Bestimmung von T-2-Toxin in pflanzlichen Nahrungsmitteln

Zusammenfassung Ein Verfahren zur quantitativen Bestimmung von T-2-Toxin in verschimmeltem Reis bzw. Mais durch Extraktion, dünnschicht-chromatographische Trennung und Fluorescenzintensitätsmessung der mit H₂SO₄ behandelten DC-Platte wird vorgestellt. Fluorescenzabsorptions- und Fluorescenzemissionsspektrum werden angegeben. Die Abhängigkeit der Mycotoxinkonzentration von der Fluorescenzintensität wird durch eine Gleichung beschrieben. Die analytische Detektion von T-2-Toxin läßt sich durch ein 4-(p-Nitrobenzyl)pyridin-Derivat und dessen Absorptionsspektrum bestätigen. Versuche mit zugesetztem T-2-Toxin zeigten einen Analysenfehler von weniger als 10%.

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Determination of T-2-toxin in vegetable foodstuffs1. T-2-toxin in mouldy rice and maize

Summary A procedure is described for the determination of T-2 toxin in extracts from mouldy rice and maize by thin-layer chromatography (TLC) and subsequent fluorescence intensity measurement of the H₂SO₄-treated TLC plates. The fluorescence absorption and emission spectra are presented. The dependence of the concentration of the mycotoxin on fluorescence intensity is described by an equation. The detection of T-2 toxin can be confirmed by colour reaction with 4-(p-nitrobenzyl)pyridine yielding a blue derivative. Experiments with added toxin revealed an analytical error smaller than 10%.

     

Generation of quaternary stereocenters by asymmetric Michael reactions: enamine regiochemistry as configuration switch

Regioselective enamine formation from cyclic β‐diketones 1 is obtained by the appropriate choice of activating agent: Brønsted acid catalyzed condensation gives endocyclic enamines 3 as the thermodynamically favored products. Activation with Lewis acid BF₃ ? OEt₂ affords betaines 8 as intermediate products, which can be reacted with L ‐valine diethylamide ( 2 ) to preferentially furnish exocyclic enamines 4 as kinetic products. Derivatives with quaternary stereocenters were accessible from both isomeric enamines by using asymmetric, copper(II )‐catalyzed Michael reactions at ambient temperature. Both regioisomers afford the triketones 7 with the same constitution but bearing the opposite absolute configuration at the quaternary stereocenter. Thus, both enantiomers of the product are prepared by using the same chiral auxiliary derived from L ‐valine.     

Using a factored dual in augmented Lagrangian methods for semidefinite programming

In the context of augmented Lagrangian approaches for solving semidefinite programming problems, we investigate the possibility of eliminating the positive semidefinite constraint on the dual matrix by employing a factorization. Hints on how to deal with the resulting unconstrained maximization of the augmented Lagrangian are given. We further use the approximate maximum of the augmented Lagrangian with the aim of improving the convergence rate of alternating direction augmented Lagrangian frameworks. Numerical results are reported, showing the benefits of the approach.     

On properties of random dissections and triangulations

In this work we study properties of random graphs that are drawn uniformly at random from the class consisting of biconnected outerplanar graphs, or equivalently dissections of large convex polygons. We obtain very sharp concentration results for the number of vertices of any given degree, and for the number of induced copies of a given fixed graph. Our method gives similar results for random graphs from the class of triangulations of convex polygons.     

Statistical inference for the optimal approximating model

In the setting of high-dimensional linear models with Gaussian noise, we investigate the possibility of confidence statements connected to model selection. Although there exist numerous procedures for adaptive (point) estimation, the construction of adaptive confidence regions is severely limited (cf. Li in Ann Stat 17:1001–1008, 1989). The present paper sheds new light on this gap. We develop exact and adaptive confidence regions for the best approximating model in terms of risk. One of our constructions is based on a multiscale procedure and a particular coupling argument. Utilizing exponential inequalities for noncentral χ ²-distributions, we show that the risk and quadratic loss of all models within our confidence region are uniformly bounded by the minimal risk times a factor close to one.     

HALORHODOPSIN and PHOTOSENSORY BEHAVIOR IN Halobacterium halobium MUTANT STRAIN L-33

Halobacterium halobium , strain L-33, which is deficient in bacteriorhodopsin (BR) but synthesizes increased amounts of halorhodopsin (HR), shows behavioral responses upon changes in fluence rate with visible light or with UV light. The observations support the earlier report (Schimz et al. , 1982). that BR is not essential for photosensing in H. halobium. In the UV-range, changes in light intensity elicit the maximal response at λ= 370 nm. In the visible range, changes in light intensity show the maximal response at Δ= 565 nm and a secondary peak at Δ= 590 nm. The latter corresponds to the absorption maximum of HR (Δ_max= 588 nm). This light-energy converting retinal pigment of H. halobium thus appears to contribute to photosensory behavior.     

PHOTOSENSORY BEHAVIOR OF A BACTERIORHODOPSIN-DEFICIENT MUTANT, ET-15, OF Halobacterium halobium

– Halobacterium halobium , strain ET-15, which does not contain detectable amounts of bacteriorhodopsin (BR) shows behavioral responses to UV and yellow-green light. Attractant stimuli. i.e. light-increases in the yellow-green range or light-decreases in the UV, suppress the spontaneous reversals of the swimming direction for a certain time. Repellent stimuli, i.e. light-decreases in the yellow-green range or light-increases in the UV, elicit an additional reversal response after a few seconds. Action spectra of both sensory photosystems, PS 370 and PS 565, were measured with attractant as well as with repellent stimuli. As in BR-containing cells, maximal sensitivity was always found at 370 nm for the UV-system and at 565 nm for the long-wavelength system. Fluence-response curves at 370 and 565 nm obtained with strain ET-15 and with a BR-containing strain show that the sensitivity of both photosystems is not reduced in the absence of BR. It is concluded that BR is required neither for PS 565 nor for PS 370. Instead retinal-containing pigments different from BR have to be assumed to mediate photosensory behavior.