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241.
Mehdi Mardanian Alena A. Nevar Nikolai V. Tarasenko 《Applied Physics A: Materials Science & Processing》2013,112(2):437-442
In this paper, we report a simple and low-cost technique for fabrication of silicon nanoparticles via electrical spark discharge between two plane silicon electrodes immersed in deionized water (DI). The pulsed spark discharge with the peak current of 60 A and a duration of a single discharge pulse of 60 μs was used in our experiment. The structure, morphology, and average size of the resulting nanoparticles were characterized by means of X-Ray Diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). TEM images illustrated nearly spherical and isolated Si nanoparticles with diameters in the 3–8 nm range. The Raman peaks of the samples were shifted to the lower wave numbers in comparison to this of bulk crystalline silicon indicating the existence of tiny particles. The optical absorption spectrum of the nanoparticles was measured in the violet–visible (UV–Vis) spectral region. By measuring of the band gap we could estimate the average size of the prepared particles. The silicon nanoparticles synthesized exhibited a photoluminescence (PL) band in the violet-blue region with a double peak at around 417 and 439 nm. It can be attributed to oxide-related defects on the surface of silicon nanoparticles, which can act as the radiative centers for the electron-hole pair recombination. 相似文献
242.
243.
244.
Ivan Mosiagin Dr. Anthony J. Fernandes Alena Budinská Liana Hayriyan Prof. Dr. Kai E. O. Ylijoki Prof. Dr. Dmitry Katayev 《Angewandte Chemie (International ed. in English)》2023,62(41):e202310851
Nitroaromatic compounds represent one of the essential classes of molecules that are widely used as feedstock for the synthesis of intermediates, the preparation of nitro-derived pharmaceuticals, agrochemicals, and materials on both laboratory and industrial scales. We herein disclose the efficient, mild, and catalytic ipso-nitration of organotrimethylsilanes, enabled by an electrophilic N-nitrosaccharin reagent and allows chemoselective nitration under mild reaction conditions, while exhibiting remarkable substrate generality and functional group compatibility. Additionally, the reaction conditions proved to be orthogonal to other common functionalities, allowing programming of molecular complexity via successive transformations or late-stage nitration. Detailed mechanistic investigation by experimental and computational approaches strongly supported a classical electrophilic aromatic substitution (SEAr) mechanism, which was found to proceed through a highly ordered transition state. 相似文献
245.
Andrey Aslandukov Pascal L. Jurzick Dr. Maxim Bykov Alena Aslandukova Dr. Artem Chanyshev Dr. Dominique Laniel Dr. Yuqing Yin Fariia I. Akbar Dr. Saiana Khandarkhaeva Dr. Timofey Fedotenko Dr. Konstantin Glazyrin Dr. Stella Chariton Prof. Vitali Prakapenka Dr. Fabrice Wilhelm Dr. Andrei Rogalev Dr. Davide Comboni Dr. Michael Hanfland Prof. Natalia Dubrovinskaia Prof. Leonid Dubrovinsky 《Angewandte Chemie (International ed. in English)》2023,62(47):e202311516
A series of isostructural Ln3O2(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high-pressure (25–54 GPa) high-temperature (2000–3000 K) conditions in laser-heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single-crystal X-ray diffraction (SCXRD) as well as corroborated by X-ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln3O2(CN3) solids are composed of the hitherto unknown CN35− guanidinate anion—deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln3O2(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln3O2(CN3) compounds are recoverable to ambient conditions. The stabilization of the CN35− guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry. 相似文献
246.
Karel Mach Helena Antropiusová Vladimiŕ Hanuš Alena Dosedlová 《Transition Metal Chemistry》1980,5(1):5-10
Summary The reduction of Cp2TiCl2 with LiAlH4 in olefinic solvents at temperatures above 100° leads to the formation of µ-(
5 :
5-fulvalene)-di-µ-chloro-bis(
5-cyclopentadienyl-titanium) (1) and finally to µ-(
5 :
15-fulvalene)-di-µ-hydrido-bis (
5-cyclopentadienyltitanium). The first step of the reduction includes mainly the formation of the dimer of bis(
5-cyclopentadienyl)titanium(III) chloride, (Cp2TiCl)2. The mechanism of its conversion into (1) involves the formation of an intermediate bis(
5-cyclopentadienyl)titanium(III) hydride species which reacts immediately with the olefinic solvent to give bis(
5-cyclopentadienyl)alkyltitanium(III) compounds. The formation of the fulvalene ligand in (1) is explained by the interaction of the alkyltitanium compound with the cyclopentadienyl ligands of (Cp2TiCl)2 resulting in hydrogen transfer to the olefinic solvent. 相似文献
247.
248.
Alina K. Bakunova Alena Yu. Nikolaeva Tatiana V. Rakitina Tatiana Y. Isaikina Maria G. Khrenova Konstantin M. Boyko Vladimir O. Popov Ekaterina Yu. Bezsudnova 《Molecules (Basel, Switzerland)》2021,26(16)
Among industrially important pyridoxal-5’-phosphate (PLP)-dependent transaminases of fold type IV D-amino acid transaminases are the least studied. However, the development of cascade enzymatic processes, including the synthesis of D-amino acids, renewed interest in their study. Here, we describe the identification, biochemical and structural characterization of a new D-amino acid transaminase from Haliscomenobacter hydrossis (Halhy). The new enzyme is strictly specific towards D-amino acids and their keto analogs; it demonstrates one of the highest rates of transamination between D-glutamate and pyruvate. We obtained the crystal structure of the Halhy in the holo form with the protonated Schiff base formed by the K143 and the PLP. Structural analysis revealed a novel set of the active site residues that differ from the key residues forming the active sites of the previously studied D-amino acids transaminases. The active site of Halhy includes three arginine residues, one of which is unique among studied transaminases. We identified critical residues for the Halhy catalytic activity and suggested functions of the arginine residues based on the comparative structural analysis, mutagenesis, and molecular modeling simulations. We suggested a strong positive charge in the O-pocket and the unshaped P-pocket as a structural code for the D-amino acid specificity among transaminases of PLP fold type IV. Characteristics of Halhy complement our knowledge of the structural basis of substrate specificity of D-amino acid transaminases and the sequence-structure-function relationships in these enzymes. 相似文献
249.
250.
A norbornene-mediated palladium-catalyzed sequence is described in which two alkyl-aryl bonds and one alkenyl-aryl bond are formed in one pot with use of microwave irradiation. A variety of symmetrical and unsymmetrical oxygen-, nitrogen-, silicon-, and sulfur-containing tricyclic heterocycles were synthesized from a Heck acceptor and an aryl iodide containing two tethered alkyl halides. This approach was further applied to the synthesis of a tricyclic mescaline analogue. 相似文献