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1.
2.
Yellowish crystals of K2[(UO2)As2O7] ( 1 ) have been synthesized by solid‐state reactions method. The structure of 1 [orthorhombic, Pmmn, a = 12.601(2), b = 13.242(2), c = 5.621(1) Å, V = 937.9(3) Å3, Z = 4] has been solved by direct methods and refined to R1 = 0.049, wR2 = 0.1060 for 1059 observed reflections. The structure of 1 is based upon [(UO2)As2O7]2? sheets formed by corner sharing between [UO6]6? distorted octahedra and [As2O7]4? polyarsenate groups. The K+ cations are either in eightfold or tenfold coordination and are located between the sheets. The topology of the uranyl arsenate sheet is related to silicate minerals of the melilite group and related synthetic silicate, aluminate and germanate compounds. 相似文献
3.
Topological properties of clusters are used to extract critical parameters. This method is tested for the bulk properties ofd=2 percolation and thed=2, 3 Ising model. For the latter we obtain an accurate value of the critical temperatureJ/k
B
T
c=0.221617(18). In the case of thed=3 Ising model with film geometry the critical value of the surface coupling at the special transitions is determined as J1c/J=1.5004(20) together with the critical exponents
1
m
=0.237(5) and=0.461(15). 相似文献
4.
5.
Omar Deeb Prof. Monika Leibscher Dr. Jörn Manz Prof. Wulf von Muellern Tamar Seideman Prof. 《Chemphyschem》2007,8(2):322-328
We propose an approach for separating nuclear spin isomers with coherent light and illustrate it by numerical calculations using fulvene as a model system. The scheme employs the equivalence of torsion and interchange of equivalent H-atoms in a class of molecules of which fulvene is a simple example. The exchange symmetry couples with the rotational symmetry to produce a spatial distinction between the two photo-excited nuclear spin isomers, and wavepacket interferometry is applied to separate the species. 相似文献
6.
Gaseous Acetates Thermoanalytical and mass-spectrometrical observations are undertaken with some acetates and oxiacetates. The volatilization of copper(I) acetate takes place like that of the silver acetate as M2Ac2+ (besides the deposition of Ag). On the volatilization of the anhydrous compounds Cu2Ac4, Cr2Ac4, Rh2Ac4, and Mo2Ac4 in the vacuum of a mass spectrometer is observed that Cu2Ac4 vaporizes dissociative as Cu2Ac2+ (+ 2 “Ac”), while the other compounds vaporize as M2Ac4+ and simultaneously is formed an oxidic (e.g. Cr2O4) or metallic residue. PdAc2 vaporizes in the mass spectrometer as a trimeric molecule Pd3Ac6. M4OAc6, which is formed from the dihydrates, vaporizes in a mass spectrometer with M ? Co, Mn as M4OAc6+. Other complexes of the same type appear as Be4OAc5+, Mg4OAc5+, and Zn4OAc5+. 相似文献
7.
We used a combination of theoretical and experimental methods to derive the spectroscopic properties of imidazolium-based ionic liquids. Vibrational frequencies, NMR chemical shifts, and quadrupole coupling constants react in comparable manner to changes in the chemical environment. This suggests that both the IR and the NMR spectroscopic properties reflect a similar type of electronic perturbation caused by hydrogen bonding. These relationships of the spectroscopic properties provide detailed information about structural complexes and may thus serve as good indicators of ion-pair formation. They also help to decide which spectroscopic tool is the most sensitive for investigating molecular interactions. The measurement of only one spectroscopic property allows the prediction of other properties that cannot be so easily measured. In some cases, this is the only way to obtain reliable coupling constants for deriving molecular correlation times from macroscopic NMR relaxation times, thus opening a new path for studying structure-dynamics relations in ionic liquids. 相似文献
8.
Detection of autofluorescence at the skin surface is highly influenced by melanin and hemoglobin. Epidermal absorption and scattering may also be an influencing factor and is represented in this article as a quantitative parameter, epidermal thickness. To examine this parameter we measured the 370 nm fluorescence in vivo after excitation with 330 nm and the 455 nm fluorescence after excitation with 330 and 370 nm. Measurements were performed on sun-exposed skin at the dorsal aspect of the forearm and shoulder and on nonexposed buttock skin. Skin pigmentation and redness of the same body sites were measured by reflectance spectroscopy. The thickness of the stratum corneum and the cellular part of epidermis was quantified by light microscopy of skin biopsies. Multiple regression analysis was used to find correlations between autofluorescence and the potential influencing factors. We found a highly significant correlation of skin autofluorescence with pigmentation and redness for both emission wavelengths (Em). A small but significant correlation to epidermal thickness was found only for excitation wavelength (Ex) 370 nm and Em455 nm if body site was included in the analysis. No correlation between Ex330:Em370 and Ex330:Em455 and thickness of epidermis was found. For practical use, correction of skin autofluorescence for pigmentation is essential, correction for redness is of less importance and correction for epidermal thickness is unnecessary. 相似文献
9.
Siethoff C Orth M Ortling A Brendel E Wagner-Redeker W 《Journal of mass spectrometry : JMS》2004,39(8):884-889
A liquid chromatographic/tandem mass spectrometric method was developed and validated for the quantitation of capecitabine and its metabolite 5-fluorouracil in human plasma. The simultaneous determination of both analytes was achieved by a column switching method using a trapping column and two analytical columns with different stationary phases. Isocratic elution was used for the separation of capecitabine on a C18 column whereas 5-fluorouracil was separated using gradient elution on an non-polar carbon phase. The calibration curves were linear for both compounds with a correlation factor (R2) > 0.9993 for 5-fluorouracil and >0.9942 for capecitabine. The assay was validated in the concentration range 5.00-1000 ng ml(-1) for both compounds. The intra-day precision was better than 10% for 5-fluorouracil and better than 11% for capecitabine whereas the inter-day precision was better than 8% for 5-fluorouracil and better than 14% for capecitabine. 相似文献
10.
Different virtual screening techniques are available as alternatives to high throughput screening. These different techniques have been rarely used together on the same target. We had the opportunity to do so in order to discover novel blockers of the voltage-dependent potassium channel Kv1.5, a potential target for the treatment of atrial fibrillation. Our corporate database was searched, using a protein-based pharmacophore, derived from a homology model, as query. As a result, 244 molecules were screened in vitro, 19 of them (7.8%) were found to be active. Five of them, belonging to five different chemical classes, exhibited IC50 values under 10 microM. The performance of this structure-based virtual screening protocol has been compared with those of similarity and ligand-based pharmacophore searches. The analysis of the results supports the conventional wisdom of using as many virtual screening techniques as possible in order to maximize the chance of finding as many chemotypes as possible. 相似文献