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731.
Katrin Kittler Holger Hoffmann Franziska Lindemann Matthias Koch Sascha Rohn Ronald Maul 《Analytical and bioanalytical chemistry》2014,406(24):5765-5774
Cylindrospermopsin (CYN) is a cyanobacterial toxin associated with human and animal poisonings. Due to its toxicity in combination with its widespread occurrence, the development of reliable methods for selective, sensitive detection and accurate quantification is mandatory. Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis using stable isotope dilution analysis (SIDA) represents an ideal tool for this purpose. U-[15N5]-CYN was synthesized by culturing Aphanizomenon flos-aquae in Na15NO3-containing cyanobacteria growth medium followed by a cleanup using graphitized carbon black columns and mass spectrometric characterization. Subsequently, a SIDA-LC-MS/MS method for the quantification of CYN in freshwater and Brassica matrices was developed showing satisfactory performance data. The recovery ranged between 98 and 103 %; the limit of quantification was 15 ng/L in freshwater and 50 μg/kg dry weight in Brassica samples. The novel SIDA was applied for CYN determination in real freshwater samples as well as in kale and in vegetable mustard exposed to toxin-containing irrigation water. Two of the freshwater samples taken from German lakes were found to be CYN-contaminated above limit of quantification (17.9 and 60.8 ng/L). CYN is systemically available to the examined vegetable species after exposure of the rootstock leading to CYN mass fractions in kale and vegetable mustard leaves of 15.0 μg/kg fresh weight and 23.9 μg/kg fresh weight, respectively. CYN measurements in both matrices are exemplary for the versatile applicability of the developed method in environmental analysis. 相似文献
732.
Keller S Wang J Chandra M Berger R Marx A 《Journal of the American Chemical Society》2008,130(40):13188-13189
The distinct base pairing property of DNA is an advantageous phenomenon that has been exploited in the usage of DNA as scaffold for directed self-organization to form nanometer-sized objects in a desirable fashion. Herein we report the construction of three-dimensional DNA-based networks that can be generated and amplified by the DNA polymerase chain reaction (PCR). The approach is flexible allowing tuning of the meshes of the network by variation of the size of the template. Additionally, further diversification can be introduced by employment of chemically modified nucleotides in PCR allowing the introduction of functionalities and reporter moieties. 相似文献
733.
Determination of polyamines in biological fluids possesses medical diagnostic relevance. Despite the vast panel of analytical methods developed for polyamines they are not applied in routine clinical usage, mainly due to the time and labor consuming sample preparation step and complicated derivatization procedures. Thus, new simpler methods are needed. This paper describes a single hollow fiber SLM extraction method of polyamines followed by simple pre-column derivatization with tosyl chloride and HPLC-UV analysis. The influence of different parameters such as the extraction time, organic phase composition, acceptor pH, donor pH, acceptor volume, donor volume and stirring speed on the transport parameters and enrichment was studied and discussed. The optimized method was applied to real matrices such as urine and plasma. 相似文献
734.
In this work single and double ionization spectra of the homo- and heteronuclear argon/krypton dimers and trimers are calculated by means of propagator methods where a four-component implementation was employed for the single ionizations. Scalar relativistic effects play only a minor role for the outer valence spectral structure, whereas spin-orbit coupling and electron correlation have to be treated adequately in order to reproduce the features correctly. Nonradiative decay mechanisms of subvalence vacancies in the argon and krypton dimers and trimers are discussed both for the interatomic Coulombic decay and the electron transfer mediated decay (ETMD). In the heteronuclear triatomic system which serves as a model for larger clusters, a possible ETMD process of the Ar 3s vacancy is found for the linear arrangement of the atoms. In the bent configuration the ETMD channel is closed. 相似文献
735.
Petrovic AG Polavarapu PL Drabowicz J Lyzwa P Mikołajczyk M Wieczorek W Balińska A 《The Journal of organic chemistry》2008,73(8):3120-3129
N-alpha-Phenylethyl-t-butylsulfinamide is a complicated system for determining molecular stereochemistry because of numerous possibilities for assigning the absolute configuration and a predominant conformation. Two diastereomers of N-alpha-phenylethyl-t-butylsulfinamide derived from (-)-(S)-alpha-phenylethyl amine, a (+)-diastereomer and a (-)-diastereomer, have been synthesized and their experimental chiroptical spectroscopic properties have been measured. These properties include vibrational circular dichroism, electronic circular dichroism and optical rotatory dispersion. Using these experimental data, in conjunction with corresponding density functional theoretical predictions, the absolute configuration and predominant conformations of these two diastereomers have been determined. Also, the absolute configuration of (-)-diastereomer has been independently confirmed by determining its structure from X-ray diffraction data. 相似文献
736.
Jian Zhang Dr. Wenhui He Dr. Thomas Quast Dr. João R. C. Junqueira Dr. Sascha Saddeler Prof. Dr. Stephan Schulz Prof. Dr. Wolfgang Schuhmann 《Angewandte Chemie (International ed. in English)》2023,62(8):e202214830
Electrochemically converting nitrate to ammonia is an essential and sustainable approach to restoring the globally perturbed nitrogen cycle. The rational design of catalysts for the nitrate reduction reaction (NO3RR) based on a detailed understanding of the reaction mechanism is of high significance. We report a Cu2O+Co3O4 tandem catalyst which enhances the NH3 production rate by ≈2.7-fold compared to Co3O4 and ≈7.5-fold compared with Cu2O, respectively, however, most importantly, we precisely place single Cu2O and Co3O4 cube-shaped nanoparticles individually and together on carbon nanoelectrodes provide insight into the mechanism of the tandem catalysis. The structural and phase evolution of the individual Cu2O+Co3O4 nanocubes during NO3RR is unveiled using identical location transmission electron microscopy. Combining single-entity electrochemistry with precise nano-placement sheds light on the dynamic transformation of single catalyst particles during tandem catalysis in a direct way. 相似文献
737.
Dr. Hemlata Agarwala Xiaoyu Chen Julien R. Lyonnet Dr. Ben A. Johnson Prof. Dr. Mårten Ahlquist Prof. Dr. Sascha Ott 《Angewandte Chemie (International ed. in English)》2023,62(17):e202218728
Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, due to the large barrier for C−O bond cleavage. Illustrated with ruthenium polypyridyl catalysts, we herein propose a mechanistic route that involves one metal center that acts as both Lewis base and Lewis acid at different stages of the catalytic cycle, by density functional theory in corroboration with experimental FTIR. The nucleophilic character of the Ru center manifests itself in the initial attack on CO2 to form [ Ru -CO2]0, while its electrophilic character allows for the formation of a 5-membered metallacyclic intermediate, [ Ru -CO2CO2]0,c, by addition of a second CO2 molecule and intramolecular cyclization. The calculated activation barrier for C−O bond cleavage via the metallacycle is decreased by 34.9 kcal mol−1 as compared to the non-cyclic adduct in the two electron reduced state of complex 1 . Such metallacyclic intermediates in electrocatalytic CO2 reduction offer a new design feature that can be implemented consciously in future catalyst designs. 相似文献
738.
Tietze LF Redert T Bell HP Hellkamp S Levy LM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(8):2527-2535
The Pd-catalyzed domino Tsuji-Trost-Heck-Mizoroki reactions of compounds 18, 27, and 34, respectively, each containing an allyl acetate and a halogen aryl moiety, lead to the formation of hexahydronaphthacenes 2 and 3 and octahydroanthracene 4 in 62-81 % yield. The octahydroanthracene and hexahydronaphthacene motifs are found in many natural products, for example, the tetracycline antibiotics. 相似文献
739.
740.
Influence of plasticizer type on the properties of polymer electrolytes based on chitosan 总被引:1,自引:0,他引:1
Pawlicka A Danczuk M Wieczorek W Zygadło-Monikowska E 《The journal of physical chemistry. A》2008,112(38):8888-8895
Polymer electrolytes were obtained by the casting technique from a solution containing chitosan, hydrochloric acid, and plasticizer such as glycerol, ethylene glycol, and sorbitol. The transparent membranes with good ionic conductivity properties were characterized by impedance and UV-vis spectroscopies, thermal analysis (DSC), and X-ray diffraction. The best ionic conductivity values of 9.5 x 10(-4) S cm(-1) at room temperature and 2.5 x 10(-3) S cm(-1) at 80 degrees C were obtained for the sample containing 59 wt% of glycerol and an equimolar amount of HCl with respect to NH2 groups in chitosan. The temperature dependence of the ionic conductivity exhibits an Arrhenius behavior with activation energy of 16.6 kJ mol(-1). The thermal analysis indicates that both glass transition temperature (-87 degrees C) and crystallinity are low for this electrolyte. The samples with 13 wt% of LiCF3SO3 showed that the ionic conductivity values of 2.2 x 10(-5) S cm(-1) at room temperature and 4 x 10(-4) S cm(-1) at 80 degrees C are predominantly amorphous and showed a low glass transition temperature of about -73 degrees C. 相似文献