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31.
Grigorii G. Sivets Elena N. Kalinichenko Igor A. Mikhailopulo 《Helvetica chimica acta》2007,90(9):1818-1836
Convergent syntheses of the 9‐(3‐X‐2,3‐dideoxy‐2‐fluoro‐β‐D ‐ribofuranosyl)adenines 5 (X=N3) and 7 (X=NH2), as well as of their respective α‐anomers 6 and 8 , are described, using methyl 2‐azido‐5‐O‐benzoyl‐2,3‐dideoxy‐2‐fluoro‐β‐D ‐ribofuranoside ( 4 ) as glycosylating agent. Methyl 5‐O‐benzoyl‐2,3‐dideoxy‐2,3‐difluoro‐β‐D ‐ribofuranoside ( 12 ) was prepared starting from two precursors, and coupled with silylated N6‐benzoyladenine to afford, after deprotection, 2′,3′‐dideoxy‐2′,3′‐difluoroadenosine ( 13 ). Condensation of 1‐O‐acetyl‐3,5‐di‐O‐benzoyl‐2‐deoxy‐2‐fluoro‐β‐D ‐ribofuranose ( 14 ) with silylated N2‐palmitoylguanine gave, after chromatographic separation and deacylation, the N7‐β‐anomer 17 as the main product, along with 2′‐deoxy‐2′‐fluoroguanosine ( 15 ) and its N9‐α‐anomer 16 in a ratio of ca. 42 : 24 : 10. An in‐depth conformational analysis of a number of 2,3‐dideoxy‐2‐fluoro‐3‐X‐D ‐ribofuranosides (X=F, N3, NH2, H) as well as of purine and pyrimidine 2‐deoxy‐2‐fluoro‐D ‐ribofuranosyl nucleosides was performed using the PSEUROT (version 6.3) software in combination with NMR studies. 相似文献
32.
Ihor R. Muts Falko M. Schappacher Vasyl’ I. Zaremba 《Journal of solid state chemistry》2007,180(8):2202-2208
New indides SrAu3In3 and EuAu3In3 were synthesized by induction melting of the elements in sealed tantalum tubes. Both indides were characterized by X-ray diffraction on powders and single crystals. They crystallize with a new orthorhombic structure type: Pmmn, Z=2, a=455.26(9), b=775.9(2), c=904.9(2) pm, wR2=0.0425, 485 F2 values for SrAu3In3 and a=454.2(2), b=768.1(6), c=907.3(6) pm, wR2=0.0495, 551 F2 values for EuAu3In3 with 26 variables for each refinement. The gold and indium atoms build up three-dimensional [Au3In3] polyanionic networks, which leave distorted hexagonal channels for the strontium and europium atoms. Within the networks one observes Au2 atoms without Au-Au contacts and gold zig-zag chains (279 pm Au1-Au1 in EuAu3In3). The Au-In and In-In distances in EuAu3In3 range from 270 to 290 and from 305 to 355 pm. The europium atoms within the distorted hexagonal channels have coordination number 14 (8 Au+6 In). EuAu3In3 shows Curie-Weiss behavior above 50 K with an experimental magnetic moment of 8.1(1) μB/Eu atom. 151Eu Mössbauer spectra show a single signal at δ=−11.31(1) mm/s, compatible with divalent europium. No magnetic ordering was detected down to 3 K. 相似文献
33.
A new spectrofluorimetric method to determine epristeride (EP) has been developed, which based on the EP has a strong ability to quench the intrinsic fluorescence of bovine serum albumin (BSA). There was the relationship between the fluorescence quenching intensity of BSA (ΔF = FBSA − FBSA-EP) and the concentration EP. The quenching mechanism was investigated with the quenching type, the association constants, the number of binding sites and basic thermodynamic parameters. The method had been successfully applied to the analysis of EP in real samples and the obtained results were in good agreement with the results of official method-HPLC. 相似文献
34.
Susan Robertson David Ellis Georgina M. Rosair Alan J. Welch 《Journal of organometallic chemistry》2003,680(1-2):286-293
The reaction of the labelled carborane ligand [3-Et-7,8-Ph2-7,8-nido-C2B9H8]2− with a source of {Pt(PMe2Ph)2}2+ affords non-isomerised 1,2-Ph2-3,3-(PMe2Ph)2-6-Et-3,1,2-closo-PtC2B9H8 (1). The analogous reaction between [3-F-7,8-Ph2-7,8-nido-C2B9H8]2− and {Pt(PMe2Ph)2}2+ yields 1,8-Ph2-2,2-(PMe2Ph)2-4-F-2,1,8-closo-PtC2B9H8 (3). Compound 1 has a heavily slipped structure (Δ 0.72 Å), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the reaction is evident from the fact that it reverts to isomerised 1,8-Ph2-2,2-(PMe2Ph)2-4-Et-2,1,8-closo-PtC2B9H8 (2) slowly at room temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2 and 3 may be explained most simply by the rotation of a CB2 face of an intermediate based on the structure of 1. Compounds 1–3 were characterised by a combination of spectroscopic and crystallographic techniques. 相似文献
35.
36.
FlorianC. Stintzing Florian Kugler Reinhold Carle Jürgen Conrad 《Helvetica chimica acta》2006,89(5):1008-1016
Due to their inherent liability towards highly acidic conditions previously considered to be a prerequisite for data acquisition, betaxanthin structure dereplication by NMR spectroscopy has been scarcely reported and was, hitherto, exclusively based on 1H‐NMR data interpretation. Applying only slightly acidic conditions, we herein report the first 13C‐NMR data of two betaxanthins, i.e., indicaxanthin ( 1 ), isolated from yellow‐orange cactus pear fruits (Opuntia ficus‐indica [L.] Mill . cv. ‘Gialla’), and of miraxanthin V ( 2 ) from yellow Swiss chard petioles (Beta vulgaris L. ssp. cicla [L.] Alef . cv. ‘Bright Lights’), as derived by gHSQC‐ and gHMQC‐NMR experiments and inverse detection. 相似文献
37.
Juan Méndez-Vivar 《Journal of Sol-Gel Science and Technology》2006,38(2):159-166
Sols composed of dibutyltin dilaureate (DTL) and tetraethyl orthosilicate (TEOS) were prepared using a mixture of methyl ethyl
ketone (MEK) and acetone as the solvent in order to study the interaction between the oligomeric Sn and Si species. The hydrolysis
molar ratio r (r=nH2O/nM (M: Si, Sn or Si+Sn) was 2. The use of an acid or basic catalyst was avoided, as the sols are intended to be used in
the formulation of potential stone consolidants. The sols were studied by several spectroscopic techniques including Small
Angle X-ray Scattering (SAXS), 29Si and 119Sn NMR, Fourier Transform Infrared (FTIR) spectroscopy and X-ray diffraction (XRD). According to the spectroscopic results
the lauric acid produced by the hydrolysis of DTL modifies the condensation path of the Si species, leading to the formation
of two types of oligomeric chains: linear swollen and multiparticle diffusion-limited aggregates, depending on the molar ratio
Sn/Si. The 29Si NMR results indicated that the hydrolysis of DTL catalizes the condensation of the Si species, giving as a result higher
condensation extents of the Si species in the Sn-Si sols compared to a pure Si sol. Based on the Radial Distribution functions
(RDF) and the FTIR results, heterocondensation occurred. 相似文献
38.
Jakub Čížek Ivan Procházka Radomír Kužel Rinat K. Islamgaliev 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):873-887
Summary. Ultra-fine grained (UFG) Cu (grain size 80 nm) containing 0.5 wt.% Al2O3 nanoparticles (size 20 nm) was prepared by high pressure torsion (HPT). Positron lifetime spectroscopy was employed to characterize
the microstructure of this material, especially with respect to types and concentration of lattice defects. The evolution
of microstructure with increasing temperature was studied by positron lifetime spectroscopy and X-ray diffraction measurements.
The thermal stability of the Cu + 0.5 wt.% Al2O3 nanocomposite was compared with that of pure UFG Cu prepared by the same technique. The processes taking place during thermal
recovery of the initial nanoscale structure in both studied materials are described.
Received October 5, 2001. Accepted (revised) December 20, 2001 相似文献
39.
40.
The new electrolytic dissolution in batch of aluminum alloys samples as grains or turns and the determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb and Ti by ICP OES was investigated. In on-line electrodissolution procedures described in the literature, samples were restricted to be in the form of solid blocks or plates with one polished flat face. Here, the sample was loaded in the barrel of a modified disposable syringe (the anodic semi-cell) and pressed with a modified plunger fitted with a platinum disk to establish electrical contact with the analyte. This arrangement was introduced in a beaker containing the electrolyte (1 mol L−1 HNO3) and a platinum wire as the cathode. The resulting solution from electrodissolution (0.6 A) was used for the ICP OES determinations. The influence of the aluminum concentration increase on the determination of the elements was evaluated. Electrodissolution of certified reference materials and commercial samples revealed relative errors lower than 10% for the elements Fe, Cu, Mg, Ni, Cr, Zn and Ti (when their content is above 0.1%). Higher inaccuracies (>10%) were observed for Mn and for Fe in B.C.S. 268/1 reference material certified. The proposed method presented a relative standard deviations (R.S.D.) lower or circa 10% to all of the elements (except Pb). In comparison with traditional acid dissolution, the proposed electrodissolution method is relatively fast (about 30 min), it is clean (there is no projection of solution) and simple (heating and fumes exhaust system were not necessaries). 相似文献