Recent Applications of Paired Electrolysis in Organic Synthesis

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Recent Applications of Paired Electrolysis in Organic Synthesis


Abstract

Recent years have witnessed a renaissance of organic electrochemistry since the cheap, safe, sustainable electron could be employed as a traceless redox agent to facilitate redox conversions. Additionally, divergent selectivity could be achieved by tuning the potential or current of the electrochemical reaction. Compared to electrooxidation or electroreduction reactions, paired electrolysis represents a more practical and energy-efficient strategy that delivers the products by making use of both anodic and cathodic reactions simultaneously. This mini-review summarized the breakthroughs and recent advances in this fascinating field and mainly is divided into three parts: parallel, sequential, and convergent paired electrolysis.

Assessing the biodegradability of tire tread particles and influencing factors

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ABSTRACT

Abrasion of tire tread, caused by friction between vehicle tires and road surfaces, causes release of tire wear particles (TWPs) into various environmental compartments. TWPs contribute to chemical-, microplastic-, and particulate matter pollution. Their fate remains largely unknown, especially regarding the extent and form in which they persist in the environment. This study investigated 1) the biodegradability of tread particles (TPs) in the form of ground tire tread, 2) how accelerated UV-weathering affect their biodegradability, and 3) which TP constituents are likely contributors to TP biodegradability based on their individual biodegradability. A series of closed bottle tests, with aerobic aqueous medium inoculated with activated sludge, were carried out for pristine TPs, UV-weathered TPs, and selected TP constituents; natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and treated distillate aromatic extracts (TDAE). Biodegradation was monitored by manometric respirometry quantifying biological oxygen consumption over 28 days. Pristine TP biodegradability was found to be 4.5%. UV-weathered TPs showed higher biodegradability of 6.7% and 8.0% with similar and increased inoculum concentration, respectively. The observed TP biodegradation was mainly attributed to biodegradation of NR and TDAE, with individual biodegradability of 35.4% and 8.0%, respectively. IR and BR showed negligible biodegradability. These findings indicate biodegradability of individual constituents is decreased by a factor of 2 to 5 when compounded into TPs. Through scanning electron microscope (SEM) analysis, biodegradation was found to cause surface erosion. Processes of TP biodegradation are expected to change throughout their lifetime as new constituents are incorporated from the road and others degrade and/or leach out. Tire emissions likely persist as particles with an increased fraction of synthetic rubbers and carbon black.

Advances in Continuous Flow Fluorination Reactions

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Advances in Continuous Flow Fluorination Reactions

Fluorination reactions are important in constructing organofluorine motifs in pharmaceuticals and agrochemicals, but they pose challenges due to their hazardous nature, high exothermicity, and limited selectivity and scalability. This review explores recent continuous flow techniques that addressed challenges of fluorination reactions, including gas-liquid reactions, packed-bed reactors, in-line purifications, reaction telescoping, large-scale reactions as well as flow photoredox- and electrocatalysis.


Abstract

Fluorination reactions are important in constructing organofluorine motifs, which contribute to favorable biological properties in pharmaceuticals and agrochemicals. However, fluorination reagents and reactions are associated with various problems, such as their hazardous nature, high exothermicity, and poor selectivity and scalability. Continuous flow has emerged as a transformative technology to provide many advantages relative to batch syntheses. This review article summarizes recent continuous flow techniques that address the limitations and challenges of fluorination reactions. Approaches based on different flow techniques are discussed, including gas-liquid reactions, packed-bed reactors, in-line purifications, streamlined multistep synthesis, large-scale reactions well as flow photoredox- and electrocatalysis.

LPMO‐like activity of bioinspired copper complexes: from model substrate to extended polysaccharides

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Polysaccharide oxidative depolymerization is highly desirable to achieve recalcitrant biomass valorization. Inspired by recently discovered Lytic Polysaccharide Monooxygenases, mononuclear copper complexes have been prepared and studied in the literature. However, the activities were evaluated on different substrates and under various conditions. In this work we intended to establish a robust and reproducible activity assay, in aqueous solution at a pH close from neutrality and under mild conditions. We have evaluated several complexes on substrates of increasing complexity: the model substrate para-nitrophenyl-β-D-glucopyranoside (p-NPG), cellobiose (glucose dimer), as well as on extended substrates (chitin, cellulose and bagasse from agave). The different assays were compared and proof-of-concept that bioinspired complexes can oxidatively promote polysaccharide depolymerization was obtained. Finally, we measured level of hydroxyl radicals released by the complexes under comparable experimental conditions and mechanistic pathways are discussed.

Elucidating the Effect of Nitrogen Occupancy on the Hydrogen Evolution Reaction for a Series of Titanium Oxynitride Electrocatalysts

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Titanium nitride (TiN) shows desirable properties for use as an electrocatalyst and catalyst support, as it possesses high electrical conductivity and excellent corrosion resistance. However, the effect of oxygen content in the nitride lattice on its ability to drive the hydrogen evolution reaction (HER) is not well understood. Here, a series of titanium oxynitrides (TiNxO1-x) with varied nitrogen occupancy (0.53 ≤ x ≤1.0) in the bulk have been fabricated by ammonolysis. Their specific activities towards the HER were normalised by the surface areas determined by BET and electrochemical methods. We show that the specific activities of these oxynitrides are strongly correlated with the bulk nitrogen occupancy, despite the similar surface composition derived from XPS analysis. Furthermore, a removal of the oxygen content in the bulk or at the surface was attributed to the upgraded performance (up to 25% increase) seen during extended chronoamperometry (CA) tests. Our results show that minimising bulk oxygen content in this class of material is critical to achieve a more conductive and active material for the HER.

Orange peels and Chlorella vulgaris supplementation ameliorate gamma radiation‐induced oxidative stress by regulating TGF‐β and NOX2/NOX4 signaling pathways

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Abstract

Numerous studies revealed that Chlorella vulgaris and orange peels are potential sources for many valuable compounds such as flavonoids, which are natural polyphenols with antioxidant capacities that lessen oxidative stress via suppressing ROS levels. Thus, this study was designed to investigate their radioprotective efficiency either alone or in combination as natural food supplements. Sixty-four male Albino rats were divided into eight groups (n = 8) as follows: control, orange peel (10% in diet), C. vulgaris (1% in diet), orange peel + C. vulgaris, gamma irradiated (2Gy twice per week up to 8Gy), orange peel + gamma irradiation, C. vulgaris + gamma irradiation, and orange peel + C. vulgaris + gamma irradiation. After the experiment, blood serums were collected for biochemical analysis, whole bloods were collected for blood picture, bone marrows were collected for GSH, MDA, TGF-β, NOX2 and NOX4, and liver tissues were collected for histopathological evaluation. Current study revealed that exposure to gamma irradiation induced a significant disturbance in liver function markers (ALT and AST), kidney function markers (urea and creatinine), cholesterol and triglycerides levels in serum. In addition, a significant decrease in WBCs, RBCs, PLT, and Hb in blood of irradiated rats. Moreover, a significant elevation in TGF-β, NOX2, NOX4 activities, and MDA level, while showed a marked decrease in GSH concentration. Furthermore, hepatic inflammation appeared in the histopathological examination. Orange peels or C. vulgaris treatments showed acceptable amelioration in all measured parameters, combination between orange peels and C. vulgaris showed statistically significant additive amelioration in radiation induced disturbance.

Green Synthesis of 3,4‐Unsubstituted Isoquinolones through Rhodium(III)‐Catalyzed C‒H Activation and Annulation in Ethanol

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A mild and convenient synthesis of 3,4-unsubstituted isoquinolones has been achieved from N-methoxybenzamides and vinylene carbonate as an acetylene surrogate with a versatile rhodium(III) catalyst. The reaction proceeded at room temperature in biomass derived ethanol solvent. This protocol avoids the use of stoichiometric external oxidant, as the vinylene carbonate served as the internal oxidant. The C‒H/N‒H activation and annulation manifold proceeded with broad substrate scope and excellent levels of regioselectivities. The preliminary mechanistic studies suggest facile and reversible chelation-assisted C‒H rhodation. Diversification of 3,4-unsubstituted isoquinolones provide access to 4-substituted isoquinolones and 3,4-unsubstituted isoquinolines, which are complementary to the previously reported protocols.

Mechanistic Investigations into the Catalytic Mode of a Dehydratase Complex Involved in the Biosynthesis of Lantibiotic Cacaoidin

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Mechanistic Investigations into the Catalytic Mode of a Dehydratase Complex Involved in the Biosynthesis of Lantibiotic Cacaoidin

Herein, we report that the dehydration process of lantibiotic cacaoidin involves a dehydratase complex, which is composed of a phosphotransferase CaoK and a lyase CaoY in a 1 : 1 molar ratio. We show that fusing CaoK to CaoY enables the resulting enzyme CaoYK to exert enhanced solubility and dehydration activity.


Comprehensive Summary

Dehydration of serine/threonine residues necessitates the activity of a dehydratase enzyme (domain) during the biosynthesis of RiPP. Recently, it was reported that dehydration in the thioviridamide pathway relies on a distinct dehydratase complex that showcases the activities of a phosphotransferase TvaC for serine/threonine phosphorylation and a lyase TvaD for subsequent phosphate elimination. Herein, we report that dehydration reactions in the pathway of lantibiotic cacaoidin involves a similar dehydratase complex, CaoK/CaoY. Remarkably, this dehydratase complex exhibits flexible enzymatic activity and tolerates significant variations in its substrate peptide sequence. By binding with the leader peptide (LP) sequence of precursor peptide CaoA, the dehydration reactions proceed in a directional manner from the C-terminus of the core peptide (CP) to the N-terminus, and C-terminally truncated variants of CP are acceptable. We show that fusing CaoK to CaoY in a 1 : 1 molar ratio enables the resulting enzyme CaoYK to exert enhanced dehydration activity. CaoK binds with the LP to improve its own solubility and to ensure the phosphate transfer activity, while CaoY functions in a manner independently of LP. This work advances our understanding of the dehydration process during cacaoidin formation, and provides useful enzymes and methods for the studies of the rapidly emerging RiPPs.

1H‐Perfluorohexane—An efficient modifier for ethylene tri‐/tetramerization

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1H-Perfluorohexane—An efficient modifier for ethylene tri-/tetramerization

Synthesis routes and molecular structure of the PNSiP ligand.


Silicon-bridged/N, P (PNSiP) ligand/Cr (III) catalyst system based on different fluorinated hydrocarbons as modifiers have been explored for ethylene selective tri-/tetramerization. Modifiers like 1H-Perfluorohexane (1H-PFH), Hexafluorobenzene (HFB), and Perfluorobiphenyl (PFB) have been proven to show a significant influence on ethylene oligomerization toward 1-hexene and 1-octene of the catalytic system. Among them, 1H-PFH showed the most significant promotion effect in improving activity from 0.95 × 106 g·(mol Cr·h)−1 to as much as 5.66 × 106 g·(mol Cr·h)−1 at high temperature 90°C. Through the analysis of nuclear magnetic resonance (NMR) spectroscopy and ultraviolet visible diffuse reflectance spectroscopy (UV–vis DRS) results, we concluded that 1H-PFH can react with an amount of trimethylaluminum (TMA) contained in the cocatalyst modified methylaluminoxane (MMAO) and the solubility of Cr (III) in solvent can be increased after adding 1H-PFH. Furthermore, the possible reaction routes of 1H-PFH with TMA and MMAO were proposed.