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81.
Sixteen chemical drugs, often found in adulterated Chinese medicine, were studied by high performance liquid chromatography/atmospheric ionization mass spectrometry. Under optimal conditions, three pairs of compounds were either coeluted or unresolved. The lack of chromatographic resolution and the lack of specificity in UV detection were overcome by a method based on high performance liquid chromatography/electrospray mass spectrometry. This method was capable of detecting the adulterants based on their retention times, molecular ions, and characteristic fragments resulting from in‐source collision induced dissociation. 相似文献
82.
We examine the crystallization and chain conformation behavior of semicrystalline poly(ethylene oxide) (PEO) and amorphous poly(vinyl acetate) (PVAc) mixtures with wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS) experiments. For blends with PEO weight fractions (wtPEO) greater than or equal to 0.3, below the melting point of PEO, the WAXD patterns reveal that crystalline PEO belongs to the monoclinic system. The unit‐cell parameters are independent of wtPEO. However, the bulk crystallinity determined from WAXD decreases as wtPEO decreases. The scattered intensities from SAXS experiments show that the systems form an ordered crystalline/amorphous lamellar structure. In a combination of WAXD and SAXS analysis, the related morphological parameters are assigned correctly. With the addition of amorphous PVAc, both the average amorphous layer thickness and long spacing increase, whereas the average crystalline layer thickness decreases. We find that a two‐phase analysis of the correlation function from SAXS, in which the scattering invariant is linearly proportional to the volume fraction of lamellar stacks, describes quantitatively the crystallization behavior of PEO in the presence of PVAc. When wtPEO is close to 1, the samples are fully spaced‐filled with lamellar stacks. As wtPEO decreases from 1.0 to 0.3, more PVAc chains are excluded from the interlamellar region into the interfibrillar region. The fraction outside the lamellar stacks, which is completely occupied with PVAc chains, increases from 0 to 58%. Because the radius of gyration of PVAc with a random‐coil configuration determined from SANS is smaller than the average amorphous layer thickness from SAXS, we believe that the amorphous PVAc chains still persist with a random‐coil configuration even when the blends form an ordered structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2705–2715, 2001 相似文献
83.
Ya‐Ching Shen Yu‐Hui Chen Tsong‐Long Hwang Jih‐Hwa Guh Ashraf Taha Khalil 《Helvetica chimica acta》2007,90(7):1391-1398
Chemical investigation of the gorgonian coral Junceella fragilis, collected by scuba diving in Taiwan, resulted in the isolation of four new briarane‐type diterpenoids, frajunolides A–D ( 1 – 4 ), along with three known briaranes. Their structures were elucidated on the basis of spectroscopic studies, especially 1‐ and 2D‐NMR as well as HR‐MS experiments. The inhibitory effect of all isolated metabolites towards superoxide‐anion generation and elastase release by human neutrophils in response to formylmethionyl‐leucyl‐phenylalanine/dihydrocytochalasin B (FMLP/CB) was evaluated. 相似文献
84.
85.
This report discusses an analysis of least-squares finite element for a steady electromagnetic field in 2-D. The Maxwell equations for the magnetic field strength H are written into a first-order linear system of PDE. The analysis shows that the regular finite element spaces with piecewise linear polynomials can be chosen to represent the H and the conducted electric density J. The error of the numerical results in H-1 norm should be bounded by Ch. 相似文献
86.
Ya‐Ching Shen Yuan‐Bin Cheng Yu‐Hui Chen Ashraf Taha Khalil Chin‐Lien Ko 《中国化学会会志》2005,52(6):1263-1268
Three new clerodane diterpene derivatives were isolated from the leaves of Casearia membranacea Hance collected in Taiwan. The isolated metabolites were identified as caseamembrins P (1), Q (2), and R (3). Identification of the structures was based on detailed analysis of the spectral data, especially 2D NMR. 相似文献
87.
ZnO‐Coated Carbon Nanotubes: Inter‐Diffusion of Carboxyl Groups and Enhanced Photocurrent Generation 下载免费PDF全文
Chia‐I Hung Dr. Hua‐Chiang Wen Yao‐Cheng Lai Dr. Shih‐Hsin Chang Prof. Dr. Wu‐Ching Chou Prof. Dr. Wen‐Kuang Hsu 《Chemphyschem》2015,16(4):812-816
ZnO is a defect‐governed oxide and emits light at both visible and UV regimes. This work employs atomic layer deposition to produce oxide particles on oxygenated carbon nanotubes, and the composites only show emission profiles at short wavelengths. The quenching of defect‐related emissions at long wavelengths is verified, owing to carboxyl diffusion into oxygen vacancies, and doping is supported by ZnCO3 formation in oxide lattice. Fully coated tubes display an increased photocurrent and the quantum efficiency increases by 22 % relative to the bare nanotubes. 相似文献
88.
89.
Characterization of Novel Aminobenzylcantharidinimides and Related Imides by Proton NMR Spectra and Their Effects on NO Induction 下载免费PDF全文
Ing‐Jy Tseng Pen‐Yuan Lin Shiow‐Yunn Sheu Wan‐Ni Tung Ching‐Tung Lin Mei‐Hsiang Lin 《中国化学会会志》2015,62(1):59-63
Various acidic anhydrides including cantharidin were converted into corresponding aminobenzylcantharidinimide 3a and analogous imides 3b~k (at the ortho, meta, and para positions) with 35%~87% yields by reacting with aminobenzylamines and triethylamine. The two methyl side chains of cantharidinimides 3ao , 3am , and 3ap, and related imides had more than two chiral centers; the lone pair of electrons of nitrogen displayed a different chemical shift and coupling constant in H‐NMR spectra when the amino group of benzylamine was in the ortho position. These cantharidinimides had parent aniline, pyridine, and naphthalene plane structures, and the primary amine nucleophilicity and basicity might reflect the inductive electron’s negative effect on chemical shifts. We prepared cantharidinimides by heating the reactants cantharidin 1a , aliphatic and aromatic acid anhydrides, primary benzylic amines, and aniline derivatives to ca. 200 °C with 3 mL of dry toluene, and 1~2 mL of triethylamine in high‐pressure sealed tubes (Buchi glasuster 0032) to produce cantharidinimides and their analogues in good yields. The para‐aminobenzylic imides showed greater inhibition of nitric oxide (NO) synthesis by NO synthase (NOS) than did ortho‐ and meta‐aminobenzylic imides. Compound 3fp , para‐aminobenzylic norbonane‐imide, had the most potent effect on inducible NOS among the tested compounds and showed 35% inhibition. 相似文献
90.
Assuming that the disc material can be modeled either as Mooney–Rivlin or as Hookean and the steel ring enclosing the disc as Hookean, the energy release rates as a function of the crack length are evaluated and compared. Two loadings are considered––one in which the surface of the star shape hole in the disc is loaded by a uniform pressure and the other in which the temperature of the composite body is uniformly raised. It is found that the linear and the nonlinear analyses give qualitatively similar results for the two loadings. For each load, the energy release rate increases with an increase in the starter crack length, reaches a maximum value and then decreases gradually. 相似文献