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991.
Rashed MS Aboul-Enein HY AlAmoudi M Jakob M Al-Ahaideb LY Abbad A Shabib S Al-Jishi E 《Biomedical chromatography : BMC》2002,16(3):191-198
Glyceric acid is a highly polar chiral carboxylic acid that is usually not detected during routine organic acid analysis. Increased excretion is observed in two phenotypically distinct and rare inherited metabolic diseases, D-glyceric aciduria, and L-glyceric aciduria (also known as primary hyperoxaluria type 2). The determination of the exact configuration of the excreted glyceric acid is necessary for the accurate diagnosis of D-glyceric aciduria and for the differentiation between type 1 and type 2 primary hyperoxaluria. The separation of the two stereoisomers was achieved using a narrow-bore ristocetin A glycopeptide antibiotic silica gel bonded column. Triethylamine acetate at pH 4.1 with 10% methanol was used as mobile phase. The column was directly interfaced to a triple quadrupole tandem mass spectrometer and the electrospray ion source was operated in the negative ion mode. Three parent-to-daughter transitions were employed to specifically detect eluting glyceric enantiomers from essentially untreated urine samples. The two forms of glyceric acid were satisfactorily separated at 3.6 and 4.5 min. Application of the method led to the confirmation of three cases of D-glyceric aciduria from three different families. Two other cases are suspected to be L-glyceric aciduria but further confirmation is needed. The method allowed the detection of the glyceric acid stereoisomers in control urine where it was found without exception that L-glyceric was the predominate metabolite. 相似文献
992.
Zahid Hassan Hidayat Hussain Viqar Uddin Ahmad Shazia Anjum Gennaro Pescitelli Tibor Kurtn Karsten Krohn 《Tetrahedron: Asymmetry》2007,18(24):2905-2909
The absolute configuration of 1β,10β-epoxydesacetoxymatricarin 1, a sesquiterpenoid isolated from Carthamus oxycantha, was established by TDDFT CD calculations in combination with single crystal X-ray analysis. Since the solid-state CD spectrum shows contributions from intermolecular interactions in the crystal, 1 represents a test case for our solid-state CD/TDDFT approach. 相似文献
993.
Sami H. Mahmood Maen A. Gharaibeh Hassan Abu-Safia Ahmad S. Saleh 《Hyperfine Interactions》1993,77(1):255-264
We report the results of a Mössbauer study of the alloy sytem FeAl1?x Co x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN2 temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases. 相似文献
994.
995.
996.
The internal solid contact sensor for the determination of doxycycline hydrochloride (DC) was developed based on a conducting polypyrrole (PPy) film immobilized on a glassy carbon electrode surface casted by a plasticized polyvinyl chloride (PVC) membrane containing an ion-pair compound of DC with tetraphenylborate (TPB) and dibutylphthalate (DBP) as plasticizer. Effects of various factors for the electropolymerization of pyrrole or aniline, including monomer concentration, acidity or inorganic salt and thickness of polymer film were investigated experimentally. It was found that the slope and the linear range of SCSs changed with both the different concentration of monomer and of KCl in electrolyte solution and with the different substrate material and a marked influence of the change of solution pH on the potential response of sensor occurred when sample solution pH>3.5. Under the condition of pH 2.8, the sensor showed a near-Nernstian response over the range of DC concentration of 1.0x10(-2)-1.0x10(-5) mol l(-1) with the slope (at 25 degrees C) of 54.4 mV per decade. The detection limit obtained was 4.0x10(-6) mol l(-1).The sensor was successfully applied to determination of DC in pharmaceutical formulation. 相似文献
997.
N. M. Hassan C. A. Nash H. H. Saito J. C. Marra 《Journal of Radioanalytical and Nuclear Chemistry》2003,258(1):21-31
Batch kinetic and column experiments have been carried out at 25, 35, and 45 °C to examine the effect of temperature on SuperLig® 644 cesium (Cs) removal from simulated Hanford tank waste supernate. The simulated solution mimicked the composition of the low-activity waste supernate from tank 241-AN-105 in the U.S. DOE Hanford site. Small quantities of toxic metals, such as Cd, Cr, Fe, and Pb were spiked into the simulant to evaluate the metal's competitiveness with Cs for sorption on SuperLig® 644 resin. The results indicated that the temperature affects the removal of Cs and metal ions, although the effect was not the same for all metal ions. The extent of Cs removal decreased with an increase in temperature. The Cs capacity at breakthrough point was 0.015, 0.013, and 0.011-mmole/g dry resin at 25, 35 and 45 °C, respectively. The column was effectively eluted to less than 1% (0.1 C/C
0) of the feed concentration with approximately 10 BVs of 0.5M nitric acid. The resin showed limited affinity for toxic metal ions (Cr, Cd, Fe, and Pb) as compared to Cs. Based on the batch kinetic data, the Cs uptake of the resin was not hampered by the presence of the toxic metals in solution. 相似文献
998.
N. M. Hassan 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(1):57-59
Summary Batch equilibrium and kinetic measurements were performed for Cs+ exchange in silicotitanate zeolite (Ionsiv® TIE-96) at 30 and 60 °C. The Langmuir isotherm equation provided a good fit of the equilibrium data. The heats of exchange reaction between Cs+ in the aqueous solution and Na+ in the zeolite structure were derived from the equilibrium data. The results indicate that the exchange mechanism is different from that of physical adsorption on heterogeneous materials. The apparent diffusion coefficients and activation energy were derived from the kinetic data and the values obtained for inter-diffusion of Cs+ and Na+ cations in the zeolite structure were 1.33 . 10-12 and 1.04 . 10-12 cm2 . s-1 at 30 and 60 °C, respectively. The activation energy for Cs+ was 1.7 kcal/mol, suggesting that the Cs+ cation can access easily all the sites in the zeolite framework. Thus, the exchange of Cs+ with Na+ in the zeolite was not hindered by ion-sieve effects. 相似文献
999.
Determination of Baicalin in Traditional Chinese Preparation by High Performance Liquid Chromatography with Chemiluminescence Detection 总被引:5,自引:0,他引:5
Er Bao LIU* Hong Qing WEI Xiu Li ZHAO Xiao Xia LI Feng Xian JIANG School of Chemistry Material Science Shanxi Normal University Linfen 《中国化学快报》2004,15(9):1067-1070
Herbal medicine, a form of complementary and alternative medicine, is becoming increasingly popular in the world1. Scutellariae radix is the root of Scutellariabaica -lensis georgi. The primary active constituent includes baicalin as follows: Clinical studies showed that baicalin exhibited therapeutic functions of antifever, moistening aridity, anti-inflammatory and detoxifying 2 and it is also an anti-abortion agent as well as can scavenge free radicals and against oxidation3. So it is… 相似文献
1000.
Issa Yavari Hassan Kabiri-Fard Shahram Moradi 《Monatshefte für Chemie / Chemical Monthly》2002,133(11):1459-1468
Summary. Ab initio calculations at the HF/6-31G* level of theory for geometry optimization and the MP2/6-31G*//HF/6-31G* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C
2-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol−1 more stable than the C
S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C
S-symmetric boat-boat geometry is 19.1 kJ·mol−1. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C
1) transition state which is 43.5 kJ·mol−1 above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol−1 more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair
and boat-chair is 69.5 kJ·mol−1, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol−1. The C
S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol−1 more stable than the C
S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C
S) transition state which is 37.2 kJ·mol−1 above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol−1 less stable than the crown conformation.
Corresponding author. E-mail: isayavar@yahoo.com
Received March 25, 2002; accepted April 3, 2002 相似文献