Hydrogen Fluoride-pyridine Research Articles

Fluorination of vanadates with organic fluorinating agents

The organic fluorinating agents [bis(2-methoxyethyl)amino]sulfur trifluoride (Deoxo-fluor®), diethylaminosulfur trifluoride (DAST), and N-fluorobenzenesulfonimide (NFSI) were used to inspect the efficiency of fluorination of monovanadate, HxVO4(3−x)− (V1), and decavanadate, HxV10O28(6−x)− (V10), in solution by 51V NMR spectroscopy. It was observed that either VOF4− or VO2F2− can be generated in acetonitrile solutions at room temperature after one hour selectively for HxVO4(3−x)−, while HxV10O28(6−x)− is more sensitive towards reduction and only NFSI can be used to generate VOF4−. The differences in reactivity can be attributed to the electrophilicity of fluorine in Deoxo-fluor® and DAST, and its nucleophilicity in NFSI. Tetrabutylammonium fluoride, triethylamine trifluoride, and hydrogen fluoride–pyridine adduct were also used under the same conditions for comparison of the efficiency and selectivity of fluorination. It was observed that only HF.pyridine provided a complete transformation of V1 and V10 into VOF4−. The pilot experiments introduced in this work are the first example of fluorination of polyoxometalates with organic fluorination agents and other less commonly used fluorides with organic cations and show their great potential in the synthesis of polyoxometalates with fluorido ligand.

Conversion Reactions and Redox Changes on the Surface of Lithium-Ion Battery Cathode Materials during Chemical Vapor Treatment for ALD

Atomic layer deposition (ALD) has emerged as a promising technology for applying ultrathin protective coatings on lithium-ion battery (LIB) cathode surfaces to improve their cycling stability. While there have been numerous reports evaluating the electrochemical performance of these surface-modified cathode materials, the chemical changes induced on the surface of the cathode materials by the ALD coatings and the individual ALD precursors are not fully studied. We performed a systematic investigation to understand the interfacial changes of 12 different cathode materials upon coating with aluminum oxide (Al2O3) using trimethyl aluminum (TMA) and H2O, and aluminum fluoride (AlF3) using TMA and hydrogen fluoride pyridine (HFPy). We also explored the effects of the individual TMA and HFPy precursors on the cathode surfaces. The surface composition and microstructure of these cathode materials, which range from simple transition metal oxides (e.g., NiO and MnO) to complex multi-element cathode materials (e.g., LiNixMn1-x-yCoyO2, NMC), were studied via X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The XPS measurements reveal that the transition metals in the cathode materials undergo selective oxidation/reduction depending upon the nature of the precursor, the coating, and the cathode material. Furthermore, XPS and STEM measurements show the conversion of surface carbonate species to the corresponding metal fluorides upon HF exposure. This conversion reaction is self-limiting but extends hundreds of nanometers below the surface in the case of Li2CO3. ALD and chemical vapor treatment provide new avenues to systematically control the interface of the cathode materials in LIBs that are not possible by conventional coating methods.

Elucidating the Surface Chemistry of Atomic Layer Deposition on Complex Metal Oxide Cathode Materials

Current research in the field of lithium-ion batteries (LIBs) is geared towards stabilizing the electrode-electrolyte interfaces to improve the LIB cycling stability and storage capacity. In particular, irreversible reactions between non-aqueous electrolytes and metal oxide cathode surfaces can corrode the active material and reduce LIB performance. Protective coatings on the cathode surface can mitigate these issues, and atomic layer deposition (ALD) is well-suited to prepare ultrathin, conformal, corrosion-resistant barrier layers on the surface of the electrodes. While there are reports that some metal oxide and metal fluoride barrier coatings on select cathodes can improve LIB performance, there is no general understanding of why certain ALD coating/cathode combinations are beneficial while others are not. This problem is complicated by the move towards complex LIB cathodes such as lithium nickel manganese cobalt oxide (NMC) materials that may have multiple phases present on the surface including hydroxides and carbonates. Understanding how the ALD precursors react on these materials to create protective coatings is challenging and requires a systematic study to elucidate the surface chemistry of the ALD precursors with each component of the complex oxide surface. Therefore, this work aims at understanding the effects of ALD precursor exposures and ALD coatings on the surface electronic structure of LIB cathode materials.Al2O3 and AlF3 were selected as prototypical metal oxide and metal fluoride surface coatings as they are widely reported in literature due to their ability to act as barrier coatings on cathodes. Additionally, the ALD precursor vapors used for these coatings, i.e., trimethyl aluminium (TMA) and hydrogen fluoride pyridine (HFpy), were adsorbed on the surfaces of these cathode materials under typical ALD conditions to observe their effect on the surface composition and electronic state. The cathode materials chosen for this study included all of the component oxides for NMC cathodes (i.e. Li, Ni, Mn, and Co) in all common oxidation states (e.g., MnO, MnO2, and Mn2O3) as well as selected ternary, quaternary, and quinary forms. In each case, the substrate surface was characterized using X-ray photoelectron spectroscopy (XPS) before and after surface treatment to elucidate changes in the surface composition and charge state induced by the individual ALD precursors and the ultrathin coating. Overall, this fundamental study will assist in the design and synthesis of novel ALD barrier coatings that demonstrate the highest sensitivity on multi-element cathode materials, ultimately leading to robust electrode-electrolyte interfaces for high-performance LIBs.

One-Step Synthesis of 2-Fluoroadenine Using Hydrogen Fluoride Pyridine in a Continuous Flow Operation

We report the development of a one-pot synthesis of 2-fluoroadenine from an inexpensive 2,6-diaminopurine starting material using diazonium chemistry in a continuous fashion. Given the sensitivity of this transformation to temperature, we conducted critical experiments to study the exothermicity of the reaction and the heat removal, which were critical for the development of the process. Our goal was to improve the yield and purity of this pharmaceutical intermediate (2-fluoroadenine) and develop a more robust process.

The Major Storage Protein in Potato Tuber Is Mobilized by a Mechanism Dependent on Its Phosphorylation Status

The role of the protein phosphorylation mechanism in the mobilization of vegetative storage proteins (VSPs) is totally unknown. Patatin is the major VSP of the potato (Solanum tuberosum L.) tuber that encompasses multiple differentially phosphorylated isoforms. In this study, temporal changes in the phosphorylation status of patatin isoforms and their involvement in patatin mobilization are investigated using phosphoproteomic methods based on targeted two-dimensional electrophoresis (2-DE). High-resolution 2-DE profiles of patatin isoforms were obtained in four sequential tuber life cycle stages of Kennebec cultivar: endodormancy, bud break, sprouting and plant growth. In-gel multiplex identification of phosphorylated isoforms with Pro-Q Diamond phosphoprotein-specific stain revealed an increase in the number of phosphorylated isoforms after the tuber endodormancy stage. In addition, we found that the phosphorylation status of patatin isoforms significantly changed throughout the tuber life cycle (P < 0.05) using the chemical method of protein dephosphorylation with hydrogen fluoride-pyridine (HF-P) coupled to 2-DE. More specifically, patatin phosphorylation increased by 32% from endodormancy to the tuber sprouting stage and subsequently decreased together with patatin degradation. Patatin isoforms were not randomly mobilized because highly phosphorylated Kuras-isoforms were preferably degraded in comparison to less phosphorylated non-Kuras isoforms. These results lead us to conclude that patatin is mobilized by a mechanism dependent on the phosphorylation status of specific isoforms.

Regiospecific Three-Component Aminofluorination of Olefins via Photoredox Catalysis.

Direct visible-light-mediated aminofluorination of styrenes has been developed with high regioselectivity. Shelf-stable N-Ts-protected 1-aminopyridine salt was used as the nitrogen-radical precursor, and the commercially available hydrogen fluoride-pyridine was used as the nucleophilic fluoride source. The synthesis of an analogue of LY503430 was performed to demonstrate the synthetic value of this strategy.

Catalytic, asymmetric difluorination of alkenes to generate difluoromethylated stereocenters.

Difluoromethyl groups possess specific steric and electronic properties that invite their use as chemically inert surrogates of alcohols, thiols, and other polar functional groups important in a wide assortment of molecular recognition processes. We report here a method for the catalytic, asymmetric, migratory geminal difluorination of β-substituted styrenes to access a variety of products bearing difluoromethylated tertiary or quaternary stereocenters. The reaction uses commercially available reagents (m-chloroperbenzoic acid and hydrogen fluoride pyridine) and a simple chiral aryl iodide catalyst and is carried out readily on a gram scale. Substituent effects and temperature-dependent variations in enantioselectivity suggest that cation-π interactions play an important role in stereodifferentiation by the catalyst.

Intramolecular oxyacetoxylation of N-allylamides: an expeditious synthesis of oxazolines and oxazines by using a PhI(OAc)2/hydrogen fluoride-pyridine system.

The synthesis of oxazolines and oxazines from N-allylamides was accomplished via an unprecedented reaction set. This reaction involved an intramolecular cyclization of N-allylamides resulting from nucleophilic attack of the allylamine on the benzoxazin-4-one. Unlike the previous literature, the isolable N-allylamide could readily be subjected to exo and endo fashion ring-closure under conditions to afford the title compounds.

Evidence for phosphorylation of the major seed storage protein of the common bean and its phosphorylation-dependent degradation during germination

Phaseolin is the major seed storage protein of common bean, Phaseolus vulgaris L., accounting for up to 50% of the total seed proteome. The regulatory mechanisms responsible for the synthesis, accumulation and degradation of phaseolin in the common bean seed are not yet sufficiently known. Here, we report on a systematic study in dormant and 4-day germinating bean seeds from cultivars Sanilac (S) and Tendergreen (T) to explore the presence and dynamics of phosphorylated phaseolin isoforms. High-resolution two-dimensional electrophoresis in combination with the phosphoprotein-specific Pro-Q Diamond phosphoprotein fluorescent stain and chemical dephosphorylation by hydrogen fluoride-pyridine enabled us to identify differentially phosphorylated phaseolin polypeptides in dormant and germinating seeds from cultivars S and T. Phosphorylated forms of the two subunits of type α and β that compose the phaseolin were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) and MALDI-TOF/TOF tandem MS. In addition, we found that the levels of phosphorylation of the phaseolin changed remarkably in the seed transition from dormancy to early germination stage. Temporal changes in the extent of phosphorylation in response to physiological and metabolic variations suggest that phosphorylated phaseolin isoforms have functional significance. In particular, this prospective study supports the hypothesis that mobilization of the phaseolin in germinating seeds occurs through the degradation of highly phosphorylated isoforms. Taken together, our results indicate that post-translational phaseolin modifications through phosphorylations need to be taken into consideration for a better understanding of the molecular mechanisms underlying its regulation.

Hypervalent Iodine Mediated para-Selective Fluorination of Anilides

A metal-free method for the direct regioselective fluorination of anilides has been developed. In the presence of bis(tert-butylcarbonyloxy)iodobenzene (PhI(OPiv)(2)) and hydrogen fluoride-pyridine, the para-fluorination products of anilides were obtained in moderate to good yields. Because of its operational safety and the use of readily available reagents, this new procedure provides facile access to a variety of para-fluorinated anilides.

Metal-free intramolecular aminofluorination of alkenes mediated by PhI(OPiv)2/hydrogen fluoride–pyridine system

A convenient, metal-free intramolecular aminofluorination of alkenes has been developed. Employing readily available PhI(OPiv)(2) and hydrogen fluoride-pyridine in the presence of BF(3)·OEt(2), tosyl-protected pent-4-en-1-amines were converted to 3-F-piperidines in one step in good yields as well as high stereoselectivity.

Reaction of 1,2-Orthoesters with HF−Pyridine: A Method for the Preparation of Partly Unprotected Glycosyl Fluorides and Their Use in Saccharide Synthesis

Glycosyl fluorides can be prepared in an efficient manner by treatment of pyranose- or furanose-derived 1,2-orthoesters, with hydrogen fluoride pyridine (HF-py). The method is compatible with the presence of a variety of protecting groups, including tert-butyldiphenyl silyl ethers, and can be applied to sugar derivatives with free hydroxyl groups, thus avoiding the need for the protection-deprotection steps.

A study of the Candida albicans cell wall proteome

Considering the importance of proteins in the structure and function of the cell wall of Candida albicans, we analyzed the cell wall subproteome of this important human pathogen by LC coupled to MS (LC-MS) using different protein extraction procedures. The analyzed samples included material extracted by hydrogen fluoride-pyridine (HF-pyridine), and whole SDS-extracted cell walls. The use of this latter innovative procedure gave similar data as compared to the analysis of HF-pyridine extracted proteins. A total of 21 cell wall proteins predicted to contain a signal peptide were identified, together with a high content of potentially glycosylated Ser/Thr residues, and the presence of a GPI motif in 19 of them. We also identified 66 "atypical" cell wall proteins that lack the above-mentioned characteristics. After tryptic removal of the most accessible proteins in the cell wall, several of the same expected GPI proteins and the most commonly found "atypical" wall proteins were identified. This result suggests that proteins are located not only at the cell wall surface, but are embedded within the cell wall itself. These results, which include new identified cell wall proteins, and comparison of proteins in blastospore and mycelial walls, will help to elucidate the C. albicans cell wall architecture.

IPy2BF4/HF-Pyridine: A New Combination of Reagents for the Transformation of Partially Unprotected Thioglycosides and n-Pentenyl Glycosides to Glycosyl Fluorides

The combination of bis(pyridinium)iodonium (I) tetrafluoroborate (IPy2BF4), and hydrogen fluoride pyridine (HF-py) forms an iodine monofluoride (IF) synthetic equivalent that can be used in the preparation of partially unprotected glycosyl fluorides from partially unprotected n-pentenyl glycosides and thioglycosides, thus avoiding the need for the protection/deprotection steps normally required in that transformation.

Biomechanics of isolated tomato (Solanum lycopersicum L.) fruit cuticles: the role of the cutin matrix and polysaccharides

The mechanical characteristics of the cuticular membrane (CM), a complex composite biopolymer basically composed of a cutin matrix, waxes, and hydrolysable polysaccharides, have been described previously. The biomechanical behaviour and quantitative contribution of cutin and polysaccharides have been investigated here using as experimental material mature green and red ripe tomato fruits. Treatment of isolated CM with anhydrous hydrogen fluoride in pyridine allowed the selective elimination of polysaccharides attached to or incrusted into the cutin matrix. Cutin samples showed a drastic decrease in elastic modulus and stiffness (up to 92%) compared with CM, which clearly indicates that polysaccharides incorporated into the cutin matrix are responsible for the elastic modulus, stiffness, and the linear elastic behaviour of the whole cuticle. Reciprocally, the viscoelastic behaviour of CM (low elastic modulus and high strain values) can be assigned to the cutin. These results applied both to mature green and red ripe CM. Cutin elastic modulus, independently of the degree of temperature and hydration, was always significantly higher for the ripe than for the green samples while strain was lower; the amount of phenolics in the cutin network are the main candidates to explain the increased rigidity from mature green to red ripe cutin. The polysaccharide families isolated from CM were pectin, hemicellulose, and cellulose, the main polymers associated with the plant cell wall. The three types of polysaccharides were present in similar amounts in CM from mature green and red ripe tomatoes. Physical techniques such as X-ray diffraction and Raman spectroscopy indicated that the polysaccharide fibres were mainly randomly oriented. A tomato fruit CM scenario at the supramolecular level that could explain the observed CM biomechanical properties is presented and discussed.

SYNTHESIS AND IN VITRO ANTI-HCV ACTIVITY OF β-D- and L-2′-DEOXY-2′-FLUORORIBONUCLEOSIDES

Based on the discovery of β-D-2′-deoxy-2′-fluorocytidine as a potent anti-hepatitis C virus (HCV) agent, a series of β-D- and l-2′-deoxy-2′-fluororibonucleosides with modifications at 5 and/or 4 positions were synthesized and evaluated for their in vitro activity against HCV and bovine viral diarrhea virus (BVDV). The introduction of the 2′-fluoro group was achieved by either fluorination of 2,2′-anhydronucleosides with hydrogen fluoride-pyridine or potassium fluoride, or a fluorination of arabinonucleosides with DAST. Among the 27 analogues synthesized, only the 5-fluoro compounds, namely β-D-2′-deoxy-2′,5-difluorocytidine (5), had anti-HCV activity in the subgenomic HCV replicon cell line, and inhibitory activity against ribosomal RNA. As β-D-N4-hydroxycytidine (NHC) had previously shown potent anti-HCV activity, the two functionalities of the N4-hydroxyl and the 2′-fluoro were combined into one molecule, yielding β-D-2′-deoxy-2′-fluoro-N4-hydroxycytidine (12). However, this nucleoside showed neither anti-HCV activity nor toxicity. All the l-forms of the analogues were devoid of anti-HCV activity. None of the compounds showed anti-BVDV activity, suggesting that the BVDV system cannot reliably predict anti-HCV activity in vitro.

Synthesis and anti-viral activity of a series of d- and l-2′-deoxy-2′-fluororibonucleosides in the subgenomic HCV replicon system

Based on the discovery of (2′ R)- d-2′-deoxy-2′-fluorocytidine as a potent anti-hepatitis C virus (HCV) agent, a series of d- and l-2′-deoxy-2′-fluororibonucleosides with modifications at 5- and/or 4-positions were synthesized and evaluated for their in vitro activity against HCV and bovine viral diarrhea virus (BVDV). The key step in the synthesis, the introduction of 2′-fluoro group, was achieved by either fluorination of 2,2′-anhydronucleosides with hydrogen fluoride–pyridine or potassium fluoride, or a fluorination of arabinonucleosides with DAST. Among the 27 analogues synthesized, only the 5-fluoro compound, namely (2′ R)- d-2′-deoxy-2′,5-difluorocytidine ( 13), demonstrated potent anti-HCV activity and toxicity to ribosomal RNA. The replacement of the 4-amino group with a thiol group resulted in the loss of activity, while the 4-methylthio substituted analogue ( 25) exhibited inhibition of ribosomal RNA. As N 4-hydroxycytidine (NHC) had previously shown potent anti-HCV activity, we combined the two functionalities of the N 4-hydroxyl and the 2′-fluoro into one molecule, resulting (2′ R)- d-2′-deoxy-2′-fluoro- N 4-hydroxycytidine ( 23). However, this nucleoside showed neither anti-HCV activity nor toxicity. All the l-forms of the analogues were devoid of anti-HCV activity. None of the compounds showed anti-BVDV activity, suggesting that the BVDV system cannot always predict anti-HCV activity.

An efficient chemical method for dephosphorylation of phosphopeptides.

Phosphate moieties found on serine, threonine or tyrosine residues in peptides, e.g., in proteolytic digests of proteins, were cleaved using hydrofluoric acid or hydrogen fluoride-pyridine without side reactions.

Preparation of Acyl Fluorides with Hydrogen Fluoride‐Pyridine and 1,3‐Dicyclohexylcarbodiimide.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ultrafast pump–probe spectroscopy of strongly hydrogen-bonded hydrogen fluoride–pyridine complexes

We present a study on the vibrational dynamics of the HF/FHF stretch combination vibration of HF–pyridine complexes in diluted pyridine solution. The relaxation of the excited vibration is observed to occur in two steps. In the first step, energy is transferred from the excited combination vibration to the hydrogen bond F–H⋯F modes with a time constant of 0.51±0.09 ps. In a second relaxation process these hydrogen bond modes decay with a time constant of 2.6±0.3 ps.