The abstraction reaction of hydrogen from formaldehyde by OH radical plays an important role in formaldehyde oxidation. The reaction involves a bimolecular association to form a chemically activated hydrogen-bonded reaction complex followed by a unimolecular reaction of the complex to generate the products. The reaction rate is usually considered to be pressure-independent by assuming equilibrium between the reactants and the complex. However, our nonequilibrium calculations based on the chemically significant eigenmode of the master equation, carried out with our recently developed program, indicate that the reaction complex makes the rate constant dependent on pressure at low temperatures ( < 200 K). The calculations include anharmonicity, variational effects, and multi-dimensional tunneling. We find that the reaction rate constant reaches a low-pressure limit at pressures below 10 Torr over the whole investigated temperature range (20-1800 K), which explains why the available low-temperature experiments, which are for pressures below 2 Torr, did not observe the pressure dependence. A new extension of the master-equation program is used to explore the time evolutions of the concentrations of the OH radical and the complex under pseudo-first-order conditions. The time-dependent evolution of the concentrations of the complex at a low temperature provide direct evidence for the stabilization of the reaction complex at high pressures, and it shows the negligible role of the stabilized reaction complex at low pressures. The picture that emerges is qualitatively consistent with our previous study of the reaction of methanol with OH in that the tunneling in the unimolecular step from the complex to the products affects the phenomenological reaction rate constants differently at high and low pressures and leads to a significant pressure effect.
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http://dx.doi.org/10.1039/d2fd00024e | DOI Listing |
Heliyon
January 2025
Nuclear Chemistry Division, Department of Chemistry, Atomic Energy Commission, P. O. Box: 9061, Damascus, Syrian Arab Republic.
Molecular scale information is needed to understand ions coordination to mineral surfaces and consequently to accelerate the design of improved adsorbents. The present work reports on the use of two-dimensional correlation Fourier Transform infra-red spectroscopy (2D-COS-FTIR) and hetero 2D-COS-FTIR- X-ray diffraction (XRD) to probe the mechanism of Cr(VI) removal from aqueous solutions by activated carbon (AC) and its composite with PWO (AC-composite). The adsorption data at an initial Cr(VI) concentration of 320 mg L (320 ppm) revealed maximum adsorption capacities of 65 mg g for AC and 73 mg g for AC-composite, corresponding to removal percentages of 83 % and 94 %, respectively.
View Article and Find Full Text PDFJ Phys Chem C Nanomater Interfaces
January 2025
Institut für Chemie und Biochemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany.
Since water is both a product and a common reactant impurity in the (partial) methanol oxidation to methyl formate (MeFo) on gold, its effect on the isothermal selectivity to methyl formate was investigated under well-defined single-collision conditions employing pulsed molecular beam experiments and in situ IRAS measurements. Both a flat Au(111) and a stepped Au(332) surface were used as model catalysts to elucidate how water affects the reactivity of low-coordinated step sites as compared to (111) terrace sites employing a range of reaction conditions. The interactions of water with methanol/methoxy as well as with oxygen species are addressed.
View Article and Find Full Text PDFBioact Mater
May 2025
Bioscience and Biomedical Engineering Thrust, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, 511400, China.
Tumor microenvironment governs various therapeutic tolerability of cancer such as ferroptosis and immunotherapy through rewiring tumor metabolic reprogramming like Warburg metabolism. Highly expressed carbonic anhydrases (CA) in tumor that maintaining the delicate metabolic homeostasis is thus the most potential target to be modulated to resolve the therapeutic tolerability. Hence, in this article, a self-healable and pH-responsive spermidine/ferrous ion hydrogel loaded with CA inhibitor (acetazolamide, ACZ) and glucose oxidase (ACZ/GOx@SPM-HA Gel) was fabricated through the Schiff-base reaction between spermidine-dextran and oxidized hyaluronic acid, along with ferrous coordination.
View Article and Find Full Text PDFHerein, a novel magnetic resorcinol-formaldehyde-supported isatin-Schiff-base/Fe complex (FeO@RF-ISB/Fe) is prepared and characterized and its catalytic performance is investigated in the synthesis of pyrano[2,3-]pyrimidines. The FeO@RF-ISB nanomaterial was prepared through the chemical immobilization of (3-aminopropyl)trimethoxysilane over the FeO@RF composite, followed by treatment with isatin. The FeO@RF-ISB was then reacted with FeCl·6HO to afford the FeO@RF-ISB/Fe nanocatalyst.
View Article and Find Full Text PDFChemistry
January 2025
Dalian University of Technology, No.2 Linggong Road, Ganjingzi District, Dalian, CHINA.
Dynamic control of DNA circuit functionality is essential for constructing chemical reaction networks (CRNs) that implement complex functions. The triplex has been utilized for dynamically regulating the diverse functionalities of DNA circuits due to its distinctive pH responsiveness. However, it is challenging for triplexes to independently regulate the functionality of DNA circuits, as various triplexes were often required for DNA circuits to function in complex environments, which adds complexity to the design and control of dynamic circuits.
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