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141.
Samuel Melaku Rita Cornelis Frank Vanhaecke Richard Dams Luc Moens 《Mikrochimica acta》2005,150(3-4):225-231
A simple, sensitive and inexpensive method for the speciation of Cr(VI) and Cr(III) in river and industrial wastewater was developed, optimized and validated. Samples were collected, filtered and then chromium species were determined in the filtrate. In the filtrate, total Cr was determined directly by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). A portion of the filtered sample was buffered to pH 6.4, extracted with Amberlite LA-2/MIBK and finally Cr(VI) was determined in the organic extract and Cr(III) in the aqueous phase using GFAAS. The method was evaluated by analysis of the certified reference material, CRM 544, and good accuracy was obtained. The limit of detection for Cr(VI) and Cr(tot)/Cr(III) was found to be 0.30 and 0.08 µg L−1, respectively, and a precision expressed as relative standard deviation of better than 11% was achieved for nine replicates. A number of water samples from the Tinishu Akaki River, Ethiopia, and wastewater samples from a chemical plant in Germany, were analysed. In addition to the GFAAS method, Cr(tot) was also determined using ICP-MS (in CRM 544, lyophilized water, and Tinishu Akaki River water samples) and Cr(tot) and Cr(VI) using UV-VIS spectrophotometry (in CRM 544 and industrial wastewater samples). Good agreement between the different methods was found. 相似文献
142.
Cantat T Jaroschik F Nief F Ricard L Mézailles N Le Floch P 《Chemical communications (Cambridge, England)》2005,(41):5178-5180
New samarium carbene complexes have been synthesized and characterized by X-ray diffraction analysis; the carbenic nature was assessed by reactivity studies. 相似文献
143.
Pérez J Morales D Nieto S Riera L Riera V Miguel D 《Dalton transactions (Cambridge, England : 2003)》2005,(5):884-888
Cationic complexes [Mo(eta(3)-allyl)(CO)2L3]+ (L3 = either nitrogen-donor tridentate ligand or three monodentate ligands) were prepared in high yield and under mild conditions using as precursors either the triflato complex [Mo(eta(3)-allyl)(OTf)(CO)2(NCMe)2] or the combination of the chloro complex [Mo(eta(3)-allyl)Cl(CO)2(NCMe)2] and the salt NaBAr'(4)(Ar'= 3,5-bis(trifluoromethyl)phenyl). The tridentate ligands employed were 2,2':6',2'-terpyridine (terpy) and cis,cis-1,3,5-cyclohexanetriamine (CHTA), whereas the monodentate ligands imidazole (im) and 3,5-dimethylpyrazole (dmpz) were chosen. In order to stabilize the labile intermediates, an excess of acetonitrile was used in most of the syntheses. However, the pyrazole complex was prepared through a nitrile-free route to avoid reactions at the coordinated nitrile. The solid state structures of [Mo(eta(3)-methallyl)(CO)2(terpy)]OTf (2), [Mo(eta(3)-methallyl)(CO)2(CHTA)]BAr'4 (3), [Mo(eta(3)-methallyl)(CO)2(NCMe)3]BAr'4 (4), [Mo(eta(3)-allyl)(CO)2(im)3]OTf (5) and [Mo(eta(3)-allyl)(CO)2(dmpz)3]BAr'4 (6) were determined by means of single-crystal X-ray diffraction. 相似文献
144.
Self-replicating peptide systems hold great promise for a wide range of technological applications, as well as to address fundamental questions pertaining to the molecular origins of life. The development of self-replicating compounds capable of high efficiency, however, has remained elusive. Here we disclose a successful strategy whereby modulation of coiled-coil stability results in remarkable catalytic efficiency for self-replication. By shortening the peptide to the minimum length necessary for coiled-coil formation a highly efficient self-replicating system was obtained due to very low background reaction rates, bringing the efficiency close to naturally occurring enzymes. 相似文献
145.
Hétérocycles à fonction quinone. 7. Benzo[f]quinazolinediones-7,10 à action antitumorale potentielle
Hlne Parrot-Lopez Jean-Michel Delacotte Jean Renault Suzanne Cros 《Journal of heterocyclic chemistry》1986,23(4):1039-1043
Few benzo[f]quinazoline-7,10-diones 4a-c are prepared by oxidation, with potassium nitrosodisulfonate, of the corresponding benzo[f]quinazolinamines, made by reduction of the nitro analogues which were obtained from 8-methoxybenzo[f]quinazolin-1(2H)-one. The compound 4a shows an interesting cytotoxicity. 相似文献
146.
3-Hydroperoxy-1,3,6-trimethyl-2-phenyl indolines coming from the sensitized photooxygenation of the indoles in presence of KBH4 rearrange partially in basic methanol into the corresponding 3-hydroxy-6-methoxymethyL indolines. 相似文献
147.
The examination of 19F chemical shifts for ca. 650 F-alkylated compounds of general formula CF3(CF2)nCF2X led to the following conclusions: the CF2 groups α to X are very sensitive to the nature of X, and are spread over a range of 85 ppm. The effect of the length of the F-alkyl chain decreases rapidly, so that δCF2(α) can already be considered as characteristic of X for n = 1 or 2 for most practical purposes. Solvent effects (in 9 different solvents having ε = 1.8 to 52.1) were found to be rather small except for the F-alkyl iodides. A chart which indicates the domain in which the CF2(α) resonance signal is to be expected is given for 42 different series of F-alkylated compounds; it is expected to provide the synthetic chemist with a useful tool for the identification and characterization of such compounds. 相似文献
148.
Andrzej Małecki Jalees A.K. Tareen Jean Pierre Doumerc Louis Rabardel Jean Claude Launay 《Journal of solid state chemistry》1985,56(1):49-57
Kinetics of thermal decomposition in vacuum of Co3O4 powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co3O4 proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)2/3 = ktn where the activation energy varies with the degree of decomposition. 相似文献
149.
Eupatorium cannabinum subsp. corsicum (L.), an aromatic plant, is an endemic subspecies from Corsica. The essential oil from aerial parts of E. cannabinum subsp. corsicum was studied by GC, GC/MS and 13C NMR. One hundred and forty-seven components were identified representing 93.6% of the total amount. The main constituents are germacrene D (28.5%), alpha-phellandrene (19.0%) and para-cymene (5.2%). A particularity of this essential oil is the presence of monoterpene esters derived from nerol, lavandulol, borneol, thymol and 8,9-dehydrothymol. These compounds have been investigated using GC/MS in different ionization modes like electron impact (EI), positive chemical ionization (PCI) and negative chemical ionization (NCI). 相似文献
150.
Kohtani M Jones TC Schneider JE Jarrold MF 《Journal of the American Chemical Society》2004,126(24):7420-7421
High-temperature ion mobility measurements have been performed for alpha-helical Ac-A15K+H+ and globular Ac-KA15+H+ peptides. The alpha-helical and globular conformations do not melt into random coils as the temperature is raised. Instead, both conformations survive to the point where the peptide signals vanishes due to fragmentation. This occurs at 600 K for the globular Ac-KA15+H+ peptide and at 725 K for the alpha-helical Ac-A15K+H+. For the helical Ac-A15K+H+ peptide it appears that fragmentation is triggered by disruption of the helical conformation. 相似文献