Characterization and activity of copper-on-carbon catalysts for low-temperature selective reduction of nitric oxide with ammonia

The activities for NO reduction with ammonia in the presence and absence of O₂ have been examined over copper salts supported on activated carbon (AC) and carbon black (CB) which have been characterized by application of X-ray diffraction and scanning electron microscopy before and after use in the reduction process. The beneficial effects of increases in loading and the introduction of oxygen are demonstrated. On the most active catalyst and under optimum conditions 100% reduction of the NO to N₂ occurs at 180 °C and Cu, Cu₂O and CuO on the catalyst are shown to be present at various stages of the preparation and reduction process with large crystallites of metallic copper detected on the AC catalyst of optimum loading. Deactivation and regeneration of the catalysts is also examined. A mechanism for the redox process is proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mechanism of the inhibition of calmodulin-dependent neuronal nitric oxide synthase by flaxseed protein hydrolysates

This work was aimed at producing potential nutraceutical peptides from flaxseed protein hydrolysate that can bind to calmodulin (CaM) and inhibit the activity of CaM-dependent neuronal nitric oxide synthase (nNOS), an enzyme that has been implicated in some forms of human diseases. Flaxseed protein isolate was hydrolyzed with alcalase, and the resultant protein hydrolysate was passed through a 1000-Da M.W. cut-off membrane to isolate low-M.W. peptides. The permeate from the membrane was loaded onto a cation-exchange column, and adsorbed peptides were separated into fractions I and II that had a content of 42 and 51% basic amino acids, respectively. Kinetic analyses showed that both fractions were capable of binding to CaM, which led to reductions in the activity of nNOS; the inhibition constant (K _j ) was 5.97 and 2.55 mg/mL for fractions I and II, respectively. Double reciprocal plots showed that the mode of enzyme inhibition was mostly noncompetitive. Estimation of nNOS structure by fluorescence spectroscopy indicated that binding of the peptides to CaM led to a gradual unfolding of enzyme structure as levels of the fractions were increased. We concluded that the flaxseed protein-derived peptides may be used as ingredients for the formulation of therapeutic foods.     

Catalytic activity of coke activated with sulphuric acid for the reduction of nitric oxide

The catalytic activity of coke activated with sulphuric acid for the reduction of nitric oxide with ammonia at 150 °C was investigated. With the original coke the yield of nitrogen after 90 min reaction was only 10% and activation of the coke by the impregnation in sulphuric acid and subsequent heat treatment at ≈450 °C markedly enhanced the activity to a nitrogen yield as much as 70%. The activity decreased in repeated runs probably because of a surface coverage effect of the water produced, but the activity could be restored by further heat treatment at 400 °C.     

Aspirin analogues as dual cyclooxygenase-2/5-lipoxygenase inhibitors: synthesis, nitric oxide release, molecular modeling, and biological evaluation as anti-inflammatory agents

Analogues of aspirin were synthesized through an efficient one-step reaction in which the carboxyl group was replaced by an ethyl ester, and/or the acetoxy group was replaced by an N-substituted sulfonamide (SO(2)NHOR(2):R(2) =H, Me, CH(2)Ph) pharmacophore. These analogues were designed for evaluation as dual cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibitors. In vitro COX-1/COX-2 isozyme inhibition studies identified compounds 11 (CO(2) H, SO(2)NHOH), 12 (CO(2)H, SO(2)NHOCH(2)Ph), and 16 (CO(2)Et, SO(2)NHOH) as highly potent and selective COX-2 inhibitors (IC(50) range: 0.07-0.7 μM), which exhibited appreciable in vivo anti-inflammatory activity (ED(50) range: 23.1-31.4 mg kg(-1)). Moreover, compounds 11 (IC(50) =0.2 μM) and 16 (IC(50) =0.3 μM), with a sulfohydroxamic acid (SO(2)NHOH) moiety showed potent 5-LOX inhibitory activity. Furthermore, the SO(2)NHOH moiety present in compounds 11 and 16 was found to be a good nitric oxide (NO) donor upon incubation in phosphate buffer at pH 7.4. Molecular docking studies in the active binding site of COX-2 and 5-LOX provided complementary theoretical support for the experimental biological structure-activity data acquired.     

Fertilizer-induced nitric oxide emissions from agricultural soils

We summarize and evaluate 23 studies of the effect of fertilizer use on nitric oxide (NO) emission from agricultural soils. To quantify this effect we selected only field-scale studies with duration of at least one complete growing season and excluded studies with a legume as the principle crop. Only 6 studies met the established criteria, resulting in a total of 12 observations of soil/crop/fertilizer combinations, all in temperate areas. For these studies, the amount of NO emitted was linearly related to the amount of fertilizer applied (R² = 0.64) and about 0.5% of applied nitrogen was emitted as NO during the crop growing season. The available data are too limited to separate the effects of fertilizer type, soil type, or crop management.     

Electrochemical high-content screening of nitric oxide release from endothelial cells

Release of nitric oxide (NO) is of high importance for regulating endothelial cell functions during vasodilatation, vascular remodeling, and angiogenesis. Thus, a direct and reliable real-time method for NO detection that takes into account time-dependent variations of the NO concentration in the complex reaction within the diffusion zone above the cells is vital for obtaining information about the role of NO in intracellular endothelial signal transduction and its impact on the surrounding cells. In this study, the time course of vascular endothelial growth factor E (VEGF-E) stimulated NO release from transformed human umbilical vein endothelial cells (T-HUVEC) was investigated by means of metalloporphyrin-based NO sensors employed in an electrochemical robotic system. The NO sensor was obtained by electrochemically induced deposition of Ni(II) tetrakis(p-nitrophenylporphyrin) on a 50-microm diameter platinum disk electrode which was integrated, together with a 25-microm diameter platinum disk, in a double-barrel electrode arrangement. The second electrode was used as a guidance sensor for the automatic and highly reproducible positioning of the NO sensor at a known distance from a layer of adherently growing cells by using z-approach curves in the negative feedback mode of scanning electrochemical microscopy (SECM). The electrochemical robotic system allows the fully automated detection of NO with high sensitivity and selectivity to be performed in real time within 96-well microtiter plates. A functional cell assay was established to allow the standardized detection of NO released upon stimulation from T-HUVEC with a sensor positioned at a known distance above the endothelial cells. The overall system was evaluated by automatic detection of NO release from T-HUVEC upon stimulation with VEGF-E after incubation with a variety of drugs that are known to act on different sites in the complex signal-transduction pathway that finally invokes NO release.     

Active sites of H-ZSM5 catalysts for the oxidation of nitric oxide by oxygen

The catalytic activities of H-ZSM5-18, H-ZSM5-150, Li-ZSM5-18, and H-Mag (numerical suffixes mark the Si/Al ratios of zeolites, H-Mag is the proton exchanged form of the layered sodium silicate, magadiite) were compared for the oxidation of NO by O₂ at different ratios of reactants at reaction temperatures from 25 to 600°C. H-ZSM5-18 typically has activity maxima near 25 and 400°C at most O₂/NO reactant ratios. Regardless of the partial pressures of reactants, NO±1/2O₂ NO₂ equilibria are attained at 400°C and above. The H-ZSM5-150 and Li-ZSM5-18 zeolites are only active at temperatures near 25°C. H-Mag is practically inactive at the reaction conditions used. Results indicate that Lewis acidic lattice aluminium ions and silanol hydroxyls are not active in the oxidation of NO to NO₂ over H-ZSM5 zeolites. Brønsted acidic bridging hydroxyls are probably active sites for this reaction at temperatures above 200°C.     

Nitric oxide reduction by char and carbon monoxide: Fundamental kinetics of nitric oxide reduction in fluidizedbed combustion of coal

The reduction of nitric oxide during combustion of coal char in a fluidized-bed combustor was examined with respect to two reactions : a char-catalysed reaction; and a char-consuming reaction, which control nitric oxide emissions. The relative importance of the two reactions was investigated by measuring detailed material balances for the reactions. The product distribution was explained in terms of three fundamental parallel reaction paths. Reaction rates were investigated with a fixed-bed flow reactor over the temperature range 883–1194 K, the same as the fluidized bed combustor.     

Alumina supported manganese oxides for the low-temperature selective catalytic reduction of nitric oxide with ammonia

Alumina supported manganese oxides exhibit a high and selective activity for the catalytic reduction of nitric oxide with ammonia (SCR) between 385 and 575 K. Samples with 3–15 wt.-% manganese were studied at space velocities between 22 000–116 000 h⁻¹ and at standard conditions of 500 ppm NO, 550 ppm NH₃ and 2% O₂. Manganese acetate results in a better dispersion of the manganese oxide on the support and a higher specific catalyst activity than manganese nitrate as precursor, for which crystalline structures could be detected. Temperature-programmed reduction revealed that acetate yields Mn₂O₃ and nitrate mainly MnO₂ on the γ-alumina support. The nitric oxide conversion per amount of manganese is fairly independent of the loading for the catalysts prepared from each precursor. The use of ¹⁵NH₃ reveals that it reacts in a 1:1 molar ratio with nitric oxide towards ¹⁵NN and/or ¹⁵NNO. The SCR activity (to nitrogen) is strongly dependent on the oxygen partial pressure, whereas water inhibits reversibly. Lattice oxygen of the catalyst is not able to maintain the SCR reaction in the absence of oxygen. The nitrous oxide formation is independent of the oxygen partial pressure, but increases with increasing manganese loading and with temperature, resulting in lower selectivities for nitrogen formation. The nitrogen and nitrous oxide formation probably occur at different sites. Above 525 K ¹⁵NH₃ oxidation occurs, yielding mainly ¹⁵N₂O and ¹⁵NO, depending on the temperature. The nitrous oxide is not further reduced by ammonia over this type of catalyst. The addition of tungsten to the catalyst increases the selectivity for nitrogen considerably. The stability of the ex-acetate catalyst is good, for at least 600 h the activity remained constant. The catalysts are sensitive towards sulphur dioxide, the ex-acetate catalysts the least, due to the strong interaction with the alumina support, as is revealed by TPR.     

Studies of the selective reduction of nitric oxide by hydrocarbons

The selective reduction of nitric oxide with isobutane in the presence and absence of oxygen has been studied over Cu-ZSM-5-14-114 and compared to the simple decomposition reaction. In the presence of sufficient oxygen, complete combustion of the hydrocarbon was observed, whereas in its absence, acid catalysis accompanied by dehydrogenation associated with coking occurred. The effect of adding nitric oxide to the HC/He stream in the absence of oxygen was small; the conversion to nitrogen was little affected by the hydrocarbon. When oxygen was added, however, the decomposition was complete at 573 K even at high space velocities (e.g., SVH 10⁴) even though the combustion was not. Isobutane (an alkane) was more effective than C₃H₆ (an alkene) for the selective reduction; this is not generally the case. The presence of excess oxygen inhibited aging of the catalyst.     

Fe-chlorophyllin promotes the growth of wheat roots associated with nitric oxide generation

Effects of Fe-chlorophyllin on the growth of wheat root were investigated in this study. We found that Fe-chlorophyllin can promote root growth. The production of nitric oxide in wheat root was detected using DAF-2DA fluorescent emission. The intensity of fluorescent in the presence of 0.1 mg/L Fe-chlorophyllin was near to that observed with the positive control of sodium nitroprusside (SNP), the nitric oxide donor. IAA oxidase activity decreased with all treatments of Fe-chlorophyllin from 0.01 to 10 mg/L. At the relatively lower Fe-chlorophyllin concentration of 0.1 mg/L, the activity of IAA oxidase displayed a remarkable decrease, being 40.1% lower than the control. Meanwhile, Fe-chlorophyllin treatment could increase the activities of reactive oxygen scavenging enzymes, such as superoxide dismutase (SOD) and peroxidase (POD), as determined using non-denaturing polyacrylamide gel electrophoresis. These results indicate that Fe-chlorophyllin contributes to the growth of wheat root associated with nitric oxide generation.     

Characterization of C-alkyl amidines as bioavailable covalent reversible inhibitors of human DDAH-1

C‐Alkyl amidine analogues of asymmetric N^ω,N^ω‐dimethyl‐L ‐arginine are dual‐targeted inhibitors of both human DDAH‐1 and nitric oxide (NO) synthase, and provide a promising scaffold for the development of therapeutics to control NO overproduction in a variety of pathologies including septic shock and some cancers. Using a two‐part click‐chemistry‐mediated activity probe, a homologated series of C‐alkyl amidines were ranked for their ability to inhibit DDAH‐1 within cultured HEK 293T cells. N⁵‐(1‐Iminopentyl)‐L ‐ornithine was determined to be the most potent compound in vitro (K_d=7 μM ) as well as in cultured cells, and the binding conformation and covalent reversible mode of inhibition was investigated by comparison of interactions made with DDAH‐1 and a catalytically inactive C274S variant, as gauged by X‐ray crystallography and isothermal titration calorimetry. By interrupting the ability of the inhibitor to form a covalent bond, the contribution of this interaction could be estimated. These results suggest that further stabilization of the covalent adduct is a promising strategy for lead optimization in the design of effective reagents to block NO synthesis.     

Simultaneous catalytic reduction of sulfur dioxide and nitric oxide

The present work reports a catalytic system for the simultaneous reduction of SO₂ and NO using CO as a reducing agent. The catalyst contains lanthanum oxysulfide and cobalt sulfides. Experimental results showed that at temperature above 450°C, SO₂ and NO conversions are greater than 98 and 99%, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen dioxide effect in the reduction of nitric oxide by propane in oxidizing atmosphere

The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO₂ and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C₃H₈ does not differ significantly from that of NO₂. In the absence of oxygen, the reduction of NO₂ by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO₂ formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process.     

Fluorescence of 1,2-diaminoanthraquinone and its nitric oxide reaction product within macrophage cells

Nitric oxide (NO) is involved in many biological processes. Aromatic ortho-diamine derivatives are commonly used in the fluorescence imaging of NO in living cells. ortho-diamino (o-diamino) compounds are believed to react with NO in an oxygenated medium leading to the formation of a triazole derivative. One such o-diamino compound, 1,2-diaminoanthraquinone (DAA), is a nontoxic probe for the detection of NO in living tissues and cells. The formation of the DAA triazole derivative (DAA-TZ) upon reaction of DAA with NO/O(2) within cells has not been demonstrated previously. The aim of this study was to confirm that DAA-TZ is the species formed intracellularly when DAA reacts with NO in the presence of oxygen. The chemical synthesis and characterisation of DAA-TZ was performed together with intracellular studies of DAA and DAA-TZ. Raw 264.7 macrophages were loaded with the DAA or DAA-TZ under conditions of no-stimulation or stimulation with interferon-γ and lipopolysaccharide to produce NO. Confocal microscopy was used to image the DAA-loaded macrophage cells. Analysis of the emission spectra allowed precise discrimination of the fluorescence of each species in the macrophage cells, and confirmed the identity of DAA-TZ as the intracellular reaction product between DAA and NO in the presence of oxygen.