Presence Of Excess Ammonia Research Articles

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron‐Containing Frustrated Lewis Pairs (FLPs)

AbstractXanthene‐backbone FLPs featuring secondary borane functions −B(ArX)H (where ArX=C6F5 (ArF) or C6Cl5 (ArCl)) have been targeted through reactions of the dihydroboranes Me2S ⋅ BArXH2 with [4,5‐xanth(PR2)Li]2 (R=Ph, iPr), and investigated in the synthesis of related cationic systems via hydride abstraction. The reactivity of these systems (both cationic and charge neutral) with ammonia have been probed, with a view to probing the potential for proton shuttling via N−H bond ‘activation.’ We find that in the case of four‐coordinate boron systems (cationic or change neutral), the N−H linkage remains intact, supported by a NH⋅⋅⋅P hydrogen bond which is worth up to 17 kcal mol−1 thermodynamically, and enabled by planarization of the flexible xanthene scaffold. For cationic three coordinate systems, N‐to‐P proton transfer is viable, driven by the ability of the boron centre to stabilise the [NH2]− conjugate base through N‐to‐B π bonding. This proton transfer can be shown to be reversible in the presence of excess ammonia, depending on the nature of the B‐bound ArX group. It is viable in the case of C6F5 substituents, but is prevented by the more sterically encumbering and secondary donor‐stabilising capabilities of the C6Cl5 substituent.

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron-Containing Frustrated Lewis Pairs (FLPs).

Xanthene-backbone FLPs featuring secondary borane functions -B(ArX)H (where ArX=C6F5 (ArF) or C6Cl5 (ArCl)) have been targeted through reactions of the dihydroboranes Me2S ⋅ BArXH2 with [4,5-xanth(PR2)Li]2 (R=Ph, iPr), and investigated in the synthesis of related cationic systems via hydride abstraction. The reactivity of these systems (both cationic and charge neutral) with ammonia have been probed, with a view to probing the potential for proton shuttling via N-H bond 'activation.' We find that in the case of four-coordinate boron systems (cationic or change neutral), the N-H linkage remains intact, supported by a NH⋅⋅⋅P hydrogen bond which is worth up to 17 kcal mol-1 thermodynamically, and enabled by planarization of the flexible xanthene scaffold. For cationic three coordinate systems, N-to-P proton transfer is viable, driven by the ability of the boron centre to stabilise the [NH2]- conjugate base through N-to-B π bonding. This proton transfer can be shown to be reversible in the presence of excess ammonia, depending on the nature of the B-bound ArX group. It is viable in the case of C6F5 substituents, but is prevented by the more sterically encumbering and secondary donor-stabilising capabilities of the C6Cl5 substituent.

Enhanced aerosol particle growth sustained by high continental chlorine emission in India

Many cities in India experience severe deterioration of air quality in winter. Particulate matter is a key atmospheric pollutant that impacts millions of people. In particular, the high mass concentration of particulate matter reduces visibility, which has severely damaged the economy and endangered human lives. But the underlying chemical mechanisms and physical processes responsible for initiating haze and fog formation remain poorly understood. Here we present the measurement results of chemical composition of particulate matter in Delhi and Chennai. We find persistently high chloride in Delhi and episodically high chloride in Chennai. These measurements, combined with thermodynamic modelling, suggest that in the presence of excess ammonia in Delhi, high local emission of hydrochloric acid partitions into aerosol water. The highly water-absorbing and soluble chloride in the aqueous phase substantially enhances aerosol water uptake through co-condensation, which sustains particle growth, leading to haze and fog formation. We therefore suggest that the high local concentration of gas-phase hydrochloric acid, possibly emitted from plastic-contained waste burning and industry, causes some 50% of the reduced visibility. Our work implies that identifying and regulating gaseous hydrochloric acid emissions could be critical to improve visibility and human health in India. Half of the reduced visibility due to haze formation in cities in India is attributed to local emission of gas-phase hydrochloric acid from waste-burning and industry, according to measurements of particulate matter and thermodynamic modelling.

Selective catalytic reduction of NOx over Cu- and Fe-exchanged zeolites and their mechanical mixture

SCR-NH3 activities of Cu-SAPO-34 (Cu-CZC) and Fe-Mordenite (Fe-MOR) and their mechanical mixture (50:50) were investigated in the temperature range 150–450 °C using operando FTIR spectroscopy. Structural and textural studies assessed the quality of the material synthesis, while in situ IR characterisation allowed the quantification of the acidic sites at the surface of the zeolites, as well as the cationic distribution inside the pores. As expected, Cu-CZC showed high NOx activity at lower temperatures (75% of NOx conversion at T < 300 °C), while Fe-MOR was more active (>85%) at higher temperatures (300–450 °C). The co-presence of Cu and Fe in the mechanical mixture catalyzes the undesirable oxidation of ammonia and leads to the formation of NO, especially at high temperatures. However, the mechanical mixture of Cu-CZC and Fe-MOR has been found to efficiently operate in the presence of excess ammonia (NH3/NOx = 1.3) in a much broader temperature range comparing to the catalysts modified with only one transition metal (Fe or Cu) and also respect to a sample containing both cations in a single zeolitic framework, thus opening new opportunities in the catalytic reduction of NOx.

Aliphatic Versus Aromatic Nucleophilic Attack of NH3 on Trialkoxy-trinitrobenzenes in the Preparation of TATB

1,3,5-Trimethoxy-2,4,6-trinitrobenzene, 1,3,5-triethoxy-2,4,6-trinitrobenzene, and 1,3-dimethoxy-2,4,6-trinitro-5-propoxybenzene were used in a comparative amination study to evaluate the effect that alkyl ether chain length has on directing the nucleophile in the preparation of 1,3,5-triamino-2,4,6-trinitrobenzene. The results indicated that in the presence of excess ammonia, the aromatic propyl ether carbon is more susceptible to nucleophilic attack than the aromatic methyl ether carbons. Amination of 1,3,5-triethoxy-2,4,6-trinitrobenzene yielded the purest 1,3,5-triamino-2,4,6-trinitrobenzene. The implications of these results on the nucleophilic amination reaction are discussed.

Determination of Amines in the Presence of Excess Ammonia by Ion Chromatography-Mass Spectrometry

A new method for the simultaneous determination of several amines in the presence of an excess of ammonia by ion chromatography-mass spectrometry detection was developed. Current methods using ion chromatography with suppressed conductivity detection are not selective enough to determine small amines at the required level of 10 microg/L or preferably lower in the presence of a large excess of ammonia (approximately 1 mg/L) without resorting to time-consuming sample pre-treatment techniques. By using mass spectrometric detection, which is capable of resolving eluting compounds on their m/z values, an additional dimension of confirmation is added to the analysis. Detection based on the analytes m/z value overcomes problems such as co-elution or background interferences that complicate the quantification when using conductivity detection. The optimal conditions for mass spectrometry detection of amines in the presence of an excess of ammonia were investigated by a four-factor central composite design. The four factors investigated were scan time, cone voltage, probe temperature, and needle voltage. Evaluation of the obtained experimental data showed that detection limits were up to a factor of 100 lower when using mass spectrometry as the detection technique instead of the conventional suppressed conductivity detection. Detection limits of 1 microg/L and lower can be achieved for the six amines investigated in the presence of a large excess of ammonia (approximately 1 mg/L).

Quantum chemical study of gas-phase reactions of trimethylaluminium and triethylaluminium with ammonia in III–V nitride semiconductor crystal growth

We have discussed the gas-phase parasitic reactions in MR 3/H 2/NH 3 (M=Al, Ga, In; R=CH 3, C 2H 5) systems following the elimination of methane or ethane in terms of the regional density functional theory by carrying out ab initio quantum chemical calculations. It is clearly shown that Al source gases enhance reactivity for both of R=CH 3 and C 2H 5. Furthermore, the difference in reactivity between M(CH 3) 3/H 2/NH 3 and M(C 2H 5) 3/H 2/NH 3 systems is discussed. We found that the substitution of ethyl groups for methyl in metal source strengthens the M–N coordination interaction, and the tendency to reduce activation energies of the elimination reaction is observed. However, the steric repulsion between ethyl groups and ammonia, which hardly takes place for R=CH 3, raises activation energies in the presence of excess ammonia.

Inactivation of Cryptosporidium parvum oocysts with ozone and monochloramine at low temperature

The rate of Cryptosporidium parvum inactivation decreased with decreasing temperature (1–20°C) for ozone and for monochloramine applied alone as well as after pre-treatment with ozone. Synergy was observed at all temperatures studied for the ozone/monochloramine sequential disinfection scheme. The synergistic effect was found to increase with decreasing temperature. The inactivation rate with monochloramine after ozone pre-treatment was 5 times faster at 20°C and 22 times faster at 1°C than the corresponding post-lag phase rates of inactivation with monochloramine at these temperatures when no ozone pre-treatment was applied. The CT required for achieving 2-logs of inactivation ranged from 11 400 mg min l −1 at 20°C to 64 600 mg min l −1 at 1°C when monochloramine was applied alone. In contrast, the CT required for an overall sequential inactivation of 2-logs ranged from 721 mg min l −1 at 20°C to 1350 mg min l −1 at 1°C when applying monochloramine after ozone pre-treatment. The presence of excess ammonia in the monochloramine solutions was not responsible for the synergy observed in ozone/monochloramine sequential disinfection.

Quantum chemical study of parasitic reaction in III–V nitride semiconductor crystal growth

We have discussed the gas-phase parasitic reactions in M(CH 3) 3/H 2/NH 3 systems following the elimination of methane by carrying out ab initio quantum chemical calculations, where M denotes Al, Ga, or In. It is clearly shown that the Al source gases enhance reactivity, and the adduct-derived chain compounds grow successively with high exothermicity. We have concluded that the strong Al–N coordination interaction contributes remarkably to the stabilization of the reaction system. In the presence of excess ammonia, we have proved that potential energy barrier of the methane elimination is reduced considerably. The methane elimination by reaction of carrier H 2 gas with M(CH 3) 3 is also exothermic.

Vibrational Spectroscopy of NH4+ Ions in Zeolitic Materials: An IR Study

It is now well accepted that the interaction of NH3 with the Bronsted acid sites of zeolites leads to the formation of NH4+ ions that are strongly H-bonded to the basic oxygens of the lattice; nevertheless, unambiguous evidence of their local siting is still lacking. In this contribution we report a detailed assignment of the IR vibrational features of NH4+ ions which reveals that mainly bidentate and tridentate species with various local symmetry are stabilized inside the cages and channels of ZSM-5, MORD, β, SAPO-34, and Y zeolites. Tetradentate species, mainly in MORD, are also found. In addition, it is shown that Fermi-type resonance interactions lead to the appearance of several bands in the ν(NH) stretching region of the vibrational spectrum that do not correspond to different NH oscillators. Finally, the solvation of NH4+ in the presence of excess ammonia is also investigated, and the IR manifestations, observed when reversibly adsorbed NH3 is present in the channels and cavities, are explained in ...

Growth and regulation of enzyme synthesis in the nitrilotriacetic acid (NTA)-degrading bacterium Chelatobacter heintzii ATCC 29600

In the aerobic bacterium Chelatobacter heintzii, growth and regulation of enzymes involved in nitrilotriacetic acid (NTA) degradation have been investigated in chemostat culture during cultivation with glucose, NTA or mixtures thereof. In batch culture mu max with NTA was 0.18 h-1 and with glucose 0.22 h-1. Growth yields for both substrates were reduced at low dilution rates. During growth with NTA specific activity of the NTA monooxygenase (NTA-MO) exhibited a maximum at D = 0.03 h-1 and gradually decreased with increasing dilution rates. In glucose-grown cells the specific activity as well as immunologically detectable NTA-MO protein was always close to the detection limit. During cultivation with different mixtures of NTA and glucose at a dilution rate of 0.06 h-1, both substrates were utilized simultaneously, irrespective of the NTA/glucose ratio and the presence of excess ammonia. Synthesis of both NTA-MO and iminodiacetic acid dehydrogenase became induced when NTA contributed to more than approximately 1-3% of the total carbon in the substrate mixture supplied. However, NTA was also degraded when the proportion of NTA in the mixture was lower than 1%, which is consistent with the low constitutive level of expression for NTA-MO observed. Results are discussed with respect to NTA biodegradation during sewage treatment and in ecosystems.

Darstellung und spektroskopische Charakterisierung von Nitridophthalocyaninatomangan(V) / Preparation and Spectroscopical Characterization of Nitridophthalocyaninatomanganese(V)

Nitridophthalocyaninatomanganese(V), MnNPc(2–), has been prepared by oxidation of [Mn(OH)2,Pc(2–)]- with chlorine in the presence of excess ammonia in dichloromethane as a chemically very stable, diamagnetic microcrystalline blue powder. The band at 1053 cm-1 in the infrared and resonance Raman spectra is assigned to v(Mn=N). The strong resonance enhancement of v(Mn=N) coincides with an electronic transition at 461 nm assigned to (N → Mn) electron transfer. The UV-VIS spectrum in 1-chloronaphthalene is compared with that of the MnNPc(2–)–H2SO4 adduct and the phthalocyanine-π-cation radical [MnNPc(1–)]+.

Evaluation of a chloramine decomposition model incorporating general acid catalysis

An existing model describing the slow decomposition of chloramines in the presence of excess ammonia was modified to incorporate general acid catalysis of monochloramine disproportionation, a key reaction in determining the rate of chloramine loss. Experiments were conducted at various reaction conditions in the presence of varying concentrations of phosphate which was used as an analog for other naturally occurring proton donors. Results were used to obtain an estimate of the specific rate constant characterizing the effect of H 2PO 4 − and to demonstrate the validity of the overall model formulation. Measured chloramine concentrations compared favorably with predicted values indicating that inclusion of the catalytic effect on monochloramine disproportionation alone appears justified in assessing the effect of phosphate. By analogy, it is expected that similar inorganic proton donors such as those of carbonate and silicate would also potentially affect only monochloramine disproportionation and that the modified model should be better capable of assessing chloramine decay in natural waters.

Dichloramine decomposition in the presence of excess ammonia

The decomposition of aqueous dichloramine in the presence of excess ammonia was studied to verify a proposed decomposition mechanism. Experiments were conducted under conditions in which the three significant reactions were isolated from others that could potentially complicate interpretation of results. The decomposition of dichloramine, producing primarily nitrogen gas and monochloramine, was initiated by mixing solutions of dichloramine and monochloramine under varying experimental conditions of pH, phosphate concentration, and initial dichloramine and monochloramine concentration. The chloramine concentrations were then monitored titrimetrically with time. Rate constants characterizing the reactions were determined using nonlinear least squares regression analysis and the reaction stoichiometry determined by comparing dichloramine loss to monochloramine formed. Phosphate did not catalyze the decomposition which suggests that the mechanism does not involve general base catalysis. A mechanism including a direct reaction of monochloramine was indicated based on both kinetic and stoichiometric considerations. The experimental results obtained at a high initial ratio of dichloramine to monochloramine could be reasonably predicted with the proposed mechanism and one set of rate constants. However, the constants were somewhat dependent on the initial dichloramine ratio. This discrepancy may be due to the existence of another reaction(s) not included in the proposed mechanism.

Ammonia Assimilation in Methylococcus capsulatus (Bath) and other Obligate Methanotrophs

Ammonia assimilation was studied using continuous cultures of three obligate methanotrophs. The type X organism, Methylococcus capsulatus (Bath), assimilated ammonia during growth on dinitrogen or nitrate via the glutamine synthetase/glutamate synthase pathway but utilized the alanine dehydrogenase pathway when grown in the presence of excess ammonia. Repression and derepression of these ammonia assimilation enzymes was demonstrated during the switchover of continuous cultures from nitrogen-free (N2-fixing) medium to medium containing high concentrations of ammonia. The properties of alanine dehydrogenase and glutamate synthase in this organism are discussed. In the type I methanotroph, Methylomonas methanica S1, the pathway of ammonia assimilation was again dependent on the source of fixed nitrogen in the growth medium, but in the type II methanotroph, ‘Methylosinus trichosporium’ OB3b, ammonia was assimilated exclusively via the glutamine synthetase/glutamate synthase pathway.

Microdetermination of aliphatic diamines and polyamines with cupric ion

The reactions of diamines and polyamines with cupric ion were investigated potentiometrically, using a copper ion-selective indicator electrode and a single-junction reference electrode. In general, cupric ion reacted with 2 mol of vic-diamines or their salts. Tetraaza compounds reacted on an equimolar basis with Cu(II). Both vic-diamines and their salts, as well as tetraaza compounds, could be titrated in the presence of excess ammonia. With cupric ion in ammoniacal solution these compounds yield a characteristic purple/violet color. Diamines separated by more than two methylene groups cannot be determined in the presence of ammonia and yield a blue color. Diamines with more than four methylene groups react with cupric ion on an equimolar basis, also yielding a blue color.

Nitrate reductase and glutamine synthetase activities, nitrate and ammonia assimilation, in the unicellular alga Cyanidium caldarium

Nitrogen-limited continuous cultures of Cyanidium caldarium contained induced levels of glutamine synthetase and nitrate reductase when either nitrate or ammonia was the sole nitrogen source. Nitrate reductase occurred in a catalytically active form. In the presence of excess ammonia, glutamine synthetase and nitrate reductase were repressed, the latter enzyme completely. In the presence of excess nitrate, intermediate levels of glutamine synthetase activity occurred. Nitrate reductase was derepressed but occurred up to 60% in a catalytically inactive form.

Partial purine deprivation causes sporulation of Bacillus subtilis in the presence of excess ammonia, glucose and phosphate.

In strains of Bacillus subtilis able to synthesize purines de novo, massive sporulation is suppressed by the combination of excess ammonia, glucose and phosphate. Purine auxotrophs, blocked in the general or the guanine-specific portion of the branched purine pathway, sporulated in such a medium when the purine required for normal growth was removed from the medium. The resulting spore titre and the sporulation frequency increased with the residual growth rate in the purine-free medium, i.e. with the leakiness of the purine mutation. Sporulation was further increased by allowing residual growth in growth-limiting amounts of guanosine. None-leaky purine mutants blocked before 5'-phosphoribosyl-5-amino-4-imidazole carboxamide also sporulated well when supplied with 5-amino-4-imidazole carboxamide at concentrations (2 mM) that supported growth at a suboptimal rate.

Induction of sporulation by inhibitory purines and related compounds

Sporulation of Bacillus subtilis can be induced, in the presence of excess ammonia, glucose and phosphate, by many purine derivatives under conditions of partial growth inhibition. Some of the compounds are known inhibitors of purine nucleotide synthesis. For most compounds the effect is counteracted by adenine and guanine. Partial growth inhibition by amethopterin (methotrexate) causes sporulation in the absence of purines but not in their presence. Unable to induce sporulation at any concentration are inhibitors of DNA, RNA, and protein synthesis as well as base or amino acid analogs that are incorporated into these polymers.

Relation between Glutamine Synthetase and Nitrogenase Activities in the Symbiotic Association between Rhizobium japonicum and Glycine max

The activity and extent of adenylylation of glutamine synthetase was examined in both free-living and bacteroid forms of Rhizobium japonicum in the presence of excess ammonia. Ammonia caused an apparent repression of glutamine synthetase in free-living R. japonicum and adenylylation of the enzyme was also increased. In contrast, neither the activity nor the extent of adenylylation of the bacteroid enzyme was consistently affected by ammonium treatment of bacteroid suspensions. Similar results were obtained after ammonium treatment of soybean plants even though nitrogenase activity was reduced markedly. We have been unable to demonstrate ammonium repression of nitrogenase activity in R. japonicum-Glycine max symbiotic association that is mediated through bacteroid glutamine synthetase. This result is in contrast to the situation in nitrogen-fixing strains of Klebsiella where a role of glutamine synthetase in the regulation of nitrogenase has been reported.