Influence of temperature and short-term storage on the stability of norepinephrine in plasma samples

Catecholamines, as endogenous substances, are subject to biological degradation. The conditions of plasma handling for the determination of norepinephrine were investigated by using plasma samples of patients and control subjects with special regard to temperature and duration of storage. Previous studies have reported a remarkable i.v. stability of plasma norepinephrine for several hours. Here these findings were supported in a series of plasma samples which were kept either at 0° C or at room temperature. Another series of samples, which had been frozen immediately after collection, stored and rethawed, showed, however, great losses in norepinephrine within 1 to 2 h upon standing. This degradation of norepinephrine could not be attributed to monomaine oxidase (MAO) activity, because the addition of the MAO inhibitor pargyline was found to have no influence on the stability of norepinephrine. Recommendations for handling and storing of plasma samples for norepinephrine determinations are given.     

New Results on the Preparation and Reactivity of Benzo[c]thiophenes

Abstract

Preparation of benzo[c]thiophenes with particular substituents on the benzene or thiophene moiety is described and their cycloaddition, oxidation, and reduction reactions are discussed.     

Bicyclo[3.2.1]octa-3,6-dien-2-yl cation: a bishomoantiaromate

Antiaromatic compounds with a closed loop of 4n p-electrons are relatively unstable and often difficult to study. We report in this article the synthesis of alcohols 2-(4'-fluorophenyl)bicyclo[3.2.1]octan-2-ol 11, 2-(4'-fluorophenyl)bicyclo[3.2.1]oct-3-en-2-ol 12, and 2-(4'-fluorophenyl)bicyclo[3.2.1]octa-3,6-dien-2-ol 13 and their transformations into corresponding carbocations 14-16, respectively, in a superacidic medium (FSO3H/SO2ClF) at -120 degrees C. Cations 14-16 are characterized by NMR analysis (1H, 13C, 19F), and 15 and 16 are further characterized by quenching in NaOCH3/H3COH at -120 degrees C. The relative stabilities of 14-16 are determined experimentally by 19F NMR spectroscopy. Cation 16 is found to be experimentally less stable than cation 15 by 3.7 kcal/mol. DFT calculations (structure and energy: B3LYP/6-31G(d); NMR: B3LYP/6-311+G(2d,p)) are performed for alcohols 11-13 and bicyclo[3.2.1]octyl cations 6, 7, 9, 14-16, 26, 28, and 30. In the case of 11-16, data from DFT calculations is in good agreement with experimental data. Because 6,7-dimethylenebicyclo[3.2.1]oct-3-en-2-yl cation 26 is more stable than cation 7 by 1.69 kcal/mol, the inductive effect of sp(2)-hybridized carbon atoms C6 and C7 in carbocations 6 and 16 cannot be the reason for the destabilization of 6 relative to 7 and 16 relative to 15. Destabilization of 6 relative to 7 and 16 relative to 15 and the calculated NICS of 6 (+4.17 ppm) and 16(+3.3 ppm) document that 6 and 16 are bishomoantiaromates.     

Establishing reactor operations from uranium targets used for the production of plutonium

This paper presents results from the examination of a number of archived neutron-irradiated uranium targets used for past plutonium production testing. Three of these targets were destructively characterized using Los Alamos National Laboratory actinide analytical chemistry capabilities. A validated conduct-of-operations protocol was followed for this characterization effort. Chemical analyses included measurements for radionuclides, uranium assay, uranium isotopic abundances, trace actinides, trace metals, and non-metals. Material scientists also examined materials for morphological and microstructural properties and individual particles were examined for trace impurities. After characterization of the targets was completed, a reactor modeling effort was undertaken to corroborate target details in historical records. Time since irradiation calculations utilized both activation and fission products. The described examination of uranium targets has a tremendous impact from a safeguards verification and nuclear forensics perspective.     

Susceptible-infected-recovered epidemics in populations with heterogeneous contact rates

Heterogeneity of contact patterns is recognized as an important feature for realistic modeling of many epidemics. During an outbreak, the frequency of contacts can vary a great deal from person to person and period to period. Contact heterogeneity has been shown to have a large impact on epidemic thresholds and the final size of epidemics. We develop and apply a model which incorporates an arbitrary distribution of contact rates. The model consists of a low-dimensional system of ordinary differential equations which incorporates arbitrary heterogeneity by making use of generating functions of the contact rate distribution. We show further how this model can be applied to the study of simple intervention strategies, such as quarantine of public venues with probability proportional to size. The dynamic model allows us to investigate the effects of gradually implementing such strategies in response to an ongoing epidemic, and we investigate these strategies using data on the contact patterns within a large US city.     

Stabile carbeniumionen—XXIV: Monoaryl-halogen-carbeniumionen. untersuchungen über den substituenteneinfluss von chlor und fluor

The ?-Fluorephenyl-methyl-fluoro-, -chloro and -bromo-carbenium ions as well as the ?-Fluorophenyl-difluoro- and -dichloro-carbenium ions have been prepared in SbF₅/SO₂ClF respectively SbF₅/SO₂ and characterized by ¹H- and ¹⁹F-NMR-Spectroscopy. It could be shown that in the case where the halogen is directly attached to the positive center fluorine does not stabilize better than chlorine.     

Messung von Stickoxiden im ppt-Bereich durch Chemiluminescenz mit O3

Zusammenfassung Ein hochempfindliches Gerät zum Nachweis von NO and NO₂ in der freien Atmosphäre wird vorgestellt. Das Meßprinzip ist Chemiluminescenz mit O₃. NO₂ wird durch einen vorgeschalteten Photolysekonverter in NO umgewandelt. Die Nachweisgrenze (2) beträgt bei einer Integrationszeit von 200 s ca. 5 ppt für NO und ca. 10 ppt für NO₂. Mögliche Interferenzen werden durch eine verbesserte Bestimmung des Nullpunkts erfaßt und korrigiert. Durch diese Prozedur werden innerhalb der Nachweisgrenze keine Querempfindlichkeiten mehr beobachtet. Die Eichung ist auf NBS-Standards zurückgeführt und stimmt innerhalb 10% mit unabhängigen Verfahren überein. Messungen des Vertikalprofils von NO und NO₂ in der Troposphäre demonstrieren die Leistungsfähigkeit des Geräts.

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Measurements of nitrogen oxides at ppt levels by chemiluminescence with O₃

Summary A sensitive chemiluminescent detector for the measurement of NO and NO₂ in the unpolluted atmosphere is described. For NO₂ measurement, a photolytic converter is employed. For a 200 s integration time, a detection limit (2) of 5 and 10 ppt is achieved for NO and NO₂, respectively. Interferences are measured and corrected by using a chemical zeroing procedure. Remaining interferences are below the detection limit. The calibration is based on NBS standards and agrees with independent techniques within 10%. Measurements of the vertical profile of NO and NO₂ in the troposphere exemplify the performance of the instrument.

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Herrn Prof. Dr. W. Fresenius zum 70. Geburtstag gewidmet