Presence Of NH Research Articles

Studies on the Condensation Pathway to and Properties of Diiron Azadithiolate Carbonyls

Reaction of Fe(2)(SH)(2)(CO)(6) and HCHO, which gives Fe(2)[(SCH(2))(2)NH](CO)(6) in the presence of NH(3), affords the possible intermediate Fe(2)(SCH(2)OH)(2)(CO)(6), which has been characterized crystallographically as its axial-equatorial isomer. Fe(2)(SCH(2)OH)(2)(CO)(6) was shown to react with ammonia and amines to give Fe(2)[(SCH(2))(2)NR](CO)(6) (R = H, alkyl). Related hemithioacetal intermediates were generated by treatment of Fe(2)(SH)(2)(CO)(6) with RC(O)C(O)R (R = H, Ph, 4-F-C(6)H(4)) to give cycloadducts. The benzil derivative Fe(2)[S(2)C(2)(OH)(2)Ph(2)](CO)(6), a C(2)-symmetric species, was also characterized crystallographically. The acylated azadithiolate Fe(2)[(SCH(2))(2)NAc](CO)(6) was prepared by reaction of Li(2)Fe(2)S(2)(CO)(6) with (ClCH(2))(2)NC(O)Me. DNMR experiments show that the free energies of activation for rotation of the amide bond are the same for Fe(2)[(SCH(2))(2)NAc](CO)(6) and Fe(2)[(SCH(2))(2)NAc](CO)(4)(PMe(3))(2), which implies that the ligands on the iron centers do not strongly affect the basicity of the nitrogen. As a control, we showed that the thioamide Fe(2)[(SCH(2))(2)NC(S)Me](CO)(6) does exhibit a significantly higher barrier to rotation, attributable to the increased double-bond character of the N-C(S) bond.

Mechanistic Investigation of Deactivation of Ru/Al2O3 Catalyst for Preferential CO Oxidation in the Presence of NH3

The preferential CO oxidation (PROX) on a Ru/Al2O3 catalyst was investigated at 115−185 °C in the presence of 21−75 ppm NH3. With an increase in [O2]/[CO] ratios, the CO conversion decreased, though it increased in the absence of NH3. In the presence of NH3, the catalytic activity was high at high temperature, which indicates that O2 was consumed over the upstream of the catalyst bed and that the reaction atmosphere in most portions of catalyst bed was reductive. Thus, a reduction atmosphere kept the catalyst active. For the H2 oxidation without CO, the catalyst was immediately deactivated in the presence of NH3, which indicates that the activation of oxygen was suppressed. In the in-situ IR spectra, a band assigned to nitrosyls appeared during the poisoning, and the intensity increased with time on stream. In addition, the band intensity of monocarbonyls decreased with an increase in that of multicarbonyls and nitrosyls. The presence of multicarbonyls indicates that the nitrosyls stabilized the oxidized ...

The Impact of Ammonia Photo-Oxidation Under UV Light from Low Pressure Mercury Lamps on Bromate Decay in Water

This research examines the influence of ammonia photo-oxidation on the reduction of the water contaminant, bromate (BrO3-) as a potential removal strategy. It has long been recognized that aqueous ammonia (NH3) has the potential to accelerate the photodecomposition of bromate. This phenomenon has never been studied in dilute solutions whereby its impact during water treatment with UV low-pressure lamps may be used advantageously. It is hypothesized that the accelerated rate of BrO3- photodecomposition in the presence of NH3 is attributed to the generation of an additional supply of electrons as ammonia photo-oxidation occurs. The findings revealed that the rate of bromate photo-decay is increased in the presence of ammonia even in dilute ammonia and BrO3- solutions and the reaction is further accelerated in basic solutions and solutions containing chloride ions. Nitrate is the final stable reaction product formed with prolonged irradiation, followed by a depression of pH. Hypobromous acid was undetected at these concentrations. It was also found that ammonia oxidation occurred in the presence of bromide ions even in acidic solution. The hypothesis that electrons are made available for electron scavengers when ammonia oxidation occurs was verified using sulphur hexafluoride as an electron scavenger.

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.

Ammonia-based hydrogen source for fuel cell applications

Generation of hydrogen from the reaction of ammonia ( NH 3 ) with magnesium hydride ( MgH 2 ) was studied. Experiments were conducted at near ambient temperatures (75– 150 ∘ C ), which are lower than that required by ammonia cracking and/or metal hydride thermal decomposition reactions. Effects of selected catalysts/promoters for the production of hydrogen by the NH 3 – MgH 2 reaction were evaluated. Addition of ammonium chloride ( NH 4 Cl ) accelerated the NH 3 – MgH 2 reaction. MgH 2 doped with either PdCl 2 or PtCl 4 also showed increased reactivity towards NH 3 for H 2 production in the presence of NH 4 Cl . Results from this study demonstrated the feasibility of hydrogen production from ammonia-based reactions in support of potable hydrogen fuel cells. These preliminary results warrant further systematic studies to elucidate the activation mechanism of PdCl 2 or PtCl 4 as catalysts, as well as the role of NH 4 Cl as an additive, a reactant and/or a catalyst in the reaction system of interest.

Characterization and kinetic study of carbon-based briquettes for the reduction of NO

Carbon-based catalytic briquettes have been prepared for the reduction of NO in the presence of NH 3 at low temperatures (100–250 °C). In general terms, the reduction efficiency is promoted by an increase in the support porosity, and especially, by an oxidizing treatment prior to the impregnation. The apparent rate constants for the catalytic briquettes doped with the ashes of a petroleum coke are within the same order of magnitude as other catalysts for selective catalytic reduction (SCR) of NO at low temperature, demonstrating the feasibility of using them for this purpose.

Pd/C‐Catalyzed Deoxygenation of Phenol Derivatives Using Mg Metal and MeOH in the Presence of NH4OAc.

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Cleaning Up η Carinae: Detection of Ammonia in the Homunculus Nebula

We report the first detection of ammonia in the Homunculus nebula around eta Carinae, which is also the first detection of emission from a polyatomic molecule in this or any other luminous blue variable (LBV) nebula. Observations of the NH3 (J,K)=(3,3) inversion transition made with the Australia Telescope Compact Array reveal emission at locations where infrared H2 emission had been detected previously, near the strongest dust emission in the core of the Homunculus. We also detect ammonia emission from the so-called ``strontium filament'' in the equatorial disk. The presence of NH3 around eta Car hints that molecular shells around some Wolf-Rayet stars could have originated in prior LBV eruptions, rather than in cool red supergiant winds or the ambient interstellar medium. Combined with the lack of any CO detection, NH3 seems to suggest that the Homunculus is nitrogen rich like the ionized ejecta around eta Car. It also indicates that the Homunculus is a unique laboratory in which to study unusual molecule and dust chemistry, as well as their rapid formation in a nitrogen-rich environment around a hot star. We encourage future observations of other transitions like NH3 (1,1) and (2,2), related molecules like N2H+, and renewed attempts to detect CO.

Deactivation of Ru/Al2O3 Catalyst for Preferential CO Oxidation in the Presence of Low-concentration NH3 by Nitrosyl Species

Abstract The behavior of a Ru/Al2O3 catalyst for the preferential CO oxidation in the presence of low-concentration NH3 (21–75 ppm) was investigated. In contrast to the results in the absence of NH3, the catalyst was rapidly deactivated at higher [O2]/[CO] ratios in the presence of NH3. NH3 was oxidized to nitrosyl species, which was strongly adsorbed on Ru and suppressed the activation of both oxygen and CO. At low [O2]/[CO] ratios, the catalyst exhibited a stable activity even in the presence of NH3, and the deactivated catalyst was rapidly regenerated.

Electrogenic ammonium transport by renal Rhbg

The recently cloned, non-erythrocyte Rh glycoproteins (Rhbg and Rhcg) are expressed in the intercalated cells of the renal collecting duct. The apical Rhcg and the basolateral Rhbg are likely involved in NH 3 and/or NH 4 + transport, yet the characteristics of this transport are not yet certain. In this study we investigated the mechanism of NH 4 + transport by Rhbg and Rhcg expressed in Xenopus oocytes. We used a two-electrode voltage-clamp and ion-selective microelectrodes to measure NH 4 +-induced currents (I NH4) and changes in pH i, respectively. In oocytes expressing Rhcg, exposure to bath [NH 4 +] of 2.5–20 mM induced inward currents that were slightly more than those in H 2O-injected (control) oocytes. I–V plots in the presence of NH 4 + showed a small increase in slope conductance only at positive potentials. On the other hand, in oocytes expressing Rhbg, 5 mM NH 4 + induced an inward I NH4 of –79 nA, decreased pH i (ΔpH i) by 0.13 at a rate (dpH i/dt) of –2 7 × 10 −4 pH/s and depolarized the cell by 45 mV. These changes were significantly more than those in control oocytes. I–V plots in the presence of NH 4 + showed substantial increase in conductance. Amiloride (1 mM) inhibited I NH4, ΔpH i and dpHi/dt in oocytes expressing Rhbg but not in control oocytes. Raising bath [NH 4 +] in increments from 1 to 20 mM elicited a faster dpH i/dt, a larger decrease in pH i and a larger depolarization. Net NH 4 + flux by Rhbg (estimated from dpHi/dt) was proportional to [NH 4 +] gradient and followed saturation kinetics with an apparent K m of 2.3 mM. Methyl ammonium (5 mM) induced a current of –63 nA in Rhbg oocytes but did not cause any change in control oocytes. These data indicate that: 1) Rhbg transport of NH 4 + is electrogenic. 2) Methyl ammonium is transported by Rhbg. 3) NH 4 + transport by Rhbg is saturated at high concentrations with Michaelis–Menten kinetics.

Molecular structure and catalytic activity of V 2O 5/TiO 2 catalysts for the SCR of NO by NH 3: In situ Raman spectra in the presence of O 2, NH 3, NO, H 2, H 2O, and SO 2

In situ Raman spectroscopy has been used at temperatures up to 400 °C under O 2, NH 3/N 2, H 2/N 2, NH 3/NO/O 2/N 2, O 2/H 2O/N 2, and SO 2/O 2/N 2 for studying the influence of these gases on the molecular structure of V 2O 5/TiO 2 catalysts with V surface density, n s , in the range 2.5–18.7 VO x /nm 2. The catalyst activities for the SCR of NO by NH 3 have been determined to derive structure–activity relationships in combination with the Raman data. Isolated monovanadates and polyvanadates are formed at various proportions (depending on the loading) on the catalyst surface under dehydrated conditions. The band positions and characteristics are discussed in terms of possible configurations for the dispersed VO x species. The bands observed, the surface composition, and the bond conservation rule allow to propose a small size for the V O V chains of polyvanadates (i.e., 2, 3). The reducing action of NH 3 is favored in the presence of adjacent V sites; at low loadings, the presence of NH 3 has no effect on the structural properties of surface VO x . The reducibility in H 2 follows an opposite trend and is favored at low n s , as indicated by both in situ Raman and H 2-TPR. The SO 2 presence affects only the molecular structure of catalysts with low n s , for which a significant part of surface TiO 2 sites are vacant; the effect (judged from the in situ Raman data) is merely one of driving the dispersed vanadia species in a state of “virtually” high surface density by crowding them together, thereby providing more adjacent V sites for activation of NH 3 in SCR reaction conditions. The NO TOF values initially increase with increasing n s , suggesting that the number of active sites per V atom increases with increasing n s below monolayer. The formation of adjacent V O Ti sites is favored either at increasing n s or at conditions of “virtually” high n s (in the presence of SO 2). The increase in the number of such centers per V atom correlates with the increase in TOF values with increasing n s .

Pd/C-Catalyzed Deoxygenation of Phenol Derivatives Using Mg Metal and MeOH in the Presence of NH4OAc

A Pd/C-catalyzed deoxygenation method of phenolic hydroxyl groups via aryl triflates or mesylates using Mg metal in MeOH at room temperature was developed. The addition of NH4OAc dramatically affects the reactivity and reaction rate. This method is particularly attractive to provide an environmentally benign and widely applicable removal method of phenolic alcohols under quite mild reaction conditions.

Highlighting threading dislocations in MOVPE-grown GaN using an in situ treatment with SiH 4 and NH 3

Fast-turnaround, accurate methods for the assessment of threading dislocation (TD) densities in GaN are an essential research tool. Here, we present an in situ surface treatment in which GaN is exposed to a SiH 4 flux at 860 °C in the presence of NH 3. Following a 240 s exposure to SiH 4, pits associated with screw or mixed-type TD were found to have more than doubled in diameter, as measured by atomic force microscopy (AFM). These pits are associated with step-edge terminations. Additional small pits had appeared, not associated with step-edge terminations, which are believed to relate to edge-type TDs. The total density of pits on the treated surface corresponded to the total dislocation density measured by transmission electron microscopy. Pits related to edge-type TDs are often overlooked in AFM of untreated GaN. As the SiH 4 treatment time is increased, the measured dislocation density initially increases, but after a 240 s treatment all the TDs may be observed. The pit width initially increases with treatment time, but then plateaus. The SiH 4 treatment is effective in increasing dislocation pit size on both n- and p-type material, and has also been used on partially coalesced GaN layers.

Growth dynamics of Azospirillum lipoferum at steady and transitory states in the presence of NH

The objective of this paper was to study the adaptation dynamics and biochemical response of Azospirillum lipoferum grown in a continuous culture at various environmental shifts. The kinetics of A. lipoferum Sp 59b grown at steady states in a microaerobic chemostatic environment deviated from a typical Monod kinetics in both low and high dilution rates (D) due to several metabolic shifts that occurred in the microbial cell. When NH4Cl was exhausted (at low D), the microbial cell partitioned carbon flow in order to sustain growth, nitrogen fixation and assimilation processes (occurred via the glutamate synthase reaction). Increasing D the specific activities of the enzymes involved in the tricarboxylic acid cycle and the respiration rate were decreased. At transitory states, under optimal for nitrogen fixation dissolved oxygen (DO) concentrations, ammonium nitrogen negatively affected, besides nitrogen fixing activity, the bacterial growth. At sub-optimal for nitrogen fixation DO concentration (i.e. 1.56 microM) and 0.1 g l(-1) NH4Cl in the fed medium, the activities of citrate synthase and succinate dehydrogenase were significantly reduced. Important shifts in both carbon and nitrogen metabolism occur in A. lipoferum grown in the presence of the ammonium nitrogen, while the boundaries of ammonium nitrogen concentration in which A. lipoferum can be adapted depend on the DO concentration in the growth environment. Studies on growth dynamics and physiology of A. lipoferum, grown in experimental model systems, can contribute to an efficient application of these bacteria as plant-growth-promoting-agents.

Facile Synthesis and Fungicidal Activity of Novel 4,4′‐Bis[2′′‐(5′′′‐substituted rhodanin‐3′′′‐yl)thiazol‐4′′‐yl]bibenzyls.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design and solvothermal synthesis of luminescent copper(i)-pyrazolate coordination oligomer and polymer frameworks

Two luminescent coordination compounds, [Cu(Pz)]3 (1) and [Cu2(Bpz)]n (2), were isolated from solvothermal reactions of Cu(NO3)2 with 3,5-dimethylpyrazole (HPz) and 3,3',5,5'-tetra-methyl-4,4'-bipyrazole (H2Bpz) respectively in the presence of NH3, of which 1 was revealed to be a planar trimer and 2 a three-dimensional framework, presenting a rare 3-connected binodal (6(2).10)(6.10(2)) topology and eight-fold interpenetration.

Light-Triggered Action Potentials and Changes in Quantum Efficiency of Photosystem II in Anthoceros Cells

Capillary microelectrodes and pulse amplitude-modulated microfluorometry were used to study light-triggered changes in cell membrane potential, chlorophyll fluorescence, and photochemical yield of PSII in chloroplasts of a hornwort Anthoceros sp. The action potential was generated by illuminating the plant sample for a few seconds. It was accompanied by a reversible decrease in quantum efficiency of PSII and by nonphotochemical quenching of fluorescence that continued as long as 10 min after the light stimulus. The presence of ammonium ions (2 mM) enhanced the amplitude and prolonged the duration of dark changes of fluorescence parameters in accordance with the reported increase in duration and amplitude of the light-triggered action potential in the presence of NH 4 + . A rapid retardation of PSII activity within the first seconds of illumination was also evident from absorbance changes at 810 nm reflecting the redox conversions of chlorophyll P700. The PSII-dependent stage of reduction in the induction curves of P700 absorbance was strongly suppressed, and the amplitudes of signals induced by white and far-red light (717 nm) differed insignificantly. It is concluded that a short-term irradiation triggers the generation of ΔpH at the thylakoid membranes, which is accompanied by inhibition of the plasma membrane H+ pump and by reversible inactivation of PSII due to increased thermal dissipation of chlorophyll excitations.

The weak bases NH3 and trimethylamine inhibit the medium and slow afterhyperpolarizations in rat CA1 pyramidal neurons

The weak bases NH(3) and trimethylamine (TMeA), applied externally, are widely used to investigate the effects of increasing intracellular pH (pH(i)) on neuronal function. However, potential effects of the compounds independent from increases in pH(i) are not usually considered. In whole-cell patch-clamp recordings from rat CA1 pyramidal neurons, bath application of 1-40 mM NH(4)Cl or TMeA HCl reduced resting membrane potential and input resistance, inhibited the medium and slow afterhyperpolarizations (AHPs) and their respective underlying currents, mI(ahp) and sI(ahp), and led to the development of depolarizing current-evoked burst firing. Examined in the presence of 1 microM TTX and 5 mM TEA with 10 mM Hepes in the recording pipette, NH(3) and TMeA increased pH(i) and the magnitudes of depolarization-evoked intracellular [Ca(2+)] transients, Ca(2+)-dependent depolarizing potentials, and inward Ca(2+) currents but reduced the slow AHP and sI(ahp). When internal H(+) buffering power was raised by including 100 mM tricine in the patch pipette, the effects of NH(3) and TMeA to increase pH(i) and augment Ca(2+) influx were attenuated whereas the reductions in the slow AHP and sI(ahp) (as well as membrane potential and input resistance) were maintained. The findings indicate that increases in pH(i) contribute to the increases in Ca(2+) influx observed in the presence of NH(3) and TMeA but not to the reductions in membrane potential, input resistance or the magnitudes of AHPs. The results have implications for the interpretation of data from experiments in which pH(i) is manipulated by the external application of NH(3) or TMeA.

A Novel Synthesis, Including Asymmetric Synthesis of α‐Quaternary α‐Amino Acid Methyl Esters from Ketones via Sulfinyloxiranes.

AbstractFor Abstract see ChemInform Abstract in Full Text.