A series of Keggin-based compounds constructed by conjugate ring-rich pyrazine and quinoxaline derivatives

2016 ◽  
Vol 45 (35) ◽  
pp. 13925-13936 ◽  
Author(s):  
Aixiang Tian ◽  
Yan Tian ◽  
Yali Ning ◽  
Xue Hou ◽  
Huaiping Ni ◽  
...  
Keyword(s):  
Quinoxaline Derivatives ◽  
Keggin Anions ◽  
First Time ◽  
P Ligands

Ligands L1 and L2 are utilized in POM chemistry for the first time. Different Keggin anions induce distinct 2D structures of compounds 1/2 and 3/4 in Ag–L1 and Ag–L2 systems, respectively. By adding AgI and CuI to the PMo12–L2 system different 3 and 5 were formed.

One-Pot Synthesis of Thiazolo[3,4-a]Quinoxalines from 1,2-Diamines, Aryl Isothiocyanates and Ethyl Bromopyruvate

2017 ◽  
Vol 41 (12) ◽  
pp. 712-714 ◽  
Author(s):  
Mohammad Piltan
Keyword(s):  
Chromatographic Separations ◽  
One Pot ◽  
One Pot Synthesis ◽  
Three Component Reaction ◽  
Wide Range ◽  
Quinoxaline Derivatives ◽  
First Time ◽  
Aryl Isothiocyanates ◽  
Ethyl Bromopyruvate

Some hitherto unreported thiazolo[3,4- a]quinoxaline derivatives have been synthesised in excellent yields via a one-pot, three-component reaction of benzene-1,2-diamines, ethyl bromopyruvate and aryl isothiocyanates in MeCN, for the first time. The protocol avoids the use of any catalysts or chromatographic separations and provides a wide range of novel thiazolo[3,4- a]quinoxalines.

Synthesis of free and ligated 1,2-thiaphosphetanes – expanding the pool of strained P-ligands

2019 ◽  
Vol 55 (11) ◽  
pp. 1615-1618 ◽  
Author(s):  
Andreas Wolfgang Kyri ◽  
Florian Gleim ◽  
David Becker ◽  
Gregor Schnakenburg ◽  
Arturo Espinosa Ferao ◽  
...  
Keyword(s):  
Metal Complex ◽  
Coordination Sphere ◽  
Free Ligand ◽  
First Time ◽  
P Ligands

The 1,2-thiaphosphetane heterocycle could be synthesized for the first time in the coordination sphere of a metal complex (I) from which the free ligand (II) could be obtained, too.

scholarly journals Formation of α-hydroxycarbonyl and α-dicarbonyl compounds during degradation of monosaccharides

2008 ◽  
Vol 25 (No. 3) ◽  
pp. 119-130 ◽  
Author(s):  
O. Novotný ◽  
K. Cejpek ◽  
J. Velíšek
Keyword(s):  
Molecular Weight ◽  
Aldol Condensation ◽  
Model Systems ◽  
Reaction Pathways ◽  
Low Molecular Weight ◽  
Dicarbonyl Compounds ◽  
Cannizzaro Reaction ◽  
Quinoxaline Derivatives ◽  
Sugar Degradation ◽  
First Time

The formation of &alpha;-hydroxycarbonyl and &alpha;-dicarbonyl compounds from monosaccharides (glucose, fructose, arabinose, glyceraldehyde, and 1,3-dihydroxyacetone) was studied in three different model systems comprising an aqueous and alkaline solution of potassium peroxodisulfate (K<sub>2</sub>S<sub>2</sub>O<sub>8</sub>), and a solution of sodium hydroxide, respectively. In total, six &alpha;-hydroxycarbonyl (in the form of O-ethyloximes) and six &alpha;-dicarbonyl compounds (as quinoxaline derivatives) were identified by GC/MS and quantified. Acetol, glycolaldehyde, 1,3-dihydroxyacetone, methylglyoxal, and glyoxal were the most abundant low molecular weight carbonyls. Within the model systems studied, the yield of &alpha;-hydroxycarbonyl and &alpha;-dicarbonyl compounds was 0.32&minus;4.90% (n/n) and 0.35&minus;9.81% (n/n), respectively. The yield of &alpha;-dicarbonyls was higher than that of &alpha;-hydroxycarbonyls only in aqueous solution of K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> and in the other two model systems an inverse ratio of these two carbonyl types was found. For the first time, ethylglyoxal was identified as a sugar degradation product and several mechanisms explaining its formation were proposed. The achieved data indicated that low molecular weight &alpha;-hydroxycarbonyl and &alpha;-dicarbonyl compounds are predominantly formed by a direct retro-aldol reaction and &alpha;- and &beta;-dicarbonyl cleavage. It was evident that some compounds were produced from the sugar fragmentation products. Thus, isomerisation, reduction of dicarbonyls by formaldehyde (cross-Cannizzaro reaction), and mutual disproportionation are possible reaction pathways participating in the formation of &alpha;-hydroxycarbonyl compounds. Oxidation and disproportionation of &alpha;-hydroxycarbonyl precursors as well as the aldol condensation of low molecular weight carbonyl species (followed by subsequent reactions) play an important role in the formation of several &alpha;-dicarbonyl compounds.

Asymmetric Copper–Catalyzed Propargylic Amination with Amine Hydrochloride Salts

2021 ◽  
Author(s):  
Jian Huang ◽  
Hanhan Kong ◽  
Sijia Li ◽  
Ruijin Zhang ◽  
Haodong Qian ◽  
...  
Keyword(s):  
Amine Hydrochloride ◽  
Copper Salts ◽  
Propargylic Esters ◽  
First Time ◽  
P Ligands

The highly enantioselective copper-catalyzed propargylic amination of propargylic esters with amine hydrochloride salts has been realized for the first time using copper salts with chiral N,N,P-ligands. This method features a...

Annulate lamellae in the Sertoli cells of guinea pig testis after unilateral torsion of the spermatic cord

1984 ◽  
Vol 42 ◽  
pp. 196-197
Author(s):  
J. Chakraborty ◽  
A. P. Sinha Hikim ◽  
J. S. Jhunjhunwala
Keyword(s):  
Sertoli Cells ◽  
Guinea Pigs ◽  
Spermatic Cord ◽  
Present Report ◽  
Cell Types ◽  
Annulate Lamellae ◽  
Spermatogenic Cells ◽  
Electron Microscopic ◽  
Structural Details ◽  
First Time

Although the presence of annulate lamellae was noted in many cell types, including the rat spermatogenic cells, this structure was never reported in the Sertoli cells of any rodent species. The present report is based on a part of our project on the effect of torsion of the spermatic cord to the contralateral testis. This paper describes for the first time, the fine structural details of the annulate lamellae in the Sertoli cells of damaged testis from guinea pigs.One side of the spermatic cord of each of six Hartly strain adult guinea pigs was surgically twisted (540°) under pentobarbital anesthesia (1). Four months after induction of torsion, animals were sacrificed, testes were excised and processed for the light and electron microscopic investigations. In the damaged testis, the majority of seminiferous tubule contained a layer of Sertoli cells with occasional spermatogonia (Fig. 1). Nuclei of these Sertoli cells were highly pleomorphic and contained small chromatinic clumps adjacent to the inner aspect of the nuclear envelope (Fig. 2).

Electron spectroscopic imaging and diffraction

1991 ◽  
Vol 49 ◽  
pp. 706-707
Author(s):  
M. Rühle ◽  
J. Mayer ◽  
J.C.H. Spence ◽  
J. Bihr ◽  
W. Probst ◽  
...  
Keyword(s):  
Materials Science ◽  
Electron Spectroscopic Imaging ◽  
Magnetic Filter ◽  
Magnetic Imaging ◽  
Illumination System ◽  
Probe Size ◽  
Diffraction Patterns ◽  
Fritz Haber ◽  
Koehler Illumination ◽  
First Time

A new Zeiss TEM with an imaging Omega filter is a fully digitized, side-entry, 120 kV TEM/STEM instrument for materials science. The machine possesses an Omega magnetic imaging energy filter (see Fig. 1) placed between the third and fourth projector lens. Lanio designed the filter and a prototype was built at the Fritz-Haber-Institut in Berlin, Germany. The imaging magnetic filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient area detection. The energy dispersion at the exit slit (Fig. 1) results in ∼ 1.5 μm/eV which allows imaging with energy windows of ≤ 10 eV. The smallest probe size of the microscope is 1.6 nm and the Koehler illumination system is used for the first time in a TEM. Serial recording of EELS spectra with a resolution < 1 eV is possible. The digital control allows X,Y,Z coordinates and tilt settings to be stored and later recalled.

A Novel TEM Technique for Characterizing As-Grown CVD Diamond Films

1991 ◽  
Vol 49 ◽  
pp. 956-957 ◽  
Author(s):  
Z.L. Wang ◽  
J. Bentley ◽  
R.E. Clausing ◽  
L. Heatherly ◽  
L.L. Horton
Keyword(s):  
Diamond Films ◽  
Chemical Vapor ◽  
Growth Direction ◽  
Dark Field ◽  
Growth Surface ◽  
Specimen Preparation ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
First Time ◽  
Microstructural Studies

Microstructural studies by transmission electron microscopy (TEM) of diamond films grown by chemical vapor deposition (CVD) usually involve tedious specimen preparation. This process has been avoided with a technique that is described in this paper. For the first time, thick as-grown diamond films have been examined directly in a conventional TEM without thinning. With this technique, the important microstructures near the growth surface have been characterized. An as-grown diamond film was fractured on a plane containing the growth direction. It took about 5 min to prepare a sample. For TEM examination, the film was tilted about 30-45° (see Fig. 1). Microstructures of the diamond grains on the top edge of the growth face can be characterized directly by transmitted electron bright-field (BF) and dark-field (DF) images and diffraction patterns.

A microscopic marker experiment study on high temperature oxidation of Ni-Al alloy

1986 ◽  
Vol 44 ◽  
pp. 514-515
Author(s):  
Shou-kong Fan
Keyword(s):  
Transport Mechanism ◽  
High Temperature Oxidation ◽  
Transverse Section ◽  
Al Alloy ◽  
Metal Interface ◽  
Electron Microscopic ◽  
Temperature Oxidation ◽  
Analytical Electron ◽  
Microscopic Studies ◽  
First Time

Transmission and analytical electron microscopic studies of scale microstructures and microscopic marker experiments have been carried out in order to determine the transport mechanism in the oxidation of Ni-Al alloy. According to the classical theory, the oxidation of nickel takes place by transport of Ni cations across the scale forming new oxide at the scale/gas interface. Any markers deposited on the Ni surface are expected to remain at the scale/metal interface after oxidation. This investigation using TEM transverse section techniques and deposited microscopic markers shows a different result,which indicates that a considerable amount of oxygen was transported inward. This is the first time that such fine-scale markers have been coupled with high resolution characterization instruments such as TEM/STEM to provide detailed information about evolution of oxide scale microstructure.

Direct imaging of charge transfer

1996 ◽  
Vol 54 ◽  
pp. 680-681
Author(s):  
Yimei Zhu ◽  
J. Tafto
Keyword(s):  
Charge Transfer ◽  
Electron Diffraction ◽  
Scattering Amplitude ◽  
High Temperature Superconductors ◽  
Charge Carriers ◽  
Image Charge ◽  
Net Charge ◽  
Long Time ◽  
Electron Holes ◽  
First Time

The electron holes confined to the CuO2-plane are the charge carriers in high-temperature superconductors, and thus, the distribution of charge plays a key role in determining their superconducting properties. While it has been known for a long time that in principle, electron diffraction at low angles is very sensitive to charge transfer, we, for the first time, show that under a proper TEM imaging condition, it is possible to directly image charge in crystals with a large unit cell. We apply this new way of studying charge distribution to the technologically important Bi2Sr2Ca1Cu2O8+δ superconductors.Charged particles interact with the electrostatic potential, and thus, for small scattering angles, the incident particle sees a nuclei that is screened by the electron cloud. Hence, the scattering amplitude mainly is determined by the net charge of the ion. Comparing with the high Z neutral Bi atom, we note that the scattering amplitude of the hole or an electron is larger at small scattering angles. This is in stark contrast to the displacements which contribute negligibly to the electron diffraction pattern at small angles because of the short g-vectors.

Recent developments in low-voltage SEM of polymers

1993 ◽  
Vol 51 ◽  
pp. 866-867
Author(s):  
S.J. Krause ◽  
W.W. Adams
Keyword(s):  
Low Voltage ◽  
Chromatic Aberration ◽  
Thermal Electron ◽  
Analytical Technique ◽  
Recent Developments ◽  
Beam Currents ◽  
New Generation ◽  
First Time ◽  
Voltage Scanning ◽  
Beam Damage

Over the past decade low voltage scanning electron microscopy (LVSEM) of polymers has evolved from an interesting curiosity to a powerful analytical technique. This development has been driven by improved instrumentation and in particular, reliable field emission gun (FEG) SEMs. The usefulness of LVSEM has also grown because of an improved theoretical and experimental understanding of sample-beam interactions and by advances in sample preparation and operating techniques. This paper will review progress in polymer LVSEM and present recent results and developments in the field.In the early 1980s a new generation of SEMs produced beam currents that were sufficient to allow imaging at low voltages from 5keV to 0.5 keV. Thus, for the first time, it became possible to routinely image uncoated polymers at voltages below their negative charging threshold, the "second crossover", E2 (Fig. 1). LVSEM also improved contrast and reduced beam damage in sputter metal coated polymers. Unfortunately, resolution was limited to a few tenths of a micron due to the low brightness and chromatic aberration of thermal electron emission sources.

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