Lewis Acid-Assisted Reduction of Nitrite to Nitric and Nitrous Oxide via the Elusive Nitrite Radical Dianion

Reduction of nitrite anions [NO2]- takes place in a myriad of environments such as in the soil as part of the biogeochemical nitrogen cycle as well as in acidified nuclear waste. Nitrite reduction typically takes place within the coordination sphere of a redox active transition metal. Lewis acid coordination, however, can dramatically modify the reduction potential of this polyoxoanion to allow for reduction under non-aqueous conditions (-0.74 V vs. NHE). This strategy enables the isolation of a borane-capped nitrite dianion [NO2]2- along with its spectroscopic study consistent with reduction to the N(II) oxidation state. Protonation of the nitrite dianion results in facile loss of nitric oxide (NO) while reaction of the nitrite dianion with nitric oxide results in disproportionation to nitrous oxide (N2O) and nitrite, connecting three redox levels in the global nitrogen cycle.

Biophysical and in silico characterization of NrtA: A protein-based host for aqueous nitrate and nitrite recognition

Nitrate and nitrite are key components of the global nitrogen cycle. As such, Nature has evolved proteins as biological supramolecular hosts for the recognition, translocation, and transformation of both nitrate...

Review on bimetallic catalysts for electrocatalytic denitrification

Accelerated industrialization disrupts the global nitrogen cycle, resulting in alarmingly increased nitrate in groundwater and other water bodies. Electrocatalytic nitrate reduction (NO3RR) with high automation can effectively remove nitrate from polluted water, thus avoiding nitrate accumulation. However, the sluggish cathode reaction kinetics severely hampered the efficiency of NO3RR. Developing high-performance cathode catalysts is of great significance for boosting NO3RR. Compared with pure metal catalysts, bimetal catalysts can further improve the cathode activity and selectivity to nitrogen or ammonia in the electrocatalytic process, attracting extensive research interest. In this review, we discussed the background of denitrification requirements and the development status of bimetallic denitrification catalyst. Metallic cathode catalysts, such as noble-metal, 3d transition metal, main group metal, are described emphatically. Finally, present challenges and future outlook on bimetallic denitrification catalysts are depicted.

Biophysical and in silico characterization of NrtA: A protein-based host for aqueous nitrate and nitrite recognition

Nitrate and nitrite are key components of the global nitrogen cycle. As such, Nature has evolved proteins as biological supramolecular hosts for the recognition, translocation, and transformation of both nitrate and nitrite. To understand the supramolecular principles that govern these anion-protein interactions, here, we employ a hybrid biophysical and in silico approach to characterize the thermodynamic properties and protein dynamics of NrtA from the cyanobacterium Synechocystis sp. PCC 6803 for the recognition of nitrate and nitrite.

Satellite-Based Analysis of Spatial–Temporal Distributions of NH3 and Factors of Influence in North China

NH3 is an important part of the global nitrogen cycle as the most important atmospheric alkaline gas. NH3 reacts rapidly with acidic substances and accelerates the generation of particulate matter (PM2.5), which has important effects on the atmosphere and climate change. In this study, satellite NH3 column data were used to analyze spatial and temporal distributions of NH3 in China, and because of high concentrations and rates of change, North China was selected for more detailed analysis. Qualitative analysis was conducted to understand the relations between concentrations of NH3 and those of SO2 and NO2. Last, the random forest method was used to quantify relations between concentrations of atmospheric NH3 and factors influencing those concentrations, such as meteorological factors, NH3 self-emission, and concentrations of SO2 and NO2. Satellite-retrieved NH3 column concentrations showed an increasing trend during the 11 years from 2008 to 2018, and the rate of increase in summer was faster than that in winter. In those 11 years, NH3 self-emission had the greatest influence on NH3 concentrations. Concentrations of SO2 and NO2 had some effect and were negatively correlated with NH3 concentrations. The effect of SO2 on NH3 concentration was greater than that of NO2. Atmospheric NH3 concentration was also affected by meteorological conditions (temperature, relative humidity, pressure, and wind). In summer, temperature is the most important factors of meteorological conditions and relative humidity is the most important factors in winter. Therefore, to better control atmospheric NH3 concentrations, it is particularly important to formulate practical NH3 emission reduction policies and to consider the effects of SO2 and NO2 emission reduction policies.

Cross-Activation of Two Nitrogenase Gene Clusters by CnfR1 or CnfR2 in the Cyanobacterium Anabaena variabilis

Cyanobacterial nitrogen fixation is important in the global nitrogen cycle, in oceanic productivity, and in many plant and fungal symbioses. While the proteins that mediate nitrogen fixation have been well characterized, the regulation of this complex and expensive process is poorly understood in cyanobacteria.

Novel nitrite reductase domain structure suggests a chimeric denitrification repertoire in Phylum Chloroflexi

Denitrification plays a central role in the global nitrogen cycle, reducing and removing nitrogen from marine and terrestrial ecosystems. The flux of nitrogen species through this pathway has a widespread impact, affecting ecological carrying capacity, agriculture, and climate. Nitrite reductase (Nir) and nitric oxide reductase (NOR) are the two central enzymes in this pathway. Here we present a previously unreported Nir domain architecture in members of Phylum Chloroflexi. Phylogenetic analyses of protein domains within Nir indicate that an ancestral horizontal transfer and fusion event produced this chimeric domain architecture. We also identify an expanded genomic diversity of a rarely reported nitric oxide reductase subtype, eNOR. Together, these results suggest a greater diversity of denitrification enzyme arrangements exist than have been previously reported.

Aircraft observations of NO2 and NH3 over selected locations in Germany

<p>Anthropogenic atmospheric emissions of the reactive nitrogen components nitrogen dioxide (NO<sub>2</sub>) and ammonia (NH<sub>3</sub>) have majorly altered the global nitrogen cycle in the past 100 years, with devastating consequences to biodiversity, soil, water and air quality. Thanks to effective legislation, NO2 emissions are declining worldwide. Unfortunately, this is not the case for NH3 for which a recent study reports yearly increases of around 2% in Europe and the U.S. and up to 6% in East Asia. </p><p>Both species are currently actively monitored with several satellite sounders, which provide daily global measurements. Yet, the spatial resolution of current sounders is inadequate for resolving the highly heterogonous spatial distributions of both species. This is particularly the case for point source emitters, for which satellites are currently only able to quantify the largest and most isolated ones. To fill the important gap in the monitoring landscape, a satellite called Nitrosat has been proposed in answer to ESA’s Earth Explorer call.  The satellite would allow making simultaneous measurements of NO<sub>2</sub> and NH<sub>3</sub> at a spatial resolution of 500 meter. In support to the Nitrosat proposal, ESA has funded a project called NITRO-CAM (Nitrogen cycle airborne measurements), which aims at mapping simultaneously NO<sub>2</sub> and NH<sub>3</sub> in the Greater Berlin area using aircraft measurements. It is the results of this campaign that are presented here. These can be seen as proof-of-concept for Nitrosat, but are also interesting in their own right. A larger focus is given to NH<sub>3</sub>, for which the presented measurements are the first of their kind.</p><p>Campaign flights were performed in the surroundings of Berlin in the autumn of 2020. A follow-up campaign is foreseen in early spring. Measurements are performed with BIRA’s UV-VIS spectrometer newly-developed SWING instrument for NO<sub>2</sub> and TELOPS thermal infrared HYPER-CAM for NH<sub>3</sub>. Surveying gapless areas of at least 10 by 10 km, the measurements enable capturing the emissions of both point and area sources, and are suitable for degrading at various hypothetical satellite instrument footprints.  For NO<sub>2</sub> specifically, Berlin and nearby power plants are targeted, while for NH<sub>3</sub> the Piesteritz fertilizer factory is targeted, as well as rural areas in the surroundings of Berlin.   </p>