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Ternary Lithium Rare Earth Nitrates with Lonesome Nitrate Ions: Li3[M(NO3)5](NO3) (M = Gd? Lu, Y). The Crystal Structure of Li3Er(NO3)6 Single crystals of the ternary nitrate Li3Er(NO3)6 are obtained from a solution of “Er(NO3)3” in the melt of LiNO3. In Li3Er(NO3)6 (monoclinic, P21/n, Z = 4; a = 776.0(1); b = 748.86(8); c = 2 396(1) pm; β = 90.76(3)°; R1 = 0.0490; wR2 = 0.0792), Er3+ is surrounded by five bidentate nitrate ligands yielding the anionic units [Er(NO3)5]2?. These are arranged in the direction of the 21 screw axis. Two lonesome NO3? ions are in the middle of such a “helix” and are connected by Li+ with the anions [Er(NO3)5]2?. The helices are moved against each other by about half of the lattice constant a and are connected by further Li+ ions. 相似文献
3.
Guldi DM Hirsch A Scheloske M Dietel E Troisi A Zerbetto F Prato M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):4968-4979
Control over the interchromophore separation, their angular relationship, and the spatial overlap of their electronic clouds in several ZnP-C(60) dyads (ZnP=zinc porphyrin) is used to modulate the rates of intramolecular electron transfer. For the first time, a detailed analysis of the charge transfer absorption and emission spectra, time-dependent spectroscopic measurements, and molecular dynamics simulations prove quantitatively that the same two moieties can produce widely different electron-transfer regimes. This investigation also shows that the combination of ZnP and C(60) consistently produces charge recombination in the inverted Marcus region, with reorganization energies that are remarkably low, regardless of the solvent polarity. The time constants of electron transfer range from the mus to the ps regime, the electronic couplings from a few tens to several hundreds of cm(-1), and the reorganization energies remain below 0.54 eV and can be as low as 0.16 eV. 相似文献
4.
The development and in-house testing of a method for the detection and quantification of cocoa butter equivalents in cocoa butter and plain chocolate is described. A database consisting of the triacylglycerol profile of 74 genuine cocoa butter and 75 cocoa butter equivalent samples obtained by high-resolution capillary gas liquid chromatography was created, using a certified cocoa butter reference material (IRMM-801) for calibration purposes. Based on these data, a large number of cocoa butter/cocoa butter equivalent mixtures were arithmetically simulated. By subjecting the data set to various statistical tools, reliable models for both detection (univariate regression model) and quantification (multivariate model) were elaborated. Validation data sets consisting of a large number of samples (n = 4050 for detection, n = 1050 for quantification) were used to test the models. Excluding pure illipé fat samples from the data set, the detection limit was determined between 1 and 3% foreign fat in cocoa butter. Recalculated for a chocolate with a fat content of 30%, these figures are equal to 0.3-0.9% cocoa butter equivalent. For quantification, the average error for prediction was estimated to be 1.1% cocoa butter equivalent in cocoa butter, without prior knowledge of the materials used in the blend corresponding to 0.3% in chocolate (fat content 30%). The advantage of the approach is that by using IRMM-801 for calibration, the established mathematical decision rules can be transferred to every testing laboratory. 相似文献
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Milen Raytchev Elke Mayer Nicole Amann Hans-Achim Wagenknecht Torsten Fiebig 《Chemphyschem》2004,5(5):706-712
5-(Pyren-1-yl)-2'-deoxyuridine (PydU) and 5-(Pyren-1-yl)-2'-deoxycytidine (PydC) were used as model nucleosides for DNA-mediated reductive electron transport (ET) in steady-state fluorescence and femtosecond time-resolved transient absorption spectroscopy studies. Excitation of the pyrene moiety in PydU and PydC leads to an intramolecular electron transfer that yields the pyrenyl radical cation and the corresponding pyrimidine radical anion (dU.- and dC.-. By comparing the excited state dynamics of PydC and PydU, we derived information about the energy difference between the two pyrimidine radical anion states. To determine the influence of protonation on the rates of photoinduced intramolecular ET, the spectroscopic investigations were performed in acetonitrile, MeCN, and in water at different pH values. The results show a significant difference in the basicity of the generated pyrimidine radical anions and imply an involvement of proton transfer during electron hopping in DNA. Our studies revealed that the radical anion dC.- is being protonated even in basic aqueous solution on a picosecond time scale (or faster). These results suggest that protonation of dC.- may also occur in DNA. In contrast, efficient ET in PydU could only be observed at low pH values (< 5). In conclusion, we propose--based on the free energy differences and the different basicities--that only dT.- but not dC.- can participate as an intermediate charge carrier for excess electron migration in DNA. 相似文献
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8.
Simultaneous determination of ondansetron and tropisetron in human plasma using HPLC with UV detection 总被引:4,自引:0,他引:4
Bauer S Störmer E Kaiser R Tremblay PB Brockmöller J Roots I 《Biomedical chromatography : BMC》2002,16(3):187-190
A rapid and sensitive HPLC method for the simultaneous quantitation of ondansetron and tropisetron, two serotonin (5-HT) receptor antagonists frequently used in treatment and prevention of nausea and emesis, is described. The procedure involves liquid-liquid extraction of human plasma with dichloromethane coupled with reversed-phase HPLC and UV detection. The lower limits of quantification (LOQ) were 0.62 ng/mL for ondansetron and 1.25 ng/mL or tropisetron. Intra- and inter-assay coefficients of variation ranged from 1.5 to 7.5% and 5.3 to 13.7%, respectively. The sensitivity and precision were sufficient for determination of plasma concentrations after therapeutic administration of both drugs and the method can be used for the estimation of pharmacokinetic parameters. 相似文献
9.
Genetically modified organisms (GMOs) entered the European food market in 1996. Current legislation demands the labeling of food products if they contain <1% GMO, as assessed for each ingredient of the product. To create confidence in the testing methods and to complement enforcement requirements, there is an urgent need for internationally validated methods, which could serve as reference methods. To date, several methods have been submitted to validation trials at an international level; approaches now exist that can be used in different circumstances and for different food matrixes. Moreover, the requirement for the formal validation of methods is clearly accepted; several national and international bodies are active in organizing studies. Further validation studies, especially on the quantitative polymerase chain reaction methods, need to be performed to cover the rising demand for new extraction methods and other background matrixes, as well as for novel GMO constructs. 相似文献
10.
Reactions of Uranium Pentabromide. Crystal Structures of PPh4[UBr6], PPh4[UBr6] · 2CCl4, (PPh4)2[UBr6] · 4CH3CN, and (PPh4)2[UO2Br4] · 2CH2Cl2 PPh4[UBr6] and PPh4[UBr6] · 2CCl4 were obtained from UBr5 · CH3CN and tetraphenylphosphonium bromide in dichloromethane, the latter being precipitated by CCl4. Their crystal structures were determined by X-ray diffraction. PPh4[UBr6]: 2101 observed reflexions, R = 0.090, space group C2/c, Z = 4, a = 2315.5, b = 695.0, c = 1805.2 pm, β = 96.38°. PPh4[UBr6] · 2CCl4: 2973 reflexions, R = 0.074, space group P21/c, Z = 4, a = 1111.5, b = 2114.2, c = 1718.7 pm, β = 95.42°. Hydrogen sulfide reduces uranium pentabromide to uranium tetrabromide. Upon evaporation, bromide is evolved from solutions of UBr5 with 1 or more then 3 mol equivalents of acetonitrile in dichlormethane yielding UBr4 · CH3CN and UBr4 · 3CH3CN, respectively. These react with PPh4Br in acetonitrile affording (PPh4)2[UBr6] · 4CH3CN, the crystal structure of which was determined: 2663 reflexions, R = 0.050, space group P21/c, Z = 2, a = 981.8, b = 2010.1, c = 1549.3 pm, β = 98.79°. By reduction of uranium pentabromide with tetraethylammonium hydrogen sulfide in dichloromethane (NEt4)2[U2Br10] was obtained; (PPh4)2[U2Br10] formed from UBr4 and PPh4Br in CH2Cl2. Both compounds are extremely sensitive towards moisture and oxygen. The crystal structure of the oxydation product of the latter compound, (PPh4)2[U02Br4]· 2 CH2Cl2, was determined: 2163 reflexions, R = 0.083, space group C2/c, Z = 4, a = 2006.3, b = 1320.6, c = 2042,5 pm, β = 98.78°. Mean values for the UBr bond lengths in the octahedral anions are 266.2 pm for UBr6-, 276.7 pm for UBr62? and 282.5 pm for UO2Br42? 相似文献