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1.
Bartholomus Pieber Jamal A. Malik Cristian Cavedon Sebastian Gisbertz Aleksandr Savateev Daniel Cruz Tobias Heil Guigang Zhang Peter H. Seeberger 《Angewandte Chemie (International ed. in English)》2019,58(28):9575-9580
Cross‐coupling reactions mediated by dual nickel/photocatalysis are synthetically attractive but rely mainly on expensive, non‐recyclable noble‐metal complexes as photocatalysts. Heterogeneous semiconductors, which are commonly used for artificial photosynthesis and wastewater treatment, are a sustainable alternative. Graphitic carbon nitrides, a class of metal‐free polymers that can be easily prepared from bulk chemicals, are heterogeneous semiconductors with high potential for photocatalytic organic transformations. Here, we demonstrate that graphitic carbon nitrides in combination with nickel catalysis can induce selective C?O cross‐couplings of carboxylic acids with aryl halides, yielding the respective aryl esters in excellent yield and selectivity. The heterogeneous organic photocatalyst exhibits a broad substrate scope, is able to harvest green light, and can be recycled multiple times. In situ FTIR was used to track the reaction progress to study this transformation at different irradiation wavelengths and reaction scales. 相似文献
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Dr. Bartholomäus Pieber Dr. Menny Shalom Prof. Dr. Markus Antonietti Prof. Dr. Peter H. Seeberger Dr. Kerry Gilmore 《Angewandte Chemie (International ed. in English)》2018,57(31):9976-9979
Solid reagents, leaching catalysts, and heterogeneous photocatalysts are commonly employed in batch processes but are ill‐suited for continuous‐flow chemistry. Heterogeneous catalysts for thermal reactions are typically used in packed‐bed reactors, which cannot be penetrated by light and thus are not suitable for photocatalytic reactions involving solids. We demonstrate that serial micro‐batch reactors (SMBRs) allow for the continuous utilization of solid materials together with liquids and gases in flow. This technology was utilized to develop selective and efficient fluorination reactions using a modified graphitic carbon nitride heterogeneous catalyst instead of costly homogeneous metal polypyridyl complexes. The merger of this inexpensive, recyclable catalyst and the SMBR approach enables sustainable and scalable photocatalysis. 相似文献
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Sinner FM Gatschelhofer C Mautner A Magnes C Buchmeiser MR Pieber TR 《Journal of chromatography. A》2008,1191(1-2):274-281
Monolithic capillary columns were prepared via ring-opening metathesis polymerization (ROMP) using norborn-2-ene (NBE) and 1, 4, 4a, 5, 8, 8a-hexahydro-1, 4, 5, 8-exo,endo-dimethanonaphthalene (DMN-H6) as monomers. The monolithic polymer was copolymerized with Grubbs-type initiator RuCl(2)(PCy(3))(2)(CHPh) and a suitable porogenic system within the confines of fused silica capillaries of different inner diameter (I.D.). The first part of the study focused on batch-to-batch reproducibility of ROMP-derived capillary monoliths. Capillary monoliths of 200 microm I.D. showed good reproducibility in terms of retention times, with relative standard deviations (RSD) of 1.9% for proteins and 2.2% for peptides. However, the separately synthesized capillary monoliths revealed pronounced variation in back pressure with RSD values of up to 31%. These variations were considerably reduced by cooling of the capillaries during polymerization. Using this optimized preparation procedure capillary monoliths of 100 and 50 microm I.D. were synthesized and the effects of scaling down the column I.D. on the morphology and on the reproducibility of the polymerization process were investigated. In the second part, the applicability of ROMP-derived capillary monoliths to a separation problem common in medical research was assessed. A 200 microm I.D. monolithic column demonstrated excellent separation behavior for insulin and various insulin analogs, showing equivalent separation performance to Vydac C4 and Zorbax C3-based stationary phases. Moreover, the high permeability of monoliths enabled chromatographic separations at higher flow rates, which shortened analysis time to about one third. For the analysis of insulin in human biofluid samples, enhanced sensitivity was achieved by using a 50 microm I.D. ROMP-derived monolith. 相似文献
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Summary: Raman spectroscopy was applied to perform a comprehensive morphological analysis of polyethylene (PE) ski base materials at different processing levels. The morphological characterization included determination and evaluation of Raman spectra and examination of the crystallinity values by differential scanning calorimetry (DSC). A good agreement between Raman and DSC crystallinity fractions was obtained, thus corroborating the Raman spectroscopy approach. While for the PE grade with the lowest average molar mass no significant morphological changes due to processing from the raw material via the extruded film to the post-treated film was found, higher molar mass PE grades exhibited a decrease of crystallinity, but an increase of the amorphous fraction along the process chain. 相似文献
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Schlemmer B Gatschelhofer C Pieber TR Sinner FM Buchmeiser MR 《Journal of chromatography. A》2006,1132(1-2):124-131
Monolithic columns for capillary HPLC were prepared via ring-opening metathesis polymerization (ROMP) from cis-cyclooctene (COE), tris(cyclooct-4-enyl-1-oxy)methylsilane (CL) as monomers, 2-propanol and toluene as porogens and RuCl(2)(Py)(2)(IMesH(2))(CHC(6)H(5)) (Py=pyridine, IMesH(2)=1,3-dimesityl-4,5-dihydroimidazolin-2-ylidene) as initiator within the confines of 200 microm i.d. fused silica columns. For evaluation of the novel monolithic capillary HPLC columns, a protein standard consisting of six proteins in the molecular weight range of 5800-66000 g/mol, i.e. ribonuclease A, insulin, albumin, lysozyme, myoglobin and beta-lactoglobulin, was used. Reproducibility of synthesis was checked by determining the relative standard deviation (RSD) in retention times (t(R)), which was found to be in the range of 2.9-3.9% for all analytes. Variations in polymer kinetics were realized by adding different amounts of free pyridine and had a significant influence on the monolith's morphology, the backpressure and retention times. On the contrary, variations in monomer content and COE to CL ratio showed only minor changes on these parameters. Long-term stability of 1000 runs at 50 degrees C showed excellent stability of the columns and no significant alteration in separation performance was observed in combination with slightly decreased retention times (approx. 1.6-7.2% for all analytes). 相似文献
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Pasic A Koehler H Schaupp L Pieber TR Klimant I 《Analytical and bioanalytical chemistry》2006,386(5):1293-1302
A new microdialysis-based glucose-sensing system with an integrated fiber-optic hybrid sensor is presented. Design and dimensions
of the cell are adapted for its coupling with commercially available microdialysis techniques, thereby providing a new system
for continuous glucose monitoring. The glucose level is detected via oxygen consumption which occurs as a consequence of enzymatic
reaction between immobilized glucose oxidase and glucose. The use of gas-permeable Tygon tubing ensures complete and constant
air-saturation of the measuring fluid in the cell. Nevertheless, a reference oxygen optode is used to detect and to compensate
response changes caused by events like bacterial growth, temperature fluctuations, or failure of the peristaltic pump. In
contrast to widely used electrochemical sensors, the response of the microdialysis-based fiber-optic glucose sensor is highly
selective, making this sensor approach particularly advantageous for continuous glucose monitoring of patients in intensive
care units. The effects of flow rate, pH, temperature, and common interferences on the sensor response are presented and discussed
in detail. The sensor is evaluated in vitro using a 3-day continuous test in glucose-spiked plasma. The ability to measure
glucose in humans is demonstrated by coupling the flow-through cell and commercially available microdialysis catheter CMA60.
A 24-h monitoring test using this setup is successfully applied to a healthy volunteer. 相似文献
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Kumar GS Pieber B Reddy KR Kappe CO 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(20):6124-6128
Peroxides and ethers in flow: 2-Carbonyl-substituted phenols and β-ketoesters react safely with ethers in a microreactor environment using a copper catalyst and an organic peroxide (TBHP). This protocol results in unsymmetrical acetal scaffolds not easily available otherwise (see scheme). 相似文献