Ni-catalyzed enantioconvergent deoxygenative reductive cross-coupling of unactivated alkyl alcohols and aryl bromides.

Transition metal-catalyzed enantioconvergent cross-coupling of an alkyl precursor presents a promising method for producing enantioenriched C(sp3) molecules. Because alkyl alcohol is a ubiquitous and abundant family of feedstock in nature, the direct reductive coupling of alkyl alcohol and aryl halide enables efficient access to valuable compounds. Although several strategies have been developed to overcome the high bond dissociation energy of the C - O bond, the asymmetric pattern remains unknown. In this report, we describe the realization of an enantioconvergent deoxygenative reductive cross-coupling of unactivated alkyl alcohol (ß-hydroxy ketone) and aryl bromide in the presence of an NHC activating agent. The approach can accommodate substituents of various sizes and functional groups, and its synthetic potency is demonstrated through a gram scale reaction and derivatizations into other compound families. Finally, we apply our convergent method to the efficient asymmetric synthesis of four ß-aryl ketones that are natural products or bioactive compounds.

Enantioselective Construction of Quaternary Stereocenters via Cooperative Photoredox/Fe/Chiral Primary Amine Triple Catalysis.

The catalytic and enantioselective construction of quaternary (all-carbon substituents) stereocenters poses a formidable challenge in organic synthesis due to the hindrance caused by steric factors. One conceptually viable and potentially versatile approach is the coupling of a C-C bond through an outer-sphere mechanism, accompanied by the realization of enantiocontrol through cooperative catalysis; however, examples of such processes are yet to be identified. Herein, we present such a method for creating different compounds with quaternary stereocenters by photoredox/Fe/chiral primary amine triple catalysis. This approach facilitates the connection of an unactivated alkyl source with a tertiary alkyl moiety, which is also rare. The scalable process exhibits mild conditions, does not necessitate the use of a base, and possesses a good functional-group tolerance. Preliminary investigations into the underlying mechanisms have provided valuable insights into the reaction pathway.

Hardware Trojan Attacks on the Reconfigurable Interconnections of Field-Programmable Gate Array-Based Convolutional Neural Network Accelerators and a Physically Unclonable Function-Based Countermeasure Detection Technique.

Convolutional neural networks (CNNs) have demonstrated significant superiority in modern artificial intelligence (AI) applications. To accelerate the inference process of CNNs, reconfigurable CNN accelerators that support diverse networks are widely employed for AI systems. Given the ubiquitous deployment of these AI systems, there is a growing concern regarding the security of CNN accelerators and the potential attacks they may face, including hardware Trojans. This paper proposes a hardware Trojan designed to attack a crucial component of FPGA-based CNN accelerators: the reconfigurable interconnection network. Specifically, the hardware Trojan alters the data paths during activation, resulting in incorrect connections in the arithmetic circuit and consequently causing erroneous convolutional computations. To address this issue, the paper introduces a novel detection technique based on physically unclonable functions (PUFs) to safeguard the reconfigurable interconnection network against hardware Trojan attacks. Experimental results demonstrate that by incorporating a mere 0.27% hardware overhead to the accelerator, the proposed hardware Trojan can degrade the inference accuracy of popular neural network architectures, including LeNet, AlexNet, and VGG, by a significant range of 8.93% to 86.20%. The implemented arbiter-PUF circuit on a Xilinx Zynq XC7Z100 platform successfully detects the presence and location of hardware Trojans in a reconfigurable interconnection network. This research highlights the vulnerability of reconfigurable CNN accelerators to hardware Trojan attacks and proposes a promising detection technique to mitigate potential security risks. The findings underscore the importance of addressing hardware security concerns in the design and deployment of AI systems utilizing FPGA-based CNN accelerators.

Positive Effects of Organic Amendments on Soil Microbes and Their Functionality in Agro-Ecosystems.

Soil microbial characteristics are considered to be an index for soil quality evaluation. It is generally believed that organic amendments replacing chemical fertilizers have positive effects on changing microbial activity and community structure. However, their effects on different agro-ecosystems on a global scale and their differences in different environmental conditions and experimental durations are unclear. This study performed a meta-analysis based on 94 studies with 204 observations to evaluate the overall effects and their differences in different experimental conditions and duration. The results indicated that compared to chemical fertilizer, organic amendments significantly increased total microbial biomass, bacterial biomass, fungal biomass, Gram-positive bacterial biomass and Gram-negative bacterial biomass, and had no effect on the ratio of fungi to bacteria and ratio of Gram-positive bacteria to Gram-negative bacteria. Meanwhile, land use type, mean annual precipitation and soil initial pH are essential factors affecting microbial activity response. Organic-amendment-induced shifts in microbial biomass can be predominantly explained by soil C and nutrient availability changes. Additionally, we observed positive relationships between microbial functionality and microbial biomass, suggesting that organic-amendment-induced changes in microbial activities improved soil microbial functionality.

Meta-Analysis of Organic Fertilization Effects on Soil Bacterial Diversity and Community Composition in Agroecosystems.

Application of organic fertilizers or their combination with chemical fertilizers is a feasible practice for improving soil fertility and reducing soil degradation in agroecosystems, and these regulations are mainly mediated though soil microbial communities. Despite bacteria ranking among the most abundant and diverse groups of soil microorganisms, the effects of long-term organic fertilization (OF) and chemical-organic fertilization (COF) on soil bacterial diversity and community composition remain unclear. In this study, we conducted a meta-analysis and demonstrated that OF had no significant effect on bacterial alpha diversity. Application of chemical fertilizer and crop residue significantly decreased bacterial Richness index. Both OF and COF significantly altered bacterial community structure, with these changes being predominately attributed to shifts in soil pH. For bacterial phyla, both OF and COF significantly increased the relative abundance of Proteobacteria and Bacteroidetes, suggesting that OF and COF may cause the enrichment of copiotrophic taxa. In addition, COF significantly increased the relative abundance of Gammaproteobacteria but decreased the relative abundance of Acidobacteria. Overall, our results suggest that organic and chemical-organic fertilization can effectively maintain bacterial diversity and enhance soil fertility in agroecosystems, and the alteration of soil bacterial community structure is closely intertwined with soil pH.

Influence of Core Type and Shell Thickness on Avian-Inspired Structural Colors Produced from Melanin Nanoparticle Assemblies.

Hollow melanosomes found in iridescent bird feathers, including violet-backed starlings and wild turkeys, enable the generation of diverse structural colors. It has been postulated that the high refractive index (RI) contrast between melanin (1.74) and air (1.0) results in brighter and more saturated colors. This has led to several studies that have synthesized hollow synthetic melanin nanoparticles and fabricated colloidal nanostructures to produce synthetic structural colors. However, these studies use hollow nanoparticles with thin shells (<20 nm), even though shell thicknesses as high as 100 nm have been observed in natural melanosomes. Here, we combine experimental and computational approaches to examine the influence of the varying polydopamine (PDA, synthetic melanin) shell thickness (0-100 nm) and core material on structural colors. Experimentally, a concomitant change in overall particle size and RI contrast makes it difficult to interpret the effect of a hollow or solid core on color. Thus, we utilize finite-difference time-domain (FDTD) simulations to uncover the effect of shell thickness and core on structural colors. Our FDTD results highlight that hollow particles with thin shells have substantially higher saturation than same-sized solid and core-shell particles. These results would benefit a wide range of applications including paints, coatings, and cosmetics.

Iron-Catalyzed Reductive Cross-Coupling of Alkyl Electrophiles with Olefins.

In terms of its abundance and its minimal toxicity, iron has advantages relative to other transition metals. Although alkyl-alkyl bond construction is central to organic synthesis, examples of iron-catalyzed alkyl-alkyl couplings of alkyl electrophiles are relatively sparse. Herein we report an iron catalyst that achieves cross-coupling reactions of alkyl electrophiles wherein olefins, in the presence of a hydrosilane, are used in place of alkylmetal reagents. Carbon-carbon bond formation proceeds at room temperature, and the method employs commercially available components (Fe(OAc)2 , Xantphos, and Mg(OEt)2 ); interestingly, this set of reagents can be applied directly to a distinct hydrofunctionalization of olefins, hydroboration. Mechanistic studies are consistent with the generation of an alkyl radical from the alkyl electrophile, as well as with reversibility for elementary steps that precede carbon-carbon bond formation (olefin binding to iron and ß-migratory insertion).

Evaluation of the freshness of rainbow trout (Oncorhynchus mykiss) fillets by the NIR, E-nose and SPME-GC-MS.

A comparison study on the freshness of rainbow trout (Oncorhynchus mykiss) fillets in the course of their sale was performed using near-infrared spectroscopy (NIRS), solid-phase microextraction combined with gas chromatography-mass spectrometry (SPME-GC-MS), and the electronic nose (E-nose) technique. Quantitative analysis of the volatile salt nitrogen (TVB-N) of rainbow trout fillets with different freshness using NIR combined with the partial least squares (PLS) method revealed that the predicted values of TVB-N of the samples were significantly correlated with the true values (P < 0.01). SPME-GC-MS combined with E-nose analysis demonstrated that there were significant differences in the volatile flavor components of rainbow trout fillets at different freshness, and E-nose combined with principal component analysis (PCA) and linear discriminant analysis (LDA) could achieve rapid and non-destructive freshness ranking of rainbow trout fillets based on volatile flavor characteristics. Consequently, the NIRS and E-nose non-destructive testing techniques are capable of acting as rapid screening tools for detecting the freshness of rainbow trout fillets during their sale.

Asymmetric Synthesis of Protected Unnatural α-Amino Acids via Enantioconvergent Nickel-Catalyzed Cross-Coupling.

Interest in unnatural α-amino acids has increased rapidly in recent years in areas ranging from protein design to medicinal chemistry to materials science. Consequently, the development of efficient, versatile, and straightforward methods for their enantioselective synthesis is an important objective in reaction development. In this report, we establish that a chiral catalyst based on nickel, an earth-abundant metal, can achieve the enantioconvergent coupling of readily available racemic alkyl electrophiles with a wide variety of alkylzinc reagents (1:1.1 ratio) to afford protected unnatural α-amino acids in good yield and ee. This cross-coupling, which proceeds under mild conditions and is tolerant of air, moisture, and a broad array of functional groups, complements earlier approaches to the catalytic asymmetric synthesis of this valuable family of molecules. We have applied our new method to the generation of several enantioenriched unnatural α-amino acids that have previously been shown to serve as useful intermediates in the synthesis of bioactive compounds.

The Asymmetric Synthesis of Amines via Nickel-Catalyzed Enantioconvergent Substitution Reactions.

Chiral dialkyl carbinamines are important in fields such as organic chemistry, pharmaceutical chemistry, and biochemistry, serving for example as bioactive molecules, chiral ligands, and chiral catalysts. Unfortunately, most catalytic asymmetric methods for synthesizing dialkyl carbinamines do not provide general access to amines wherein the two alkyl groups are of similar size (e.g., CH2R versus CH2R1). Herein, we report two mild methods for the catalytic enantioconvergent synthesis of protected dialkyl carbinamines, both of which use a chiral nickel catalyst to couple an alkylzinc reagent (1.1-1.2 equiv) with a racemic partner, specifically, an α-phthalimido alkyl chloride or an N-hydroxyphthalimide (NHP) ester of a protected α-amino acid. The methods are versatile, providing dialkyl carbinamine derivatives that bear an array of functional groups. For couplings of NHP esters, we further describe a one-pot variant wherein the NHP ester is generated in situ, allowing the generation of enantioenriched protected dialkyl carbinamines in one step from commercially available amino acid derivatives; we demonstrate the utility of this method by applying it to the efficient catalytic enantioselective synthesis of a range of interesting target molecules.

Quaternary stereocentres via catalytic enantioconvergent nucleophilic substitution reactions of tertiary alkyl halides.

The development of efficient methods, particularly catalytic and enantioselective processes, for the construction of all-carbon quaternary stereocentres is an important (and difficult) challenge in organic synthesis due to the occurrence of this motif in a range of bioactive molecules. One conceptually straightforward and potentially versatile approach is the catalytic enantioconvergent substitution reaction of a readily available racemic tertiary alkyl electrophile by an organometallic nucleophile; however, examples of such processes are rare. Here we demonstrate that a nickel-based chiral catalyst achieves enantioconvergent couplings of a variety of tertiary electrophiles (cyclic and acyclic α-halocarbonyl compounds) with alkenylmetal nucleophiles to form quaternary stereocentres with good yield and enantioselectivity under mild conditions in the presence of a range of functional groups. These couplings, which probably proceed via a radical pathway, provide access to an array of useful families of organic compounds, including intermediates in the total synthesis of two natural products, (-)-eburnamonine and madindoline A.

A novel electronic nose for the detection and classification of pesticide residue on apples.

Excessive pesticide residues are a serious problem faced by food regulatory authorities, suppliers, and consumers. To assist with this challenge, this work aimed to develop a method of detecting and classifying pesticide residue on fruit samples using an electronic nose, through the application of three different data-recognition algorithms. The apple samples carried various concentrations of two known pesticides, namely cypermethrin and chlorpyrifos. Data collection was performed using a PEN3 electronic nose equipped with 10 metal oxide semiconductor (MOS) sensors. In order to classify and analyze these pesticide residues on the apple samples, principal component analysis (PCA), linear discriminant analysis (LDA), and support vector machine (SVM) results were combined with sensor output responses to realize MOS sensor array data visualization. The results indicated that all three data-recognition algorithms accurately identified the pesticide residues in the apple samples, with the PCA algorithm exhibiting the best classification and discrimination ability. Consequently, this work has shown that the MOS electronic nose, in combination with data-recognition algorithms, can provide support for the rapid and non-destructive identification of pesticide residues in fruits and can provide an effective tool for the detection of pesticide residues in agricultural products.

Effects of supplemental nitrogen application on physiological characteristics, dry matter and nitrogen accumulation of winter rapeseed (Brassica napus L.) under waterlogging stress.

Waterlogging stress is a common limiting factor for winter rapeseed, which greatly affects the growth and potential production. The present study was conducted to investigate the effects of waterlogging with different durations (0day (D0), 6days (D6) and 9days (D9)) and supplemental nitrogen fertilization (N1, 0 kg ha-1; N2, 30 kg ha-1; N3, 60 kg ha-1 and N4, 90 kg ha-1) on the physiological characteristics, dry matter and nitrogen accumulation in winter rapeseed (Chuanyou36). The results showed that the supplementary application of nitrogen fertilizer could effectively improve the physiological indexes of winter rapeseed in both pot and field experiments. The supplemental nitrogen increased the chlorophyll content in leaves, enhanced the activities of SOD, CAT, and POD, and decreased the MDA content in leaves and roots of rapeseed. The chlorophyll contents, the antioxidant enzyme activity of leaves and roots significantly increased under D6N3 and D9N4 conditions in both (pot and field) experiments. However, MDA contents significantly decreased compared with waterlogging without nitrogen application. Moreover, the application of nitrogen fertilizer after waterlogging increased the accumulation of dry matter and nitrogen in rapeseed at different growth stages. Therefore, waterlogging stress significantly inhibited the growth and development of rapeseed, but the application of nitrogen fertilizer could effectively reduce the damage of waterlogging. The N-induced increase in waterlogging tolerance of rapeseed might be attributed to the strong antioxidant defense system, maintenance of photosynthetic pigments and the nutrient balance.

Convergent Catalytic Asymmetric Synthesis of Esters of Chiral Dialkyl Carbinols.

Because chiral dialkyl carbinols, as well as their derived esters, are significant as intermediates and end points in fields such as organic, pharmaceutical, and biological chemistry, the development of efficient approaches to their asymmetric synthesis is an important endeavor. In this report, we describe a method for the direct catalytic enantioselective synthesis of such esters, beginning with an alkyl halide (derived from an aldehyde and an acyl bromide), an olefin, and a hydrosilane, catalyzed by nickel, an earth-abundant metal. The method is versatile, tolerating substituents that vary in size and that bear a range of functional groups. We further describe a four-component variant of this process, wherein the alkyl halide is generated in situ, thus obviating the need to isolate either an alkyl electrophile or an alkylmetal, while still effecting an alkyl-alkyl coupling. Finally, we apply our convergent method to the efficient catalytic enantioselective synthesis of three esters that are bioactive themselves or that have been utilized in the synthesis of bioactive compounds.

Design of UAV Downwash Airflow Field Detection System Based on Strain Effect Principle.

Accurate measurement of the downwash flow field of plant protection unmanned aerial vehicles (UAVs) is essential for analyzing the spatial distribution of droplets. To realize on-line rapid detection of the downwash flow field of a multi-rotor UAV, a flexible polypropylene detection device based on the principle of full bridge strain effect was proposed. Its performance principle was based on the physical deformation caused by wind pressure. The Fluid Flow and Static Structural modules of ANSYS 16.0 finite element software were used to simulate one-way fluid-solid coupling interaction. The surface of the resistive strain gauge embedded in the flexible detecting structure responded well to wind speed variation, hence it was suitable for downwash airflow wind field detection. By solving the strain force on the surface of the flexible detection structure, the length and layout of the grating wire of the strain gauge on the surface of the flexible detection structure were optimized. Meanwhile at 4 m·s-1 wind speed, the output voltage at varied bridge flexible acquisition systems in the acquisition card was measured. Results indicated coefficient of variation of 3.67%, 1.63% and 1.5%, respectively, which proved the good data acquisition consistency of the system. Through calibration test, the regression equation for the relationship between output voltage and wind speed for three unique sensor signal measuring circuits was established. The determination coefficients R2 for single bridge, half bridge and full bridge circuits were 0.9885, 0.9866 and 0.9959, respectively. In conclusion, by applying the multi-rotor plant protection UAV test platform, the results indicated the maximum relative error of the wind speed at each sampling point of the system at 1.0 m altitude was below 5.61%. Simulated and measured value had an RMSE maximum error of 0.1246 m·s-1. Moreover, downwash airflow detection not only has high accuracy but also has high sensitivity. Thus, there is convenience and practicability in the plant protection offered by this approach. The rapid measurement of UAV wind field and the established two-dimensional wind field model can provide a basis for precise application of agricultural aviation.

Tandem Pd-Catalyzed Intermolecular Allylic Alkylation/Allylic Dearomatization Reaction of Benzoylmethyl pyridines, Pyrazines, and Quinolines.

An efficient synthesis of nitrogen-containing heterocycles via Pd-catalyzed tandem allylic alkylation and dearomatization reactions was reported. In this reaction design, heteroarenes such as pyridines, pyrazines, and quinolines serve as bis-nucleophiles by installing a benzoyl group at the C2 benzylic position. With but-2-ene-1,4-diyl dimethyl dicarbonate as the bis-electrophile, the tandem Pd-catalyzed intermolecular allylic alkylation/allylic dearomatization reaction of benzoylmethyl-substituted heteroarenes has been developed. 2,3-Dihydroindolizine, 6,7-dihydropyrrolo[1,2- a]pyrazine, and 1,2-dihydropyrrolo[1,2- a]quinolin derivatives were obtained in moderate to good yields.

Iridium-Catalyzed Intramolecular Asymmetric Allylic Dearomatization of Benzene Derivatives.

Guided by the mechanistic insights from computational studies, we have developed an Ir-catalyzed asymmetric intramolecular allylic dearomatization reaction of benzene derivatives. Under the optimized conditions consisting of a readily available Ir catalyst, a series of spiro[4.5]cyclohexadiene compounds were delivered in reasonable yields (up to 79 %) with good enantioselectivity (up to 99 % ee). The introduction of a malonate diester-type substituent serves as a key strategy to guide the nucleophilic reactivity of the benzene ring.

Efficient Synthesis of N-Alkylated 4-Pyridones by Copper-Catalyzed Intermolecular Asymmetric Propargylic Amination.

Copper-catalyzed intermolecular asymmetric propargylic amination with 4-hydroxypyridines has been realized for the first time. In the presence of Cu complex derived from Pybox ligand, the N-propargylated 4-pyridones were obtained under mild reaction conditions with up to 99 % yield and 95 % ee. The Pybox ligand bearing a 4-F-phenyl substituent plays a key role for the high enantioselectivity. The products can be easily transformed to the core structure of quinolizidine alkaloids.

Iridium-Catalyzed Intramolecular Asymmetric Allylic Alkylation of Hydroxyquinolines: Simultaneous Weakening of the Aromaticity of Two Consecutive Aromatic Rings.

Intramolecular asymmetric allylic alkylation reactions of 5- and 7-hydroxyquinoline derivatives were realized by a chiral Ir/NHC catalyst. A series of functionalized cyclic enones were afforded in excellent yields (up to 99%) and high enantioselectivity (up to 97% ee). Theoretical computations revealed that the aromaticity of the two consecutive rings of hydroxyquinoline substrates is significantly weakened. A highly efficient formal synthesis of (-)-gephyrotoxin was accomplished based on this method.

Iridium-Catalyzed Intramolecular Asymmetric Allylic Dearomatization Reaction of Benzoxazoles, Benzothiazoles, and Benzimidazoles.

An iridium-catalyzed intramolecular asymmetric allylic dearomatization reaction of benzoxazoles, benzothiazoles, and benzimidazoles was developed. The reaction was found to be compatible with a wide range of five-membered-ring electron-deficient heteroaromatic compounds and furnished the corresponding dearomatized heterocycles in high yield with excellent enantioselectivity.