Formaldehyde, glyoxal, and methylglyoxal in air and cloudwater at a rural mountain site in central Virginia

As part of the Shenandoah Cloud and Photochemistry Experiment (SCAPE), we measured formaldehyde (HCHO), glyoxal (CHOCHO), and methylglyoxal (CH3C(O)CHO) concentrations in air and cloudwater at Pinnacles (elevation 1037 m) in Shenandoah National Park during September 1990. Mean gas‐phase concentrations of HCHO and CHOCHO were 980 and 44 pptv, respectively. The concentration of CH3C(O)CHO rarely exceeded the detection limit of 50 pptv. Mean cloudwater concentrations of HCHO and CHOCHO were 9 and 2 μM, respectively; the mean CH3C(O)CHO concentration was below its detection limit of 0.3 μM. The maximum carbonyl concentrations were observed during stagnation events with high O3, peroxides, and CO. Outside of these events the carbonyls did not correlate significantly with O3, CO, or NOy. Carbonyl concentrations and concentration ratios were consistent with a major source for the carbonyls from isoprene oxidation. Oxidation of CH4 supplies a significant background of HCHO. The carbonyl concentrations were indistinguishable in two size fractions of cloudwater having a cut at d=18 μm. Gas‐ and aqueous‐phase concentrations of HCHO from samples collected during a nighttime cloud event agree with thermodynamic equilibria within a factor of 2. Samples collected during a daytime cloud event show HCHO supersaturation by up to a factor of 4. Positive artifacts in the cloudwater samples due to hydrolysis of hydroxymethylhydroperoxide (HOCH2OOH) could perhaps account for this discrepancy

Detection of methyl, hydroxymethyl and hydroxyethyl hydroperoxides in air and precipitation.

It is well established that organic peroxides are formed by OH-radical-induced oxidation of hydrocarbons under atmospheric conditions1. Peroxyacyl nitrates have been known to be constituents of polluted air since the 1950s2,3. In a recent study we have shown that the gas-phase reaction of ozone with a variety of natural and anthropogenic alkenes can contribute to the formation of hydro-philic organic peroxides4. Indications that such peroxides are actually present in the environment have been obtained previously by measurements of the peroxide content of cloudwater and rain. In the absence of a specific analytical method the peroxide content after selective enzymatic destruction of the hydrogen peroxide was taken to be the organic peroxide fraction5-7. In this letter we report the determination by high-performance liquid chroma-tography of methyl (MHP; CH3OOH), hydroxymethyl (HMP; HOCH2OOH) and 1-hydroxyethyl (HEP; CH3CH(OH)OOH) hydroperoxides, in addition to H2O2, and present some preliminary concentration ranges in air and precipitation. The existence of this class of atmospheric trace constituents raises questions about possible adverse biological effects

Hydroxymethyl hydroperoxide and bis(hydroxymethyl) peroxide fom gas-phase ozonolysis of naturally occurring alkenes.

Ozonolysis is one of the main pathways for degradation of alkenes in the atmosphere, where the reaction is associated with smog formation1 and the haze that often occurs over forests2,3. In recent decades, ground-level ozone concentrations have greatly increased4,5. The possibility of significant damage to plants by ozone and its products has consequently been raised in discussions of ‘waldsterben’, the large-scale dying of trees in northern Europe and North America6–9. With particular regard to the formation of peroxides, we have used 13C- nuclear magnetic resonance (NMR) to investigate the water-soluble products of the gas-phase ozonolysis of isoprene and several terpenes, which are emitted into the atmosphere in large quantities (108–109 tonnes yr−1 globally) by trees3,10,11. All these alkenes yield bis(hydroxymethyl)peroxide (BHMP; HOCH2OOCH2OH). The apparent precursor of BHMP is hydroxymethyl hydroperoxide (HMP; HOCH2OOH), which results from addition of water to the ozonolysis intermediate. As both HMP and BHMP have various toxic effects on plant cells and enzymes12–14, we point out here an indirect way by which ozone may adversely affect forests

Erfassung organischer Chemikalien biogenen und anthropogenen Ursprungs in unterschiedlich belasteten Regionen mit und ohne Waldschaeden Endbericht

Available from TIB Hannover: FR 1766 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Metal-modified nucleobase pairs and triplets as cytosine receptors

A preorganized cationic receptor 2 for cytosine (C) is described which is composed of trans-a2PtII (a=NH3 or CH3NH2) cross-linked modules with adenine (A), guanine (G), and uracil (U) or thymine (T) model nucleobases. The functions of these three modules are as follows: i) Adenine orientates the two other bases at right angles, thus producing the L-shape of the receptor. ii) Guanine is the primary receptor. iii) Uracil or thymine act as coreceptors. Compared with the normal Watson–Crick pair between G and C, the association constant between 2 and C increases by a factor of 3 (in DMSO). As deduced from 1H NMR spectroscopy and confirmed by the X-ray crystal structure of the C adduct 4 b, cytosine is fixed through five hydrogen bonds to the receptor, one of which involves the aromatic H(5) of C. A comparison of C binding is made with a structurally related linkage isomer receptor as well as the precursor molecule trans-[a2PtAG]2+. The potential of modular, cationic receptors is illustrated