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31.
The methanolic extract of the aerial parts of Datura innoxia afforded a new withanolide, daturacin, the structure of which was elucidated as (20R, 22S)-21,24-epoxy-1,6-dioxo-14alpha-methoxy-5beta-witha-2,25(27)-dienolide (1) by an analysis of the spectroscopic data, including extensive NMR experiments. 相似文献
32.
The leaves of Morinda citrifolia, Linn. afforded a new benzofuran and a bis-nor-isoprenoid, blumenol C, hitherto unreported from this source. The structures of these have been elucidated as 5-benzofuran carboxylic acid-6-formyl methyl ester (1) and 4-(3'(R)-hydroxybutyl)-3,5,5, trimethyl-cyclohex-2-en-1-one (2) respectively through spectroscopic studies. The NMR data (including 1D, 2D techniques) and stereochemistry at C-3' of Compound 2 is also being reported for the first time. 相似文献
33.
Antoine?AyacheEmail author Murad S.?Taqqu 《Journal of Fourier Analysis and Applications》2003,9(5):451-471
Consider the fractional Brownian motion process $B_H(t), t\in [0,T]$,
with parameter $H\in (0,1)$.
Meyer, Sellan and Taqqu have developed
several random wavelet representations for
$B_H(t)$, of the form $\sum_{k=0}^\infty
U_k(t)\epsilon_k$ where $\epsilon_k$ are Gaussian random
variables and where the functions $U_k$ are not random. Based on the
results of Kühn and Linde, we say that the
approximation $\sum_{k=0}^n U_k(t)\epsilon_k$ of $B_H(t)$
is optimal if
$$
\displaystyle
\left( E \sup_{t\in [0,T]} \left| \sum_{k=n}^\infty U_k(t)
\epsilon_k\right|^2 \right)^{1/2} =O
\left( n^{-H} (1+\log n)^{1/2} \right),
$$
as $n\rightarrow\infty$. We show that the random wavelet
representations given in Meyer, Sellan and
Taqqu are optimal. 相似文献
34.
Muhammad Aslam Mirza Abdul Jabbar Kandhro Muhammad Yar Khuhawar Rafee Arain 《Journal of separation science》2009,32(18):3169-3177
An analytical procedure has been developed for the separation of Cu(II), Ni(II), Co(II), Fe(II), Pd(II), Th(IV), V(IV), and determination of Fe(II), Co(II), Ni(II), and V(IV) by MEKC after chelation with bis(salicylaldehyde)tetramethylethylenediimine (H2SA2Ten). Uncoated fused silica capillary was used with an applied voltage of 30 kV with photo‐diode array detection at 228 nm. SDS was added as micellar medium at pH 8.2 with sodium tetraborate buffer (0.1 M). Linear calibrations were established within 0.015–1000 μg/mL of each element with LOD within 5–67 ng/mL. The method was applied for the determination of vanadium from crude oil and ore samples in the range 0.34–2.40 and 114.2–720.7 μg/g with RSD 1.7–3.8 and 0.98–2.30% (n = 3), respectively. Fe, Ni, and Co present in crude oil and ore samples were also determined with RSD 1.3–2.8, 1.1–4.1, and 1.2–3.5% (n = 3), respectively. The results were compared with that of supplier's specifications and atomic absorption spectrometry (AAS). Method was evaluated by standard addition technique. 相似文献
35.
Selective protection of one of the hydroxyl group in 1,n-symmetrical diols is achieved by P_2O_2/SiO_2-catalyzed reaction of the diol with dihydropyran under solvent-free conditions at room temperature.This selective protection is simple and it occurred under economically cheap conditions in high yield.The deprotected diol is simply obtained by refluxing of this compound in methanol using the same catalyst without any byproduct formation or additional purifications. 相似文献
36.
Muhammad Saleem Naseem Akhter Muhammad Shaiq Ali Mamona Nazir Naheed Riaz Muhammad Moazzam Muhammad Arshad Abdul Jabbar 《Magnetic resonance in chemistry : MRC》2009,47(3):263-265
Chromatographic analysis of the alcoholic extract from Salsola imbricata yielded two new secondary metabolites, salisomide (1) and salisoflavan (2). Their structures were established with the help of spectroscopic techniques including COSY, HMQC and HMBC NMR experiments. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
37.
Abdel‐Sattar S. Hamad Elgazwy 《应用有机金属化学》2009,23(1):32-43
Oxidative addition reactions of quinolines 1a , b with Pd(dba)2 in the presence of PPh3 (1:2) in acetone gave dinuclear palladium complexes [Pd(C,N‐2‐C9 H4N‐CHO‐3‐R‐6)Cl(PPh3)]2 [(R = H ( 2a ), R = OMe ( 2b ), which were reacted with isocyanide XyNC (Xy = 2,6‐Me2C6H3) to give novel iminoacyl quinolinylpalladium complexes 3a , b in good yields (81 and 77%). Cyclopalladated complexes 3a , b were also obtained in low yields (39 and 33.5%) via one‐pot reaction of 1a , b with isonitrile XyNC:Pd(dba)2 (4:1). The reaction of 3a , b with Tl(TfO) (TfO = triflate, CF3SO3) in the presence of H2O or EtOH causes depalladation reactions of complexes to provide the corresponding organic compounds 4a , b , 5a , b and 6a , b in yields of 41, 27 and 18 ? 19%, respectively. The products were characterized by satisfactory elemental analyses and spectral studies (IR, 1H, 13C and 31P NMR). The crystal structures 2a , 3a and 3b were determined by X‐ray diffraction studies. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
38.
Using the method of molecular dynamics (MD), we have estimated the solubility of hydrogen in heavy hydrocarbons for a range of temperatures and pressures. Heavy hydrocarbon systems are known to be challenging not only for experimental measurements but also for reliable estimations using traditional equations of state (EOS). The simulation system used was designed with semi-permeable membranes to mimic actual experimental studies of gas solubility. Binary interaction parameters between the solute gas and the solvent (heavy hydrocarbons) components were adjusted when necessary to improve agreement with experimental results and then used in subsequent multi-component studies. Temperature and pressure ranges studied included higher temperatures and pressures which are especially difficult to investigate experimentally. Simulation results were finally used to adjust the binary interaction parameters (BIP) in simulation packages (e.g. Aspen) to enable quick and reliable predictions. 相似文献
39.
采用初湿浸渍和溶胶凝胶法分别制备了Li/MgO催化剂和Li/MgO纳米催化剂. 比较两种Li/MgO催化剂对于甲烷氧化偶联反应的催化性能. 采用X射线衍射、BET吸附和透射电镜进行了表征.在973-1073 K和总压力为101 kPa下对催化剂进行了测试. 实验结果表明,Li/MgO纳米催化剂比普通催化剂对于甲烷氧化偶联反应表现为更高的甲烷转换率,较高选择性和较高的的主要产品(乙烷和乙烯)的产率. 相似文献
40.
Enver Murad 《Hyperfine Interactions》1998,111(1-4):251-259
Mössbauer spectroscopic studies of soils are generally centered around the characterization of Fe3+ oxides, making use of distinctive magnetic properties of the different oxides and the high sensitivity of the technique for magnetically ordered phases. Most work on clays and clay minerals, in contrast, focuses on the determination of the oxidation state of iron, iron structural site occupancies and distortions, and the transformations that take place during clay firing. 相似文献