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81.
Elfriede Simon M. G. Weller Reinhard Niessner 《Analytical and bioanalytical chemistry》1998,360(7-8):824-826
The aim of the described method was the characterization of a “atrazine-mercaptopropionic acid” humic acid conjugate, which
was required for the calibration of immunoassays to determine bound residues. In order to estimate the amount of bound triazine,
an oxidative nucleophilic substitution reaction of the covalently linked “atrazine-mercaptopropionic acid” to a new triazine
derivative “atrazine-methoxyethanol” was performed. This cleavage product was quantified by gas chromatography. The conditions
for this cleavage procedure were optimized and applied to the “atrazine-mercaptopropionic acid” humic acid conjugate and to
a humic acid blank. The amount of bound “atrazine-mercaptopropionic acid” was calculated to 16.6 ± 2.5 μmol triazine per gram
humic acid, which is equivalent to 0.39 ± 0.07% atrazine.
Received: 7 August 1997 / Accepted: 12 September 1997 相似文献
82.
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84.
Maldonado-Valderrama J Fainerman VB Galvez-Ruiz MJ Martín-Rodriguez A Cabrerizo-Vílchez MA Miller R 《The journal of physical chemistry. B》2005,109(37):17608-17616
The rheological behavior of beta-casein adsorption layers formed at the air-water and tetradecane-water interfaces is studied in detail by means of pendant drop tensiometry. First, its adsorption behavior is briefly summarized at both interfaces, experimentally and also theoretically. Subsequently, the experimental dilatational results obtained for a wide range of frequencies are presented for both interfaces. An interesting dependence with the oscillation frequency is observed via the comparative analysis of the interfacial elasticity (storage part) and the interfacial viscosity (loss part) for the two interfaces. The analysis of the interfacial elasticities provides information on the conformational transitions undergone by the protein upon adsorption at both interfaces. The air-water interface shows a complex behavior in which two maxima merge into one as the frequency increases, whereas only a single maximum is found at the tetradecane interface within the range of frequencies studied. This is interpreted in terms of a decisive interaction between the oil and the protein molecules. Furthermore, the analysis of the interfacial viscosities provides information on the relaxation processes occurring at both interfaces. Similarly, substantial differences arise between the gaseous and liquid interfaces and various possible relaxation mechanisms are discussed. Finally, the experimental elasticities obtained for frequencies higher than 0.1 Hz are further analyzed on the basis of a thermodynamic model. Accordingly, the nature of the conformational transition given by the maximum at these frequencies is discussed in terms of different theoretical considerations. The formation of a protein bilayer at the interface or the limited compressibility of the protein in the adsorbed state are regarded as possible explanations of the maximum. 相似文献
85.
86.
Diastereoselective and enantioselective reduction of the β-ketoester by yeast to provided the chiral starting material for a synthesis of 4RS,6S,7S-serricornine, having the same configuration as the natural product. This material was converted into optically active and diastereomerically pure 6S,7S-anhydro-serricornine (). 相似文献
87.
Christine Bauhofer Hansjürgen Mattausch Reinhard K. Kremer Arndt Simon 《无机化学与普通化学杂志》1995,621(9):1501-1507
The Gadolinium Carbide Halides, Gd4C2X3 (X = Cl, Br) The compounds Gd4C2X3 (X = Cl, Br) and Tb4C2Br3 have been prepared by reaction of the metals (RE), REX3, and C in sealed Ta capsules at 1 100° and 1 300°C, respectively. Monophasic samples of Gd4C2Br3 and Tb4C2Br3 were obtained by reacting stoichiometric mixtures of the starting materials for five days. The needle shaped crystals are bronze-coloured and sensitive to air and moisture. Gd4C2X3 crystallizes in the space group Pnma (No. 62) with lattice constants a = 1 059.6(4), b = 368.4(1), c = 1 962.7(8) pm (Gd4C2Cl3), a = 1 084.4(1), b = 373.0(1), c = 2 036.1(1) pm (Gd4C2Br3). According to Guinier photographs, Tb4C2Br3 is isotypic (a = 1 074.3(2), b = 370.6(1), c = 2 019.4(1) pm). In the crystal structure C is octahedrally coordinated by Gd. The Gd6 octahedra are linked via common edges to form corrugated layers. The X-anions coordinate all free edges and corners of these layers and connect them via Xi? Xi contacts parallel [001]. Gd4C2Br3 shows metallic conductivity. The magnetic susceptibility follows at high temperatures a Curie Weiss law with an effective moment of 7.95 μB. At temperatures below 50 K antiferromagnetic order is observed. 相似文献
88.
Krahl T Stösser R Kemnitz E Scholz G Feist M Silly G Buzaré JY 《Inorganic chemistry》2003,42(20):6474-6483
The structure of the very strong solid Lewis acid aluminum chlorofluoride (ACF, AlCl(x)F(3-x), x = 0.05-0.3) was studied by IR, ESR, Cl K XANES, (19)F MAS NMR, and (27)Al SATRAS NMR spectroscopic methods and compared with amorphous aluminum fluoride conventionally prepared by dehydration of alpha-AlF(3) x 3H(2)O. The thermal behavior of both compounds was investigated by DTA and XRD. In comparison to ACF, amorphous AlF(3) prepared in a conventional way is not catalytically active for the isomerization reaction of 1,2-dibromohexafluoropropane, which requires a very strong Lewis acid. Both compounds are mainly built up of corner-sharing AlF(6) octahedra forming a random network. The degree of disorder in ACF is higher than in amorphous AlF(3). Terminal fluorine atoms were detected in ACF by (19)F NMR. The chlorine in ACF does not exist as a separate, crystalline AlCl(3) phase. Additionally, chlorine-containing radicals, remaining from the synthesis, are trapped in cavities of ACF. These radicals are stable at room temperature but do not take part in the catalytic reaction. 相似文献
89.
A method is described for the simultaneous quantitative determination of monoamines and related compounds from urine and brain tissue samples in the pg-range, using a GC/MF instrument LKB-2091 provided with a multiple ion detection (MID) system and capillary columns. The simultaneous detection of “fingerprints” with fourteen and more compounds during one single GC run was achieved after the intoduction of “time gates” for the detection of the different characteristic masses. Several modifications to the LKB equipment permitted exact reproducibility of retention times, which is essential for the use of “time gates”. The detection of “fingerprints” with these acidic, basic and alcoholic substances was achieved by the extraction of the dried biological samples with silylating agents. 相似文献
90.
Product distribution of peroxynitrite decay as a function of pH, temperature, and concentration. 总被引:2,自引:0,他引:2
The decay of peroxynitrite [O=NOO(-), oxoperoxonitrate(1-)] was examined as a function of concentration (0.050-2.5 mM), temperature (5-45 degrees C), and pH (2.2-10.0). Below 5 degrees C and pH 7, little amounts of the decomposition products nitrite and dioxygen are formed, even when the peroxynitrite concentration is high (2.5 mM). Instead, approximately > or =90% isomerizes to nitrate. At higher pH, decomposition increases at the expense of isomerization, up to nearly 80% at pH 10.0 at 5 degrees C and 90% at 45 degrees C. Much less nitrite and dioxygen per peroxynitrite are formed when the peroxynitrite concentration is lower; at 50 microM and pH 10.2, < or =40% decomposes. In contrast to two other reports (Pfeiffer, S.; Gorren, A. C. F.; Schmidt, K.; Werner, E. R.; Hansert, B.; Bohle, D. S.; Mayer, B. J. Biol. Chem. 1997, 272, 3465-3470, and Coddington, J. W.; Hurst, J. K.; Lymar, S. V. J. Am. Chem. Soc. 1999, 121, 2438-2443), we find that the extent of decomposition is dependent on the peroxynitrite concentration. 相似文献