► Nitrous oxide reductase catalyses the last step of the denitrification pathway in bacteria. ► Structure of the “CuZ center” of purple nitrous oxide reductase. ► New insights to structure and mechanism of nitrous oxide reductase. ► Spectroscopic features and catalytic parameters of the different redox form of nitrous oxide reductase. ► Inter-subunit electron transfer from the CuA center to the catalytic CuZ center of nitrous oxide. Nitrous oxide is a potent greenhouse gas, whose atmospheric concentration has been increasing since the introduction of the Haber Bosch process led to the widespread use of nitrogenous fertilizers. One of the pathways to its destruction is reduction to molecular nitrogen by the enzyme nitrous oxide reductase found in denitrifying bacteria. This enzyme catalyzes the last step of the denitrification pathway. It has two copper centers, a binuclear CuA center, similar to the one found in cytochrome oxidase, and the CuZ center, a unique tetranuclear copper center now known to possess either one or two sulfide bridges. Nitrous oxide reductase has been isolated in different forms, depending on the oxidation state and molecular forms of its Cu centers. Recently, the structure of a purple form, which has both centers in the oxidized state, revealed that the CuZ center has the form [Cu S ]. This review summarizes the biogenesis and regulation of nitrous oxide reductase, and the spectroscopic and kinetic properties of nitrous oxide reductase. The proposed activation and catalytic mechanism, as well as, electron transfer pathways are discussed in the light of the various structures of the CuZ center.
Nitrous oxide (N O), a potent greenhouse gas, can be emitted during wastewater treatment, significantly contributing to the greenhouse gas footprint. Measurements at lab-scale and full-scale wastewater treatment plants (WWTPs) have demonstrated that N O can be emitted in substantial amounts during nitrogen removal in WWTPs, however, a large variation in reported emission values exists. Analysis of literature data enabled the identification of the most important operational parameters leading to N O emission in WWTPs: (i) low dissolved oxygen concentration in the nitrification and denitrification stages, (ii) increased nitrite concentrations in both nitrification and denitrification stages, and (iii) low COD/N ratio in the denitrification stage. From the literature it remains unclear whether nitrifying or denitrifying microorganisms are the main source of N O emissions. Operational strategies to prevent N O emission from WWTPs are discussed and areas in which further research is urgently required are identified.
This review article summarizes efforts to use nitrous oxide (N 2 O, 'laughing gas') as a reagent in synthetic chemistry. The focus will be on reactions which are carried out in homogeneous solution under (relatively) mild conditions. First, the utilization of N 2 O as an oxidant is discussed. Due to the low intrinsic reactivity of N 2 O, selective oxidation reactions of highly reactive compounds are possible. Furthermore, it is shown that transition metal complexes can be used to catalyze oxidation reactions, in some cases with high turnover numbers. In the final part of this overview, the utilization of N 2 O as a building block for more complex molecules is discussed. It is shown that N 2 O can be used as an N-atom donor for the synthesis of interesting organic molecules such as triazenes and azo dyes. Nitrous oxide (N 2 O, 'laughing gas') is a very inert molecule. Still, it can be used as a reagent in synthetic organic and inorganic chemistry, serving as O-atom donor, as N-atom donor, or as a oxidant in metal-catalyzed reactions.
Nitrous oxide (N2O) is an important anthropogenic greenhouse gas and agriculture represents its largest source. It is at the heart of debates over the efficacy of biofuels, the climate-forcing impact of population growth, and the extent to which mitigation of non-CO2 emissions can help avoid dangerous climate change. Here we examine some of the major debates surrounding estimation of agricultural N2O sources, and the challenges of projecting and mitigating emissions in coming decades. We find that current flux estimates using either top-down or bottom-up methods are reasonably consistent at the global scale, but that a dearth of direct measurements in some areas makes national and sub-national estimates highly uncertain. We also highlight key uncertainties in projected emissions and demonstrate the potential for dietary choice and supply-chain mitigation.
This review article summarizes efforts to use nitrous oxide (N2O, 'laughing gas') as a reagent in synthetic chemistry. The focus will be on reactions which are carried out in homogeneous solution under (relatively) mild conditions. First, the utilization of N2O as an oxidant is discussed. Due to the low intrinsic reactivity of N2O, selective oxidation reactions of highly reactive compounds are possible. Furthermore, it is shown that transition metal complexes can be used to catalyze oxidation reactions, in some cases with high turnover numbers. In the final part of this overview, the utilization of N2O as a building block for more complex molecules is discussed. It is shown that N2O can be used as an N-atom donor for the synthesis of interesting organic molecules such as triazenes and azo dyes.
Pernicious anaemia screen was negative, and the cerebrospinal fluid was acellular with normal protein and absent oligoclonal bands. N2O has been used commonly as an inhalational anaesthetic agent.1 2 It has however become a popular recreational drug, with a large 2012 UK survey of over 22 000 people involved in regular recreational drug use in the dance and clubbing scene, revealing that about 50% consumed N2O recreationally at some stage.1 It is easily accessible over the internet and on the streets at low cost, in the form of ‘whippets’ or bulbs, which are aerosol chargers used in canisters of whipped cream.1 3 It has been suggested that risk of neurological impairment increases with consumption of >10 bulbs/day.4 Toxic effects of N2O are mediated by irreversible inactivation of vitamin B12 resulting in reduced recycling of homocysteine to methionine, thereby preventing methylation of myelin proteins and causing demyelination within the central and peripheral nervous system, although ischaemic neuropathy has also been suggested as an additional mechanism.1 Most reported cases of neurotoxicity relate to the development of subacute combined degeneration of the spinal cord as observed in the current case. Furthermore, she also had encephalopathy with periventricular white matter changes, which have been observed rarely in other reports.5 Similarly, skin changes as observed in our patient have been rarely reported and are postulated to relate to the stimulation of melanocytes to produce melanin from the B12 deficiency-induced reduction in glutathione levels.
Forest ecosystems may provide strong sources of nitrous oxide (N2O), which is important for atmospheric chemical and radiative properties. Nonetheless, our understanding of controls on forest N2O emissions is insufficient to narrow current flux estimates, which still are associated with great uncertainties. In this study, we have investigated the quantitative and qualitative relationships between N-cycling and N2O production in European forests in order to evaluate the importance of nitrification and denitrification for N2O production. Soil samples were collected in 11 different sites characterized by variable climatic regimes and forest types. Soil N-cycling and associated production of N2O was assessed following application of 15N-labeled nitrogen. The N2O emission varied significantly among the different forest soils, and was inversely correlated to the soil C: N ratio. The N2O emissions were significantly higher from the deciduous soils (13 ng N2O-N cm(-3) d(-1)) than from the coniferous soils (4 ng N2O- N cm(-3) d(-1)). Nitrate (NO3-) was the dominant substrate for N2O with an average contribution of 62% and exceeding 50% at least once for all sites. The average contribution of ammonium (NH4+) to N2O averaged 34%. The N2O emissions were correlated with gross nitrification activities, and as for N2O, gross nitrification was also higher in deciduous soils (3.4 mu gNcm(-3) d(-1)) than in coniferous soils (1.1 mu gNcm(-3) d(-1)). The ratio between N2O production and gross nitrification averaged 0.67% (deciduous) and 0.44% (coniferous). Our study suggests that changes in forest composition in response to land use activities and global change may have implications for regional budgets of greenhouse gases. From the study it also became clear that N2O emissions were driven by the nitrification activity, although the N2O was produced per se mainly from denitrification. Increased nitrification in response to accelerated N inputs predicted for forest ecosystems in Europe may thus lead to increased greenhouse gas emissions from forest ecosystems.
Nitrous oxide (N 2 O) emissions from wastewater treatment plants vary substantially between plants, ranging from negligible to substantial (a few per cent of the total nitrogen load), probably because of different designs and operational conditions. In general, plants that achieve high levels of nitrogen removal emit less N 2 O, indicating that no compromise is required between high water quality and lower N 2 O emissions. N 2 O emissions primarily occur in aerated zones/compartments/periods owing to active stripping, and ammonia-oxidizing bacteria, rather than heterotrophic denitrifiers, are the main contributors. However, the detailed mechanisms remain to be fully elucidated, despite strong evidence suggesting that both nitrifier denitrification and the chemical breakdown of intermediates of hydroxylamine oxidation are probably involved. With increased understanding of the fundamental reactions responsible for N 2 O production in wastewater treatment systems and the conditions that stimulate their occurrence, reduction of N 2 O emissions from wastewater treatment systems through improved plant design and operation will be achieved in the near future.