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排序方式: 共有79条查询结果,搜索用时 15 毫秒
1.
Marilena Vasilescu Titus Constantinescu Mariana Voicescu Helge Lemmetyinen Elina Vuorimaa 《Journal of fluorescence》2003,13(4):315-322
The spectrophotometric study of luminol (LH2) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH2 absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L2–) formation at 3 × 10–4 – 2.4 × 10–3
M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH2-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH2-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH+
3 cation formation. In LH2-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH2-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed. 相似文献
2.
V. Badescu M. Radu M. Zaharescu A. Vasilescu 《Journal of Sol-Gel Science and Technology》1994,2(1-3):43-49
Gas-chromatography coupled with mass spectrometry was used to investigate the hydrolysis and condensation of tetra-ethoxysilane (TEOS) in nonparental solvents (MeOH and nPrOH). In the presence of nonparental solvents, the reaction that advanced at highest rate is alkoxy group scrambling, that changes the precursor at the molecular level. Subsequent stages of hydrolysis-polycondensation process are essentially determined by the reactivity of the new molecular species formed. 相似文献
3.
4.
The sulfur mustard, HD, a chemical warfare agent, has been studied by ab initio quantum molecular computations (HF /6-31G * and 6-31G ) on its various forms (neutral, ethylene sulfonium, and free carbonium ions). The geometries of these molecules have been completely optimized and the minimal energy conformations determined with their associated charge distributions. We discuss these results on electrostatic properties with respect to the mechanism of DNA alkylation by HD and compare them with our previous study of the nitrogen mustard mechlorethamine. 相似文献
5.
Conformational transformations of the tetraenic nystatin chromophore under the influence of solvents and UV irradiation have been studied by absorption, fluorescence and wide-line NMR spectroscopy. 相似文献
6.
Bercu C Oncescu T Lupan L Bandula R Vasilescu M Sandu T Mitran L 《Analytical and bioanalytical chemistry》1996,355(5-6):753-755
The influence of SDS upon the molecular properties of proflavine (3,6-diaminoacridine), acridine yellow (2,7-dimethyl-3,6-diaminoacridine) and methylene blue (3,7-bis-dimethylamino-phenothiazine) was studied comparatively to their properties in that of aqueous media. The absorption and emission spectra of the three dyes in SDS aqueous solution (1-100 mmol/l) were recorded. The spectroscopic data also allowed the evaluation of the critical micellization concentration (CMC), acidity constants in fundamental (pk(a)) and excited (pK(*)(a)) states, and lifetimes of excited singlet states. 相似文献
7.
Ramona Penu Ioana Vasilescu Sandra A. V. Eremia Florentina Gatea Gabriel-Lucian Radu Simona-Carmen Litescu 《Central European Journal of Chemistry》2013,11(6):968-978
The present work describes the development of a nanocomposite system and its application in construction of a new amperometric biosensor applied in the determination of total polyphenolic content from propolis extracts. The nanocomposite system was based on covalent immobilization of laccase on functionalized indium tin oxide nanoparticles and it was morphologically and structural characterized. The casting of the developed nanocomposite system on the surface of a screen-printed electrode was used for biosensor fabrication. The analytical performance characteristics of the settled biosensor were determined for rosmarinic acid, caffeic acid and catechol (as laccase specific substrate). The linearity was obtained in the range of 1.06×10?6 ? 1.50×10?5 mol L?1 for rosmarinic acid, 1.90×10?7 ? 2.80×10?6 mol L?1 for caffeic acid and 1.66×10?6 ? 7.00×10?6 mol L?1 for catechol. A good sensitivity of amperometric biosensor 141.15 nA µmol?1 L?1 and fair detection limit 7.08×10?8 mol L?1 were obtained for caffeic acid. The results obtained for polyphenolic content of propolis extracts were compared with the chromatographic data obtained by liquid-chromatography with diode array detection. 相似文献
8.
Three new mesoionic oxazolo[3,2-b]pyridazin-2-one derivatives, in different solutions have been investigated by UV-Vis absorption, steady-state and time-resolved fluorescence methods. The effect of substituents on the extension of conjugation of the pi-electrons from mesoionic oxazolone has been evidenced by bathochromic shifts of the absorption and fluorescence maxima positions. The fluorescence decay data could be fitted to single-exponential or double-exponential function. The lifetime values are much higher in aprotic polar solvents and in the case of the derivatives that present an extension of the conjugation of pi-electrons. The properties of the compounds present a solvent dependence, being tested in micellar solutions as potential molecular probe "sensitive" to the environment polarity. 相似文献
9.
Bogdan Constantinescu Angela Vasilescu Martin Radtke Uwe Reinholz Claire Pacheco Laurent Pichon Ernest Oberländer-Târnoveanu 《Applied Physics A: Materials Science & Processing》2012,109(2):395-402
A thorough microscopic investigation by SR XRF and micro-PIXE brings insight into the probable techniques used in the manufacture of thirteen Dacian gold bracelets, one of the most spectacular archaeological finds ever on the territory of Romania. 相似文献
10.
The microstructure of water soluble nanoaggregates based on polyelectrolyte complex formed by the cationic comb-type copolymer
poly(acrylamide -co-[3- (methacryloyl-amino)propyl] trimethylammonium chloride)-graft- polyacrylamide [P(AM-co-MAPTAC)-g-PAM]
and the anionic linear polyelectrolyte sodium polyacrylate (NaPA) was investigated using the fluorescence probe technique.
The fluorescence probe were 1-anilinonaphthalene-8-sulfonic acid (ANS), pyrene (Py) and 1,10-bis(1-pyrene) decane (PD). The
fluorescence properties in polyelectrolyte complex solutions, which are sensitive to either micropolarity (ANS, Py) or microviscosity
(PD), were related to the quantities obtained in different pure or mixed solvents. Micropolarities were quantified utilizing
the polarity common index (Reichardt) E
T(30). ANS and Py showed a variation of the micropolarity with the charge ratio of the two polymers, with the lowest polarity
reached at the complex neutralization. The PD probe, by its excimer-to-monomer fluorescence intensities ratio, enabled us
to evidence the effect of the composition and the comb-type copolymer grafting density on the microviscosity of the interpolyelectrolytes
aggregates. It has been found that the microviscosity increased with the density of the grafting PAM chains. 相似文献