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51.
Erik Larsson 《Fresenius' Journal of Analytical Chemistry》1930,79(5-6):170-175
Zusammenfassung Auf Grund der Dissoziatio nskonstanten der Thioglykolsäure,- und-Thiomilchsäure,-Mercaptoisobuttersäure,-Thiomalamidsäure und Thioäpfelsäure wurde gezeigt, dass von diesen Säuren nur die-Mercaptoisobuttersäure und Thioäpfelsäure gut mit Phenolphthalein alkalimetrisch titriert werden können, aber auch nur dann, wenn man viel Indikator benutzt. Bei den anderen Säuren hat man Indikatoren mit saurerem Umschlag zu wählen. Für die ersten drei Säuren dürften Neutralrot und Phenolrot geeignete Indikatoren sein. Dies wird auch bei der Thioglykolsäure experimentell erwiesen. Für die alkalimetrische Titration von-Thiomalamidsäure soll man Bromthymolblau als Indikator verwenden. 相似文献
52.
Drahl C Cravatt BF Sorensen EJ 《Angewandte Chemie (International ed. in English)》2005,44(36):5788-5809
Researchers in the post-genome era are confronted with the daunting task of assigning structure and function to tens of thousands of encoded proteins. To realize this goal, new technologies are emerging for the analysis of protein function on a global scale, such as activity-based protein profiling (ABPP), which aims to develop active site-directed chemical probes for enzyme analysis in whole proteomes. For the pursuit of such chemical proteomic technologies, it is helpful to derive inspiration from protein-reactive natural products. Natural products use a remarkably diverse set of mechanisms to covalently modify enzymes from distinct mechanistic classes, thus providing a wellspring of chemical concepts that can be exploited for the design of active-site-directed proteomic probes. Herein, we highlight several examples of protein-reactive natural products and illustrate how their mechanisms of action have influenced and continue to shape the progression of chemical proteomic technologies like ABPP. 相似文献
53.
Rolf Gleiter Jens Spanget-Larsen Erik W. Thulstrup Ichiro Murata Kazuhiro Nakasuji Christian Jutz 《Helvetica chimica acta》1976,59(5):1459-1468
The photoelectron (PE.) spectra of azuleno[l, 2, 3-cd]phenalene ( 1 ) and azuleno- [5,6,7-cd]phenalene( 2 ) have been recorded. The first five bands of both compounds could be assigned to transitions corresponding to removal of electrons from 4a2, 6b1, 5b1, 3a2 and 4bl orbitals. This assignment is based mainly on a comparison between the observed ionization potentials and orbital energies calculated in a HMO and a PPP model. The UV./VIS. polarized absorption spectrum of 1 in the region 10000–45000 cm?1 has been measured by means of the stretched film technique. The measurements were performed in polyethylene sheets at 77°K. Several bands could be assigned to π* ← π transitions calculated by a PPP-CI method. A comparison between the electronic structures of 1 and 2 is made by means of a simple HMO diagram. 相似文献
54.
55.
Erik G.P. da Silva Ana Carolina do N. Santos Antnio C.S. Costa Dalva M. da N. Fortunato Ndia M. Jos Maria G.A. Korn Walter N.L. dos Santos Srgio L.C. Ferreira 《Microchemical Journal》2006,82(2):159-162
In the present work, a slurry sampling flame atomic absorption spectrometric method to determine directly manganese and zinc in powdered chocolate samples is proposed. The optimization step was performed using univariate methodology involving the following factors: nature and concentration of the acid solution, sonication time, and particle size. The established conditions led to the use of a sample mass of 150 mg, 2.0 mol L− 1 nitric acid solution, sonication time of 15 min, and a slurry volume of 50 mL. This method allows the determination of manganese and zinc with detection limit of 52 and 61 ng g− 1, respectively, and a precision expressed as relative standard deviation (RSD) of 2.6% and 3.2% (both, n = 10) for contents of manganese and zinc of 52.4 and 100.0 μg g− 1, respectively. The proposed method was applied for determination of manganese and zinc in five powdered chocolate samples. In these, the manganese content varied from 42.8 to 52.7 and from 88.6 to 102.4 μg g− 1 of zinc. The analytical results were compared with the results obtained by analysis of these samples after digestion using open vessel and acid bomb digestion procedures and determination using FS-FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results. 相似文献
56.
Gar B. Hoflund Steven D. Gardner David R. Schryer Billy T. Upchurch Erik J. Kielin 《Reaction Kinetics and Catalysis Letters》1996,58(1):19-26
The influence of promoters on Pt/SnOx/SiO2 and Au/MnOx low-temperature CO oxidation catalysts has been investigated under stoichiometric reaction conditions with no CO2 added to the feed gas. The performance of Pt/SnOx/SiO2 catalysts is improved significantly by the addition of 1 wt.% Fe but reduced by the addition of 5 wt.%Fe, 1 wt.% Sb, 5 wt.% Sb, 1 wt.% As, 5 wt.%As and 1.8 wt.% P. The performance of Au/MnOx is improved significantly by the addition of 1 at.% Ce but reduced by the addition of 1 at.% Co. For the catalysts and conditions examined, the Au/MnOx catalysts are superior to the Pt/SnOx/SiO2 catalysts with respect to both activity and decay characteristics. 相似文献
57.
The mass spectra of six isomers of methylnitroimidazoles are reported and discussed. All compounds exhibit strong molecular ions, along with the characteristic fragmentations of aromatic nitro compounds. In some cases ortho effects—losses of OH., H2O, CHO., CH2O—are observed, due to interactions of adjacent substituents. 相似文献
58.
Zusammenfassung Der Schwefel in Wolframoxiden und Wolframpulvern wird im Wasserstoffstrom bei 800°C in H2S übergeführt, der in Cadmium-Zinkacetat-Lösung absorbiert und anschließend jodometrisch titriert wird. Die Anwesenheit von WO3 ermöglicht eine quantitative Umwandlung von Sulfatschwefel in H2S. Die Standardabweichung beträgt für ein Wolframoxid mit 310 ppm S±13 ppmS und für ein Wolfram-Metallpulver mit 45 ppm S±1 ppm S.
Herrn Prof. Dr.E. Hayek zum 60. Geburtstag gewidmet. 相似文献
Sulfur is converted into hydrogen sulphide by hydrogenation at 800°C. This H2S is absorbed in a cadmium-zinc acetate solution and titrated iodometrically. The presence of WO3 makes possible a quantitative conversion of sulphate sulphur into H2S. The standard deviation is ±13 ppm S for WO3 containing 310 ppm S, and ±1 ppm S for metallic tungsten powder containing 45 ppm S.
Herrn Prof. Dr.E. Hayek zum 60. Geburtstag gewidmet. 相似文献
59.
The existence of two transitions with opposite MCD in the 38000–45000 cm?1 absorption of thiophene is demonstrated. The B-term for the lowest transition is negative, while it is positive for the higher one. Quantum mechanical calculations in the π-electron approximation resulted in energies, oscillator strengths and MCD terms in good agreement with the observed spectra. 相似文献
60.
[reaction: see text] A stereoselective synthesis of (-)-ilimaquinone (4) is presented. The synthetic strategy is based on a novel radical decarboxylation and quinone addition methodology that produces quinone 7 from reaction of thiohydroxamic acid derivative 8 with benzoquinone (9). Final functionalization of 7 to ilimaquinone (4) is achieved by exploring the electronic effects of the residual thiopyridyl group. 相似文献