Absence Of NO Research Articles

Redox interplay at copper oxide-(Ce,Zr)O x interfaces: influence of the presence of NO on the catalytic activity for CO oxidation over CuO/CeZrO 4

A catalyst composed of copper oxide supported on cerium–zirconium mixed oxide (CuO x /CeZrO 4) has been studied with respect to its activity for CO oxidation under stoichiometric conditions employing either oxygen or oxygen with a small amount of NO as oxidant. The nature of copper oxide entities, as well as the redox properties of the catalyst following interactions with CO and O 2–NO, has been studied by XPS, EPR, and static NO adsorption infrared spectroscopy while in situ DRIFTS has been employed to follow processes occurring at the catalyst surface under reaction conditions. Characterization of the copper oxide species in both fully oxidized and partially reduced states reveals that they are significantly affected by interactions with the underlying support. On the basis of catalytic activity results and in combination with analysis of the evolution of particular Cu + carbonyls, comparing the CO oxidation reaction in the presence and absence of NO, it is proposed that the two basic factors affecting the catalytic performance of this type of system are the facility for achieving a partially reduced state for the copper oxide phase at the interfacial zone and the redox properties of the CuO x /CeZrO 4 interface.

Nitrosation of cysteine and reduced glutathione by nitrite at physiological pH.

Unlike the formation of nitrosothiols by nitrous acid, our study revealed that NO2- effectively reacted with L-cysteine or reduced glutathione (GSH) at pH 7.0 and 7.4, to form orange-pink products of S-nitrosocysteine (CySNO) or S-nitrosoglutathione (GSNO). The reactions were in a concentration-dependent manner. These products exhibited not only peak absorbances at around 340 and 540 nm, but also unique colors and patterns of mobility on cellulose thin layer chromatographic plates. In comparison, the S-nitrosation of dithiothreitol was noted exclusively under acidic pH. In addition, the S-nitrosation of hemoglobin (Hb) by either peroxynitrite (PN) or NO2- at pH 6.0 was detected via Western blot. The half-life of degradation of CySNO in NO2- solution was significantly shorter than that of GSNO at a wide range of pH. In the absence of NO2-, degradation of GSNO was facilitated by incubation with L-cysteine, but not L-serine. In the signaling process involving NO -->PN --> NO2- --> CySNO/GSNO --> NO, L-cysteine may function as a NO-carrier to reach shorter-distance targets, and also an "activator" to release NO from GSNO. Furthermore, L-cysteine may play a vital role in reducing (severe) oxidative stress.

Elucidation of the Surprising Role of NO in N 2 O Decomposition over FeZSM-5

The decomposition of N2O is strongly promoted by NO over steam-activated FeZSM-5. The promoting effect of NO is catalytic, and in addition to NO2, О2 is formed much more extensively at lower temperatures than in the absence of NO. The promotion effect only requires low NO concentrations in the feed, with no significant improvements at molar NO/N2O feed ratios higher than 0.25. No inhibition by NO was identified even at a molar NO/N2O feed ratio of 10, suggesting different sites for NO adsorption and oxygen deposition by N2O. The latter sites seem to be remote from each other. Transient experiments using in situ FT-IR/MS and Multitrack over FeZSM-5 further elucidate the mechanism of NO promotion. The release of oxygen from the catalyst surface during direct N2O decomposition is a rate-determining step due to the slow oxygen recombination, which is favored by high reaction temperatures. NO addition promotes this oxygen desorption, acting as an oxygen transfer agent, probably via NO2 species. Adsorbed NO may facilitate the migration of atomic oxygen to enhance their recombination. Less than 0.9% of Fe seems to participate in this promotion. A model is proposed to explain the phenomena observed in NO-assisted N2O decomposition, including NO2 decomposition.

Kinetic and Spectroscopic Characterization of Cluster-Derived Supported Pt–Au Catalysts

Silica-supported bimetallic Pt–Au catalysts prepared via different synthetic routes have been investigated in terms of their structural properties, adsorption of CO, and catalytic activity for the selective catalytic reduction of NO by propylene, the oxidation of propylene in the absence of NO, and the 16O/ 18O homoexchange reaction. Catalysts prepared by incipient wetness impregnation from individual Pt and Au precursors exhibited characteristics very similar to those of monometallic Pt catalysts, indicating that in these cases the presence of Au did not affect the catalytic performance of Pt in any significant way. This behavior is consistent with a model in which the two metals remain segregated due to their miscibility gap, and only Pt participates in the adsorption of CO and the reactions under consideration. In contrast, catalysts prepared from a Pt 2Au 4(CC tBu) 8 organo–bimetallic cluster precursor exhibited different behavior both in terms of CO adsorption and their catalytic activity for the three reactions examined. The combination of the kinetic, spectroscopic, and structural characterization data suggests that in this case Pt and Au remain intimately mixed in the form of Pt–Au bimetallic particles and that the presence of Au in these particles modifies the behavior of Pt.

Simultaneous Removal of SOx and NOx Using Slaked Lime at Low Temperature

The activity of slaked lime for the simultaneous absorption of SOx and NOx from flue gases of coal combustion has been studied using a fixed bed reactor at 90 °C. The slaked lime samples were prepared by swelling the natural lime using water vapor. It was found that NO and SO2 enhanced the adsorption of each other. The results of IR showed that SO2 was absorbed as SO42- salt by Ca(OH)2 in the presence of NO; however, it was mainly absorbed as SO32- salt in the absence of NO. It is interesting that NO could not be absorbed by the slaked lime without SO2 at the low temperature, while it was converted to NO3- salts with the presence of SO2. This implied that some species formed from SO2 played a role as catalysts for the adsorption of NO by the slaked lime, which indicated a possible way to remove SOx and NOx simultaneously from the flue gases of coal combustion.

Differential mechanisms of endothelium-dependent vasodilator responses in human myometrial small arteries in normal pregnancy and pre-eclampsia.

Pre-eclampsia is a pregnancy-specific disorder associated with hypertension and proteinuria, characterized by alterations in endothelial cell function. In the present study we have compared responses to the endothelium-dependent vasodilator, bradykinin, in small myometrial arteries from normal pregnant and non-pregnant women and women with pre-eclampsia, in order to assess the relative contributions of nitric oxide, endothelium-derived hyperpolarizing factor (EDHF) and prostanoids in mediating endothelium-dependent vasodilatation. Bradykinin-induced concentration-dependent relaxation in arteries isolated from the three subject groups did not differ with regard to sensitivity or maximum response. Responses to bradykinin in all three groups were unaffected by cyclo-oxygenase inhibition alone, and were similarly unaffected by partial depolarization. The nitric oxide synthase (NOS) inhibitor, N-nitro-l-arginine methyl ester, significantly attenuated the responses to bradykinin in arteries from non-pregnant women and almost abolished responses in arteries from women with pre-eclampsia. However, in arteries from normal pregnant women, bradykinin-induced responses were maintained in the presence of NOS inhibition. Inhibition of NOS combined with partial depolarization abolished responses to bradykinin in these vessels. These results support the suggestion that, in the absence of NO, an EDHF can mediate vasodilator responses to bradykinin during normal pregnancy, an effect not apparent in arteries from non-pregnant women or women with pre-eclampsia. The up-regulation of EDHF-type function may represent a vascular adaptation to normal pregnancy that is absent in pre-eclampsia, and this might contribute to the clinical features of the disease.

NO-Assisted N2O Decomposition over Fe-Based Catalysts: Effects of Gas-Phase Composition and Catalyst Constitution

The decomposition of N2O is strongly promoted by NO over Fe catalysts supported on zeolites (ex-framework FeMFI catalysts, sublimed Fe/ZSM-5, ion-exchanged Fe–ZSM-5, Fe-beta, and Fe–USY) and conventional supports (Fe/Al2O3 and Fe/SiO2) in a wide temperature range (550–900 K). Mixtures of NO and O2 in the N2O-containing feed lead to the same promoting effect as NO only. The promoting effect of NO is catalytic, and in addition to NO2, O2 is formed much more extensively at lower temperatures than in the absence of NO. The promotion effect only requires low NO concentrations in the feed, with no significant improvements at molar NO/N2O feed ratios higher than 0.25. No inhibition by NO was identified even at a molar NO/N2O feed ratio of 10, suggesting different sites for NO adsorption and oxygen deposition by N2O. The latter sites seem to be remote from each other. Multitrack experiments on ex-framework FeZSM-5 show that release of oxygen from the catalyst surface during direct N2O decomposition is a rate-determining step, due to the slow oxygen recombination, which is favored by high reaction temperatures. NO addition promotes this oxygen desorption. Adsorbed NO accommodates oxygen from N2O and the formed adsorbed NO2 can react with a second oxygen from the neighboring site, thus accelerating the recombination of oxygen from N2O. Less than 0.9% of the Fe seems to participate in this promotion. Adsorbed NO may even facilitate the migration of atomic oxygen to enhance their recombination. A model is proposed to explain the phenomena observed in the NO-assisted N2O decomposition, including NO2 decomposition.

Bimetallic PtAu cluster-derived catalysts for the selective catalytic reduction of NO by propylene

The selective catalytic reduction of nitric oxide by propylene in the presence of excess oxygen has been investigated over a series of silica supported Pt and PtAu catalysts. Cluster-derived catalysts were prepared by wet impregnation using a Pt 2Au 4(CC tBu) 8 organometallic cluster precursor, and compared to catalysts obtained by incipient wetness impregnation using individual Pt and Au salts. The addition of Au by co-impregnation resulted only to a small shift (20–25 °C) in the light-off of propylene towards higher temperatures. A markedly different catalytic behavior was observed in the case of cluster-derived catalysts, where a 150 °C delay was observed both in the temperature of maximum NO reduction and the light-off of propylene in the presence and in the absence of NO. Most importantly, the selectivity towards N 2 increased by 50% compared to the monometallic Pt catalysts. The results of characterization studies indicate that the monometallic Pt/SiO 2 and the co-impregnated PtAu/SiO 2 samples have similar metal particle sizes. A more narrow particle size distribution was observed with the cluster-derived bimetallic sample.

Effect of ACE inhibitors and angiotensin II type 1 receptor antagonists on endothelial NO synthase knockout mice with heart failure.

The beneficial effects of ACE inhibitors (ACEi) or angiotensin II type 1 receptor antagonists (AT(1)-ant) are reportedly mediated by NO in heart failure (HF). We hypothesized that in the absence of endothelial NO synthase (eNOS), (1) left ventricular (LV) dysfunction and myocardial remodeling would be more severe after myocardial infarction (MI), and (2) the cardioprotective effect of ACEi and AT(1)-ant would be diminished or absent in mice with HF after MI. eNOS knockout mice (eNOS-/-) and wild-type C57BL/6J (C57) mice (+/+) were subjected to MI by ligating the left coronary artery. One month after MI, each strain was treated with vehicle, ACEi (enalapril, 20 mg/kg per day), or AT(1)-ant (valsartan, 50 mg/kg per day) for 5 months. Echocardiography was performed, and systolic blood pressure was measured before MI and monthly thereafter. Interstitial collagen fraction and myocyte cross-sectional area were examined histologically. We found that (1) compared with C57 mice, eNOS-/- mice that underwent sham surgery had significantly increased systolic blood pressure (P<0.05) and increased LV mass both initially and at 1 to 3 months, although cardiac function and histological findings did not differ between strains; (2) the development of HF and myocardial remodeling were similar after MI in both strains; and (3) ACEi improved cardiac function and remodeling in C57 mice, as evidenced by increased LV ejection fraction (LVEF) and LV shortening fraction (LVSF) and decreased diastolic LV dimension, mass, myocyte cross-sectional area, and interstitial collagen fraction, but these benefits were absent or diminished in eNOS-/- mice (for C57 versus eNOS-/-: increase in LVEF after ACEi, 14.2 +/- 2% versus -4.9 +/- 2.5%, respectively [P<0.001]; increase in LVSF, 8.6 +/- 2.1% versus -7.2 +/- 2.8%, respectively [P<0.01]; and decrease in LV mass, -16.6 +/- 15 versus 73 +/- 23 mm(3), respectively [P<0.01]). AT(1)-ant had benefits similar to those of ACEi, which were also absent or diminished in eNOS-/- mice (for C57 versus eNOS-/-: increase in LVEF after AT(1)-ant, 13.5 +/- 1.8% versus -9.8 +/- 3%, respectively [P<0.001]; increase in LVSF, 6.1 +/- 1.6% versus -3.8 +/- 3.1%, respectively [P<0.01]). Our data suggest that the absence of NO does not alter the development of HF after MI; however, it significantly decreases the cardioprotective effects of ACEi or AT(1)-ant.

Salt-sensitive hypertension in conscious rats induced by chronic nitric oxide blockade

This study examined the effects of alterations in salt-intake on blood pressure (BP) in rats chronically treated intravenously with or without the nitric oxide synthase (NOS) inhibitor N G-nitro- l-arginine methyl ester (L-NAME) (8.6 mg/kg/day). The changes in mean arterial pressure (MAP), the renal cortical and medullary blood flow (CBF and MBF), and the sodium balance were determined by implanted optical fibers and laser-Doppler flow measurement techniques in the conscious rats. The results showed that high salt intake (7.4 mEq/day) elevates CBF (139% ± 15%), but has no significant effect on MAP or MBF in control rats; in L-NAME-treated rats, high salt intake elevates MAP, produces no change in CBF, and decreases MBF (51% ± 14%), as well as increasing the sodium balance (0.26 ± 0.23 mEq/day to 1.29 ± 0.47 mEq/day). The present experiments indicated that NO appears to maintain the MBF during high salt intake and to prevent the changes in MAP, and, in the absence of NO, salt-sensitive hypertension develops. Nitric oxide plays an important role in the development of salt-sensitive hypertension with the change of MBF.

Selective catalytic reduction of NO and NO 2 at low temperatures

The fast SCR reaction using equimolar amounts of NO and NO 2 is a powerful means to enhance the NO x conversion over a given SCR catalyst. NO 2 fractions in excess of 50% of total NO x should be avoided because the reaction with NO 2 only is slower than the standard SCR reaction. At temperatures below 200 °C, due to its negative temperature coefficient, the ammonium nitrate reaction gets increasingly important. Half of each NH 3 and NO 2 react to form dinitrogen and water in analogy to a typical SCR reaction. The other half of NH 3 and NO 2 form ammonium nitrate in close analogy to a NO x storage-reduction catalyst. Ammonium nitrate tends to deposit in solid or liquid form in the pores of the catalyst and this will lead to its temporary deactivation. The various reactions have been studied experimentally in the temperature range 150–450 °C for various NO 2/NO x ratios. The fate of the deposited ammonium nitrate during a later reheating of the catalyst has also been investigated. In the absence of NO, the thermal decomposition yields mainly ammonia and nitric acid. If NO is present, its reaction with nitric acid on the catalyst will cause the formation of NO 2.

The electrical response of evaporated cobalt phthalocyanine thin films on exposure to NO 2

A comprehensive study has been performed to investigate the response of cobalt phthalocyanine (CoPc) thin films to the effects of ambient NO 2. Evaporated CoPc films were provided with interdigitated planar gold electrodes and exposed to NO 2 concentrations of 5–100 ppm. In all cases the samples showed ohmic behaviour at room temperature, with current levels at 10 V applied voltage typically varying between 30 nA in the absence of NO 2 to over 100 nA when exposed to 100 ppm NO 2. The samples were also subjected to cycling of the NO 2 concentration, when the gas supply was alternately switched on and off for periods of 20 min. The response to a step increase in NO 2 concentration, as well as the response when the NO 2 was switched off were investigated. Initially the current increased rapidly, but this became slower after the exposure time increased. When the NO 2 was switched off a sharp decrease in current was observed, followed by a slower decrease. These results were interpreted by reference to earlier work. The NO 2 was initially rapidly chemisorbed onto the surface of the CoPc in the form of NO 2 − ions, which later slowly diffused into the bulk of the material. It was observed that at room temperature an equilibrium concentration could not be obtained within the time period investigated. Adsorption appeared to follow a Freundlich-type power-law isotherm.

Tumoricidal Activity of Endothelial Cells: INHIBITION OF ENDOTHELIAL NITRIC OXIDE PRODUCTION ABROGATES TUMOR CYTOTOXICITY INDUCED BY HEPATIC SINUSOIDAL ENDOTHELIUM IN RESPONSE TO B16 MELANOMA ADHESION IN VITRO

The mechanism of NO- and H(2)O(2)-induced tumor cytotoxicity was examined during B16 melanoma (B16M) adhesion to the hepatic sinusoidal endothelium (HSE) in vitro. We used endothelial nitric-oxide synthetase gene disruption and N(G)-nitro-l-arginine methyl ester-induced inhibition of nitric-oxide synthetase activity to study the effect of HSE-derived NO on B16M cell viability. Extracellular H(2)O(2) was removed by exogenous catalase. H(2)O(2) was not cytotoxic in the absence of NO. However, NO-induced tumor cytotoxicity was increased by H(2)O(2) due to the formation of potent oxidants, likely ( small middle dot)OH and (-)OONO radicals, via a trace metal-dependent process. B16M cells cultured to low density (LD cells), with high GSH content, were more resistant to NO and H(2)O(2) than B16M cells cultured to high density (HD cells; with approximately 25% of the GSH content found in LD cells). Resistance of LD cells decreased using buthionine sulfoximine, a specific GSH synthesis inhibitor, whereas resistance increased in HD cells using GSH ester, which delivers free intracellular GSH. Because NO and H(2)O(2) were particularly cytotoxic in HD cells, we investigated the enzyme activities that degrade H(2)O(2). NO and H(2)O(2) caused an approximately 75% (LD cells) and a 60% (HD cells) decrease in catalase activity without affecting the GSH peroxidase/GSH reductase system. Therefore, B16M resistance to the HSE-induced cytotoxicity appears highly dependent on GSH and GSH peroxidase, which are both required to eliminate H(2)O(2). In agreement with this fact, ebselen, a GSH peroxidase mimic, abrogated the increase in NO toxicity induced by H(2)O(2).

Methanol Oxidation and Its Interaction with Nitric Oxide

An experimental and theoretical study of the oxidation of methanol in the absence and in the presence of NO has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 700−1500 K. The influence of the temperature, oxygen concentration, and presence of NO on the concentrations of methanol, CO, CO2, and NO has been analyzed. A reaction mechanism based on the model of Glarborg et al.1 for hydrocarbons/NO interactions, updated in relation to the methanol reaction subset has been used for calculations. The results show that the oxidation regime of methanol for different air excess conditions is very similar in the absence of NO, but significant differences are observed when NO is present. The presence of NO implies a different behavior depending on the stoichiometry, in the way that such presence results in a inhibition of methanol conversion for richest conditions, while it promotes methanol oxidation for very lean conditions. The experimental results are analyzed in terms of detailed chemistry and the main issues are discussed.

New Pd/CexZr1−xO2/Al2O3 three-way catalysts prepared by microemulsion: Part 2. In situ analysis of CO oxidation and NO reduction under stoichiometric CO+NO+O2

The light-off behavior for CO oxidation and NO reduction under stoichiometric CO+NO+O2 gas mixtures of a series of palladium catalysts supported on ceria–zirconia, ceria–zirconia/alumina and alumina has been examined by means of catalytic activity tests, and by DRIFTS, XANES and EPR spectroscopies. The results show the promoting effect of the Zr–Ce mixed oxide on both reactions. The extent of promotion depends on the characteristics of the promoter entities present for each catalyst and on the nature of the reaction. As observed in the absence of NO, CO oxidation was mainly enhanced by contact between Pd and 3D aggregated promoter entities, although an inhibiting effect of NO on CO oxidation, attributed to passivation of the interface sites due to formation of oxidized states of Pd, was observed at low temperatures. In contrast, the higher activity for NO reduction over catalysts supported on ceria–zirconia/alumina suggests that most active sites for that reaction involve Pd interacting with dispersed promoter entities.

Unique markers of chlorine atom chemistry in coastal urban areas: The reaction with 1,3‐butadiene in air at room temperature

Chlorine atoms are generated in the marine boundary layer, including coastal urban areas, through heterogeneous reactions of sea‐salt particles. However, there are no measurements of tropospheric chlorine atoms, and few measurements of their precursors due to the difficulty in specifically identifying and measuring parts per trillion levels of these highly reactive species. We report here studies which suggest an alternate approach for elucidating the role of chlorine atoms in the chemistry of coastal urban areas: the identification and measurement of unique chlorine‐containing products from the reactions of Cl with organics, in this case 1,3‐butadiene, in air. The reaction of chlorine atoms with 1,3‐butadiene (19–61 ppm), which is emitted by motor vehicles, was studied at 1 atm pressure in air at room temperature in both the absence and presence of NO (0–20 ppm). Cl2 (4–16 ppm) was photolyzed to generate chlorine atoms, and the products were identified and measured using gas chromatography‐mass spectrometry (GC‐MS) and long path (40 m) Fourier transform infrared spectroscopy (FTIR). We identified 4‐chlorocrotonaldehyde (CCA) as a unique chlorine‐containing product from the Cl atom reaction with 1,3‐butadiene in both the presence and absence of NO. The yield of CCA was (29±7)% (2σ) in the absence of NO and (65±20)% (2σ) in its presence. The yield of chloromethyl vinyl ketone (CMVK), another chlorine‐containing compound from this reaction, was measured to be (19±4)% (2σ) in the absence of NO; it was not observed in its presence. The reaction system was modeled using ACUCHEM to clarify the reaction paths and to allow extrapolation to ambient air conditions. These studies predict that CCA will be formed in coastal urban areas in the early morning hours at concentrations of ∼100 ppt, which should be readily detectable by GC‐MS and GC with electron capture detection (ECD). Some studies were also carried out on the isoprene reaction, and some potential unique products of its reaction with chlorine atoms are suggested as candidates for field investigations.

Diurnal Fluctuations of Nitrate Uptake and In Vivo Nitrate Reductase Activity in Pima and Acala Cotton

This study was conducted to determine whether diurnal fluctuations of nitrate reductase activity in two cotton species, Pima (Gossypium barbadense L.) and Acala (Gossypium hirsutum L.), are regulated by NO−3 uptake or leaf NO−3 concentration. The two species differ greatly in their N use efficiency. The seedlings were grown for 25 d in nutrient solutions containing 0.05, 0.10 or 1.0 mM NO−3 under a 14‐h light/10‐h dark cycle at 30°C/20°C. Uptake rates were measured by following NO−3 depletion from the uptake solutions at 20°C or 30°C. Nitrate reductase activity (NRA) in fully expanded first true leaves was determined by an anaerobic method in vivo. Upon illumination uptake rates for both species, measured at 30°C, increased until they plateaued in about 5 h and were maintained at that level for the remainder of the light period and the following dark cycle. When measured at 20°C in the dark, however, the uptake rates decreased 25 to 30% for the first 3 h and then remained constant. Leaf NRA increased rapidly during the first hour of illumination, reached a plateau and then decreased after 4 to 6 h of illumination. The decline was more rapid when NRA was assayed in the absence of NO−3 In darkness, NRA levels were low and did not fluctuate. Upon illumination, leaf NO−3 concentration also increased for about 7 h and then decreased gradually. The results indicate that (i) the diurnal rhythm of NO−3 uptake is modulated by temperature rather than by light/dark transitions, and (ii) while the increase in NRA upon illumination may be regulated by NO−3 flux from roots to shoots, the decrease in NRA under prolonged illumination is independent of that flux.

Angiotensin II is involved in nitric oxide synthase and cyclo-oxygenase inhibition-induced leukocyte-endothelial cell interactions in vivo.

1. Chronic inhibition of nitric oxide synthase (NOS) provokes a hypertensive state which has been shown to be angiotensin II (Ang-II) dependent. In addition to raising blood pressure, NOS inhibition also causes leukocyte adhesion. The present study was designed to define the role of Ang-II in hypertension and in the leukocyte-endothelial cell interactions induced by acute NOS or cyclo-oxygenase (COX) inhibition using intravital microscopy within the rat mesenteric microcirculation. 2. While pretreatment with an Ang-II AT(1) receptor antagonist (losartan) reversed the prompt increase in mean arterial blood pressure (MABP) caused by indomethacin, it had no effect on the increase evoked by systemic L-NAME administration. 3. Pretreatment with losartan inhibited the leukocyte rolling flux, adhesion and emigration which occurs after 60 min NOS inhibition by 83, 80 and 70% respectively, and returned leukocyte rolling velocity to basal levels. 4. Losartan significantly reduced the leukocyte-endothelial cell interaction elicited by COX inhibition. In contrast, leukocyte recruitment induced by acute mast cell activation was not inhibited by losartan. 5. AT(1) receptor blockade also prevented the drop in haemodynamic parameters such as mean red blood cell velocity (V(mean)) and shear rate caused by NOS and COX inhibition. 6. In this study, we have demonstrated a clear role for Ang-II in the leukocyte-endothelial cell interactions and haemodynamic changes which arise in the absence of NO or prostacyclin (PGI(2)). This is of interest since leukocyte recruitment, which culminates in the vascular lesions that occur in hypertension, atherosclerosis and myocardial ischemia-reperfusion injury, might be prevented using AT(1) Ang-II receptor antagonists.

Formate species in the low-temperature oxidation of dimethyl ether

The oxidation of dimethyl ether (DME, 340 ppm in 10% O 2) has been studied experimentally in an atmospheric pressure laminar flow reactor in the temperature range from 240°C to 700°C for residence times in the range 2–4 s. The influence of nitric oxide additions up to 620 ppm to the feed gases has also been investigated. Products of reaction were determined by FTIR. In the absence of NO, reaction is first detected at about 260°C. The products in the low-temperature region include formaldehyde (HCHO), and formic acid (HCOOH). The addition of NO leads to the appearance of methyl formate (CH 3OCHO). While the overall behaviour of the system can be explained qualitatively in terms of typical low-temperature hydrocarbon ignition, recently published chemical kinetic models for DME ignition do not allow for the formation of these formate species. We find no experimental evidence for the formation of hydroperoxymethyl formate (HPMF, HOOCH 2OCHO) which is predicted by the models to be a significant stable intermediate at temperatures below 350°C. Since both formic acid and methyl formate have potentially harmful health effects, these observations may have significant implications for use of DME as a diesel fuel.

The reactions of atomic chlorine with acrolein, methacrolein and methyl vinyl ketone

An investigation into the reactions between Cl atoms and acrolein (1), methacrolein (2) and methyl vinyl ketone (3) is presented. Values of the rate constants for the reactions have been determined by an absolute technique for the first time. At a pressure of 1.6 Torr, the rate constants obtained were: k1 = 1.1 ± 0.2, k2 = 3.3 ± 0.6 and k3 = 0.99 ± 0.20 in units of 10−10 cm3 molecule−1 s−1. k1 was also determined at atmospheric pressure using a relative-rate technique. The rate constant obtained was (2.2 ± 0.3) × 10−10 cm3 molecule−1 s−1; the larger value compared with that for 1.6 Torr is thought to reflect a true dependence of the reaction rate on pressure. The final products of the reactions performed under an atmosphere of synthetic air were investigated using FTIR spectroscopy. The only chlorinated organic species identified as products of the reactions were chloroacetaldehyde in the case of reaction of Cl atoms with acrolein; chloroacetone with methacrolein; and chloroacetaldehyde with methyl vinyl ketone. Branching ratios for abstraction (the fraction of reactions occurring by abstraction relative to the sum of addition and abstraction processes) were found to be 0.22 ± 0.13 for acrolein, 0.18 ± 0.02 for methacrolein and <0.03 for methyl vinyl ketone. The reaction of Cl atoms with methacrolein proceeds ia a mechanism that involves the decomposition of the methyl vinyl radical. The decomposition of this radical in synthetic air, and in the absence of NO, appears to lead to the formation of significantly more CO than previously thought. This observation is in agreement with the work of J. J. Orlando, S. E. Paulson and G. S. Tyndall, Geophys. Res. Lett., 1999, 26, 2191 (ref. 1), who studied the decomposition of the radical under different conditions.