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961.
The K-Selectride reduction at low temperature (-45°C) of 7-oxo-5α-holestan-3β-yl acetate and methyl 7-oxo-3α-hydroxy-5(β-cholanoate resulted in almost quantitative yield of the 7α-alcohol in the 5α-compound but only moderate yield of the 5β-analog. The simultaneous reduction of two carbonyl groups in the 3 and 7 positions afforded good to excellent yields of the diaxial diol in planar steroids (methyl 3,7-dioxo-5α-cholanoate, 3,7-dioxo-5α-cholestane and methyl 3,7-dioxo-5α-cholestan-27-oate) and only 14% of 3α,7α-(OH)2 from methyl 3,7-dioxo-5β-cholanoate. 相似文献
962.
Hans König 《Analytical and bioanalytical chemistry》1973,266(2):119-124
The separation of a mixture of 22 bactericides has been achieved by gas chromatography on columns with silicone rubber W-982 as stationary phase with temperatures between 100° and 300°C. The unchanged compounds as well as their silylation products have been used. The latter are more conveniently used especially for the quantitative determination. To be able to calculate the retention indices after Kovats gas chromatography has been performed isothermally at 180°C for the more volatile compounds and at 250°C for all other bactericides.The retention indices obtained under these conditions are tabulated together with the limits of detection. 相似文献
963.
Paloma Sevillano Sven Koenig Daniel Himmel Olaf Fuhr Dieter Fenske 《无机化学与普通化学杂志》2005,631(11):2236-2240
The reactions of [Co2(CO)8] with E(SiMe3)2 (E = Se, Te) in CH2Cl2 result in the formation of the compounds [Co4Se2(CO)10]> ( 1 ) and [Co4Te2(CO)11] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ4‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ2‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph2PC≡CPPh2 (dppa), the reaction of [Co2(CO)8] with Se(SiMe3)2 leads to the formation of [Co8Se4(CO)16(μ‐dppa)2] ( 3 ). During the reaction two molecules of [Co2(CO)8] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ3‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups. 相似文献
964.
The three-coordinate nickel-carbene complex (dtbpe)Ni=CPh2 (3) was prepared from the thermolysis of the diphenyldiazoalkane complex (dtbpe)Ni(N,N':eta2-N2CPh2) (2) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane). Complex 3 was structurally characterized by single-crystal X-ray diffraction methods (Ni-C = 1.836(2) A). Complex 3 reacts with 2 equiv of CO2 to afford (dtbpe)Ni{OC(O)CPh2C(O)O} (4), with diphenylketene to give (dtbpe)Ni{OC(=CPh2)CPh2} (5), with excess CO to transfer the carbene fragment and generate diphenylketene and (dtbpe)Ni(CO)2 (6), with sulfur dioxide to give the metallasulfone (dtbpe)Ni{C,S:eta2-S(O)2CPh2} (7), and with the Br?nsted acid [HNMe2Ph][B(C6F5)4] to give the alkyl cation [(dtbpe)Ni(CHPh2)][B(C6F5)4] (8). Complexes 4, 5, and 7 have also been characterized by single-crystal X-ray diffraction methods. 相似文献
965.
Daniel Krois Mario Simonetti Erich Wünsch 《Monatshefte für Chemie / Chemical Monthly》1989,120(11):1029-1041
Summary For the identification of a protein predicted by DNA sequence analysis of the TTV1 virus from the archaebacteriumThermoproteus tenax, the trieicosapeptide H-Thr-Pro-Thr-Pro-Thr-Pro-Thr-Tyr-Asp-Ile-Thr-Tyr-Val-Val-Phe-Asp-Val-Thr-Pro-Ser-Pro-Thr-Pro-OH, corresponding to the protein fragment 79–101, was prepared by conventional methods of peptide synthesis. This sequence portion may possibly represent a suitable protein specific immunepitope.
Zur Hypothese eines TTV1 Virus/Thermoproteus tenax F154-Proteins. Teil II: Synthese des Protein-fragments 79–101
Zusammenfassung Für den Nachweis der Expression des Proteins F154 — nach einer Sequenzanalyse des Genoms des TTV1 Virus im ArchaebakteriumThermoproteus tenax postuliert — wurde das Peptid H-Thr-Pro-Thr-Pro-Thr-Pro-Thr-Tyr-Asp-Ile-Thr-Tyr-Val-Val-Phe-Asp-Val-Thr-Pro-Ser-Pro-Thr-Pro-OH (Proteinfragment 79–101) mit Hilfe konventioneller Peptidsynthese hergestellt. Diese Peptidsequenz sollte ein geeignetes proteinspezifisches Immunepitop darstellen.相似文献
966.
Allison M. Mills Daniel Brunling Michael Ruck 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):i70-i72
A redetermination of the structure of `La32.66Fe11S60' in the trigonal space group Rm led to the new formula La52Fe12S90 and to a redefinition of the structure type. In the structure, the Fe2+ cations occur in Fe2S9 dimers of face‐sharing octahedra (with 3m symmetry). The dimers are linked by face‐ and vertex‐sharing bi‐ and tricapped LaS6 trigonal prisms (with m symmetry) to form a three‐dimensional network containing two types of cuboctahedral cavities. The larger cavities remain empty, while the smaller ones accommodate alternative sites for disordered La3+ cations. 相似文献
967.
Valérie Chevalier-Billosta Jean-Paul Joseleau Alain Cochaux Katia Ruel 《Cellulose (London, England)》2007,14(2):141-152
The composition and ultrastructural arrangement of cell wall polymers in wood fibres have determining influence on the properties
of wood derived materials. It is therefore important to improve our understanding of the relationship between fibres organisation,
the modifications induced by pulping treatments, and the resulting paper sheet mechanical properties. The different treatments
to which fibres are subjected during the manufacturing of pulps and papers induce morphological and micro-structural alterations
due to the removal of wall constituents and of microfibrillar elements. The impact of pulping processes on fibres was investigated
at the ultrastructural scale of transmission electron microscopy. Particular attention was given to the effects of beating
in refiners at various intensities on the ultrastructure of fibres. The most characteristic effects consisted of delaminations,
microfibril disorganisation, and even fractures, of varying importance depending on the intensity of the mechanical refining.
The consequences of internal alterations and surface modifications of the fibres were examined in relation to the paper sheet
mechanical properties. Correlations between the type of alteration observed in the fibres and its possible impact on a given
paper mechanical property are suggested. With similar approaches, the effects of drying and recycling were studied. 相似文献
968.
Stereoselectivity of reductive amination of (R)-1-hydroxy-1-phenylpropan-2-one by methylamine was studied. From the four isomers possible, only two are produced by this
reaction. These are marked as (−)-(1R,2S)-ephedrine (desired product) and (+)-(1S,2R)-ephedrine. The reaction stereoselectivity depends both on the type of the catalyst and reaction conditions. The most suitable
type is the supported platinum. However, this catalyst rapidly deactivates. With a decreasing activity of Pt catalyst, the
stereoselectivity decreases. It is also decreased during the production of the second liquid phase (water) in the reaction
mixture. 相似文献
969.
Gabriela Flores-Ramírez Manuel Rivera Alfredo Morales-Pablos Joel Osuna Xavier Soberón Paul Gaytán 《BMC chemical biology》2007,7(1):1
Background
The effect of single and multiple amino acid substitutions in the green fluorescent protein (GFP) from Aequorea victoria has been extensively explored, yielding several proteins of diverse spectral properties. However, the role of amino acid deletions in this protein -as with most proteins- is still unknown, due to the technical difficulties involved in generating combinatorial in-phase amino acid deletions on a target region. 相似文献970.
A new chelating polymeric sorbent has been developed using Merrifield chloromethylated resin anchored with quinoline-8-ol (HQ). The modified polymeric resin was characterized by FT-IR spectroscopy and elemental analysis. The HQ anchored resin showed superior binding affinity for U(VI) over Th(IV) and La(III). The influence of various physicochemical parameters on the recovery of U(VI) were optimized by both static and dynamic methods. The phase exchange kinetic studies performed for U(VI) revealed that <5 min was sufficient for reaching equilibrium metal ion sorption. The maximum sorption capacity of HQ anchored resin for U(VI) was found to be 120.30 mg g−1 of resin which is higher than other solid phase extraction sorbents reported so far excepting N,N-dibutyl, N′-benzoyl thiourea sorbed Amberlite XAD-16. The developed HQ anchored polymeric resin is highly selective as none of the extraneous species were found to have any deleterious effect. Solid phase extraction (SPE) studies performed using HQ anchored polymeric resin offered enrichment factor of 100 and the lowest concentration below which recoveries become non-quantitative is 5 μg l−1. The accuracy of the developed SPE method in conjunction with Arsenazo III procedure was tested by analyzing marine sediment (MESS-3) and soil (IAEA–Soil 7) reference materials. Furthermore, the above procedure has been successfully employed for the analysis of real soil and sediment samples. 相似文献