed that Ga species exhibited the lower tendency to incorporate into the ZSM-5 zeolite framework compared to Al species. The gallium-doped aluminosilicate (GaAlZ5), possessing the largest specific surface area and highest acid content, demonstrated a superior aromatic selectivity of 85.6% and propane conversion of 66.1%, which exceeded those of gallosilicate (GaSiZ5) by 22.5% and 5.6%, respectively. Moreover, the intergranular mesopores in GaAlZ5 enhanced the mass-transfer rate of aromatics, effectively suppressed the formation of coke precursors, and endowed the catalyst with excellent long-term stability as well as regeneration stability. This work provides a facile synthesis strategy and systematic theoretical support for the design of high-stability and high-selectivity Ga-based zeolite catalysts for propane aromatization.

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This graphical abstract illustrates the bifunctional tandem pathway of propane aromatization, where propane is activated to propylene via dehydrogenation over Ga-based Lewis acid sites, followed by aromatization under the synergy of Brønsted and Lewis acid sites. This work reports a Ga-modified ZSM-5 zeolite (GaAlZ5) with optimized acid properties and pore structure, which delivers 66.1% propane conversion and 85.6% aromatics selectivity with excellent recyclability, providing a facile approach for light alkane valorization.

The present energy landscape with impetus on fuel cells, requires the design of efficient and durable bifunctional electrocatalysts for advancing energy conversion technologies. In the present study, a controllable strategy aiming at optimum composition of electrocatalysts was achieved by tailoring nickel oxide nanorods onto g-C₃N₄ surfaces, serving as active supports for noble metals. The ethylene glycol reduction method is utilized to anchor these noble metals (10 wt.% of palladium, platinum, and ruthenium separately) on the compositionally tuned NiO/g-C₃N₄ composite, resulting in enhanced active site exposure and catalytic performance. Of the three, Ru–NiO/g-C₃N₄ showed an extremely low overpotential of 20 mV vs. RHE at 10 mA cm^–2 for hydrogen evolution reaction. On the other hand, the other two catalysts, Pd-NiO/g-C₃N₄ and Pt-NiO/g-C₃N₄ show very low half-wave potential of 0.923 and 0.940 V vs. RHE for ORR, respectively. The present study summarizes the understanding of the cooperation in these electrocatalysts among the constituents, namely, noble metal/transition metal oxide–carbon nanostructures, for an enhanced electrochemical performance aiming at the design of bifunctional electrocatalysts and their application in sustainable energy systems.

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Advanced electrocatalysts designed for energy conversion technologies by anchoring various noble metal nanoparticles such as palladium, platinum, or ruthenium, onto nickel oxide nanorods supported by graphitic carbon nitride. The left plot evaluates their performance for the HER, and the right plot assesses their ORR. The synergistic engineering of this noble metal/transition metal oxide–carbon interface delivers enhanced electrocatalytic activity and structural stability for both electrochemical processes.

This review presents the feasibility of evanescent field-based fiber optic sensors across a wide range of applications. We evaluated two distinct sensing platforms based on localized surface plasmon resonance (LSPR) and a metal-free porphyrin-based fiber optic sensor. To maximize evanescent field penetration depth and sensitivity, U-bent and D-shaped fiber probe geometries were employed. For LSPR-based U-bent sensors, nanoparticle distribution was optimized, which is essential for controlling plasmonic coupling and maximizing sensitivity. Further, these probes are used for various applications, including the field of biosensing, water safety monitoring, and clinical diagnostics. Additionally, the review explores the unique potential of these platforms for monitoring ultrafast thermal dynamics of materials. In parallel, porphyrinimmobilized optical fiber probes were reviewed as powerful spectroscopic sensing platforms by monitoring UV-Vis absorption changes in Soret and Q bands, enabling selective detection of volatile gases and metal ions. The spectral feature changes during various analyte interactions produce high-dimensional data that necessitate advanced analysis techniques. These were analyzed using both unsupervised and supervised algorithms for spectral classification and analyte identification, with a focus on the critical role of spectral preprocessing in enhancing classification accuracy. Collectively, these platforms provide a comprehensive framework for next-generation, stable, and remote fiber-optic sensing systems.

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The graphical abstract depicts two distinct evanescent-fi eld-based optical fiber sensing platforms. One platform employs a metal-nanoparticle-based fiber-optic probe, in which analyte binding to the fiber core surface induces changes in the LSPR absorption spectrum. The other utilizes porphyrin-immobilized optical fiber probes, where analyte interactions induce characteristic changes in the Soret and Q bands of the porphyrin absorption spectrum. These spectral changes enable analyte identification through machine learning-assisted spectral analysis.