Binaphthyl-based chiral covalent organic frameworks for chiral drug separation.

Separation of racemic drugs is of great importance and interest in chemistry and pharmacology. Here, we report the bottom-up synthesis of the binaphthyl-based chiral covalent organic frameworks (CCOFs), (R)-BHTP-COF. Then, high-performance liquid chromatography (HPLC) columns were prepared using (R)-BHTP-COF as a chiral stationary phase (CSP).

Mechanistic Investigation on the Regioselectivity of Electrochemical Co(II)-Catalyzed [2 + 2 + 2] Cycloaddition of Terminal Acetylenes.

In this paper, the regioselectivity of electrochemical Co(II)-catalyzed [2 + 2 + 2] cycloaddition of terminal alkynes was investigated using density functional theory. We explored in detail the energy profiles for both 1,2,4- and 1,3,5-regioselectivity pathways and revealed the origin of the regioselectivity. Two kinds of conformational isomers derived from the different coordination modes of alkynes with cobaltacyclopentadiene have been found, which were formed through electrochemically mediated redox processes.

From antioxidant defense to genotoxicity: Deciphering the tissue-specific impact of AgNPs on marine clam Ruditapes philippinarum.

The escalating use of silver nanoparticles (AgNPs) across various sectors for their broad-spectrum antimicrobial capabilities, has raised concern over their potential ecotoxicological effects on aquatic life. This study explores the impact of AgNPs (50 μg/L) on the marine clam Ruditapes philippinarum, with a particular focus on its gills and digestive glands. We adopted an integrated approach that combined in vivo exposure, biochemical assays, and transcriptomic analysis to evaluate the toxicity of AgNPs.

Seawater quality criteria and ecotoxicity risk assessment of zinc oxide nanoparticles based on data of resident marine organisms in China.

Water quality criteria (WQC) for zinc oxide nanoparticles (ZnO NPs) are crucial due to their extensive industrial use and potential threats to marine organisms. This study conducted toxicity tests using marine organisms in China, revealing LC or EC values for ZnO NPs ranging from 0.36 to 95.

Carboxylic-Phosphoric Anhydrides as Direct Electrophiles for Decarbonylative Hirao Cross-Coupling of Carboxylic Acids: DFT Investigation of Mechanistic Pathway.

In this anniversary issue, we present a DFT study of the mechanism of decarbonylative Hirao cross-coupling of carboxylic-phosphoric anhydrides to afford aryl phosphonates. Traditionally, the direct activation of carboxylic acids to participate in decarbonylative couplings is performed in the presence of carboxylic acid anhydride activators. We discovered that direct dehydrogenative decarbonylative phosphorylation of benzoic acid can be performed in high yield via dehydrogenative and decarbonylative coupling in the presence of phosphite as dual activating and nucleophilic reagent, enabling direct decarbonylative phosphorylation.

Identification of Alkoxy Radicals as Hydrogen Atom Transfer Agents in Ce-Catalyzed C-H Functionalization.

The intermediacy of alkoxy radicals in cerium-catalyzed C-H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)-alkoxide complexes have been synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance and transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified alkoxy radicals as the sole heteroatom-centered radical species generated via ligand-to-metal charge transfer (LMCT) excitation.

Effects of electrostatic drag on the velocity of hydrogen migration - pre- and post-transition state enthalpy/entropy compensation.

Ab initio molecular dynamics calculations were used to explore the underlying factors that modulate the velocity of hydrogen migration for 1,2 hydrogen shifts in carbocations in which different groups interact noncovalently with the migrating hydrogen. Our results indicate that stronger electrostatic interactions between the migrating hydrogen and nearby π-systems lead to slower hydrogen migration, an effect tied to entropic contributions from the hydrogen + neighboring group substructures.

Phytochemical identification of Lithocarpus polystachyus extracts by ultra-high-performance liquid chromatography-quadrupole time-of-flight-MS and their protein tyrosine phosphatase 1B and α-glucosidase activities.

Lithocarpus polystachyus leaves exhibit antidiabetic activity and is consumed as a herbal tea in China. In this study, phytochemical profiles of L. polystachyus leaves were identified and characterized by ultra-high-performance liquid chromatography-quadrupole time-of-flight-MS in both positive and negative ion modes.

A Computational Mechanistic Study of Pd(II)-Catalyzed Enantioselective C(sp)-H Borylation: Roles of APAO Ligands.

A computational mechanistic study has been performed on Pd(II)-catalyzed enantioselective reactions involving acetyl-protected aminomethyl oxazolines (APAO) ligands that significantly improved reactivity and selectivity in C(sp)-H borylation. The results support a mechanism including initiation of C(sp)-H bond activation generating a five-membered palladacycle and ligand exchange, followed by HPO-promoted transmetalation. These resulting Pd(II) complexes further undergo sequential reductive elimination by coordination of APAO ligands and protonation to afford the enantiomeric products and deliver Pd(0) complexes, which will then proceed by oxidation and deprotonation to regenerate the catalyst.

Mechanistic Exploration of Cp*Co/Rh-Catalyzed Carboamination/Olefination of N-Phenoxyacetamides with Alkenes.

A computational study of Cp*Co/Rh-catalyzed carboamination/olefination of N-phenoxyacetamides with alkenes was carried out to elucidate the catalyst-controlled chemoselectivity. The reaction of the two catalysts shares a similar process that involves N-H and C-H activation as well as alkene insertion. Then the reaction bifurcates at the generated seven-membered metallacycle.

Mechanistic Exploration of the Competition Relationship between a Ketone and C═C, C═N, or C═S Bond in the Rh(III)-Catalyzed Carbocyclization Reactions.

The introduction of a C═O, C═C, C═S, or C═N bond has emerged as an effective strategy for carbocycle synthesis. A computational mechanistic study of Rh(III)-catalyzed coupling of alkynes with enaminones, sulfoxonium ylides, or α-carbonyl-nitrones was carried out. Our results uncover the roles of dual directing groups in the three substrates and confirm that the ketone acts as the role of the directing group while the C═C, C═N, or C═S bond serves as the cyclization site.

Highly sensitive and selective detection of Pd ions using a ferrocene-rhodamine conjugate triple channel receptor in aqueous medium and living cells.

Herein, a novel ferrocene-rhodamine receptor conjugated with an allylimine bridge was facilely synthesized. This triple channel receptor can selectively and sensitively monitor Pd ions through chromogenic, fluorogenic and electrochemical assays in aqueous medium with a low detection limit (8.46 × 10 M) and a fast response (<8 min).

The underlying factors controlling the Pd-catalyzed site-selective alkenylation of aliphatic amines.

The Pd(ii)-catalyzed site-selective δ-C(sp)-H alkenylation in the presence of more accessible γ-C(sp)-H bonds is investigated by DFT calculations. Migratory insertion is found to be both the rate-limiting and the selectivity-determining step. The origin of the unusual site-selectivity is originally attributed to the different steric repulsion between the alkyne and palladacycle; however, our theoretical results reveal that the inherent electronic effect instead of steric repulsion determines the site-selectivity.

Solvent Mediating a Switch in the Mechanism for Rhodium(III)-Catalyzed Carboamination/Cyclopropanation Reactions between N-Enoxyphthalimides and Alkenes.

Recently, a new synthetic methodology of rhodium-catalyzed carboamination/cyclopropanation from the same starting materials at different reaction conditions has been reported. It provides an efficient strategy for the stereospecific formation of both carbon- and nitrogen-based functionalities across an alkene. Herein we carried out a detailed theoretical mechanistic exploration for the reactions to elucidate the switch between carboamination and cyclopropanation as well as the origin of the chemoselectivity.

Computational Mechanistic Study of Redox-Neutral Rh(III)-Catalyzed C-H Activation Reactions of Arylnitrones with Alkynes: Role of Noncovalent Interactions in Controlling Selectivity.

The mechanism of redox-neutral Rh(III)-catalyzed coupling reactions of arylnitrones with alkynes was investigated by density functional theory (DFT) calculations. The free energy profiles associated with the catalytic cycle, involving C(sp)-H activation, insertion of alkyne, transfer of O atom, cyclization and protodemetalation, are presented and analyzed. An overwhelming preference for alkyne insertion into Rh-C over Rh-O is observed among all pathways, and the most favorable route is determined.

The intrinsically disordered N-terminal domain of thymidylate synthase targets the enzyme to the ubiquitin-independent proteasomal degradation pathway.

The ubiquitin-independent proteasomal degradation pathway is increasingly being recognized as important in regulation of protein turnover in eukaryotic cells. One substrate of this pathway is the pyrimidine biosynthetic enzyme thymidylate synthase (TS; EC 2.1.

Role of N-terminal residues in the ubiquitin-independent degradation of human thymidylate synthase.

Thymidylate synthase (TS) catalyses the reductive methylation of dUMP to form dTMP, a reaction that is essential for maintenance of nucleotide pools during cell growth. Because the enzyme is indispensable for DNA replication in actively dividing cells, it is an important target for cytotoxic drugs used in cancer chemotherapy, including fluoropyrimidines (e.g.

Structural determinants for the intracellular degradation of human thymidylate synthase.

Thymidylate synthase (EC 2.1.1.