Cu(ii)–tBu–PHOX catalyzed enantioselective malonate addition onto 3-hydroxy 2-oxindoles: application in the synthesis of dimeric pyrroloindoline alkaloids

2018 ◽  
Vol 54 (57) ◽  
pp. 7963-7966 ◽  
Author(s):  
K. Naresh Babu ◽  
Lakshmana K. Kinthada ◽  
Partha Pratim Das ◽  
Alakesh Bisai
Keyword(s):  
Active Species ◽  
X Ray ◽  
Epr Experiments

Cu(ii)–PHOX-catalyzed malonate addition onto 3-hydroxy 3-indolyl-2-oxindoles afforded products in >99% ee. A Cu(ii)-species has been identified as an active species based on detailed X-ray, NMR, CV and EPR experiments.

scholarly journals Preparation and Photocatalytic Performances of WO3/TiO2 Composite Nanofibers

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Xiuping Han ◽  
Binghua Yao ◽  
Keying Li ◽  
Wenjing Zhu ◽  
Xuyuan Zhang
Keyword(s):  
Photoelectron Spectroscopy ◽  
Photocatalytic Oxidation ◽  
Composite Nanofibers ◽  
Photogenerated Electron ◽  
Xrd Analysis ◽  
Catalytic Performance ◽  
Active Species ◽  
X Ray ◽  
Bet Analysis ◽  
Electron Holes

The use of sunlight for photocatalytic oxidation is an ideal strategy, but it is limited by factors such as insufficient light absorption intensity of the photocatalyst and easy recombination of photogenerated electron holes. TiO2 is favored by researchers as an environment-friendly catalyst. In this paper, TiO2 is combined with WO3 to obtain a nanofiber with excellent catalytic performance under sunlight. The WO3/TiO2 composite nanofibers were synthesized by using the electrospinning method. The X-ray diffraction (XRD) analysis indicated that WO3 was successfully integrated onto the surface of TiO2. The photodegradation performance and photocurrent analysis of the prepared nanofibers showed that the addition of WO3 really improved the photocatalytic performance of TiO2 nanofibers, methylene blue (MB) degradation rate increased from 72% to 96%, and 5% was the optimal composite mole percentage of W to Ti. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectra (UV-Vis DRS), and Brunauer-Emmett-Teller (BET) analysis further characterized the properties of 5% WO3/TiO2 nanofibers. The H2 generation rate of 5% WO3/TiO2 nanofibers was 107.15 μmol·g−1·h−1, in comparison with that of TiO2 nanofibers (73.21 μmol·g−1·h−1) under the same condition. The 5% WO3/TiO2 produced ·OH under illumination, which played an important role in the MB degradation. Also, the enhanced photocatalytic mechanism was also proposed based on the detailed analysis of the band gap and the active species trapping experiment. The results indicated that the effective separation of Z-scheme photogenerated electron-hole pairs and transfer system constructed between TiO2 and WO3 endowed the excellent photocatalytic activity of 5% WO3/TiO2 nanofibers.

Process Control Applications of the Peltier Cooled SI (LI) Detector Based EDXRF Spectrometer

1988 ◽  
Vol 32 ◽  
pp. 31-37
Author(s):  
Anthony R. Harding
Keyword(s):  
Process Control ◽  
Silicon Crystal ◽  
Conveyor Belt ◽  
Cryogenic Liquid ◽  
Active Species ◽  
Peltier Effect ◽  
Production Plant ◽  
Plating Bath ◽  
X Ray ◽  
On Line

AbstractThe demand for on-line analyzers capable of compositional determinations in petroleum and chemical process streams has increased dramatically in recent years. Total control of production plant processes and resources requires the analysis of feed, intermediate, and product materials. This paper will describe a rugged, on-stream energy dispersive X-ray fluorescence (EDXRF) analyzer configured for the continuous determination of composition in solid and liquid samples. The detector in the X-ray sensor is a lithium-drifted silicon crystal which is thermoelectrically cooled (Peltier effect) to achieve operational temperatures. This approach to detector cooling offers advantages over traditional cryogenic liquid cooling when EDXRF is used in the process control environment.Three applications of the thermoelectrically-cooled detector-based EDXRF spectrometer will be presented here. The first is the analysis of a catalyst solution to monitor depletion of the active species. Second, two components of a plating bath solution will be determined simultaneously in a flowing sample stream. In the third application, the spectrometer will be oriented in a downward looking configuration to monitor inorganic constituents in absorbent samples as they are transported by conveyor belt to the X-ray measurement area.

scholarly journals Solution X-Ray Absorption Spectroscopy (XAS) for Analysis of Catalytically Active Species in Reactions with Ethylene by Homogeneous (Imido)vanadium(V) Complexes—Al Cocatalyst Systems

Catalysts ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1016 ◽  
Author(s):  
Kotohiro Nomura
Keyword(s):  
Active Species ◽  
Oxidation States ◽  
Donor Ligands ◽  
Ethylene Dimerization ◽  
Edge Structure ◽  
Donor Ligand ◽  
X Ray ◽  
Catalytically Active ◽  
Type V ◽  
X Ray Absorption

Solution V K-edge XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) analysis of vanadium(V) complexes containing both imido ligands and anionic ancillary donor ligands (L) of type, V(NR)(L)X2 (R = Ar, Ad (1-adamantyl); Ar = 2,6-Me2C6H3; X = Cl, Me, L = 2-(ArNCH2)C5H4N, OAr, WCA-NHC, and 2-(2’-benzimidazolyl)pyridine; WCA-NHC = anionic NHCs containing weak coordinating B(C6F5)3), which catalyze ethylene dimerization and/or polymerization in the presence of Al cocatalysts, has been explored. Different catalytically actives species with different oxidation states were formed depending upon the Al cocatalyst (MAO, Me2AlCl, AliBu3, etc.) and the anionic ancillary donor ligand employed. The method is useful for obtainment of the direct information of the active species (oxidation state, basic framework around the centered metal) in solution, and for better understanding in catalysis mechanism and organometallic as well as coordination chemistry.

scholarly journals Photocrystallography

2007 ◽  
Vol 64 (1) ◽  
pp. 259-271 ◽  
Author(s):  
Jacqueline M. Cole
Keyword(s):  
Structural Changes ◽  
Three Dimensional ◽  
Research Area ◽  
Active Species ◽  
X Ray Diffraction ◽  
X Ray ◽  
Future Possibility ◽  
New Research ◽  
Exciting Area

This review describes the development and application of a new crystallographic technique that is starting to enable the three-dimensional structural determination of molecules in their photo-activated states. So called `photocrystallography' has wide applicability, particularly in the currently exciting area of photonics, and a discussion of this applied potential is put into context in this article. Studies are classified into four groups: photo-structural changes that are (i) irreversible; (ii) long-lived but reversible under certain conditions; (iii) transient with photo-active lifetimes of the order of microseconds; (iv) very short lived, existing at the nanosecond or even picosecond level. As photo-structural changes relative to the `ground state' can be subtle, this article necessarily concentrates on small-molecule single-crystal X-ray diffraction given that high atomic resolution is possible. That said, where it is pertinent, references are also made to related major advances in photo-induced macromolecular crystallography. The review concludes with an outlook on this new research area, including the future possibility of studying even more ephemeral, femtosecond-lived, photo-active species.

scholarly journals Degradation of Acid Red B by Manganese doped iron oxychloride and Permonosulfate: Performance and Inhomogeneous Activation Mechanism

2021 ◽  
Author(s):  
Rong Chen ◽  
Dan Zhao ◽  
Yanmao Dong ◽  
Chengrun Cai ◽  
Yan Yuan ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Ph Value ◽  
Active Species ◽  
Ion Concentration ◽  
Activation Mechanism ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Initial Ph

Abstract manganese doped iron oxychloride (Mn-FeOCl) was synthesized by partial pyrolysis method. The Mn-FeOCl was used as heterogeneous catalyst to activate permonosulfate (PMS) for the degradation of azo dye acid red B(ARB) for the first time. The Mn-FeOCl was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction spectroscopy (XRD). The effects of Mn-FeOCl dosage, PMS concentration, initial pH value, Cl ion concentration and humic acid (HA) dosage on the degradation of ARB by Mn-FeOCl/PMS were investigated. Results showed that the ARB was degraded effectively by Mn-FeOCl/PMS. The mineralization rate of ARB reached 42.5%. As the Mn-FeOCl dosage was 0.1g/L, PMS concentration was 1mmol/L, and ARB concentration was 0.05mmol/L, the degradation rate of ARB reached 99.4% in 30 minutes. With the increase of PMS dosage, Mn-FeOCl dosage, Cl− ion concentration and initial pH value, the decolorization effect of ARB increased. The reaction mechanism was analyzed by free radical quenching experiment and XPS. The main active species were determined as ·OH and SO4·− which generated by PMS activation. The SO4·−−was the main active species.

scholarly journals Ru0·Run+/Al2O3 as a Versatile Catalyst in the Isomerization of Allyl Alcohol

2021 ◽  
Vol 9 ◽  
Author(s):  
Julián Enciso ◽  
Alfonso Ramírez ◽  
Carlos Ostos ◽  
Adriana Echavarría ◽  
Misael Córdoba ◽  
...  
Keyword(s):  
Surface Area ◽  
Heterogeneous Catalyst ◽  
Pore Volume ◽  
Allyl Alcohol ◽  
Active Species ◽  
X Ray Diffraction ◽  
X Ray ◽  
Isomerization Product ◽  
Redox Sites ◽  
Alcohol Conversion

This study focuses on examining the isomerization of allyl alcohol using ruthenium (Ru) supported on alumina as a heterogeneous catalyst. The synthesized Ru/Al solids were characterized by various characterization techniques. The content of Ru was estimated by the energy dispersive x-ray technique. The x-ray diffraction (XRD) confirmed the presence of phases in the support and active species in the catalysts. The surface area of the support after Ru impregnation and the pore volume were determined by nitrogen physisorption. The analysis of programmed temperature (TPR and TPO) shows different redox sites which is confirmed by XPS. The catalytic results suggest a dependence on the amount of available metallic Ru, as well as the importance of the continuous regeneration of the metal using H2 to achieve a good conversion of the allyl alcohol. For comparison purposes, the commercial Ru on alumina 5% (CAS 908142) was used. The results show up to 68% alcohol conversion and 27% yield of the isomerization product using Ru(1,5.4h)/Al catalyst in comparison with 86% conversion and 39% yield of the isomerization product using CAS 908142. In contrast, our catalysts always presented higher TOF values (149–160) in comparison with CAS 908142 (101).

scholarly journals 6-Arylimino-2-(2-(1-phenylethyl)naphthalen-1-yl)-iminopyridylmetal (Fe and Co) Complexes as Highly Active Precatalysts for Ethylene Polymerization: Influence of Metal and/or Substituents on the Active, Thermostable Performance of Their Complexes and Resultant Polyethylenes

Molecules ◽  
2020 ◽  
Vol 25 (18) ◽  
pp. 4244 ◽  
Author(s):  
Wenhua Lin ◽  
Liping Zhang ◽  
Jiahao Gao ◽  
Qiuyue Zhang ◽  
Yanping Ma ◽  
...  
Keyword(s):  
Elevated Temperature ◽  
Single Crystal ◽  
Ethylene Polymerization ◽  
Active Species ◽  
Single Site ◽  
X Ray ◽  
X Ray Crystallography ◽  
Molecular Weights ◽  
Highly Active ◽  
Cobalt Center

A series of 6-arylimino-2-(2-(1-phenylethyl)naphthalen-1-yl)iminopyridines and their iron(II) and cobalt(II) complexes (Fe1–Fe5, Co1–Co5) were synthesized and routinely characterized as were Co3 and Co5 complexes, studied by single crystal X-ray crystallography, which individually displayed a distorted square pyramidal or trigonal bipyramid around a cobalt center. Upon treatment with either methyluminoxane (MAO) or modified methyluminoxane (MMAO), all complexes displayed high activities regarding ethylene polymerization even at an elevated temperature, enhancing the thermostability of the active species. In general, iron precatalysts showed higher activities than their cobalt analogs; for example, 10.9 × 106 g(PE) mol−1 (Co) h−1 by Co4 and 17.0 × 106 g(PE) mol−1 (Fe) h−1 by Fe4. Bulkier substituents are favored for increasing the molecular weights of the resultant polyethylenes, such as 25.6 kg mol−1 obtained by Co3 and 297 kg mol−1 obtained by Fe3. A narrow polydispersity of polyethylenes was observed by iron precatalysts activated by MMAO, indicating a single-site active species formed.

scholarly journals Extending electron paramagnetic resonance to nanoliter volume protein single crystals using a self-resonant microhelix

2019 ◽  
Vol 5 (10) ◽  
pp. eaay1394 ◽  
Author(s):  
Jason W. Sidabras ◽  
Jifu Duan ◽  
Martin Winkler ◽  
Thomas Happe ◽  
Rana Hussein ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Single Crystals ◽  
Active Site ◽  
Measured Signal ◽  
Paramagnetic Resonance ◽  
X Ray ◽  
X Ray Crystallography ◽  
X Band ◽  
Electron Paramagnetic ◽  
Epr Experiments

Electron paramagnetic resonance (EPR) spectroscopy on protein single crystals is the ultimate method for determining the electronic structure of paramagnetic intermediates at the active site of an enzyme and relating the magnetic tensor to a molecular structure. However, crystals of dimensions typical for protein crystallography (0.05 to 0.3mm) provide insufficient signal intensity. In this work, we present a microwave self-resonant microhelix for nanoliter samples that can be implemented in a commercial X-band (9.5 GHz) EPR spectrometer. The self-resonant microhelix provides a measured signal-to-noise improvement up to a factor of 28 with respect to commercial EPR resonators. This work opens up the possibility to use advanced EPR techniques for studying protein single crystals of dimensions typical for x-ray crystallography. The technique is demonstrated by EPR experiments on single crystal [FeFe]-hydrogenase (Clostridium pasteurianum; CpI) with dimensions of 0.3 mm by 0.1 mm by 0.1 mm, yielding a proposed g-tensor orientation of the Hox state.

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