The unique high-resolution feature offered by 14N magic-angle spinning (MAS) NMR spectroscopy of ammonium ions has been used to characterize the crystal structures of various ammonium molybdates by their 14N quadrupole coupling parameters, i.e., CQ, the quadrupole coupling constant, and etaQ, the asymmetry parameter. Two polymorphs of diammonium monomolybdate, (NH4)2MoO4, recently structurally ...

In the in-situ remediation of ammonium (NH4+) in groundwater by a sequential reactive barrier filled with zeolite, it is of great importance to understand the mechanisms of NH4+ sorption to zeolite. In this study, the effect of dissolved natural organic matter on NH4+ sorption to natural Chinese clinoptilolite was studied by batch experiments taking humic acid (HA) as a model substance. The sur...

Enhanced soil ammonium (NH4+) concentrations in wetlands often lead to graminoid dominance, but species composition is highly variable. Although NH4+ is readily taken up as a nutrient, several wetland species are known to be sensitive to high NH4+ concentrations or even suffer toxicity, particularly at low soil pH. More knowledge about differential graminoid responses to high NH4+ availability ...

Genetic manipulation of nitrogenase and key glutamate-forming enzymes can provide mutants that excrete fixed N2 as NH4+. A derepressed N2 fxation mutant (SK-24) has been isolated , which excretes up to 20.2 mumol of fixed N2 as NH4+ per mg of cell protein in 24 hr at room temperature. Biochemical analysis shows that this mutant, which requires glutamate for growth, releases fixed N2 as NH4+ int...

The obligately ammonia-oxidizing bacterium Nitrosomonas europaea was incubated in medium containing 50 mM ammonium. Changes in the concentration of nitrite, the pH, and the NH4 and NH2OH-dependent O2 uptake activities of the cell suspension were monitored. The NH4 -dependent O2 uptake activity doubled over the first 3 h of incubation and then slowly returned to its original level over the follo...

l h e pyruvate dehydrogenase kinase-catalyzed inactivation of the pyruvate dehydrogenase complex was studied using dialyzed, soluble proteins from mitochondria purified from green leaf tissue of Pisum sativum 1. seedlings. At subsaturating ATP concentrations, K+ or NH4+, but not Na+, stimulated the pyruvate dehydrogenase kinase by lowering the K,,,(ATP). Micromolar concentrations of NH4+ were r...

The purpose of this study is to investigate the capacity of natural Turkish zeolite for NH4-N removal from landfill leachate. The effects of modification and initial concentration on the removal of NH4-N from leachate were also investigated. The kinetics of adsorption of NH4-N has been discussed using three kinetic models, i.e., the pseudo-second order model, the Elovich equation, the intrapart...

Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH4+ ), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (Fv /Fm ) was a sensitive indicator of NH4+ toxicity, manifested by a suppression of Fv /Fm in a dose-dependent manner. Tw...

NH4 nutrition provokes mild toxicity by enhancing H2O2 accumulation, which acts as a signal activating systemic acquired acclimation (SAA). Until now, induced resistance mechanisms in response to an abiotic stimulus and related to SAA were only reported for exposure to a subsequent abiotic stress. Herein, the first evidence is provided that this acclimation to an abiotic stimulus induces resist...

A study to assess the various gases emitted by motorcycles in a metropolitan State, Uyo, in Nigeria was carried out. Two hundred commercial motorcycles the mostly available means of transport were used for the study drawn from seven motorcycle parks. The gases examined were nitrogen dioxide, sulphur dioxide, carbon monoxide, chlorine, hydrogen sulphide and ammonia. The overall collection result...