A new fluorinated azidoethane1-azido-1,1,2,2-tetrafluoroethanewas prepared in quantitative yield by the addition of an azide anion to tetrafluoroethylene in a protic medium. The title azide was ...shown to be thermally stable and insensitive to impact. Copper(I)-catalyzed 3 + 2 cycloaddition with alkynes afforded 4-substituted N-tetrafluoroethyl-1,2,3-triazoles which underwent rhodium(II)-catalyzed transannulation with nitriles to novel N-tetrafluoroethylimidazoles or the reaction with triflic acid to enamido triflates. 3 + 2 Cycloaddition of the title azide with primary amines afforded novel 5-difluoromethyl tetrazoles.
A mild trifluoromethylation reaction of N,N‐disubstituted hydroxylamines that is tolerant towards a variety of functional groups, including nitriles, alcohols, ketones, esters, amides, imides, and ...nitrogen heterocycles, is reported. The key feature of this reaction is the activation of the CF3 reagent with either trimethylsilyl triflate or LiClO4 and partial or full deprotonation of the substrate with tetramethylguanidine or lithium diisopropylamide. Products were obtained in up to 80 % yield. Preliminary mechanistic studies suggested that the reaction follows a radical pathway in which the deprotonated hydroxylamine and a Lewis or Brønsted acid activated CF3 reagent engages in a single‐electron‐transfer step to generate a pair of radicals that recombine to afford the desired product. The trifluoromethylation procedure was successfully used in the modification of secondary nitrogen groups of pharmaceutically relevant targets (Fluoxetine and Mefloquine), which afforded new derivatives containing a novel N‐trifluoromethoxy moiety.
Electrophilic trifluoromethylation of dialkyl hydroxylamines with hypervalent iodine(III) reagents gives access to compounds containing the virtually unexplored NOCF3 functional group. Aspects concerning synthesis, properties, and reaction mechanism are presented. The transformation is also applicable to hydroxylamines derived from common drugs and shows a broad functional group tolerance.
Concentration profiles and overall flow parameters were measured in a 0.37-mm-sand-mixture flow above a plane stationary deposit in a pressurized circular pipe of the inner diameter of 150 mm. The ...new data and additional data from the literature are used to propose a tentative transport formula of the Meyer-Peter and Müller type, and a slip-ratio formula, for flows at high shear stress in enclosed conduits.
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Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•Fine-to-medium sand addition to coarse-sand slurry flow reduces friction in pipe.•Friction reduction is result of flow stratification in bimodal slurry flow.•Thin layer of finer particles separates ...sliding bed from pipe wall.•PTV & PIV detect different velocities of coarse and fine particles at pipe bottom.•Friction reducing mechanism can be implemented to models for bimodal slurry flow.
Pipe flows of bimodal aqueous slurries of two fractions of sand (coarse sand of particle mass-median size of 1.56 mm and fine-to-medium sand of mass-median size of 0.22 mm) are tested in a laboratory loop (pipe internal diameter of 100 mm) to study the frictional loss reduction due to the presence of the finer fraction in the bimodal slurry. The tested bimodal slurry flows (mean solids volumetric concentrations of 0.23, 0.30, 0.45 respectively) are compared with their coarse slurry counterparts (flows of one-species slurry at solids concentrations of 0.17, 0.24, 0.34 respectively, without the finer fraction) in tests which include measurements of solids distribution in a pipe cross section and measurements of local velocity of solid particles at the bottom of the pipe. The tests reveal a presence of a sliding bed in the bimodal slurry flow and a development of a thin fine-particle layer at the interface between the bottom of the sliding bed and the pipe wall. The measured difference in local velocities of fine particles and coarse particles at the bottom of the pipe indicates that the fine-particle layer effectively separates the sliding bed from the pipe wall hence it is responsible for the reduction of sliding friction at the wall and reduction of the overall frictional loss in bimodal flow compared to its coarse slurry counterpart. The identified loss reducing mechanism can improve modelling of stratified settling slurry flows composed of solids fractions of different sizes interacting with each other in a pipe.
New open-chain and water-soluble hypervalent iodine reagents were synthesized and used for the transfer of fluoroalkyl groups to sulfur atoms of cysteine and cysteine-containing peptides under ...biocompatible conditions. Some of the reagents displayed excellent reactivity despite their limited stability in aqueous media. In reactions with a short cysteine-containing peptide, in addition to the expected
S
-fluoroalkylated product, a range of side-products were obtained. The amount of side-products depended on the conditions used (type of reagent, concentration, and pH). With highly activated hypervalent iodine reagents, a new reactive mode was observed - reaction with disulfides to form fluoroalkyl thiols.
New activated and water-soluble hypervalent iodine reagents were synthesized and used for fluoroalkyl group transfer to cysteine and in reactions with disulfides.
An electrophilic trifluoromethylation of ketene silyl acetals (KSAs) by hypervalent iodine reagents 1 and 2 has been developed. The reaction proceeds under very mild conditions in the presence of a ...catalytic amount of trimethylsilyl bis(trifluoromethanesulfonyl)imide (up to 2.5 mol %) as a Lewis acid providing a direct access to a variety of secondary, tertiary, and quaternary α-trifluoromethyl esters and lactones in high yield (up to 98%).
An extended stereoscopic method, which identifies, and tracks particles based on their colour in solid-liquid flow, is tested for its capability to separately measure velocity distributions of ...particles of two fractions transported as bimodal sediment mixture in water flow through a laboratory flume. The principle of the tested method extension is a use of colour-based processing of images collected by two high-speed cameras which enables to filter out particles of one fraction from the image and leave particles of the other fraction in the image based on a selected colour hue range. The modified images are then processed by the original stereoscopic method to produce velocity distribution of particles of the individual fraction in the flow. The method extension is first tested in simple vertical flow carrying neutrally buoyant spherical particles of two distinct colours in a recirculation cell. In the next step, lightweight plastic particles of two fractions of different properties (size, shape, density) and colours are introduced to flow through a laboratory flume and velocity distributions of the two fractions are measured separately at flow conditions which mimic intense transport of bimodal combined-load in an open channel. Results exhibit a very good agreement with previous measurements with unimodal sediment in hydraulically similar flow.
Vertical concentration distributions of solids conveyed in Newtonian fluids can be modelled using Rouse-Schmidt type distributions. Observations of solids conveyed in turbulent low Reynolds number ...visco-plastic carriers, suggest that solids are more readily suspended than their Newtonian counterparts, producing higher concentrations in the centre of the pipe. A Newtonian concentration profile model was adapted to include typical turbulent viscosity distributions within the pipe and particle motion calculated using non-Newtonian sheared settling. Predictions from this and the unmodified model, using the same wall viscosity, are compared with the chord averaged profile extracted from tomographic data obtained using a 50 mm horizontal pipe.
Disuccinimidyl dibutyric urea (DSBU) is a mass spectrometry (MS)-cleavable cross-linker that has multiple applications in structural biology, ranging from isolated protein complexes to comprehensive ...system-wide interactomics. DSBU facilitates a rapid and reliable identification of cross-links through the dissociation of its urea group in the gas phase. In this study, we further advance the structural capabilities of DSBU by remodeling the urea group into an imide, thus introducing a novel class of cross-linkers. This modification preserves the MS cleavability of the amide bond, granted by the two acyl groups of the imide function. The central nitrogen atom enables the introduction of affinity purification tags. Here, we introduce disuccinimidyl disuccinic imide (DSSI) as a prototype of this class of cross-linkers. It features a phosphonate handle for immobilized metal ion affinity chromatography enrichment. We detail DSSI synthesis and describe its behavior in solution and in the gas phase while cross-linking isolated proteins and human cell lysates. DSSI and DSBU cross-links are compared at the same enrichment depth to bridge these two cross-linker classes. We validate DSSI cross-links by mapping them in high-resolution structures of large protein assemblies. The cross-links observed yield insights into the morphology of intrinsically disordered proteins and their complexes. The DSSI linker might spearhead a novel class of MS-cleavable and enrichable cross-linkers.
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