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71.
Rafael Usón Pascual Lahuerta Daniel Carmona Luis A. Oro 《Transition Metal Chemistry》1980,5(1):327-329
Summary The preparation of the covalent Rh(OCIO3)(CS)(PCy3)2 and Rh(OClO3)(CS)(PPh3)(PCy3) perchlorato complexes is described, These complexes react with mono- or bidentate nitrogen donor ligands to give new cationic complexes of the [Rh(CS)(PCY3)2L]ClO4 and [Rh(CS)(PPh,)(PCy3)L]ClO4 types, 相似文献
72.
Marta Gonzlez‐lvarez Gloria Alzuet Jos Luis García‐Gimnez Benigno Macías Joaquín Borrs 《无机化学与普通化学杂志》2005,631(11):2181-2187
Three flavonoid copper(II) complexes Cu2(quercetin)(CH3COO)3(CH3OH) ( 1 ), Cu(anthrarufin)(CH3COO)·1/2H2O ( 2 ) and Cu(naringin)(OCH3)(CH3OH)2 ( 3 ) have been synthesized and characterized by elemental analysis, IR, electronic absorption and EPR (X‐band) spectroscopy. The complexes have a strong protective action over the Δsod1 mutant of S. cerevisiae against reactive oxygen radicals generated by an external source of free radicals (H2O2 or the superoxide‐generating, menadione). On the other hand, the complexes cleave DNA efficiently even in the absence of reducing agents. The main reactive oxygen species responsible for the DNA strand cleavage have been determined using radical scavengers. A probably mechanism of the DNA damage is proposed. 相似文献
73.
WO3 and WO3:P (5 mol% H3PO4) thin films were prepared using the sol-gel route and the electrochromic properties of the films were investigated using
in situ spectroelectrochemical methods. The measurements were performed in propylene carbonate solution with 0.1 M LiClO4 as electrolyte. During the cathodic polarization at –0.8 V a blue coloration is observed with a reversible variation between
14% and 84% of the transmittance at λ=633 nm. The kinetics for the bleaching process is faster for the WO3:P film than for the undoped WO3 film.
Electronic Publication 相似文献
74.
Soto-Chinchilla JJ Gámiz-Gracia L García-Campaña AM Imai K García-Ayuso LE 《Journal of chromatography. A》2005,1095(1-2):60-67
The determination of seven sulfonamides by means of HPLC with chemiluminescence detection is proposed for the first time. The analytes are derivatized with fluorescamine, separated and subsequently they participate in the post-column chemiluminescence (CL) peroxyoxalate system using imidazole as a catalyst. Among the different peroxyoxalates tested, bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate provides higher sensitivities and stabilities, avoiding precipitation problems. A rigorous optimization of the significant variables by means of experimental designs has been developed in order to reconcile the chromatographic conditions with the CL reaction. The method provides detection limits in the low microgl(-1) range and has been satisfactorily applied to the analysis of spiked raw milk samples. 相似文献
75.
Synthesis of an N-protected derivative of 2-amino-2'-deoxyadenosine (dA') from 2'-deoxyguanosine is reported. The syntheses of several oligodeoxynucleotides containing this modified nucleoside are described, together with physical characterization via melting studies and CD conformational analysis. As expected, the 2-amino group is seen to add to the duplex stability. Although the sequence d(TA')3 was found to undergo a salt-induced conformational transition, mixed sequences such as d(CGTA'CG) did not display this behavior. All guanine residues present in these sequences were O6 protected, either with the cyanoethyl group or the 4-nitrophenylethyl group, to eliminate guanine degradation during phosphorylation and condensation reactions. Procedures for the introduction and removal of these O6 protecting groups are described. 相似文献
76.
Rodríguez JL Souto RM Fernández-Mérida L Pastor E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(9):2134-2142
Spectroelectrochemical studies on the reactivity of butanol isomers on Pt electrodes in perchloric acid medium led to the observation of structural effects that result from the different arrangements of atoms in the organic molecules. The use of differential electrochemical mass spectrometry (DEMS) to detect volatile products showed that all four isomers react on the electrode, though different product yields were observed for each compound. In spite of the differences in the electrochemical behaviour of the butanol isomers, a series of general processes accounts for the results obtained. The formation of strongly adsorbed residues by a dehydration process leading to the formation of a C=C bond was proposed for all isomers. Electroreduction of the adsorbates produces C(4) and C(3) alkanes, and the latter reveal the existence of a fragmentation process. The C(4) hydrocarbons can be formed by hydrogenation of these residues and by hydrogenolysis of alcohol molecules in the bulk solution which react at the electrode with adsorbed hydrogen. On the other hand, CO(2) is formed during electrooxidation of the adsorbed species. Partial-oxidation products containing a carbonyl group were detected from 0.2 M solutions of 1-butanol, isobutyl alcohol and sec-butyl alcohol. The tertiary alcohol tert-butyl alcohol only reacts in its adsorbed state. 相似文献
77.
Transition structures associated with the C-C bond-formation step of the proline-catalyzed intermolecular aldol reaction
between acetone and isobutyraldehyde have been studies using density functional theory methods at the B3LYP/6-31G** computational
level. A continuum model has been selected to represent solvent effects. For this step, which is the stereocontrolling and
rate-determining step, four reactive channels corresponding to the syn and anti arrangement of the active methylene of the
enamine relative to the carboxylic acid group of l-proline and the re and si attack modes to both faces of the aldehyde carbonyl group have been analyzed. The B3LYP/6-31G**
energies are in good agreement with experiment, allowing us to explain the origin of the catalysis and stereoselectivity for
these proline-catalyzed aldol reactions.
Received: 2 April 2002 / Accepted: 18 July 2002 / Published online: 11 October 2002
Acknowledgements. This work was supported by research funds provided by the Ministerio de Educación y Cultura of the Spanish Government by
DGICYT (project PB98–1429). All the calculations were performed on a Cray–Silicon Graphics Origin 2000 of the Servicio de
Informática de la Universidad de Valencia. We are most indebted to this center for providing us with computer capabilities.
Correspondence to: L. R. Domingo e-mail: domingo@utopia.uv.es 相似文献
78.
The synthesis of dendrons with the end-capped 5-(N,N-dimethylamino)naphthyl-1-ethynyl unit connected to conjugated naphthylethynyl or p-phenylethynyl chains, as the branches of the 1,3,5-substituted benzene core, have been undertaken by heterocoupling reaction between 1,3,5-triiodobenzene and the convenient end-capped 5-(N,N-dimethylamino)naphthylacetylene or 5-(N,N-dimethylamino)naphthylethynylphenylacetylene in the presence of the palladium-copper catalyst system, in excellent yields. The influence of the alternating naphthylethynyl-phenylethynyl chains on the fluorescence emission radiation, in the dendron structures, has been analyzed. 相似文献
79.
López-Alarcón C Squella JA Núñez-Vergara LJ Baez H Camargo C 《Rapid communications in mass spectrometry : RCM》2002,16(24):2229-2238
A gas chromatography/mass spectrometry (GC/MS) method for the qualitative and quantitative determination of the calcium-channel antagonists C-4-substituted 1,4-dihydropyridines, and their corresponding N-ethyl derivatives, is presented. Also, the electrochemical oxidation and the reactivity of the compounds with alkyl radicals derived from 2,2'-azobis-(2-amidinopropane) were monitored by GC/MS. Mass spectral fragmentation patterns for the C-4-substituted 1,4-dihydropy-ridine parent drugs were significantly different from those of their oxidation products, generated either by electrochemical oxidation or by reaction with alkyl radicals. However, for N-ethyl-1,4-dihydropyridine compounds it was not possible to detect the final products (pyridinium salts) using these experimental conditions. 相似文献
80.
Lead is extracted from urine with ammonium pyrrolidien dithiocrbamate into methyl isobutyl ketone, and 20 μl of the extract is injected into a water carrier stream in a flow-injection/atomic absorption system. The procedure is simple, quick, accurate and reproducible. Recoveries are 96–105%. The mean urine lead contents of 20 unexposed and 20 printing-press lead exposed workers was found to be 39.0 ± 8.3 and 71.7 ± 26.3 μg Pb l?1, respectively. 相似文献