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41.
Mono-, di- and tri-alkyl-substituted allenes were potentiostatically oxidized in methanol at graphite and Pt anodes. At the former electrode, α-methoxylated ketones (due to 4F/mole electricity consumption) and esters (6F/mole) were the major products. At a Pt anode, intermediate products such as vinyl-ether derivatives (2F/mole) were characterised too. Unlike the anodic oxidation of alkenes and alkynes previously reproted in the literature, dimerisation is not a typical process in the allenes' oxidation, since of all the products obtained only a sole dimer has been observed. The mechanism for the formation of most products is discussed. 相似文献
42.
Preparation and Properties of Formed Aluminium Oxide. I. Influence of the Precipitation Conditions of the Boehmite Hydrogel on the Pore Structure of Formed Aluminium Oxide A report is given on the influence of the precipitation conditions of boehmite (pH value, temperature, concentration and residence time in the precipitation suspension) on the cavity structure of aluminium oxide spheres, made by coagulation of boehmite hydrosol in ammonia liquor and subsequent thermal treatment at 110 and 600°C. The boehmite hydrogel was obtained at continuous precipitation conditions by neutralisation of sodium aluminate solution with nitric acid. It is shown that the difference in the pore structure of the formed aluminium oxide obtained by varying the precipitation conditions were caused by the special morphological features of the boehmite crystallization in the precipitation process. 相似文献
43.
James Y. Becker Larry L. Miller Frank R. Stermitz 《Journal of Electroanalytical Chemistry》1976,68(2):181-191
The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has Ep=0.55 V vs. Ag/Ag+. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated. 相似文献
44.
A radiochemical neutron activation analysis (RNAA) combustion method coupled with a neutron exposure normalization technique was used to determine low g/kg mercury levels in three National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs). Two coals (sub-bituminous and bituminous) and a diet material were analyzed. The results obtained provided recommended values of approximately 5 g/kg for SRM 1548a Typical Diet, 24 g/kg for SRM 1635 Trace Elements in Coal (sub-bituminous), and 100 g/kg for SRM 1632b Trace Elements in Coal (bituminous). 相似文献
45.
Luesch H Hoffmann D Hevel JM Becker JE Golakoti T Moore RE 《The Journal of organic chemistry》2003,68(1):83-91
The biosynthesis of the unusual amino acid 4-methylproline in the Nostoc genus of cyanobacteria was investigated on the genetic and enzymatic level. Two genes involved in the biosynthesis were cloned and the corresponding enzymes, a zinc-dependent long-chain dehydrogenase and a Delta(1)-pyrroline-5-carboxylic acid (P5C) reductase homologue, were overexpressed in Escherichia coli and biochemically characterized. Putative substrates were synthesized to test enzyme substrate specificities, and deuterium labeling studies were carried out to reveal the stereospecificities of the enzymatic reactions with respect to the substrates as well as to the coenzymes. 相似文献
46.
Acyl- and Alkylidenephosphines. XXVII. Molecular and Crystal Structure of Methyl-[(N-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphine . Methyl[(N-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphine 1a formed via an addition of methylbis(trimethylsilyl)phosphine to phenyl isothiocyanate [1], crystallizes in the monoclinic centrosymmetric space group P21/n with following dimensions of the unit cell determined at a temperature of measurement of ?80±3°C: a=1041.2(4);b=1706.9(12);c=1001.1(6)pm; β=106.41(4)°; Z = 4. An X-ray structure determination (Rw = 0.039) confirms the constitution of the compound as already derived from its nmr spectra. One trimethylsilyl group is bound to the phosphorus atom, whereas the other is connected with the sp2-hybridized nitrogen atom. Characteristic rounded bond lenghts and angles are: P? Si 231, P? CH3 184, P? C(S) 187, C?S 167, N? C(S) 137, and N? Si 181 pm as well as P? C? S 122°, P? C? N 117°, and S? C? N 121°. 相似文献
47.
Johanna Sabine Becker Jochen Westheide Anatolij I. Saprykin Horst Holzbrecher Uwe Breuer Hans -Joachim Dietze 《Mikrochimica acta》1997,125(1-4):153-160
For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La
x
Sr
y
MnO3 cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.Dedicated to Professor Dr. rer. nat. Hubertus Nickel on the occasion of his 65th birthday 相似文献
48.
Breuer U Holzbrecher H Gastel M Becker JS Dietze HJ 《Analytical and bioanalytical chemistry》1995,353(3-4):372-377
For the quantification of heterostructure depth profiles the knowledge of relative sensitivity factors (RSF) and the influence of matrix effects on the measured profiles is necessary. Matrix dependencies of the measured ion intensities have been investigated for sputtered neutral mass spectrometry (SNMS) and MCs(+)-SIMS. The use of Cs as primary ions for SNMS is advantageous compared to Ar because the depth resolution is improved without changing RSFs determined under Ar bombardment. No significant amount of molecules has been found in the SNMS spectra under Cs bombardment. Using MCs(+)-SIMS the RSFs are matrix dependent. An improvement of depth resolution can be achieved by biasing the sample against the primary ion beam for SNMS due to a reduction of the net energy of the primary ions and a resulting more gracing impact angle. 相似文献
49.
The interlaboratory variability in the quantification of adsorbable organically bound halogens (AOX) in industrially contaminated
soil is presented. Three consecutive rounds of a proficiency testing scheme, in which between 88 and 119 routine laboratories
participated, yielded relative reproducibility standard deviations between 7 and 20% at AOX contents between 10.9 and 268 mg
kg−1. Nineteen laboratories with established proficiency were invited to participate in the certification of the AOX content in
three soil reference materials meant for the internal quality control in analytical laboratories. The certified values are
(1349 ± 59) mg kg−1, (80 ± 7) mg kg−1 and (102 ± 8) mg kg−1, respectively. 相似文献
50.