Pyridoxol, protected by acetylation of the hydroxyl groups, has been converted to its N-oxide which upon reaction with perfluoroacetie anhydride yields a 2-nor-2-hydroxymethylpyridoxol derivative as an intermediate. This compound undergoes acyl migration from the 3-position. Protection of the pyridoxol hydroxyls by benzylalion followed by the same treatment yields the unrearranged α2-hydroxy derivative. This compound has been converted to a series of α2-substituted pyridoxols (X = -Cl, -Br, -OCOCH3, -OCH3, -OC2H5). 相似文献
X-Ray Structural Analyses of Cyclododecasulfur (S12) and Cyclododecasulfur-1-Carbon-disulfide (S12 · CS2) S12 · CS2 crystallizes in space group R&3macr;m–D with hexagonal lattice constants a = 1066.8(3), c = 1155.1(4) pm, Z = 3, dcalc. = 2.04 g · cm?3. The S12 molecules occupy sites of D3d symmetry with bond distance (dss) of 205.4(1) pm, bond angles (α) of 105.80(5) and 106.65(6)º and torsional angle (τ) of 87.20(7)º. The CS2 molecule interacts only very weakly with the S12 units. S12 crystallizes in space group Pnnm–D with lattice constants a = 472.5(2), b = 910.4(3), c = 1453.2(3) pm, Z = 2, dcalc = 2.045 g · cm?3. The molecules with mean parameters d = 205.2 pm, α 106.6º, τ 88.0º occupy sites of C2h symmetry. 相似文献
A unique matrix system consisting mostly of 4-nitrophenol has shown to be very effective for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of large DNA oligomers when a cooled sample stage was used to prevent the sublimation of this matrix under vacuum. Using this 4-nitrophenol matrix with UV laser desorption, detection of picomole quantities of DNA oligomers containing up to approximately 800 nucleotides was routinely achieved. The effectiveness of this matrix was further demonstrated by the observation of a double-stranded DNA oligomer larger than 1000 base pairs, seen as a denatured single-stranded species, with a molecular ion mass exceeding 300 000 Da. The potential applications of 4-nitrophenol as a matrix for DNA sizing are discussed. 相似文献
Measurements of the major cations Ca and Mg by the technique of diffusive gradients in thin films (DGTs) were systematically evaluated. The concentration in solution was calculated using Fick’s first law of diffusion from the directly measured flux to the DGT device. A selective cation exchange resin (Bio-Rad Chelex®100), which has been used extensively with DGT for trace metals, such as Cd2+, Cu2+ and Ni2+, was used for this work.
Elution of Ca and Mg from the resin with 1 M HNO3 was very reproducible. Measurements of Ca and Mg concentrations in synthetic solutions agreed well with the theoretical predictions. The negative response on uptake caused by lowered pH was investigated. Uptake was found to decline below pH 5. The capacity of the DGT device for Ca and Mg was also investigated to establish maximum deployment times for given concentrations.
Experiments with filtered and modified lake water show that DGT can be used to measure Ca and Mg when trace metals are present in the solution. An in situ deployment of DGT combined with an ultrafiltration study suggest that the Mg concentration measured by DGT is similar to the concentration found in the fraction <1 kDa. 相似文献
Zusammenfassung Die spektrometrische Analyse von weiß erstarrtem Roheisen (auf C, Si, Mn, P, S, Cu) ist mit der gleichen Anregung und in der gleichen Funkzeit wie diejenige von Stahl möglich. Eine spezielle Kalibriertechnik mit Stahlproben garantiert ein ausreichend reproduzierbares und richtiges Resultat in relativ kurzer Zeit (20 sec).
Emission-spectrometrical analysis of pig iron
The conditions of pig iron analysis by using a direct reading spectrometer for routine determination of C, Si, Mn, P, S and Cu, the influence of sampling and a new calibration technique of the instrument are described. The whole time needed for complete spectrometrical analysis is about 20 sec.
Wir sind Herrn T. Nientiedt für zahlreiche Anregungen und Diskussionen zu Dank verpflichtet. 相似文献
Trimethylsilyl Derivatives of Vb-Elements. VI. Synthesis, Molecular and Crystal Structure of Tetrakis(trimethylsilyl)distibine Compared with Tetraphenyldistibine Tetrakis(trimethylsilyl)distibine already isolated by Breunig et al. [9] from cleavage reactions of tris(trimethylsilyl)stibine may also be obtained in high yields from lithium bis(trimethylsilyl)antimonide · 2THF and 1,2-dibromoethane in n-pentane. This compound intensely red in the solid state, but only slightly yellow in solution or in the melt crystallizes in the monoclinic space group P21/c with a = 680.6(1); b = 1672.8(2); c = 1190.0(1) pm; β = 119.01(5)°; Z = 2 at +20°C. An X-ray structure determination (R = 0.017) shows the bis(trimethylsilyl)-stibino groups to be arranged in a transoid position. Characteristic bond lengths and angles are: Sb? Sb 286.7(1); Sb? Si 259.4 pm; Si? Sb? Si 94.46(3); Sb? Sb? Si 98.68(3) and 94.43(3)°. As in similiar 2,2′,5,5′-tetramethyldistibolyl published recently by Ashe III et al. [8] this crystal structure, too, is characterized by a nearly linear sequence of Sb? Sb groups. Compared with the sum of van-der-Waals radii the intermolecular Sb-Sb contact in such a chain is shortened from 440 to 399 pm. This probably allows electronic interactions of unknown type responsible for the colour of the crystals. In keeping with this assumption an analogous formation of chains is not found in solid, only yellow tetraphenyldistibine 5 the structure of which has already been studied by Rehder et al. [44]. 相似文献
A method, named “cold oxidation” was developed, by which structures of isotropic looking pyrocarbon coatings of nuclear fuel particles can be made visible. It is based on a dry oxidation of the pyrocarbon at room temperature by highly excited oxygen. The amorphous parts of the pyrocarbon coatings burn off more quickly than the pyrocarbon itself and thereby a relief-like coating structure appears. It could be shown that a connection exists between the structure of the pyrocarbon coatings after “cold oxidation” and their behaviour under fast neutron irradiation. 相似文献