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11.
The gas-phase infrared absorption spectra of neutral benzyl and tropyl, isomers of formula C7H7, have been measured in the 400-1800 cm-1 spectral region. In addition, a quantum chemical calculation has been performed to model the infrared spectra. For the benzyl radical, the theory shows satisfactory overlap with the experiment, although vibrations involving the CH2 group might be anharmonic. The tropyl radical, which is subject to the Jahn-Teller effect, seems well modeled for the out-of-plane vibrational modes, but less so for the in-plane vibrational modes. 相似文献
12.
A very selective method is described for the determination of doxorubicin in rat plasma. Doxorubicin is extracted from the plasma on a pretreated octadecyl silane column and eluted with phosphate buffer pH 2.6/methanol (25/75, v/v) containing sodium 1-heptanesulfonate as ion-pairing agent. The extraction procedure is suitable for samples which contain doxorubicin encapsulated in liposomes if Triton X-100 is added. A portion of the evaporated eluate is used for high-performance reversed-phase chromatography with the same eluent and a fluorescence detector. Daunorubicin is used as internal standard. Extraction of doxorubicin from plasma is quantitative. The calibration graph is linear for 0.2-100 μg l?1 doxorubicin with a limit of detection of 0.2 μg l?1 for 0.5 ml of plasma. The relative standard error of estimate of the calibration was typically 3%. 相似文献
13.
Stortelder A Buijs JB Bulthuis J van der Vies SM Gooijer C van der Zwan G 《Journal of photochemistry and photobiology. B, Biology》2005,78(1):53-60
The time-resolved fluorescence properties of the bacteriophage T4 capsid protein gp23 are investigated. The structural characteristics of this protein are largely unknown and can be probed by recording time-resolved and decay-associated fluorescence spectra and intensity decay curves using a 200 ps-gated intensified CCD-camera. Spectral and decay data are recorded simultaneously, which makes data acquisition fast compared to time-correlated single-photon counting. A red-shift of the emission maximum within the first nanosecond of decay is observed, which can be explained by the different decay-associated spectra of fluorescence lifetimes of the protein in combination with dipolar relaxation. In addition, iodide quenching experiments are performed, to study the degree of exposure of the various tryptophan residues. A model for the origin of the observed lifetimes of 0.032 +/- 0.003, 0.39 +/- 0.06, 2.1 +/- 0.1 and 6.8 +/- 0.8 ns is presented: the 32 ps lifetime can be assigned to the emission of a buried tryptophan residue, the 0.4 and 2.1 ns lifetimes to two partly buried residues, and the 6.8 ns lifetime to a single tryptophan outside the bulk of the folded gp23. 相似文献
14.
Gert -Martin Greuel 《manuscripta mathematica》1977,21(3):227-241
Let f{xo,...,xn} define a germ of a complex analytic hypersurface (Xo,0) with isolated singularity. We show that the number of cusps of the unfolded discriminant curve is an invariant of the Jacobian algebra {x,o},...,xn/(f/xo,...,f/xn) of f. Moreover we show that this number + 1 equals the sum of the Milnor numbers of (Xo,0) and of the polar curve of (Xo,0). Our result generalizes formulas of Iversen and Lê for plane curves to arbitrary dimensions. 相似文献
15.
Walter M. F. Fabian Gert Kollenz Yunus Akcamur Tevfik Riza Kök Makbule Teczan Mehmet Akkurt Wolfgang Hiller 《Monatshefte für Chemie / Chemical Monthly》1992,123(3):265-275
Summary 4-Benzoyl-5-phenylfuran-2,3-dione (1) and the urethanes2 combine under loss of carbon monoxide yielding the open chain dibenzoylacetic acid derivatives3 and4. 3a, b only can be cyclized to the oxazinone5. The keto-enole tautomerism3 4 is further investigated with aid of semiempirical quantum chemical calculations, based upon the molecular geometry of3a, deduced from an X-ray study.
Frau Univ. Prof. Dr. Helga Wittmann mit den besten Wünschen zum 70. Geburtstag gewidmet. 相似文献
16.
By14C-labeling it is shown that the ring contraction reaction of 1,4-benzothiazin-2,3-4H-dione (1), leading via benzthiazol-2-carbonic acid (2) finally to benzthiazole (3), proceeds via hydrolytic opening of the thiolactone-bond in1, irrespectively of H+ or OH– catalysis. 相似文献
17.
18.
E. V. Gert 《Cellulose (London, England)》1996,3(1):217-228
For preparation of various modified forms of microcrystalline cellulose, an optional combination is proposed of hydrolytic activity with other properties of nitric acid such as, adduct forming ability (manifested as Knecht compound formation), oxidizing, bleaching and nitrating. The manifestation of a chosen acid function is reached by variation of the reaction conditions: concentration, temperature, time, etc. The sole-reagent continuous procedure involving several operations made in a predetermined sequence allows the use of a more simple technological scheme and saves energy, time and materials. The features of transformation of fibrous and microcrystalline forms of native cellulose into cellulose-II through the Knecht compound are discussed. Purely acidic transformation schemes of native cellulose into microcrystalline cellulose hydrate and amorphous low-nitrate powder cellulose according to the above scheme are considered. Morphological features as well as distinguishing properties — enhanced hydrophilicity, sorption activity and degree of whiteness — of the prepared materials are pointed out. The possibility of obtaining uniformly oxidized forms of powder cellulose according to this scheme and the outlook for the use of nitrogen(IV) oxide as a multifunctional reagent are discussed. 相似文献
19.
Laloup M Ramirez Fernandez Mdel M Wood M De Boeck G Henquet C Maes V Samyn N 《Journal of chromatography. A》2005,1082(1):15-24
A rapid and sensitive method for the analysis of delta9-tetrahydrocannabinol (THC) in preserved oral fluid was developed and fully validated. Oral fluid was collected with the Intercept, a Food and Drug Administration (FDA) approved sampling device that is used on a large scale in the U.S. for workplace drug testing. The method comprised a simple liquid-liquid extraction with hexane, followed by liquid chromatography-tandem mass spectrometry (LC-MS-MS) analysis. Chromatographic separation was achieved using a XTerra MS C18 column, eluted isocratically with 1 mM ammonium formate-methanol (10:90, v/v). Selectivity of the method was achieved by a combination of retention time, and two precursor-product ion transitions. The use of the liquid-liquid extraction was demonstrated to be highly effective and led to significant decreases in the interferences present in the matrix. Validation of the method was performed using both 100 and 500 MicroL of oral fluid. The method was linear over the range investigated (0.5-100 ng/mL and 0. 1-10 ng/mL when 100 and 500 microL, respectively, of oral fluid were used) with an excellent intra-assay and inter-assay precision (relative standard deviations, RSD <6%) for quality control samples spiked at a concentration of 2.5 and 25 ng/mL and 0.5 and 2.5 ng/mL, respectively. Limits of quantification were 0.5 and 0.1 ng/mL when using 100 and 500 microL, respectively. In contrast to existing GC-MS methods, no extensive sample clean-up and time-consuming derivatisation steps were needed. The method was subsequently applied to Intercept samples collected at the roadside and collected during a controlled study with cannabis. 相似文献
20.
The kinetics of conversion of an edge-linked double cube, in this case [{Mo(3)PdS(4)(H(2)O)(9)}(2)](8+), to the corresponding single cube [Mo(3)(PdX)S(4)(H(2)O)(9)](4+), has been studied for the first time. Reaction is induced by six reagents X = CO, two water-soluble phosphines, Cl(-), Br(-), and NCS(-), which complex at the tetrahedral Pd. The first stage of reaction is fast and is accompanied by color changes, e.g. purple to dark blue in the case of Cl(-), assigned as double to single cube conversion. With X = CO and the two phosphines, when absorbance changes are intense enough for stopped-flow monitoring with reactants at =1 mM, rate constants 10(-)(5) k/M(-)(1) s(-)(1) at 25 degrees C are as follows: CO, 1.11; PTA, 27.8; P(C(6)H(4)SO(3))(3)(3)(-), 9.6; at I = 2.00 (Li(pts)). The reactions are independent of [H(+)] in the range 0.30-2.00 M, and no substitution at the Mo's is observed. The first stages with X = Cl(-), Br(-), and NCS(-) were too fast to monitor, but equilibrium constants K(1)/M(-)(1) were determined, Cl(-) (490), Br(-) (8040), and NCS(-) (630), by UV-vis spectrophotometry. Two subsequent kinetic stages are assigned to substitution at the Mo's. Similar behavior is observed for [Mo(3)FeS(4)(H(2)O)(10)](4+), which was selected because substitution at the Fe is also fast and there is no known double-cube formation. For both Mo(3)Pd and Mo(3)Fe the latter two stages can be explained by substitution at nonidentical (two alpha and one beta) H(2)O's on each Mo or by the presence of mixed-valent Mo(III)(2)Mo(IV) forms which are sufficiently long-lived to give a kinetic discrimination. In the case of NCS(-) an additional step, 0.015 s(-)(1), independent of [NCS(-)] is assigned to the isomerization Pd-NCS --> Pd-SCN. On removal of e.g. Cl(-) by chromatography or addition of Ag(+), the double cube re-forms. 相似文献