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排序方式: 共有398条查询结果,搜索用时 31 毫秒
161.
162.
163.
In this paper we report the synthesis of some new oxo and sulphido bridged tungsten(V) complexes with N-ethylanilindithiocarbamate and N,N-methylcyclohexyldithiocarbamate as ligands. These complexes have been characterised by analytical, magnetochemical and spectral methods. The results permit us to assign the formulate: W2O3(LL)4, W2O4(LL)2, W2O2S2(LL)2 and W2O3S(LL)2. The low magnetic moments observed in these complexes, are due either to an interaction through the bridging atoms or to a direct spin-spin interaction. IR and electronic absorption spectra of these complexes are sensitive to substitution of sulphur atoms into the bridge system. The systematic changes upon bridge modification are useful in characterizing the compounds and in clarifying assignments of W-O and W-S bridge stretching frequencies. The results are discussed on the basis of structural information available for tungsten complexes. 相似文献
164.
The influence of different hydroxylated additives (methanol, ethyleneglycol, glycerol, erythritol, xylitol, and sorbitol) on the plastein reaction catalyzed by α-chymotrypsin has been studied at different substrate concentrations. The results obtained showed that the increase in the polyol concentration and the number of hydroxylic groups per molecule enhanced the plastein yield. However, when the substrate concentration was also increased, a decrease in this activation effect was observed. In the case of a 3M xylitol solution, the plastein reaction was studied by both quantification of free amino groups and gel-permeation chromatography at different substrate concentrations. The overall analysis of the results allowed us to postulate a schematic integration of all chymotryptic reactions as a general mechanism of the plastein synthesis, as well as to conclude that the presence of additives in the reaction media, as water-activity reducing agents, increase the condensation pathway of the α-chymotrypsin action on the plastein synthesis. 相似文献
165.
T. Pérez-Ruiz C. Martínez Lozano V. Tomás J. Carpena 《Analytical and bioanalytical chemistry》1998,361(5):492-495
The interaction of diflunisal and naproxen with several surfactants was studied. Spectrofluorimetric methods were developed for the determination of both drugs in sodium dodecylsulfate micellar medium. The mixture of these drugs was resolved by synchronous fluorescence spectrometry using two scans. At Δλ = 20 nm, only naproxen yields a detectable signal that is unaffected by the presence of diflunisal. At Δλ = 110 nm the signal of diflunisal is not influenced by the presence of an up to 3-fold excess of naproxen. Mixtures containing naproxen/ diflunisal in ratios from 50:1 to 1:50 were analyzed with good results. The linear calibration ranges of both drugs were ca 0.02–2.0 μg mL–1. The method has satisfactorily been applied to a mixture of both drugs in serum. 相似文献
166.
M A Romero Rodriguez M L Vazquez Oderiz J Lopez Hernandez J Simal Lozano 《Journal of chromatographic science》1992,30(11):433-437
Liquid chromatographic methodology for determination of vitamin C and organic acids in different fruits (whortleberry, blackberry, red currant, black currant, raspberry, babaco, feijoa, kiwano, passion fruit, red and yellow tamarillos, medlar, and persimmon) cultivated in Galicia, Spain are developed. Both methods use a C18 column and an RP-18 precolumn for the stationary phase. High-performance-liquid-chromatographic-(HPLC-) grade water is brought to pH 2.2 with sulphuric acid for the mobile phase. The flow rate is 0.4 mL/min, and UV detection is at 254 nm for vitamin C and 214 nm for organic acids. Coefficients of variation of 1.84, 1.20, 1.00, and 2.60% are obtained for the vitamin C, quinic acid, malic acid and citric acid, respectively. 相似文献
167.
Ionic liquid ion sources: suppression of electrochemical reactions using voltage alternation 总被引:1,自引:0,他引:1
The problem of electrochemical decomposition due to extraction of single polarity ions from a novel ionic liquid ion source (ILIS) is solved by periodically alternating the voltage source so that the potential difference that appears across the double layer formed between the emitter conductive material and the liquid is maintained below the electrochemical window limit, thus eliminating electronic reactions. The ionic liquid EMI-BF(4) is used to externally wet a solid tungsten emitter, establishing a physical boundary with a certain liquid-metal contact area. Theoretical and experimental evidence suggests that this area is close to the effective surface involved in the double layer charging dynamics. The extent of this surface is relatively large, thus increasing the net capacitance and consequently the double layer charging time, demonstrating that low frequency voltage alternation of the order of 1 Hz is enough to obtain clean and reliable ion emission. 相似文献
168.
de La Cruz Garcia C Lopez Hernandez J Simal Lozano J 《Journal of chromatography. A》2000,891(2):367-370
A gas chromatographic method that employs flame ionization detection, a DB-Wax capillary column with helium as the carrier gas, and a split-splitless (1:15) injector was used to determine the effects of different heat treatments on the fatty-acid content of whole green beans (Phaseolus vulgaris, L.). A one-step-extraction-methylation method was used to obtain fatty acid methyl esters from raw and steamed, boiled, pressure-cooked, and microwave-cooked green beans. The fatty-acid profile changed slightly, but heat treatment produced an increase in the fatty-acid content. 相似文献
169.
A. E. Lozano J. De Abajo J. G. De La Campa 《Journal of polymer science. Part A, Polymer chemistry》1993,31(5):1203-1210
Polyisophthalamides containing benzoyl pendent groups were prepared from 5-benzoylisophthaloyl chloride and seven aromatic diamines, and their properties were compared with those of unsubstituted polyisophthalamides. The incorporation of one pendent benzoyl group per repeat unit brought about a decrease in the glass transition temperature of 10–30°C, relative to the unmodified polymers, while the thermal resistance (programmed TGA) remained unchanged or went down slightly. Other properties investigated were mechanical properties, solubility, and water absorption. © 1993 John Wiley & Sons, Inc. 相似文献
170.
S. Otin J. M. Lozano C. Gutierrez Losa 《Journal of Thermal Analysis and Calorimetry》1985,30(6):1393-1396
Excess molar enthalpies,H
E
, at atmospheric pressure and 303.15 K are reported for binary mixtures of 1-chlorohexane with diethyl oxalate, diethyl malonate, diethyl succinate, diethyl glutarate, diethyl adipate, diethyl pimelate and diethyl sebacate. These experimental results, together with those obtained previously on the excess enthalpies of aliphatic diester+n-hexane mixtures, are interpreted in terms of molecular surface interactions between aliphatic, chlorinated and carboxylate groups. Comparison of the enthalpy interchange parameters reveals a decrease of the intermolecular interactions with decreasing intramolecular COO-COO distance in the diester molecule.
Zusammenfassung Bei Atmosphärendruck und 303,15 K gemessene molare Überschußenthalpien (H E werden für binäre Gemische von 1-Chlorhexan mit Diäthyloxalat, Diäthylmalonat, Diäthylsuccinat, Diäthylglutarat, Diäthyladipat, Diäthylpimelat bzw. Diäthylsebacat angegeben. Diese experimentellen Ergebnisse werden zusammen mit den früher für Gemische von aliphatischen Diestern und n-Hexan erhaltenen Resultaten als molekulare Oberflächenwechselwirkungen zwischen aliphatischen, chlorierten und Carboxylatgruppen interpretiert. Ein Vergleich der Enthalpieaustauschparameter läßt eine Verminderung der intermolekularen Wechselwirkungen mit abnehmendem intramolekularem Abstand zwischen den COO-Gruppen erkennen.
(H E ) 303,15 K 1- , , , , , . , + -, , . COO-COO .相似文献