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排序方式: 共有399条查询结果,搜索用时 265 毫秒
121.
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In the present work, some polymeric additives were prepared to use as viscosity index improvers and pour point depressants for lube oil via copolymerization of hexadecylacrylate and dodecylacrylate with styrene. Structure of the prepared compounds was confirmed by infrared spectroscopy and nuclear magnetic resonance. The molecular weights of the prepared copolymers were determined by using gel permeation chromatograph. The efficiency of the prepared terpolymers as viscosity index improvers and pour point depressants for lube oil was investigation. It was found that all the prepared terpolymers are effective as viscosity index improvers and pour point depressants. The viscosity index of the prepared terpolymers increases with increasing the concentration of the additives and increases by increasing the percentage of hexadecylacrylate until 70%. The best result for viscosity index of the prepared terpolymers is when the percentage of styrene is 10%. The pour point of the prepared compound decreases with decreasing concentration of additive used. 相似文献
124.
Chemical investigation of the EtOAc extract of the mangrove-derived endophyte Corynespora cassiicola, isolated from Laguncularia racemosa (Combretaceae), afforded five new secondary metabolites, named coryoctalactones A–E (1–5). The structures of the new compounds were determined on the basis of 1D- and 2D-NMR spectroscopy as well as high-resolution mass spectrometry. The absolute configuration of the side chain in 1–3 and 5 were tentatively deduced based on biogenetic consideration in comparison with xestodecalactones, previously isolated from C. cassiicola. All isolated compounds were evaluated for their antimicrobial, cytotoxic, and antitrypanosomal activities. 相似文献
125.
Moustafa Sh. Ibrahim Amal H. Werida Safaa El-din H. Etaiw 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2441-2451
New supramolecular complexes [(Me 3 Sn)(Ph 3 Sn) 2 Fe(CN) 6 ] (I) and [(n-Bu 3 Sn)(Ph 3 Sn) 2 Fe(CN) 6 ] (II) are readily accessible by straightforward self-assembly of [Fe(CN) 6 ] 3? and hydrated R 3 Sn+/R′ 3 Sn + ions (R = Ph, and R′ = Me or n-Bu). The structural characterization of (I) and (II) is compared with well-documented supramolecular complex containing only Ph 3 Sn + unit, [(Ph 3 Sn) 3 Fe(CN) 6 ]. These novel compounds have wide internal cavities capable of encapsulating voluminous organic compounds, and they behave as host acceptors forming charge transfer complexes (CTC). Thiophene compounds acting as guest donor species are encapsulated within the cavities of the three-dimensional (3D) supramolecular hosts. The structure and physical properties of these hosts and host–guest systems were studied by X-ray powder diffraction, IR, UV/Vis., and magnetic measurements. 相似文献
126.
Samer Aouad Amal Aoun Mira Skaf Madonna Labaki John El Nakat Bilal El Khoury Pierre Obeid Edmond Abi-Aad Antoine Aboukaïs 《Comptes Rendus Chimie》2013,16(10):868-871
The effects of CoxMgyAl2Oz mixed oxides composition and ruthenium addition on the oxidation of propylene and carbon black (CB) were investigated. Different reactive cobalt and ruthenium oxide species were formed following calcination at 600 °C. The addition of ruthenium was beneficial for the CB oxidation under “loose contact” conditions and for propylene oxidation when the cobalt content was intermediate to low. The calculated activation energy for CB oxidation was decreased from 151 kJ mol−1 for the uncatalyzed reaction to 111 kJ mol−1 over the best catalyst. 相似文献
127.
Keith E. Levine Li Han Andrea C. McWilliams Amal S. Essader Kelly E. Amato Reshan A. Fernando Donna B. Browning Lisa C. Greene David S. Ensor Nigel J. Walker Veronica G. Robinson Bradley J. Collins 《Mikrochimica acta》2014,181(1-2):171-179
The objective of this study was to characterize an assortment of as received, commercially available, non-functionalized multiwalled carbon nanotubes (MWCNT) samples (n?=?24) using thermogravimetric analysis, energy dispersive X-ray fluorescence spectrometry, high-resolution transmission electron microscopy and scanning electron microscopy. Each sample was assigned to one of six types based on nominal length and diameter. Some of the samples from the product assortment exhibited significant differences in purity and morphology from their nominal values. Variability in the physicochemical properties of MWCNTs may be a significant factor in why many toxicological investigations have findings that are difficult to reproduce. Therefore, it is strongly recommended that investigators studying these materials present characterization information in addition to providing their source. Figure
TGA and XRF purity by type of MWCNT sample. The objective of this study was to characterize an assortment of commercially available, non-functionalized of multiwalled carbon nanotubes (MWCNT) samples using thermogravimetric analysis, energy dispersive X-ray fluorescence spectrometry, high-resolution transmission electron microscopy and scanning electron microscopy. Variability in the physicochemical properties of MWCNTs may be a significant factor in why many toxicological investigations have findings that are difficult to reproduce. Therefore, it is strongly recommended that investigators studying these materials present characterization information with their research findings in addition to providing their source. 相似文献
128.
Antonius R.B. Ola Abdessamad Debbab Tibor Kurtán Heike Brötz-Oesterhelt Amal H. Aly Peter Proksch 《Tetrahedron letters》2014
Chemical investigation of the endophytic fungus Diaporthe melonis, isolated from Annona squamosa, yielded two new dihydroanthracenone atropodiastereomers, diaporthemins A (1) and B (2), together with the known flavomannin-6,6′-di-O-methyl ether (3). The structures of the new compounds were established on the basis of extensive 1D and 2D NMR spectroscopy, as well as by high resolution mass spectrometry and by CD spectroscopy. Compounds 1–3 were tested for their antimicrobial activity against a multi-resistant clinical isolate of Staphylococcus aureus 25697, a susceptible reference strain of S. aureus ATCC 29213 and against Streptococcus pneumoniae ATCC 49619. Compound 3 strongly inhibited S. pneumonia growth with a MIC value of 2 μg/mL, and showed moderate activity against the S. aureus multi-resistant clinical isolate and susceptible reference strain (MIC 32 μg/mL), whereas 1 and 2 were not active against the tested strains. 相似文献
129.
Maha M. Abdelrahman Amal B. Ahmed Mahmoud A. Omar Sayed M. Derayea Nada S. Abdelwahab 《Journal of separation science》2020,43(15):2981-2988
Citicoline and piracetam were subjected separately to different stress conditions as recommended by the international conference on harmonization. In addition, new stability indicating thin layer chromatographic and ultra high performance liquid chromatographic methods have been developed and validated for simultaneous determination of citicoline and piracetam in presence of their degradation products. Separation on the proposed thin layer chromatographic method was carried out using a developing system containing methanol:chloroform:ammonium chloride buffer (9:1:2, v/v/v) on silica gel plates at 230 nm. On the other hand, the mobile phase in the ultra high performance liquid chromatographic method was composed of water (containing 0.1% triethylamine):ethanol (92:8, v/v). The flow rate was 1 mL/min and ultraviolet detection was at 230 nm. Moreover, results of the developed methods were statistically compared to those obtained by the reported high‐performance liquid chromatography method and no significant difference between them was found. The greenness profile of ultra high performance liquid chromatographic method was assessed and compared with those of the previously published high‐performance liquid chromatography methods, it was noticed that the proposed ultra high performance liquid chromatographic method more environmentally friendly and greener than other methods. 相似文献
130.
Ultrathin Hexagonal Hybrid Nanosheets Synthesized by Graphene Oxide‐Assisted Exfoliation of β‐Co(OH)2 Mesocrystals
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Dr. Suzi Deng Dr. Christie Thomas Cherian Xiao li Liu Hui Ru Tan Li Hsia Yeo Dr. Xiaojiang Yu Prof. Andrivo Rusydi Prof. B. V. R. Chowdari Prof. Hai Ming Fan Prof. Chorng Haur Sow 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12444-12452
In the present study, we report the synthesis of a high‐quality, single‐crystal hexagonal β‐Co(OH)2 nanosheet, exhibiting a thickness down to ten atomic layers and an aspect ratio exceeding 900, by using graphene oxide (GO) as an exfoliant of β‐Co(OH)2 nanoflowers. Unlike conventional approaches using ionic precursors in which morphological control is realized by structure‐directing molecules, the β‐Co(OH)2 flower‐like superstructures were first grown by a nanoparticle‐mediated crystallization process, which results in large 3D superstructure consisting of ultrathin nanosheets interspaced by polydimethoxyaniline (PDMA). Thereafter, β‐Co(OH)2 nanoflowers were chemically exfoliated by surface‐active GO under hydrothermal conditions into unilamellar single‐crystal nanosheets. In this reaction, GO acts as a two‐dimensional (2D) amphiphile to facilitate the exfoliation process through tailored interactions between organic and inorganic molecules. Meanwhile, the on‐site conjugation of GO and Co(OH)2 promotes the thermodynamic stability of freestanding ultrathin nanosheets and restrains further growth through Oswald ripening. The unique 2D structure combined with functionalities of the hybrid ultrathin Co(OH)2 nanosheets on rGO resulted in a remarkably enhanced lithium‐ion storage performance as anode materials, maintaining a reversible capacity of 860 mA h g?1 for as many as 30 cycles. Since mesocrystals are ubiquitous and rich in morphological diversity, the strategy of the GO‐assisted exfoliation of mesocrystals developed here provides an opportunity for the synthesis of new functional nanostructures that could bear importance in clean renewable energy, catalysis, photoelectronics, and photonics. 相似文献