Insight into the bimetallic structure sensibility of catalytic nitrate reduction over Pd-Cu nanocrystals.

Catalytic reduction of nitrate over bimetallic catalysts has emerged as a technology for sustainable treatment of nitrate-containing groundwater. However, the structure of bimetallic has been much less investigated for catalyst optimization. Herein, two main types of Pd-Cu bimetallic nanocrystal structures, heterostructure and intermetallic, were prepared and characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that two individual Pd and Cu nanocrystals with a mixed interface exist in the heterostructure nanocrystals, while Pd and Cu atoms are uniformly distributed across the intermetallic Pd-Cu nanocrystals. The catalytic nitrate reduction experiments were carried out in a semibatch reactor under constant hydrogen flow. The nitrate conversion rate of the heterostructure Pd-Cu nanocrystals supported on α-Al2O3, γ-Al2O3, SBA-15, and XC-72R exhibited 3.82-, 6.76-, 4.28-, 2.44-fold enhancements relative to the intermetallic nanocrystals, and the nitrogen and nitrite were the main products for the heterostructure and intermetallic Pd-Cu nanocrystals, respectively. This indicates that the catalytic nitrate reduction over Pd-Cu catalyst is sensitive to the bimetallic structures of the catalysts, and heterostructure bimetallic nanocrystals exhibit better catalytic performances on both the activity and selectivity, which may provide new insights into the design and optimization of catalysts to improve catalytic activity and selectivity for nitrate reduction in water.

Absorption mechanism of SO3 on various alkaline absorbents in the presence of SO2.

Sulfur trioxide (SO3) as a condensable particle matter has a significant influence on atmospheric visibility, which easily arouses formation of haze. It is imperative to control the SO3 emission from the industrial flue gas. Three commonly used basic absorbents, including Ca(OH)2, MgO and NaHCO3 were selected to explore the effects of temperature, SO2 concentration on the SO3 absorption, and the reaction mechanism of SO3 absorption was further illustrated. The suitable reaction temperature for various absorbents were proposed, Ca(OH)2 at the high temperatures above 500°C, MgO at the low temperatures below 320°C, and NaHCO3 at the temperature range of 320-500°C. The competitive absorption between SO2 and SO3 was found that the addition of SO2 reduced the SO3 absorption on Ca(OH)2 and NaHCO3, while had no effect on MgO. The order of the absorption selectivity of SO3 follows MgO, NaHCO3 and Ca(OH)2 under the given conditions in this work. The absorption process of SO3 on NaHCO3 follows the shrinking core model, thus the absorption reaction continues until NaHCO3 was exhausted with the utilization rate of nearly 100%. The absorption process of SO3 on Ca(OH)2 and MgO follows the grain model, and the dense product layer hinders the further absorption reaction, resulting in low utilization of about 50% for Ca(OH)2 and MgO. The research provides a favorable support for the selection of alkaline absorbent for SO3 removal in application.

2D copper-iron bimetallic metal-organic frameworks for reduction of nitrate with boosted efficiency and ammonia selectivity.

Electrocatalytic reduction of nitrate to ammonia has been considered a promising and sustainable pathway for pollutant treatment and ammonia has significant potential as a clean energy. Therefore, the method has received much attention. In this work, Cu/Fe 2D bimetallic metal-organic frameworks were synthesized by a facile method applied as cathode materials without high-temperature carbonization. Bimetallic centers (Cu, Fe) with enhanced intrinsic activity demonstrated higher removal efficiency. Meanwhile, the 2D nanosheet reduced the mass transfer barrier between the catalyst and nitrate and increased the reaction kinetics. Therefore, the catalysts with a 2D structure showed much better removal efficiency than other structures (3D MOFs and Bulk MOFs). Under optimal conditions, Cu/Fe-2D MOF exhibited high nitrate removal efficiency (87.8%) and ammonium selectivity (89.3%) simultaneously. The ammonium yielded up to significantly 907.2 µg/(hr·mgcat) (7793.8 µg/(hr·mgmetal)) with Faradaic efficiency of 62.8% at an initial 100 mg N/L. The catalyst was proved to have good stability and was recycled 15 times with excellent effect. DFT simulations confirm the reduced Gibbs free energy of Cu/Fe-2D MOF. This study demonstrates the promising application of Cu/Fe-2D MOF in nitrate reduction to ammonia and provides new insights for the design of efficient electrode materials.

Do selectivity filter carbonyls in K+ channels flip away from the pore? Two-dimensional infrared spectroscopy study.

Molecular dynamics simulations revealed that the carbonyls of the Val residue in the conserved selectivity filter sequence TVGTG of potassium ion channels can flip away from the pore to form hydrogen bonds with the network of water molecules residing behind the selectivity filter. Such a configuration has been proposed to be relevant for C-type inactivation. Experimentally, X-ray crystallography of the KcsA channel admits the possibility that the Val carbonyls can flip, but it cannot decisively confirm the existence of such a configuration. In this study, we combined molecular dynamics simulations and line shape theory to design two-dimensional infrared spectroscopy experiments that can corroborate the existence of the selectivity filter configuration with flipped Val carbonyls. This ability to distinguish between flipped and unflipped carbonyls is based on the varying strength of the electric field inside and outside the pore, which is directly linked to carbonyl stretching frequencies that can be resolved using infrared spectroscopy.

Synthesis of Aryl Naphthoquinones and Maleimides via Pd(II)-Catalyzed Template-Assisted m-C(sp2)-H Functionalization Reaction.

An efficient approach for the synthesis of substituted aryl naphthoquinones via a Pd(II)-catalyzed template-assisted m-C(sp2)-H bond functionalization reaction of arylmethane sulfonates have been demonstrated. The method involves usage of less expensive and abundant pharmacologically important scaffold naphthoquinone. A wide range of arylmethane sulfonates were examined and found to be compatible with the protocol. The protocol has also been further extended to the synthesis of various substituted aryl maleimide scaffolds. A plausible reaction mechanism has also been proposed to account for the selective distal m-C(sp2)-H bond functionalization reaction.

REACTION KINETICS OF THE BENZYLATION OF ADENINE IN DMSO: REGIO-SELECTIVITY GUIDED BY ENTROPY.

The factors governing the regio-selectivity of the alkylation of adenine have been of interest for many years due to the biological importance of adenine derivatives, however, no reaction kinetic studies have been conducted. Herein, we report the rate constants and activation parameters of the benzylation of adenine under basic conditions in DMSO in the absence and presence of 15-crown-5 ether using real-time 1H NMR spectroscopy. The reaction is second-order for the formation of the N9- and N3-benzyladenine products, with a regio-selectivity factor 2.3 in favour of the N9-adduct. The Gibbs free energy of activation amounts to 87±2 kJ mol-1 for both reactions. The formation of the N9-adduct is more activated by 7 kJ mol-1, but its effect is offset by a less negative activation entropy, demonstrating that the long-contested reason for the regioselectivity in the benzylation of adenine is dominated by compensation of entropy and enthalpy in the transition state. The kinetic parameters obtained in the presence of the 15-crown-5 ether indicate that the crown ether forms a complex with an adenine-sodium ion-pair, increasing the activation barrier. However, the Gibbs free energy in the absence and presence of the crown ether remains constant.

A linearized modeling framework for the frequency selectivity in neurons postsynaptic to vibration receptors.

Vibration is an indispensable part of the tactile perception, which is encoded to oscillatory synaptic currents by receptors and transferred to neurons in the brain. The A2 and B1 neurons in the drosophila brain postsynaptic to the vibration receptors exhibit selective preferences for oscillatory synaptic currents with different frequencies, which is caused by the specific voltage-gated Na+ and K+ currents that both oppose the variations in membrane potential. To understand the peculiar role of the Na+ and K+ currents in shaping the filtering property of A2 and B1 neurons, we develop a linearized modeling framework that allows to systematically change the activation properties of these ionic channels. A data-driven conductance-based biophysical model is used to reproduce the frequency filtering of oscillatory synaptic inputs. Then, this data-driven model is linearized at the resting potential and its frequency response is calculated based on the transfer function, which is described by the magnitude-frequency curve. When we regulate the activation properties of the Na+ and K+ channels by changing the biophysical parameters, the dominant pole of the transfer function is found to be highly correlated with the fluctuation of the active current, which represents the strength of suppression of slow voltage variation. Meanwhile, the dominant pole also shapes the magnitude-frequency curve and further qualitatively determines the filtering property of the model. The transfer function provides a parsimonious description of how the biophysical parameters in Na+ and K+ channels change the inhibition of slow variations in membrane potential by Na+ and K+ currents, and further illustrates the relationship between the filtering properties and the activation properties of Na+ and K+ channels. This computational framework with the data-driven conductance-based biophysical model and its linearized model contributes to understanding the transmission and filtering of vibration stimulus in the tactile system.

Conserved gatekeeper methionine regulates the binding and access of kinase inhibitors to ATP sites of MAP2K1, 4, and 7: Clues for developing selective inhibitors.

Mitogen-activated protein kinase kinases (MAP2Ks) 1, 4, and 7 are potential targets for treating various diseases. Here, we solved the crystal structures of MAP2K1 and MAP2K4 complexed with covalent inhibitor 5Z-7-oxozeaenol (5Z7O). The elucidated structures showed that 5Z7O was non-covalently bound to the ATP binding site of MAP2K4, while it covalently attached to cysteine at the DFG-1 position of the deep ATP site of MAP2K1. In contrast, we previously showed that 5Z7O covalently binds to MAP2K7 via another cysteine on the solvent-accessible edge of the ATP site. Structural analyses and molecular dynamics calculations indicated that the configuration and mobility of conserved gatekeeper methionine located at the central ATP site regulated the binding and access of 5Z7O to the ATP site of MAP2Ks. These structural features provide clues for developing highly potent and selective inhibitors against MAP2Ks. Abbreviations: ATP, adenosine triphosphate; FDA, Food and Drug Administration; MAP2Ks, mitogen-activated protein kinase kinases; MD, molecular dynamics; NSCLC, non-small cell lung cancer; 5Z7O, 5Z-7-oxozeaenol; PDB, protein data bank; RMSD, root-mean-square deviation.

Photothermal Synergistic Effect Induces Bimetallic Cooperation to Modulate Product Selectivity of CO2 Reduction on Different CeO2 Crystal Facets.

Product selectivity of solar-driven CO2 reduction and H2O oxidation reactions has been successfully controlled by tuning the spatial distance between Pt/Au bimetallic active sites on different crystal facets of CeO2 catalysts. The replacement depth of Ce atoms by monatomic Pt determines the distance between bimetallic sites, while Au clusters are deposited on the surface. This space configuration creates a favourable microenvironment for the migration of active hydrogen species (*H). The *H is generated via the activation of H2O on monatomic Pt sites and migrate towards Au clusters with a strong capacity for CO2 adsorption. Under concentrated solar irradiation, selectivity of the (100) facet towards CO is 100%, and the selectivity of the (110) and (111) facets towards CH4 is 33.5% and 97.6%, respectively. Notably, the CH4 yield on the (111) facet is as high as 369.4 µmol/g/h, and the solar-to-chemical energy efficiency of 0.23% is 33.8 times higher than that under non-concentrated solar irradiation. The impacts of high-density flux photon and thermal effects on carriers and *H migration at the microscale are comprehensively discussed. This study provides a new avenue for tuning the spatial distance between active sites to achieve optimal product selectivity.

Cobalt-Catalyzed Intramolecular Markovnikov Hydrocarbonylation of Unactivated Alkenes via Hydrogen Atom Transfer.

A cobalt-catalyzed intramolecular Markovnikov hydroalkoxycarbonylation and hydroaminocarbonylation of unactivated alkenes has been developed, enabling highly chemo- and regioselective synthesis of α-alkylated γ-lactones and α-alkylated γ-lactams in good yields. The mild reaction conditions allow use of mono-, di- and trisubstituted alkenes bearing a variety of functional groups. Preliminary mechanistic studies suggest the reaction proceeds through a CO-mediated hydrogen atom transfer (HAT) and radical-polar crossover (RPC) process, in which a cationic acylcobalt(IV) complex is proposed as the key intermediate.

Kinetic and in silico structural characterization of norbelladine O-methyltransferase of Amaryllidaceae alkaloids biosynthesis.

Amaryllidaceae alkaloids (AAs) are a diverse group of alkaloids exclusively reported from the Amaryllidaceae plant family. In planta, their biosynthesis is still not fully characterized, however, a labeling study established 4'-O-methylnorbelladine as the key intermediate compound of the pathway. Previous reports have characterized O-methyltransferases from several Amaryllidaceae species. Nevertheless, the formation of the different O-methylnorbelladine derivatives (3'-O-methylnorbelladine, 4'-O-methylnorbelladine, and 3'4'-O-dimethylnorbelladine), the role, and the preferred substrates of O-methyltransferases are not clearly understood. In this study, we performed the biochemical characterization of an O-methyltransferase candidate from Narcissus papyraceus (NpOMT) in vitro and in vivo, following biotransformation of norbelladine in Nicotiana benthamiana having transient expression of NpOMT. Docking analysis was further used to investigate substrate preferences, as well as key interacting residues of NpOMT. Our study shows that NpOMT methylates norbelladine preferentially at the 4'-OH position in vitro and in planta. Interestingly, NpOMT also catalyzed the synthesis of 3',4'-O-dimethylnorbelladine from norbelladine and 4'-O-methylnorbelladine during in vitro enzymatic assay. Furthermore, we show that NpOMT methylates 3,4-dihydroxybenzylaldehyde and caffeic acid in a non-regiospecific manner to produce meta/para monomethylated products. This study reveals a novel catalytic potential of an Amaryllidaceae O-methyltransferase and its ability to regioselectively methylate norbelladine in the heterologous host Nicotiana benthamiana.

A preliminary study of the temperature-responsive selective extraction performance of hydrogel derived from sulfobetaine methacrylate.

BACKGROUND: The limited extraction selectivity caused by the single extraction selection mechanism of solid phase extraction (SPE) technology is one of the bottlenecks restricting its development. The development of environmentally sensitive materials provides a new opportunity to solve this problem. Based on this, we developed the sulfobetaine methacrylate hydrogel with abundant pore structure, a large number of adsorption sites and especially temperature responsiveness, and used as adsorbent for the extraction of pesticide residues in lychees. RESULTS: The new hydrogel adsorbent was prepared by free radical copolymerization with sulfobetaine methacrylate as monomer, and used for the extraction of benzoylurea insecticides from lychees. Interestingly, the hydrogel showed an almost opposite temperature-selective extraction trend for different benzoylurea insecticides with similar structure and polarity, and opposite hydrophilicity, which may be caused by the temperature-sensitive and the special action site of the hydrogel, and the change of the diffusion of aqueous solution. In addition, the analysis method of three hydrophilic benzoylurea insecticides by sulfobetaine methacrylate hydrogel-SPE-HPLC was established. Under optimal conditions, the low limits of detection (0.030 µg L-1) and quantification (0.10 µg L-1), and the wide linear ranges (0.10-50.0 µg L-1) were achieved. Its application in lychee samples were also tested, and the satisfactory results were obtained, with the spiked recoveries from 80.79 % to 108.31 %. SIGNIFICANCE: This was a great breakthrough in the selective extraction of similar targets. These properties, combined with low-cost, biodegradable raw materials and convenient, green synthesis method make the sulfobetaine methacrylate hydrogel a very promising solid phase adsorbent. Temperature-responsive selective mode can greatly enrich the selective extraction mechanism and promote its development and application in complex actual samples.

Secosteroid diacylhydrazines as novel effective agents against hormone-dependent breast cancer cells.

This research aimed to develop novel selective secosteroids that are highly active against hormone-dependent breast cancer. A simple and convenient approach to N'-acylated 13,17-secoestra-1,3,5(10)-trien-17-oic acid hydrazides was disclosed and these novel types of secosteroids were screened for cytotoxicity against the hormone-dependent human breast cancer cell line MCF7. Most secosteroid N'-benzoyl hydrazides have demonstrated high cytotoxicity against MCF7 cells with IC50 values below 5µM, which are superior to that of the reference drug cisplatin. Hit compounds 2c, 2e and 2i were characterized by high cytotoxicity (IC50 = 1.6-1.9µM) and very good selectivity towards MCF7 breast cancer cells. The lead secosteroids 2c, 2e and 2i also exhibit antiestrogenic effects and alter the expression of cell cycle regulating proteins. The effect of selected compounds on PARP (poly(ADP-ribose) polymerase) and Bcl-2 (B-cell CLL/lymphoma 2) indicates their proapoptotic potential. The synthesized secosteroids may be considered as new promising anti-breast cancer agents targeting ERα and apoptosis pathways.

Highly Selective Production of C2+ Oxygenates from CO2 in Strongly Acidic Condition by Rough Ag-Cu Electrocatalyst.

The acidic electrocatalytic conversion of CO2 to multi-carbon (C2+) oxygenates is of great importance in view of enhancing carbon utilization efficiency and generating products with high energy densities, but suffering from low selectivity and activity. Herein, we synthesized Ag-Cu alloy catalyst with highly rough surface, by which the selectivity to C2+ oxygenates can be greatly improved. In a strongly acidic condition (pH=0.75), the maximum C2+ products Faradaic efficiency (FE) and C2+ oxygenates FE reach 80.4% and 56.5% at -1.9 V versus reversible hydrogen electrode, respectively, with a ratio of FEC2+ oxygenates to FEethylene up to 2.36. At this condition, the C2+ oxygenates partial current density is as high as 480 mA cm-2. The in situ Raman measurements and control experiments indicate that the high generation of C2+ oxygenates over the catalyst originates from its large surface roughness and Ag alloying.

Determination of hATG8 Binding Selectivity of AIM (Autophagy-Interacting Motif) Peptides Using Native Electrospray Ionization Mass Spectrometry.

Establishing the hATG8 binding selectivity of AIM (autophagy-interacting motif) sequences found within autophagy system proteins provides insights into their biological roles, and in the case of disease-associated AIM mutations, potential pathophysiological mechanisms. Given the sometimes small differences in affinity for an individual AIM amongst the six hATG8 proteins, establishing AIM preferences can be experimentally challenging. We describe a native mass spectrometry method that is suitable for detecting such differences, using synthetic AIM peptides and recombinant hATG8 proteins, to probe hATG8-AIM interactions in the gas phase. Binding preferences of a single AIM peptide against multiple hATG8s, or two AIM peptides against a single hATG8 (e.g., wild-type versus mutant AIM), may be determined.

Enhancement of ammonia synthesis via electrocatalytic reduction of low-concentration nitrate using co-doped MIL-101(Fe) nanostructured catalysts.

In the domain of electrocatalytic NO3- reduction (NO3-RR) for the treatment of low-concentration nitrate-containing domestic or industrial wastewater, the conversion of NO3- into NH4+ holds significant promise for resource recovery. Nevertheless, the central challenge in this field revolves around the development of catalysts exhibiting both high catalytic activity and selectivity. To tackle this challenge, we design a two-step hydrothermal combine with carbonization process to fabricate a cobalt-doped Fe-based MOF (MIL-101) catalyst at 800 °C temperatures. The aim was to fully leverage cobalt's demonstrated high selectivity in NO3- electroreduction and enhance activity by promoting electron transfer through the d-band of Fe. The results indicate that the synthesized catalyst inherits multiple active sites from its precursor, with the co-doping process optimized through the topological properties of the MOF. Elemental analysis and oxidation state testing were employed to scrutinize the fundamental characteristics of this catalyst type and comprehend how these features may influence its efficiency. Electrochemical analysis revealed that, even under conditions of low NO3- concentration, the Cox@MIL-Fe catalyst achieved an impressive nitrate conversion rate of 98 % at -0.9 V vs. RHE. NH4+ selectivity was notably high at 87 %, and the by-product NO2- levels remained at a minimal threshold. The Faradaic efficiency for NH4+ reached 74 %, with ammonia yield approaching 0.08 mmol h-1 cm-2. This study furnishes indispensable research data for the design of Fe-based electrocatalysts for nitrate reduction, offering profound insights into the modulation of catalysts to play a pivotal role in the electroreduction of nitrate ions.

Symbiotic Algae of Acoel Species in the Seto Inland Sea and Symbiont Selectivity in the Hosts.

Praesagittifera naikaiensis is an acoel flatworm that inhabits the sandy beaches in the intertidal zone of the Seto Inland Sea. This species carries Tetraselmis sp., a green unicellular chlorophyte, as a symbiont in its body, and depends on algal photosynthetic products to survive. However, the eggs of P. naikaiensis contain no symbiotic algae, and juvenile P. naikaiensis acquire symbionts from the surrounding environment through horizontal transfer after hatching, thereby establishing new symbiotic relationships in each generation. Other acoel species, Symsagittifera spp., also inhabit the Seto Inland Sea shores and acquire symbiotic green algae via horizontal transfers. To characterize their symbionts, these acoels were collected from a wide area of the Seto Inland Sea and partial nucleotide sequences of the chloroplast ribulose diphosphate carboxylase large subunit (rbcL) of the symbiotic algae were determined and used for molecular phylogenetic analysis. Symbionts of both P. naikaiensis and Symsagittifera spp. belonged to the genus Tetraselmis but were phylogenetically distant, and both species established symbiotic relationships with different symbionts even when they were sympatric. To test whether each species selects specific algae in the environment for symbiosis, we established algal strains from P. naikaiensis and Symsagittifera sp. symbionts and conducted uptake experiments on aposymbiotic juveniles of P. naikaiensis. The results suggest that symbiotic algae from Symsagittifera could be taken up by P. naikaiensis juveniles, but were unable to establish a normal symbiotic relationship with the juveniles.

Bis(phosphinophenyl)amido-Ligated Binuclear Rare-Earth Metal Complexes for Highly cis-1,4-Selective Polymerization of 1,3-Conjugated Dienes.

A series of binuclear rare-earth metal complexes based on the ligands containing bis(phosphinophenyl)amido-PNP unit are successfully synthesized. All the ligands and the corresponding binuclear complexes are fully characterized by NMR spectra (1H, 13C, and 31P). In conjunction with [Ph3C][B(C6F5)4], all the binuclear complexes exhibited high catalytic activity and high cis-1,4-selectivity (>99%) toward the polymerization of 1,3-conjugated dienes (isoprene, ß-myrcene and ß-farnesene) with excellent livingness at room temperature or even 80 °C.

Investigating the quality of extraction and quantification of bioactive compounds in berries through liquid chromatography and multivariate curve resolution.

Berries are a rich source of natural antioxidant compounds, which are essential to profile, as they add to their nutritional value. However, the complexity of the matrix and the structural diversity of these compounds pose challenges in extraction and chromatographic separation. By relying on multivariate curve resolution alternating least squares (MCR-ALS) ability to extract components from complex spectral mixtures, our study evaluates the contributions of various extraction techniques to interference, extractability, and quantifying different groups of overlapping compounds using liquid chromatography diode array detection (LC-DAD) data. Additionally, the combination of these methods extends its applicability to evaluate polyphenol degradation in stored berry smoothies, where evolving factor analysis (EFA) is also used to elucidate degradation products. Results indicate that among the extraction techniques, ultrasonication-assisted extraction employing 1% formic acid in methanol demonstrated superior extractability and selectivity for the different phenolic compound groups, compared with both pressurized liquid extraction and centrifugation of the fresh berry smoothie. Employing MCR-ALS on the LC-DAD data enabled reliable estimation of total amounts of compound classes with high spectral overlaps. Degradation studies revealed significant temperature-dependent effects on anthocyanins, with at least 50% degradation after 7 months of storage at room temperature, while refrigeration and freezing maintained fair stability for at least 12 months. The EFA model estimated phenolic derivatives as the main possible degradation products. These findings enhance the reliability of quantifying polyphenolic compounds and understanding their stability during the storage of berry products.

Unraveling C-Selective Ring-Opening of Phosphiranes with Carboxylic Acids and Other Nucleophiles: A Mechanistically-Driven Approach.

Phosphiranes are weak Lewis bases reacting with only a limited number of electrophiles to produce the corresponding phosphiranium ions. These salts are recognized for their propensity to undergo reactions with oxygen pronucleophiles at the phosphorus site, leading to the formation of phosphine oxide adducts. Building on a thorough mechanistic understanding, we have developed an unprecedented approach that enables the selective reaction of carboxylic acids, and other nucleophiles, at the carbon site of phosphiranes. This method involves the photochemical generation of highly reactive carbenes, which react with 1-mesitylphosphirane to yield ylides. The latter undergoes a stepwise reaction with carboxylic acids, resulting in the production of the desired phosphines. In addition to DFT calculations, we have successfully isolated and fully characterized the key intermediates involved in the reaction.