126 research outputs found
Delayed-detached eddy simulation for optical path control on backward-facing step flow
No full textA feedback flow control is designed to reduce the aero-optical distortions behind a backward facing step. The delayed-detached eddy simulation, based on the Spalart-Allmaras turbulence model, is developed to simulate the unsteady density variations caused by the shear layer. A database from simulations of both an unforced baseline flow and open-loop forced flows is built using the proper orthogonal decomposition. An Artificial Neural Network and an Auto-Regressive eXogenous model are used to build a reduced order model of the flow field. Closed loop controllers for a suction-blowing actuator were simulated using the reduced order model. Finally, the actuation results from the closed-loop simulation are validated by re-computing the forced flow. The results show that aero-optical distortions can be reduced via the feedback flow controller based on the reduced order model
Probing the functional motifs for interaction between 5S rRNA and 23S rRNA by a SELEX approach
No full textN-Heterocyclic carbene-catalyzed deaminative cross-coupling of aldehydes with Katritzky pyridinium salts
No full textThis journal is © The Royal Society of Chemistry.By employing an N-heterocyclic carbene (NHC) catalyst, we developed a versatile catalytic system that enables deaminative cross-coupling reactions of aldehydes with redox-active pyridinium salts. Katritzky pyridinium salts behave as single-electron oxidants capable of generating alkyl radicals enabled by the redox properties of the enolate form of Breslow intermediates. The resultant alkyl radical undergoes efficient recombination with the NHC-bound aldehyde-derived carbonyl carbon radical for the formation of a C-C bond. The mild and transition metal-free reaction conditions tolerate a broad range of functional groups, and its utility has been further demonstrated by the modification of a series of peptide feedstocks and application to the three-component dicarbofunctionalization of olefins11sciescopu
Visible-light-induced cascade radical ring-closure and pyridylation for the synthesis of tetrahydrofurans
No full text© 2019 The Royal Society of Chemistry. Reported is a novel visible-light-enabled alkoxy radical ring-closure and pyridylation from N-alkenyloxypyridinium salts serving as both alkoxy radical precursors and heteroaryl sources. This strategy features a photoredox tandem radical process involving a sequential fragmentation of an N-alkoxypyridinium salt, a radical cyclization process, and a pyridylation process. This method exhibited broad substrate scope, good functional group compatibility, and metal-free mild conditions, offering a powerful synthetic tool for assembling various pyridine-tethered tetrahydrofurans and late-stage functionalization of complex biorelevant molecules. Moreover, radical cascade cyclization could be successfully achieved, leading to the synthesis of previously challenging and important pyridine-tethered bicyclic oxaspiro ring systems11sci
Site-Selective Functionalization of Pyridinium Derivatives via Visible-Light-Driven Photocatalysis with Quinolinone
No full textThe selective installation of phosphinoyl and carbamoyl moieties on the pyridine scaffold is an important transformation in synthetic and medicinal chemistry. By employing quinolinone as an efficient organic photocatalyst, we developed a catalytic system driven by visible light that forms phosphinoyl and carbamoyl radicals, which react with various heteroarenium derivatives under mild, transition-metal-free conditions. This straightforward and environmentally friendly synthetic method represents a new approach to site-divergent pyridine functionalization that offers considerable advantages in both simplicity and efficiency. Ambient temperature is sufficient for the formation of the reactive radicals, and the site-selectivity can be switched from C2 to C4 by changing the radical coupling sources. Under standard reaction conditions, phosphinoyl radicals give access to C4 products, while carbamoyl radicals selectively give C2 products. We found that the carbamoyl radical overcomes the intrinsic preference for forming the ortho-product by allowing the oxo functionality of the carbamoyl radical to electrostatically engage the nitrogen of the pyridinium substrate, which preferentially gives the ortho-product. The phosphinoyl radical cannot engage in the same interaction, because the phosphorus is too large. This novel synthetic route tolerates a broad range of substrates and provides a convenient and powerful synthetic tool for accessing the core structures of numerous privileged scaffolds.
Intravital imaging of peritubular microcirculation impairment in cisplatininduced acute kidney injury
No full textDespite the accumulation of cisplatin in proximal tubules, direct visualization of the surrounding peritubular microcirculation, including its change in cisplatin-induced acute kidney injury (AKI), is lacking. Here, using fluorescence and cellular angiography through video-rate high-resolution intravital microscopy, progressive disturbance of peritubular microcirculation in cisplatin-induced AKI in mice was demonstrated. Fluorescence angiography revealed increasing perfusion defects, with a stepwise rise in time to peak (TTP), originating from capillaries surrounding S1 segments. Cellular angiography demonstrated a progressive decrease in the velocity and track length of individual erythrocytes during AKI progression, accompanied by a sequential decrease in the functional capillary ratio (FCR). Changes in the perfusion area, TTP, and FCR preceded significant changes in blood urea nitrogen and cystatin C, suggesting the potential for early diagnosis. Although neutrophil infiltration near proximal tubules increased throughout the progression, it did not cause obstruction of the peritubular microcirculation. Depletion of neutrophils increased mortality due to systemic side effects, whereas functional inactivation of neutrophils using an anti-CD11b antibody improved peritubular microcirculation in cisplatin-induced AKI. This approach enables direct visualization and quantification of peritubular microcirculation and immune cell dynamics, providing insights into renal pathophysiology and potential therapeutic strategies.
Visible-Light-Induced Pyridylation of Remote C(sp3)?H Bonds by Radical Translocation of N-Alkoxypyridinium Salts
No full textMetal-free, visible-light-induced site-selective heteroarylation of remote C(sp3)?H bonds has been accomplished through the design of N-alkoxyheteroarenium salts serving as both alkoxy radical precursors and heteroaryl sources. The transient alkoxy radical can be generated by the single-electron reduction of an N-alkoxypyridinium substrate by a photoexcited quinolinone catalyst. Subsequent radical translocation of the alkoxy radical forms a nucleophilic alkyl radical intermediate, which undergoes addition to the substrate to achieve remote C(sp3)?H heteroarylation. This cascade strategy provides a powerful platform for remote C(sp3)?H heteroarylation in a controllable and selective manner and is well suited for late-stage functionalization of complex bioactive molecules. ⓒ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhe
Site-Selective Functionalization of Pyridinium Derivatives via Visible-Light-Driven Photocatalysis with Quinolinone
No full text© Copyright 2019 American Chemical Society.The selective installation of phosphinoyl and carbamoyl moieties on the pyridine scaffold is an important transformation in synthetic and medicinal chemistry. By employing quinolinone as an efficient organic photocatalyst, we developed a catalytic system driven by visible light that forms phosphinoyl and carbamoyl radicals, which react with various heteroarenium derivatives under mild, transition-metal-free conditions. This straightforward and environmentally friendly synthetic method represents a new approach to site-divergent pyridine functionalization that offers considerable advantages in both simplicity and efficiency. Ambient temperature is sufficient for the formation of the reactive radicals, and the site-selectivity can be switched from C2 to C4 by changing the radical coupling sources. Under standard reaction conditions, phosphinoyl radicals give access to C4 products, while carbamoyl radicals selectively give C2 products. We found that the carbamoyl radical overcomes the intrinsic preference for forming the ortho-product by allowing the oxo functionality of the carbamoyl radical to electrostatically engage the nitrogen of the pyridinium substrate, which preferentially gives the ortho-product. The phosphinoyl radical cannot engage in the same interaction, because the phosphorus is too large. This novel synthetic route tolerates a broad range of substrates and provides a convenient and powerful synthetic tool for accessing the core structures of numerous privileged scaffold
The Win-Win Solution for Mobility and Environmental Quality
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