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41.
J. N. Spencer Travis F. Ganunis Abrahim I. Zafar Shaym Puppala James L. Ealy Larry J. Fenton Sunita Gupta C. H. Yoder J. E. Mihalick 《Journal of solution chemistry》1992,21(9):1005-1012
Equilibrium constants and enthalpies of hydrogen-bond formation of mcresol to various cyclic (crown) and acyclic polyethers have been determined in benzene solvent. Equilibrium constants indicated no evidence for an operative macrocyclic effect; the relationship between the increasing size of the equilibrium constant and the number of ether oxygens was rationalized with a simple statistical thermodynamic model. Enthalpies of interactions ranged between –19 and –23 kJ-mol–1. In agreement with PCILO calculations, enthalpies of interaction were essentially independent of the number of oxygen atoms in the ether; no significant difference in enthalpies of interaction between cyclic and acyclic ethers was found. 相似文献
42.
Naila Raziq Muhammad Shaiq Ali Salman Zafar Muhammad Imran Ali 《Natural product research》2015,29(24):2265-2270
Phytochemical investigations on Hypericum oblongifolium led to the isolation of a flavone named folicitin (1) and a bicyclic conjugated lactone, folenolide (2) from the ethyl acetate fraction of methanolic extract. Both metabolites were characterised as new compounds based on detailed spectroscopic analyses. In vitro anti-oxidant potential of both the compounds was evaluated by the DPPH radical scavenging assay. Compound 1 exhibited significant antioxidant activity while compound 2 was found inactive. 相似文献
43.
The aim of this study is to evaluate the effect of Ramadan fasting on the fat-soluble antioxidants [all-trans-retinol (vitamin A) and α-tocopherol (vitamin E)] in healthy Pakistani subjects. Thirty (30) healthy male volunteers (aged 30–50 years) with Ramadan fasting have participated in the study. Blood sampling from these subjects was conducted 1 day before and on 15th and 28th days of Ramadan. The serum levels of vitamin A and vitamin E were measured using liquid chromatography linked with UV–visible (HPLC–UV). The comparison between the samples taken at different times was made by Minitab software applying two samples and paired t-test at (p?<?0.05) as significant. No significant changes have been found in the levels of all-trans-retinol before and during Ramadan values. The levels of α-tocopherol on 28th Ramadan have been decreased significantly when compared with its values before Ramadan (p?<?0.0001). It is concluded that there is nonsignificant change in the levels of vitamin A during the month of Ramadan while the levels of α-tocopherol have been decreased significantly on the 28th day of Ramadan. It is therefore suggested that the fasting of Ramadan has effect on the levels of α-tocopherol and food-based interventions might be necessary to modify the diet during Ramadan. 相似文献
44.
Ebrahimi M Huang K Lu X McNab IR Polanyi JC Waqar Z Yang J Lin H Hofer WA 《Journal of the American Chemical Society》2011,133(41):16560-16565
Adsorbates on metals, but not previously on semiconductors, have been observed to display long-range repulsive interactions. On metals, due to efficient dissipation, the repulsions are weak, typically on the order of 5 meV at 10 ?. On the 7×7 reconstruction of the Si(111) surface, charge transport through the surface has been demonstrated by others using charge injection by STM tips. Here we show that for both physisorbed brominated molecules, and for chemisorbed Br-atoms, induced charge-transfer in the Si(111)-7×7 surface can lead to a strong repulsive interaction between adsorbates, calculated as 200 meV at 13.4 ?. This large repulsive interaction must be channeled through the surface since it causes widely spaced "one-per-corner-hole" patterns of physisorption (three cases--directly observed here) and subsequent chemisorption (four cases observed). The patterns were observed by ultrahigh vacuum scanning tunneling microscopy for four different brominated hydrocarbon adsorbates; 1,2-dibromoethane, 1-bromopropane, 1-bromopentane, and bromobenzene, deposited individually on the surface. In every case, adsorbates were overwhelmingly more likely to be found singly than multiply adjacent to a corner-hole, constituting a distinctive pattern having a probability p = 7 × 10(-5) compared to a random distribution. 相似文献
45.
N-[1-Alkylpyridin-4(1H)-ylidene]amides (PYAs) are a new class of easily prepared, neutral N-donor ligands that share some features in common with N-heterocyclic carbenes. They are strongly electron-donating toward metal centers, and a palladium(II) complex of one of these ligands has been shown to successfully catalyze both the Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions. 相似文献
46.
Shahid Hussain Arshad Muhammad Nawaz Naeem Nazra Sultana Zafar Iqbal Abdul Ghafar Shah 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(8):999-1016
In the present work, vibration characteristics of thin functionally graded cylindrical shells are studied under the influence
of various boundary conditions. Fabrication of FGM cylindrical shell is carried out by using exponential volume fraction law.
Strain- and curvature-displacements relationships are taken from Love’s thin shell theory. The frequency equation in the form
of eigenvalue problem is obtained by adapting the Rayleigh-Ritz method. Characteristic beam functions are assumed to approximate
the axial modal dependence. Effects of exponential volume fraction law on the natural frequencies of the FGM cylindrical shells
for various boundary conditions are studied against circumferential wave number, length to radius ratio and thickness to radius
ratio for different values of power law exponents. Results evaluated show good agreement with those available in the literature. 相似文献
47.
Dark transient capacitance measurements have been used to investigate the deeplevel content of red GaP LEDs. Thermal emission rate data is obtained and the 0.75 eV “killer” centre is identified from the signature. 相似文献
48.
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A Raman scattering study of the pressure induced phase transition in thallium azide is discussed. The transition appears to be triggered by the softening of a mode at 33 cm?1, which is shown by a Green's function calculation to be anharmonically coupled to another mode of the same symmetry at 48 cm?1. 相似文献