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排序方式: 共有819条查询结果,搜索用时 31 毫秒
21.
Sidra Jabeen Zhe Zeng Mohammednoor Altarawneh Xiangpeng Gao Anam Saeed Bogdan Z. Dlugogorski 《国际化学动力学杂志》2019,51(9):696-710
This contribution investigates thermal decomposition of leucine, as a representative model compound for amino acids in algal biomass. We map out potential energy surface for a wide array of unimolecular and self-condensation reactions operating in the decomposition of leucine. Decarboxylation and dehydration of leucine ensues by eliminating CO2 and –OH, respectively, from the –COOH group attached to the α-carbon. The molecular channel for deamination involves cleavage of NH2 from α-carbon of leucine. The activation energies for direct elimination of CO2, NH3, and H2O from a leucine molecule lie within 20.7 kJ/mol of each other. Activation energies for these decomposition pathways reside below the bond dissociation enthalpy of H–C(α) of 323.1 kJ/mol. The decarboxylation, deamination, and dehydration pathways, via radical-prompted pathways, systematically require lower energy barriers, in reference to closed-shell reaction corridors. Detailed computations at the CBS-QB3 level provide the Arrhenius rate parameters for the unimolecular and bimolecular reactions, and standard enthalpies of formation, standard entropies, and heat capacities for all the products and intermediates. A kinetic analysis of gas-phase reactions, within the context of a plug-flow reactor model, accounts qualitatively for the formation of major products observed experimentally in the thermal degradation of the condensed-phase leucine. Among notable N-containing species, the model predicts the prevailing of NH3 over HCN and HNCO, in addition to corresponding appreciable concentrations of amines, imines, and nitriles. Our detailed kinetic investigation illustrates a negligible contribution of the self-condensation reactions of leucine in the gas phase. 相似文献
22.
Guan-Yeow Yeap Elango Hrishikesan Yi-Huan Chan Wan Ahmad Kamil Mahmood 《Journal of fluorescence》2017,27(1):105-110
A new chalcone-based probe containing coumarin and naphthol at both ends has been synthesized via aldol condensation. The uniqueness of the newly derived probe can be ascribed to the presence of naphthol and coumarin units acting as binding site and signaling element, respectively. The fluorogenic behaviors toward various anions were investigated. The probe was characterized by various spectroscopic techniques and the in-depth study led to show excellent selectivity and sensitivity for fluoride ions. The hydrogen bonding thus formed with fluoride anion provides remarkable fluorometric responses. The interactions of the probe with fluoride ions were determined by fluorescence, FT-IR and NMR spectroscopic techniques. The exploratory studies by fluorescent spectral changes augur well for the naked-eye sensing applications. 相似文献
23.
24.
Rahman Hosseinzadeh Mahmood Tajbakhsh Maryam Mohadjerani Parizad Rezaei Mohammad Alikarami 《合成通讯》2013,43(17):3023-3031
An efficient synthesis of diaryl ethers by the copper-catalyzed arylation of phenols with a variety of aryl iodide susing KF/Al2O3 as a suitable base and CuI and 1,3 diphenyl-1,3 propandione as the catalyst is described. 相似文献
25.
Reza Rooki Faramarz Doulati Ardejani Ali Moradzadeh Mahmood Norouzi 《Journal of Dispersion Science and Technology》2013,34(3):402-410
Foam, as a non-Newtonian fluid, plays an important role in the underbalanced drilling technique in oil field development. The rheological properties of drilling fluids, such as foam, have a direct effect on flow characteristics and hydraulic performance. Two rheological models—the Herschel–Bulkley model and power law—were fitted to two foam systems in this study. Computational fluid dynamics (CFD) was used to simulate the effect of the rheological models on solid–liquid (cuttings transport) hydraulics in concentric and eccentric annulus during the foam drilling operation. The simulation results are compared to the experimental data from previous studies. The results of CFD using the power law model are in good agreement with experimental results in horizontal annulus with respect to the Herschel–Bulkley model with relative error less than 8%. Thus, for CFD cuttings transport for simulations in inclined and horizontal annulus, it is best to use the power law's rheological model parameters. 相似文献
26.
Zal U’yun Wan Mahmood Mei Wo Yii 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(3):1727-1732
The purpose of this study was to estimate the sedimentation rate in the Sungai Linggi estuary using the constant initial concentration of unsupported or excess 210Pb model and verified with 137Cs method. Five sediment cores were collected on 25 January 2011 using gravity corer with the inner tube of 50 cm length and 7.5 cm diameter. The total 210Pb activities in the sediment cores profile at all sampling stations were varied and upper than those obtained for supported 210Pb i.e. 226Ra, indicated disequilibrium among 210Pb and its grandparents in the 238U decay series. Meanwhile, the lower 137Cs activities were observed at all sampling stations due to no significant sources of 137Cs releases were transferred into Malaysian marine. The estimation of sedimentation rate indicated the agreement of 210Pb and 137Cs method with a general presence of deep mixing in the Sungai Linggi estuary. Therefore, the apparent sedimentation rates calculated from 210Pb profiles generally reflect the true value with the range from 0.70 to 1.97 cmyr?1. High sedimentation rate was observed at some sampling stations which are located in river channel, estuary and closer to mainland. This suggested that land-use development, agriculture activities, channelization etc. introduced a large amount of sediment loaded into those areas. 相似文献
27.
Aumaih H. Allawi Modher Y. Mohammed Nabeel B. Ayrim Mustafa A. Alheety Ahmed R. Mahmood 《印度化学会志》2022,99(8):100596
The research included the synthesis of a new complex of manganese with 3,4,5-tri-methoxybenzoic acid in the presence of triethylamine as a base to which gives the complex with formula [Mn (TMB)2].2H2O. This complex was characterized by FTIR, CHN, magnetic susceptibility and thermal analysis. Furthermore, this complex was used as a novel precursor of manganese in preparing the attapulgite-MnO2 nanocomposite by one-pot addition method using ultrasound. The resulting nanocomposite was characterized by X-ray diffraction and TEM and the results prove that this composite was found as nanochannel of the diameter 45 nm decorated with 26–41 nm of MnO2 nanoparticles. The attapulgite-MnO2 nanocomposite was used in the application of hydrogen storage, and the results proved that attapulgite-MnO2 nanocomposite has the ability to store 3.55 wt% of hydrogen under a pressure of 90 bar and a temperature of 77 K. Furthermore, the measurement demonstrated that increasing the pressure increased the stored hydrogen, implying that the stored gas will be liberated by altering the pressure, implying that the storage will be of the physical kind. 相似文献
28.
Considering the significance of non-Newtonian fluid usage in manufacturing such as molten plastics, polymeric materials, pulps, and so on, significant efforts have been made to investigate the phenomenon of non-Newtonian fluids. In this article the influences of heat and mass transfer on non-Newtonian Walter's B fluid flow over uppermost catalytic surface of a paraboloid is encountered. An elasticity of the fluid layer is considered in the freestream together with heat source/sink and has the tendency to cause heat flow in the fluid saturated domain. The flow problem of two-dimensional Walter's B fluid is represented using Law of conservation of mass, momentum, heat, and concentration along with thermal and solutal chemical reactive boundary conditions. The governing equations are non-linear partial differential equation and are non-dimensionalized by employing stream function and similarity transformation. The final dimensionless equations yielded are coupled non-linear ordinary differential equations. Furthermore, shooting technique along with RK-4th order method is used to get the numerical results. Graphs and tables are modeled by using MATLAB software to check the effects of Walter's B parameter, Chemical reaction parameter and Thickness parameter on temperature, velocity, and concentration profiles. Tabular analysis shows the results of some physical parameters like skin friction coefficient, Nusselt number and Sherwood number due to the variation of Walter's B parameter, thickness parameter and chemical reactive parameter. 相似文献
29.
Nada Abdullah Yahya Tamimi Sergey Dobretsov Najwa Al Balushi Jalila Alshekaili Hamed Al Balushi Mahmood Al Kindi Syed Imran Hassan Shadia Al Bahlani Benjamin K. Tsang Ikram A. Burney 《Molecules (Basel, Switzerland)》2021,26(12)
High-grade epithelial ovarian cancer is a fatal disease in women frequently associated with drug resistance and poor outcomes. We previously demonstrated that a marine-derived compound MalforminA1 (MA1) was cytotoxic for the breast cancer cell line MCF-7. In this study, we aimed to examine the effect of MA1 on human ovarian cancer cells. The potential cytotoxicity of MA1was tested on cisplatin-sensitive (A2780S) and cisplatin-resistant (A2780CP) ovarian cancer cell lines using AlamarBlue assay, Hoechst dye, flow cytometry, Western blot, and RT-qPCR. MA1 had higher cytotoxic activity on A2780S (IC50 = 0.23 µM) and A2780CP (IC50 = 0.34 µM) cell lines when compared to cisplatin (IC50 = 31.4 µM and 76.9 µM, respectively). Flow cytometry analysis confirmed the cytotoxic effect of MA1. The synergistic effect of the two drugs was obvious, since only 13% of A2780S and 7% of A2780CP cells remained alive after 24 h of treatment with both MA1 and cisplatin. Moreover, we examined the expression of bcl2, p53, caspase3/9 genes at RNA and protein levels using RT-qPCR and Western blot, respectively, to figure out the cell death mechanism induced by MA1. A significant down-regulation in bcl2 and p53 genes was observed in treated cells compared to non-treated cells (p < 0.05), suggesting that MA1 may not follow the canonical pathway to induce apoptosis in ovarian cancer cell lines. MalforminA1 showed promising anticancer activity by inducing cytotoxicity in cisplatin-sensitive and cisplatin-resistant cancer cell lines. Interestingly, a synergistic effect was observed when MA1 was combined with cisplatin, leading to it overcoming its resistance to cisplatin. 相似文献
30.
Muddaser Shah Waheed Murad Najeeb Ur Rehman Sobia Ahsan Halim Manzoor Ahmed Hazir Rehman Muhammed Zahoor Sidra Mubin Ajmal Khan Mohamed A. Nassan Gaber El-Saber Batiha Ahmed Al-Harrasi 《Molecules (Basel, Switzerland)》2021,26(12)
In the current study, in vitro antimicrobial and antioxidant activities and in vivo anti-inflammatory and analgesic activities of Scutellaria edelbergii Rech. f. (crude extract and subfractions, i.e., n-hexane, ethyl acetate (EtOAc), chloroform, n-butanol (n-BuOH) and aqueous) were explored. Initially, extraction and fractionation of the selected medicinal plant were carried out, followed by phytochemical qualitative tests, which were mostly positive for all the extracts. EtOAc fraction possessed a significant amount of phenolic (79.2 ± 0.30 mg GAE/g) and flavonoid (84.0 ± 0.39 mg QE/g) content. The EtOAc fraction of S. edelbergii exhibited appreciable antibacterial activity against Gram-negative (Escherichia coli and Klebsiella pneumoniae) strains and significant zones of inhibition were observed against Gram-positive bacterial strains (Bacillus subtilis and Staphylococcus aureus). However, it was found inactive against Candida Albicans and Fusarium oxysporum fungal strains. The chloroform fraction was the most effective with an IC50 value of 172 and 74 µg/mL against DPPH (1,1-Diphenyl-2-picryl-hydrazyl) and ABTS assays, in comparison with standard ascorbic acid 59 and 63 µg/mL, respectively. Moreover, the EtOAc fraction displayed significant in vivo anti-inflammatory activity (54%) using carrageenan-induced assay and significant (55%) in vivo analgesic activity using acetic acid-induced writing assay. In addition, nine known compounds, ursolic acid (UA), ovaul (OV), oleanolic acid (OA), β-sitosterol (BS), micromeric acid (MA), taraxasterol acetate (TA), 5,3′,4′-trihydroxy-7-methoxy flavone (FL-1), 5,7,4′-trihydroxy-6,3′-dimiethoxyflavone (FL-2) and 7-methoxy catechin (FL-3), were isolated from methanolic extract of S. edelbergii. These constituents have never been obtained from this source. The structures of all the isolated constituents were elucidated by spectroscopic means. In conclusion, the EtOAc fraction and all other fractions of S. edelbergii, in general, displayed a significant role as antibacterial, free radical scavenger, anti-inflammatory and analgesic agents which may be due to the presence of these constituents and other flavonoids. 相似文献