Lutein and zeaxanthin in new dietary supplements—analysis and quantification

Lutein and zeaxanthin, two xanthophylls supposed to delay formation of age-related macular degeneration (AMD), are found in numerous new dietary supplements appearing on the international market. Usually, the lutein concentration ranges from 0.25 to 20 mg/serving size. The lutein contents of 14 products with lutein highlighted on the label were evaluated. Oily formulations were dissolved, and powdery capsule contents were extracted with solvents before high-performance liquid chromatography (HPLC) analysis (diode-array detector, 450 nm) using a C30 column. If lutein diesters from marigold (Tagetes erecta) were present, the extracts were saponified with methanolic KOH. To unequivocally identify carotenoids, HPLC-(atmospheric pressure chemical ionization)mass spectrometry was applied. In this study only all-trans-lutein was quantified, whereas cis isomers (approximately 1–5 area% of total lutein) were not taken into account. The lutein concentration of half of the products investigated was found to be below the amount stated, varying here from 11 to 93%. With the exception of one product, all dietary supplements contained zeaxanthin in amounts typical for the use of marigold oleoresin (6.0±1.4 area% of all-trans-lutein). The high discrepancy found between the amounts labeled and determined in half of the products may be attributed to degradation reactions or to improper storage conditions.     

Intermediates in the Methanol-to-hydrocarbons (MTH) Reaction: A Gas Phase Study of the Unimolecular Reactivity of Multiply Methylated Benzenium Cations

In order to reach a deeper insight into the reaction mechanism of the zeolite catalyzed methanol to hydrocarbons reaction (MTH), the proposed reaction intermediates, i.e., a series of multiply methyl-substituted benzenium ions has been generated in the gas phase by chemical ionization. The fragmentations of the corresponding long-lived (metastable) ions have been investigated. While expulsion of H₂ dominates for the lower homologues, elimination of methane dominates for the higher homologues, accompanied by increasing amounts CH₃^·. Loss of larger fragments relevant to the MTH-reaction, in particular ethene, propene and even butene, is also observed in minor amounts. This latter finding is consistent with a proposed reaction cycle in the MTH reaction known as the paring mechanism, and the feasibility of this mechanism has thus been demonstrated. The metastable gas-phase ions studied here are considerably more energetic than those residing in a zeolite catalyst, but they were found to decompose with markedly higher selectivity towards alkenes as compared to those activated by collision-induced dissociation (CID).     

Monohydroperoxides of linoleic acid in endoplasmic lipids of rats exposed to tetrachloromethane

An accurate method for the quantitative determination of hydroperoxy and hydroxy fatty acids in liver microsomes is presented which involves the use of¹⁸O-labeled internal standards. The method is employed for the determination of hydroperoxides in rat liver microsomes after aerobic incubation with Fe²⁺/ADP and in microsomes from animals exposed to 75 mg tetrachloromethane/kg body weight. The amounts found after artificial microsomal “lipid peroxidation” are almost two orders of magnitude larger than those in microsomes from tetrachloromethaneexposed animals.     

A measuring method for quick determination of local heat transfer coefficients in spray water cooling within the range of stable film boiling

Within the framework of research investigations described in this paper, a measuring method for the determination of heat transfer coefficients in the range of stable film boiling has been developed for water spray cooling in the secondary cooling zone of continuous casting machines. Based on investigations by ³), a water cooled test sample with a measuring field of 20 × 20 mm² was constructed. For this sample geometry, a special evaluation method has been developed which permits quick evaluation in on-line procedure. Result of measurements are sections for the heat transfer coefficient arising from different spray water distributions. On the one hand, these can be used as calculation figures for the determination of the solidification profile and the solidification rate. On the other hand, the measuring results serve as an assessment basis for nozzle constructions. Practical use of the measuring results confirms the usefulness of the measuring method on a laboratory scale. In addition, the validity of the measuring results has been demonstrated by comparing them with an unsteady state method in accordance with ²).     

Realization theory in Hilbert space

A representation theorem for infinite-dimensional, linear control systems is proved in the context of strongly continuous semigroups in Hilbert spaces. The result allows for unbounded input and output operators and is used to derive necessary and sufficient conditions for the realizability in a Hilbert space of a time-invariant, causal input-output operator ℐ. The relation between input-output stability and stability of the realization is discussed. In the case of finite-dimensional input and output spaces the boundedness of the output operator is related to the existence of a convolution kernel representing the operator ℐ. This research has been supported by the Nuffields Foundation.     

Abhängigkeit der Streckgrenze und der Übergangstemperatur der Kerbschlagzähigkeit von der Abschreckalterung von Baustählen im Vergleich mit der Theorie des Sprödbruches

Einfluß der Abschreckalterung auf Streckgrenze und Übergangstemperatur der Kerbschlagzähigkeit. Deutungsmöglichkeiten mit Hilfe der Cottrell-Theorie. Einfluß der Ausscheidungen auf die Größen σ_i, k_y und k bzw. k₀ sowie deren Einfluß auf T_ü.