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121.
122.
V. G. Berezkin A. A. Korolev I. V. Malyukova R. G. Mardanov 《Russian Chemical Bulletin》1997,46(12):2064-2073
The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using
a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention
depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases:
helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than
relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention
values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption
nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997. 相似文献
123.
124.
Much improved catalytic carbon-carbon bond-forming reactions between aryl chlorides and Grignard reagents has been achieved using nickel(II) ion on nanoporous carbon. 相似文献
125.
Thomas F. Brodasky 《Journal of separation science》1978,1(5):239-244
Two new acyltetramic acids related to streptolydigin have been isolated from fermentations of Streptomyces lydicus. The principal members of this complex were resolved by TLC on silica gel. However, the methods of detection, permanganate spray or bioautography, were not suitable for both crude fermentation broths and purified extracts. Gas chromatography is unsuitable for the detection of either underivatized or silylated streptolydigins. High performance liquid chromatography (HPLC) particularly on triethylaminoethyl cellulose is rapid and sensitive and is the method of choice for the analysis of both crude and purified samples. Using high performance liquid chromatography, two components were detected in the complex, which are not observed using any of the other chromatographic procedures. 相似文献
126.
Pina Romaniello 《Journal of fluorine chemistry》2004,125(2):145-149
The effect of fluorine atoms on the second-order optical nonlinear response of 4-nitro-4′-methoxy-trans-stilbene and polyene derivatives containing up to three double bonds (n=1, 2, 3) has been investigated within a semiempirical context (PM3 Hamiltonian). Experimental data reported in literature indicate a βvec(SHG) value of 34, 47 and 76 (×10−30 esu) for n=1, 2, 3, respectively, at 0.65 eV in CHCl3 solutions. Our calculations show that fluorinating the nitrophenyl group the βvec(SHG) is doubled. Further increase in the second-order nonlinear response can be obtained fluorinating the CC bond linkers between the aromatic moieties.Besides, the effect of different donor-acceptor pairs has been studied and the results interpreted in the two-state model context.Some results concerning the third-harmonic generation (THG), γ (THG), are presented, and a possible interpretation proposed. 相似文献
127.
B. S. Fedorov N. I. Golovina L. S. Barinova V. V. Arakcheeva G. V. Lagodzinskaya M. V. Loginova R. F. Trofimova V. Z. Laishev V. F. Lazarev S. P. Smirnov I. Sh. Abdrakhmanov A. I. Firkin L. O. Atovmyan 《Russian Chemical Bulletin》1992,41(12):2185-2188
1,1,4,4-Tetranitrobutane-2,3-diol reacts with formaldehyde, forming 2,2-dinitropropane-1,3-diol or a cyclic ether — 4,4-dinitro-2,3-dihydroxytetrahydrofuran — as a function of the reaction conditions.Institute of Chemical Physics, Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2755–2759, December, 1992. 相似文献
128.
An application of automated on-line HPLC-HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off-line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed. 相似文献
129.
Two methods are proposed, one for the location of saddle points and one for the calculation of steepest-descent paths on multidimensional surfaces. Both methods are based on a constrained simplex optimization technique that avoids the evaluation of gradients or second derivative matrices. Three chemical reactions of increasing structural complexity are studied within the PRDDO SCF approximation. Predicted properties of reaction hypersurfaces are in good overall agreement with those determined by gradient minimization and gradient following algorithms in connection with various ab initio SCF methods. Computational efforts required by the new procedures are discussed. 相似文献
130.
Gar B. Hoflund Steven D. Gardner David R. Schryer Billy T. Upchurch Erik J. Kielin 《Reaction Kinetics and Catalysis Letters》1996,58(1):19-26
The influence of promoters on Pt/SnOx/SiO2 and Au/MnOx low-temperature CO oxidation catalysts has been investigated under stoichiometric reaction conditions with no CO2 added to the feed gas. The performance of Pt/SnOx/SiO2 catalysts is improved significantly by the addition of 1 wt.% Fe but reduced by the addition of 5 wt.%Fe, 1 wt.% Sb, 5 wt.% Sb, 1 wt.% As, 5 wt.%As and 1.8 wt.% P. The performance of Au/MnOx is improved significantly by the addition of 1 at.% Ce but reduced by the addition of 1 at.% Co. For the catalysts and conditions examined, the Au/MnOx catalysts are superior to the Pt/SnOx/SiO2 catalysts with respect to both activity and decay characteristics. 相似文献