Metal-Free Phosphination and Continued Functionalization of Pyridine: A Theoretical Study.

This study investigates the mechanism of metal-free pyridine phosphination with P(OEt)3, PPh3, and PAr2CF3 using density functional theory calculations. The results show that the reaction mechanism and rate-determining step vary depending on the phosphine and additive used. For example, phosphination of pyridine with P(OEt)3 occurs in five stages, and ethyl abstraction is the rate-determining step. Meanwhile, 2-Ph-pyridine phosphination with PPh3 is a four-step reaction with proton abstraction as the rate-limiting step. Energy decomposition analysis of the transition states reveals that steric hindrance in the phosphine molecule plays a key role in the site-selective formation of the phosphonium salt. The mechanism of 2-Ph-pyridine phosphination with PAr2CF3 is similar to that with PPh3, and analyses of the effects of substituents show that electron-withdrawing groups decreased the nucleophilicity of the phosphine, whereas aryl electron-donating groups increased it. Finally, TfO- plays an important role in the C-H fluoroalkylation of pyridine, as it brings weak interactions.

Forging the Tetracyclic Core Framework of Rhodomolleins XIV and XLII: A Ring-Distortion Approach.

A ring distortion approach for the synthesis of an advanced intermediate en route to rhodomolleins XIV and XLII was described, which led to successful construction of the 5/8/5/5 tetracyclic core framework of the kalmane diterpenoids. Key steps of the strategy include an oxidative dearomatization-induced (ODI)-Diels-Alder cycloaddition, a Dowd-Beckwith rearrangement, and a bioinspired Wagner-Meerwein rearrangement.

High-Quality Single Crystalline Sc0.37Al0.63N Thin Films Enabled by Precise Tuning of III/N Atomic Flux Ratio during Molecular Beam Epitaxy.

We attained wurtzite ScxAl1-xN (0.16 ≤ x ≤ 0.37) thin films by varying the Sc and Al fluxes at a fixed active nitrogen flux during plasma-assisted molecular beam epitaxy. Atomic fluxes of Sc and Al sources via measured Sc percentage in as-grown ScxAl1-xN thin films were derived as the feedback for precise determination of the ScxAl1-xN growth diagram. We identified an optimal III/N atomic flux ratio of 0.78 for smooth Sc0.18Al0.82N thin films. Further increasing the III/N ratio led to phase separation under N-rich conditions, validated by the observation of high-Sc-content hillocks with energy-dispersive X-ray spectroscopy mapping. At the fixed III/N ratio of 0.78, we found that phase separation with high-Al-content hillocks occurs for x > 0.37, which is substantially lower than the thermodynamically dictated threshold Sc content of ~0.55 in wurtzite ScxAl1-xN. We postulate that these wurtzite-phase purity degradation scenarios are correlated with adatom diffusion and the competitive incorporation process of Sc and Al. Therefore, the ScxAl1-xN growth window is severely restricted by the adatom kinetics. We obtained single crystalline Sc0.37Al0.63N thin films with X-ray diffraction (002)/(102) ω rocking curve full-width at half-maximums of 2156 arcsec and 209 arcsec and surface roughness of 1.70 nm. Piezoelectric force microscopy probing of the Sc0.37Al0.63N epilayer validates unambiguous polarization flipping by 180°.

Lamellar Ti3C2 MXene composite decorated with platinum-doped MoS2 nanosheets as electrochemical sensing functional platform for highly sensitive analysis of organophosphorus pesticides.

Precisely detecting organophosphorus pesticides (OPs) is paramount in upholding human safety and environmental preservation, especially in food safety. Herein, an electrochemical acetylcholinesterase (AChE) sensing platform entrapped in chitosan (Chit) on the glassy carbon electrodes (GCEs) decorated with Pt/MoS2/Ti3C2 MXene (Pt/MoS2/TM) was constructed for the detection of chlorpyrifos. It is worth noting that Pt/MoS2/TM possesses good biocompatibility, remarkable electrical conductivity, environmental stability and large specific surface area. Besides, the heterostructure formed by the composite of TM and MoS2 improves the conductivity and maintains the original structure, which is conducive to improving the electrochemical property. The coordination effect between the individual components enables the even distribution of functional components and enhances the electrochemical performance of the biosensor (AChE-Chit/Pt/MoS2/TM). Under optimal efficiency and sensitivity, the AChE-Chit/Pt/MoS2/TM/GCE sensing platform exerts comparable analytical performance and a wide concentration range of chlorpyrifos from 10-12 to 10-6 M as well as a low limit of detection (4.71 × 10-13 M). Furthermore, the biosensor is utilized to detect OPs concerning three kinds of fruits and vegetables with good feasibility and recoveries (94.81% to 104.0%). This work would provide a new scheme to develop high-sensitivity sensors based on the two-dimensional nanosheet/laminar hybrid structure for practical applications in environmental monitoring and agricultural product detection.

Integrated doped-Ru electrocatalyst with excellent H adsorption-desorption and active site on hollow tubular structures for boosting efficient hydrogen evolution.

Electrochemical water splitting for hydrogen production is an ideal process for clean energy production. However, highly active and low-cost electrocatalysts are essential and challenging. In this work, a multi-component Cu-based catalyst (Ru-M-C-Cu), synergized with ruthenium (Ru) heteroatom doping, was synthesized via a facile immersion-calcination-immersion method. Based on the cotton biomass substrate, a hollow tubular structure was obtained. By virtue of its distinctive structure and high carbon content, cotton biomass assumed a dual role as a sacrificial template and a reducing agent in the eco-friendly synthesis of electrocatalysts, which was instrumental in the creation of a multi-component system augmented by heteroatom doping. The multi-component system was constructed by in-situ transformation and redox reaction during calcination in an oxygen-free environment. The Ru-M-C-Cu catalyst exhibited a competitive overpotential of 108 mV at a current density of 10 mA cm-2 for alkaline hydrogen evolution reaction (HER). The satisfactory catalytic performance of Ru-M-C-Cu can be attributed to the fact that the Ru-O-Cu catalytic centers enhanced the adsorption and desorption abilities of the Cu-O active sites toward hydrogen. Furthermore, the hollow tubular structure allowed the electrolyte to make full contact with the active sites of the Ru-M-C-Cu catalyst, thus accelerated the HER kinetics. The catalyst showed structural and chemical stability after a 12-hour successive test. Besides, the production cost of Ru-M-C-Cu was significantly reduced by 99.1 % than that of commercial 20 % Pt/C, showing the potential as an alternative catalyst by offering a more accessible and sustainable source. This work provides a new design of sustainable low-budget electrocatalysts with the proposed strategies expected for producing clean and renewable hydrogen energy.

A novel neutral xylanase with high SDS resistance from Volvariella volvacea: characterization and its synergistic hydrolysis of wheat bran with acetyl xylan esterase.

A neutral xylanase (XynII) from Volvariella volvacea was identified and characterized. Unlike other modular xylanases, it consists of only a single GH10 catalytic domain with a unique C-terminal sequence (W-R-W-F) and a phenylalanine and proline-rich motif (T-P-F-P-P-F) at N-terminus, indicating that it is a novel GH10 xylanase. XynII exhibited optimal activity at pH 7 and 60 °C and stability over a broad range of pH 4.0-10.0. XynII displayed extreme highly SDS resistance retaining 101.98, 92.99, and 69.84 % activity at the presence of 300 mM SDS on birchwood, soluble oat spelt, and beechwood xylan, respectively. It remained largely intact after 24 h of incubation with proteinase K at a protease to protein ratio of 1:50 at 37 °C. The kinetic constants K(m) value towards beechwood xylan was 0.548 mg ml⁻¹, and the k(cat)/K(m) ratio, reflecting the catalytic efficiency of the enzyme, was 126.42 ml mg⁻¹ s⁻¹ at 60 °C. XynII was a true endo-acting xylanase lacking cellulase activity. It has weak activity towards xylotriose but efficiently hydrolyzed xylans and xylooligosaccharides larger than xylotriose mainly to xylobiose. Synergistic action with acetyl xylan esterase (AXEI) from V. volvacea was observed for de-starched wheat bran. The highest degree of synergy (DS 1.42) was obtained in sequential reactions with AXEI digestion preceding XynII. The high SDS resistance and intrinsic stability suggested XynII may have potential applications in various industrial processes especially for the detergent and textile industries and animal feed industries.

Determination of active vitamin B12 (cobalamin) in dietary supplements and ingredients by reversed-phase liquid chromatography: Single-laboratory validation.

Vitamin B12 dietary supplement can be critical to the alleviation strategies against micronutrient malnutrition and food insecurity. An HPLC-DAD method has been developed and validated, per AOAC SMPR 2016.017 (Standard Method Performance Requirements), for the quantitation of four bioactive forms of vitamin B12 (adenosylcobalamin, cyanocobalamin, hydroxocobalamin, methylcobalamin) from dietary ingredients and supplements. The method achieves chromatographic baseline resolution of vitamin B12 forms on a modern column platform without the expensive requirement of an ultra-high pressure liquid chromatography and/or mass spectrometry. The method has a wide analytical range (0.0005%w/w-85%w/w), high precision (reproducibility relative standard deviations ranged from 1.43% to 4.67%), and high accuracy (>96% spike recovery rate for 11 out of 12 accuracy testing data points). The method detection and quantification limits are less than 0.16 and 0.52 µg/mL, respectively. To our best knowledge, it is simpler, less time-consuming, and more economical than other published methods for its intended uses.