Edge-pinning effect of graphene nanoflakes sliding atop graphene

Edge effect is one of the detrimental factors preventing superlubricity in laminar solid lubricants. Separating the friction contribution from the edge atom and inner atom is of paramount importance for rational design of ultralow friction across scales in van der Waals heterostructures. To decouple these contributions and provide the underlying microscopic origin at the atomistic level, we considered two contrast models, namely, graphene nanoflakes with dimerized and pristine edges sliding on graphene monolayer based on extensive ab initio calculations. We found the edge contribution to friction is lattice orientation dependence. In particular, edge pinning effect by dimerization is obvious for misaligned contact but suppressed in aligned lattice orientation. The former case providing local commensuration along edges is reminiscent of Aubry's pinned phase and the contribution of per edge carbon atom to the sliding potential energy corrugation is even 1.5 times more than that of an atom in bilayer graphene under commensurate contact. Furthermore, we demonstrated that the dimerized edges as high frictional pinning sites are robust to strain engineering and even enhanced by fluorination. Both structural and chemical modification in the tribological system constructed here offers the atomic details to dissect the undesirable edge pinning effect in layered materials which may give rise to the marked discrepancies in measured friction parameters from the same superlubric sample or different samples with the same size and identical preparation.Comment: 18 pages,6 figure

Epithelioid inflammatory myofibroblastic sarcoma: a case report and brief literature review

Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is a rare variant of the inflammatory myofibroblastic tumor, characterized by more aggressive clinical course and nuclear membrane staining of anaplastic lymphoma kinase (ALK) with ALK rearrangement. An elderly male came to the clinic because of an accidental abdominal mass. Abdominal and pelvic enhanced CT revealed a tumor apparently orginated from mesenchymal tissue. Subsequently, the abdominal mass and multiple organ resection was performed, and the mass was pathologically confirmed as EIMS. The patient developed Clavien-Dindo Grade III postoperative complications and was discharged after his condition improved. He received doxorubicin monotherapy after operation, but only one cycle was administered due to severe vomiting. The follow-up of 5 months after operation showed no evidence of recurrence. Given the rarity of EIMS, and ALk inhibitors have a long and robust effect on patients with ALK gene tumors, it is very important for clinicians to be familiar with the clinicopathological features of EIMS, which will contribute to the accurate diagnosis of EIMS and reduce misdiagnosis

Synthèse totale du cymoside et études synthétiques vers l'ophiorrhine A

Le cymoside est un alcaloïde indolomonoterpénique isolé de Chimarrhis cymosa, qui présente un squelette hexacyclique fusionné en forme de cage. Cette structure sans précédent possède un motif furo [3,2-b] indoline qui est rare. La biosynthèse postulée du cymoside implique une cyclisation oxydante unique en cascade directement à partir de la strictosidine ce qui est en contraste avec de nombreux autres alcaloïdes indolomonoterpéniques. Inspirés par cette considération biosynthétique, nous avons réalisé cette transformation sans précédent à partir de l’aglycone adéquatement protégé de la strictosidine en présence d'une oxaziridine. La clé du succès de cette réaction biomimétique est l'utilisation d'un groupement nosyl protecteur de l'amine secondaire N4, qui masque la réactivité de cette dernière et oriente la sélectivité faciale de l'oxydation du noyau indole en hydroxyindolénine. L'addition de l'éther d’énol de la partie terpénique sur la fonction imine de cette indolenine est suivie par le piégeage de l'oxocarbénium généré par le groupe hydroxyle sur l’indoline pour délivrer la charpente furo [3,2-b] indoline de la substance naturelle. La première synthèse totale du cymoside a finalement été réalisée par une introduction tardive du fragment β-D-glucose, avec un rendement de 1,7% en 6 étapes à partir de l'éther éthylique racémique de l’aglycone de la sécologanine. Cette première synthèse a été significativement améliorée en partant du tétraacétate de sécologanine énantiopure au lieu de son aglycone racémique. La cyclisation oxydante clé et bioinspirée entre l'indole et l'éther d’énol du tétraacétate de strictosidine protégé a été efficace et cela en présence du fragment glucose. La synthèse de deuxième génération a ainsi été réalisée en 4 étapes et avec un rendement de 18% à partir du tétraacétate de sécologanine, et était plus concise et directe que la première synthèse totale.Une étude préliminaire a également été entreprise pour réaliser la synthèse totale de l'ophiorrhine A, présentant une structure polycyclique fusionnée avec une connectivité spirocyclique en C3 via une cycloaddition intramoléculaire bioinspirée de Diels-Alder d'une indolopyridone. Cette cycloaddition clé a été évaluée avec succès sur un substrat modèle simplifié donnant le cycloadduit correspondant avec un rendement de 28% au reflux du bromobenzène. Cependant, l'acylation de dérivés d'indoles avec l'acide carboxylique de l’aglycone de la sécologanine n'a pas réussi à produire l'intermédiaire indolopyridone désiré qui est clé pour la suite de la synthèse. Une approche alternative a été examinée pour former l'indolopyridone requise par oxydation d'une indolopyridine. La condensation Pictet-Spengler du L-tryptophane avec l'éther éthylique de l’aglycone de la sécologanine suivie de d’une aromatisation décarboxylante dans des conditions oxydantes a donné la ß-carboline correspondant à l'aglycone de la strictosidine. La méthylation de la pyridine ainsi formée a donné le sel de N-méthylpyridinium souhaité. Malheureusement, l'oxydation ultérieure en indolopyridone s’est montrée problématique et plusieurs tentatives ont échoué. La cycloaddition intramoléculaire de Diels-Alder du sel de N-méthylpyridinium n'a pas non plus réussi. L'oxydation du sel de pyridinium en pyridone est toujours à l'étude.Cymoside is a monoterpene indole alkaloid isolated from Chimarrhis cymosa, displaying an unprecedented caged hexacyclic fused-skeleton encompassing a rare furo[3,2-b]indoline motif. Unlike many other monoterpene indole alkaloids, the biosynthesis of cymoside involves a unique oxidative cyclization cascade from strictosidine. Inspired by this biosynthetic consideration, we achieved this unprecedented transformation from an adequately protected strictosidine aglycone in the presence of an oxaziridine. Key to the success of this biomimetic reaction is the use of a nosyl protecting group of the N4 secondary amine, which masks the reactivity of the latter and directs the facial selectivity of the oxidation of the indole nucleus into a hydroxyindolenine. Addition of the enol ether of the terpenic moiety to this imine was followed by the trapping of the generated oxocarbenium by the hydroxyl to deliver the furo[3,2-b]indoline framework of the natural product. The first total synthesis of cymoside was finally achieved by a late-stage introduction of the β-D-glucose, in 1.7 % yield in 6 steps from the racemic ethyl ether of secologanin aglycone. This first synthesis was significantly improved by starting from enantiopure secologanin tetraacetate instead of its racemic aglycon. The key bioinspired oxidative cyclization between the indole and the C16-C17 enol ether of protected strictosidine tetraacetate proceeded well in the presence of the glucose moiety. The second generation synthesis was accomplished in 4 steps and 18 % yield from secologanin tetraacetate, and was more concise and straightforward than the first one.A preliminary study was also undertaken to achieve the total synthesis of ophiorrhine A, displaying a polycyclic-fused structure with a spirocyclic connectivity at C3 via a bioinspired intramolecular Diels-Alder cycloaddition of an indolopyridone. This key cycloaddition was successfully evaluated on a simplified model substrate yielding the corresponding cycloadduct in 28 % yield in refluxing bromobenzene. However, the acylation of indole derivatives with the carboxylic acid of secologanin aglycone failed to produce the corresponding key indolopyridone intermediate. An alternative approach was examined to form the required indolopyridone via oxidation of a pyridine ring. Successive Pictet-Spengler condensation of L-tryptophan with secologanin aglycone ethyl ether and decarboxylative aromatization in oxidative conditions yielded the β-carboline corresponding to strictosidine aglycone. Methylation of the latter yielded the desired N-methylpyridinium salt. Unfortunately, the subsequent oxidation into the indolopyridone was problematic and several attempts failed. Intramolecular Diels-Alder cycloaddition of the N-methylpyridinium salt also did not succeed. The oxidation of the pyridinium into a pyridine are still under investigation

Bioinspired Divergent Oxidative Cyclization of Strictosidine and Vincoside Derivatives: Second Generation Enantioselective Total Synthesis of (–)-Cymoside

We report our second generation synthesis of (–)-cymoside as well as the formation of a new hexacyclic-fused furo[3,2-b]indoline framework. After a Pictet-Spengler condensation between secologanin tetraacetate and tryptamine, the course of the cyclization of the 7-hydroxyindolenine intermediate generated by oxidation with an oxaziridine, depends on the stereochemistry of the 3-position. The 3-(S)-strictosidine stereochemistry delivered efficiently the scaffold of cymoside via intramolecular coupling with the C16-C17 enol ether, while the 3-(R)-vincoside stereochemistry directed towards the reaction with the C18-C19 terminal alkene and the formation of the unexpected caged compound.</p

Bioinspired Divergent Oxidative Cyclization from Strictosidine and Vincoside Derivatives: Second Generation Total Synthesis of Cymoside and Access to an Original Hexacyclic‐Fused Furo[3,2‐b]indoline

International audienceWe report our second generation synthesis of (-)-cymoside as well as the formation of a new hexacyclic-fused furo[3,2-b]indoline framework. After a Pictet-Spengler condensation between secologanin tetraacetate and tryptamine, the course of the cyclization of the 7-hydroxyindolenine intermediate generated by oxidation with an oxaziridine, depends on the stereochemistry of the 3-position. The 3-(S)-strictosidine stereochemistry delivered efficiently the scaffold of cymoside via intramolecular coupling with the C16-C17 enol ether, while the 3-(R)-vincoside stereochemistry directed towards the reaction with the C18-C19 terminal alkene and the formation of the unexpected caged compound

Enantioselective Total Synthesis of Cymoside through a Bioinspired Oxidative Cyclization of a Strictosidine Derivative

International audienceThe first total synthesis of the caged monoterpene indole alkaloid cymoside is reported. This natural product displays a unique hexacyclic-fused skeleton whose biosynthesis implies an early oxidative cyclisation of strictosidine. Our approach to the furo[3,2-b]indoline framework relied on an unprecedented biomimetic sequence which started by the diastereoselective oxidation of the indole ring into a hydroxyindolenine which triggered the addition of an enol ether and was followed by the trapping of an oxocarbenium intermediate

Bioinspired Intramolecular Diels-Alder Cycloaddition for the Total Synthesis of Ophiorrhine A via Ophiorrhine G and Ophiorrhiside E

We report the first total synthesis of the monoterpene indole alkaloids ophiorrhine A via a late stage bioinspired intramolecular Diels-Alder cycloaddition to form the intricate bridged and spirannic polycyclic system. Several strategies were investigated to construct the indolopyridone moiety of ophiorrhiside E, the postulated biosynthetic precursor of ophiorrhine A. Eventually, the Friedel-Crafts-type coupling of indolyl-acetamide with secologanin-derived acid chloride delivered ophiorrhine G. Cyclode-hydratation of a protected form of the latter was followed by the desired spontaneous intramolecular Diels-Alder cycloaddition of protected ophiorrhiside E leading to ophiorrhine A

Electrochemical Dearomative 2,3-Difunctionalization of Indoles

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Electrochemical Dearomative 2,3-Difunctionalization of Indoles

We report the use of electrochemistry to perform a direct oxidative dearomatization of indoles leading to 2,3-dialkoxy or 2,3-diazido indolines under undivided conditions at a constant current. This operationally simple electro-oxidative procedure avoids the use of an external oxidant and displays an excellent functional group compatibility. The formation of the two C-O or C-N bonds is believed to arise from the oxidation of the indoles into radical cation intermediates

Flexoelectricity Driven Fano Resonance in Slotted Carbon Nanotubes for Decoupled Multifunctional Sensing

Multifunctionality, interference-free signal readout, and quantum effect are important considerations for flexible sensors equipped within a single unit towards further miniaturization. To address these criteria, we present the slotted carbon nanotube (CNT) junction features tunable Fano resonance driven by flexoelectricity, which could serve as an ideal multimodal sensory receptor. Based on extensive ab initio calculations, we find that the effective Fano factor can be used as a temperature-insensitive extrinsic variable for sensing the bending strain, and the Seebeck coefficient can be used as a strain-insensitive intrinsic variable for detecting temperature. Thus, this dual-parameter permits simultaneous sensing of temperature and strain without signal interference. We further demonstrate the applicability of this slotted junction to ultrasensitive chemical sensing which enables precise determination of donor-type, acceptor-type, and inert molecules. This is due to the enhancement or counterbalance between flexoelectric and chemical gating. Flexoelectric gating would preserve the electron–hole symmetry of the slotted junction whereas chemical gating would break it. As a proof-of-concept demonstration, the slotted CNT junction provides an excellent quantum platform for the development of multistimuli sensation in artificial intelligence at the molecular scale