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排序方式: 共有142条查询结果,搜索用时 15 毫秒
1.
Characteristic fragment ions obtained in Fast atom bombardment (FAB) mass spectroscopy of ribose alkylated Uridine 5'-monophosphate (5'-UMP) derivatives in negative ion mode are described. All the compounds examined exhibited either [M]- or quasimolecular ion [M - H]- the fragmentations can be used to characterize these nucleotides. 相似文献
2.
Solid phase crystallization of plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon (alpha-Si:H) in alpha-Si:H/Al and Al/alpha-Si:H structures has been investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Radiative heating has been used to anneal films deposited on carbon-coated nickel (Ni) grids at temperatures between 200 and 400 degrees C for TEM studies. alpha-Si:H films were deposited on c-Si substrates using high vacuum (HV) PECVD for the XRD studies. TEM studies show that crystallization of alpha-Si:H occurs at 200 degrees C when Al film is deposited on top of the alpha-Si:H film. Similar behavior was observed in the XRD studies. In the case of alpha-Si:H deposited on top of Al films, the crystallization could not be observed at 400 degrees C by TEM and even up to 500 degrees C as seen by XRD. 相似文献
3.
Richard Cremlyn Naseem Akhtar 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):247-255
Abstract Pyrrolidine, morpholine, and β-hydroxyethylmorpholine have been phosphorylated with phosphorus oxychloride, phenylphosphorodichloridate, p-chlorophenylphosphorodichloridate and thiophosphoryl chloride. The resultant phosphorodichloridates have been condensed with a wied range of nucleophilic reagents, e.g. amines, hydrazines, phenols and isobutanol. Piperazine with phosphorus oxychloride (2 mols) gave the N(1) N(4)-diphosphorotetrachloridate, which was characterized as the tetracyclohexylamidate. β-Hydroxyethylpiperazine was similarly phosphorylated to the N,O-diphosphorotetrachloridate which was characterized as the tetraphenylhydrazidate. Condensation of pyrrolidine (2 mols) with phosphorus oxychloride (1 mol) afforded N,N′-dipyrrolidinophosphorochloridate which was reacted with phenylhydrazide and sodium azide. The phosphoroazide with triphenylphosphine afforded the corresponding triphenylphosphinimine. N-Phenyl N′-pyrrolidinophosphorochloridate with aqueous pyridine gave the corresponding pyrophosphoramide and the stability of the pyrophosphoramide towards hydrolysis was examined. 1,2-Cyclohexanediol was phosphorylated with phenylphosphorodichloridate and thiophosphorylchloride. Trans-4-t-Butylcyclohexyl N,N′-diphenylhydrazinophosphorothioate by reaction with formaldehyde gave a tetra-azaphosphorine P-sulfide. Trans-4-t-Butylcyclohexyl N-phenyl N′-phenylphosphorodiamidic hydrazide reacted with 1,4-dibromobut-2-ene to give a 1,2-diazahex-4-ene. 相似文献
4.
We have reported the reductive cleavage of azlactones1 and phenylhydrazones2 of carbonyl compounds in the presence of a suitable catalyst. In this paper a general method involving a one step synthesis of β-amino acid3,4, in good yield, through catalytic reduction of oximes of α-β-unsaturated acid is reported. This method involves the reaction of α, β-unsaturated acid with hydroxylamine hydrochloride in the presence of sodium acetate. Markovnikov's rule is followed in the synthesis of oximes of α, β-unsaturated acids. 相似文献
5.
Sn(IV)Cl4 catalyst provided a rapid and efficient deprotection method for the phenolic THP and MOM ethers and sequel intramolecular Friedel–Crafts alkylation reaction of THP and MOM protected chalcone epoxides under mild conditions. The reaction took 2–3 min to give the products in excellent yield (90–98%) at 0 °C without affecting the other functional groups. 相似文献
6.
Dr. Mégane Muschi Anusha Lalitha Dr. Saad Sene Dr. Damien Aureau Dr. Mathieu Fregnaux Dr. Imène Esteve Dr. Lucie Rivier Dr. Naseem Ramsahye Dr. Sabine Devautour-Vinot Dr. Clémence Sicard Prof. Nicolas Menguy Dr. Christian Serre Prof. Guillaume Maurin Prof. Nathalie Steunou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10439-10444
An innovative strategy is proposed to synthesize single-crystal nanowires (NWs) of the Al3+ dicarboxylate MIL-69(Al) MOF by using graphene oxide nanoscrolls as structure-directing agents. MIL-69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM-HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL-69(Al) NWs involving size-confinement and templating effects. The formation of MIL-69(Al) seeds and the self-scroll of GO sheets followed by the anisotropic growth of MIL-69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures. 相似文献
7.
8.
Naseem Peerzada 《Mikrochimica acta》1986,90(1-2):43-48
The use ofN-benzyltrimethylammonium methoxide as a digesting solvent, for the determination of zinc(II) in biological samples using anodic-stripping voltammetry is reported. It was found possible to determine zinc directly in biological samples containing such metals as copper(II), lead(II), iron(III), arsenic(III) and selenium(IV). The results for zinc in bovine liver and oyster tissue are reported. 相似文献
9.
Muhammad Saleem Naseem Akhter Muhammad Shaiq Ali Mamona Nazir Naheed Riaz Muhammad Moazzam Muhammad Arshad Abdul Jabbar 《Magnetic resonance in chemistry : MRC》2009,47(3):263-265
Chromatographic analysis of the alcoholic extract from Salsola imbricata yielded two new secondary metabolites, salisomide (1) and salisoflavan (2). Their structures were established with the help of spectroscopic techniques including COSY, HMQC and HMBC NMR experiments. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
10.
Nazar Mohammad Ranjha Ikram Ullah Khan Shahzad Naseem 《Journal of Sol-Gel Science and Technology》2009,50(3):281-289
Flurbiprofen loaded PCL/PVP blend microspheres were prepared by o/w solvent evaporation method using various concentrations
of gelatin as emulsifying agent. Microsphere recovery decreased with a decrease in the concentration of the emulsifier in
the dispersion. Encapsulation efficiency and drug loading of microspheres increased with decrease in concentration of emulsifying
agent. Hydration rate, encapsulation efficiency and drug loading of microspheres increased with increase in concentration
of PVP. Rheological properties showed free flowing nature of microspheres. SEM (Scanning electron microscope) revealed microspheres
were discrete, spherical and became porous with decrease in concentration of emulsifying agent but smooth with higher concentration
of emulsifying agent. FTIR (Fourier transform infrared spectroscopy) spectra of pure and encapsulated flurbiprofen in all
formulation showed no significant difference in characteristic peaks, suggesting stability of flurbiprofen during encapsulation
process. X-RD (X-ray powder diffractometry) of pure flurbiprofen shows sharp peaks, which decreases on encapsulation, indicating
dispersion at molecular level and hence decrease in the crystallinity of drug in microspheres. Microspheres showed an enteric
nature at pH 1.2 and a sustained release pattern at pH 6.8. Rapid drug release was observed in microspheres with higher concentration
of PVP (polyvinylpyrrolidone), PVP acts as channeling agent. Formulation with low concentration of emulsifying agent also
showed a fast release due to porous structure. Drug release kinetics followed zero order at pH 1.2 while at pH 6.8 Higuchi
model was best fitted and was found non fickian. 相似文献