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21.
Ion-exchanger phase Spectrophotometry withp-nitrochlorophosphonazo (CPApN) has been developed for the determination of scandium. The linear range is 1–8 g of scandium in 50 ml of solution, using 0.8 g of resin, with an apparent molar absorptivity of 2.76 × 105 1 mol–1 cm–1. Aluminum and rare earth elements in reasonable amounts do not interfere. The method has been applied successfully to the determination of scandium in alloys, with relative standard deviations of 2–4%. 相似文献
22.
Quarez E Hsu KF Pcionek R Frangis N Polychroniadis EK Kanatzidis MG 《Journal of the American Chemical Society》2005,127(25):9177-9190
The nature of the thermoelectric materials Ag(1-x)Pb(m)SbTe(m+2) or LAST-m materials (LAST for Lead Antimony Silver Tellurium) with different m values at the atomic as well as nanoscale was studied with powder/single-crystal X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. Powder diffraction patterns of different members (m = 0, 6, 12, 18, infinity) are consistent with pure phases crystallizing in the NaCl-structure-type (Fmm) and the proposition that the LAST family behaved as solid solutions between the PbTe and AgSbTe2 compounds. However, electron diffraction and high resolution transmission electron microscopy studies suggest the LAST phases are inhomogeneous at the nanoscale with at least two coexisting sets of well-defined phases. The minority phase which is richer in Ag and Sb is on the nanosized length scale, and it is endotaxially embedded in the majority phase which is poorer in Ag and Sb. Moreover, within each nanodomain we observe extensive long range ordering of Ag, Pb, and Sb atoms. The long range ordering can be confirmed by single crystal X-ray diffraction studies. Indeed, data collections of five different single crystals were successfully refined in space groups of lower symmetry than Fmm including P4/mmm and Rm. The results reported here provide experimental evidence for a conceptual basis that could be employed when designing high performance thermoelectric materials and dispel the decades long belief that the systems (AgSbTe2)(1-x)(PbTe)x are solid solutions. 相似文献
23.
24.
Jo‐Nan Chen Fang‐Ming Hsu Hui‐Chun Wang Chung‐Wen Wu Pao‐Swu Cheng Wen‐Liang Tsai 《中国化学会会志》2006,53(4):931-938
Four series of compounds 11?50 containing terminal alicyclic rings such as cyclohexylmethyl, cyclopentylmethyl, cyclobutylmethyl, and cyclopropylmethyl rings were synthesized and their liquid crystal behavior studied. The ring size and the length of flexible alkoxy chain influence the phase formation in different ways. While the smaller ring and the shorter alkoxy chain tend to favor the formation of the N phase, the larger ring and the longer alkoxy chain tend to favor the formation of the SmC phase. All the compounds except 11 and 21 exhibit SmA phases. The widest temperature range of the N, SmA, and SmC phases are found in the compounds 41 , 46 , and 20 , respectively, which are 75 °C for 41 , 115 °C for 46 , and 100 °C for 20 . 相似文献
25.
The retention properties of calcitonins on a reversed-phase column are examined using salmon calcitonin as the model compound. The effect of the concentration of organic modifier, buffer strength, pH of the mobile phase, and ion-pair reagent are studied. In the absence of an ionic modifier in the eluent the calcitonin peak shapes are not symmetrical. The addition of 0.1% trifluoroacetic acid (TFA), however, results in good peak characteristics without the need to add nonvolatile salts. The retention of the calcitonins was found to be very sensitive to the concentration of the organic modifier (acetonitrile) present in the mobile phase. A change of pH between 2 and 5 has only a slight effect of the k' of salmon calcitonin, but the k' increases significantly at higher pH values. The addition of a phosphate buffer to the mobile phase and an increase in the buffer concentration (0-0.2 M) causes a decrease in the retention of salmon calcitonin. Evidence shows that reproducible, quantitatively measurable data can be obtained using reversed-phase chromatography if the ion-pairing reagent and organic modifier concentrations are carefully controlled. The system also shows a good selectivity for the calcitonin series. Therefore, both highly selective methods (qualitative) as well as quantitative methods for analytical, pharmaceutical, and manufacturing use can be developed by adjusting the high-performance liquid chromatography (HPLC) conditions as discussed. 相似文献
26.
The fragmentation patterns of 3-methyl-2-butyl trifluoroacetate and 2-methyl-2-butyl trifluoroacetate were investigated by GC/MS/MS, with electron impact and collision-induced dissociation, on regular and isotope-labeled (deuterium and 18O) esters. The atoms found in various fragments could be traced back to specific positions in the parent molecules. In this way, molecular rearrangements potentially occurring during the formation of esters by trifluoroacetolysis of 3-methyl-2-butyl p-toluenesulfonate or trifluoroacetic acid addition to various 2-methylbutenes could be shown. Rearrangements also occurred during the fragmentation, particularly during the expulsion of the small fragments CO, C2H4 and F2CO. For the decompositions of oxygen-containing ions these rearrangements were highly specific. By contrast, alkyl cations lead to fragments that are fully scrambled (statistical label distribution). Alkene radical cations ([CnH2n]+ ˙) fragment to daughter ions that are extensively, but less than statistically scrambled. Hydrogen scrambling may also occur in fluoroalkyl cation fragments. 相似文献
27.
(Z, E)-9, 11-Tetradecadienyl-l-acetate (1), a major component of the sex pheromone of Spodoptera litura (F.), and (Z, E}-9, 11-pentadecadienyl-1-acetate (2) were synthesized by the Wittig reaction between (E)-2-alkenal (3) and the ylid derived from 9-hydroxynonyltriphenylphosphonium bromide (4). 相似文献
28.
The influence of floc structure and floc concentration on the drag acting on a floc is investigated theoretically. A two-layer model is adopted to describe floc structure, and a cell model is used to simulate a floc dispersion. The influences of the key parameters of the problem under consideration, including floc concentration, Reynolds number, the ratio (permeability of outer layer/permeability of inner layer), and the ratio (thickness of outer layer/thickness of inner layer), on the drag coefficient are discussed. We show that the more heterogeneous the floc structure is, the greater the drag and the more significant the deviation of curve of variation of drag coefficient against Reynolds number from a Stokes-law-like relation. The drag on a floc declines with the decrease in floc concentration, and, due to the convective flow of the fluid, the distortion of streamlines surrounding a floc becomes more serious and the deviation of the variation of the curve of drag against Reynolds number from a Stokes-law-like relation is more significant. 相似文献
29.
Three of the main oxygen-containing fragments resulting from 3-methyl-2-butyl trifluoroacetate (11) had been identified previously as the 1-triflnoroacetoxyethyl cation (m/z 141, 12, product of simple cleavage), and the products of single (m/z 142) and double hydrogen transfer (m/z 143, protonated ethyl trifluoroacetate). Collisionally activated dissociation of m/z 142 and the isotopomers resulting from 11-2-d, 11-1-d3, 11-5,6-d6, and 11-18O2 has established that m/z 142 is the oxygen protonated 1-trifluoroacetoxyethyl free radical (17) formed by hydrogen shift irom a γ-methyl group to oxygen in the molecular ion, rather than in a complex (18) between 12 and the 2-propyl free radical, as expected based on a mechanistic model existing in the literature. The second hydrogen transferred originates in the other γ-methyl group; its migration may occur, but does not have to, in the complex between 17 and a molecule of propene, prior to dissociation of the two fragments. Collision-activated dissociation has now shown that the m/z 140 ion observed in the spectrum is the molecular ion of vinyl trifluoroacetate, possibly formed by a hydrogen transfer from 12 to the 2-propyl radical in the complex 18. The hydrogen migration to oxygen exhibits no isotope effect, whereas the transfers to carbon atoms exhibit small primary and α secondary kinetic isotope effects. Exclusive migration of the tertiary hydrogen from C(3) occurs in the formation of 2-methylbutene cation radical (m/z 70) from the molecular ion. The hydrocarbon ion fragments and the heteroatom-containing fragments are formed from 11 by disjoint pathways. 相似文献
30.
Treatment of ethyl 2-(pyridin-2-ylsulfonyl)hexanoate with tributylstannane and azobis(2-methyl-2-propanitrile) (AIBN) in benzene at reflux for 36 h resulted in hydrogenolysis to give ethyl hexanoate (60%), whereas no reaction was observed after 48 h at reflux with ethyl 2-(phenylsulfonyl)hexanoate. Ethyl 2-(pyrimidin-2-ylsulfonyl)hexanoate underwent quantitative hydrogenolysis within 1 h under these conditions. This represents a mild new methodology for removal of the synthetically useful sulfone moiety. Substitution of Bu(3)SnD for Bu(3)SnH gave access to alpha-deuterium-labeled esters. Treatment of the alpha-(pyrimidin-2-ylsulfonyl) enolates derived from several esters with Selectfluor gave high yields of the 2-fluoro-2-(pyrimidin-2-ylsulfonyl)alkanoates, which were smoothly desulfonylated [Bu(3)SnH (2 equiv)/AIBN/benzene/Delta] to give 2-fluoroalkanoates. "Catalytic" tin hydride, generated from tribuytltin chloride (0.15 equiv) and excess polymethylhydrosiloxane in the presence of potassium fluoride, also effected removal of the pi-deficient alpha-(pyrimidin-2-ylsulfonyl) moiety from acid derivatives in high yields. Desulfonylation is suggested to proceed via alkoxy ketyl-type radicals and tin enolates. 相似文献