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121.
Saadullah G. Aziz Abdulrahman O. Alyoubi Shaaban A. Elroby 《Molecular physics》2017,115(20):2565-2576
Kojic acid is a polyfunctional heterocyclic compound, with several important reaction centres; it has a wide range of applications in the cosmetic, medicine, food, agriculture and chemical industries. The present study aims at better insight into its electronic structure and bonding characteristics. Thus, density functional theory at the M06-2x /6-311++G** level of theory is used to investigate its ground state electronic and acid–base properties. Protonation and deprotonation enthalpies are computed and analysed. The ability of Kojic acid to form both water complexes and dimers is explored. Several different complexes and dimer structures were examined. Natural bond order and quantum topology features of the charge density were analysed. The origin of the stability of the studied complexes and dimer structures can be traced to hydrogen bonding, π-conjugative and non-covalent dispersive interactions. 相似文献
122.
Raju Suresh Kumar Alagar Ramar Subbu Perumal Abdulrahman I. Almansour Natarajan Arumugam Mohamed Ashraf Ali 《合成通讯》2013,43(20):2763-2772
Three-component reaction of 1-[(4-chlorophenyl)sulfanyl]acetone, malononitrile, and substituted aromatic aldehydes in the presence of sodium ethoxide under simple mixing at ambient temperature for 5–8 min afforded highly functionalized 4H-pyrans in good to excellent yields. 1,3-Dipolar cycloaddition of nitrile oxides over the nitrile functionality of the 4H-pyrans furnished 1,2,4-oxadiazoles in moderate yields.
Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for full experimental and spectral details. 相似文献
123.
Abdulrahman A. Al-Majed Fathalla Belal Mohammed A. Abounassif Naser Y. Khalil 《Mikrochimica acta》2003,141(1-2):1-6
A highly sensitive fluorimetric method has been developed for the determination of gentamicin. The method is based on its
coupling with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in 50% (v/v) methanolic phosphate buffer (pH 7.2) to give an
intensely fluorescent product having excitation and emission wavelengths at 465 nm and 530 nm, respectively. The experimental
parameters were carefully studied and incorporated into the procedure. The fluorescence-concentration plot is rectilinear
over the range 0.56–2.8 μg/mL (r = 0.999) with minimum detectability (S/N = 2) of 0.11 μg/mL (1.6 × 10−7 mol/L). The method was applied successfully to the determination of the drug in pharmaceutical dosage forms and the percentage
recoveries were satisfactorily accurate and precise. The method was further applied to spiked human plasma samples, the percentage
recovery was 97.9 ± 3.4. The interference encountered from endogenous amino acids could be eliminated through selective complexation
with freshly prepared copper (II) hydroxide. A proposal of the reaction pathway is presented. The method can measure the intact
drug, and can be used in presence of possible interference.
Received April 18, 2001; accepted April 10, 2002 相似文献
124.
Muhammad Muhsin Faraz Anvarhusein A. Isab Mshari A. Alotaibi Abdulrahman I. Alharthi Muhammad Nawaz Tahir Muhammad Monim-ul-Mehboob Saeed Ahmad 《Russian Journal of Inorganic Chemistry》2017,62(7):925-930
Zinc(II) complexes of 4-aminoantipyrine (AAP), [Zn(AAP)2X2] (X = Cl–, I–) and [Zn(AAP)(CN)2] · 2H2O were prepared and characterized by elemental analysis, IR and NMR (1H & 13C) spectroscopy. The crystal structure of [Zn(AAP)2Cl2] (1) was determined by X-ray crystallography. The structural analysis of 1 shows that the complex exists as a monomeric nonionic molecule with zinc atom bound to two AAP ligands and two chloride ions adopting a distorted tetrahedral geometry. In [Zn(AAP)2(CN)2] · 2H2O, the appearance of a band at 2162 cm–1 in IR and resonances around 142 ppm in the 13C NMR spectra indicated the binding of cyanide to zinc(II). 相似文献
125.
Functionalized nanoparticles based solid‐phase membrane micro‐tip extraction and high‐performance liquid chromatography analyses of vitamin B complex in human plasma 下载免费PDF全文
Imran Ali Umma Kulsum Zeid A. AL‐Othman Abdulrahman Alwarthan Kishwar Saleem 《Journal of separation science》2016,39(14):2678-2688
Iron nanoparticles were prepared by a green method following functionalization using 1‐butyl‐3‐methylimidazolium bromide. 1‐Butyl‐3‐methylimidazole iron nanoparticles were characterized using FTIR spectroscopy, energy dispersive X‐ray fluorescence, X‐ray diffraction, scanning electron microscopy and transmission electron microscopy. The nanoparticles were used in solid‐phase membrane micro‐tip extraction to separate vitamin B complex from plasma before high‐performance liquid chromatography. The optimum conditions obtained were sorbent (15 mg), agitation time (30 min), pH (9.0), desorbing solvent [water (5 mL) + methanol (5 mL) + sodium hydroxide (0.1 N) + acetic acid (d = 1.05 kg/L, pH 5.5), desorbing volume (10 mL) and desorption time (30 min). The percentage recoveries of all the eight vitamin B complex were from 60 to 83%. A high‐performance liquid chromatography method was developed using a PhE column (250 × 4.6 mm, 5.0 μm) and water/acetonitrile (95:5, v/v; pH 4.0 with 0.1% formic acid) mobile phase. The flow rate was 1.0 mL/min with detection at 270 and 210 nm. The values of the capacity, separation and resolution factor were 0.57–39.47, 1.12–6.00 and 1.84–26.26, respectively. The developed sample preparation and chromatographic methods were fast, selective, inexpensive, economic and reproducible. The developed method can be applied for analyzing these drugs in biological and environmental matrices. 相似文献
126.
NO and OH* emission characteristics of very-lean to stoichiometric ammonia–hydrogen–air swirl flames
Xuren Zhu Abdulrahman A. Khateeb Thibault F. Guiberti William L. Roberts 《Proceedings of the Combustion Institute》2021,38(4):5155-5162
One of the main concerns regarding ammonia combustion is its tendency to yield high nitric oxide (NO) emissions. Burning ammonia under slightly rich conditions reduces the NO mole fraction to a low level, but the penalties are poor combustion efficiency and unburnt ammonia. As an alternative solution, this paper reports the experimental investigation of premixed swirl flames fueled with ammonia-hydrogen mixtures under very-lean to stoichiometric conditions. A gas analyzer was used to measure the NO mole fraction in the flame and post flame regions, and it was found that low NO emissions (as low as 100 ppm) in the exhaust were achieved under very lean conditions (? ≈ 0.40). Low NO emission was also possible at higher equivalence ratios, e.g. ? = 0.65, for very large ammonia fuel fractions (XNH3 > 0.90). 1-D flame simulations were performed to elaborate on experimental findings and clarify the observations of the chemical kinetics. In addition, images of OH* chemiluminescence intensity were captured to identify the flame structure. It was found that, for some conditions, the OH* chemiluminescence intensity can be used as a proxy for the NO mole fraction. A monotonic relationship was discovered between OH* chemiluminescence intensities and NO mole fraction for a wide range of ammonia-hydrogen blends (0.40 < ? < 0.90 and 0.25 < XNH3 < 0.90), making it possible to use the low-cost OH* chemiluminescence technique to qualify NO emission of flames fueled with hydrogen-enriched ammonia blends. 相似文献
127.
Lu-Lu Geng Xiao-Jun Yang Abdulrahman Ali Alsolami 《Mathematical Methods in the Applied Sciences》2023,46(2):1809-1820
In the paper, we consider some fractional integral formulas in terms of the Riemann–Liouville, Erdélyi–Kober type, and Weyl fractional integral operators and present the general fractional kinetic model involving the hypergeometric superhyperbolic sine function via the Gauss hypergeometric series. 相似文献
128.
Abdulrahman Abdul-Hadi Wedad Al-Qadhi Enayat El-Zeen 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(2):261-266
Uranium, thorium and potassium contents in 16 different rock samples from various sites in Republic of Yemen were determined
using three different techniques of analysis: γ-spectrometry, Instrumental neutron activation analyses (INAA) and X-ray fluorescence
(XRF). The concentration range for thorium, uranium and potassium were found to be from 9,810 ± 272 to 3.6 ± 1.3 ppm, 1,072 ± 40
to 1.2 ± 0.7 ppm and 11 ± 1 to 0.26 ± 0.05%, respectively. 相似文献
129.
130.
A simple kinetic spectrophotometric method was developed for the determination of josamycin in its dosage forms. The method is based on oxidation of the drug with alkaline potassium permanganate at room temperature for a fixed time of 20 min and measuring the produced green color at 611 nm. The absorbance-concentration plot is rectilinear over the range of 2-10 microg/mL (2.4 x 10(6)-1.2 x 10(-5)M) with minimum detectability of 1.0 microg/mL (1.2 x 10(-6)M). The determination of josamycin by fixed concentration and the rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was applied successfully to commercial tablets, and statistical analysis showed that the results compared favorably with those obtained by reference methods. The effect of sensitizers and surfactants on the performance of the proposed method was also studied. A proposal of the reaction pathway was presented. 相似文献