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91.
Schaal J Dekowski B Wiesner B Eichhorst J Marter K Vargas C Keller S Eremina N Barth A Baumann A Eisenhardt D Hagen V 《Chembiochem : a European journal of chemical biology》2012,13(10):1458-1464
We have developed and characterized efficient caged compounds of the neurotransmitter octopamine. For derivatization, we introduced [6-bromo-8-(diethylaminomethyl)-7-hydroxycoumarin-4-yl]methoxycarbonyl (DBHCMOC) and {6-bromo-7-hydroxy-8-[(piperazin-1-yl)methyl]coumarin-4-yl}methoxycarbonyl (PBHCMOC) moieties as novel photo-removable protecting groups. The caged compounds were functionally inactive when applied to heterologously expressed octopamine receptors (AmOctα1R). Upon irradiation with UV-visible or IR light, bioactive octopamine was released and evoked Ca2+ signals in AmOctα1R-expressing cells. The pronounced water solubility of compounds 2-4 in particular holds great promise for these substances as excellent phototriggers of this important neurotransmitter. 相似文献
92.
Owing to possible adulteration and health concerns, it is important to discriminate between natural and synthetic food ingredients. A new method for compound-specific isotope analysis (CSIA) by coupling high-temperature reversed-phase liquid chromatography to isotope ratio mass spectrometry (HT-RPLC/IRMS) was developed for discrimination of natural and synthetic caffeine contained in all types of drinks. The analytical parameters such as stationary phase, column inner diameter, and column temperature were optimized for the separation of caffeine directly from drinks (without extraction). On the basis of the carbon isotope analysis of 42 natural caffeine samples including coffee beans, tea leaves, guaraná powder, and maté leaves, and 20 synthetic caffeine samples from different sources by high-temperature reversed-phase liquid chromatography coupled to isotope ratio mass spectrometry, it is concluded that there are two distinguishable groups of caffeine δ(13)C-values: one between -25 and -32‰ for natural caffeine, and the other between -33 and -38‰ for synthetic caffeine. Isotope analysis by HT-RPLC/IRMS has been applied to identify the caffeine source in 38 drinks. Four mislabeled products were detected due to added but nonlabeled synthetic caffeine with δ(13)C-values lower than -33‰. This work is the first application of HT-RPLC/IRMS to real-world food samples, which showed several advantages: simple sample preparation (only dilution), high throughput, long-term column stability, and high precision of δ(13)C-value. Thus, HT-RPLC/IRMS can be a very promising tool in stable isotope analysis of nonvolatile compounds. 相似文献
93.
Compound-specific isotope analysis (CISA) of nonvolatile analytes has been enabled by the introduction of the first commercial interface to hyphenate liquid chromatography with an isotope ratio mass spectrometer (LC-IRMS) in 2004, yet carbon isotope analysis of unpolar and moderately polar compounds is still a challenging task since only water as the eluent and no organic modifiers can be used to drive the separation in LC. The only way to increase the elution strength of aqueous eluents in reversed phase LC is the application of high temperatures to the mobile and stationary phases (HT-LC-IRMS). In this context we present the first method to determine carbon isotope ratios of pharmaceuticals that cannot be separated by already existing separation techniques for LC-IRMS, such as reversed phase chromatography at normal temperatures, ion-chromatography, and mixed mode chomatography. The pharmaceutical group of sulfonamides, which is generally mixed with trimethoprim in pharmaceutical products, has been chosen as probe compounds. Substance amounts as low as 0.3 μg are sufficient to perform a precise analysis. The successful applicability and reproducibility of this method is shown by the analysis of real pharmaceutical samples. The method provides the first tool to study the pharmaceutical authenticity as well as degradation and mobility of such substances in the environment by using the stable isotopic signature of these compounds. 相似文献
94.
95.
Dorothea Pietzsch Sabine Ochsner Jasmin Mantilla-Contreras Ulrich Hampicke 《Landscape Research》2013,38(4):523-539
Abstract Dry grasslands represent unique ecosystems that are known for high biodiversity. Land use changes have led to a decline in Europe. Shrub encroachment is a major problem in incorrectly or unmanaged areas, and affects not only flora and fauna but also leads to changes in the appearance of the landscape. Our study was conducted on the island of Hiddensee, north-east Germany, where today dry grasslands are endangered by shrub encroachment. We analysed the current land use under consideration of farming costs as well as current agricultural subsidies. Our results show that revenues of low-intensity cattle husbandry only account for 61% of total costs and that farming becomes profitable only with subsidies. Our study illustrates that goats can be a cost-efficient solution for areas with high shrub cover in contrast to manual clearing. The maintenance of dry grasslands is therefore more cost-efficient with grazing animals than with technical-manual labour. 相似文献
96.
Weber D Mourzina Y Brüggemann D Offenhäusser A 《Journal of nanoscience and nanotechnology》2011,11(2):1293-1296
Gold nanopillars are grown in patterns inside a porous anodic alumina template. On selected positions, defined by a gold "seed" pattern, gold is electroplated into the pores, while a barrier layer underneath the porous template blocks the deposition on the rest of the surface. Large-scale arrays of free-standing nanopillar islands are obtained after selective etching of the alumina template. 相似文献
97.
F. Ulberth Robert Gabernig Dorothea Roubicek 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1998,206(1):21-24
The quantitative aspects of triglyceride profiling of milk fat by capillary column gas chromatography (GC) were investigated.
Fifty samples of pure Austrian milk fat were tested as described in Annex III of the European Community (EC) Commission regulation
no. 454/95 by using a packed as well as a short metal capillary column. Capillary GC was equivalent to the packed column in
terms of analytical precision (relative standard deviation of repeated injections). All samples tested fulfilled the purity
criteria (S-values), irrespective of the chromatographic technique used. Nevertheless, the S-values obtained by capillary
GC deviated to some extent from those of the packed column. The differences exceeded the value for reproducibility laid down
in Annex III, EC regulation no. 454/95 in 18 of 50 cases. As a consequence, the equivalency of capillary GC for determining
the purity of milk fat according to EC regulation no. 454/95 should be re-assessed.
Received: 4 April 1997 / Revised version: 26 June 1997 相似文献
98.
HPLC has been used for the determination of vanillin,p-hydroxybenzaldehyde, vanillic acid,p-hydroxybenzoic acid, ethyl vanillin, piperonal and coumarin in CO2 extracts and alcoholic extracts of vanilla beans. Ethyl vanillin, piperonal and coumarin were found in none of the samples. By measuring vanillin,p-hydroxybenzaldehyde, vanillic acid andp-hydroxybenzoic acid a great difference between the amount and the ratio of these main components of the usual alcoholic vanilla extracts and the CO2 vanilla extracts was shown. The present requirements for vanilla extracts and products containing vanilla extracts refer only to the composition of alcoholic extracts for which, in contrast to CO2 vanilla extracts, many studies have been published. The critical examination of products containing CO2 vanilla extracts by using the ratios of vanilla compounds found in the present literature could lead to erroneous complaints. For the purpose of estimating the influence of the extraction solvent on the yield of vanillin, one sample of vanilla beans of each provenance was extracted besides the CO2 extraction also with the solvents ethanol-water according to the method for a single-fold extract and with the solvents dichloromethane and hexane. In all three cases dichloromethane was found to be the best solvent. Furthermore, the ethanol-water extraction tended to give 6–22% more vanillin than the CO2 extraction. To achieve unequivocal results, the examination of more samples is necessary. 相似文献
99.
The growth of multi-walled carbon nanotube (MWCNT) forests was investigated using an atmospheric pressure plasma jet (APPJ) system with a mixture of helium and acetylene gases. The MWCNT forests grown on Fe catalyst were compared with those grown on Ni. The growth of MWCNT forests using Fe as the catalyst was better than the growth of MWCNT forests using Ni. The MWCNT forests grown using Fe catalyst and with a plasma power of 30 W were about 17 ± 9% taller than for the plasma off. We were unable to grow MWCNTs using Ni catalyst with the plasma power off; but curly MWCNTs were grown using Ni catalyst if the plasma power was 30 W. It is found that MWCNT growth is enhanced using an APPJ. The height of the forests produced using this APPJ system was also better than that reported by other researchers using either CVD or PECVD systems. 相似文献
100.
Holzer and Holzer [M. Holzer, W. Holzer, Tantrix? rotation puzzles are intractable, Discrete Applied Mathematics 144(3) (2004) 345–358] proved that the Tantrix? rotation puzzle problem with four colors is NP-complete, and they showed that the infinite variant of this problem is undecidable. In this paper, we study the three-color and two-color Tantrix? rotation puzzle problems (3-TRP and 2-TRP) and their variants. Restricting the number of allowed colors to three (respectively, to two) reduces the set of available Tantrix? tiles from 56 to 14 (respectively, to 8). We prove that 3-TRP and 2-TRP are NP-complete, which answers a question raised by Holzer and Holzer [M. Holzer, W. Holzer, Tantrix? rotation puzzles are intractable, Discrete Applied Mathematics 144(3) (2004) 345–358] in the affirmative. Since our reductions are parsimonious, it follows that the problems Unique-3-TRP and Unique-2-TRP are DP-complete under randomized reductions. We also show that the another-solution problems associated with 4-TRP, 3-TRP, and 2-TRP are NP-complete. Finally, we prove that the infinite variants of 3-TRP and 2-TRP are undecidable. 相似文献