Highly sodium-selective fluoroionophore based on conformational restriction of oligoethyleneglycol-bridged biaryl boron-dipyrromethene

A non-PET and non-PCT fluoroionophore has been designed and synthesized based on the combination of a biaryl boron-dipyrromethene fluorophore with an oligoethyleneglycol bridge. A specific red-shift response of absorption for NaClO4 in acetonitrile was demonstrated based on conformational restriction triggered by cation recognition at the bridge. The concentration of Na+ can be determined accurately using fluorescence due to a high extinction coefficient (epsilon = 50 000), a high fluorescence quantum yield (Phif = 0.68), and the sharpness of absorption and emission peaks of the boron-dipyrromethene derivative.     

Preparation,characteristics, and application of an asparaginase tube

Conditions for the preparation of an asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) tube using polyacrylamide gel were investigated. The apparent yield of activity of the asparaginase tube was about 20%; the activity of the tube was dependent on inner surface area. The optimum pH of the asparaginase tube shifted by 1 pH unit to the acid side in comparison with that of native enzyme. The apparent Michaelis constant of the tube was about 200 times higher than that of the native enzyme. The half-life of the asparaginase tube in continuous operation was estimated to be 16 days at 37°C. The tube was found to be resistant to attack by proteolytic enzyme. The L-asparagine level in blood plasma of a dog was lowered to 1/4 by the performance of an extracorporeal shunt using the asparaginase tube.     

Synthesis of surface organopalladium intermediates in coupling reactions: the mechanistic insight

The design and synthesis of surface transient organometallic intermediates on nanopalladium supported on layered double hydroxides is conceived and developed for the first time. The formation of only one STO intermediate in all the Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions during their reaction sequences and the excellent isolated yields of each of the coupling products from the corresponding organometallic complexes not only validate the mechanism but also demonstrate the evolution of the single-site heterogeneous catalyst.     

Metal-Free Photoredox-Catalyzed Hydrodefluorination of Fluoroarenes Utilizing Amide Solvent as Reductant

A metal-free photoredox-catalyzed hydrodefluorination of fluoroarenes was achieved by using N,N,N’,N’-tetramethyl-para-phenylenediamine ( 1 ) as a strong photoreduction catalyst. This reaction was applicable not only to electron-rich monofluoroarenes but also to polyfluoroarenes to afford non-fluorinated arenes. The experimental mechanistic studies indicated that the amide solvent NMP plays an important role for regeneration of the photocatalyst, enabling additive-free photoreduction catalysis.     

Tungsten(0)- and rhenium(I)-catalyzed tandem cyclization of acetylenic dienol silyl ethers based on geminal carbo-functionalization of alkynes

Tungsten(0)- and rhenium(I)-catalyzed reactions of acetylenic dienol silyl ethers based on the concept of geminal carbo-functionalization of alkynes are reported. Treatment of 3-siloxy-1,3-diene-7-ynes with catalytic amounts of [W(CO)(6)] or [ReCl(CO)(5)] under photoirradiation conditions gives synthetically useful bicyclo[3.3.0]octane derivatives in good yields. Extremely high catalytic activity is noted for the rhenium(I) complex. The reaction has been extended to substrates containing a nitrogen atom in their tethers. In this case, two kinds of synthetically useful heterocyclic compounds-the 2-azabicyclo[3.3.0]octane derivatives 9 and the monocyclic dihydropyrroles 10, with allenyl substituents-are obtained, and selective preparation of either product can be achieved through the use of an appropriate combination of the nitrogen substituent and the type of the rhenium(I) catalyst. The 2-azabicyclo[3.3.0]octane derivatives 9 are obtained selectively by carrying out treatment of N-Ns derivatives in the presence of [ReCl(CO)(4)(PPh(3))], whereas the dihydropyrrole derivatives 10 are obtained by treatment of N-Mbs derivatives with [ReCl(CO)(5)]/AgSbF(6) . Finally, we have applied this geminal carbo-functionalization to one-carbon-elongated substrates containing N-Ts moieties in their tethers. Selective 5-exo cyclization is achieved in the presence of gold(I) or rhenium(I) catalysts, whereas 6-endo cyclization is observed on use of [W(CO)(6)].     

Detection of reactive tetrahedral intermediates in a deep cavitand with an introverted functionality

Labile hemiaminal intermediates are stabilized by binding in a deep cavitand with an introverted aldehyde functionality. The aldehyde is attached to the cavitand via an anthracene spacer that rotates rapidly about the cavitand rim. The half-lives of these hemiaminals vary from 30 min to over 100 h at ambient temperature, due to hydrogen bonding with the organized peptide-like framework at the cavitand rim. The intermediates are sufficiently long-lived to allow study by 2D NMR techniques requiring many hours of acquisition time. Mechanistic analysis of the dehydration step shows first-order kinetics. The analogous "extroverted" reaction was also performed, where the addition took place outside the cavitand, displaying standard steady-state kinetics; no hemiaminal was observed. The cavitand shows strong selectivity based not on binding affinity but upon the rate of the product-forming step. A 10:1 ratio of product imines was obtained, while the initial binding ratio was 1:1. The cavitand acts as a mimic of enzymes in that it uses weak binding forces to stabilize reactive intermediates and isolates them from the medium. The synthetic environment allows direct detection and analysis of the intermediates, as opposed to natural systems that must be analyzed indirectly.     

Ni(0)-promoted hydroxycarboxylation of 1,2-dienes by reaction with CO2 and O2

[structure: see text]. A novel method for the preparation of hydroxy carboxylic acid derivatives has been developed by O2-oxidation of pi-allylnickel intermediates generated by Ni(0)-mediated coupling of 1,2-dienes with CO2.     

Energy-gaining formation and catalytic behavior of active structures in a SiO(2)-supported unsaturated Ru complex catalyst for alkene epoxidation by DFT calculations

The formation and catalytic behavior of active structures in a SiO(2)-supported unsaturated Ru complex catalyst for alkene epoxidation were studied by means of hybrid density functional theory (DFT) calculations. An energy-gaining route for the catalyst activation was found to allow the formation of active unsaturated Ru complexes and the remarkable alkene epoxidation via an exothermic reaction path between isobutyraldehyde and oxygen. In the proposed Bartlett mechanism, Ru promotes the formation of peracid intermediate and facilitates the intermolecular hydrogen transfer in the peracid intermediate, while alkene molecules do not directly coordinate to the Ru site. It was found that stilbene epoxidation is easier to achieve than ethene epoxidation thanks to the electron donating phenyl groups.