Multifunctional integrated metamaterials for radar-infrared-visible compatible multispectral stealth.

Metamaterials offer exciting opportunities for developing multispectral stealth due to their unique electromagnetic properties. However, currently transparent radar-infrared-visible compatible stealth metamaterials typically involve complex hierarchical designs, leading to thickness and transparency limitations. Here, we propose an integrated metamaterial for multispectral stealth with high transparency. Our design features an ITO/dielectric/ITO sandwich structure, with the upper-layer ITO acting as a resonator for broadband microwave absorption while maintaining a high filling ratio to suppress infrared (IR) radiation. Experimental results demonstrate excellent performance, with over 90% microwave absorption in 8-18 GHz, an IR emissivity of approximately 0.36 in 3-14 µm, an average optical transmittance of 74.1% in 380-800 nm, and a thickness of only 2.4 mm. With its multispectral compatibility, the proposed metamaterial has potential applications in stealth and camouflage fields.

Multi-spectral compatible metasurface with low infrared emissivity, independent microwave complex-amplitude control, and high visible transparency.

With the rapid development of communication technology and detection technology, it is difficult for devices operating in a single spectrum to meet the application requirements of device integration and miniaturization, resulting in the exploration of multi-spectrum compatible devices. However, the functional design of different spectra is often contradictory and difficult to be compatible. In this work, a transparent slit circular metasurface with a high filling ratio is proposed to achieve the compatibility of microwave, infrared and visible light. In the microwave, based on the Pancharatnam-Berry phase theory, the continuous amplitude and binary phase can be customized only by rotating the slit angle to achieve an Airy beam function at 8-12 GHz. In the infrared, the mean infrared emissivity is reduced to 0.3 at 3-14 µm by maintaining high conductive filling ratio, and in visible light, based on the transparency of materials, the mean transmittance can achieve 50% at 400-800 nm. All the results can verify the multi-spectral compatibility performance, which can also verify the validity of our design method. Importantly, the multi-spectral compatible metasurface contributes an option for multifunctional integration, which can be further applied in communication, camouflage, and other fields.

Direct access to carbamates via acylation of arylamines with dialkyl azodicarboxylates under metal-free conditions.

A novel C-N coupling of various arylamines with dialkyl azodicarboxylates under metal-free conditions for the rapid assembly of carbamates has been achieved. This established protocol features mild reaction conditions, simple operation, broad substrate scope, moderate to excellent yields and good tolerance of functional groups. Moreover, the potential synthetic utility of products was exemplified by a series of intriguing chemical operations.

Recent Advances in the Synthesis of 3,n-Fused Tricyclic Indole Skeletons via Palladium-Catalyzed Domino Reactions.

3,n-fused (n = 4-7) tricyclic indoles are pervasive motifs, embedded in a variety of biologically active molecules and natural products. Thus, numerous catalytic methods have been developed for the synthesis of these skeletons over the past few decades. In particular, palladium-catalyzed transformations have received much attention in recent years. This review summarizes recent developments in the synthesis of these tricyclic indoles with palladium-catalyzed domino reactions and their applications in the total synthesis of representative natural products.

Transcriptomics for Drought Stress Mediated by Biological Processes in-relation to Key Regulated Pathways in Gossypium darwinii.

BACKGROUND: Wild cotton Gossypium darwinii, an allotetraploid harbours important traits useful for tolerating abiotic stress, i.e., drought, salt and good genetic stability, hence these characteristics can be transferred to cultivated cotton for genetic improvement. MATERIALS AND METHODS: In this study, we analyzed the RNA-seq transcriptomes from leaves of G. darwinii seedlings with and without drought stress. A total of 86.7 million valid reads with an average length of 95.79 bp were generated from the two samples and 58,960 transcripts with a length of more than 500 bp were assembled. We searched the known proteins on the strength of sequence similarity; these transcripts were annotated with COG, KEGG and GO functional categories. According to gene expression abundance RPKM value, we carried out RT-qPCR analysis to determine the expression pattern of the obtained transcription factors. RESULTS: A total of 58,960 genes was differentially expressed (DEG), with 32,693 and 25,919 genes found to be upregulated and downregulated, respectively. Through gene ontology and KEGG pathways, the upregulated genes were found to associate with all the GO terms, molecular functions (MF), biological process (BP) and cellular components (CC), which are highly linked to enhancing drought stress tolerance. CONCLUSION: The study provides an in-depth knowledge of regulation of pathways and genes involved in photosynthesis during drought stress in G. darwinii. These pathways and genes were found to be significantly downregulated and this information could be further utilized by cotton breeders in developing a more drought tolerant cotton germplasm.

Design, Catalyst-Free Synthesis of New Novel α-Trifluoromethylated Tertiary Alcohols Bearing Coumarins as Potential Antifungal Agents.

A new method for the synthesis of α-trifluoromethylated tertiary alcohols bearing coumarins is described. The reaction of 3-(trifluoroacetyl)coumarin and pyrrole provided the target compounds with high yields under catalyst-free, mild conditions. The crystal structure of compound 3fa was investigated by X-ray diffraction analysis. The biological activities, such as in vitro antifungal activity of the α-trifluoromethylated tertiary alcohols against Fusarium graminearum, Fusarium oxysporum, Fusarium moniliforme, Rhizoctonia solani Kuhn, and Phytophthora parasitica var nicotianae, were investigated. The bioassay results indicated that compounds 3ad, 3gd, and 3hd showed broad-spectrum antifungal activity in vitro. Compound 3cd exhibited excellent fungicidal activity against Rhizoctonia solani Kuhn, with an EC50 value of 10.9 µg/mL, which was comparable to that of commercial fungicidal triadimefon (EC50 = 6.1 µg/mL). Furthermore, molecular docking study suggested that 3cd had high binding affinities with 1W9U, like argifin.

Synthesis of Novel Indole Schiff Base Compounds and Their Antifungal Activities.

A series of novel indole Schiff base derivatives (2a-2t) containing a 1,3,4-thiadiazole scaffold modified with a thioether group were synthesized, and their structures were confirmed using FT-IR, 1H NMR, 13C NMR, and HR-MS. In addition, the antifungal activity of synthesized indole derivatives was investigated against Fusarium graminearum (F. graminearum), Fusarium oxysporum (F. oxysporum), Fusariummoniliforme (F.moniliforme), Curvularia lunata (C. lunata), and Phytophthora parasitica var. nicotiana (P. p. var. nicotianae) using the mycelium growth rate method. Among the synthesized indole derivatives, compound 2j showed the highest inhibition rates of 100%, 95.7%, 89%, and 76.5% at a concentration of 500 µg/mL against F. graminearum, F. oxysporum, F.moniliforme, and P. p. var. nicotianae, respectively. Similarly, compounds 2j and 2q exhibited higher inhibition rates of 81.9% and 83.7% at a concentration of 500 µg/mL against C. lunata. In addition, compound 2j has been recognized as a potential compound for further investigation in the field of fungicides.

Enzymatic Enantioselective anti-Markovnikov Hydration of Aryl Alkenes.

The addition of water to alkenes is an important method for the synthesis of alcohols, but the regioselectivity of acid-catalyzed hydration of terminal alkenes yields secondary alcohols according to Markovnikov's rule, making it difficult to obtain primary alcohols. Here we report a styrene monooxygenase that catalyzes the anti-Markovnikov hydration of the terminal aryl alkenes under anaerobic conditions. This hydration provides primary alcohols in good yields (up to 100 %), excellent anti-Markovnikov regioselectivity (>99 : 1), and good enantiomeric purity (60-83 % ee). Residues Asn46, Asp100, and Asn309 are essential for catalysis suggesting an acid-base mechanism with a carbanion-like intermediate that could account for the anti-Markovnikov regioselectivity. Our work reveals a new enzymatic tool with unusual regioselectivity based on the promiscuous catalytic activity of a monooxygenase.

Extraordinary p-d Hybridization Interaction in Heterostructural Pd-PdSe Nanosheets Boosts C-C Bond Cleavage of Ethylene Glycol Electrooxidation.

Advanced electrocatalysts for complete oxidation of ethylene glycol (EG) in direct EG fuel cells are strongly desired owing to the higher energy efficiency. Herein, Pd-PdSe heterostructural nanosheets (Pd-PdSe HNSs) have been successfully fabricated via a one-step approach. These Pd-PdSe HNSs feature unique electronic and geometrical structures, in which unconventional p-d hybridization interactions and tensile strain effect co-exist. Compared with commercial Pd/C and Pd NSs catalysts, Pd-PdSe HNSs display 5.5 (6.6) and 2.5 (2.6) fold enhancement of specific (mass) activity for the EG oxidation reaction (EGOR). Especially, the optimum C1 pathway selectivity of Pd-PdSe HNSs reaches 44.3 %, illustrating the superior C-C bond cleavage ability. Electrochemical in situ FTIR spectroscopy and theoretical calculations demonstrate that the extraordinary p-d hybridization interaction and tensile strain effect could effectively reduce the activation energy of C-C bond breaking and accelerate CO* oxidation, boosting the complete oxidation of EG and improving the catalytic performance.

Ultra-wideband flexible transparent metamaterial with wide-angle microwave absorption and low infrared emissivity.

Optically transparent metamaterials with the performance of infrared radar compatible stealth have been designed and manufactured on the basis of the continuous in-depth research on single-band stealth technology. In this paper, metamaterials are designed through theoretical calculations and modeling simulations. The designed structure can achieve higher than 90% broadband (8.7-32 GHz) absorption at wide-angle (45 degrees), emissivity of 0.3 in infrared atmospheric window, and optical transparency. In addition, the material can be bent, which greatly expands its application scenarios. The experimental results are consistent with the theoretical calculation and simulation results.

Compatible stealth design of infrared and radar based on plasmonic absorption structure.

In this paper, a metamaterial structure with radar and infrared (IR) compatible stealth characteristics is designed based on the principle of plasmonic absorbing structure (PAS). Due to the lack of reports on PAS-based IR radar compatible stealth, this article combines PAS and IR frequency selective surfaces to achieve the desired purpose. Through mathematical modeling and dispersion engineering of the unit cell proposed, a PAS with ultra-wideband wave absorption is realized. The low emissivity of the IR atmospheric window band is realized by means of the simulation and analysis of the IR frequency selective surface with different indium tin oxide (ITO) occupation ratios. The absorptivity of designed structure is higher than 90% from 4GHz to 28.6GHz, and the emissivity of the IR atmospheric window is only 0.3. The experience of the fabricated sample is consistent with the theoretical analysis and the simulation. Our method enriches the implementation strategies of radar-IR compatibility and has reference significance for multi-spectrum compatible stealth.

Genetic-algorithm-empowered metasurface design: simultaneous realization of high microwave frequency-selection and low infrared surface-emissivity.

With the improvement of equipment integration, it is difficult to meet the increasing functional requirements with the function of a single spectrum. In this work, a multispectral functional metasurface (MFM) is designed to achieve multispectral compatibility between microwave and infrared using multi-optimization. For microwaves, a frequency selective surface (FSS) is designed to achieve frequency selectivity. And for infrared, a twice genetic algorithm (GA) is employed to further increase the metallic filling ratio, thus reducing the infrared emissivity while maintaining the performance of microwave FSS. In order to verify our design and method, the MFM is fabricated and measured, and all the results are consistent with the theoretical design. The performance of FSS can achieve 3dB bandwidth in 7.2-11.2GHz with low insertion losses and stability, and meanwhile the mean infrared emissivity has been reduced to 0.24 in 3-14µm. In summary, the designed multispectral compatible metasurface has wide application value in radome. What's more, the multi-optimization method for designing the multispectral metasurface can also be extended to other fields.

Broadband surface wave coupler with low infrared emission and microwave reflection.

Metasurfaces possess excellent capabilities to flexibly manipulate electromagnetic waves in multiple frequency domains, which show great potential application in multispectral stealth. Herein, a broadband surface waves coupler based on the design of thin Pancharatnam-Berry (PB) phase gradient metasurfaces (PGMs) of thickness 0.12λ0 is proposed to reduce infrared emission and microwave reflection simultaneously. Low infrared emission results from the high filling ratio of the indium-tin-oxide (ITO) on the surface, and low microwave reflection results from the conversion from propagating waves to surface waves. Intriguingly, this design is also capable of acting as a simple circular polarized (CP) discriminator because orthogonal CP waves are coupled into surface waves propagating along opposite directions. A proof-of-concept prototype is simulated and measured to validate the effectiveness of our methodology. The results indicate that the broadband surface waves coupler shows low infrared emissivity less than 0.28 from 3 to 14 µm and has microwave reflection reduction larger than 10 dB in 7.3-9.5 GHz. The exceptional performances of the proposed broadband surface waves coupler make us believe that our design offers an alternative strategy for multispectral stealth and multifunctional application.

Simultaneous reduction of microwave reflection and infrared emission enabled by a phase gradient metasurface.

Metasurfaces have shown promising applications in radar-infrared compatible stealth because of its superior electromagnetic wave control capabilities, but, to date, the majority of designs still suffer from the defects of large thickness, limited working bandwidth, relatively high infrared emissivity and so on. Here, an exotic phase gradient metasurface (PGM) is proposed to achieve low microwave reflection and low infrared emission concurrently, which has a small thickness of about 0.10λ0. The microwave reflection reduction larger than 10 dB in 14-20 GHz is attributed to the anomalous reflection for arbitrary LP incident waves, and the infrared emissivity less than 0.28 from 3 to 14 µm is due to the indium-tin-oxide (ITO) with low infrared emissivity and high filling ratio. Also, the designed PGM can also realize beam deflection for orthogonal CP waves because of the meta-atoms' isotropic characteristics. Our methodology is fully verified by numerous simulations and experiments and may open a new avenue for radar-infrared compatible stealth research.

Optically transparent coding metasurface with simultaneously low infrared emissivity and microwave scattering reduction.

In this paper, an optically transparent coding metasurface structure based on indium tin oxide (ITO) thin films with simultaneously low infrared (IR) emissivity and microwave scattering reduction is proposed. To this end, two ITO coding elements which can reflect 0° and 180° phase responses are firstly designed. Based on these two elements, four coding sequences with different scattering patterns are designed. Three of them can realize anomalous reflections and the fourth can realize random diffusion of normal incident electromagnetic (EM) waves. A prototype of the random diffusion coding metasurface was fabricated and measured. The experimental results show that for normal incident EM waves, at least 10dB backward scattering reduction from 3.8GHz to 6.8GHz can be achieved, and the structure is polarization insensitive. The averaged transmittance of visible light through the coding metasurface reaches up to 72.2%. In addition, due to the high occupation ratio of ITO on the outside of the coding metasurface, a low IR emissivity of about 0.275 is obtained. Good consistency between the experiment and simulation results convincingly verifies the coding metasurface. Due to its multispectral compatibility, the proposed coding metasurface may find potential applications in multi-spectral stealth, camouflage, etc.

Novel 6a,12b-Dihydro-6H,7H-chromeno[3,4-c] chromen-6-ones: Synthesis, Structure and Antifungal Activity.

A new series of coumarin derivatives, 7-hydroxy-7-(trifluoromethyl)-6a,12b-dihydro-6H,7H-chromeno[3,4-c]chromen-6-ones 3a-p, were synthesized via Michael addition, transesterification and nucleophilic addition from the reaction of 3-trifluoroacetyl coumarins and phenols in the presence of an organic base. The products were characterized by infrared spectroscopy (IR), hydrogen nuclear magnetic resonance spectroscopy (1H-NMR), carbon nuclear magnetic resonance spectroscopy (13C-NMR) and high-resolution mass spectrometer (HRMS). Single crystal X-ray analysis of compounds 3a and 3n clearly confirmed their assigned chemical structures and their twisted conformations. Compound 3a crystallized in the orthorhombic system, Pbca, in which a = 8.6244(2) Å, b = 17.4245(4) Å, c = 22.5188(6) Å, α = 90°, ß = 90°, γ = 90°, v = 3384.02(14) Å3, and z = 8. In addition, the mycelial growth rate method was used to examine the in vitro antifungal activities of the title compounds 3a-p against Fusarium graminearum and Fusarium monitiforme at 500 µg/mL. The results showed that compound 3l exhibited significant anti-Fusarium monitiforme activity with inhibitory index of 84.6%.

An efficient solvent-free synthesis of 2-hydroxy-2-(trifluoromethyl)-2H-chromenes using silica-immobilized L-proline.

An efficient synthesis of 2-hydroxy-2-(trifluoromethyl)-2H-chromene-3-carboxylates was carried out under solvent-free conditions in an oven or microwave oven via the Knoevenagel condensation of salicylaldehydes with ethyl trifluoroacetoacetate followed by intramolecular cyclization in the presence of silica-immobilized L-proline. The structures of the title compounds were characterized by IR, ¹H-NMR, ¹³C-NMR, HRMS and X-ray single crystal diffraction. The improved method described herein is economical, easily-operated and environmentally friendly. Furthermore, the catalyst can be recovered conveniently and reused without obvious loss of activity.

Highly Chemoselective Synthesis of Azaarene-Equipped CF3-Tertiary Alcohols under Metal-Free Conditions and Their Fungicidal Activities.

A highly chemoselective reaction between α,ß-unsaturated trifluoromethyl ketones with azaarenes under metal-free conditions was carried out, affording a range of valuable azaarene-equipped CF3-tertiary alcohols in moderate to excellent yields (up to 95% yield) with good tolerance of functional groups, and their structures were confirmed by NMR, HRMS, and X-ray diffraction for validation. This method features simple reaction conditions (only solvent), high atom- and step-economy, and broad substrate scope. Moreover, most of the target products exhibited promising fungicidal activities, and compound 3al exhibited 91.65% fungicidal activity against R. solani, with an EC50 value of 0.18 mg/mL.

Synthesis of 1-(ß-coumarinyl)-1-(ß-indolyl)trifluoroethanols through regioselective Friedel-Crafts alkylation of indoles with ß-(trifluoroacetyl)coumarins catalyzed by Sc(OTf)3.

A highly efficient Friedel-Crafts alkylation of indole derivatives with ß-(trifluoroacetyl)coumarins using Sc(OTf)3 as a catalyst has been developed, which gives regioselective 1,2-adducts to afford 1-(ß-coumarinyl)-1-(ß-indolyl)trifluoroethanols. A series of tertiary trifluoroethanols containing different indole and coumarin groups were synthesized in moderate to excellent yields (up to 95%) in the presence of 5 mol% catalyst in a short time (only 2 minutes at least). A mechanism of the reaction, in which the trace amount of water plays the role of proton transfer in catalyzing circulation was proposed and confirmed.

Menthyl 2-oxo-2H-chromene-3-carboxyl-ate.

The title compound, C(20)H(24)O(4), was synthesized from the reaction of 2-oxo-2H-chromene-3-acyl chloride and menthol. The mean plane of the ester group and that of the four essentially planar (maximum deviation 0.0112 Å) C atoms of the chair-form cyclo-hexyl ring form dihedral angles of 43.8 (3) ° and 81.8 (1)°, respectively, with the mean plane of the coumarin ring system. In the crystal structure, weak inter-molecular C-H⋯O hydrogen bonds connect the mol-ecules into a two-dimensional network.