Sampling and sample-preparation strategies based on solid-phase microextraction for analysis of indoor air

Applications of solid-phase microextraction (SPME) to the sampling and analysis of volatile organic compounds in indoor air are reviewed, including a summary of quantification methods, coatings, compounds, concentrations, sampling locations and times, and detection limits. Strategies for on-site and off-site sampling and analysis, advantages and challenges associated with SPME for air sampling are discussed.     

Nucleoside H-Phosphonates. 17. Synthetic and (31)P NMR Studies on the Preparation of Dinucleoside H-Phosphonothioates

Formation of H-phosphonothioate diesters via condensation of H-phosphonate monoesters with a hydroxylic component in the presence of various coupling agents and possible side reactions that may accompany this process were studied using (31)P NMR spectroscopy. Optimal reaction conditions, which eliminate or significantly suppress the side reactions, have been designed and assessed in syntheses of dinucleoside H-phosphonothioate diesters.     

Spectroscopic and theoretical investigation of molecular complexes of 2,4,6-trinitropyridine-1-oxide with some pyridine derivatives

Summary Stability constants and enthalpies of formation were determined forEDA complexes of 2,4,6-trinitropyridine-1-oxide (TNPO) with some pyridine bases. Energies of transition,hv _CT , calculated by the SCF MO CI-1 PPP method fit well the corresponding experimental data. Based on these results, geometries for the systems under study are proposed.

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Spektroskopische und theoretische Untersuchung von molekularen Komplexen des 2,4,6-Trinitropyridin-1-oxids mit einigen Pyridinderivaten

Zusammenfassung Es wurden Stabilitätskonstanten und Bildungsenthalpiewerte einigerEDA-Komplexe von 2,4,6-Trinitropyridin-1-oxid mit ausgewählten Pyridinbasen bestimmt. Dabei wurde eine gute Übereinstimnmung zwischen den Anregungsenergienhv _CT aus den UV-VIS-Spektren und den mit der SCF-MO-CI-1 PPP-Methode errechneten Werten gefunden. Es werden für die untersuchten Komplexe entsprechende Strukturen vorgeschlagen.

     

Stoffwechselprodukte von Mikroorganismen. 237. Mitteilung. (2S, 3R, 4R, 6R)-2,3,4-Trihydroxy-6-methylcyclohexanon aus zwei Actinomyceten-Stämmen

(2S, 3R, 4R, 6R)-2,3,4-Trihydroxy-6-methylcyclohexanone from Two Strains of Actinomycetes A tetrazolium-blue positive compound was isolated from two strains of acinomycetes. Its constitution and relative configuration 1 were determined by spectroscopic methods, and the absolute configuration by degradation to (+)-(R)-methylsuccinic acid.     

Circular dichroism of 9,10-dihydrophenanthrene derivatives reveals both the absolute configuration and conformation: a novel approach to Mislow's helicity rule

The absolute configuration and the conformation of 9,10-trans-disubstituted 9,10-dihydrophenanthrenes, known chiral metabolites of phenanthrene-9,10-oxide, have been determined by circular dichroism. The absolute configuration assignment is based on the sign of the long-wavelength Cotton effect (A-band), which is conformation invariant and originates from benzylic chirality. This provides a new interpretation of the Mislow biphenyl-helicity rule for the case of the 9,10-dihydrophenanthrene chromophore. The sign of the B-band Cotton effect reflects the conformation of the biphenyl chromophore in 9,10-dihydrophenanthrenes. It is shown that the origin of chiroptical properties of 9,10-dihydrophenanthrenes is closely related to those of 5,6-trans-disubstituted 1,3-cyclohexadienes.     

Ab initio calculations of relativistic and electron correlation effects in polyatomics using the universal Gaussian basis set: XeF2

Ab initio accurate all-electron relativistic molecular orbital Dirac–Fock self-consistent field calculations are reported for the linear symmetric XeF₂ molecule at various internuclear distances with our recently developed relativistic universal Gaussian basis set. The nonrelativistic limit Hartree–Fock calculations were also performed for XeF₂ at various internuclear distances. The relativistic correction to the electronic energy of XeF₂ was calculated as ～ ?215 hartrees (?5850 eV) by using the Dirac–Fock method. The dominant magnetic part of the Breit interaction correction to the nonrelativistic interelectron Coulomb repulsion was included in our calculations by both the Dirac–Fock–Breit self-consistent field and perturbation methods. The calculated Breit correction is ～6.5 hartrees (177 eV) for XeF₂. The relativistic Dirac–Fock as well as the nonrelativistic HF wave functions predict XeF₂ to be unbound, due to neglect of electron correlation effects. These effects were incorporated for XeF₂ by using various ab initio post Hartree–Fock methods. The calculated dissociation energy obtained using the MP 2(full) method with our extensive basis set of 313 primitive Gaussians that included d and f polarization functions on Xe and F is 2.77 eV, whereas the experimental dissociation energy is 2.78 eV. The calculated correlation energy is ～ ?2 hartrees (?54 eV) at the predicted internuclear distance of 1.986 Å, which is in excellent agreement with the experimental Xe—F distance of 1.979 Å in XeF₂. In summary, electron correlation effects must be included in accurate ab initio calculations since it has been shown here that their inclusion is crucial for obtaining theoretical dissociation energy (D_e) close to experimental value for XeF₂. Furthermore, relativistic effects have been shown to make an extremely significant contribution to the total energy and orbital binding energies of XeF₂. © 1995 John Wiley & Sons, Inc.     

Microanalysis of Volatile Organic Compounds (VOCs) in Water Samples – Methods and Instruments

Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants. Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages of these techniques are discussed and novel developments are also taken into consideration.     

Some Gauge-natural operators on linear connections

We determine explicitly all geometrical operators transforming a linear connection on a vector bundle :EM and a classical linear connection on the base manifoldM into a classical linear connection on the total spaceE.     

Cauchy boundary andb-incompleteness of space-time

It is shown that if a space-time (M, g) is time-orientable and its Levi-Civita connection [in the bundle of orthonormal frames over (M, g)] is reducible to anO(3) structure, one can naturally select a nonvanishing timelike vector field and a Riemann metricg ⁺ onM. The Cauchy boundary of the Riemann space (M, g ⁺) consists of endpoints ofb-incomplete curves in (M, g); we call it theCauchy singular boundary. We use the space-time of a cosmic string with a conic singularity to test our method. The Cauchy singular boundary of this space-time is explicitly constructed. It turns out to consist of what should be expected.