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1.
β-Aminocrotonic esters are of great importance as stabilizers for the production of clearly transparent food packaging of PVC. For the purpose of studying the migration into foods a thin-layer Chromatographic and a polarographic method were elaborated. The TLC method consists of the visual comparison of the intensity of the spots after treatment with Fast Blue B salt. The polarographic determination is carried out after nitrosation of the stabilizer. By the TLC method 10?7 g of ester per spot are still detectable; the concentration which is still determinable by cathode-ray polarography is 5×10?7 g of ester and by conventional d.c. polarography 5×10?6g of ester per ml of final solution. After extraction with acetonitrile traces of the stabilizer which are migrated into edible oil are still determinable down to 2 ppm by the methods described. 相似文献
2.
On reaction with ‘O’-donors or O2, the synthetic P-450 analogue 2 undergoes O-insertion at a nonactivated C? H bond of the covalently bound substrate. The mechanism of O-insertion with O2 most likely involves homolytic cleavage of the O? O bond followed by O-insertion via radical recombination. 相似文献
3.
F. Henneberger U. Woggon J. Puls Ch. Spiegelberg 《Applied physics. B, Lasers and optics》1988,46(1):19-25
We report on large optical nonlinearities due to specific many-body effects in high-density electron-hole pair systems. On bulk CdS we study the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature. Steady-state saturable absorption at mW-power levels and four-wave mixing with first-order efficiencies as large as 2% of the incoming light are demonstrated on a 1m slab. On CuBr microcrystallites embedded in glass we investigate the changes of the exciton absorption caused by many-exciton effects both at cryo and room temperature. In contrast to bulk semiconductors, we observe a blue shift of the exciton peak at resonant optical excitation. In addition, strong saturation of absorption with very large contrast shows up. We find Lorentzian saturation intensities in the 100 kW/cm2 range. 相似文献
4.
U. Woggon O. Wind F. Gindele E. Tsitsishvili M. Mü ller 《Journal of luminescence》1996,70(1-6):269-280
The optical transition energies have been determined for the lowest electron-hole pair states of CdSe quantum dots embedded in glass. The data obtained by photoluminescence, differential absorption and photoluminescence excitation spectroscopy have been compared and a general size dependence could be established. Based on theoretical calculations, the dominant features in the spectra have been assigned to the different transitions from the ground state to the one-pair states. Within the lowest one pair transition, a fine structure due to exchange interaction has been observed. The change in the optical properties with increasing intensity has been studied and the two-pair states identified in luminescence. Spectrally broad optical gain has been found due to stimulated transitions involving both one- and two-pair states. 相似文献
5.
A silver-nanowire cavity is functionalized with CdSe nanocrystals and optimized towards cavity quantum electrodynamics by varying the nanocrystal-nanowire distance d and cavity length L. From the modulation of the nanocrystal emission by the cavity modes a plasmon group velocity of v (gr) approximately 0.5c is derived. Efficient exciton-plasmon-photon conversion and guiding is demonstrated along with a modification in the spontaneous emission rate of the coupled exciton-plasmon system. 相似文献
6.
A Raman laser based on a bulk silicon single crystal with 1.127 μm emission wavelength is demonstrated. The Si crystal with 30 mm length was placed into an external cavity and pumped by a Q-switched Nd:YAG master oscillator power amplifier system. Strong defocusing of the pump and Raman laser beam by free carriers was compensated by an intracavity lens. Raman laser operation with a pulse duration of 2.5 ns was identified by a Raman laser threshold significantly lower than the single-pass stimulated Raman-scattering threshold. Linear absorption losses of the 1.06415 μm pump radiation are strongly reduced by cooling the Si crystal to a temperature of 10 K. 相似文献
7.
Zusammenfassung
-Aminocrotonsäureester spielen als PVC-Stabilisatoren bei der Herstellung glasklarer Lebensmittelverpackungen eine bedeutende Rolle. Zur Verfolgung der Migration in Lebensmittel wird eine dünnschichtchromatographische und eine polarographische Methode beschrieben. Das dünnschicht-chromatographische Verfahren besteht im visuellen Fleckenvergleich des mit Echtblausalz B sichtbar gemachten Esters. Die polarographische Bestimmung erfolgt nach vorangegangener Nitrosierung des Stabilisators. Dünnschicht-chromatographisch lassen sich noch 0,1 g Ester/Fleck nachweisen; die noch bestimmbare Grenzkonzentration beträgt für den Kathodenstrahlpolarographen 0,5 g Ester/ml Meßlösung, für den konventionellen Gleichspannungspolarographen 5 g Ester/ml. In Speiseöl migrierte Stabilisatorspuren lassen sich nach Extraktion mit Acetonitril noch in Mengen bis zu 2 ppm mit den angegebenen Methoden erfassen.
Bereich Fremdstoffe in Nahrung und Ernährung 相似文献
On the determination of -aminocrotonic esters after migration into foodsContribution to the testing of plastic commodities
-Aminocrotonic esters are of great importance as stabilizers for the production of clearly transparent food packaging of PVC. For the purpose of studying the migration into foods a thin-layer Chromatographic and a polarographic method were elaborated. The TLC method consists of the visual comparison of the intensity of the spots after treatment with Fast Blue B salt. The polarographic determination is carried out after nitrosation of the stabilizer. By the TLC method 10–7 g of ester per spot are still detectable; the concentration which is still determinable by cathode-ray polarography is 5×10–7 g of ester and by conventional d.c. polarography 5×10–6g of ester per ml of final solution. After extraction with acetonitrile traces of the stabilizer which are migrated into edible oil are still determinable down to 2 ppm by the methods described.
Bereich Fremdstoffe in Nahrung und Ernährung 相似文献
8.
9.
Georgios Papazoglou Jorge Sierra Katharina Homberger Armin Guggisberg Wolf-Dietrich Woggon Manfred Hesse 《Helvetica chimica acta》1991,74(3):565-571
Aphelandrine ( 1 ) is shown to be biosynthesized in the root cells of Aphelandra tetragona (VAHL ) NEES from labelled putrescine ( 4 ), spermidine ( 5 ), and cinnamic acid ( 3 ). Whether spermine ( 6 ) and the (p-hydroxycinnamoyl)spermidine 8 are precursors of 1 is uncertain, since the latter is hydrolysed to a large extent before incorporation, and the former is metabolized to 4 and 5 . Methionine ( 7 ) is the source of the 3-aminopropyl unit of 5 and 6 . 相似文献