A survey of several electrophilic ammonia reagents for the N-amination of indole- and pyrrole-containing heterocycles revealed that monochloramine (NH(2)Cl) is an excellent reagent for this transformation. Pyrroles and indoles containing a variety of substitution were aminated on nitrogen with isolated yields ranging from 45% to 97%. 相似文献
We study the mobility of short ssDNA fragments (approximately 30-500 bases) separated by capillary electrophoresis in entangled polymer solutions. Although this corresponds to what is commonly called the Ogston regime, the corresponding sieving concept has never been defined properly nor tested quantitatively. We consider three formulas that have been suggested to fit data in this range of ssDNA sizes, and we discuss how their free parameters are related to actual physical parameters. We test these formulas with new data obtained in our laboratory using a commercial poly-N,N-dimethylacrylamide sieving matrix. Our results show that all three formulas provide decent fits. However, the traditional Ogston equation produces fitting parameters that appear to lack physical meaning. Surprisingly, all three approaches predict that the effective pore size and fiber radius are almost equal. This is the first step towards the development of a systematic approach to optimizing sequencing systems for this size range. 相似文献
The low-temperature (77 K) emission and excitation chlorophyll fluorescence spectra in thylakoid membranes isolated from pea mutants were investigated. The mutants have modified pigment content, structural organization, different surface electric properties and functions [Dobrikova et al., Photosynth. Res. 65 (2000) 165]. The emission spectra of thylakoid membranes were decomposed into bands belonging to the main pigment protein complexes. By an integration of the areas under them, the changes in the energy distribution between the two photosystems as well as within each one of them were estimated. It was shown that the excitation energy flow to the light harvesting, core antenna and RC complexes of photosystem II increases with the total amount of pigments in the mutants, relative to the that to photosystem I complexes. A reduction of the fluorescence ratio between aggregated trimers of LHC II and its trimeric and monomeric forms with the increase of the pigment content (chlorophyll a, chlorophyll b, and lutein) was observed. This implies that the closer packing in the complexes with a higher extent of aggregation regulates the energy distribution to the PS II core antenna and reaction centers complexes. Based on the reduced energy flow to PS II, i.e., the relative increased energy flow to PS I, we hypothesize that aggregation of LHC II switches the energy flow toward LHC I. These results suggest an additive regulatory mechanism, which redistributes the excitation energy between the two photosystems and operates at non-excess light intensities but at reduced pigment content. 相似文献
Novel copolymers of trisubstituted ethylene monomers, alkyl and alkoxy ring-substituted 2-phenyl-1,1-dicyanoethylenes, RC6H4CH=C(CN)2 (where R is 2-ethyl, 4-i-propyl, 4-butyl, 4-i-butyl, 4-t-butyl, 2-ethoxy, and 4-hexyloxy) and styrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR. The order of relative reactivity (1/r1) for the monomers is 4-t-butyl (1.45) > 4-i-propyl (1.38) > 2-ethyl (1.37) > 4-hexyloxy (1.33) > 4-i-butyl (1.24) > 2-ethoxy (1.13) > 4-butyl (1.04). High Tg of the copolymers, in comparison with that of polystyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (1–10% wt.), which then decomposed in the 500–800°C range. 相似文献
The purpose of this study was to assess the effect of chemical shift artifacts and fat suppression between contrast-enhanced T1-weighted fast spin-echo (FSE) sequence with fat suppression and contrast-enhanced T1-weighted fluid attenuated inversion recovery (FLAIR) sequence with fat suppression in magnetic resonance imaging (MRI) of the thoracic spine at 3.0T. Forty patients, who underwent MRI examination, were recruited and analyzed both qualitatively and quantitatively. Due to chemical shift artifacts in the T1-weighted FSE, 14 of the patients were found to be of non-diagnostic value. On the contrary, in 11 of those 14 patients, no chemical shift artifacts were observed in the T1-weighted FLAIR sequence. Regarding the efficiency of fat suppression, both sequences achieved successful fat suppression. Consequently, the use of T1-weighted FLAIR fat suppression after contrast administration sequence seems to eliminate or significantly reduce image quality deterioration stemming from chemical shift artifacts in thoracic spine examinations. 相似文献
Cadmium (Cd) is a heavy metal that occurs in all areas of the environment, including the food chain. In the body, it causes oxidative stress by producing free radicals that are harmful to the cells. Grape seed extract (GSE) contains a wide range of biologically active components that help to neutralize the adverse effects of free radicals. In this study, the effects of GSE prepared form semi-resistant grapevine cultivar Cerason, which is rich in phenolics, on biochemical markers of brown rats exposed to the effects of cadmium were monitored. GSE increased the plasma antioxidant activity and, in the kidneys and the liver, Cd content was significantly lowered by GSE co-administration. Accordingly, the increase in creatinine content and alanine aminotransferase activity and the decrease of catalase and superoxide dismutase activities caused by cadmium were slowed down by GSE co-administration. The results of this work reveal that grape seed extract offers a protective effect against the intake of heavy metals into the organism. 相似文献
Cyclo-bisintercalands are macrocyclic systems containing aromatic subunits, which are commonly used as hosts for aromatic molecules and as DNA intercalators. In this article, a step-by-step synthesis of a series of cyclo-bisintercalands containing 3,6-diaminoacridines as aromatic units, and connected by rigid spacers of different lengths, is reported. In addition, we describe herein a more efficient synthetic alternative, involving single-step template-directed processes. The new routes allow the easy synthetic access to these macrocyclic systems with acceptable yields. The synthesized cyclo-bisintercalands and their precursors have been structurally characterized by UV–visible and NMR methods. Preliminary biological activity assays performed on the bisintercalands and cyclo bisintercalands revealed interesting cytotoxic properties against different tumor cell lines, especially in the case of the bisintercalands, highlighting their potential as cancer chemotherapeutic agents. 相似文献
Effects of the precursor of active metal and of the reduction temperature upon activity and selectivity in selective hydrogenation of crotonaldehyde by Pt/SnO2 and Ru/SnO2 catalysts were studied. Experiments were performed in the liquid phase with a group of solvents tested: propan-2-ol, toluene, hexane and tetrahydrofuran. The best results were achieved with catalysts from ex-nitrate precursors/Pt(NH3)4(NO3)2 and Ru(NO)(NO3)2/reduced at 150° C. Propan-2-ol was evaluated as the most appropriate solvent to gain high yields of crotylalcohol in this study. A new hydrogenation product, 2-methylprop-2-en-1-ol (methallylalcohol), was observed. 相似文献
Thin-layer chromatography (TLC) is a simple, fast and inexpensive separation method which can be applied to virtually all natural products including oligosaccharides. Unfortunately, however, the unequivocal identification of a TLC spot is normally difficult. Fortunately, this problem can be minimized when mass spectrometry (MS) such as matrix-assisted laser desorption and ionization time-of-flight is used to identify the TLC spots. This work is dedicated to the TLC/MS analysis of oligosaccharides derived from native chondroitin sulfate and hyaluronan. We will show that the thickness of the silica gel layer (200 versus 100 µm) has a tremendous influence on the quality of the mass spectra: a reduced silica gel thickness enhances the spectral quality and, in particular, improves the achievable signal-to-noise ratio. Additionally, unwanted formylation of the GAG oligosaccharides (which occurs due to the high moiety of formic acid in the mobile phase) can also be minimized if MS-grade HPTLC plates are used.