Isotopomeric analysis of N2O dissolved in a river in the Tokyo metropolitan area

River water has been suggested as a potential source of nitrous oxide (N₂O), which is a greenhouse gas that is accumulating rapidly in the troposphere and which is a precursor to stratospheric NO_x that depletes ozone. Previous studies on freshwater N₂O sources have specifically examined estuaries where sedimentary N₂O production might be important and a few points near anthropogenic nitrogen sources such as agricultural or municipal wastewater areas. Here we present the first observation of a temporal and horizontal distribution of N₂O and its isotopomers between the midstream and estuary of an urban river. Surface water was supersaturated (100–6800%) with N₂O at all stations during the study period. The average or maximum saturation value was greater than described in most previous reports. High N₂O concentrations were observed near sewage plants and the unique signature of isotopomer ratios implied direct N₂O addition from the plants. The isotopomer ratios also suggested N₂O production/consumption at the sediment‐water interface. Fluxes and isotopomer ratios of N₂O, from the river to the atmosphere, estimated from our observations, indicated that the urban river is indeed a source of atmospheric N₂O and that its production could be distinguished from other natural or anthropogenic sources using isotopomer ratios. Copyright © 2009 John Wiley & Sons, Ltd.     

Ab initio calculations of nitrogen oxide reactions: formation of N2O2, N2O3, N2O4, N2O5, and N4O2 from NO, NO2, NO3, and N2O

Ab initio computational methods were used to obtain Delta(r)H(o), Delta(r)G(o), and Delta(r)S(o) for the reactions 2 NO <=> N(2)O(2) (I), NO+NO(2) <=> N(2)O(3) (II), 2 NO(2) <=> N(2)O(4) (III), NO(2)+NO(3) <=> N(2)O(5) (IV), and 2 N(2)O <=> N(4)O(2) (V) at 298.15 K. Optimized geometries and frequencies were obtained at the CCSD(T) level for all molecules except for NO, NO(2), and NO(3), for which UCCSD(T) was used. In all cases the aug-cc-pVDZ (avdz) basis set was employed. The electronic energies of all species were obtained from complete basis set extrapolations (to aug-cc-pV5Z) using five different extrapolation methods. The [U]CCSD(T)/avdz geometries and frequencies of the N(x)O(y) compounds are compared with literature values, and problems associated with the values and assignments of low-frequency modes are discussed. The standard entropies are compared with values cited in the NIST/JANAF tables [NIST-JANAF Thermochemical Tables, J. Phys. Chem. Ref. Data Monograph No. 9, 4th ed. edited by M. W. Chase, Jr. (American Chemical Society and American Institute of Physics, Woodbury, NY, 1988)]. With the exception of I, in which the dimer is weakly bound, and V, for which thermodynamic data appears to be lacking, the calculated standard thermodynamic functions of reaction are in good agreement with literature values obtained both from statistical mechanical and various equilibrium methods. A multireference-configuration interaction calculation (MRCI+Q) for I provides a D(e) value that is consistent with previous calculations. The combined uncertainties of the NIST/JANAF values for Delta(r)H(o), Delta(r)G(o), and Delta(r)S(o) of II, III, and IV are discussed. The potential surface for the dissociation of N(2)O(4) was explored using multireference methods. No evidence of a barrier to dissociation was found.     

Stability of nitrogen-oxygen cages N12O2, N14O2, N14O3, and N16O4

Molecules consisting entirely of nitrogen have been studied extensively for their potential as high energy density materials (HEDM). However, many such molecules are too unstable to serve as practical energy sources. This has prompted many studies of molecules that are mostly nitrogen but which incorporate heteroatoms into the structure to provide additional stability. In the current study, cages of three-coordinate nitrogen are viewed as candidates for stabilization by insertion of oxygen atoms into the nitrogen framework. Cages of N12, N14, and N16 with four-membered rings are studied because four-membered rings have been previously shown to be a destabilizing influence. Insertion of oxygen atoms, which converts N-N bonds to N-O-N bonding groups, relieves ring strain and can potentially result in stable molecules. These molecules are studied by theoretical calculations, using Hartree-Fock and Moller-Plesset (MP3 and MP4) theories, to determine the dissociation energies of the molecules. The primary result of the study is that stable molecules can result from oxygen insertion but that oxygen-oxygen proximity destabilizes the insertion products.     

Photooxidation of polystyrene by O2 and N2O

Strips of polystyrene held in a flowing O₂ or N₂O atmosphere have been exposed to 240-600 nm radiation. The extent of photooxidation has been followed by x-ray photoelectron spectroscopy (XPS). Although N₂O is a more reactive gas than O₂, it produces a less oxidized polymer surface. This surprising observation can be correlated to the photochemistry occurring at the gas/polystyrene interface. © 1992 John Wiley & Sons, Inc.     

Quenching of I(2P1/2) by NO2, N2O4, and N2O

Quenching of excited iodine atoms (I(5p5, 2P1/2)) by nitrogen oxides are processes of relevance to discharge-driven oxygen iodine lasers. Rate constants at ambient and elevated temperatures (293-380 K) for quenching of I(2P1/2) atoms by NO2, N2O4, and N2O have been measured using time-resolved I(2P1/2) --> I(2P3/2) 1315 nm emission. The excited atoms were generated by pulsed laser photodissociation of CF3I at 248 nm. The rate constants for I(2P1/2) quenching by NO2 and N2O were found to be independent of temperature over the range examined with average values of (2.9 +/- 0.3) x 10(-15) and (1.4 +/- 0.1) x 10(-15) cm3 s(-1), respectively. The rate constant for quenching of I(2P1/2) by N2O4 was found to be (3.5 +/- 0.5) x 10(-13) cm3 s(-1) at ambient temperature.     

Synthesis of O2'-methyluridine, O2'-methylcytidine, N4,O2'-dimethylcytidine and N4,N4,O2'-trimethylcytidine from a common intermediate

A facile synthesis of the title compounds from a readily accessible precursor, 3',5'-O-bis-protected O4-(2-nitrophenyl)uridine, is described.     

Synthesis and characterization of sulfuryl diazide, O2S(N3)2

Sulfuryl diazide, O(2)S(N(3))(2), previously described as an "exceedingly explosive" compound, has been isolated and characterized by IR (Ar matrix, gas) and Raman (solid) spectroscopy, and its structure has been determined by X-ray crystallography. It has a melting point of -15 °C and can be handled in small quantities in gas, liquid, and solid states. Vibrational spectroscopic studies suggest the presence of only one conformer in both gas and solid states, and the X-ray crystallography revealed an anti conformation of the two azido groups with respect to the NSN plane. Calculations predict the anti (C(2)) conformer to be 6.6 kJ mol(-1) lower in energy than the syn (C(s)) one at the CBS-QB3 level of theory. The related chlorosulfuryl azide, ClSO(2)N(3), has also been prepared and characterized by IR and Raman spectroscopy.     

Nitrogen isotopomer site preference of N2O produced by Nitrosomonas europaea and Methylococcus capsulatus Bath

The original article to which this Erratum refers was published in Rapid Communications in Mass Spectrometry 17 (7) 2003, 738–745.     

Nitrogen isotopomer site preference of N2O produced by Nitrosomonas europaea and Methylococcus capsulatus Bath

The relative importance of individual microbial pathways in nitrous oxide (N(2)O) production is not well known. The intramolecular distribution of (15)N in N(2)O provides a basis for distinguishing biological pathways. Concentrated cell suspensions of Methylococcus capsulatus Bath and Nitrosomonas europaea were used to investigate the site preference of N(2)O by microbial processes during nitrification. The average site preference of N(2)O formed during hydroxylamine oxidation by M. capsulatus Bath (5.5 +/- 3.5 per thousand) and N. europaea (-2.3 +/- 1.9 per thousand) and nitrite reduction by N. europaea (-8.3 +/- 3.6 per thousand) differed significantly (ANOVA, f((2,35)) = 247.9, p = 0). These results demonstrate that the mechanisms for hydroxylamine oxidation are distinct in M. capsulatus Bath and N. europaea. The average delta(18)O-N(2)O values of N(2)O formed during hydroxylamine oxidation for M. capsulatus Bath (53.1 +/- 2.9 per thousand) and N. europaea (-23.4 +/- 7.2 per thousand) and nitrite reduction by N. europaea (4.6 +/- 1.4 per thousand) were significantly different (ANOVA, f((2,35)) = 279.98, p = 0). Although the nitrogen isotope value of the substrate, hydroxylamine, was similar in both cultures, the observed fractionation (delta(15)N) associated with N(2)O production via hydroxylamine oxidation by M. capsulatus Bath and N. europaea (-2.3 and 26.0 per thousand, respectively) provided evidence that differences in isotopic fractionation were associated with these two organisms. The site preferences in this study are the first measured values for isolated microbial processes. The differences in site preference are significant and indicate that isotopomers provide a basis for apportioning biological processes producing N(2)O.     

A comparative study of rotational temperatures using diatomic OH,O2 and N2+ molecular spectra emitted from atmospheric plasmas

From the application point of view, gas temperature is one of the most important parameters for atmospheric plasmas. Based on the fact that the gas temperature is closely related with the rotational temperature of an atmospheric plasma, a spectroscopic method of measuring the rotational temperature is described in this work by analyzing OH, O₂ and N₂⁺ molecular spectra emitted from the atmospheric plasma in ambient air. The OH and N₂⁺ molecular spectra are emitted because of the oxygen, hydrogen and nitrogen atoms existing in the ambient air. The O₂ diatomic molecular spectrum is emitted from the oxygen plasma that is frequently produced for atmospheric plasma applications. In order to utilize a spectrometer with modest spectral resolution, a synthetic diatomic molecular spectrum was compared with the experimentally obtained spectrum. The rotational temperatures determined by the above three different molecular spectra are in good agreement within 2.4% error. In the case of a plasma with low gas temperature, the temperature measured by a thermocouple was compared to verify the accuracy of the spectroscopic method, and the results show excellent agreement. From the study, it was found that an appropriate diatomic molecular species can be chosen to be used as a thermometer depending on experimental circumstances.     

Die sechsgliedrigen Ringsysteme PIIISi2N2O, [PVSi2N2O]⊕ und PVSi2N2O

Compounds I-X of the sixmembered ring system PSi₂N₂O with phosphorus in different oxidation and bond numbers, collected in Schema 1, have been prepared for the first time and confirmed in their structure by elemental analysis as well as by infrared and¹H- and³¹P-spectroscopy.

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Mit Auszügen aus der DissertationK. P. Giesen, Techn. Univ. Braunschweig 1972.     

The reactions of isotopically labeled N15NO+ with CO,NO, O2, N2, NO2, and N2O

The reactions of labeled N¹⁵NO⁺ with CO, NO, O₂, ¹⁸O₂, N₂, NO₂, and N₂O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.     

Quenching of N2(A3Σu+) by O2, O,N, and H

Metastable N₂(A³Σ_u⁺), υ = 0, υ = 1, molecules are produced by a pulsed Tesla-type discharge of a dilute N₂/Ar gas mixture. Rate coefficients for quenching these metastable levels by O₂, O, N, and H were obtained by time-resolved emission measurements of the (0, 6) and (1, 5) Vegard–Kaplan bands. In units of cm³/mole · sec at 300°K and with an experimental uncertainty of ±20%, these rate coefficients for N₂(A³Σu⁺) are Within the limits of error these coefficients apply to quenching N₂(A³Σ_u⁺) υ′ = 1 as well.     

Dual isotope and isotopomer ratios of N2O emitted from a temperate grassland soil after fertiliser application

The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (equivalent to 25 and 75 kg N ha(-1)) were simultaneously measured, using a new automated soil incubation system, which replaces soil atmosphere (N2 dominated) with a He+O2 mixture. Dual isotope and isotopomer ratios of the emitted N2O were also determined. Total N2O and N2 fluxes were significantly lower (P<0.001) in the control (0 kg N) than in the 25 and 75 kg N treatments. The total N2O flux was significantly higher (P<0.001) in the 75 kg N than in the 25 kg N treatment. The general patterns of N2O and N2 fluxes were similar for both fertiliser treatments. The total gaseous N loss in the control treatment was nearly all N2, whereas in the fertiliser treatment more N2O than N2 was emitted from the soil. The ratio N2O/N2 fluxes as measured during the experiment suggested three phases in N2O production, in phase 1 nitrification>denitrification, in phase 2 denitrification>nitrification, and in phase 3 denitrification (and total denitrification)>nitrification. Dual delta15N and delta18O isotope and isotopomer (delta15Nalpha and delta15Nbeta) value ratios of emitted N2O also pointed towards an increasing dominance of the production of N2O by denitrification and total denitrification. The site preference value from the soil-emitted N2O was lower than the troposphere value. This confirmed that the enhanced troposphere N2O site preference could result from back injection of N2O from the stratosphere. The measurements of N2O/N2 flux ratio and the isotopic content of emitted N2O pointed, independently, to similar temporal trends in N2O production processes after fertiliser application to grassland soil. This confirmed that both measurements are suitable diagnostic tools to study the N2O production process in soils.     

Synthesis of (15N2)[17O]Urea, (15N2)[O2, O4-17O2]Uridine,and (15N3)[O2-17O]Cytidine

A general synthetic approach for the synthesis of ¹⁵N- and ¹⁷O-doubly labelled pyrimidine nucleosides is described. The ¹⁵N isotopes in uridine and the ¹⁷O isotope in the urea-derived carbonyl group of uridine and cytidine originate from (¹⁵N₂)[¹⁷O]urea ( 5 ) which was synthesized from ¹⁵NH₄Cl, thiophosgene ( 1 ), and H₂[¹⁷O]. The third ¹⁵N isotope of cytidine in 4-position stems from the substitution of the 1,2,4-triazole moiety of (¹⁵N₂)[O²-¹⁷O]uridine derivative 8a/b with ¹⁵NH₄OH. Hydrolysis of the same key intermediate 8a/b with Na[¹⁷O]H/H₂[¹⁷O] introduced the second ¹⁷O isotope into the 4-position of uridine. The ¹⁵N- and ¹⁷O-NMR spectra of the target compounds 12 and 14 in phosphate-buffered H₂O serve as references for heteronuclear NMR spectra of labelled RNA fragments.