Absence Of NH Research Articles

Cage Match: Comparing the Anion Binding Ability of Isostructural Versus Isofunctional Pairs of Metal-Organic Nanocages.

Affinities of six anions (mesylate, acetate, trifluoroacetate, p-toluenecarboxylate, p-toluenesulfonate, and perfluorooctanoate) for three related Pt2+ -linked porphyrin nanocages were measured to probe the influence of different noncovalent recognition motifs (e. g., hydrogen bonding, electrostatics, π bonding) on anion binding. Two new hosts of M6 L3 12+ (1b) and M4 L2 8+ (2) composition (M=(en)Pt2+ , L=(3-py)4 porphyrin) were prepared in a one-pot synthesis and allowed comparison of hosts that differ in structure while maintaining similar N-H hydrogen-bond donor ability. Comparisons of isostructural hosts that differ in hydrogen-bonding ability were made between 1b and a related M6 L3 12+ nanoprism (1a, M=(tmeda)Pt2+ ) that lacks N-H groups. Considerable variation in association constants (K1 =1.6×103 M-1 to 1.3×108 M-1 ) and binding mode (exo vs. endo) were found for different host-guest combinations. Strongest binding was seen between p-toluenecarboxylate and 1b, but surprisingly, association of this guest with 1a was only slightly weaker despite the absence of NH⋅⋅⋅O interactions. The high affinity between p-toluenecarboxylate and 1a could be turned off by protonation, and this behavior was used to toggle between the binding of this guest and the environmental pollutant perfluorooctanoate, which otherwise has a lower affinity for the host.

Genetics and regulation of nitrogen fixation in Paenibacillus brasilensis PB24

Biological nitrogen fixation (BNF), performed by diazotrophic prokaryotes, is responsible for reducing dinitrogen (N2) present in the biosphere into biologically available forms of nitrogen. Paenibacillus brasilensis PB24 is a diazotrophic Gram-positive bacterium and is considered ecologically and industrially important because it is able to produce antimicrobial substances and 2,3-butanediol. However, the genetics and regulation of its nitrogen fixing (nif) genes have never been assessed so far. Therefore, the present study aimed to (i) identify the structural and regulatory genes related to BNF in the PB24 genome, (ii) perform comparative genomics analysis of the nif operon among different Paenibacillus species and (iii) study the expression of these genes in the presence and absence of NH4. Strain PB24 showed a nif operon composed of nine genes (nifBHDKENXhesAV), with a conserved synteny (with small variations) among the Paenibacillus species evaluated. BNF regulatory genes, glnK and amtB (encoding GlnK signal transduction protein and AmtB transmembrane protein, respectively) and glnR and glnA genes (encoding the transcription factor GlnR and glutamine synthetase) were found in the PB24 genome. Primers were designed for qPCR amplification of the nitrogenase structural (nifH, nifD and nifK) and regulatory (glnA and amtB) BNF genes. The structural gene expression in PB24 was up- and downregulated in the absence and presence of NH4, respectively. The gene expression levels indicated a GlnR-mediated repression of genes associated with ammonium import (amtBglnK) and BNF (nif genes). Additionally, the regulatory mechanism of GlnR in P. brasilensis PB24 differed from the other Paenibacillus evaluated, considering the different distribution of binding sites recognized by GlnR.

Influence of soil on groundwater geochemistry in a carbonate aquifer, southern Italy

The role of soil compositions in influencing groundwater geochemistry in carbonate aquifers is still little known. Nothing is known regarding the influence of pyroclastic soils (andisol) within the carbonate Apennines in central-southern Italy, despite their wide distribution. In this study we analyze some physical and chemical properties of pyroclastic soil at the Acqua dei Faggi experimental site (southern Italy), to assess its influence on groundwater geochemistry. Chemical analyses were carried out on saturated paste extracts and a physical analogue model was developed through two column experiments. Physico-chemical properties of rainwater and spring water, and some microbiological features of the soil medium were also taken into consideration. The studied soil has a great influence in modifying rainwater chemistry during percolation. About the 50% of HCO 3 and Ca 2+ in spring water is due to interaction between percolation water and soil medium, and equilibrium with calcite is reached at this stage. The Na + /K + ratio is buffered by clay minerals in the soil by primary silicates in the pyroclastic cover. Cl and SO 4 2concentrations in spring water are very close to that of soil infiltration water during short-term interaction with soil, but a decline is showed during long-term cause to the anions adsorption effect in the andisol. Chemical and microbiological investigations show the existence of a soil microbial community that allows denitrification and nitrate reduction. Infiltration processes cause anoxic conditions within the soil medium, therefore the absence of NH 4 + in spring water throughout the observation period should be due to anammox processes. These findings suggest that hydrochemistry and spring chemographs may be significantly influenced by several factors, such as relationships between soil and rainwater, vegetation, and microbial communities, which are not necessarily correlated with lithological and structural features of carbonate aquifers.

Toward the mechanism of NH4+ sensitivity mediated by Arabidopsis GDP‐mannose pyrophosphorylase

The ascorbic acid (AA)-deficient Arabidopsis thaliana mutant vtc1-1, which is defective in GDP-mannose pyrophosphorylase (GMPase), exhibits conditional hypersensitivity to ammonium (NH(4) (+) ), a phenomenon that is independent of AA deficiency. As GMPase is important for GDP-mannose biosynthesis, a nucleotide sugar necessary for protein N-glycosylation, it has been thought that GDP-mannose deficiency is responsible for the growth defect in vtc1-1 in the presence of NH(4) (+) . Therefore, the motivation for this work was to elucidate the growth and developmental processes that are affected in vtc1-1 in the presence of NH(4) (+) and to determine whether GDP-mannose deficiency generally causes NH(4) (+) sensitivity. Furthermore, as NH(4) (+) may alter cytosolic pH, we investigated the responses of vtc1-1 to pH changes in the presence and absence of NH(4) (+) . Using qRT-PCR and staining procedures, we demonstrate that defective N-glycosylation in vtc1-1 contributes to cell wall, membrane and cell cycle defects, resulting in root growth inhibition in the presence of NH(4) (+) . However, by using mutants acting upstream of vtc1-1 and contributing to GDP-mannose biosynthesis, we show that GDP-mannose deficiency does not generally lead to and is not the primary cause of NH(4) (+) sensitivity. Instead, our data suggest that GMPase responds to pH alterations in the presence of NH(4) (+) .

Selective catalytic reduction of NO with NH3 on iron zeolite monolithic catalysts: Steady-state and transient kinetics

An experimental study of steady-state and transient selective catalytic reduction (SCR) of NO with NH3 on both commercial and in-house synthesized Fe-ZSM-5 (MFI type) monolith catalysts is presented. The reaction system was studied in a bench-flow reactor spanning a range of temperature, space velocity and washcoat thickness, affording an assessment of activity and selectivity, reaction pathways, temperature window, mass transport and pore diffusion effects. Experiments included NH3 uptake and temperature-programmed desorption, steady-state and transient NO and NH3 oxidation and standard SCR (NO+NH3+O2) reaction studies. Differential kinetics studies were performed for the standard SCR reaction and NO oxidation reaction systems to determine reaction orders and activation energies. In the temperature range of 200–300°C the standard SCR reaction was found to be nearly first-order and half-order with respect to NO and O2, respectively, but moderately negative-order (−0.3) with respect to NH3. Agreement in the kinetics for both reaction systems suggests that the oxidation of NO is the rate determining step, in line with recent literature studies. Rate inhibition by ammonia appears to be the result of blockage of NO oxidation reaction sites; a necessary step for the standard SCR reaction. Water is shown to inhibit the oxidation of NO significantly and of NH3 to a moderate extent, while having only a negligible effect on the standard SCR reaction. A mechanistic-based kinetic model is proposed in which NH3 reacts with surface bound NO2 and nitrous acid via a NH4NO2 intermediate. A mechanism in which gaseous NO reacts with adsorbed oxygen (Eley Rideal like reaction) cannot be ruled out. In the absence of NH3 these surface species inhibit the adsorption of NO and/or O2 during NO oxidation. Both external mass transfer limitations and washcoat diffusion limitations were ruled out for moderate temperature conditions (≤300°C). However, experiments on monoliths with different washcoat thicknesses conclusively show the appearance of washcoat diffusion limitations at higher temperatures.

Synthesis of nanocrystalline magnesium nitride (Mg 3N 2) powder using thermal plasma

Nanocrystalline magnesium nitride (Mg 3N 2) powder was synthesized from bulk magnesium by thermal plasma at atmospheric pressure. Magnesium vapor was generated through heating the bulk magnesium by DC plasma jet and reacted with ammonia gas. Injecting position and flow rates of ammonia gas were controlled to investigate an ideal condition for Mg 3N 2 synthesis. The synthesized Mg 3N 2 was cooled and collected on the chamber wall. Characteristics of the synthesized powders for each experimental condition were analyzed by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and thermogravity analysis (TGA). In absence of NH 3, magnesium metal powder was formed. The synthesis with NH 3 injection in low temperature region resulted in a formation of crystalline magnesium nitride with trigonal morphology, whereas the mixture of magnesium metal and amorphous Mg 3N 2 was formed when NH 3 was injected in high temperature region. Also, vaporization process of magnesium was discussed.

Enhanced removal of NH 3 during composting by a biotrickling filter inoculated with nitrifying bacteria

A biotrickling filter (BTF) was used to treat NH 3 emitted from the exhaust gases of cattle manure compost. Results of the non-biofilm experiment suggested that NH 3 could not be removed effectively only through biofilm adsorption. The absence of NH 4 + bio-oxidation resulted in an increase in free ammonia, which had a negative effect on NH 3 removal. After biofilm culture, NH 3 removal efficiency fluctuated between 67.2% and 94.3% because the presence of a biofilm extended the liquid residence time in the packing. When the biofilm was inoculated with nitrifying bacteria comprised of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), which were screened from a cattle manure solution, the average removal efficiencies became 59.9% and 15.0% higher than those of the non-biofilm and biofilm culture experiments, respectively. AOB and NOB could still oxidize ammonia and nitrite, respectively, even when the free nitrous acid concentration was as high as 37.6 mg/L. With an empty bed retention time of 96.0 s and a removal efficiency of 99%, NH 3 elimination capacities were attained at 57.1, 28.6, and 23.7 g-N/(m 3 h) for the first segment, the first and second segment, and the whole BTF, respectively. These results demonstrate that the BTF under study is a viable alternative for the treatment of NH 3 during composting.

Biohydrogen production from beet molasses by sequential dark and photofermentation

Biological hydrogen production using renewable resources is a promising possibility to generate hydrogen in a sustainable way. In this study, a sequential dark and photofermentation has been employed for biohydrogen production using sugar beet molasses as a feedstock. An extreme thermophile Caldicellulosiruptor saccharolyticus was used for the dark fermentation, and several photosynthetic bacteria ( Rhodobacter capsulatus wild type, R. capsulatus hup − mutant, and Rhodopseudomonas palustris) were used for the photofermentation. C. saccharolyticus was grown in a pH-controlled bioreactor, in batch mode, on molasses with an initial sucrose concentration of 15 g/L. The influence of additions of NH 4 + and yeast extract on sucrose consumption and hydrogen production was determined. The highest hydrogen yield (4.2 mol of H 2/mol sucrose) and maximum volumetric productivity (7.1 mmol H 2/L c.h) were obtained in the absence of NH 4 +. The effluent of the dark fermentation containing no NH 4 + was fed to a photobioreactor, and hydrogen production was monitored under continuous illumination, in batch mode. Productivity and yield were improved by dilution of the dark fermentor effluent (DFE) and the additions of buffer, iron-citrate and sodium molybdate. The highest hydrogen yield (58% of the theoretical hydrogen yield of the consumed organic acids) and productivity (1.37 mmol H 2/L c.h) were attained using the hup − mutant of R. capsulatus. The overall hydrogen yield from sucrose increased from the maximum of 4.2 mol H 2/mol sucrose in dark fermentation to 13.7 mol H 2/mol sucrose (corresponding to 57% of the theoretical yield of 24 mol of H 2/mole of sucrose) by sequential dark and photofermentation.

Mercury oxidation by hydrochloric acid over TiO 2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO 2 catalysts, 1 wt.% MO x/TiO 2 where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg 0 oxidation and the NO reduction measurements both in the presence and absence of NH 3. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO 2 surface. For all catalysts studied, the Hg 0 oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO 3 ~ V 2O 5 > Cr 2O 3 > Mn 2O 3 > Fe 2O 3 > CuO > NiO. The Hg 0 oxidation activity of all catalysts was depressed considerably by adding NH 3 to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH 3. The activity trend of the Hg 0 oxidation in the presence of NH 3 was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg 0 oxidation activities in the NH 3 present condition. The catalyst having high NO reduction activity such as V 2O 5/TiO 2 showed high Hg 0 oxidation activity. The result obtained in this study suggests that the oxidation of Hg 0 proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH 3. NH 3 adsorption may predominate over the adsorption of HCl in the presence of NH 3.

Effect of thermal treatment on room-temperature ferromagnetism in Co-doped ZnO powders

The Co-doped ZnO powders were synthesized by sol–gel method, and treated at different temperatures (673–873 K) in the presence or absence of NH 3 atmosphere for 0.5 and 2 h, respectively. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) show that better crystal structure can cause larger ferromagnetism and the second phase (Co 3O 4) is the reason for saturation magnetization decrease of the sample sintered at higher temperature in air. XPS and nuclear magnetic resonance (NMR) prove the existence of Co 2+ ions in the Zn 0.9Co 0.1O and the absence of Co clusters, indicating intrinsic ferromagnetism of the samples treated in air. However, strong ferromagnetism of the samples annealed in NH 3 is ascribed to cobalt nitride formed during annealing.

Kinetics of selective catalytic reduction of NO by NH 3 on Fe-Mo/ZSM-5 catalyst

The catalyst of Fe-Mo/ZSM-5 has been found to be more active than Fe-ZSM-5 and Mo/ZSM-5 separately for selective catalytic reduction (SCR) of nitric oxide (NO) with NH 3. The kinetics of the SCR reaction in the presence of O 2 was studied in this work. The results showed that the observed reaction orders were 0.74–0.99, 0.01–0.13, and 0 for NO, O 2 and NH 3 at 350–450°C, respectively. And the apparent activation energy of the SCR was 65 kJ/mol on the Fe-Mo/ZSM-5 catalyst. The SCR mechanism was also deduced. Adsorbed NO species can react directly with adsorbed ammonia species on the active sites to form N 2 and H 2O. Gaseous O 2 might serve as a reoxidizing agent for the active sites that have undergone reduction in the SCR process. It is also important to note that a certain amount of NO was decomposed directly over the Fe-Mo/ZSM-5 catalyst in the absence of NH 3.

An NH 4+-sensitive component dominates high-affinity K + uptake in tomato plants

High-affinity K + uptake has been studied in tomato plants grown under different conditions. K + starvation induced a high-affinity K + uptake with a K m of 10.5 ± 1.1 μM. This system was inhibited by the presence of NH 4 + in the uptake solution and the inhibition was similar for plants grown in the absence or in the presence of NH 4 +. High-affinity K + uptake was inhibited in plants grown in the presence of NaCl without NH 4 + but not in plants grown with NaCl and with NH 4 +. A full-length cDNA has been isolated that probably encodes a high-affinity K + uptake system, LeHAK5. The gene encoding LeHAK5 is induced in K +-starved plants and the presence of NH 4 + in the growth solution further increases LeHAK5 expression. In K +-starved plants grown with NaCl in the absence of NH 4 + LeHAK5 expression is almost abolished but when plants are grown with NaCl in the presence of NH 4 + a strong expression of the gene is detected. The LeHAK5 expression pattern parallels the presence of high-affinity K + uptake in tomato plants which suggests that this gene is encoding an important component of K + uptake in the micromolar range of K + concentrations.

RETRACTED: Electrodeposition and characterization of manganese coatings obtained from an acidic chloride bath containing ammonium thiocyanate as an additive

The influence of ammonium thiocyanate (NH 4 SCN) on the electrodeposition and morphology of manganese coatings obtained from a chloride-based acidic solution was investigated by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) measurements. The EQCM data are presented as plots of dΔm/dt versus E, known as massograms. Because massograms are not confounded by the hydrogen evolution reaction, they more clearly show the manganese reduction and oxidation processes. By comparing the voltammograms with their corresponding massograms, it was possible to differentiate mass changes due to Faradaic processes from those involving no net charge transfer. Morphology, elemental composition profiles, and the structure of the manganese coatings were analyzed by scanning electron microscopy (SEM), glow discharge spectrometry (GDS), and X-ray diffraction (XRD). The results showed that in the absence of NH 4 SCN, Mn(OH) 2(s) is formed in the potential range -0.9 to -1.1 V vs. SCE because of the hydrogen-evolution reaction in this region. At more cathodic potentials, Mn(OH) 2(s) was incorporated into a β-manganese deposit. Both of these species undergo dissolution by apparently non-Faradaic processes during the potential scan in the positive direction. In the presence of NH 4 SCN, the percentage of codeposited Mn(OH) 2(s) decreased, and sulfur was detected in the lower layers of the manganese coatings. Moreover, the formation of α- and γ-manganese was favored.

A kinetic study of the gill (Na+, K+)-ATPase, and its role in ammonia excretion in the intertidal hermit crab, Clibanarius vittatus

To better comprehend the role of gill ion regulatory mechanisms, the modulation by Na(+), K(+), NH(4)(+) and ATP of (Na(+), K(+))-ATPase activity was examined in a posterior gill microsomal fraction from the hermit crab, Clibanarius vittatus. Under saturating Mg(2+), Na(+) and K(+) concentrations, two well-defined ATP hydrolyzing sites were revealed. ATP was hydrolyzed at the high-affinity sites at a maximum rate of V=19.1+/-0.8 U mg(-1) and K(0.5)=63.8+/-2.9 nmol L(-1), obeying cooperative kinetics (n(H)=1.9); at the low-affinity sites, hydrolysis obeyed Michaelis-Menten kinetics with K(M)=44.1+/-2.6 mumol L(-1) and V=123.5+/-6.1 U mg(-1). Stimulation by Na(+) (V=149.0+/-7.4 U mg(-1); K(M)=7.4+/-0.4 mmol L(-1)), Mg(2+) (V=132.0+/-5.3 U mg(-1); K(0.5)=0.36+/-0.02 mmol L(-1)), NH(4)(+) (V=245.6+/-9.8 U mg(-1); K(M)=4.5+/-0.2 mmol L(-1)) and K(+) (V=140.0+/-4.9 U mg(-1); K(M)=1.5+/-0.1 mmol L(-1)) followed a single saturation curve and, except for Mg(2+), obeyed Michaelis-Menten kinetics. Under optimal ionic conditions, but in the absence of NH(4)(+), ouabain (K(I)=117.3+/-3.5 mumol L(-1)) and orthovanadate inhibited up to 67% of the ATPase activity. The inhibition studies performed suggest the presence of F(0)F(1), V- and P-ATPases, but not Na(+)-, K(+)- or Ca(2+)-ATPases as contaminants in the gill microsomal preparation. (Na(+), K(+))-ATPase activity was synergistically modulated by NH(4)(+) and K(+). At 20 mmol L(-1) K(+), a maximum rate of V=290.8+/-14.5 U mg(-1) was seen as NH(4)(+) concentration was increased up to 50 mmol L(-1). However, at fixed NH(4)(+) concentrations, no additional stimulation was found for increasing K(+) concentrations (V=135.2+/-4.1 U mg(-1) and V=236.6+/-9.5 U mg(-1) and for 10 and 30 mmol L(-1) NH(4)(+), respectively). This is the first report to detail ionic modulation of gill (Na(+), K(+))-ATPase in C. vittatus, revealing an asymmetrical, synergistic stimulation of the enzyme by K(+) and NH(4)(+), as yet undescribed for other (Na(+), K(+))-ATPases, and should provide a better understanding of NH(4)(+) excretion in pagurid crabs.

Nitrogenase proteins from Gluconacetobacter diazotrophicus, a sugarcane-colonizing bacterium

Gluconacetobacter diazotrophicus Pal-5 grew well and expressed nitrogenase activity in the absence of NH 4 + and at initial O 2 concentrations greater than 5% in the culture atmosphere. G. diazotrophicus nitrogenase consisted of two components, Gd1 and Gd2, which were difficult to separate but were purified individually to homogeneity. Their compositions were very similar to those of Azotobacter vinelandii nitrogenase, however, all subunits were slightly smaller in size. The purified Gd1 protein contained a 12:1 Fe/Mo ratio as compared to 14:1 found for Av1 purified in parallel. Both Gd2 and Av2 contained 3.9 Fe atoms per molecule. Dithionite-reduced Gd1 exhibited EPR features at g = 3.69, 3.96, and 4.16 compared with 3.64 and 4.27 for Av1. Gd2 gave an S = 1/2 EPR signal identical to that of Av2. A Gd1 maximum specific activity of 1600 nmol H 2 (min mg of protein) −1 was obtained when complemented with either Gd2 or Av2, however, more Av2 was required. Gd2 had specific activities of 600 and 1100 nmol H 2 (min mg protein) −1 when complemented with Av1 and Gd1, respectively. The purified G. diazotrophicus nitrogenase exhibited a narrowed pH range for effective catalysis compared to the A. vinelandii nitrogenase, however, both exhibited maximum specific activity at about pH 7. The Gd-nitrogenase was more sensitive to ionic strength than the Av–nitrogenase.

Supramolecular Assembling through Anionic Iodine Secondary Bonds: Synthesis and X‐ray Characterization of (Et4N)[PhTeI4] and (Et4N)[(β‐Naphthyl)TeI4

Abstract[PhTe]2 and [(β‐naphthyl)Te]2 react with iodine and tetraethylammonium iodide in toluene/methanol to give (Et4N)[PhTeI4] and (Et4N)[(β‐Naphthyl)TeI4]. The complexes were analysed by single crystal X‐ray diffraction affording the centrosymmetric monoclinic space group P21/c. In the novel compounds only anionic interactions of the types Te···I and I···I take place, cation‐anion effective contacts do not occur. Both anions [PhTeI4] and [(β‐naphthyl)TeI4] exhibit square pyramidal coordination at tellurium, with the iodine atoms in the basal positions and the organic groups apical. The tellurium centers achieve an octahedral coordination in the whole lattices through Te···I secondary bonds with the adjacent ionic species. Only the Te–I‐ and I–I‐secondary bonds behave as structure‐forming interactions in the self‐organization of the supramolecular anionic gatherings. New evidences show that for organyltellurates (Q)[PhTeX4] (Q = protonated amines, amides or amino acids; X = Cl, Br, I), NH···X hydrogen bondings are able to hinder the anionic halogen‐halogen secondary interactions. In case of the more frequent I···I interactions, they have been observed only in the absence of NH···I hydrogen bonds.

Evidence for the participation of lattice nitrogen from vanadium aluminum oxynitrides in propane ammoxidation

The participation of the nitrogen from the lattice of a series of vanadium aluminum oxynitride catalysts (VAlONs) during propane ammoxidation to acrylonitrile was made evident by temporal analysis of products (TAP) at 773 K in the absence of NH 3 and O 2. Moreover, the influence of the presence of gaseous oxygen and/or gaseous ammonia on the catalytic performance of this new catalytic material was studied. Propane conversion increases in the presence of O 2, but it is not affected by NH 3. Propene and acrolein are also formed from propane in the absence of O 2 and are intermediates towards acrylonitrile. In the absence of NH 3 and O 2, the acrylonitrile yield increases with nitrogen content for the same V/Al ratio and decreases with increasing V/Al ratio at constant nitrogen content. Propene yield decreases with nitrogen content and with increasing V/Al ratio. Almost no influence of either nitrogen content or V/Al ratio on the CO 2 yield is observed. The presence of oxygen increases the CO 2 yield at the expense of acrylonitrile and, even more so, of propene. Ammonia does not influence the product distribution in the absence of O 2. The amount of acrolein formed is almost constant, regardless of nitrogen content, V/Al ratio, and reactant mixture, but vanishes when mixed oxides rather then oxynitrides are used. Single-pulse experiments performed with labeled ammonia confirmed the participation of lattice nitrogen in the ammoxidation.

Effect of the reductant nature on the catalytic removal of N 2O on Fe-zeolite-β catalysts

The catalytic reduction of N 2O by H 2, NH 3, CO, propene and n-decane, in the presence of O 2, has been studied on two Fe-zeolite-β (Fe-BEA) catalysts. In the following experimental conditions (GHSV=35 000 h −1, 2000 ppm N 2O, 3% O 2), CO starts to reduce N 2O from 473 K and is the most efficient reductant in the low temperature domain. The absence of strong adsorption and the ability to reduce Fe III oxo-cations can be put forward to explain this behaviour. At medium temperature range n-decane become very reactive to reduce N 2O. Finally, in the absence of NH 3 slip, this reductant can be considered as an excellent candidate owing to the harmless of its reduction products.

Photochemical production of dissolved inorganic nitrogen and primary amines from dissolved organic nitrogen in waters of two estuaries and adjacent surficial groundwaters

Recent studies have shown that in a number of humic-rich surface waters in North America, NH 4 + is released when dissolved organic matter (DOM) is exposed to sunlight. However, photochemical NH 4 + production has not been observed in all surface waters, and factors that contribute to it are not well understood. We hypothesized that the presence or absence of NH 4 + photoproduction may be affected by the light exposure history of DOM. The present study was undertaken to determine whether DOM from surficial groundwaters, with minimal light exposure history, would produce labile nitrogen (N) photoproducts more consistently. In this study, estuarine surface waters and surficial groundwaters, collected just adjacent to estuaries in Georgia and South Carolina, USA, were exposed to sunlight to quantify the photochemical production of NH 4 + , dissolved primary amines (DPA), and NO 2 - . The photoproduction of NH 4 + was observed in 4 of 5 irradiated estuarine surface water samples but in only 2 of 13 groundwater samples. In contrast, NH 4 + concentrations decreased in 5 of 13 groundwater samples when exposed to sunlight. The results indicate that a small amount of NH 4 + may be lost from waters in which groundwater-derived DOM is first exposed to sunlight. No consistent trends were observed in the photoproduction or loss of DPA and NO 2 - .

Transport of NH(3)/NH in oocytes expressing aquaporin-1.

The aim of this study was to determine whether expressing aquaporin (AQP)-1 could affect transport of NH(3). Using ion-selective microelectrodes, the experiments were conducted on frog oocytes (cells characterized by low NH(3) permeability) expressing AQP1. In H(2)O-injected oocytes, exposure to NH(3)/NH (20 mM, pH 7.5) caused a sustained cell acidification and no initial increase in pH(i) (as expected from NH(3) influx), and the cell depolarized to near 0 mV. The absence of Na(+), the presence of Ba(2+), or raising bath pH (pH(B)) did not inhibit the magnitude of the pH(i) decrease or result in an initial increase in pH(i) when NH(3)/NH was added. However, after the cell was acidified (because of NH(3)/NH), raising pH(B) to 8.0 caused a slow increase in pH(i) but had no effect on membrane potential. The changes in pH(i) with raising pH(B) did not occur in the absence of NH(3)/NH. In AQP1 oocytes, exposure to NH(3)/NH usually resulted in little or no change in pH(i), and in the absence of Na(+) there was a small increase in pH(i) (the cell still depolarized to near 0 mV). However, after exposure to NH(3)/NH, raising pH(B) to 8.0 caused pH(i) to increase more than two times faster than in control oocytes. This increase in pH(i) is likely the result of increased NH(3) entry and not the result of NH transport. These results indicate that 1) the oocyte membrane, although highly permeable to NH, has a significant NH(3) permeability and 2) NH(3) permeability is enhanced by AQP1.