Hydrogenation of solid hydrogen cyanide HCN and methanimine CH2NH at low temperature

International audienceContext. Hydrogenation reactions dominate grain surface chemistry in dense molecular clouds and lead to the formation of complex saturated molecules in the interstellar medium. Aims. We investigate in the laboratory the hydrogenation reaction network of hydrogen cyanide HCN. Methods. Pure hydrogen cyanide HCN and methanimine CH2NH ices are bombarded at room temperature by H-atoms in an ultra-high vacuum experiment. Warm H-atoms are generated in an H2 plasma source. The ices are monitored with Fourier-transform infrared spectroscopy in reflection absorption mode. The hydrogenation products are detected in the gas phase by mass spectroscopy during temperature-programmed desorption experiments. Results. HCN hydrogenation leads to the formation of methylamine CH3NH2, and CH2NH hydrogenation leads to the formation of methylamine CH3NH2, suggesting that CH2NH can be a hydrogenation-intermediate species between HCN and CH3NH2. Conclusions. In cold environments the HCN hydrogenation reaction can produce CH3NH2, which is known to be a glycine precursor, and to destroy solid-state HCN, preventing its observation in molecular clouds ices

Feasibility and efficacy of early lung cancer diagnosis with chest computed tomography in HIV-infected smokers

International audienceOBJECTIVE: Lung cancer screening with chest computed tomography (CT) is beneficial in smokers aged 55 to 74 years. We studied the risks, benefits and feasibility of early lung cancer diagnosis with CT in HIV-infected smokers. DESIGN AND SETTING: French, multicentre, single round chest CT study in France, realized between February 2011 and June 2012. PARTICIPANTS: Patients were HIV-infected smokers at least 40 years, at least 20 pack-years, with a CD4 T-lymphocyte nadir count below 350 cells/μl. INTERVENTION: Single chest CT with a proposed standardized workup algorithm of positive images. MAIN OUTCOME MEASURE: The outcome was the number of histologically proven lung cancers diagnosed by CT with a 2-year follow-up. RESULTS: Median age of the 442 included patients was 49.8 years, 81.6% were under 55 years, 84% were men, median smoking was 30 pack-years, median nadir and last CD4 cell counts were 168 and 574 cells/μl, respectively, and 90% of patients had a plasma HIV RNA below 50 copies/ml. A positive image at baseline was reported in 94 (21%) patients, and 15 (3.4%) patients had 18 invasive procedures with no serious adverse events. Lung cancer was diagnosed in 10 patients (six at early stages), of which nine (2.0%, 95% confidence interval: 0.9-3.8) were CT detected, and eight in patients below 55 years. CONCLUSION: Early lung cancer diagnosis with CT in HIV-infected smokers was feasible, safe, and yielded a significant number of cancers. Lung cancer screening of HIV-infected smokers with an important history of immunodeficiency revealed a substantial number of cancers at younger ages than the targeted range in the general populatio

Photochimie des Carboxamides (formamide, urée) (étude par spectrométrie infrarouge et application au milieu interstellaire)

La comparaison de spectres ISO de glaces interstellaires dans la région autour de 1700cm-1 avec le spectre obtenu en laboratoire, après irradiation VUV de HNCO et de ses photo-produits dans la glace, conduit à des similitudes telles que nous pouvons envisager la présence de formaldéhyde, de formamide (HC(O)NH2) et d'urée (NH2(CO)NH2) dans les glaces interstellaires. L'étude du comportement VUV (Vacuum Ultra-Violet) de l'urée et du formamide à basse température en matrice cryogénique et en phase solide permettra donc à la fois d'améliorer les modèles de chimie interstellaire mais aussi d'améliorer notre connaissance de la photochimie des amides qui reste jusqu'alors assez mal connue. La photolyse du formamide et de l'urée (R-CO-NH2) en matrice montre l'existence de deux voies prédominantes, conduisant à la formation de HNCO + RH et CO + RNH2. Nous avons également mis en évidence, pour la première fois que ces deux amides via la transition n-p*, se décomposaient pour former en matrice le complexe HNCO : RH mais aussi RCN : H2O. Ce processus de déshydratation photochimique est réalisé en deux étapes : (i) isomérisation de l'amide en acide imidique (R(OH)C=NH) réalisée à partir de la transition n-p*, (ii) décomposition photochimique de l'acide imidique en RCN + H2O mais aussi HNCO + RH. En phase condensée (solide pur et matrice d'eau), nous avons montré que ces deux amides pouvaient être une source d'ion OCN-, de CO et de C02, mais également de nitrile R-CN. Au cours de notre étude nous avons également montré que le carbodiimide HNCNH pouvait être formé dans les grains interstellaires à partir du cyanamide NH2CN à la fois par un processus photochimique mais aussi par un processus d'isomérisation thermique catalysé par une surface de glace d'eau.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

IR induced photochemistry of glycolaldehyde in nitrogen matrix

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Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

International audienceSurface processes and radical chemistry within interstellar ices are increasingly suspected to play an important role in the formation of complex organic molecules (COMs) observed in several astrophysical regions and cometary environments. We present new laboratory experiments on the low-temperature solid state formation of complex organic molecules – glycolaldehyde, ethylene glycol, and polyoxymethylene – through radical-induced reactivity from VUV photolysis of formaldehyde in water-free and water-dominated ices. Radical reactivity and endogenous formation of COMs were monitored in situ via infrared spectroscopy in the solid state and post photolysis with temperature programmed desorption (TPD) using a quadripole mass spectrometer. We show the ability of free radicals to be stored when formed at low temperature in water-dominated ices, and to react with other radicals or on double bonds of unsaturated molecules when the temperature increases. It experimentally confirms the role of thermal diffusion in radical reactivity. We propose a new pathway for formaldehyde polymerisation induced by HCO radicals that might explain some observations made by the Ptolemy instrument on board the Rosetta lander Philae. In addition, our results seem to indicate that H-atom additions on H 2 CO proceed preferentially through CH 2 OH intermediate radicals rather than the CH 3 O radical

Detection of glyceraldehyde and glycerol in VUV processed interstellar ice analogues containing formaldehyde: a general formation route for sugars and polyols

International audienceComplex organic molecules (COMs) have been identified toward high-and low-mass pro-tostars as well as molecular clouds. Among them sugar-like and polyol two carbon-bearing molecules such as glycolaldehyde and ethylene glycol are of special interest. Recent laboratory experiments have shown that they can efficiently be formed via atom addition reactions between accreting H-atoms and CO molecules or via energetic processes (UV, electrons) on ice analogues containing methanol or formaldehyde. In this study we report new laboratory experiments on the low temperature solid state formation of complex organic molecules-the first sugar glyceraldehyde and its saturated derivative glycerol-through VUV photolysis performed at three different temperatures (15, 50 and 90 K) of astrochemically relevant ices composed of water and formaldehyde. We get evidence that the species production depends on the ice temperature during photolysis. The results presented here indicate that a general scheme of aldose and polyol formation is plausible and that heavier COMs than GA and EG could exist in interstellar environments. We propose a general pathway involving radical-formaldehyde reactions as common initiation step for aldose and polyol formation. Future telescope observations may give additional clues on their presence in star forming regions as observations are currently limited because of the detection thresholds

Vacuum ultraviolet (VUV) photodecomposition of urea isolated in cryogenic matrix: First detection of isourea

International audienceVacuum ultraviolet (VUV) irradiation at wavelengths of lambda > 160 nm of urea-h(4) (NH2CONH2) and urea-d(4) (ND2COND2) has been monitored by Fourier transform infrared spectroscopy in argon and xenon matrixes. Several primary photoproducts, such as HNCO:NH3 (isocyanic acid:ammonia), CO:N2H4 (carbon monoxide: hydrazine) molecular complexes, and isourea (H2N(OH)C=NH), which is reported for the first time, were characterized. The assignment of complexes was achieved by co-depositing the pairs of respective species, whereas the isourea identification was based on the comparison between the experimental and theoretical (B3LYP) infrared spectra. Isourea is found in the argon matrix in its most stable (s-Z)-(E) configuration. It is an intermediate in the VUV decomposition process; its dehydration leads to the NH2CN:H2O complex. In the xenon matrix, the photochemistry of urea yields the HNCO:NH3 complex as a major product, whereas the CO:N2H4 complex is observed in trace amounts. The observed differences between the argon and xenon matrixes suggest the crossing between S, and T, potential surfaces of urea to be responsible for the formation of the HNCO:NH3 complex. A comparison is also performed with other carboxamides, such as formamide (HCONH2) or acetamide (CH3CONH2)

Methanol ice VUV photoprocessing: GC-MS analysis of volatile organic compounds

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Carbodiimide production from cyanamide by UV irradiation and thermal reaction on amorphous water ice

International audienceCyanamide (NH2CN), an interstellar molecule, is a relevant molecule in prebiotic chemistry, because it can be converted into urea in liquid water. Carbodiimide (HNCNH) the most stable cyanamide isomer. is able to assemble amino acids into peptides. In this work, using FTIR spectroscopy, we show that carbodiimide can be formed from cyanamide at low temperature (10 K), by a photochemical process in argon matrix, in water matrix, or in solid film. We also report experimental evidence about the carbodiimide formation when cyanamide is condensed at low temperature (50-140 K) on an amorphous water ice surface, or when it is trapped in the water ice. The water ice acts as a catalyst. This isomerization reaction occurs at low temperature 14 (T < 100 K), which agrees with those expected in the interstellar clouds composed of dust grains in which water is the most predominant compound. Finally, the hydrolysis reaction of cyanamide or carbodiimide leading to urea or isourea formation is not observed under our experimental conditions