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991.
Hana Palá?ková Jana Holubová Milan Erben 《Journal of organometallic chemistry》2007,692(17):3758-3764
Vanadocene dichloride (1) reacts with sulfur-containing amino acids, cysteine and methionine, giving new complexes with five- or six-membered chelate ring, but the structure of isolated compounds is affected by the pH value of the reaction mixture. Methionine reacts with aqueous 1 in the pH range of 3-8 affording chelate structure [Cp2V(N,O-met)]Cl (4). Similar reaction with cysteine gives two different products depending on pH. In the acidic solution, the complex [Cp2V(O,S-cys)]Cl (2) is present, whereas in neutral media the compound [Cp2V(N,S-cys)] (3) could be identified. On inspection of spectroscopic measurements, particularly EPR and vibrational spectroscopy, it is evident that sulfur atom of amino acid is bonded directly to the vanadium atom of [Cp2V]2+ moiety. For the purpose of comparison the complexes [Cp2V(O,S-mpa)] (5) and [Cp2V(N,S-csam)]+ (6a) with related chelating ligands, 3-mercaptopropionic acid (mpa) and cysteamine (csam), respectively, were prepared and spectroscopically characterized. The structure of the complex [Cp2V(N,S-csam)]BPh4 (6b) was also determined by X-ray diffraction analysis. 相似文献
992.
Purine and pyrimidine nucleotides influence many metabolic pathways and their analogs have been widely used in medicine. A capillary electrophoretic method was developed for measuring intracellular nucleotides. The final BGE consisted of 40 mM citric acid with addition of 0.8 mM CTAB titrated by gamma-aminobutyric acid to pH 4.4. The electrophoretic separations were carried out in an uncoated silica capillary (id/od - 75/375 microm; effective/total length - 90/97 cm). The method allows a complete separation of 21 nucleotides and deoxynucleotides within 15 min with separation efficiencies up to 400,000 theoretical plates per meter. Due to the use of an acidic separation medium, the method offers a high selectivity toward the studied analytes versus possible interferences from matrices. Sample preparation was optimized in order to shorten work-time and prevent analyte degradation. The method was applied for analyzing nucleotides in human erythrocytes and Chinese hamster ovary cells. Diagnostic potential for inherited metabolic disorders of nucleotide metabolism is presented. 相似文献
993.
Electrospray ionization of aqueous silver nitrate is used for the preparation of the disilver-oxide cation Ag2O+ in the gas phase. The mass-selected cation is capable of activating C-H bonds of simple alkanes other than methane via H-atom abstraction, i.e., Ag2O+ + R-H --> Ag2OH+ + R* (R = C2H5, C3H7, C4H9). Clean O-atom transfer from Ag2O+ is observed with ethene as a neutral reagent, whereas oxygenation and allylic C-H abstraction compete in the case of propene. The gaseous Ag2O+ cation can thus be regarded as a minimalist model for the problems associated with the silver-mediated epoxidation of olefins more complex than ethene itself. The experimental findings are fully supported by the results of quantum chemical studies, thereby providing deep mechanistic insight into the reactions in the idealized gas phase, which also might have implications for further improvements in applied catalysis. 相似文献
994.
The bimolecular reactions of several hydrocarbon dications C(m)H(n)(2+) (m = 6-10, n = 4-9) with neutral benzene are investigated by tandem mass spectrometry using a multipole instrument. Not surprisingly, the major reaction of C(m)H(n)(2+) with benzene corresponds to electron transfer from the neutral arene to the dication resulting in the pair of monocationic products C(m)H(n)(+) + C(6)H(6)(+). In addition, also dissociative electron transfer takes place, whereas proton transfer from the C(m)H(n)(2+) dication to neutral benzene is almost negligible. Interestingly, the excess energy liberated upon electron transfer from the neutral arene to the C(m)H(n)(2+) dication is not equally partitioned in the monocationic products in that the cations arising from the dicationic precursor have a higher internal energy content than the monocations formed from the neutral reaction partner. In addition to the reactions leading to monocationic product ions, bond-forming reactions with maintenance of the two-fold charge are observed, which lead to a condensation of the C(m)H(n)(2+) dications with neutral benzene under formation of intermediate C(m+6)H(n+6)(2+) species and then undergo subsequent losses of molecular hydrogen or neutral acetylene. This reaction complements a recently proposed dicationic route for the formation of polycyclic aromatic hydrocarbons under extreme conditions such as they exist in interstellar environments. 相似文献
995.
The bimolecular reactivity of molecular dications in the gas phase is reviewed from an experimental point of view. Recent research has demonstrated that in addition to the ubiquitous occurrence of electron transfer in the reactions of gaseous dications with neutral molecules, bond-forming reactions play a much larger role than anticipated before. Thus, quite a number of hydrogen-containing dications show proton transfer to neutral reagents as an abundant or even as the major pathway, and also the nature of the neutral reagent itself is decisive for the amount of proton transfer which takes place. Further, several hydrocarbon dications C(m)H(n)(2+) of medium size (m = 6-14, n = 6-10) undergo bond-forming reactions with unsaturated hydrocarbons such as acetylene or benzene, thereby offering new routes for the formation of larger aromatic compounds under extreme conditions such as interstellar environments. Likewise, recent results on the bimolecular reactivity of multiply charged metal ions have revealed the occurrence of a number of new bond-forming reactions which open promising prospects for further research. 相似文献
996.
Katrlík J Vostiar I Sefcovicová J Tkác J Mastihuba V Valach M Stefuca V Gemeiner P 《Analytical and bioanalytical chemistry》2007,388(1):287-295
Novel and selective microbial amperometric biosensors that use Gluconobacter oxydans cells to monitor the bacterial bioconversion of glycerol (Gly) to 1,3-propanediol (1,3-PD) are described. Two different mediators,
ferricyanide and flexible polyvinylimidazole osmium functionalized polymer (Os-polymer), were employed to prepare two different
microbial biosensors, both of which gave high detection performance. The good operational stabilities of both types of biosensor
were underlined by the ability to detect 1,3-PD throughout 140 h of continuous operation. Both microbial biosensor systems
showed excellent selectivity for 1,3-PD in the presence of a high excess of glycerol [selectivity ratios (1,3-PD/Gly) of 118
or 245 for the ferricyanide and Os-polymer systems, respectively]. Further, the robustness of each microbial biosensor was
highlighted by the high reliability of 1,3-PD detection achieved (average RSD of standards <2%, and well below 4% for samples).
The biosensor implementing the Os-polymer mediator exhibited high selectivity towards 1,3-PD detection and allowed moderate
sample throughput (up to 12 h−1) when integrated into a flow system. This system was used to monitor the concentration of 1,3-PD during a real bioprocess.
Results from biosensor assays of 1,3-PD in bioprocess samples taken throughout the fermentation were in a very good agreement
with results obtained from reference HPLC assays (R
2 = 0.999). 相似文献
997.
998.
Kroupová J Bártová E Fojt L Strasák L Kozubek S Vetterl V 《Bioelectrochemistry (Amsterdam, Netherlands)》2007,70(1):96-100
The effect of magnetic fields on the living systems is studied in vivo or in vitro in very broad spectrum of organisms, cells and tissues. The mechanism of their acting is not known until now. We studied low-frequency magnetic field effect on cytoskeleton and on the structure of chromatin in human cells. We used cell line of small lung carcinoma (A549) and the effects of magnetic field on cytoskeleton and higher-order chromatin structure were analyzed 96 h of magnetic field exposure. Magnetic field generated by the cylindrical soil was homogenous and the cells were cultivated at 37 degrees C in humidified atmosphere containing 5% CO(2). Magnetic field induction was B(m)=2 mT and the net frequency f=50 Hz. In such affected and control cells the F-actin was estimated using FITC-conjugated Phalloidin and mitochondria were studied using MitoTracker (Molecular Probes). Images of cytoskeleton and genetic loci were acquired using confocal microscopy and analysis was performed by FISH 2.0 software. Slight morphological changes of F-actin filaments and mitochondria were observed in affected cells and nuclear condensation was found. These effects could be related to the process of cell death apoptosis probably induced by magnetic field. The studies aimed at centromeric heterochromatin (9cen) did not show statistically significant changes. Therefore, we suggest that magnetic field has no influence on higher order chromatin structure but certain changes could be observed on the level of cytoskeleton. However, these statements need a thorough verification. Our preliminary experiments will be extended and the effect of magnetic field on another structures of cytoskeleton and cell nuclei will be further studied. 相似文献
999.
Hájková K Pulkrabová J Schůrek J Hajslová J Poustka J Nápravníková M Kocourek V 《Analytical and bioanalytical chemistry》2007,387(4):1351-1363
A wide range of estrogenic contaminants has been detected in the aquatic environment. Among these, natural and synthetic steroid
estrogens, typically present in municipal sewage-treatment plant (STP) effluents, are the most potent. In this study a new
GC–MS method has been developed for direct analysis of five major steroid estrogens (estrone, 17β-estradiol, 17α-ethinylestradiol,
dienestrol, and diethylstilbestrol) in river sediments. Four GC–MS systems used for analysis of underivatized analytes in
purified extracts were compared. Relatively low detection limits (1.5–5 ng g−1 dried sediment) and good repeatability of GC splitless injection (RSD 1–2%) were achieved by use of a system combining low-pressure
gas chromatography with a single-quadrupole mass analyzer (LP-GC–MS). Use of orthogonal gas chromatography (GC×GC) hyphenated
with high-speed time-of-flight mass spectrometry (HSTOF-MS) enabled not only significantly better resolution of target analytes,
and their unequivocal identification, but also further improvement (decrease) of their detection limits. In addition to these
outcomes, use of this unique GC×GC–TOF-MS system enabled identification of several other non-target chemicals, including pharmaceutical
steroids, present in purified sediment extracts. 相似文献
1000.
Horáková J Petr J Maier V Tesarová E Veis L Armstrong DW Gas B Sevcík J 《Electrophoresis》2007,28(10):1540-1547
A new on-line preconcentration technique was developed that makes possible to determine nanomolar concentrations of weak acidic analytes in CE. The method consists of long-running electrokinetic sample injection and stacking (electrokinetic immobilization) of the analytes at a boundary of two electrolytes with different pH values (pH 9.5 and 2.5) and consequent mobilization of the stacked uncharged analytes in a micellar system (containing SDS micelles). Several factors including buffer concentration, pH, applied voltage, time of preconcentration, and SDS concentration were tested to optimize the analysis method. An about 4600-fold increase of the sample concentration (in comparison with the standard CZE) can be achieved during the preconcentration step. Two preservatives applied in food industry -- benzoic acid and sorbic acid were used as model samples. The applicability of the proposed method in food analysis was demonstrated by determination of nanomolar concentrations of benzoic acid in sunflower oil. An extended version of the computer program Simul was used for modeling both the preconcentration and mobilization processes taking place in the capillary. 相似文献