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21.
D. E. Vance V. F. Belt T. J. Oatts D. K. Mann 《Journal of Radioanalytical and Nuclear Chemistry》1998,234(1-2):143-147
The determination of neptunium-237 (237Np) traditionally has been performed by alpha spectrometry or neutron activation analysis. These methods are labor intensive
and require several days for completion. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a possible alternative for237Np determinations. This paper describes the analytical method developed for samples that have significant levels of uranium
present. The lower reporting limits achievable by ICP-MS are competitive with the counting methods, but the real advantage
for this laboratory lies in the lower cost and faster turnaround time provided by ICP-MS. 相似文献
22.
Studies on Alkyl Metal Alkoxides of Aluminium, Gallium, and Indium. III. Properties and Vibrational Spectra of Dialkylgallium- and Indium Alkoxides The preparation and the properties of dialkyl metal alkoxides R2MOR′ (with R = CH3, CD3, C2H5; R′ = CH3, CD3 and M = Ga, In) are described. The vibrational data (IR and Raman) of the trimeric methyl derivatives point to puckered six-membered M3O3-ring systems. 相似文献
23.
The oxidative decomposition of various ketones (including acetone, 2-butanone, 4-heptanone, cyclopentanone and cyclohexanone) over dehydrated TiO(2) (P25) powder is investigated by electron paramagnetic resonance (EPR) spectroscopy. For the first time, a series of thermally unstable radical intermediates are observed both on the activated and reduced TiO(2) surface, depending on the adopted experimental conditions. These radical intermediates are identified as organoperoxy-based species of general formula ROO(.-) and RCO(3) (.-). They are formed by reaction of photogenerated charge carriers (either trapped electrons or trapped holes) with the adsorbed ketones in the presence of molecular oxygen. The organoperoxy intermediates are thermally unstable and decompose at temperatures in the region of 180-250 K. This work demonstrates that free-radical pathways involving both organoperoxy and superoxide radicals can be responsible for the thermal- and photodecomposition of ketones over polycrystalline TiO(2) (P25). 相似文献
24.
The efficient catalytic activation of donor–acceptor aminocyclopropanes lacking the commonly used diester acceptor is reported here in a (3 + 2) dearomative annulation with indoles. Bench-stable tosyl-protected aminocyclopropyl esters were converted into cycloadducts in 46–95% yields and up to 95 : 5 diastereomeric ratio using catalytic amounts of triethylsilyl triflimide. Tricyclic indoline frameworks containing four stereogenic centers including all-carbon quaternary centers were obtained.A catalytic dearomatization of indoles with D–A aminocyclopropane monoesters for the synthesis of highly substituted indolines. 相似文献
25.
We describe a five-step synthesis of a PGH2 analogue from (R)-glyceraldehyde acetonide via formation of 1,2(S)-0-isopropylidene-hex-3(E)-en-5-one, conjugate addition of prostanoid C13- C20 side-chain as the cuprate with C1-C7 side-chain used to quench the resultant enolate, and finaily acid-catalysed ketal exchange to provide the desired analogue. 相似文献
26.
The mass spectra of 10 isomeric trimethylcyclohexanes and six cis–trans isomeric 1,2,3,5-tetramethylcyclohexanes are discussed. The thermochemically stable isomers show a higher abundance of the [M? CH3]+ ions and a lower abundance of the [M? C2H5]+ ions than the strained isomers. The log of the intensity ratio for loss of methyl and ethyl from the molecular ions correlates well with the strain energies and with the mean number of gauche arrangements of the stereoisomers. 相似文献
27.
Bashall A Bond AD Doyle EL García F Kidd S Lawson GT Parry MC McPartlin M Woods AD Wright DS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(15):3377-3385
Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported. 相似文献
28.
Fourier transform near-infrared (FT-NIR) spectroscopy was used to quantify rapidly the ethanol (34-49% v/v), propylene glycol (20-35% v/v) and water (11-20% m/m) contents within a multi-component pharmaceutical oral liquid by measurement directly through the amber plastic bottle packaging. Spectra were collected in the range 7302-12,000 cm-1 and calibration models set-up using partial least-squares regression (PLSR) and multiple linear regression. Reference values for the three components were measured using capillary gas chromatography (ethanol and propylene glycol) and Karl Fischer (water) assay procedures. The calibration and test sets consisted of production as well as laboratory batches that were made to extend the concentration ranges beyond the natural production variation. The PLSR models developed gave standard errors of prediction (SEP) of 1.1% v/v for ethanol, 0.9% v/v for propylene glycol and 0.3% m/m for water. For each component the calibration model was validated in terms of: linearity, repeatability, intermediate precision and robustness. All the methods produced statistically favourable outcomes. Ten production batches independent of the calibration and test sets were also challenged against the PLSR models, giving SEP values of 1.3% v/v (ethanol), 1.0% v/v (propylene glycol) and 0.2% m/m (water). NIR transmission spectroscopy allowed all three liquid constituents to be non-invasively measured in under 1 min. 相似文献
29.
The polymer-assisted solution-phase (PASP) synthesis of a 192-member 2-D array of 1,5-biaryl pyrazoles 4[1-12,1-16] is reported. The synthesis was performed in a fully automated manner using a multiprobe top-filtration robot and incorporates a "catch and release" step to afford library compounds directly in high yield and purity. 相似文献
30.
Rammile Ettelaie Brent S. Murray Emma L. James 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):195-206
To a first approximation, the primary structure of many food proteins maybe thought of as a sequence of short hydrophobic and hydrophilic blocks. The influence of this type of structure on the steric-stabilising properties of such proteins has been considered here. In line with previous studies, using Self-Consistent-Field calculations, it has been shown that the presence of such protein molecules can lead to attraction and consequently bridging flocculation of colloidal particles. In the low adsorption energy limit for the hydrophobic groups (−1kBT), it is found that the steric potential is significantly influenced by the changes in the number of adsorbed segments, as two surfaces are brought together. This is in contrast to the well-known results in the literature for the high adsorption limiting cases, where the number of such segments remains constant. In particular, the changes in the number of adsorbed hydrophobic units are observed not to be a monotonic function of the separation distance, but increase or decrease in reasonable accord with the oscillatory nature of the steric interactions, observed for various block sizes. Effects of the addition of a moderately sized hydrophilic side chain to the above molecules have also been studied. It is found that, in principle, such a modification can lead to a purely repulsive steric potential in solutions of these hybrid biopolymers. At the hydrophilic side chain sizes considered here, the surface affinity of the molecules is observed not to be drastically different compared to those of unmodified proteins. 相似文献