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Monthly Archives: September 2023
Recent Advances in Aptasensors for Rapid Pesticide Residues Detection
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Facile and Cost‐effective Synthesis of CoP@N‐doped Carbon with High Catalytic Performance for Electrochemical Hydrogen Evolution Reaction
This work proposes a new facile, cost-effective, and safe preparation method for CoP loaded on N-doped carbon using inexpensive starting materials. The optimized ratio in the starting materials allowed CoP loaded on N-doped carbon to show high hydrogen evolution activity with 202 mV of overpotential at 10 mA/cm2 and stability.
Abstract
The manufacture of efficient and low-cost hydrogen evolution reaction (HER) catalysts is regarded as a critical solution to achieve carbon neutrality. Herein, we developed an economical method to synthesize a CoP-anchored N-doped carbon catalyst via one-step pyrolysis using inexpensive starting materials (cobalt ion salt, phytic acid, and glycine). The size of the CoP nanoparticles was controlled by adjusting the Co/P ratio of the catalysts. Nanoscale CoP particles with adequate exposure to active sites were uniformly anchored on the surface of the conductive nitrogen-doped carbon substrate, ensuring the rapid transfer of electrons and species. When Co/P=0.89, the as-made catalyst exhibited outstanding HER activity, with an extraordinarily low overpotential of 202 mV at 10 mA cm−2 and long-term stability.
Dichlorocarbene: From Jack Hine to Robert Moss
A select history of dichlorocarbene chemistry between 1950 and 2010 will be presented. This is not a comprehensive review; rather, it is a personal perspective on the contributions of two respected colleagues. Jack Hine discovered a new mechanism—alpha elimination—to form carbenes. Moss (and his preceptor Closs) discovered the concept of carbenoids. Dichlorocarbene is the reactive intermediate that spanned the research efforts of Hine and Moss and stimulated their important contributions to organic synthesis and mechanistic thinking.
Abstract
A select history of dichlorocarbene chemistry between 1950 and 2010 will be presented. This is not a comprehensive review; rather, it is a personal perspective on the contributions of two respected colleagues, the reactive intermediate that spanned their research efforts, and their important contributions to organic synthesis and mechanistic thinking.
Design and Simulation of a Low‐Temperature Thermal Desalination System
A low-temperature thermal desalination system based on the spray-assisted vacuum flash operation was designed with the passive heating of saline water and effective condensation of water vapor. The flash drum was designed effectively by simulation of the droplet dynamics. A corrugated plate heat exchanger and a thermosyphon solar water heater were designed to optimize the system.
Abstract
The prototype of a low-temperature thermal desalination system treating 2500 L day−1 of saline water was designed thermally and geometrically, to be integrated with a vacuum spray flash drum and spray nozzles, a plate heat exchanger-type condenser, and a thermosyphon solar water heater to produce potable water for a small community. The design bases were the feed flow rate, the feed temperature from 45 to 65 °C, the salinity of 0.035 kg kg−1, and the vacuum drum pressure from 2 to 6 kPa absolute. The estimated yield of potable water based on the simulated droplet dynamics was in the range of 68.91–75.80 %. The plate heat exchanger and the thermosyphon solar water heater were designed for effective condensation and passive heating, respectively.
Efficient contact between H2O and N‐coordinate Ru nanoparticles in three‐dimensionally ordered macro/mesoporous carbon boosting alkaline HER
Comprehensive Summary
In this study, a novel approach is proposed to achieve the uniformly dispersed Ru nanoparticles with N coordination loaded on three-dimensionally ordered macro/mesoporous carbon (3DOMMC) through simultaneous pyrolysis of Ru3+ and cyanamide on 3DOMMC.In an alkaline medium, the synthesized catalysts exhibit exceptional hydrogen evolution reaction (HER) performance. Specifically, Ru-N/3DOMMC demonstrates a significantly low overpotential of 13.8 mV to achieve a current density of 10 mA cm-2, and it exhibits a mass activity 17.5 times higher than that of commercial Pt/C. The outstanding performance could be attributed to the ultrahigh Ru dispersion and more efficient contact between active sites and reactant, which derived from the large specific surface area and inter-connective three-dimensionally macro/mesoporous of 3DOMMC.
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Extending the π‐System in MnI Diimine Tricarbonyl Complexes: Impacts on Photochemistry, Electrochemistry, and CO2 Catalytic Reduction Activity
The π-system in a series of three fac-[Mn(α-diimine)(CO)3Br] complexes is extended from 2,2′-bipyridine (bpy) to 2-(2-pyridyl)quinoline (pq) to 2,2′-biquinoline (bqn). The effects on photochemical mechanism, electrochemistry, and electroreduction of CO2 is observed via cyclic voltammetry, bulk electrolysis, and UV-vis and IR spectroscopies.
Abstract
The complex [Mn(bpy)(CO)3Br], has been previously studied as both an electrocatalyst and a photocatalyst, in conjugation with a photosensitizer, for CO2 reduction to CO. This study considers the relationship between this catalytic activity and the steric and electronic nature of the aromatic diimine ligand. To this end, the π-system in the bidentate ligand is increased step-wise from 2,2′-bipyridine (bpy) to 2-(2-pyridyl)quinoline (pq) to 2,2′-biquinoline (bqn) in a series of three fac-[Mn(α-diimine)(CO)3Br] complexes. It is found that the propensity of these complexes to photochemically dimerize trends with the energy of the α-diimine π* energy. Electrochemically, it is observed that the second reduction event in these systems becomes increasingly thermodynamically favorable and approaches the potential of the first reduction event as the π-system expands. In fac-[Mn(bqn)(CO)3Br], the second reduction is more favorable than the first reduction, precluding the formation of a dimer intermediate; even though, chemical reduction of fac-[Mn(bqn)(CO)3Br] confirms that the dimer, [Mn(bqn)(CO)3Br]2 is able to form and not prevented by steric considerations. Though the second reduction potential is more positive for bqn and pq than for bpy, the CO2 reduction mechanism changes such that the overpotential for carbon dioxide reduction occurs at more negative potentials, leading to a decrease in overall catalytic activity.
Diverse Coordination Geometries Derived from Trisaminocyclohexane Ligands with Appended Outer‐Sphere Hydrogen Bond Donors
Ligands derived from cis,cis-1,3,5-triaminocyclohexane (TACH) have been prepared with pendant heterocycles that serve as outer-sphere H-bond donors. Upon coordination to Cu(I), the facially coordinating N 3 ligands create a hydrogen-bonding cavity that stabilizes (pseudo)halide anions. Reaction of the TACH-based ligands with divalent cations revealed a range of protonation states, coordination geometries, and H-bonding interactions.
Abstract
With the aim of constructing hydrogen-bonding networks in synthetic complexes, two new ligands derived from cis,cis-1,3,5-triaminocyclohexane (TACH) have been prepared that feature pendant pyrrole or indole rings as outer-sphere H-bond donors. The TACH framework offers a facial arrangement of three N-donors, thereby mimicking common coordination motifs in the active sites of nonheme Fe and Cu enzymes. X-ray structural characterization of a series of CuI-X complexes (X=F, Cl, Br, NCS) revealed that these neutral ligands (H3LR, R=pyrrole or indole) coordinate in the intended facial N 3 manner, yielding four-coordinate complexes with idealized C 3 symmetry. The N−H units of the outer-sphere heterocycles form a hydrogen-bonding cavity around the axial (pseudo)halide ligand, as verified by crystallographic, spectroscopic, and computational analyses. Treatment of H3Lpyrrole and H3Lindole with divalent transition metal chlorides (MIICl2, M=Fe, Cu, Zn) causes one heterocycle to deprotonate and coordinate to the M(II) center, giving rise to tetradentate ligands with two remaining outer-sphere H-bond donors. Further ligand deprotonation is observed upon reaction with Ni(II) and Cu(II) salts with weakly coordinating counteranions. The reported complexes highlight the versatility of TACH-based ligands with pendant H-bond donors, as the resulting scaffolds can support multiple protonation states, coordination geometries, and H-bonding interactions.
Synthesis of Aryl‐Manganese(III) Fluoride Complexes via α‐Fluorine Elimination from CF3 and Difluorocarbene Generation
Pyridinophane aryl manganese(III) fluoro complexes were synthesized via transmetalation from Zn-CF3 reagent and alpha-fluoride elimination to generate MnIII fluoride and difluorocarbene. Carbene formation was confirmed by trapping by alkenes to give difluoropropanation product.
Abstract
We report the synthesis of cyclometalated monoaryl MnIII fluoro complexes using bis(trifluoromethyl)zinc reagent, Zn(CF3)2(DMPU)2, under mild conditions via a reaction pathway that involves initial transmetalation followed by α-fluorine elimination. The formation of difluorocarbene in these reactions was detected by trapping experiments. Such facile difluorocarbene generation from MnIII results in moderate enhancement of difluoropropanation and difluoropropenation of alkenes and alkynes using Zn(CF3)2(DMPU)2 at lower temperature (20–60 °C) and short reaction time, suggesting potential application of manganese(III) perfluoroalkyl complexes as reactive species for carbene transfer reactivity.
Antifungal Properties of Essential Oils Derived from the Genus Cymbopogon: A Systematic Review
Abstract
Essential oils (EOs) are products of secondary metabolism with recognized organoleptic characteristics and biological properties. Recently, there has been a growing demand for EOs in the national and international market, mainly due to the recognition of their use as complementary medicine practices, and the increased use in the industries of pharmaceutics, cosmetics, well-being, veterinary and agroecology, boosting the productive sector. In this context, EOs from grasses of the Cymbopogon (Poaceae) are promising sources of bioactive compounds, due to their recognized biological properties, such as anti-inflammatory, antibacterial, antifungal, antidiabetic, repellent, and larvicide. Thus, the present study aims to carry out a review of the scientific literature of the main works related to the evaluation of the antifungal action of essential oils extracted from plants of the Cymbopogon genus, compiling the species that showed the best results and relating them to their main chemical constituents. This review covers the following species: C. citratus, C. flexuosus, C. winterianus, C. martinii, C. nardus, C. giganteus, C. schoenanthus, C. khasans, and C. proximus. Among them, C. citratus was the most assessed, being associated with the vast majority of studies (61.9 %), and it was also the species that showed the best results in terms of MIC.