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1.
M. Zürcher und Gisela Hoepe 《Fresenius' Journal of Analytical Chemistry》1940,119(3-4):134-136
Ohne Zusammenfassung 相似文献
2.
3.
VladimirA. Azov Franois Diederich Yoriko Lill Bert Hecht 《Helvetica chimica acta》2003,86(6):2149-2155
We report the synthesis of modified Cram‐type cavitands bearing one or two fluorescent labels for single‐molecule spectroscopic studies of vase? kite conformational switching (Scheme 3). Syntheses were performed by stepwise bridging of the four couples of neighboring H‐bonded OH groups of resorcin[4]arene bowls (Schemes 2 and 3). The new substitution patterns enable the construction of a large variety of future functional architectures. 1H‐NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature‐ and pH‐triggered vase? kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges (Table). It was discovered that vase? kite switching of cavitands is strongly solvent‐dependent. 相似文献
4.
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
5.
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
6.
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
7.
An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 mug l(-1), provided recovery percentages between 94 and 105%. A detection limit of 12 mug l(-1) was achieved and a variation coefficient of 3.4% was obtained at 0.50 mug ml(-1). 相似文献
8.
9.
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
10.
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