bluuebunny/crossref_metadata_2025_split huggingface dataset:
Insight into the Modes of Activation of Pyridinium and Bipyridinium Salts in Non‐Covalent Organocatalysis
Authors: Weiss Robin , Golisano Tamara , Pale Patrick , Mamane Victor 
Published: August 2021

AbstractA series of pyridinium and bipyridinium salts were prepared and their catalytic properties were evaluated in the aza‐Diels‐Alder reaction between imines and Danishefsky diene. Depending on the substituents of the pyridinium/bipyridinium rings and on the nature of the counterion, two mechanisms of activation were demonstrated. In case of non‐substituted rings, the substrate is activated through charge transfer involving the aryl ring on the C‐side of the imine. When halogen atoms were introduced on the catalysts, the activation mode switched to halogen bond involving the imine nitrogen lone pair. Moreover, alternative activation modes based on hydrogen bonding and radical cation were ruled out. This work allowed us to develop two families of catalysts whose potential was demonstrated in the cycloaddition of various imines with Danishefsky diene. The first family is composed of the simple methyl pyridinium triflate and dioctyl bipyridinium triflate. The former is active only with imines bearing a p‐methoxyphenyl group on the C‐side and the latter was found to be efficient with imines bearing different substituents on both the N‐ and C‐sides of the imines. The second family is based on halogenated pyridinium salts which proved active with almost all considered imines.magnified image
Pharmacological Inhibition of Core Regulatory Circuitry Liquid–liquid Phase Separation Suppresses Metastasis and Chemoresistance in Osteosarcoma
Authors: Lu Bing , Zou Changye , Yang Meiling , He Yangyang , He Jincan , Zhang Chuanxia , Chen Siyun , Yu Jiaming , Liu Kilia Yun , Cao Qi , Zhao Wei 
Published: August 2021

AbstractLiquid–liquid phase‐separated (LLPS) transcriptional factor assemblies at super‐enhancers (SEs) provide a conceptual framework for underlying transcriptional control in mammal cells. However, the mechanistic understanding of LLPS in aberrant transcription driven by dysregulation of SEs in human malignancies is still elusive. By integrating SE profiling and core regulatory circuitry (CRC) calling algorithm, the CRC of metastatic and chemo‐resistant osteosarcoma is delineated. CRC components, HOXB8 and FOSL1, produce dense and dynamic phase‐separated droplets in vitro and liquid‐like puncta in cell nuclei. Disruption of CRC phase separation decreases the chromatin accessibility in SE regions and inhibits the release of RNA polymerase II from the promoter of SE‐driven genes. Importantly, absence of CRC key component causes a reduction in osteosarcoma tumor growth and metastasis. Moreover, it is shown that CRC condensates can be specifically attenuated by the H3K27 demethylase inhibitor, GSK‐J4. Pharmacological inhibition of the CRC phase separation results in metastasis suppression and re‐sensitivity to chemotherapy drugs in patient‐derived xenograft model. Taken together, this study reveals a previously unknown mechanism that CRC factors formed LLPS condensates, and provides a phase separation‐based pharmacological strategy to target undruggable CRC components for the treatment of metastatic and chemo‐resistant osteosarcoma.
Design Zwitterionic Amorphous Conjugated Micro‐/Mesoporous Polymer Assembled Nanotentacle as Highly Efficient Sulfur Electrocatalyst for Lithium‐Sulfur Batteries
Authors: Liu Jiabing , Li Haipeng , Wang Jiayi , Zhang Yongguang , Luo Dan , Zhao Yan , Li Yebao , Yu Aiping , Wang Xin , Chen Zhongwei 
Published: August 2021

AbstractThe commercial application of lithium‐sulfur (LiS) batteries is seriously hampered by the sluggish redox kinetics and the shuttle effect of lithium polysulfides (LiPSs). In this study, a novel conjugated micro/mesoporous polymer (ST‐CMP) is developed by rational design of the organic condensation reaction of squaric acid and 1,3,5‐Tris(4‐aminophenyl)benzene, which can uniformly wrap onto carbon nanotube (CNT) as assembled nanotentacle, serving as the highly efficient sulfur electrocatalyst for LiS batteries. In this composite, the cross‐linked CNT conductive network significantly improves the electron transfer and reaction kinetics of active materials. In addition, the ST‐CMP assembled nanotentacle prevents the restacking or aggregation of ST‐CMP, favoring the exposure of active sites on ST‐CMP for efficient LiPSs chemical interaction. The abundant polymeric zwitterions in ST‐CMP with uniformly distributed positively polarized N atoms and negatively polarized O atoms can not only empower comprehensive regulation of LiPSs adsorption, but also simultaneously allow accelerated LiPSs catalytic conversion, rendering admirable redox reaction kinetics. With these merits, the obtained S/ST‐CMP@CNT composites exhibit a high initial specific capacity of 1307 mAh g−1 at 0.2 C with an ultralow capacity fading rate of 0.047% per cycle after 500 cycles at 1 C, exhibiting great potential in developing LiS batteries with decent performance.
Fluctuation of particles during funnel flow discharge from flat‐bottomed silos
Authors: Zhang Dancheng , Yang Xiaodong , Zhan Jinhui , Liu Xiaoxing 
Published: August 2021

AbstractAlthough resonant motion of particles during mass flow discharge from silos has been extensively investigated by earlier researchers, the appearance of such phenomenon during funnel flow discharge has not been emphasized. In this work, the flow behavior of particles during funnel flow discharge from flat‐bottomed silos has been investigated by conducting three‐dimensional Discrete Element Method (DEM) simulations. It is found that particles in the upper part of flowing zone move collectively, manifested by the oscillatory fluctuations of the velocity and the non‐Gaussian characteristics of the fluctuations of individual velocity around the average. Correlation analysis and discrete Fourier transform have been performed to characterize the emission and propagation of velocity fluctuation. It is found that the observed resonant motion of particles is induced by the regular fluctuation of contact force between particles, and there exists an intermediate region in the converging part of the flowing zone. The bottom boundary of this region corresponds to the emission source from which the velocity wave propagates upward and downward. Its upper boundary coincides with that of the converging part of the flowing zone and is featured by the most violent fluctuation of contact force. The simulation results thus suggest that the discharge of granular assembly seems to be determined by the rheological behavior of particles in this intermediate region.
Variations in morphological and epidermal features of shade and sun leaves of two species: Quercus bambusifolia and Q. myrsinifolia
Authors: Maslova Natalia P. , Karasev Eugeny V. , Xu Sheng‐Lan , Spicer Robert A. , Liu Xiao‐Yan , Kodrul Tatiana M. , Spicer Teresa E. V. , Jin Jian‐Hua 
Published: August 2021

AbstractPremiseMicroclimatic differences between the periphery and the interior of tree crowns result in a variety of adaptive leaf macromorphological and anatomical features. Our research was designed to reveal criteria for sun/shade leaf identification in two species of evergreen oaks, applicable to both modern and fossil leaves. We compared our results with those in other species similarly studied.MethodsFor both Quercus bambusifolia and Q. myrsinifolia (section Cyclobalanopsis), leaves from single mature trees with well‐developed crowns were collected in the South China Botanical Garden, Guangzhou, China. We focus on leaf characters often preserved in fossil material. SVGm software was used for macromorphological measurement. Quantitative analyses were performed and box plots generated using R software with IDE Rstudio. Leaf cuticles were prepared using traditional botanical techniques.ResultsPrincipal characters for distinguishing shade and sun leaves in the studied oaks were identified as leaf lamina length to width ratio (L/W), and the degree of development of venation networks. For Q. myrsinifolia, shade and sun leaves differ in tooth morphology and the ratio of toothed lamina length to overall lamina length. The main epidermal characters are ordinary cell size and anticlinal wall outlines. For both species, plasticity within shade leaves exceeds that of sun leaves.ConclusionsMorphological responses to sun and shade in the examined oaks are similar to those in other plant genera, pointing to useful generalizations for recognizing common foliar polymorphisms that must be taken into account when determining the taxonomic position of both modern and fossil plants.
Parent B2N2‐Perylenes with Different BN Orientations
Authors: Zhang Peng‐Fei , Zeng Jing‐Cai , Zhuang Fang‐Dong , Zhao Ke‐Xiang , Sun Ze‐Hao , Yao Ze‐Fan , Lu Yang , Wang Xiao‐Ye , Wang Jie‐Yu , Pei Jian 
Published: August 2021

AbstractIntroducing BN units into polycyclic aromatic hydrocarbons expands the chemical space of conjugated materials with novel properties. However, it is challenging to achieve accurate synthesis of BN‐PAHs with specific BN positions and orientations. Here, three new parent B2N2‐perylenes with different BN orientations are synthesized with BN‐naphthalene as the building block, providing systematic insight into the effects of BN incorporation with different orientations on the structure, (anti)aromaticity, crystal packing and photophysical properties. The intermolecular dipole–dipole interaction shortens the π–π stacking distance. The crystal structure, (anti)aromaticity, and photophysical properties vary with the change of BN orientation. The revealed BN doping effects may provide a guideline for the synthesis of BN‐PAHs with specific stacking structures, and the synthetic strategy employed here can be extended toward the synthesis of larger BN‐embedded PAHs with adjustable BN patterns.
Katalytische Carbochlorocarbonylierung von ungesättigten Kohlenwasserstoffen durch C‐COCl‐Bindungsspaltung**
Authors: Denton Elliott H. , Lee Yong Ho , Roediger Sven , Boehm Philip , Fellert Maximilian , Morandi Bill 
Published: August 2021

AbstractHier wird über eine Pd‐katalysierte Difunktionalisierung ungesättigter C‐C‐Bindungen mit Säurechloriden berichtet. Formal wird die C‐COCl‐Bindung eines Säurechlorids gespalten und atomökonomisch an gespannte Alkene oder verknüpfte Alkine addiert, um neue Säurechloride zu erzeugen. Die Transformation erfordert kein exogenes CO, läuft unter milden Bedingungen ab, zeigt eine gute Toleranz für funktionelle Gruppen und liefert die isolierten Produkte hoch stereoselektiv. Die intermolekulare Reaktion toleriert dabei sowohl Aryl‐ als auch Alkenyl‐substituierte Säurechloride. Zum Gelingen der Reaktion ist notwendig, die Carbonsäuren in situ in das Säurechlorid umzuwandeln. Die Reaktion dient auch als Beispiel für temperaturabhängige Stereodivergenz, die zusammen mit möglichen Reaktionsmechanismen durch DFT‐Rechnungen untersucht wird. Zudem wird gezeigt, dass Benzofurane in einer intramolekularen Variante der Reaktion gebildet werden können. Die Derivatisierung der Produkte aus der intermolekularen Reaktion bietet einen hoch stereoselektiven Ansatz für die Synthese tetrasubstituierter Cyclopentane.
Intragenomische Decarboxylierung von 5‐Carboxy‐2′‐desoxycytidin
Authors: Kamińska Ewelina , Korytiaková Eva , Reichl Andreas , Müller Markus , Carell Thomas 
Published: August 2021

AbstractDNA besteht aus den vier kanonischen Nukleosiden dA, dC, dG und T. Zudem findet sich auch 5‐Methylcytosin (mdC) in der genomischen DNA. Die Methylierung von dC zu mdC reguliert die Transkriptionsaktivität. Daneben enthält insbesondere das Genom von Stammzellen drei weitere dC‐Derivate, die durch schrittweise Oxidation der Methylgruppe mithilfe von Tet‐Enzymen gebildet werden: 5‐Hydroxymethyl‐dC (hmdC), 5‐Formyl‐dC (fdC) und 5‐Carboxy‐dC (cadC). Es wird angenommen, dass fdC und cadC wieder in dC umgewandelt werden, wodurch ein epigenetischer Kontrollzyklus entsteht, der mit der Methylierung von dC zu mdC beginnt und mit der Oxidation und Entfernung von fdC und cadC endet. Während fdC nachweislich eine intragenomische Deformylierung zu dC durchläuft, wurde eine vergleichbare Decarboxylierung von cadC zwar postuliert, aber bisher nicht beobachtet. Hier zeigen wir mithilfe von Stoffwechselmarkierungen in verschiedenen Zelltypen, dass cadC decarboxyliert, was bestätigt, dass sowohl fdC als auch cadC Nukleoside sind, die im Genom durch Spaltung der C‐C‐Bindung direkt in dC zurückverwandelt werden.
N‐alkyl imidazole‐based homonuclear coordination complex as a neutral organocatalyst for the faster and efficient construction of 3,4‐dihydro‐2H‐1,3‐oxazine scaffold
Authors: Yıldırım Ayhan , Göker Mustafa 
Published: August 2021

AbstractIn the present work, homonuclear coordination complex including Zn (II) andN‐hexadecylimidazole ligand was used for the first time as a highly efficient homogeneous neutral organocatalyst for the synthesis of 3,4‐dihydro‐2H‐1,3‐benzoxazine monomers. Therefore,N‐alkyl orN‐aryl substituted, both mono‐benzoxazine and bis‐benzoxazine, were successfully synthesized (21 examples) via Mannich‐type condensation reactions. Effortlessly obtaining the pure product with high yields and the short reaction time makes this method more useful and advantageous than the common existing benzoxazine synthesis methods.
Effects of networks composed of epoxy/dual thiol‐curing agents on properties of shape memory polymers
Authors: Wang Yanling , Tang Longhao , Li Yongfei , Li Qiang 
Published: August 2021

AbstractProfound understanding of relationships between molecular networks with properties can make it more convenient for people to prepare and employ shape memory polymers (SMPs). In this paper, a series of epoxy SMPs were developed based on epoxy (E‐51), trimethylolpropane tris(3‐mercaptopropionate) and pentaerythritoltetrakis (3‐mercaptopropionate), and 2‐methylimidazole, through “epoxy‐thiol” click reaction. The effect of networks on key properties (heat resistance and mechanical properties shape recovery performance) was systematically investigated. Experiment results indicated that there were positive correlations between network regularity with both thermal–mechanical properties and heat resistance. In addition, regularity of network structure had an effect to restrict shape recovery speed.
Synthesis and characterization of a novel rigid rod polymer based on 2,6‐dihydroxyterephthalic acid and 2,3,5,6‐tetraminopyridine
Authors: Wang Zhongwen , Deng Yamin , Jia Xin 
Published: August 2021

AbstractPoly‐p‐phenyleneterephthalamide (PPTA) is widely used in national defense, military industry, and aerospace. However, with weak compression resistance and twist resistance, development of PPTA is greatly impeded. In this work, a novel rigid rod polymer was synthesized by polycondensation of 2,6‐dihydroxyterephthalic acid with 2,3,5,6‐tetraminopyridine which have a large quantity of hydrogen bonds between these polymer chains which provide excellent thermal properties named poly [N‐(2,5‐diamino‐6‐[imino]‐3‐pyridyl)‐4‐formyl‐2,6‐dihydroxybenzamide] (PPDA). The structure of the polymers was characterized by X‐ray diffraction and Fourier transform infrared spectroscopy. The resulting showed that PPDA has good thermal stability and crystallinity, the maximum thermal decomposition temperature close to 900°C under the nitrogen atmosphere. At the same time, PPDA was insoluble in most organic solvents and exhibited good chemical stability. This indicated a superior performance over that of the poly(2,6‐diimidazo(4,5‐b:4′5′‐e)pyridinylene‐1,4(2,5‐dihydroxy)phenylene). In addition, we can foresee that PPDA will play an important role in prospective surgery and aramid areas.
Analyzing clarification in asynchronous information‐seeking conversations
Authors: Tavakoli Leila , Zamani Hamed , Scholer Falk , Croft William Bruce , Sanderson Mark 
Published: August 2021

AbstractThis research analyzes human‐generated clarification questions to provide insights into how they are used to disambiguate and provide a better understanding of information needs. A set of clarification questions is extracted from posts on the Stack Exchange platform. Novel taxonomy is defined for the annotation of the questions and their responses. We investigate the clarification questions in terms of whether they add any information to the post (the initial question posted by the asker) and the accepted answer, which is the answer chosen by the asker. After identifying, which clarification questions are more useful, we investigated the characteristics of these questions in terms of their types and patterns. Non‐useful clarification questions are identified, and their patterns are compared with useful clarifications. Our analysis indicates that the most useful clarification questions have similar patterns, regardless of topic. This research contributes to an understanding of clarification in conversations and can provide insight for clarification dialogues in conversational search scenarios and for the possible system generation of clarification requests in information‐seeking conversations.
Passive sampler designed for per‐ and polyfluoroalkyl substances using polymer‐modified organosilica adsorbent
Authors: Hartmann Heather , Hefner Claire , Carter Erika , Liles David , Divine Craig , Edmiston Paul L. 
Published: August 2021

AbstractA passive sampler designed to measure per‐ and polyfluoroalkyl substances (PFAS) was evaluated to determine chemical uptake rates under a variety of conditions. The sampler design is simple and robust, using organosilica modified with cross‐linked amine polymer in an high density polyethylene housing retained with polypropylene mesh. The addition of amine groups as a weak ion‐exchange resin in combination with Cu2+ was designed to promote binding of short‐chain PFAS. A five‐fold improvement in perfluorobutanoic acid adsorption was measured when Cu2+ was added to the polyethylenimine polymer. The samplers showed an integrated response to all analytes tested except for short‐chain PFAS. Sampling rates of PFAS analytes from simulated groundwater were on average 10 mL/day at flow rates of 0.038–1.9 cm/min. Relatively low variability in sampling rate was observed over the range of laboratory tested conditions (representing common conditions in environmental waters) including elevated ionic strength, sulfate concentration, and humic acid content.Article Impact StatementMeasuring per‐ and polyfluoroalkyl substances in environmental samples is important for monitoring. Passive samplers can offer practical advantages for making measurements.
Systematizing the different notions of growth‐coupled product synthesis and a single framework for computing corresponding strain designs
Authors: Schneider Philipp , Mahadevan Radhakrishnan , Klamt Steffen 
Published: August 2021

AbstractA widely used design principle for metabolic engineering of microorganisms aims to introduce interventions that enforce growth‐coupled product synthesis such that the product of interest becomes a (mandatory) by‐product of growth. However, different variants and partially contradicting notions of growth‐coupled production (GCP) exist. Herein, we propose an ontology for the different degrees of GCP and clarify their relationships. Ordered by coupling degree, we distinguish four major classes: potentially, weakly, and directionally growth‐coupled production (pGCP, wGCP, dGCP) as well as substrate‐uptake coupled production (SUCP). We then extend the framework of Minimal Cut Sets (MCS), previously used to compute dGCP and SUCP strain designs, to allow inclusion of implicit optimality constraints, a feature required to compute pGCP and wGCP designs. This extension closes the gap between MCS‐based and bilevel‐based strain design approaches and enables computation (and comparison) of designs for all GCP classes within a single framework. By computing GCP strain designs for a range of products, we illustrate the hierarchical relationships between the different coupling degrees. We find that feasibility of coupling is not affected by the chosen GCP degree and that strongest coupling (SUCP) requires often only one or two more interventions than wGCP and dGCP. Finally, we show that the principle of coupling can be generalized to couple product synthesis with other cellular functions than growth, for example, with net ATP formation. This work provides important theoretical results and algorithmic developments and a unified terminology for computational strain design based on GCP.
Engineered Human Induced Pluripotent Cells Enable Genetic Code Expansion in Brain Organoids
Authors: van Husen Lea S. , Katsori Anna‐Maria , Meineke Birthe , Tjernberg Lars O. , Schedin‐Weiss Sophia , Elsässer Simon J. 
Published: August 2021

AbstractHuman induced pluripotent stem cell (hiPSC) technology has revolutionized studies on human biology. A wide range of cell types and tissue models can be derived from hiPSCs to study complex human diseases. Here, we use PiggyBac‐mediated transgenesis to engineer hiPSCs with an expanded genetic code. We demonstrate that genomic integration of expression cassettes for a pyrrolysyl‐tRNA synthetase (PylRS), pyrrolysyl‐tRNA (PylT) and the target protein of interest enables site‐specific incorporation of a non‐canonical amino acid (ncAA) in response to an amber stop codon. Neural stem cells, neurons and brain organoids derived from the engineered hiPSCs continue to express the amber suppression machinery and produce ncAA‐bearing reporter. The incorporated ncAA can serve as a minimal bioorthogonal handle for further modifications by labeling with fluorescent dyes. Site‐directed ncAA mutagenesis will open a wide range of applications to probe and manipulate proteins in brain organoids and other hiPSC‐derived cell types and complex tissue models.
Aberrant expression of lncRNAs SNHG6, TRPM2‐AS1, MIR4435‐2HG, and hypomethylation of TRPM2‐AS1 promoter in colorectal cancer
Authors: Ghasemi Tayyebeh , Khalaj‐Kondori Mohammad , Hosseinpour feizi Mohammad Ali , Asadi Parviz 
Published: August 2021

AbstractAccumulating evidence has indicated that deregulation of lncRNAs plays essential roles in colorectal cancer (CRC) carcinogenesis. The goal of this study was to analyze the expression of lncRNAs in colorectal cancer and their association with clinicopathological variables. Bioinformatics analysis of published CRC microarray data was performed to identify the important lncRNAs. The expression levels of candidate genes were assessed in the human colon cancer/normal cell lines, CRC, adenomatous colorectal polyps, and their marginal tissues by qRT‐PCR. Moreover, the methylation status of the TRPM2‐AS1 promoter was studied using qMSP assay. Furthermore, we investigated the molecular mechanisms of these lncRNAs in CRC progression using in silico analysis. Microarray analysis revealed that lncRNAs SNHG6, MIR4435‐2HG, and TRPM2‐AS1 were upregulated in CRC. These results were validated in colon cell lines. Moreover, qRT‐PCR showed that the expression levels of SNHG6 and TRPM2‐AS1 were upregulated in the colorectal tumor tissues compared with their paired tissues. Nonetheless, there was no significant increase in MIR4435‐2HG expression in CRC samples. Furthermore, we observed a significant hypomethylation of TRPM2‐AS1 promoter and its activation in CRC tissues. By in silico analysis, we found that the lncRNAs upregulation could promote proliferation and drug resistance of colorectal cancer cells via miRNAs sponging and modulation of their targets expression. In conclusion, based on our results upregulation of SNHG6 and TRPM2‐AS1, and hypomethylation of TRPM2‐AS1 promoter might be considered as potential diagnostic biomarkers for CRC initiation and development.
Endodontic management of a rare case of the geminated maxillary second molar tooth using CBCT
Authors: Ramezani Masoumeh , Asgari Shima , Adel Mamak 
Published: August 2021

AbstractThis report illustrates a rare case of a geminated maxillary right second molar tooth using CBCT in a 23‐year‐old man with severe pain. Nonsurgical endodontic treatment was performed, which gave rise to an asymptomatic tooth at the 12‐month follow‐up.