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Zuhair S. Salih Peter Stegmüller Wolfgang Pfleiderer 《Journal of heterocyclic chemistry》1988,25(5):1443-1447
Acylations of 1,3-dimethyl- ( 1 ) and 1,3,7-trimethylpyrrolo[2,3-d]pyrimidine-2,4-dione ( 2 ) with anhydrides in the presence of trifluoroacetic acid proceed well to give in good yields the corresponding 7-acyl derivatives 3–11 . The 6-trichloroacetyl derivatives 5 and 6 are sensitive towards nucleophiles, which displace the trichloromethyl group easily by formation of the corresponding 6-carboxylic acid derivatives 12–23. The newly synthesized compounds have been characterized by elemental analysis, uv and 1H nmr spectra and pKa, determinations. 相似文献
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The corrosion inhibition of mild steel in hydrochloric acid solution in the presence of three different molecular weights of polyvinyl alcohol (PVA) designated as PVA-I, PVA-II, and PVA-III corresponding to 14,000, 72,000, and 125,000 g mol?1, respectively, was investigated using electrochemical impedance spectroscopy, linear polarization resistance (LPR), and potentiodynamic polarization techniques at 25°C. It was found that PVA of different molecular weights inhibited the corrosion of mild steel in the acid environment. Inhibition efficiency (η%) increases with increase in concentration of the polymers. LPR measurements clearly show that inhibition efficiency increases with increasing molecular weight in the order PVA-III > PVA-II > PVA-I. Polarization curves indicate that PVA functions as a mixed inhibitor affecting both the anodic metal dissolution and cathodic hydrogen evolution partial reactions of the corrosion process. The experimental data obtained fitted well into Langmuir adsorption isotherm model. Physical adsorption mechanism is proposed from the thermodynamic (free energy of adsorption) parameters obtained. 相似文献
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Ionics - The adsorption and corrosion inhibition behavior of strawberry fruit extract at steel/1 M HCl and steel/0.5 M H2SO4 interfaces were investigated using gravimetric and... 相似文献
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Al-Dirbashi OY Rashed MS Jacob M Al-Ahaideb LY Al-Amoudi M Rahbeeni Z Al-Sayed MM Al-Hassnan Z Al-Owain M Al-Zeidan H 《Biomedical chromatography : BMC》2008,22(11):1181-1185
We describe an improved diagnostic method for tyrosinemia type 1 based on quantifying succinylacetone in dried blood spots by ultra-performance liquid chromatography tandem mass spectrometry. Succinylacetone extracted from a single 3/16 inch disk of specimen collection paper containing a dried blood spot was derivatized with dansylhydrazine, separated on an Acquity UPLC BEH C(18) column (2.1 x 50 mm, 1.7 microm) and detected by electrospray ionization tandem mass spectrometry. Succinylacetone derivative eluted at 0.6 min with a complete run time of 1 min. Using a 13C4 labeled succinylacetone as an internal standard, the calibration plot was linear up to 100 micromol/L with a detection limit (S/N = 3) of 0.2 micromol/L. Intra-day (n = 13) and inter-day (n = 10) variations were better than 10%. The cutoff level of succinylacetone in dried blood spots from healthy infants obtained by the current method was 0.63 micromol/L (n = 151). In dried blood spots from patients with established tyrosinemia type 1 (n = 11), concentration of succinylacetone was 6.4-30.8 micromol/L. 相似文献
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I. B. Obot E. E. Ebenso N. O. Obi-Egbedi Ayo S. Afolabi Zuhair M. Gasem 《Research on Chemical Intermediates》2012,38(8):1761-1779
The adsorption and inhibition effect of itraconazole (ICZ) on mild steel in 0.5?M HCl at 303?C333?K was studied using gravimetric and quantum chemical methods. The adsorption of ICZ has been tested thermodynamically and was found to be mainly a physical adsorption mechanism and weak chemisorption. The activation and thermodynamic functions (such as E a, $ \Updelta H^{*} ,\,\Updelta G_{\text{ads}}^{\text{o}} $ ) of dissolution and adsorption processes have been evaluated and discussed. The analyses of the results obtained showed that ICZ inhibits the corrosion of mild steel effectively at moderate temperatures and adsorbs according to the Temkin adsorption isotherm. An attempt to correlate the molecular structure to quantum chemical indices was made using a semi-empirical (PM3) method. Results of the theoretical study indicate that nitrogen and oxygen atoms (O10, O13, N17, N19, O21, N28, N42, N43, and O45) were the reactive sites. 相似文献
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Organoiron thio- and seleno-terephthaloyl chloride complexes CpFe(CO)2ECO(C6H4)COCl (E = S and Se) react with NaOH and NaNH2 to give quantitative yields of the acid Cp(CO)2ECO(C6H4)CO2H and the amide CpFe(CO)2ECO(C6H4)CONH2 respectively. These amide and acid derivatives react with the terephthaloyl chloride complexes to give a new series of imide-bridged
[CpFe(CO)2ECO(C6H4)CO]2NH and anhydride-bridged [CpFe(CO)2ECO(C6H4)CO]2O organoiron dinuclear homo and hetero dichalcogeno terephthalate complexes. The complexes were characterized by elemental
analysis, i.r. and 1H-n.m.r. spectra.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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A signal is said to have finite rate of innovation if it has a finite number of degrees of freedom per unit of time. Reconstructing signals with finite rate of innovation from their exact average samples has been studied in Sun (SIAM J. Math. Anal. 38, 1389–1422, 2006). In this paper, we consider the problem of reconstructing signals with finite rate of innovation from their average samples in the presence of deterministic and random noise. We develop an adaptive Tikhonov regularization approach to this reconstruction problem. Our simulation results demonstrate that our adaptive approach is robust against noise, is almost consistent in various sampling processes, and is also locally implementable. 相似文献
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Al-Dirbashi OY Jacob M Al-Hassnan Z Chabayta RW El-Badaoui F Rashed MS 《Biomedical chromatography : BMC》2006,20(1):54-60
We developed and validated an HPLC method with intramolecular excimer-forming fluorescence derivatization to determine methylmalonic acid, a unique biochemical marker for methylmalonic aciduria. Methylmalonic acid in urine and an internal standard were derivatized with pyrenebutyric hydrazide and separated on a C8 column. The derivatives were detected by monitoring the fluorescence at 475 nm (excitation wavelength 345 nm). At a signal-to-noise ratio of 3, the detection limit was 0.33 pmol on the column and the calibration curve was linear up to 1 mmol[sol ]L in urine. In a retrospective study on a relatively large number of known methylmalonic aciduria cases (n = 48), the method enabled us to differentiate methylmalonic aciduria cases from healthy controls (n = 52), regardless of age of patients at sampling or years of specimen storage. No interference was observed from isomeric or other dicarboxylic acids, or other urine constituents. As described, the method can be used retrospectively or prospectively for the diagnosis of methylmalonic aciduria and can be easily adopted by laboratories with no access to gas chromatography-mass spectrometry. 相似文献