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排序方式: 共有136条查询结果,搜索用时 140 毫秒
1.
Marja Himottu Kalevi Pihlaja Gza Stjer Gbor Bernth Pirjo Vainiotalo 《Journal of mass spectrometry : JMS》1991,26(5):493-497
The mass spectra of four cycloalkane/ene cis- and trans-condensed 2-thioxo-2,3,5,6-tetrahydropyrimidin-4(1H)-ones and the corresponding cycloalkane/ene cis- and trans-condensed [l,3]thiazino[3,2-a]pyrimidinones were measured. Fragmentation pathways were confirmed by metastable ion analyses and exact mass measurements. The bicyclic isomers were easy to distinguish from each other, whereas the corresponding tricyclic isomeric adducts gave fairly similar mass spectra, owing to their favoured reiro-Diels- Alder fragmentations accompanied by the migration of one or two hydrogen atoms. 相似文献
2.
Susanne K. Wiedmer Toni Andersson Marika Sündermann Marja‐Liisa Riekkola Heikki Tenhu 《Journal of Polymer Science.Polymer Physics》2007,45(19):2655-2663
Cationic polyelectrolytes were synthesized and used as semipermanent coating materials for capillaries in electrophoresis. The polyelectrolytes used were a homopolymer of poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC) and its poly(ethylene glycol) (PEG)‐grafted analogue. Two PMOTAC polyelectrolytes, with molar masses of 85,000 and 300,000 g/mol, and PEG‐grafted PMOTAC with a molar mass of 280,000 g/mol were synthesized and then characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. Attachment of the polyelectrolytes to the wall of the fused silica capillary for electrophoresis caused the electroosmotic flow (EOF) to reverse. The polyelectrolyte coatings were tested over the pH range 2–11 at different buffer ionic strengths, and the most stable and strongest anodic EOFs were obtained at acidic pH values with low ionic strength buffers. Between runs the capillary is merely rinsed for 2 or 3 min with the background electrolyte solution. With the PMOTAC coatings at pH values ≤5, the RSDs of the EOFs were less than 2.9% after 60 injections. The effects of the molar mass of the polycation and of PEGylation of PMOTAC on the interactions between the polycations and basic proteins were studied at acidic pH values. The differences in the effective electrophoretic mobilities, resolution values, and plate numbers of the proteins with the different coatings were due to the EOF, as demonstrated through calculations of reduced mobilities, relative resolution values, and relative plate numbers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2655–2663, 2007 相似文献
3.
Imahori H Fujimoto A Kang S Hotta H Yoshida K Umeyama T Matano Y Isoda S Isosomppi M Tkachenko NV Lemmetyinen H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7265-7275
Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics. 相似文献
4.
The equilibria for formation of iron(III) complexes with 1-hydroxy-7-sulpho-2-naphthoic and 1-hydroxy-4,7-disulpho-2-naphthoic acids in aqueous 0.1M sodium perchlorate medium at 25 degrees have been studied by spectrophotometric and potentiometric methods. The data are well described in terms of a series of stepwise complexes, FeL((3-rn)+)(r) in both systems (L(n-) denotes the unprotonated ligand anion). 相似文献
5.
A method for the determination of clodronate at ppm levels in aqueous solutions by HPLC is presented. Clodronate is first separated by anion exchange chromatography using a solution of nitric acid and sodium nitrate as eluent. Th-EDTA-XO mixed ligand complex is used as a postcolumn reagent for clodronate. Clodronate reacts quantitatively with this complex in slightly acid solutions, and a change in the absorbance of Th-EDTA-XO is used as a measure for the clodronate concentration. The detection limit is about 3 ppm, and the linear dynamic range of the method extends up to about 200 ppm. The RSD values varied between 5 and 16%. The effect of pH on appearance and retention of different forms of clodronate is studied. Different forms of clodronate can be separated and detected in the used anion-exchange system. 相似文献
6.
Nichkova M Park EK Koivunen ME Kamita SG Gee SJ Chuang J Emon JM Hammock BD 《Talanta》2004,63(5):1213-1223
Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are considered highly toxic contaminants and the environmental and biological monitoring of these compounds is of great concern. Immunoassays may be used as screening methods to satisfy the growing demand for rapid and low cost analysis. In this work, we describe the application of an immunoassay that uses 2,3,7-trichloro-8-methyldibenzo-p-dioxin (TMDD) as a surrogate standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to sediment and human serum samples. Sample extraction and preparation methods were developed with the aim to establish the simplest, cost-effective and efficient removal of the matrix interferences in the enzyme-linked immunosorbent assay (ELISA). The overall method for sediments is based on a hexane extraction; clean up by a multilayered silica gel column and an activated carbon column; an organic solvent exchange with DMSO–Triton X-100 and ELISA measurement. The gas chromatography–high resolution mass spectrometry (GC–HRMS) validation studies (n = 13) revealed that the method is suitable for the toxic equivalents (TEQ) screening of dioxin in sediments with a method detection limit of about 100 pg g−1 dry sediment with a precision of 13–33% R.S.D. The analysis of a large number of samples originating from different sources would be required to establish more precisely the screening level, as well as the number of false positives and negatives of dioxin TEQ by the immunoassay for sediments. The immunoassay method for sediment analysis offers improvement in speed, sample throughput, and cost in comparison to GC–HRMS. Dioxins were determined in serum samples after a simple liquid–liquid extraction and solvent exchange into DMSO–Triton X-100 without further dilution. The current method (approximate method LOQ of 200 pg ml−1 serum) is not sufficiently sensitive for the determination of dioxins in serum to measure acceptable exposure limit. 相似文献
7.
Bekers O op den Buijsch RA de Vries JE Wijnen PA van Dieijen-Visser MP 《Electrophoresis》2002,23(12):1878-1881
We describe the application of capillary electrophoresis to detect DNA fragments, obtained after amplifying a part of the apolipoprotein E (apoE) gene with polymerase chain reaction (PCR). Compared to conventional agarose slab gel electrophoresis (AGE), CE appears the method of choice with regard to resolution and sensitivity, to detect DNA fragments in the range of 20-100 base pairs. Especially discrimination between apoE2/E2 and apoE2/E3 genotypes is more reliable with CE than with AGE, this being of great clinical value in the diagnosis of familiary dysbetalipoproteinemia. 相似文献
8.
Konstantin Popov Alexei Popov Hannu Rönkkömäki Andrey Vendilo Lauri H. J. Lajunen 《Journal of solution chemistry》2002,31(6):511-520
A sequential NMR based approach is proposed for measurements of high log K values at low ionic strength. [31P] NMR technique is used to determine the protonation constants of 1,2-diaminoethane-N,N,N,N-tetra(methylenephosphonic acid) (EDTPH, H8L) at 25°C in 0.1 mol-dm–3 KNO3 and at 37°C in 0.15 mol-dm–3 NaCl at pH 11–14. For equilibrium L + H HL log K are found to be 13.3 (0.1) and 12.9 (0.1), respectively. 相似文献
9.
L. Kaila L. H. J. Lajunen P. Kokkonen 《Journal of Thermal Analysis and Calorimetry》1989,35(2):371-377
Thermal stability of the clodronic acid complex formed with sodium (Na2CCl2(HPO3)2 ·4H2O) was studied using both dynamic and isothermal thermogravimetric analyses as well as mass spectra. The thermal decomposition has two stages: dehydration and loss of two molecules of hydrogen chloride. Using the isothermal TG data the first step was found to be a phase-boundary reaction while the second step obviously cannot be described with just one reaction mechanism. The final residue of the dynamic TG analyses above 810 K was found to be sodium metaphosphate.
Zusammenfassung Sowohl mittels dynamischer und thermogravimetrischer Untersuchungen als auch and Hand von Massenspektren wurde die thermische Stabilität des mit Natrium gebildeten Säurekomplexes Na2CCl2(HPO3)2·4H2O untersucht. Die thermische Zersetzung vollzieht sich in zwei Schritten: Dehydratation und Verlust von zwei Molekülen HCl. Auf Grund der isothermen TG Angaben ist der erste Schritt eine Phasengrenzreaktion, während der zweite Schritt mit einem einzigen Reaktionsmechanismus nicht eindeutig beschrieben werden kann. Das Endprodukt der DTG Analyse oberhalb 810 K erwies sich als Natriummethaphosphat.
-Na2CCl2/HPO3/2·4H2O — , - . , , , . , , . 810 .相似文献
10.
A study was undertaken to determine the interfering effects of arsenic, bismuth, germanium, lead, selenium, tin and tellurium on trace determination of antimony by atomic-absorption spectrometry with hydride-generation. A 1% NaBH(4) solution was used as reductant and a small amount of oxygen was added to the hydrogen produced, to support the combustion and atomization of SbH(3). The interference from selenium in the determination of antimony is removed if potassium iodide-ascorbic acid solution or copper sulphate is added to the sample solution. The interference of tin and tellurium can also be avoided by adding potassium iodide-ascorbic acid solution. A possible interference mechanism is discussed. 相似文献