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421.
F. A. López M. C. Ramirez J. A. Pons A. López-Delgado F. J. Alguacil 《Journal of Thermal Analysis and Calorimetry》2008,94(2):517-522
This study presents an evaluation of the decomposition kinetic of low-grade nickeliferous laterite by thermogravimetric analysis.
Kinetic parameters were calculated using the Ozawa and the iso-conversional Friedman methods. Simplified kinetics models like
those based on the reaction order were also applied for the simulations. Two-dimensional shrinkage models of the reaction
interface mechanism were adopted as describing the thermal transformation process from non-isothermal kinetic analysis. The
iso-conversional method (model-free kinetics) reveals that the decomposition of low-grade nickeliferous laterite does not
follow a single mechanism because the determined activation energies and pre-exponential factor are not constant during the
course of the reaction. 相似文献
422.
The Simmons-Smith cyclopropanation is a widely used method to synthesize cyclopropanes from alkenes using methylene iodide and a zinc reagent. A novel class of organozinc species, RXZnCH(2)Y, has been found to efficiently cyclopropanate alkenes, including traditionally unreactive unfunctionalized alkenes. The reactivity and selectivity of this class of organozinc reagents can be regulated by tuning the electronic and/or steric nature of the RX group attached to Zn. During recent years, this class of organozinc reagent has been widely used in organic synthesis as a reagent for cyclopropanation and other useful synthetic transformations. Catalytic, asymmetric versions of this reaction have been developed providing high enantiomeric excess for unfunctionalized olefins. 相似文献
423.
424.
Kinetic and computational studies on the amidation of esters with mixtures of formamide and sodium methoxide are described. Rate studies are consistent with a fast deprotonation of formamide followed by two reversible acyl transfers affected by solvent participation. MP2 calculations suggest that the first acyl transfer between the ester and sodium formamide is rate-determining. The transition structures leading to the formation and collapse of the first tetrahedral intermediate are calculated to be isoenergetic. 相似文献
425.
Aquines O Li Z Lopez A Mendez H Ramirez J Huang GS Miller DH Pavlunin V Sanghi B Shipsey IP Xin B Adams GS Anderson M Cummings JP Danko I Napolitano J He Q Insler J Muramatsu H Park CS Thorndike EH Coan TE Gao YS Liu F Stroynowski R Artuso M Blusk S Butt J Li J Menaa N Mountain R Nisar S Randrianarivony K Redjimi R Sia R Skwarnicki T Stone S Wang JC Zhang K Csorna SE Bonvicini G Cinabro D Dubrovin M Lincoln A Asner DM Edwards KW Briere RA Brock I Chen J Ferguson T Tatishvili G Vogel H 《Physical review letters》2006,96(15):152001
Using 420 pb(-1) of data collected on the upsilon(5S) resonance with the CLEO III detector, we reconstruct B mesons in 25 exclusive decay channels to measure or set upper limits on the decay rate of upsilon(5S) into B meson final states. We measure the inclusive B cross section to be sigma(upsilon(5S) --> BB(X)) = (0.177 +/- 0.030 +/- 0.016) nb and make the first measurements of the production rates of sigma(upsilon(5S) --> B*B*) = (0.131 +/- 0.025 +/- 0.014) nb and sigma(upsilon(5S) --> BB*) = (0.043 +/- 0.016 +/- 0.006) nb, respectively. We set 90% confidence level limits of sigma(upsilon(5S) -->BB) < 0.038 nb, sigma(upsilon(5S) --> B(*)B(*)pi) < 0.055 nb and sigma(upsilon(5S) --> BBpipi) < 0.024 nb. We also extract the most precise value of the B(s)* mass to date, M(B(s)*) = (5411.7 +/- 1.6 +/- 0.6) MeV/c2. 相似文献
426.
Models for the carrier photoexcitation mechanism in molecular crystals have been established initially on the bases of measurements on oligoacenes and later applied to conjugated polymers as well. These models emphasize the localized nature of photoexcitations and describe carrier generation as a secondary process involving exciton dissociation. The results of our photoconductivity studies of single crystal tetracene are at variance with these widely accepted models, and in fact indicate that the photocarrier quantum efficiency appears independent of temperature, photon energy, and light intensity, thus featuring the hallmarks of direct interband carrier photogeneration and coherent carrier transport at band states. 相似文献
427.
Paul R. Raithby Jack Lewis Catherine A. Morewood M. Carmen Ramirez de Arellano Gregory P. Shields 《Journal of Cluster Science》2006,17(1):13-26
Thermolysis of [Ru3(CO)12] in cyclohexene for 24 h affords the complexes [Ru(CO)3(η4-C6H8)] (1), [Ru3H2(CO)9(μ2-η1:η2:η1-C6H8)] (2), [Ru4(CO)12(μ4-C6H8)] (3) [Ru4(CO)9(μ4-C6H8)(η6-C6H6)] (4a and 4b, two isomers) and [Ru5(CO)12(μ4-η2-C6H8)(η4-C6H8)] (5), where 1, 3, 4a and 4b have been previously characterised as products of the thermolysis of [Ru3(CO)12] with cyclohexa-1,3-diene. The molecular structures of the new clusters 2 and 5 were determined by single-crystal X-ray crystallography, showing that two conformational polymorphs of 5 exist in the solid state, differing in the orientation of the cyclohexa-1,3-diene ligand on a ruthenium vertex. 相似文献
428.
Wood M Laloup M Samyn N del Mar Ramirez Fernandez M de Bruijn EA Maes RA De Boeck G 《Journal of chromatography. A》2006,1130(1):3-15
Recent years have seen the development of powerful technologies that have provided forensic scientists with new analytical capabilities, unimaginable only a few years ago. With liquid chromatography-mass spectrometry (LC-MS) in particular, there has been an explosion in the range of new products available for solving many analytical problems, especially for those applications in which non-volatile, labile and/or high molecular weight compounds are being analysed. The aim of this article is to present an overview of some of the most recent applications of LC-MS (/MS) to forensic analysis. To this end, our survey encompasses the period from 2002 to 2005 and focuses on trace analysis (including chemical warfare agents, explosives and dyes), the use of alternative specimens for monitoring drugs of abuse, systematic toxicological analysis and high-throughput analysis. It is not the intention to provide an exhaustive review of the literature but rather to provide the reader with a 'flavour' of the versatility and utility of the technique within the forensic sciences. 相似文献
429.
Novel tboc‐protected ionenes with exceeding 30 kDa were prepared from the step‐growth polymerization of tert‐butyl bis[3‐(dimethylamino)propyl]carbamate and 1,12‐dibromododecane. The protected ionenes yielded pH‐sensitive, protonatable ionenes with pKa ≈ 6.6 for the conjugate acid of the protonated secondary amine. Polyplexes of the protected and deprotected ionenes, whose cytotoxicity for endothelial cells was analyzed using the MTT assay, efficiently complex plasmid DNA. Polyplexes destabilized cellular membranes as revealed using the lactate dehydrogenase assay at high concentrations. The polyplexes were successfully transfected into HBMECs at mass ratios 2, 4, 8, 12, and 16 (polymer/DNA) at polyplex concentrations less than 10 µg · mL?1.
430.
E. I. Klimova M. Martinez Garcia T. Klimova L. Ruiz Ramirez N. N. Meleshonkova 《Russian Chemical Bulletin》1999,48(11):2153-2157
3-Cyclobutyl-3-ferrocenylcyclopropene was synthesized by the reactions of mono- or dibromoferrocenylcyclopropanes with ButOK in DMSO. Treatment of dibromoferro-cenylcyclopropane with ButOK in THF afforded 3-cyclobutylidene-3-ferrocenylpropyne in 52% yield. Heterolysis of the C-C bond in the three-membered ring
of 3-cyclobutyl-3-ferrocenylcyclopropene at low and high temperatures was studied. Hydrolysis yielded 3-cyclobutyl-1H-cyclopentaferrocene and products with linear structures,viz., 3-cyclobutylidene-3-ferrocenylpropene,E- andZ-I-ferrocenyl-1-cyclobutylpropenes, and 1-cyclobutylidene-1-ferrocenylacetone. Cyclopropene reacts with 1,3-diphenylisobenzofuran
to form two Diels-Alder adducts, while the enyne does not react with 1,3-diphenylbenzofuran.
Facultad de Quimica, Universidad Nacional Autónoma de México, Cd. Universitaria, C.P. 04510, México D. F., México.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2177–2181, November, 1999. 相似文献