Ammonia Generation Research Articles

An in situ DRIFTS study of efficient lean NOx reduction with H2 + CO over Pd/Al2O3: the key role of transient NCO formation in the subsequent generation of ammonia

The catalytic reduction of NOx under oxygen rich conditions in the presence of mixed H2+CO reductant feeds occurs much more efficiently on Pd/Al2O3 than Pt/Al2O3 catalysts [Appl. Catal. B 35 (2002) 269]. In effect, CO promotes the former while poisoning the latter. Here in situ DRIFTS was used to investigate details of the reaction mechanisms on both these catalysts. Under various reaction conditions, nitrate, carbonate and bicarbonate species were observed in both cases. However, formate and isocyanate (NCO) species were observed only on the Pd/Al2O3 catalyst. Formate is shown to be spectator, whereas in contrast NCO shows significant reactivity. Although pre-adsorbed NCO is consumed in flowing NO+O2, its reactivity is much greater in H2+NO+O2. We propose that hydrolysis of NCO results in the formation of NH3 species, whose production is ultimately responsible for improved NOx reduction by Pd/Al2O3 in the presence of H2+CO.

Urea thermolysis and NOx reduction with and without SCR catalysts

Urea–selective catalytic reduction (SCR) has been a leading contender for removal of nitrogen oxides (deNOx) from diesel engine emissions. Despite its advantages, the SCR technology faces some critical detriments to its catalytic performance such as catalyst surface passivation (caused by deposit formation) and consequent stoichiometric imbalance of the urea consumption. Deposit formation deactivates catalytic performance by not only consuming part of the ammonia produced during urea decomposition but also degrading the structural and thermal properties of the catalyst surface. We have characterized the urea thermolysis with and without the urea-SCR catalyst using both spectroscopic (DRIFTS and Raman) and thermal techniques (thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)) to identify the deposit components and their corresponding thermal properties. Urea thermolysis exhibits two decomposition stages, involving ammonia generation and consumption, respectively. The decomposition after the second stage leads to the product of melamine complexes, (HNCNH)x(HNCO)y, that hinder catalytic performance. The presence of catalyst accompanied with a good spray of the urea solution helps to eliminate the second stage. In this work, kinetics of the direct reduction of NOx by urea is determined and the possibility of using additives to the urea solution in order to rejuvenate the catalyst surface and improve its performance will be discussed.

In situ ammonia generation as a strategy for catalytic NOx reduction under oxygen rich conditions.

Under highly oxygen rich conditions palladium/alumina catalysts exhibit strongly enhanced NOx reduction activity in the presence of CO:H2 mixtures due to in situ generation of ammonia via the formation and subsequent hydrolysis of isocyanate (NCO) species.

Complete genome sequence of the ammonia-oxidizing bacterium and obligate chemolithoautotroph Nitrosomonas europaea.

Nitrosomonas europaea (ATCC 19718) is a gram-negative obligate chemolithoautotroph that can derive all its energy and reductant for growth from the oxidation of ammonia to nitrite. Nitrosomonas europaea participates in the biogeochemical N cycle in the process of nitrification. Its genome consists of a single circular chromosome of 2,812,094 bp. The GC skew analysis indicates that the genome is divided into two unequal replichores. Genes are distributed evenly around the genome, with approximately 47% transcribed from one strand and approximately 53% transcribed from the complementary strand. A total of 2,460 protein-encoding genes emerged from the modeling effort, averaging 1,011 bp in length, with intergenic regions averaging 117 bp. Genes necessary for the catabolism of ammonia, energy and reductant generation, biosynthesis, and CO(2) and NH(3) assimilation were identified. In contrast, genes for catabolism of organic compounds are limited. Genes encoding transporters for inorganic ions were plentiful, whereas genes encoding transporters for organic molecules were scant. Complex repetitive elements constitute ca. 5% of the genome. Among these are 85 predicted insertion sequence elements in eight different families. The strategy of N. europaea to accumulate Fe from the environment involves several classes of Fe receptors with more than 20 genes devoted to these receptors. However, genes for the synthesis of only one siderophore, citrate, were identified in the genome. This genome has provided new insights into the growth and metabolism of ammonia-oxidizing bacteria.

The molecular pathogenesis of hepatic encephalopathy

Hepatic encephalopathy (HE) incorporates a spectrum of neuropsychiatric abnormalities seen in patients with liver dysfunction with a potential for full reversibility. Distinct syndromes are identified in acute liver failure and cirrhosis. Rapid deterioration in consciousness level and increased intracranial pressure that may result in brain herniation and death are a feature of acute liver failure whereas manifestations of HE in cirrhosis include psychomotor dysfunction, impaired memory, increased reaction time, sensory abnormalities, poor concentration and in severe forms, coma. For over a 100 years ammonia has been considered central to its pathogenesis. In the brain, the astrocyte is the main site for ammonia detoxification, during the conversion of glutamate to glutamine. An increased ammonia level raises the amount of glutamine within astrocytes, causing an osmotic imbalance resulting in cell swelling and ultimately brain oedema. The present review focuses upon the molecular mechanisms involved in the pathogenesis of HE. Therapy of HE is directed primarily at reducing ammonia generation and increasing its detoxification.

Improved alkaline stabilization of municipal wastewater sludge

In Mexico, physicochemical sludge contains high levels of pathogens; and alkaline stabilization is an alternative for their control. However, the odours caused mainly by ammonia generation represent a disadvantage. On the other hand, the ammonia is known as an effective disinfectant. The aim of this study was to evaluate the disinfectant properties of ammonia in sludge, and use it in a closed alkaline stabilization system, which, not only copes with odours but also increases the efficiency of the process. Raw sludge from a municipal wastewater treatment plant using a physicochemical process was used. Ammonia was applied in doses from 10 to 50% w/w; also, doses from 5 to 40% of CaO were applied in open and closed systems and raw and treated sludge quality was evaluated. Results showed that ammonia removed 6 and 5 logs of faecal coliforms and Salmonella spp., respectively and up to 94% of viable helminth ova. The closed system was more efficient than the open system when applying doses from 5 to 20% of CaO. Finally, the results indicate that the ammonia represents an alternative to disinfecting wastewater sludge and it can be used to enhance alkaline stabilization processes.

Absolute density measurements of ammonia produced via plasma-activated catalysis

The generation of ammonia from atomic hydrogen and nitrogen has been demonstrated by means of cavity enhanced absorption spectroscopy. The atomic species are produced in a thermal plasma source in which plasma is created from mixtures of hydrogen and nitrogen. It is shown that for large atomic flux conditions, 2% of the hydrogen and nitrogen can be converted to ammonia. The process in which the ammonia molecules are formed from atomic radicals at the fully covered surface is called plasma-activated catalysis.

Enhanced production of heterologous macrolide aglycones by fed-batch cultivation of Streptomyces coelicolor.

A media development program for the enhanced production of macrolide aglycones by Streptomyces coelicolor is described. Shake flask studies utilizing a yeast extract and a bakers' yeast increased production by 200% and 80%, respectively. However, ammonia generation and high pH were identified as potential problems in these enriched media. Studies in pH-controlled fermentors revealed that production stage pH significantly affects macrolide titers, with low pH (5.5) being more productive than high pH (6.5). Implementation of glucose feeding in shake flask cultures reduced ammonia generation and controlled production stage pH, resulting in significantly enhanced productivities. The combined effects of media supplementation and glucose feeding resulted in a three to five-fold overall improvement in total macrolide aglycone titers, and is the first reported high-level (>1 g/l) production of recombinant polyketides in a heterologous host.

The effect of pH and nucleophiles on complement activation by human proximal tubular epithelial cells.

Activation of urinary complement proteins in situ by proximal tubular epithelial cells (PTEC) may contribute to the mediation of tubulointerstitial injury in patients with significant proteinuria. However, the mechanism involved is unclear, and the role of changes in urinary pH and in the concentrations of urea or ammonia requires further clarification. The protein fraction of urine samples from nine patients with proteinuria >1.5 g/day was purified. A cell ELISA involving cultured HK-2 PTEC was used to investigate the capacity of urinary protein to promote the deposition of both C3 and C9 on the cell surface. The effect of variations in pH (5.5-8.0) and in the concentration of urea and ammonia was also examined. C3 was purified and used to further investigate the mechanism of complement deposition. Urine samples from the majority of patients induced deposition of C3 and C9 on the surface of HK-2 cells via the alternative pathway. This process was maximal at acidic pH values. Preincubation of urinary complement or serum with urea or ammonia inhibited C3 deposition. Purified C3 incubated with HK-2 cells showed no evidence of activation in the absence of other complement components. These data suggest that bicarbonate protects against complement-mediated damage in the lumen by increasing the local pH, rather than by inhibiting the generation of ammonia. PTEC appear to activate complement through provision of a 'protected site' on their surface, rather than by the activation of C3 by convertase-like protease(s).

Organic amendments as a disease control strategy for soilborne diseases of high-value agricultural crops

Manures and by-products derived from the processing of plants and animals have been used for centuries as sources of fertiliser, but beneficial or detrimental effects on plant diseases were never thoroughly investigated. We found that certain organic amendments controlled a variety of soilborne diseases of potato (including common scab and verticillium wilt), various pests (including plant parasitic nematodes) and weeds at nine field locations in Ontario and Prince Edward Island, Canada. The mechanism of disease control for highnitrogen-containing amendments is the generation of ammonia and / or nitrous acid following degradation of the amendments by microorganisms. The formation of these products to concentrations lethal to pathogens is regulated by the soil pH, organic matter content, nitrification rate, sand content and buffering capacity. Liquid swine manure reduced scab and wilt, but at only three of six locations tested. In acidic soils, swine manure killed Verticillium dahliae within a day after application, but had no effect in neutral or alkaline soils. The toxic components in the manure were identified as volatile fatty acids. Ammonium lignosulfonate reduced scab at all six sites tested. The mechanism of disease control is not yet known. Although many of these amendments reduced pathogen populations, total soil microorganism numbers increased by 10- to 1000-fold after application, indicating that not all organisms were killed. Understanding the mode of action of amendments is essential for the improvement of their effectiveness and assimilation into crop production systems. If costs can be decreased and benefits ensured, organic amendments will have a major role in reducing plant diseases. The discussion on use of these amendments is based on cost/ benefit analysis as well as societal and regulatory considerations.

Synthesis of 4,4'-(Tetramethylenedicarbonyldiamino)hai-bis(1-decylpyridinium bromide) and Its Antimicrobial and Deodorant Characteristics.

A new bis-quaternary ammonium compound (bis-QAC), 4, 4'-(tetramethylenedicarbonyldiamino) bis (1-decylpyridinium bromide) (D-136) was synthesized, and its antimicrobial and deodorant characteristics were studied. A vinyl chloride polymer sheet containing D-136 (D-136 sheet) was prepared for practical use because D-136 exhibited a wide and effective antimicrobial spectrum of activity against both bacteria and fungi. The antibacterial and antifungal efficiency of the D-136 sheet was estimated according to the film covering method and the test for fungus resistance. Results showed that the growth of both bacteria and fungi was inhibited on the D-136 sheet. Furthermore, a model test for the deodorant efficiency of water-absorbing resins (SAP) containing D-136 (D-136 SAP) was done on the assumption that it might be applied for use in disposable diapers. To prevent the offensive odor arising from excreted urine in disposable diapers, it is necessary to inhibit the propagation of ureahydrolyzing bacteria in the water-absorbing layer. The microbe used for the experiment was Proteus mirabilis IFO 3849 which produces an enzyme (urease) capable of degrading urea and other compounds present in human urine to ammonia, methylamine and the like. As for the result of the model test, the generation of ammonia from human urine was inhibited on D-136 SAP.

Alkali production by oral bacteria and protection against dental caries.

pH is a key environmental factor affecting the physiology, ecology and pathogenicity of the oral biofilms colonizing the hard tissues of the human mouth. Much attention has been focused on the production of organic acids through the metabolism of carbohydrates by pathogenic oral bacteria. Now, evidence is emerging that alkali generation, particularly through ammonia production from arginine and urea, plays major roles in pH homeostasis in oral biofilms and may moderate initiation and progression of dental caries. This short review highlights recent progress on understanding molecular genetic and physiologic aspects of ammonia generation by prominent oral bacteria.

Alkali production by oral bacteria and protection against dental caries

pH is a key environmental factor affecting the physiology, ecology and pathogenicity of the oral biofilms colonizing the hard tissues of the human mouth. Much attention has been focused on the production of organic acids through the metabolism of carbohydrates by pathogenic oral bacteria. Now, evidence is emerging that alkali generation, particularly through ammonia production from arginine and urea, plays major roles in pH homeostasis in oral biofilms and may moderate initiation and progression of dental caries. This short review highlights recent progress on understanding molecular genetic and physiologic aspects of ammonia generation by prominent oral bacteria.

Tansley Review No. 118: Post-ingestion metabolism of fresh forage.

It is generally assumed that breakdown of plant material in the rumen is a process mediated by gut microorganisms. This view arose because of the identification of a pre-gastric fermentation in the rumen, brought about by a large and diverse microbial population. The extensive use of dried and ground feed particles in forage evaluation might have helped to promote this assumption. However, although the assumption might be correct in animals feeding on conserved forage (hay and silage) where the cells of ingested forage are dead, it is possible that with grazed (living) forage, the role played by plant enzymes in the rumen has been overlooked. In a grazing situation, plant cells that remain intact on entering the rumen are not inert, but will respond to the perceived stresses of the rumen environment for as long as they are metabolically viable. Metabolic adjustments could include anaerobic and heat-shock responses that could promote premature senescence, leading to remobilization of cell components, especially proteins. Moreover, contact of plant cells with colonizing microorganisms in the rumen might promote a type of hypersensitive response, in much the same way as it does outside the rumen. After fresh plant material enters the rumen and prior to extensive plant cell-wall degradation, there is often a phase of rapid proteolysis providing N in excess of that required to maintain the rumen microbial population. The inefficient use of this ingested N results in generation of ammonia and urea in exhaled breath and urine, which promotes welfare and environmental pollution concerns. Therefore an important research goal in livestock agriculture is to find ways of decreasing this initial rate of proteolysis in the rumen. This will benefit the farmer financially (through decreased use of feed supplements), but will also benefit the environment, as N pollution can adversely affect pasture diversity and ecology. This review considers the possible responses of plant metabolism to the rumen environment, and how such considerations could alter current thinking in ruminant agriculture. Contents Summary 37 I. INTRODUCTION 37 II. DIGESTION OF PLANTS IN THE RUMEN: OLD AND NEW CONCEPTS 39 III. RUMEN-INDUCED PLANT METABOLISM: CELL DEGRADATION AND DEATH 41 IV. FUTURE PROSPECTS 50 Acknowledgements 51 References 51.

Electrochemical Reduction of a Bridging Imide: Generation of Ammonia at a Dimolybdenum Tris(-thiolate) Site

Electrochemical Reduction of a Bridging Imide: Generation of Ammonia at a Dimolybdenum Tris(-thiolate) Site

Local pH elevation mediated by the intrabacterial urease of Helicobacter pylori cocultured with gastric cells.

Helicobacter pylori resists gastric acidity by modulating the proton-gated urea channel UreI, allowing for pH(out)-dependent regulation of urea access to intrabacterial urease. We employed pH- and Ca(2+)-sensitive fluorescent dyes and confocal microscopy to determine the location, rate, and magnitude of pH changes in an H. pylori-AGS cell coculture model, comparing wild-type bacteria with nonpolar ureI-deletion strains (ureI-ve). Addition of urea at pH 5.5 to the coculture resulted first in elevation of bacterial periplasmic pH, followed by an increase of medium pH and then pH in AGS cells. No change in periplasmic pH occurred in ureI-deletion mutants, which also induced a slower increase in the pH of the medium. Pretreatment of the mutant bacteria with the detergent C(12)E(8) before adding urea resulted in rapid elevation of bacterial cytoplasmic pH and medium pH. UreI-dependent NH(3) generation by intrabacterial urease buffers the bacterial periplasm, enabling acid resistance at the low urea concentrations found in gastric juice. Perfusion of AGS cells with urea-containing medium from coculture at pH 5.5 did not elevate pH(in) or [Ca(2+)](in), unless the conditioned medium was first neutralized to elevate the NH(3)/NH(4)(+) ratio. Therefore, cellular effects of intrabacterial ammonia generation under acidic conditions are indirect and not through a type IV secretory complex. The pH(in) and [Ca(2+)](in) elevation that causes the NH(3)/NH(4)(+) ratio to increase after neutralization of infected gastric juice may contribute to the gastritis seen with H. pylori infection.

Electrochemical Reduction of a Bridging Imide: Generation of Ammonia at a Dimolybdenum Tris(μ-thiolate) Site

The electrochemical reduction of the imide complex [Mo2(cp)2(mu-SMe)3(mu-NH)]+ (1+) has been investigated in THF and MeCN electrolytes by cyclic voltammetry, controlled-potential electrolysis and coulometry. In the absence of free protons, the electrochemical reduction produces the amide derivative [Mo2(cp)2(mu-SMe)3(mu-NH2)] (2) after consumption of 1 Fmol(-1) of 1+. In THF in the presence of acid, the reduction of 1+ occurs through a two-electron process. The presence of acid also results in the shift of the equilibrium between 1+ and amide dication 2(2+) (MeCN electrolyte) or induces an isomerisation of the imide ligand (THF electrolyte). This allows the electrolysis to be conducted at a potential 600 mV less negative than the reduction potential of 1+. Controlled-potential electrolyses in the presence of acid (2 equiv HTsO) produce the ammine derivative. Ammonia is released from these compounds either by coordination of the solvent (MeCN electrolyte) or by the binding of chloride to the ammine-tosylate complex (electrolyses in THF in the presence of acid and chloride). The final products, isolated almost quantitatively (>95%), are [Mo2(cp)2(mu-SMe)3(MeCN)2]+ and [Mo2(cp)2(mu-SMe)3(mu-Cl)], respectively.

コンクリートにおけるアンモニア発生問題とその対策

コンクリートから発生するアンモニアは, 美術館の収蔵庫に保管されている文化財の変色を引き起こすとともに, 半導体や液晶を製造するクリーンルームの汚染源となる。本文は, コンクリートから発生するアンモニアに関する既往の研究の動向を取りまとめたものである。コンクリートからのアンモニア発生は, 素材であるセメントや骨材中に存在する窒化物とアンモニウムイオンを含む粘土鉱物や雲母などの層状珪酸塩に起因すること, 石灰石は上述のようなアンモニア発生物質を含んでいないこと, などの知見に基づいて, コンクリートからのアンモニア発生の対策を示したものである。

Effect of “mega dose” of vitamin C on polyamine oxidase activity in hepatic tissue or rats

EFFECT OF MEGA DOSE OF VITAMIN C ON POLYAMINE OXIDASE ACTIVITY IN HEPATIC TISSUE OR RATS G. Bjelakovi~, G.B. Bjelakovi~ 1, I. Stojanovi~, B.B. Bjelakovi6, T. Jeftovi6 Institute of Biochemistry, Clinic of Hepati-Gastroenterology, Serbia, Yugoslavia. 1Faculty of Medicine, Serbia, Yugoslavia. Polyamine oxidase (PAO) is a key enzyme in the biodegradation of polyamines. Oxidation of spermine and spermidine by PAO results in the generation of reactive aminoialdehydes, hydrogen peroxide and ammonia. L-ascorbic acid serves as effective antioxidant or at the same time pro-oxidant. In the present paper we have examined the polyamine oxidase activity and the amount of malondialdehyde in the hepatic tissue of rats treated with mega of vitamin C. The experimental animals were treated with the L-ascorbic acid in a daily dose of 12,5 mg/kg body weight intra peritonealy through fourteen days. The control animals group received 0.155 mmol/1 NaC1. Our obtained results show that the treatment of rats with ascorbic acid causes the significant decrease of polyamine oxidase activity (2.878 (0.063 U/rag prot. in the control group) and (1.752 (0.056 in the exp. group, P (0.05). The amount of MDA in the liver of animals treated with high dose of vitamin C increases (MDA in the experimental group 0.562 (0.574 nmol/mg prot. and MDA in the control group 0.327 (0.634 nmol/mg prot. P (0.001). The higher amount of malondialdehyde in the experimental group is probably a reflex of vitamin C prooxidant effects at the level of hepatic tissue. I C11/15 I

Effect of lactitol on blood ammonia response to oral glutamine challenge in cirrhotic patients: evidence for an effect of nonabsorbable disaccharides on small intestine ammonia generation

OBJECTIVE: Nonabsorbable disaccharides are widely used to decrease blood ammonia concentration. Their principal mode of action is the modification of pH and bacterial flora in the colon. The aim of the present study was to test the hypothesis that these drugs may also reduce small intestine ammonia generation. METHODS: Eight male cirrhotics without overt hepatic encephalopathy received 20 g of glutamine in 100 ml of water. Venous samples for whole blood ammonia were taken before, 30 and 60 min after the load. Immediately after the last blood sample the patients were submitted to the following psychometric tests: number connection test, Posner’s attention test, and Sternberg paradigm. After the first glutamine load, patients were started on lactitol (initial dose 20 g, three times a day). Once two bowel movements/day were obtained and maintained for at least 5 days, oral glutamine challenge and psychometric tests were repeated. RESULTS: Ammonia increased significantly after the glutamine load (from 83 ± 13 to 164 ± 30 μg/dl at 30 min and 210 ± 29 μg/dl at 60 min; mean ±SE; p = 0.006 analysis of variance) but not after glutamine load after lactitol treatment (from 77 ± 17 to 111 ± 21 μg/dl and 142 ± 24 μg/dl; p = not significant). The peak increment (127 ± 24 vs 65 ± 18 μg/dl; p = 0.008) of ammonia elevation was significantly smaller during lactitol administration. The patients’ psychometric performance after the glutamine load did not differ significantly after lactitol treatment. CONCLUSIONS: Lactitol reduces the elevation in blood ammonia that follows oral glutamine challenge. Because enterally administered glutamine is efficiently absorbed in the jejunum and, in part, metabolized to ammonia we suggest that lactitol affects small intestine ammonia generation probably by shortening the residence time of intestinal contents.