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排序方式: 共有4143条查询结果,搜索用时 31 毫秒
941.
942.
Giuseppe Pilloni Gianni Zotti Mario Martelli 《Journal of Electroanalytical Chemistry》1975,62(2):397-402
The reversible addition of carbon monoxide to [Rh(DPE)2]+ has been studied by cyclic voltammetry. The greatest contribution of this technique is that the uptake and release of CO, occurring before electron transfer, can be characterized and their rates measured.The differences in the reversibility of the CO addition between this complex and the isoelectronic isostructural cobalt and iridium ones are compared. A suggestion is made on the possible relevance of kinetic factors in the release of the CO molecule. 相似文献
943.
944.
Abstract— The catechol oxidase promoted oxidation of catechols produces electronically excited states readily detected by chlorophyll sensitized fluorescence. Both the chemiexcitation step and the transfer step are efficient. The use of chlorophyll has confirmed that the peroxidase catalyzed oxidation of dihydroxyfumarate also generates electronically excited species. It is concluded that efficient enzymatic generation of electronic energy can occur not only through the dioxetane/dioxetanone route, but also via electron transfer processes. 相似文献
945.
Bartoli G Bosco M Carlone A Locatelli M Massaccesi M Melchiorre P Sambri L 《Organic letters》2004,6(13):2173-2176
[reaction: see text] The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-beta-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)Cl] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-beta-amino alcohols. 相似文献
946.
A.M. El Sherbini Th.M. El Sherbini H. Hegazy G. Cristoforetti S. Legnaioli V. Palleschi L. Pardini A. Salvetti E. Tognoni 《Spectrochimica Acta Part B: Atomic Spectroscopy》2005,60(12):1573-1579
In quantitative Laser Induced Breakdown Spectroscopy (LIBS) measurements it is essential to account for the effect of self-absorption on the emission lines intensity. In order to quantify this effect, in this paper we propose a simple method for evaluating the ratio between the actual measured line intensity and the intensity expected in absence of self-absorption and, if necessary, correcting the effect of self-absorption on line intensity. The method, based on a homogeneous plasma model, is applicable when the plasma electron density is known and in particular to lines whose Stark broadening parameter is available. 相似文献
947.
948.
Alfredo Ricci Mariella Fiorenza M.Antonietta Grifagni Giuseppe Bartolini Giancarlo Seconi 《Tetrahedron letters》1982,23(48):5079-5082
Benzyl-, heteroaryl-, and allylsilanes, under the catalytic action of CsF or silica/TBAF, react in mild conditions with electrophiles such as σ-valero and ε-caprolactone, and with cyclohexen-2-one. 相似文献
949.
F. Bredice H. Sobral M. Villagran-Muniz H.O. Di Rocco G. Cristoforetti S. Legnaioli V. Palleschi A. Salvetti E. Tognoni 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
A Nd:YAG laser pulse was focused, in air or on a Cu target, between the plates of a planar charged capacitor. The plasma generates a transient redistribution of the electrical charges on the plates that can be easily measured as a voltage drop across a resistor connected to the ground plate. At the same time, the Stark broadening of the Hα spectral line (656.3 nm) obtained from the optical emission spectrum of the plasma was measured. In this work, we show that the peak of electrical signal measured on the resistor is, in the energy range of our laser (30 mJ to 220 mJ) and at time delays typical of Laser-Induced Breakdown Spectroscopy applications (500–5000 ns), univocally related to the temporal evolution of the Stark broadening of the Hα line. Therefore, after a proper calibration depending on the material and the experimental geometry, the peak of the electrical signal can be used to predict the temporal evolution of the electron density of the generated plasma. 相似文献
950.
Sanaâ Majid Mamia El Rhazi Aziz Amine Antonella Curulli Giuseppe Palleschi 《Mikrochimica acta》2003,143(2-3):195-204
Carbon paste electrodes modified with conducting polymers for sensitive and selective determination of lead are presented. A novel method for generating a reproducible polymer-coated electrode surface is developed. We prove that 1,8-diaminonaphthalene (1,8-DAN) mixed with a carbon paste electrode leads to a conducting polymer in acidic medium while, in the same medium, this polymer is known to be non-conducting on platinum electrode. The electrode behaviour of poly(1,8-DAN), electropolymerised into carbon paste, was investigated by cyclic voltammetry in the presence of the ferri-ferrocyanide couple.A carbon paste electrode modified with poly(1,8-DAN) was used to determine Pb2+ in aqueous solutions. Pb2+ ions were firstly complexed and then electrochemically deposited by a potential step to –0.9V. The accumulated lead after reduction was anodically stripped by differential pulse voltammetry. Different parameters, such as pH of the solution, preconcentration time, and electropolymerisation procedures were studied.For a preconcentration time of ten minutes, the calibration graph was linear from 40 to 2070ngmL–1 with r2=0.998. The detection limit was found to be 30ngmL–1, and the relative standard deviation was 6%. 相似文献