Interfacial Polarization Locked Flexible ß-Phase Glycine/Nb2CTx Piezoelectric Nanofibers.

Biomolecular piezoelectric materials show great potential in the field of wearable and implantable biomedical devices. Here, a self-assemble approach is developed to fabricating flexible ß-glycine piezoelectric nanofibers with interfacial polarization locked aligned crystal domains induced by Nb2CTx nanosheets. Acted as an effective nucleating agent, Nb2CTx nanosheets can induce glycine to crystallize from edges toward flat surfaces on its 2D crystal plane and form a distinctive eutectic structure within the nanoconfined space. The interfacial polarization locking formed between O atom on glycine and Nb atom on Nb2CTx is essential to align the ß-glycine crystal domains with (001) crystal plane intensity extremely improved. This ß-phase glycine/Nb2CTx nanofibers (Gly-Nb2C-NFs) exhibit fabulous mechanical flexibility with Young's modulus of 10 MPa, and an enhanced piezoelectric coefficient of 5.0 pC N-1 or piezoelectric voltage coefficient of 129 × 10-3Vm N-1. The interface polarization locking greatly improves the thermostability of ß-glycine before melting (≈210°C). A piezoelectric sensor based on this Gly-Nb2C-NFs is used for micro-vibration sensing in vivo in mice and exhibits excellent sensing ability. This strategy provides an effective approach for the regular crystallization modulation for glycine crystals, opening a new avenue toward the design of piezoelectric biomolecular materials induced by 2D materials.

Forming All-Carbon Quaternary Centers by Geminal Difunctionalization of Diazo Compounds with N,N-Disubstituted Anilines and Allylic Carbonates.

A novel three-component reaction of N,N-disubstituted anilines, diazo compounds, and allylic carbonates has been developed by using a rhodium-palladium dual catalysis, providing an effective protocol for the construction of tetrasubstituted esters bearing an all-carbon quaternary center as well as an allylic moiety in one pot.

Copper-catalyzed reaction of benzoxazinanones with sulfilimines: access to 2-ethynyl-benzoimidazoles via an abnormal skeletal rearrangement.

A copper-catalyzed reaction of benzoxazinanones with N-aryl sulfilimines has been developed, providing 2-ethynyl-benzoimidazoles in good to excellent yields (up to 98%) under mild reaction conditions. Importantly, the reaction proceeds via an abnormal skeletal rearrangement and annulation process, rather than an expected (4 + 1) annulation.

Catalytic aminomethylative etherification of N-allenamides with N,O-acetals enabled by Lewis/Brønsted acid catalysis.

A novel copper-catalyzed aminomethylative etherification of N-allenamides/alkoxyallenes with N,O-acetals has been realized under mild reaction conditions, in which every single atom of N,O-acetals is incorporated into the newly formed molecules. Furthermore, in the presence of a chiral phosphoric acid, the asymmetric aminomethylative etherification of N-allenamides has been accomplished using N,O-acetals as bifunctionalization reagents.

Gold-catalyzed tandem reaction of o-alkynylphenols with diazo compounds: access to 2,3-disubstituted benzofurans.

A gold-catalyzed tandem reaction of o-alkynylphenols with diazo compounds has been developed, providing the 2,3-disubstituted benzofurans in moderate to good yields under mild reaction conditions. In this protocol, the vinyl gold and gold carbene species might form during the reaction process. Control experiments have been performed to understand the reaction mechanism.

Asymmetric N-Alkylation of 1H-Indoles via Carbene Insertion Reaction.

An intermolecular enantioselective N-alkylation reaction of 1H-indoles has been developed by cooperative rhodium and chiral phosphoric acid catalyzed N-H bond insertion reaction. N-Alkyl indoles with newly formed stereocenter adjacent to the indole nitrogen atom are produced in good yields (up to 95 %) with excellent enantioselectivities (up to >99 % ee). Importantly, both α-aryl and α-alkyl diazoacetates are tolerated, which is extremely rare in asymmetric X-H (X=N, O, S et al.) and C-H insertion reactions. With this method, only 0.1 mol % of rhodium catalyst and 2.5 mol % of chiral phosphoric acid are required to complete the conversion as well as achieve the high enantioselectivity. Computational studies reveal the cooperative relay of rhodium and chiral phosphoric acid, and the origin of the chemo and stereoselectivity.

Rhodium-Catalyzed Formal C═O Bond Insertion and Sequential Acyl 1,4-N-to-O Migratory Rearrangement.

We present here a rhodium-catalyzed reaction between N-acyl pyridazinones and diazoacetates, leading to pyridazine derivatives in good yield under mild reaction conditions. This whole sequence probably proceeds through a carbene insertion into a C═O bond and an unprecedented 1,4-N-to-O acyl rearrangement reaction.

Tumor suppressive role of miR-33a-5p in pancreatic ductal adenocarcinoma cells by directly targeting RAP2A.

BACKGROUND: The suppressive effects of miR-33a-5p have been reported in colorectal cancer and lung cancer. However, the functional role of miR-33a-5p in pancreatic ductal adenocarcinoma (PDAC) has not yet been elucidated. METHODS: The expression of miR-33a-5p was determined using reverse-transcription quantitative PCR (RT-qPCR) in PDAC tissues and cell lines. The association between miR-33a-5p expression and clinical categorical parameters was analyzed by the chi-square test. Cell proliferation was analyzing by Cell Counting Kit -8 (CCK-8) assay. Transwell assay was utilized to assess cell migration and invasion. The interactions between miR-33a-5p and RAP2A were verified by luciferase reporter assay, RT-qPCR, western blot analysis and RNA immunoprecipitation (RIP) assay. RESULTS: Here, we observed for the first time that miR-33a-5p expression level was significantly decreased in PDAC tissues and cell lines. There was a significant association between decreased miR-33a-5p expression and TNM stage or lymph node metastasis. Overexpression of miR-33a-5p significantly inhibited SW1990 and PANC-1 cell proliferation, migration and invasion. Knockdown of miR-33a-5p remarkedly promoted cell proliferation, migration and invasion in BxPC-3 and ASPC-1. Mechanistically, RAP2A was confirmed as the target of miR-33a-5p in PDAC cells. Moreover, RAP2A overexpression abolished miR-33a-5p-mediated suppressive effects on SW1990 and PANC-1 cells. CONCLUSIONS: Taken together, these results suggest that miR-33a-5p exerted tumor suppressive effects on PDAC cells by targeting RAP2A, which might provide a new theoretical basis for the clinical treatment of PDAC.

Construction of C-C Axial Chirality via Asymmetric Carbene Insertion into Arene C-H Bonds.

By using diazonaphthoquinones and anilines as key reagents and through a point-to-axis chiral transfer strategy, the atroposelective synthesis via asymmetric C(sp2 )-H bond insertion reaction of arenes has been realized under rhodium catalysis, providing the resulting biaryl atropisomers in moderate to excellent yields with good enantiomeric ratios (up to 99:1). Further elaboration indicates this type of axially biaryl scaffold may have promising potentials in developing novel chiral ligands.

Chemo- and Enantioselective Insertion of Furyl Carbene into the N-H Bond of 2-Pyridones.

Asymmetric carbene insertion reactions represent one of the most important protocols to construct carbon-heteroatom bonds. The use of donor-acceptor diazo compounds bearing an ester group is however a prerequisite for achieving high enantioselectivity. Herein, we report a chemo- and enantioselective formal N-H insertion of 2-pyridones that has been accomplished for the first time with enynones as the donor-donor carbene precursors. DFT calculations indicate an unprecedented enantioselective 1,4-proton transfer from O to C. The rhodium catalyst provides a chiral pocket in which the steric repulsion and the π-π interaction of the propeller ligand play a critical role in determining the selectivities.

Forming All-Carbon Quaternary Stereocenters by Organocatalytic Aminomethylation: Concise Access to ß2,2 -Amino Acids.

The asymmetric synthesis of ß2,2 -amino acids remains a formidable challenge in organic synthesis. Here a novel organocatalytic enantioselective aminomethylation of ketenes with stable and readily available N,O-acetals is reported, providing ß2,2 -amino esters bearing an all-carbon quaternary stereogenic center in high enantiomeric ratios with a catalytic amount of chiral phosphoric acid. Typically, this transformation probably proceeds through an asymmetric counter-anion-directed catalysis. As a result, a concise, practical, and atom-economic protocol toward rapidly access to ß2,2 -amino acids has been developed.

Adaptive Selection of Truncation Radius in Calderon's Method for Direct Image Reconstruction in Electrical Capacitance Tomography.

Calderon's method has been successfully used for the direct image reconstruction in electrical capacitance tomography. In the method, the truncation radius adopted in numerical integral greatly influences the reconstruction results. In the past, the truncation radius is selected as a constant empirically according to the permittivity distribution pattern and noise level. In this paper, the influence of the truncation radius in Calderon's method on the reconstruction results was first analyzed by numerical simulation. Then, a strategy for adaptive selection of the truncation radius was proposed. The amplitude information of the elements in the scattering transform matrix computed from the Dirichlet-to-Neumann (DN) map was used to determine the range for the truncation radius selection, and the phase information was further used to select a proper truncation radius value within this selection range. Finally, experiments were carried out to verify the strategy. Experimental results showed that small relative image error and good visual effect could be obtained by using the truncation radius selected by the proposed strategy.

Investigation of Multi-Plane Scheme for Compensation of Fringe Effect of Electrical Resistance Tomography Sensor.

Conventional electrical resistance tomography (ERT) sensors suffer from the fringe effect, i.e., severe distortion of the electric field on both ends of the measurement electrodes, leading to a 3D sensing region for a 2D sensor. As a result, the objects outside an ERT sensor plane affect the sensing and hence image, i.e., deteriorating the image quality. To address this issue, a multiple-plane ERT sensor scheme is proposed in this paper. With this scheme, auxiliary sensor planes are used to provide references for the fringe effect of the measurement plane, for compensation by subtracting the weighed influence of the fringe effect. Simulation results show that the proposed scheme, either three-plane or two-plane sensor, can compensate for the fringe effect induced by objects outside the measurement plane with a variety of axial object distributions, i.e., several non-conductive bars or conductive bars placed at different cross-sectional and axial positions inside the sensor. Experiments were carried out. Images obtained with single-plane and multiple-plane ERT sensors are compared, and the proposed compensation scheme has been hence verified.

Access to N-Substituted 2-Pyridones by Catalytic Intermolecular Dearomatization and 1,4-Acyl Transfer.

A novel rhodium-catalyzed dearomatization of O-substituted pyridines to access N-substituted 2-pyridones has been developed. A computational study suggests a mechanism involving the formation of a pyridinium ylide followed by an unprecedented 1,4-acyl migratory rearrangement from O to C. Furthermore, the chiral dirhodium complexes serve as the catalyst for the asymmetric transformation with excellent enantioselective control. DFT calculations indicate the chirality is transferred from axial chirality to the central stereogenic centre. The stronger π-π interaction and CH-π interaction account for the high enantioselectivity.

Lewis Acid-Mediated Room-Temperature Cascade Reaction of 3-Hydroxyisoindolin-1-one with Alkynes.

An efficient and mild synthesis of a variety of 3-(2-oxopropyl)-isoindolinone derivatives via a BF3·Et2O catalyzed cascade reaction among 3-hydroxyisoindolin-1-one and phenylacetylene was achieved. Various isoindolinone derivatives were obtained in good to excellent yields. The process, which avoided several drawbacks such as the requirement of concentrated protic acids and metal catalysts, protecting group of nitrogen, high temperature, and multistep synthesis, includes C(sp3)-OH cleavage, C-C coupling, and hydration of alkyne.

Gold-catalyzed C5-alkylation of indolines and sequential oxidative aromatization: access to C5-functionalized indoles.

A novel protocol for the synthesis of C5-alkylated indole derivatives via a gold-catalyzed reaction of indolines with diazo compounds and subsequent oxidative aromatization has been developed. C-H bond functionalization selectively occurs at the C5-position of indolines without a directing group. The experimental operation is simple and the whole process can be manipulated in one-pot.

Rhodium-Catalyzed Regioselective N2 -Alkylation of Benzotriazoles with Diazo Compounds/Enynones via a Nonclassical Pathway.

A novel rhodium-catalyzed highly selective N2 -alkylation of benzotriazoles with diazo compounds/enynones is achieved, providing N2 -alkylated benzotriazoles in good to excellent yields and with excellent N2 selectivities. Importantly, different to traditional carbene insertion into X-H (X=N, O etc) bonds, DFT calculations disclose that this selective N2 -alkylation probably proceeds through a formal 1,3- rather than 1,2-H shift to give the final products.

Synthesis of Six-Membered Carbo-/Heterocycles via Cascade Reaction of Alkynes and Diazo Compounds.

A novel approach toward diverse six-membered carbo-/heterocycles has been developed using diazo compounds and alkyne-substituted malonates as the suitable substrates. The polyfunctionalized cyclohexenes, tetrahydropyridines, and dihydropyrans have been prepared in moderate to high yield under mild reaction conditions. Importantly, the ligand plays a significant role in this copper-catalyzed protocol.

Synthesis of seven-membered heterocycles via copper-catalyzed cross-coupling of terminal alkynes with diazo compounds and sequential Michael addition.

A novel approach to synthesize seven-membered heterocycles is established by reacting amide tethered terminal alkynes with aryl diazoacetates in a one-pot reaction. This reaction involves copper-catalyzed cross coupling followed by base-promoted intramolecular Michael addition and yields products with a medium-sized ring.

Gold/silver-catalyzed controllable regioselective vinylcarbene insertion into O-H bonds.

An unprecedented regioselective metallo-vinylcarbene insertion into O-H bonds has been achieved with vinyldiazoacetates and 2-pyridones/benzyl alcohols as ideal substrates, which displayed distinct regioselectivity by employing gold and silver catalytic systems.