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排序方式: 共有437条查询结果,搜索用时 15 毫秒
1.
2.
Eckhard Herrmann Moein Nouaman Zdirad
k Gisbert Großmann Gisela Ohms 《无机化学与普通化学杂志》1994,620(11):1879-1888
Tetraarylesters of μ-Imido-Diphosphoric Acid and its Thio Derivatives — Structure Investigations New O,O′,O″,O?-tetratolyl- and ditolyl-diphenylesters of the μ-imido-diphosphoric acid and its mono and dithio derivatives were synthesized, compared with the corresponding tetraphenylesters and investigated by 1H, 13C, and 31P NMR spectroscopy and X-ray crystal structure analysis. Structures of the O,O′,O″,O?-tetrakis-(2-methyl-phenyl)-μ-imidodiphosphate, 1b , as well as of the corresponding ortho-, meta- and para-tolylesters of the μ-imido-monothiodiphosphoric acid ( 2a , 2b , 2c ) were determined. All the compounds form dimers via N? H…?O hydrogen bonds in the crystal as well as in nonpolar solvents. The distances around the phosphorus atoms rise with decreasing electronegativity of the phosphorus substituents. Signs of the 2JP? N? P coupling constants were determined by 13C{1H, 31P} triple resonance experiments for some compounds. These constants become more negative owing to substitution of a phosphoryl by a thiophosphoryl group. 相似文献
3.
Alvaro M Formentín P García H Palomares E Sabater MJ 《The Journal of organic chemistry》2002,67(15):5184-5189
Three N-alkylpyridinium photosensitizers having chiral alkyl groups have been prepared by reacting 2,4,6-triphenylpyrylium tetrafluoroborate ion with (1R,2S)-(-)-norephedrine, (S)-(+)-2-(aminomethyl)pyrrolidine, and (R)-(-)-1-cyclohexylethylamine. Laser flash photolysis allows detection of the corresponding triplet excited states that are quenched by hydrogen atom donors and electron donors. Asymmetric quenching of the chiral triplet excited state was observed using enantiomerically pure 1,2-diamino cyclohexane as quencher. Low enantiomeric excess values (up to 7%) were measured for the photochemical cyclization of 5-methyl-4-hexenoic acid to its corresponding gamma-lactone using these chiral N-alkylpyridinium as photosensitizers. 相似文献
4.
Hegedus LS Geisler L Riches AG Salman SS Umbricht G 《The Journal of organic chemistry》2002,67(22):7649-7655
Butenolides 5a and 13 were used as optically active templates in the de novo synthesis of 4'-disubstituted nucleoside analogues. The butenolides were reduced and acylated in situ to give acetates 10 and 14. Vorbrüggen coupling gave the protected nucleoside analogues 11 and 15. Reduction of 11 gave 4'-ethoxy-2',3'-dideoxythymidine (6) and deprotection of 15 gave 4'-ethoxy-2',3'-dideoxydidehydrothymidine (7). The cis-dihydroxylation of a variety of butenolides occurred with the major product formed from oxidation of the beta-face. 相似文献
5.
Gisela Bodrogai 《Mikrochimica acta》1979,71(1-2):47-51
Zusammenfassung Verschiedene schwefelhaltige Verbindungen ergeben zu hohe Kohlenstoffwerte. Dieser Fehler kann behoben werden, indem die Einwaage im Verbrennungsschiffchen mit vorbehandeltem Cerdioxid abgedeckt oder vermischt wird.
CH determination in containing compounds sulfur
Summary Various sulfur-containing compounds yield carbon values which are too high. This error can be eliminated by covering or mixing the aliquot in combustion boats with pretreated cerium dioxide.相似文献
6.
7.
Gisela Gauchel F. D. Gauchel K. Beyermann und R. K. Zahn 《Fresenius' Journal of Analytical Chemistry》1972,259(3):183-187
Zusammenfassung Es wird über eine DNA-Bestimmung in biologischem Material durch Hochdruckflüssigkeits-Chromatographie an sphärischen Ionenaustauschern berichtet. Thymin wird durch Hydrolyse lyophilisierter Gewebe freigesetzt, durch Sublimation gereinigt und flüssigkeits-chromatographisch bei etwa 150 at Eingangsdruck bestimmt. Die Ausbeute des Verfahrens wird durch Isotopenverdünnungsanalyse überprüft. Der Einfluß von pH-Wert und Konzentration der Elutionspuffer und der Säulentemperatur wird ermittelt. Die untere quantitative Nachweisgrenze der Methode liegt bei etwa 0,5 g DNA in Geweben, die relative Standardabweichung betrug 10%.
Teil I: diese Z. 259, 177 (1972).
Geodia cydonium wurde uns dankenswerterweise von der meeresbiologischen Forschungsgruppe, Leitung Herr Prof. Dr. R. K. Zahn, zur Verfügung gestellt. 相似文献
Quantitative determination of DNA in tissues by thymine-analysisII. Determination by high-pressure ionexchange liquid chromatography
A determination of DNA in biological material by high pressure, liquid chromatography of thymine on spherical ion-exchange resins is presented. After lyophilizing and hydrolyzing the tissues, thymine is separated by sublimation and determined by means of liquid chromatography at 150 at. Yields are controlled by isotope dilution analysis. Investigations on the effect of pH and concentration of eluents and of temperature are reported. The method is suitable for a minimal amount of 0.5 g DNA in tissues with a relative standard deviation of 10%.
Teil I: diese Z. 259, 177 (1972).
Geodia cydonium wurde uns dankenswerterweise von der meeresbiologischen Forschungsgruppe, Leitung Herr Prof. Dr. R. K. Zahn, zur Verfügung gestellt. 相似文献
8.
To avoid changes in the original As species distribution in natural water after sampling, a method of immediate separation
of As(V) by anion exchange at the sampling site was developed. The procedure consists of two steps. The total concentration
of arsenic is determined in one part of the water sample acidified on site. Another part of the water samples is pressed through
a column filled with an anion exchanger. The As(III) species that is not redox-stable remains in the effluent of the sorbents
column and can be analyzed with conventional methods after stabilization by addition of conc. HNO3. As(V) is sorbed by the exchanger material. The As(V) concentration can be calculated as the difference between Assol and As(III), neglecting very low contents of methylated species.
Oxidation of Fe(II) by air followed by co-precipitation of arsenic with iron hydroxide was applied in field experiments to
minimize the As concentration in seepage and mining water. 相似文献
9.
The synthesis of a series of enantiomerically pure, C2-symmetric 4,4′,5,5′-tetrahydro-2,2′-methylenebis[oxazoles] and 4,4′,5,5′-tetrahydro-2,2′-bi(oxazoles) is reported. Copper complexes with anionic tetrahydromethylenebis[oxazole] ligands are efficient catalysts for the enantioselective cyclopropane formation from olefins and diazo compounds (up to 96% ee in the reaction of styrene with menthyl diazoacetate). Tetrahydrobi(oxazole)iridium(I) complexes were found to catalyze transfer hydrogenations of aryl alkyl ketones with i-PrOH (up to 91% ee). Tetrahydrobi(oxazole)palladium complexes can be used as enantioselective catalysts for allylic nucleophilic substitution (up to 77% ee in the reaction of PhCH?CHCH(OAc)Ph with NaHC(COOMe)2). 相似文献
10.
Reyhaneh Armin Sebastian Zühlke Gisela Grunewaldt-Stcker Felix Mahnkopp-Dirks Souvik Kusari 《Molecules (Basel, Switzerland)》2021,26(12)
Apple Replant Disease (ARD) is a significant problem in apple orchards that causes root tissue damage, stunted plant growth, and decline in fruit quality, size, and overall yield. Dysbiosis of apple root-associated microbiome and selective richness of Streptomyces species in the rhizosphere typically concurs root impairment associated with ARD. However, possible roles of Streptomyces secondary metabolites within these observations remain unstudied. Therefore, we employed the One Strain Many Compounds (OSMAC) approach coupled to high-performance liquid chromatography-high-resolution tandem mass spectrometry (HPLC-HRMSn) to evaluate the chemical ecology of an apple root-associated Streptomyces ciscaucasicus strain GS2, temporally over 14 days. The chemical OSMAC approach comprised cultivation media alterations using six different media compositions, which led to the biosynthesis of the iron-chelated siderophores, ferrioxamines. The biological OSMAC approach was concomitantly applied by dual-culture cultivation for microorganismal interactions with an endophytic Streptomyces pulveraceus strain ES16 and the pathogen Cylindrocarpon olidum. This led to the modulation of ferrioxamines produced and further triggered biosynthesis of the unchelated siderophores, desferrioxamines. The structures of the compounds were elucidated using HRMSn and by comparison with the literature. We evaluated the dynamics of siderophore production under the combined influence of chemical and biological OSMAC triggers, temporally over 3, 7, and 14 days, to discern the strain’s siderophore-mediated chemical ecology. We discuss our results based on the plausible chemical implications of S. ciscaucasicus strain GS2 in the rhizosphere. 相似文献