Photochemistry of a 1 : 1 hydrogen-bonded CH3CN : HCOOH complex under astrochemically-relevant conditions.

The interstellar medium is characterized by a complex chemistry, especially on the surface of ice grains in molecular clouds. In an attempt to investigate possible reactions leading to exobiologically-relevant species, laboratory experiments dealing with the formation of nitrogen- and oxygen-bearing organic molecules from precursors that are present in the solid phase, on the surface of ice grains, are of primary importance. The aim of the present work was to investigate the formation of a non-covalent complex between CH3CN and HCOOH. For that purpose, FT-IR spectroscopy was used in combination with the rare-gas matrix technique. The experimental spectra were compared with the theoretical ones obtained with the help of quantum-chemical calculations. This combination between a theoretical and an experimental approach allowed us to propose a structure for the hydrogen-bonded complexes experimentally observed.

Study of interaction between NO radicals and Martin's spirosilane by means of IR spectroscopy.

The matrix isolation method is used to record the IR spectrum of C18H8O2F12Si in the 4000-500 cm(-1) range. To gain an IR spectrum with a sufficient resolution, this technique was used with neon as the dilution medium at 5 K. The generated species were characterized by in situ fourier transform infrared (FT-IR) spectroscopy. Once the Martin's spirosilane 1 (C18H8O2F12Si) was characterized, its reactivity toward NO was investigated under the same experimental conditions (i.e., using neon as a dilution medium at 5 K). In this case, the use of neon at very low temperature leads to the formation of a chemically inert matrix in which the species are trapped and isolated from one another, thus hindering consecutive reactions. As a consequence, intermediates can be observed. This approach allowed us to characterize the NO adduct, leading to the formation of 1-(NO). Concentration effects as well as annealing experiments were carried out. In addition to this experimental approach, products were identified by using reference spectra. Our results proved that, in the dilute phase, the reaction between 1 and NO radicals leads to the formation of an adduct. This stable species can further react with NO to form a more stable compound: 1-(NO)2. This proves the ability of such species to trap NO.

A neon-matrix isolation study of the reaction of non-energetic H-atoms with CO molecules at 3 K.

The efficiency of HCO formation stemming from non-energetic H-atoms and CO molecules is highlighted both in the condensed phase and within a neon matrix environment, which is half-way between the condensed-phase and gas-phase. Our experiments demonstrated that HCO production within the neon-matrix needed very little or no activation energy. The efficiency of HCO formation depended only on the capability of H-atoms to diffuse in the solid and to subsequently encounter CO molecules. The novelty of the presented matrix experiment sheds light on the debated question of whether activation energy is required in order to produce HCO, because of the use of non-energetic ground state H-atoms within the neon-matrix.

Preliminary study of the influence of environment conditions on the successive hydrogenations of CO.

The successive hydrogenation of CO has been investigated by two methods. The first is hydrogenation of a CO surface. The second is co-injection of CO molecules and H atoms. Both methods have been performed at 3 and 10 K. In the first method, the interaction of H atoms with solid CO at 10 K shows that CO is consumed to form H(2)CO and CH(3)OH. No trace of species such as HCO and CH(3)O is detected. No product was observed when the same experiment was performed at 3 K. In the second method, when H and CO are codeposited at 10 K, HCO and CH(3)O are observed. In fact, the yield of these intermediate species depends on the amount of the H radicals interacting with CO molecules. At 3 K, the presence of H(2) in the solid screens the hydrogenation reaction. This causes a termination for the reaction in the stage of the formation of HCO and H(2)CO. At 10 K, H(2) cannot condense, and the reaction between CO and H is total. In this case, species such as HCO, H(2)CO, CH(3)O, and CH(3)OH are observed.

Influence of water in the UV-induced chemistry of methanol in the solid phase.

UV-irradiated methanol (CH3OH) in water ice at 3 K has been investigated with infrared spectroscopy and compared with pure methanol. The main byproducts detected are formaldehyde (H2CO), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and ethylene glycol (C2H4(OH)2). The production of H2CO, CO2, and CO is enhanced in water ice, resulting from cross reactions between the byproducts of methanol with those of water (OH and H2O2).

Nebulized sildenafil is a selective pulmonary vasodilator in lambs with acute pulmonary hypertension.

OBJECTIVE: To determine whether inhalation of aerosolized sildenafil with and without inhaled nitric oxide (NO) causes selective pulmonary vasodilation in a sheep model of pulmonary hypertension. DESIGN: A controlled laboratory study in instrumented, awake, spontaneously breathing lambs. SETTING: Animal research laboratory affiliated with a university hospital. SUBJECT: Twenty Suffolk lambs. INTERVENTIONS: Lambs were instrumented with a carotid artery catheter, a pulmonary artery catheter, and a tracheostomy tube and studied awake. After baseline measurements, pulmonary hypertension was induced by the continuous infusion of U46619, a thromboxane A2 analog. After breathing three concentrations of inhaled NO (2, 5, and 20 ppm), lambs were divided into two groups. Group 1 (n = 7) breathed aerosols containing 1, 10, and 30 mg of sildenafil alone, and group 2 (n = 4) simultaneously breathed NO (2 and 5 ppm) and aerosols containing 10 mg of sildenafil. Hemodynamic measurements were obtained before and at the end of each drug administration. Venous admixture was calculated, and plasma cyclic guanosine monophosphate and sildenafil concentrations were measured. MEASUREMENTS AND MAIN RESULTS: Aerosols containing 10 mg and 30 mg of sildenafil selectively decreased the pulmonary artery pressure by 21% +/- 3% and 26% +/- 3%, respectively (p < .05 vs. baseline pulmonary hypertension). When 10 mg of sildenafil was inhaled while simultaneously breathing 2 ppm and 5 ppm NO, the pulmonary artery pressure decreased by 35% +/- 3% and 43% +/- 2% (p < .05 vs. baseline pulmonary hypertension). Inhaled sildenafil did not impair systemic oxygenation, increase right-to-left intrapulmonary shunting, or impair the ability of inhaled NO to reduce right-to-left shunting. CONCLUSIONS: Nebulized sildenafil is a selective pulmonary vasodilator that can potentiate the pulmonary vasodilating effects of inhaled NO.