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Podstawowe techniki eksperymentalne spektroskopii NMR w fazie ciekłej

100%

Koźmiński W.

Wiadomości Chemiczne

2005

tom [Z] 59, 1-2

107--120

General overview of most important NMR techniques and applications for organic and bioorganic molecules in liquids is given. The sensitivity of NMR experiments is discussed with regard to nuclear properties, Bo field, applied method of excitation and detection, and finally concentration. In the next chapter the principles and consequences of quadrature detection are discussed. The most important techniques of quadrature detection in directly and indirectly detected domains are exemplified. In the next point the principles, advantages and disadvantages of coherence selection techniques via phase cycling and Pulsed Field Gradients are indicated and compared with respect to various applications. In the last part of present article the most important homo- (COSY, TOCSY, NOESY, and ROESY) and heteronuclear (HSQC, HMQC/HMBC) techniques used in NMR investigations in liquids are briefly reviewed. The characteristic features and experimental problems of these methods are discussed with respect to usual applications in chemistry and biochemistry.

Evidence for methyl nitrite as an exhaust component from engines with certain fuels

70%

Joseph P. M.

Archives of Environmental Protection

2008

tom Vol. 34, no. 3

21-31

In some areas of the United States (US), asthma prevalence has reached historically unprecedented highs. Three peer-reviewed studies in New York City found prevalence rates among children from 25% to 39%. That is not true in all places. For example, prevalence in Miami, Florida , was estimated to be only 6-10%. A recent study in major cities in Georgia found only 8.5%. One study in California found asthma prevalence was unrelated to local concentrations of criterion pollutants. In the US, all criterion pollutants, including PM2.5, show a downward trend over the last two decades. These facts argue against any significant influence of criterion pollutants in this crisis.These facts suggest that an unrecognized ambient pollutant may be the cause. One important study in southern California in mid-summer measured pulmonary function in children as it was related to outdoor ozone pollution. They found a negative association: higher levels of ozone were associated with improved respiratory function. We call this a "Paradoxical Ozone Association" (POA). Further evidence for a POA appears in seven other studies in Los Angeles, London, Scotland, and southeastern Canada.One plausible explanation for these observations would be the production of methyl nitrite (MN) as an exhaust product of MTBE in gasoline. Unlike ozone, MN is rapidly destroyed by sunlight. All of the POA studies were done in regions with significant methyl ether in gasoline. This explanation is strengthened by the observation that a POA has not been seen in regions without ether in gasoline.A previous AWMA paper proposed a plausible chemical model predicting that MTBE in gasoline will create MN in the exhaust. MN is highly toxic and closely related alkyl nitrites are known to induce respiratory sensitivity in humans. Funding to measure MN has not been available.