排序方式: 共有78条查询结果,搜索用时 15 毫秒
31.
Ramyah Radman Abdullah A. Al-Kahtani Wafa K. Mekhamer A. Yacine Badjah Hadj Ahmed 《Green Chemistry Letters and Reviews》2020,13(4):1-10
ABSTRACT Vicinal diols are important building blocks for chemicals and pharmaceuticals. Currently, they are produced from olefins using solvents and harmful oxidants unfavorable from an environmental and economic point of view. This work lies on the synthesis of 1,2 cyclohexane diol from cyclohexene by a green route. To achieve it, a series of Cobalt Keggin heteropolyanion salt (Co1.5PW12O40) loaded on activated carbon with different contents was prepared, characterized and tested for the synthesis of diol. The effect of various parameters such as reaction temperature, reaction time and CO2 pressure on the reaction was studied. The effect of reaction temperature in the range 60-80 °C showed that high temperatures favor diol formation while low temperatures favor cyclohexanone and a segmented concave Arrhenius graph was observed. The results of this work showed that oxidation by H2O2 in the presence of CO2 is an efficient oxidant system for the production of 1.2 cyclohexane diol over carbon activated carbon supported Co1.5PW12O40. Thanks to CO2 as a soft oxidizing agent, a conversion of 96.9% and a selectivity in 1, 2 cyclohexane diol of 64.2% was obtained. This simple, safe and environmentally method could be an alternative green route for vicinal diols production from alkenes. 相似文献
32.
Kareem Yusuf Amro K. F. Dyab Zeid A. ALOthman Ahmed Yacine Badjah-Hadj-Ahmed 《液相色谱法及相关技术杂志》2016,39(16):752-761
Sporopollenin microparticles have been prepared form Lycopodium clavatum spores, defatted and incorporated into a porous methacrylate polymer monolith to enhance liquid chromatographic performance of different sets of small neutral molecules. A stable suspension between sporopollenin microparticles and porogenic solvents composed of 1-propanol and 1,4-butandiol has proved before preparation, and seven compositions with increasing sporopollenin microparticles were prepared inside fused silica tubing. After optimizing of the preparation conditions, the structure of the stationary phase was characterized by scanning electron microscopy, surface area analysis, thermodynamic study, short- and long-term precision, and hydrodynamic properties including mechanical stability, porosity, and permeability. The columns were successfully applied to improve the separation efficiency of different mixtures using capillary liquid chromatography. Addition of very small amount of sporopollenin microparticles to the methacrylate mixture enhanced the column efficiency from 3 to 5 times for ketonic and phenolic compounds and reduced the retention with the corresponding better resolution and peak shapes for all studied compounds. 相似文献
33.
Si Ahmed K Tazerouti F Badjah-Hadj-Ahmed AY Meklati BY 《Journal of separation science》2007,30(13):2025-2036
A phenylcarbamate derivative of 2-hydroxypropyl-beta-CD bonded stationary phase was prepared by a previously described method. Its enantiomeric recognition abilities were evaluated as chiral stationary phase (CSP) in normal, polar organic and RP conditions by HPLC. The relevant structural features of the prepared stationary phase which make it an effective chiral selector are discussed. This material seems to have an excellent enantioselectivity for a variety of racemic analytes in the three modes. Hence it can be considered a highly effective multimodal column. Retention factor (k), selectivity (alpha) and resolution (R(s)) were the chosen parameters to describe the column performance. Optimization of these separations was discussed in terms of mobile phase composition, flow rate and structural patterns of the injected analytes. 相似文献
34.
Choi J Choi K Kim J Ahmed AY Al-Othman ZA Chung DS 《Journal of chromatography. A》2011,1218(41):7227-7233
In order to analyze amino acids sensitively without derivatization, we have developed carrier-mediated single drop microextraction (SDME). Nonane-1-sulfonic acid was added to an acidic sample donor solution as a carrier to form neutral ion pair complexes with amino acids. The ion pair complexes were extracted to the organic phase, covering a drop of an aqueous basic acceptor phase hanging at the tip of a capillary, and then back-extracted to the basic acceptor phase, where both the amino acids and the carrier have negative charges and the ion pair complexes are broken. The resulting extract of enriched amino acids was injected into the capillary and analyzed by capillary electrophoresis. With 20-min SDME with agitation of the donor phase, enrichment factors of four aromatic amino acids were up to 120-fold, yielding the LOD of 70-500 nM. The linear dynamic ranges for corrected peak areas were 1-100 μM with linear correlation coefficients larger than 0.9959. With internal standardization, the intraday RSDs of migration times and corrected peak areas were 0.01-0.04% and 2.0-3.7%, respectively. The capabilities of sample cleanup including desalting and preconcentration of carrier-mediated SDME were demonstrated with the analysis of human urine after minimal pretreatment of acidification and centrifugation. 相似文献
35.
Zeid Abdullah Alothman Saikh Mohammad Wabaidur Mohammad Rizwan Khan Ayman Abdel Ghafar Mohamed Abdelaty Habila Yacine Badjah Hadj Ahmed 《Journal of separation science》2012,35(21):2892-2896
In the present work, a rapid and sensitive ultra performance liquid chromatography‐mass spectrometry method has been proposed for the analysis of capsaicinoids (nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin) present in different Capsicum samples. Extraction of capsaicinoids was carried out by liquid–liquid extraction using ethanol as an extracting solvent, while the chromatographic separation was achieved by reversed phase C18 column with gradient mobile phase (solvent A: acetonitrile and solvent B: water with 0.1% formic acid). Under the optimum experimental conditions, the linear ranges were 0.5–50 μg/g with correlation coefficient (r2) >0.999 for each capsaicinoids and detection limits were 0.15, 0.05, 0.06, 0.2, and 0.1 μg/g for nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin, respectively. Run‐to‐run and day‐to‐day precisions of the method with relative standard deviations <1.5% were achieved for all analyzed capsaicinoids. The robustness of the method was determined by utilizing different injection volumes of the extracts. Furthermore, to validate the system robustness, a run of high number of capsaicinoids present in different varieties of Capsicum samples was performed in this study. All the capsaicinoids were separated in a time of less than 9 min by employing the proposed method. 相似文献
36.
The transient growth due to non-normality is investigated for the PoiseuilleRayleigh-Bénard problem of binary fluids with the Soret effect. For negative separation factors such as ψ =-0.1, it is found that a large transient growth can be obtained by the non-normal interaction of the two least-stable-modes, i.e., the upstream and downstream modes, which determine the linear critical boundary curves for small Reynolds numbers.The transient growth is so strong that the optimal energy amplification factor G(t) is up to 10~2~10~3. While for positive separation factors such as ψ = 0.1, the transient growth is weak with the order O(1) of the amplification factor, which can even be computed by the least-stable-mode. However, for both cases, the least-stable-mode can govern the long-term behavior of the amplification factor for large time. The results also show that large Reynolds numbers have stabilization effects for the maximum amplification within moderate wave number regions. Meanwhile, much small negative or large positive separation factors and large Rayleigh numbers can enlarge the maximum transient growth of the pure streamwise disturbance with the wavenumber α = 3.14. Moreover, the initial and evolutionary two-dimensional spatial patterns of the large transient growth for the pure streamwise disturbance are exhibited with a plot of the velocity vector, spanwise vorticity, temperature, and concentration field. The initial three-layer cell vorticity structure is revealed. When the amplification factor reaches the maximum Gmax, it develops into one cell structure with large amplification for the vorticity strength. 相似文献
37.
Lisa I. Pilkington Xue Yang Meng‐Wen Liu Yacine Hemar Margaret A. Brimble Jhannes Reynisson 《化学:亚洲杂志》2019,14(8):1117-1127
Several hundred (396) compounds from New Zealand flora with medicinal properties were analyzed for their physicochemical properties. It was found that approximately 10 % fulfilled all the requirements to be considered to be lead‐like, over half of the compounds were deemed to be in the drug‐like space and ≈75 % were in the known drug space. These results indicate the presence of a significant proportion of compounds that are of particular interest to pursue as potential lead compounds or therapeutics. Additionally, compound classes were analyzed separately—most carbonyl‐containing compounds (aldehydes, ketones, esters and lactones), along with phenols were the most lead‐like compounds, which also displayed very good proportions in the drug‐like and known drug space. The information presented herein can be harnessed and utilized in future work, through focussing on the compounds and compound classes that exhibit high‐levels of lead‐likeness for further development. 相似文献
38.
The possibility of improving the heat transfer is investigated numerically using finite volume method. The Reynolds number increase has a minor effect on flow structure but generates a systematic rise of Nusselt Number. The maximum heat exchange occurs when the cavity bottom is located at the potential core end. The main heat exchange occurs on the cavity bottom for every case. The stagnation Nusselt number is correlated according some problem parameters. 相似文献
39.
A re-investigation of resveratrol synthesis by Perkins reaction. Application to the synthesis of aryl cinnamic acids 总被引:1,自引:0,他引:1
A re-investigation of resveratrol synthesis by Perkins reaction allowed to improve this method and to determine the configuration of the intermediates. The results were applied to the synthesis of several aryl cinnamic acids for biological evaluation. 相似文献
40.
Mokhtar Benalia Ahmed Yacine Badjah-Hadj-Ahmed Mebrouk Djedid B. Youcef Meklati A. H. Al-Dujaili Fouad Ferkous 《Chromatographia》2007,66(7-8):565-570
The investigation of the analytical properties of two new nematic sulphur-containing liquid crystals 5-(4-methoxyphenyl)-azophenyl)-2-butylthio-1,3,4-oxadiazole
(Phase I) and 5-(4-(propoxyphenyl)-azophenyl)-2-butyl thio-1,3,4-oxadiazole (Phase II) and which comprise units of 1,3,4-oxadiazole
instead of the aromatic cycles, was carried out by gas chromatography using glass capillary columns. For this purpose, many
solutes belonging to various families and having different polarities and volatilities were injected. Comparison of the retention
data of the studied components has shown that Phase II allowed a better separation than the other phase. The two liquid crystalline
materials show a good separation of the studied isomers except for xylene. 相似文献