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11.
The extractability sequence of K(+) approximately Rb(+) > Cs(+) > Na(+) > Li(+) for the extraction with polyether foam suggests that the cation chelation mechanism might be operative. However, the same order was obtained for the extraction with 100% polypropylene oxide polyether foam which does not normally adopt a helical structure to form oxygen-rich cavities as easily or as effectively as polyethylene oxide to accommodate alkali metal ions. This result indicates that a hole-size/cation-diameter relationship may not be required for the high extraction of K(+). The extraction of alkali metal DPAs and hydroxides from methanol demonstrates the importance of the solvent effect. It indicates that the water-structure enforced ion-pairing (WSEIP) is the driving force for extraction of the ion-pairs. The extraction mechanism for ionic species can be described as an ion-pair extraction process. The overall effect of ion-pair formation in water and interaction of the extracted ions with foam appears to determine the extractability of the ions of the extractable ion-pair. 相似文献
12.
Uniform nylon 6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon 6 in unconfined (i.e., as-electrospun) and a high T(g) (340 degrees C) polyimide confined nanofibers were studied. Similar to melt-spun nylon 6 fibers, electrospun nylon 6 nanofibers also exhibited predominant, meta-stable gamma crystalline form, and the gamma-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 degrees C, gamma-form crystals gradually melted and recrystallized into the thermodynamically stable alpha-form crystals, which ultimately melted at 220 degrees C. Release of surface tension accompanied this melt-recrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; gamma-form crystals did not melt and recrystallize into alpha-form crystals until 210 degrees C, only 10 degrees C below the T(m) at 220 degrees C. After complete melting of nano-confined crystals at 240 degrees C and recrystallization at 100 degrees C, only alpha-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic alpha-form to a high temperature monoclinic form) was observed at 180-190 degrees C, which was at least 20 degrees C higher than that in unconfined nylon 6 at approximately 160 degrees C. This, again, was attributed to the confinement effect. 相似文献
13.
14.
Aspen wood substrates with varying degrees of deacetylation, xylan, and lignin removal have been prepared and submitted to
enzymatic hydrolysis with a cellulase/hemicellulase preparation for an extended constant period of hydrolysis. Controlled
deacetylation has been achieved by treating wood with various alkali metal hydroxide solutions, at various alkali/wood ratios.
It has been found that samples with the same extent of deacetylation produce the same sugar yields upon enzymatic hydrolysis.
Increased degree of deacetylation increases the yield of sugars obtained from enzymatic hydrolysis, all other compositional
parameters held constant. The acetyl group removal is proportional to the stoichiometric relation between added base and wood
acetyl content, i.e., the same number of milliequivalents of base/weight of wood remove the same extent of acetyl groups,
regardless of the concentration of the base solution. No cation effects are found among Li, Na, and K alkali hydroxide solutions,
suggesting that swelling is not as important a parameter as is the removal of the acetyl groups from the xylan backbone in
determining the extent of hydrolyzability of the resulting sample. 相似文献
15.
W. Haerdi et Ed. Mérat 《Fresenius' Journal of Analytical Chemistry》1973,264(5):376-377
A method for the rapid separation of copper(II) traces on metallic mercury is proposed. The separation is rendered possible by the reduction of Cu(II) to Cu(I) on mercury in the presence of iodide ions followed by the adsorption of the uncharged complex, Cu(I), on Hg0. After a minute of agitation, this adsorption is quantitative (90–100%) for initial concentrations of Cu(II) between 10–4 to 10–6 M and iodide cone, of 10–2 to 10–3 M at pH 3. The volumes of the aqueous solutions are of the order of 3–10 ml and those of the drops of mercury between 0.5–1 ml. The tests were made using the isotope 64Cu (T
1/2 = 12.8 h).
Trennung von Metallspuren am Quecksilbertropfen; Anwendung auf die Anreicherung von Cu(II) und Cu(I)
Zusammenfassung Die Arbeit beschreibt eine Methode zur Schnelltrennung von Kupfer(II)-Spuren auf metallischem Quecksilber. Diese Vorkonzentration ist durch die Reduktion des Cu(II) zu Cu(I) durch Hg0 in Jodidmedium und anschließende Adsorption des ungeladenen Kupferjodidkomplexes, CuJ, an diesem Metall möglich. Die Adsorption ist nach 1 min Rühren quantitativ (90–100%) für Ausgangswerte von Cu(II) zwischen 10–6 und 10–4M, im Jodidmedium von 10–3 bis 10–2 M bei pH 3. Die Volumina der wäßrigen Lösung liegen in der Größenordnung von 3–10 ml, die der Hg-Tropfen von 0,5–1 ml. Die Versuche wurden mit Hilfe von 64Cu (T 1/2 = 12,8 h) durchgeführt.
Exposé présenté à la conférence Euroanalysis I, août 28 à septembre 1, 1972, à Heidelberg, Allemagne. 相似文献
16.
Kuiry SC Megen E Patil SD Deshpande SA Seal S 《The journal of physical chemistry. B》2005,109(9):3868-3872
This article reports an easy chemical method of synthesizing boehmite nanofibers by a modified sol-gel process involving aluminum isopropoxide precursor. Nanorods of gamma-alumina have been successfully prepared after dehydration of the viscous sol at 600 degrees C for 4 h in air. The boehmite nanofibers and gamma-alumina nanorods were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy for surface chemistry and functional groups, scanning electron microscopy, high-resolution transmission electron microscopy with selected area electron diffraction, and energy-dispersed spectroscopy for morphology and structure identification. The length of the boehmite nanofibers was found to be more than 10 mum with a crystalline lattice structure. The mechanism of formation of the boehmite nanofibers included the preferential growth along the longitudinal axis due to interaction between the solvent molecules and the surface OH- groups of hydrogen bonds. It is also suggested that the boehmite nanofibers may have formed due to the inherent instability of the planar structure of the boehmite lattice. The diameter of the gamma-alumina nanorods was found to be less than 10 nm with a varying length in the range of 50-200 nm. Boehmite to gamma-Al2O3 transformation was attributed to the loss of water molecules by internal condensation of protons and hydroxyl ions. 相似文献
17.
Hong-Jie ZhangGhee Teng Tan Vu Dinh HoangNguyen Van Hung Nguyen Manh CuongDjaja Doel Soejarto John M PezzutoHarry H.S Fong 《Tetrahedron》2003,59(2):141-148
Bioassay directed-fractionation led to the identification of litseaverticillols A-H (1-8) from the leaves and twigs of Litsea verticillata Hance. These new sesquiterpenes possess a unique skeleton that was recently designated as ‘litseane’. The structures of these compounds were determined by spectroscopic means including 1D and 2D NMR data. Structural configurations were determined by ROESY experiments. Mosher ester reactions and optical rotation measurements established the sesquiterpenes 1-8 as racemates. Isolates 1-8 inhibited HIV-1 replication in HOG.R5 cells with IC50 values ranging from 2 to 15 μg/ml (8-58 μM) while affecting the growth of HOG.R5 at concentrations 2-3-fold higher. Based on this data, structure-activity relationships can be discerned, suggesting compounds of this class are good candidates for analog production. 相似文献
18.
Hydroxylamine derivatives of (S)-prolinol have been generated using a Cope elimination. These undergo reverse-Cope elimination onto a pendant double bond to give morpholine N-oxides containing three contiguous chiral centres. 相似文献
19.
The result stated in the title is proved.Research of the second author partially supported by the National Science Foundation. He would also like to thank the Banach Institute, Polish Academy of Sciences and Universität Kaiserslautern for their hospitality. 相似文献
20.
Summary We prove here:
Theorem. LetT be a countable complete superstable non -stable theory with fewer than continuum many countable models. Then there is a definable groupG with locally modular regular generics, such thatG is not connected-by-finite and any type inG
eq orthogonal to the generics has Morley rank.
Corollary. LetT be a countable complete superstable theory in which no infinite group is definable. ThenT has either at most countably many, or exactly continuum many countable models, up to isomorphism.Supported by NSF grant DMS 90-06628 相似文献