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1.
Vonderheide AP Meija J Tepperman K Puga A Pinhas AR States JC Caruso JA 《Journal of chromatography. A》2004,1024(1-2):129-137
High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(II) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei. 相似文献
2.
Matthew T. HancockAllan R. Pinhas 《Tetrahedron letters》2003,44(29):5457-5460
The conversion of an aziridine to the corresponding oxazolidinone using only carbon dioxide and a catalytic amount of lithium iodide is discussed. In all cases, either no reaction occurred or a high yield of product was obtained. HMPA has been added to the reaction mixture, as needed, to drastically improve the regioselectivity. Net retention of stereochemistry between the starting aziridine and the product oxazolidinone was observed. 相似文献
3.
E. Delée L. Le Garrec I. Jullien S. Béranger J. C. Pascal H. Pinhas 《Chromatographia》1987,24(1):357-359
Summary A routine chiral analysis has been developed to control the optical purity of chiral drugs and to monitor their asymmetric
synthesis. The recent advent of new chiral stationary phases for HPLC enabled us to achieve the direct resolution of chiral
drugs without any derivatization.
The factors affecting chiral resolution on a new alpha1-acid glycoprotein column (EnantioPac, LKB) were assessed with three beta-aminoalcohols. 相似文献
4.
We report the experimental realization of a new type of optical parametric oscillator in which oscillation is achieved by polarization rotation in a linear retarder, followed by nonlinear polarization mixing. The mixing is performed by a type II degenerate parametric downconversion in a periodically poled KTP crystal pumped by a 1064 nm pulsed Nd:YAG pump. A single, linearly polarized beam, precisely at the degenerate wavelength is generated. The output spectrum has a narrow linewidth (below the instrumentation bandwidth of 1 nm) and is highly stable with respect to variations in the crystal temperature. 相似文献
5.
The ignition of COS + O2 mixtures diluted in argon was studied behind reflected shocks in a single-pulse shock tube over the temperature range of 1100–1700°K. Ignition delay times and the distribution of reaction products before and after ignition were determined experimentally. From a total of 63 tests run at varying initial conditions, the following correlation for the induction times was derived: where β1 = +0.30, β2 = 1.12, and E = 16.9 kcal/mole. Using a reaction scheme of 14 steps, the following values were obtained by a computer modeling of the induction times: β1 = +0.22, β2 = 1.55, and E = 17.3 kcal/mole. The calculations showed that the reaction COS + S → CO + S2 caused the inhibiting effect of the COS. The reaction COS → O ± CO2 + S has a very strong accelerating effect, whereas the parallel channel COS + O → CO + SO shows the opposite effect. It was also shown that the reaction O + S2 → SO + O is very slow and does not contribute to the overall oxidation reaction. It is suggested that the rate constant given to the four-center reaction COS + SO → CO2 + S2, that is, 1011 cm3/mole · sec at 300°K is incorrect. This constant is not much higher than 108 cm3/mole · sec at 1300°K. 相似文献
6.
A detailed shock-tube investigation of the ignition in H2 + Cl2 + Ar mixtures in a shock tube is presented, and the mechanism of the reaction is discussed. Ignition delay times were determined from pressure and heat flux measurements behind reflected shock waves. The induction times measured ranged between 35 and 2100 μsec over the temperature range of 830–1260°K. The experimental results of close to seventy tests can be correlated by the relationship where the concentrations are expressed in mole/cm3. The above relationship served as a basis for a computer modeling of the ignition delay times. Ten calculations, simulating typical laboratory experiments, were run by the computer for each reaction scheme and the obtained temperature and composition dependence of the induction times were compared with the ones observed experimentally. A reaction scheme based on a simple exothermal chain propagation could not reproduce the experimental relationship. When the energy branching reaction HCl*(ν) + Cl2 → (HCl3) → HCl + Cl + Cl was added to the reaction scheme, a much better agreement with the experiment was obtained. It is believed that the above reaction does take place and that it is the main supplier of atoms to the system. 相似文献
7.
The coupling reaction of water-soluble alkyl nitriles using Fenton's reagent (Fe(II) and H2O2) is described. The best metal for the reaction is iron(II), and the greatest yields are obtained when the concentration of the metal is kept low. Hydrogen-atom abstraction is selective, preferentially producing the radical alpha to the nitrile. In order to increase the production of dinitrile, in situ reduction of iron(III) to iron(II), using a variety of reducing agents, was investigated. 相似文献
8.
James R. Hermanson Timothy M. Figley Anna L. Seibert Allan R. Pinhas 《Journal of organometallic chemistry》2008,693(11):2061-2064
The reactivity of a nucleophilic nickel acylate complex with a tungsten carbene complex, Fe(CO)5, Cr(CO)6, PPh3, and CO was investigated. With the tungsten carbene complex, a methyl transfer occurred. With the metal carbonyl complexes, the acylate group on the nickel and a carbonyl on the iron or chromium traded places. With the PPh3 and CO, the acylate anion was replaced by the phosphine or CO ligand. 相似文献
9.
M. -F. Pinhas J. M. V. Blanshard W. Derbyshire J. R. Mitchell 《Journal of Thermal Analysis and Calorimetry》1996,47(5):1499-1511
Strips of gelatin have been prepared by extrusion at different water contents varying from 20 to 50% H2O (dry weight basis, d.w.b.). The processes of subsequent hydration or dehydration of these strips were followed by dynamic mechanical thermal analysis (DMTA), wide-angle X-ray diffraction and NMR relaxation measurements. A comparison of the calculated dependence of theT g of gelatin (T g anhydrous, 200?C) on water content (using the Ten Brinke and Karasz equation) with experimental results derived from DMTA showed that freshly extruded material followed the theoretical plot below 25% H2O (d.w.b.), but at higher water contents, the7 g deviated positively, probably due in part to the effect of delayed re-equilibration of water content after thawing of separated ice crystals. The experimental results determined after storage for one week fell on a different line, with aT g of 145?C for anhydrous gelatin Possibly, theT g is elevated by crystallization — a view supported by the WAXS spectra. The NMR relaxation results also showed a profound mobilization of the gelatin protons at water contents greater than 25% d.w.b. 相似文献
10.