排序方式: 共有23条查询结果,搜索用时 312 毫秒
1.
Well‐Defined Palladium Nanoparticles Supported on Siliceous Mesocellular Foam as Heterogeneous Catalysts for the Oxidation of Water 下载免费PDF全文
Dr. Oscar Verho Dr. Torbjörn Åkermark Dr. Eric V. Johnston Karl P. J. Gustafson Dr. Cheuk‐W. Tai Henrik Svengren Dr. Markus D. Kärkäs Prof. Jan‐E. Bäckvall Prof. Björn Åkermark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5909-5915
Herein, we describe the use of Pd nanoparticles immobilized on an amino‐functionalized siliceous mesocellular foam for the catalytic oxidation of H2O. The Pd nanocatalyst proved to be capable of mediating the four‐electron oxidation of H2O to O2, both chemically and photochemically. The Pd nanocatalyst is easy to prepare and shows high chemical stability, low leaching, and recyclability. Together with its promising catalytic activity, these features make the Pd nanocatalyst of potential interest for future sustainable solar‐fuel production. 相似文献
2.
We identified and characterized two genes, LAT1 and LAT2, which encode specific l-arabinose transporters. The genes were identified in the l-arabinose fermenting yeast Ambrosiozyma monospora. The yeast Saccharomyces cerevisiae had only very low l-arabinose transport activity; however, when LAT1 or LAT2 was expressed, l-arabinose transport was facilitated. When the LAT1 or LAT2 were expressed in an S. cerevisiae mutant where the main hexose transporters were deleted, the l-arabinose transporters could not restore growth on d-glucose, d-fructose, d-mannose or d-galactose. This indicates that these sugars are not transported and suggests that the transporters are specific for l-arabinose. 相似文献
3.
Verho O Johnston EV Karlsson E Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(40):11216-11222
The synthesis of a new series of cyclopentadienylruthenium catalysts with varying electronic properties and their application in racemization of secondary alcohols are described. These racemizations involve two key steps: 1) β-hydride elimination (dehydrogenation) and 2) re-addition of the hydride to the intermediate ketone. The results obtained confirm our previous theory that the electronic properties of the substrate determine which of these two steps is rate determining. For an electron-deficient alcohol the rate-determining step is the β-hydride elimination (dehydrogenation), whereas for an electron-rich alcohol the re-addition of the hydride becomes the rate-determining step. By matching the electronic properties of the catalyst with the electronic properties of the alcohol, we have now shown that a dramatic increase in racemization rate can be obtained. For example, electron-deficient alcohol 15 racemized 30 times faster with electron-deficient catalyst 6 than with the unmodified standard catalyst 4. The application of these protocols will extend the scope of cyclopentadienylruthenium catalysts in racemization and dynamic kinetic resolution. 相似文献
4.
(13)CO exchange studies of racemization catalyst (η(5)-Ph(5)C(5))Ru(CO)(2)Cl and (η(5)-Ph(5)C(5))Ru(CO)(2)(Ot-Bu) by (13)C NMR spectroscopy are reported. CO exchange for the active catalyst form, (η(5)-Ph(5)C(5))Ru(CO)(2)(Ot-Bu) is approximately 20 times faster than that for the precatalyst (η(5)-Ph(5)C(5))Ru(CO)(2)Cl. An inhibition on the rate of racemization of (S)-1-phenylethanol was observed on addition of CO. These results support the hypothesis that CO dissociation is a key step in the racemization of sec-alcohols by (η(5)-Ph(5)C(5))Ru(CO)(2)Cl, as also predicted by DFT calculations. 相似文献
5.
Parshintsev J Ruiz-Jimenez J Petäjä T Hartonen K Kulmala M Riekkola ML 《Analytical and bioanalytical chemistry》2011,400(10):3527-3535
In this research, the two most common filter media, quartz and Teflon, were tested to obtain information about the possible
adsorption of gas-phase compounds onto filters during long sample collection of atmospheric aerosols. Particles of nanometer-size
for off-line chemical characterization were collected using a recently introduced differential mobility analyzer for size
separation. Samples were collected at an urban site (Helsinki, SMEARIII station) during spring 2010. Sampling time was 4 to
10 days for particles 50, 40, or 30 nm in diameter. Sample air flow was 4 L/min. The sampling setup was arranged so that two
samples were obtained for each sampling period almost simultaneously: one containing particles and adsorbed gas-phase compounds
and one containing adsorbed gas-phase compounds only. Filters were extracted and analyzed for the presence of selected carboxylic
acids, polyols, nitrogen-containing compounds, and aldehydes. The results showed that, in quartz filter samples, gas-phase
adsorption may be responsible for as much as 100% of some compound masses. Whether quartz or Teflon, simultaneous collection
of gas-phase zero samples is essential during the whole sampling period. The dependence of the adsorption of gas-phase compounds
on vapor pressure and the effect of adsorption on the deposited aerosol layer are discussed. 相似文献
6.
Evaluation of Fe and Ru Pincer‐Type Complexes as Catalysts for the Racemization of Secondary Benzylic Alcohols 下载免费PDF全文
Dr. Oscar Verho Prof. Dr. Matthias Beller Prof. Dr. Jan‐E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11583-11586
Fe and Ru pincer‐type catalysts are used for the racemization of benzylic alcohols. Racemization with the Fe catalyst was achieved within 30 minutes under mild reaction conditions, with a catalyst loading as low as 2 mol %. This reaction constitutes the first example of an iron‐catalyzed racemization of an alcohol. The efficiency for racemization of the Fe catalyst and its Ru analogue was evaluated for a wide range of sec‐benzylic alcohols. The commercially available Ru complex proved to be highly robust and even tolerated the presence of water in the reaction mixture. 相似文献
7.
EV Johnston O Verho MD Kärkäs M Shakeri CW Tai P Palmgren K Eriksson S Oscarsson JE Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(39):12202-12206
Palladium nanoparticles immobilized on amino-functionalized mesocellular foam constitute an efficient catalyst for the aerobic oxidation of primary and secondary alcohols to their corresponding carbonyl compounds in high to excellent yields. An exceptionally high TON of 365?000 was reached for the oxidation of 1-phenylethanol under solvent-free reaction conditions. The catalyst can be recycled many times with retained activity as shown by the identical rate curves of the first and fifth runs. 相似文献
8.
Oscar Verho Marléne D. V. Dilenstam Markus D. Kärkäs Dr. Eric V. Johnston Dr. Torbjörn Åkermark Prof. Jan‐E. Bäckvall Prof. Björn Åkermark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(52):16947-16954
By using a dimeric ruthenium complex in combination with tert‐butyl hydrogen peroxide (TBHP) as stoichiometric oxidant, a mild and efficient protocol for the oxidation of secondary benzylic alcohols was obtained, thereby giving the corresponding ketones in high yields within 4 h. However, in the oxidation of aliphatic alcohols, the TBHP protocol suffered from low conversions owing to a competing Ru‐catalyzed disproportionation of the oxidant. Gratifyingly, by switching to Oxone (2 KHSO5 ? KHSO4 ? K2SO4 triple salt) as stoichiometric oxidant, a more efficient and robust system was obtained that allowed for the oxidation of a wide range of aliphatic and benzylic secondary alcohols, giving the corresponding ketones in excellent yields. The mechanism for these reactions is believed to involve a high‐valent RuV–oxo species. We provide support for such an intermediate by means of mechanistic studies. 相似文献
9.
Jakub Czajkowski Tuukka Pryk?ri Erkki Alarousu Jaakko Palosaari Risto Myllyl? 《Optical Review》2010,17(3):257-262
Application of time domain, ultra high resolution optical coherence tomography (UHR-OCT) in printed electronics products’
quality inspection is demonstrated. Presented study was done using experimental UHR-OCT device based on a Kerr-lens mode locked
Ti:sapphire femtosecond laser, photonic crystal fibre and modified, free-space Michelson interferometer. Possibilities of
the technique are demonstrated by analysis of an RF antenna—example of printed electronics products. Measurements were done
with submicron axial resolution, offered by UHR-OCT system developed in our laboratory. Such high resolution is necessary
due to the thickness of material layers used in printed electronics. In addition to tomography imaging, numerical results
were compared with data provided by two commercially available measurement devices: Wyko NT3300 optical profiler and Dektak
8 stylus profiler (both Veeco). Comparison of profile heights and their spatial correlation is presented. Ability for full
volumetric reconstruction and accuracy justified with reference measurements prove OCT to be a reliable tool in printed electronics
product testing. 相似文献
10.
Ebben CJ Shrestha M Martinez IS Corrigan AL Frossard AA Song WW Worton DR Petäjä T Williams J Russell LM Kulmala M Goldstein AH Artaxo P Martin ST Thomson RJ Geiger FM 《The journal of physical chemistry. A》2012,116(32):8271-8290
This article summarizes and compares the analysis of the surfaces of natural aerosol particles from three different forest environments by vibrational sum frequency generation. The experiments were carried out directly on filter and impactor substrates, without the need for sample preconcentration, manipulation, or destruction. We discuss the important first steps leading to secondary organic aerosol (SOA) particle nucleation and growth from terpene oxidation by showing that, as viewed by coherent vibrational spectroscopy, the chemical composition of the surface region of aerosol particles having sizes of 1 μm and lower appears to be close to size-invariant. We also discuss the concept of molecular chirality as a chemical marker that could be useful for quantifying how chemical constituents in the SOA gas phase and the SOA particle phase are related in time. Finally, we describe how the combination of multiple disciplines, such as aerosol science, advanced vibrational spectroscopy, meteorology, and chemistry can be highly informative when studying particles collected during atmospheric chemistry field campaigns, such as those carried out during HUMPPA-COPEC-2010, AMAZE-08, or BEARPEX-2009, and when they are compared to results from synthetic model systems such as particles from the Harvard Environmental Chamber (HEC). Discussions regarding the future of SOA chemical analysis approaches are given in the context of providing a path toward detailed spectroscopic assignments of SOA particle precursors and constituents and to fast-forward, in terms of mechanistic studies, through the SOA particle formation process. 相似文献