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961.
Alberto Hernandez Gainza 《国际化学动力学杂志》2004,36(9):500-509
Halogenated hydrocarbon solvents, SolvCl, (dichloromethane, chloroform, and 1,2‐dichloroethane) react with various types of tertiary amines, A, such as tri‐n‐buthylamine, tropane derivatives (tropine and atropine) and quinine generating a quaternary ammonium salt, N‐halogenalkylammonium chloride (SolvA+Cl?). Some tertiary amines, as well as secondary and primary amines, cannot react with these solvents. This reaction has been detected and studied by both conductivity and visible spectrophotometry measures—the latter after adding a small quantity of a dye, such as bromocresol green (BCGH2), bromophenol blue (BPBH2), or tetrabromophenolphthaleinethyl ester (TBPEH). Both study methods permit the determination of the kinetic parameters, and they are in good agreement. The monoprotic TBPEH is the dye of the simplest mechanism, useful to study kinetics of amines of uncertain behavior as quinine, while BPBH2 is the best dye for quantitative determinations. Kinetics for this reaction are of first order for both amine, A, and solvent, SolvCl; activation energy, Ea, and frequency factor are also determined. Rate constants increase with the amine basicity and with a reduction in the number of the halogen atoms present in the solvent. This reaction is slow but not negligible and must be considered a side reaction of these universally used solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:500–509, 2004 相似文献
962.
Tárraga A Otón F Espinosa A Desamparados Velasco M Molina P Evans DJ 《Chemical communications (Cambridge, England)》2004,(4):458-459
The synthesis of the first tetraaza[3,3]ferrocenophane, from the previously unreported 1,1'-bis(triphenylphosphoranylidenamino)ferrocene and its conversion into a nitrogen-rich [2,2]bis[3,3]ferrocenophane is described. The electronic behaviour of these multinuclear ferrocenophanes indicates a strong electronic coupling between the iron centers. 相似文献
963.
Fermin Capitàn Ramiro Avidad Alberto Navalón Luis F. Capitán-Vallvey 《Mikrochimica acta》1992,107(1-2):65-72
A spectrofluorimetric method for the determination of aluminium at ng/ml level has been developed. The method is based on the formation of a fluorescent 11 complex between Al(III) and 2,6-bis[(o-hydroxy)phenyliminomethyl]-1-hydroxybenzene at an apparent pH of 5.0 in an aqueous-ethanol medium (70% v/v ethanol). The influence of reaction variables is discussed. The range of concentration of the method is 1.0–10.0 ng/ml aluminium, the relative standard deviation 1.5% and the limit of detection 0.1 ng/ml. The advantages of the proposed method include high sensitivity and selectivity. The method has been applied to the determination of aluminium in natural waters. 相似文献
964.
Recently Fisher and Hobart extended the original work of Buekenhout and Hubaut on extended generalized quadrangles with a certain minimal value (minimal ) for the nonempty residue intersections. We show that there is another minimal which is sometimes better than the earlier one, and we extend all this to the case of extended partial geometries. We examine especially the triangular case, and find only a few new possibilities, which we are unable to settle, although some of these look extremely interesting. 相似文献
965.
966.
Jun Ruan Wenbo Zhang Hang Zhang Yun Chen Fawad Ur Rehman Hui Jiang Steffen Strehle Alberto Pasquarelli Xuemei Wang 《中国化学快报》2018,29(6):919-921
The new boron-doped nanocrystalline diamond microelectrode arrays (BNCD-MEAs) with 16 channels were designed to detect biological signals from some activated cancer cells. Upon recordings of the released H2O2 from cancer cells stimulated by ascorbic acid (AA), it can readily detect the reactive oxygen species (ROS) released from target cells, which will be helpful for the cancer cell recognition and also beneficial for further studying the cause of relevant disease. 相似文献
967.
Exploiting Synergistic Effects in Organozinc Chemistry for Direct Stereoselective C‐Glycosylation Reactions at Room Temperature 下载免费PDF全文
Dr. Alberto Hernán‐Gómez Dr. Samantha A. Orr Dr. Marina Uzelac Dr. Alan R. Kennedy Dr. Santiago Barroso Dr. Xavier Jusseau Dr. Sébastien Lemaire Dr. Vittorio Farina Prof. Eva Hevia 《Angewandte Chemie (International ed. in English)》2018,57(33):10630-10634
Pairing a range of bis(aryl) zinc reagents ZnAr2 with the stronger Lewis acidic [(ZnArF2)] (ArF=C6F5), enables highly stereoselective cross‐coupling between glycosyl bromides and ZnAr2 without the use of a transition metal. Reactions occur at room temperature with excellent levels of stereoselectivity, where ZnArF2 acts as a non‐coupling partner although its presence is crucial for the execution of the C(sp2)–C(sp3) bond formation process. Mechanistic studies have uncovered a unique synergistic partnership between the two zinc reagents, which circumvents the need for transition‐metal catalysis or forcing reaction conditions. Key to the success of the coupling is the avoidance of solvents that act as Lewis bases versus diarylzinc compounds (e.g. THF). 相似文献
968.
Synthesis of Densely Packaged,Ultrasmall Pt02 Clusters within a Thioether‐Functionalized MOF: Catalytic Activity in Industrial Reactions at Low Temperature 下载免费PDF全文
Marta Mon Miguel A. Rivero‐Crespo Dr. Jesús Ferrando‐Soria Alejandro Vidal‐Moya Dr. Mercedes Boronat Dr. Antonio Leyva‐Pérez Prof. Dr. Avelino Corma Dr. Juan C. Hernández‐Garrido Dr. Miguel López‐Haro Prof. Dr. José J. Calvino Giulio Ragazzon Prof. Dr. Alberto Credi Dr. Donatella Armentano Dr. Emilio Pardo 《Angewandte Chemie (International ed. in English)》2018,57(21):6186-6191
The gram‐scale synthesis, stabilization, and characterization of well‐defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X‐ray snapshots of Pt02 clusters, homogenously distributed and densely packaged within the channels of a metal–organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less‐dangerous industrial reactions. 相似文献
969.
An analytical method for the simultaneous determination of bisphenol A, 4-t-octylphenol, 4-n-octylphenol, and 4-n-nonylphenol in cosmetic samples has been developed. These compounds have toxic effects on human health as they have shown to produce endocrine disrupting properties. Therefore, their presence in cosmetics should be avoided according to the current European Regulations on cosmetic products. The method is based on high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS) detection. Standard addition calibration was used to avoid matrix effects. The limits of detection values ranged between 7 and 15?ng?mL?1 (threefold of the residual standard deviation of regression lines). The proposed method was validated, and good recovery (90–106%) and repeatability values (2.7–8.2%) were obtained. Finally, the method was successfully applied to ten commercially available cosmetic samples. The good analytical features of the proposed method make it useful to carry out the quality control of cosmetic products and raw materials to assure the safety of users. 相似文献
970.
The paper focuses on the problem of long-range dependence when analysing time series of hydrological data. Three time series are analysed: the monthly rainfall in the town of Florence, Italy; the daily minimum temperatures in the same town; and, finally, the daily water inflow to Lake Maggiore, Italy. Heuristic methods and maximum likelihood estimation of a parametric model are used to investigate the Hurst phenomena and to detect whether long-range dependence is present in any of the time series. We found that long-range dependence is not present in the first series but it is present in the last two. The daily water inflow to Lake Maggiore was modelled by a fractionally differenced arima model (farima) which contains a long-range dependence component. It is shown that the fit is much better than the one provided by more traditional arima models that do not have such a component.
Sommario Lo studio considera il problema dell'identificazione dei fenomeni di dipendenza a lungo termine (long range dependence) nelle serie temporali di dati idrologici. Allo scopo sono state analizzate tre serie temporali, rispettivamente quella dei totali mensili di precipitazione rilevati alla stazione dell'Osservatorio Ximeniano de Firenze, quella delle temperature minime giornaliere per la stessa stazione e quella degli afflussi giornalieri al Lago Maggiore. Per identificare la presenza di fenomeni di dipendenza long range, attraverso la valutazione della consistenza del fenomeno di Hurst, sono stati utilizzati sia metodi euristici, sia la stima a massima verosimiglianza di un modello parametrico. Due delle tre serie analizzate sono risultate caratterizzate da tale dipendenza. Per la serie degli afflussi al Lago Maggiore, si è inoltre proceduto alla simulazione attraverso un modello arima a differenziazione frazionaria (farima), la cui struttura contiene una componente long-range. I risultati ottenuti, mostrano che tale modello fornisce risultati significativamente migliori dei tradizionali modelli arima, privi di tale componente.相似文献