Characterization of halogen···halogen interactions in crystalline dihalomethane compounds (CH2Cl2, CH2Br2 and CH2I2): a theoretical study

To improve understanding of the unimolecular decomposition mechanism of 1,2,4-butanetriol trinitrate (BTTN) in the gas phase, density functional theory calculations were performed to determine various decomposition pathways at the B3LYP/6-311G** level. Two main mechanisms for the unimolecular decomposition of BTTN were found. In the first, homolysis of one of the O–NO₂ bonds occurs to form ?NO₂ and CH₂ONO₂CHONO₂CH₂CH₂O?, which subsequently decomposes to form CH₃CHO + ?CHO + 3NO₂ + HCHO. In the second, successive HONO elimination reactions yield three HONO and OHCCH₂CHONO₂CH₂ONO₂ fragments, which subsequently decompose to form CH₃CHO + 2CO + 3HONO. We also found that the first pathway has a slightly lower activation energy than the second. The results show that the pathway involving O–NO₂ cleavage is slightly more energetically favorable than that involving HONO elimination.     

A density functional theory study of the decomposition mechanism of nitroglycerin

The detailed decomposition mechanism of nitroglycerin (NG) in the gas phase was studied by examining reaction pathways using density functional theory (DFT) and canonical variational transition state theory combined with a small-curvature tunneling correction (CVT/SCT). The mechanism of NG autocatalytic decomposition was investigated at the B3LYP/6-31G(d,p) level of theory. Five possible decomposition pathways involving NG were identified and the rate constants for the pathways at temperatures ranging from 200 to 1000 K were calculated using CVT/SCT. There was found to be a lower energy barrier to the β-H abstraction reaction than to the α-H abstraction reaction during the initial step in the autocatalytic decomposition of NG. The decomposition pathways for CHOCOCHONO₂ (a product obtained following the abstraction of three H atoms from NG by NO₂) include O–NO₂ cleavage or isomer production, meaning that the autocatalytic decomposition of NG has two reaction pathways, both of which are exothermic. The rate constants for these two reaction pathways are greater than the rate constants for the three pathways corresponding to unimolecular NG decomposition. The overall process of NG decomposition can be divided into two stages based on the NO₂ concentration, which affects the decomposition products and reactions. In the first stage, the reaction pathway corresponding to O–NO₂ cleavage is the main pathway, but the rates of the two autocatalytic decomposition pathways increase with increasing NO₂ concentration. However, when a threshold NO₂ concentration is reached, the NG decomposition process enters its second stage, with the two pathways for NG autocatalytic decomposition becoming the main and secondary reaction pathways.     

Theoretical study of the reaction mechanism of CH<Subscript>3</Subscript>NO<Subscript>2</Subscript> with NO<Subscript>2</Subscript>, NO and CO: the bimolecular reactions that cannot be ignored

The intriguing decompositions of nitro-containing explosives have been attracting interest. While theoretical investigations have long been concentrated mainly on unimolecular decompositions, bimolecular reactions have received little theoretical attention. In this paper, we investigate theoretically the bimolecular reactions between nitromethane (CH₃NO₂)—the simplest nitro-containing explosive—and its decomposition products, such as NO₂, NO and CO, that are abundant during the decomposition process of CH₃NO₂. The structures and potential energy surface (PES) were explored at B3LYP/6-31G(d), B3P86/6-31G(d) and MP2/6-311?+?G(d,p) levels, and energies were refined using CCSD(T)/cc-pVTZ methods. Quantum chemistry calculations revealed that the title reactions possess small barriers that can be comparable to, or smaller than, that of the initial decomposition reactions of CH₃NO₂. Considering that their reactants are abundant in the decomposition process of CH₃NO₂, we consider bimolecular reactions also to be of great importance, and worthy of further investigation. Moreover, our calculations show that NO₂ can be oxidized by CH₃NO₂ to NO₃ radical, which confirms the conclusion reached formerly by Irikura and Johnson [(2006) J Phys Chem A 110:13974–13978] that NO₃ radical can be formed during the decomposition of nitramine explosives.     

Coordinated nitroxyl anion is produced and released as nitrous oxide by the decomposition of iridium-coordinated nitrosothiols

The aqueous decomposition of the iridium coordinated nitrosothiols (RSNOs) trans-K[IrCl₄(CH₃CN)NOSPh] (1), and K₂[IrCl₅(NOECyS)] (2, ECyS = cysteine ethyl ester), was studied by MS analysis of the gaseous products, ESI-MS, NMR, and UV-Vis spectroscopy. Bent NO (NO⁻, nitroxyl anion), sulfenic acids and nitrite were observed as coordinated products in solution, while nitrous oxide (N₂O) and nitrogen were detected in the gas phase. The formation of coordinated NO⁻ and N₂O, a nitroxyl dimerization product, allows us to propose the formation of free nitroxyl (HNO) as an intermediate. Complex 1 decomposes 300 times slower than free PhSNO does. In both cases (1 and 2) kinetic results show a first order decomposition behavior and a very negative ΔS^≠, which strongly indicates an associative rate-determining step. A proposed decomposition mechanism, supported by the experimental data and DFT calculations, involves, as the first step, nucleophilic attack of H₂O on to the sulfur atom of the coordinated RSNO, producing an NO⁻ complex and free sulfenic acid, followed by two competing reactions: a ligand exchange reaction of this NO⁻ with the sulfenic acid or, to a minor extent, coordination of N₂O to produce an NO⁻/N₂O complex which finally renders free N₂ and coordinated NO₂⁻. Some of the produced NO⁻ is likely to be released from the metal center producing nitroxyl by protonation and finally N₂O by dimerization and loss of H₂O. In conclusion, the decomposition of these coordinated RSNOs occurs through a different mechanism than for the decomposition of free RSNOs. It involves the formation of sulfenic acids and coordinated NO⁻, which is released from the complexes and protonated at the reaction pH producing nitroxyl (HNO), and ultimately N₂O.     

Planar tetrameric metal cluster formation at room temperature induced by π?π interactions: 3D supramolecular host containing 1D channel filled with solvent methanol

A novel tetrameric metal cluster, [La₂(phen)₃(2,3-pdc)(NO₃)₄(H₂O)]₂·(CH₃OH)₂ (2,3-pdcH₂ = pyridine-2,3-dicarboxylic acid, phen = 1,10-phenanthroline), have been synthesized at room temperature from water-methanol mixture by mixing the reactants in stoichiometric ratio. 2,3-Pdc and their π?π interactions played a vital role on the construction of the core. The auxiliary ligand, phen, which blocked the outermost periphery of the molecule and their hydrophobic π?π interactions facilitate the formation of the tetrameric metal clusters. The tetrameric metal clusters are connected by supramolecular interactions to form 3D supramolecular metal organic host (MOSH) producing supramolecular channels along a-axis. These supramolecular channels are filled up by solvent methanol molecules. The luminescent investigations reveal that cluster complex exhibits strong blue emission.     

A theoretical study on the hydrogen-bonding interactions between flavonoids and ethanol/water

Ethanol and water are the solvents most commonly used to extract flavonoids from propolis. Do hydrogen-bonding interactions exist between flavonoids and ethanol/water? In this work, this question was addressed by using density functional theory (DFT) to provide information on the hydrogen-bonding interactions between flavonoids and ethanol/water. Chrysin and Galangin were chosen as the representative flavonoids. The investigated complexes included chrysin–H₂O, chrysin–CH₃CH₂OH, galangin–H₂O and galangin–CH₃CH₂OH dyads. Molecular geometries, hydrogen-bond binding energies, charges of monomers and dyads, and topological analysis were studied at the B3LYP/M062X level of theory with the 6?31++G(d,p) basis set. The main conclusions were: (1) nine and ten optimized hydrogen-bond geometries were obtained for chrysin–H₂O/CH₃CH₂OH and galangin–H₂O/CH₃CH₂OH complexes, respectively. (2) The hydrogen atoms except aromatic H1 and H5 and all of the oxygen atoms can form hydrogen-bonds with H₂O and CH₃CH₂OH. Ethanol and water form strong hydrogen-bonds with the hydroxyl, carbonyl and ether groups in chrysin/galangin and form weak hydrogen-bonds with aromatic hydrogen atoms. Except in structures labeled A and B, chrysin and galangin interact more strongly with H₂O than CH₃CH₂OH. (3) When chrysin and galangin form hydrogen-bonds with H₂O and CH₃CH₂OH, charge transfers from the hydrogen-bond acceptor (H₂O and CH₃CH₂OH in structures A, B, G, H, I, J) to the hydrogen-bond donor (chrysin and galangin in structure A, B, G, H, I, J). The stronger hydrogen-bond makes the hydrogen-bond donor lose more charge (A> B> G> H> I> J). (4) Most of the hydrogen-bonds in chrysin/galangin?H₂O/CH₃CH₂OH complexes may be considered as electrostatic dominant, while C?O2···H in structures labeled E and C?O5···H in structures labeled J are hydrogen-bonds combined of electrostatic and covalent characters. H9, H7, and O4 are the preferred hydrogen-bonding sites.     

Carbon nanotube functionalization with carboxylic derivatives: a DFT study

Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including –COOX (X?=?H, CH₃, CH₂NH₂, CH₃Ph, CH₂NO₂, and CH₂CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of ?0.23 to ?7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is ?CH₂NO₂?>?CH₂CN?>?H?>?CH₂Ph?>?CH₃?>?CH₂NH₂. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for ?H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of ?CH₂NO₂ and _?CH₂CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.     

Enantioselective cleavage of supercoiled plasmid DNA catalyzed by chiral macrocyclic lanthanide(III) complexes

The enantiomers of the Sm (III), Eu (III) and Yb (III) complexes [LnL(NO₃)₂](NO₃) of a chiral hexaazamacrocycle were tested as catalysts for the hydrolytic cleavage of supercoiled plasmid DNA. The catalytic activity was remarkably enantioselective; while the [LnL^SSSS(NO₃)₂](NO₃) enantiomers promoted the cleavage of plasmid pBR322 from the supercoiled form (SC) to the nicked form (NC), the [LnL^RRRR(NO₃)₂](NO₃) enantiomers were inactive. Kinetics of plasmid DNA hydrolysis was also investigated by agarose electrophoresis and it indicated typical single-exponential cleavage reaction. The hydrolytic mechanism of DNA cleavage was confirmed by the successful ligation of hydrolysis product by T4 ligase. The NMR study of the solutions of the complexes in various buffers indicated that the complexes exist as monomeric cationic complexes [LnL(H₂O)₃]^3 + in slightly acidic solutions and as dimeric cationic complexes [Ln₂L₂(μ-OH)₂(H₂O)₂]^4 + in slightly basic 8 mM solutions, with the latter form being a possible catalyst for hydrolysis of phosphodiester bonds.     

Selective Inhibition of Ammonium Oxidation and Nitrification-Linked N2O Formation by Methyl Fluoride and Dimethyl Ether

Methyl fluoride (CH₃F) and dimethyl ether (DME) inhibited nitrification in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CH₃F (10% [vol/vol]) and DME (25% [vol/vol]) fully inhibited NO₂^- and N₂O production from NH₄⁺ in incubations of N. europaea, while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxylamine (NH₂OH) by N. europaea and oxidation of NO₂^- by a Nitrobacter sp. were unaffected by CH₃F or DME. In nitrifying soils, CH₃F and DME inhibited N₂O production. In field experiments with surface flux chambers and intact cores, CH₃F reduced the release of N₂O from soils to the atmosphere by 20- to 30-fold. Inhibition by CH₃F also resulted in decreased NO₃^- + NO₂^- levels and increased NH₄⁺ levels in soils. CH₃F did not affect patterns of dissimilatory nitrate reduction to ammonia in cell suspensions of a nitrate-respiring bacterium, nor did it affect N₂O metabolism in denitrifying soils. CH₃F and DME will be useful in discriminating N₂O production via nitrification and denitrification when both processes occur and in decoupling these processes by blocking NO₂^- and NO₃^- production.     

Theoretical studies of some bimolecular reactions during the decomposition of CH<Subscript>3</Subscript>NO<Subscript>2</Subscript>: reactions between NO<Subscript>2</Subscript> and nine intermediates

Nitromethane (NM, CH₃NO₂) is a widely studied energetic material, and its decomposition mechanism attracts great interest. In this work, bimolecular reactions between NO₂ and nine intermediates generated during the decomposition of NM were investigated by computational chemistry methods. The mechanisms of the reactions were analyzed. The results revealed that these reactions possess small barriers and can easily occur, so they may be responsible for NO₂ loss during the decomposition of NM.     

Simulation of N2O emissions from rain-fed wheat and the impact of climate variation in southeastern Australia

The Water and Nitrogen Management model (WNMM) was applied to simulate N₂O emissions from a rain-fed wheat cropping system on a loam-textured soil for two treatments, conventional cultivation with residue burn (CC?+?BURN?+?N) and direct drill with residue retention (DD?+?RET?+?N), at Rutherglen in southeastern Australia from January 2004 to March 2005. Both treatments received the same amount of nitrogen (N) fertiliser. The WNMM satisfactorily simulated the soil water content, mineral N contents and N₂O emissions from the soil, as compared with the field observations for both treatments. The simulated nitrification-induced N₂O emissions accounted for 45% and 34% of total N₂O emissions for the treatments CC?+?BURN?+?N and DD?+?RET?+?N, respectively. The calibrated WNMM was used to simulate N₂O emissions from this soil using historic daily weather data from 1968 to 2004 and applying seven scenarios of fertiliser N application. Correlation analysis found that the annual N₂O emissions for this rain-fed wheat cropping system were significantly correlated to the annual average of daily maximum air temperature (r?=?0.51 for CC?+?BURN?+?N and 0.56 for DD?+?RET?+?N), annual rainfall (r?=??0.56 for CC?+?BURN?+?N and ?0.59 for DD?+?RET?+?N) and fertiliser N application rate (r?=?0.43 for CC?+?BURN?+?N and 0.31 for DD?+?RET?+?N). Based on the 37-year historic simulations, multivariate regression models for estimating annual N₂O emissions were developed to account for climatic variation, and explained about 50% of variations of annual N₂O emissions estimated by WNMM.     

N-substituted ethylcarbamate complexes of thorium(IV) and lanthanum(III) nitrates

N-substituted ethylcarbamates form with thorium nitrate the complexes Th(NO₃)₄·3RHNC(O)OC₂H₅ (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH) and with lanthanum nitrate the complexes La(NO₃)₃· 2RR′NC(O)OC₂H₅·3H₂O (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH; R′ = H and R = CH₃, C₆H₅; R′ = C₂H₅ or R = R′ = CH₃). In addition the anhydrous La(NO₃)₃·3(C₂H₅)₂NC(O)OC₂H₅ has been isolated. From the IR spectra it is deduced that the carbamates coordinate the metal through the carbonyl oxygen atom and that the nitrato groups act as chelated ligands. ¹H nmr spectral data of the complexes are reported and discussed.     

Effect of water table on greenhouse gas emissions from peatland mesocosms

Peatland landscapes typically exhibit large variations in greenhouse gas (GHG) emissions due to microtopographic and vegetation heterogeneity. As many peatland budgets are extrapolated from small-scale chamber measurements it is important to both quantify and understand the processes underlying this spatial variability. Here we carried out a mesocosm study which allowed a comparison to be made between different microtopographic features and vegetation communities, in response to conditions of both static and changing water table. Three mesocosm types (hummocks?+?Juncus effusus, hummocks?+?Eriophorum vaginatum, and hollows dominated by moss) were subjected to two water table treatments (0–5 cm and 30–35 cm depth). Measurements were made of soil-atmosphere GHG exchange, GHG concentration within the peat profile and soil water solute concentrations. After 14 weeks the high water table group was drained and the low water table group flooded. Measurement intensity was then increased to examine the immediate response to change in water table position. Mean CO₂, CH₄ and N₂O exchange across all chambers was 39.8 μg m^?2 s^?1, 54.7 μg m^?2 h^?1 and ?2.9 μg m^?2 h^?1, respectively. Hence the GHG budget was dominated in this case by CO₂ exchange. CO₂ and N₂O emissions were highest in the low water table treatment group; CH₄ emissions were highest in the saturated mesocosms. We observed a strong interaction between mesocosm type and water table for CH₄ emissions. In contrast to many previous studies, we found that the presence of aerenchyma-containing vegetation reduced CH₄ emissions. A significant pulse in both CH₄ and N₂O emissions occurred within 1–2 days of switching the water table treatments. This pulsing could potentially lead to significant underestimation of landscape annual GHG budgets when widely spaced chamber measurements are upscaled.     

Molecular dynamics simulation of methane hydrate dissociation by depressurisation

Methane (CH₄) hydrate dissociation and the mechanism by depressurisation are investigated by molecular dynamics (MD) simulation. The hydrate decomposition processes are studied by the ‘vacuum removal method’ and the normal method. It is found that the hydrate decomposition is promoted by depressurisation. The quasi-liquid layer is formed in the hydrate surface layer. The driving force of dissociation is found to be controlled by the concentration gradient between the H₂O molecules of the hydrate surface layer and the H₂O molecules of the hydrate inner layer. The clathrates collapse gradually, and the hydrate decomposes layer by layer. Relative to our previous MD simulation results, this study shows that the rate of the hydrate dissociation by depressurisation is slower than that by the thermal stimulation and the inhibitor injection. This study illustrated that MD simulation can play a significant role in investigating the hydrate decomposition mechanisms.     

Reactions of Low Valent Transition Metal Complexes with Hydrogen Peroxide. Are they “Fenton-Like” or not? 4. The Case of Fe(II)L,L = Edta; Hedta and Tcma

The question whether hydroxyl free radicals are formed in the reactions of divalent iron complexes Fe(II)L; L = edta; hedta; tcma (tcma = l-acetato-l,4,7-triazacyclononane) with hydrogen peroxide in neutral and slightly acidic solutions was studied by using the β elimination reaction as an assay for the formation of hydroxyl free radicals, OH. The results show that at pH<5.5 the iron(II)peroxide intermediate complex decomposes rapidly to yield free hydroxyl radicals for L=edta and hedta. This is in contrast to the mechanism of the corresponding Fe(II)nta peroxide complex, which probably decomposes to form Fe(IV)nta which then reacts with organic substrates to yield aliphatic free radicals. Thus, the non-participating ligand L has an appreciable effect on the mechanism of reaction of the metal center with hydrogen peroxide. Blank experiments using ionizing radiation as the source of CH₂CR(CH₃)OH, R = H or CH₃ radicals indicate that when L = tcma intermediates of the type LFe^III-CH₂CR(CH₃)OH_aq are formed, but their major mode of decomposition is not the β elimination reaction. Thus, the present assay for the formation of hydroxyl free radicals by the Fenton Reaction does not fit the latter system.     

Greenhouse gas dynamics in boreal, littoral sediments under raised CO2 and nitrogen supply

SUMMARY 1. The effects of increasing CO₂ and nitrogen loading and of a change in water table and temperature on littoral CH₄, N₂O and CO₂ fluxes were studied in a glasshouse experiment with intact sediment cores including vegetation (mainly sedges), taken from a boreal eutrophic lake in Finland. Sediments with the water table held at a level of 0 or at ?15 cm were incubated in an atmosphere of 360 or 720 p.p.m. CO₂ for 18 weeks. The experiment included fertilisation with NO₃^– and NH₄⁺ (to a total 3 g N m^?2). 2. Changes in the water table and temperature strongly regulated sediment CH₄ and cCO₂ fluxes (community CO₂ release), but did not affect N₂O emissions. Increase in the water table increased CH₄ emissions but reduced cCO₂ release, while increase in temperature increased emissions of both CO₂ and CH₄. 3. The raised CO₂ increased carbon turnover in the sediments, such that cCO₂ release was increased by 16–26%. However, CH₄ fluxes were not significantly affected by raised CO₂, although CH₄ production potential (at 22 °C) of the sediments incubated at high CO₂ was increased. In the boreal region, littoral CH₄ production is more likely to be limited by temperature than by the availability of carbon. Raised CO₂ did not affect N₂O production by denitrification, indicating that this process was not carbon limited. 4. A low availability of NO₃^– did severely limit N₂O production. The NO₃^– addition caused up to a 100‐fold increase in the fluxes of N₂O. The NH₄⁺ addition did not increase N₂O fluxes, indicating low nitrification capacity in the sediments.     

Catalytic effect of (H2O)n (n = 1–3) clusters on the reaction of HNO2 + HO → H2O + NO2 under tropospheric conditions

ABSTRACT

The effect of (H₂O)_n (n?=?1–3) on the HNO₂?+?HO → H₂O?+?NO₂ reaction has been investigated theoretically at the CCSD(T)/CBS//B3LYP/6-311?+?G(3df,2pd) level of theory, coupled with rate constant calculations by using variational transition state theory. Our results show that, when (H₂O)_n (n?=?1–3) was introduced into HNO₂?+?HO → H₂O?+?NO₂ reaction, the product of the reaction did not change, but the potential energy surface became quite complex, yielding two kinds of reactions, namely HNO₂···(H₂O)_n (n?=?1–3)?+?HO and HO···(H₂O)_n (n?=?1–3)?+?HNO₂. In all catalysed reactions with (H₂O)_n (n?=?1–3), the former reaction type is favourable than the latter one with its effective rate constant respectively larger by 6–1 orders of magnitude than that of latter one. Within the temperature range of 240–320?K, the relative impacts on water monomer are much more obvious than dimer and trimer. However, the effective rate constant with water is larger by 658%–17% times of magnitude, showing that the positive water effect is obvious under atmospheric conditions.     

Simulated Nitrogen Deposition Reduces CH4 Uptake and Increases N2O Emission from a Subtropical Plantation Forest Soil in Southern China

To date, few studies are conducted to quantify the effects of reduced ammonium (NH₄ ⁺) and oxidized nitrate (NO₃ ⁻) on soil CH₄ uptake and N₂O emission in the subtropical forests. In this study, NH₄Cl and NaNO₃ fertilizers were applied at three rates: 0, 40 and 120 kg N ha⁻¹ yr⁻¹. Soil CH₄ and N₂O fluxes were determined twice a week using the static chamber technique and gas chromatography. Soil temperature and moisture were simultaneously measured. Soil dissolved N concentration in 0–20 cm depth was measured weekly to examine the regulation to soil CH₄ and N₂O fluxes. Our results showed that one year of N addition did not affect soil temperature, soil moisture, soil total dissolved N (TDN) and NH₄ ⁺-N concentrations, but high levels of applied NH₄Cl and NaNO₃ fertilizers significantly increased soil NO₃ ⁻-N concentration by 124% and 157%, respectively. Nitrogen addition tended to inhibit soil CH₄ uptake, but significantly promoted soil N₂O emission by 403% to 762%. Furthermore, NH₄ ⁺-N fertilizer application had a stronger inhibition to soil CH₄ uptake and a stronger promotion to soil N₂O emission than NO₃ ⁻-N application. Also, both soil CH₄ and N₂O fluxes were driven by soil temperature and moisture, but soil inorganic N availability was a key integrator of soil CH₄ uptake and N₂O emission. These results suggest that the subtropical plantation soil sensitively responses to atmospheric N deposition, and inorganic N rather than organic N is the regulator to soil CH₄ uptake and N₂O emission.     

Synthesis, characterization, and structural studies of mercury(II) complexes of new bidentate phosphorus ylide

The reaction of Ph₂PCH₂CH₂PPh₂ (dppe) with BrCH₂C(O)C₆H₄NO₂ (1:1.05 molar ratio) in acetone produces a mixture of the new monophosphonium salt [Ph₂PCH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br (1) and the diphosphonium salt [NO₂C₆H₄C(O)CH₂PPh₂CH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br₂ (2). Compound 2 was insoluble in acetone and thus easily separated from the solution of 1. Further, by reacting both the mono- and diphosphonium salts with the appropriate bases the bidentate phosphorus ylides, [Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (3) and [NO₂C₆H₄C(O)CHPPh₂CH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (4) were obtained. The reaction of ligand 3 with mercury(II) halides in dry methanol leads to the formation of the P,P-coordinated monomeric complexes {HgX₂(Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂)₂} [X = Cl (5), Br (6), I (7)]. The structure of complex 7 being unequivocally determined by single crystal X-ray diffraction techniques. Characterization of these species was also performed by elemental analysis, IR spectroscopy and ¹H, ³¹P, and ¹³C NMR techniques. These analyses being consistent with a 2:1 stoichiometry ylide/Hg(II) for compounds 5 through 7. Results obtained from theoretical studies are also consistent with a product in which two ylides are coordinated to the Hg(II) center through their phosphine groups, being this product the most stable among all the possible products.     

A record of N2O and CH4 emissions and underlying soil processes of Korean rice paddies as affected by different water management practices

Rice is staple food of half of mankind and paddy soils account for the largest anthropogenic wetlands on earth. Ample of research is being done to find cultivation methods under which the integrative greenhouse effect caused by emitted CH₄ and N₂O would be mitigated. Whereas most of the research focuses on quantifying such emissions, there is a lack of studies on the biogeochemistry of paddy soils. In order to deepen our mechanistic understanding of N₂O and CH₄ fluxes in rice paddies, we also determined NO₃ ^? and N₂O concentrations as well as N₂O isotope abundances and presence of O₂ along soil profiles of paddies which underwent three different water managements during the rice growing season(s) in (2010 and) 2011 in Korea. Largest amounts of N₂O (2 mmol m^?2) and CH₄ (14.5 mol m^?2) degassed from the continuously flooded paddy, while paddies with less flooding showed 30–60 % less CH₄ emissions and very low to negative N₂O balances. In accordance, the global warming potential (GWP) was lowest for the Intermittent Irrigation paddy and highest for the Traditional Irrigation paddy. The N₂O emissions could the best be explained (*P < 0.05) with the δ¹⁵N values and N₂O concentrations in 40–50 cm soil depth, implying that major N₂O production/consumption occurs there. No significant effect of NO₃ ^? on N₂O production has been found. Our study gives insight into the soil of a rice paddy and reveals areas along the soil profile where N₂O is being produced. Thereby it contributes to our understanding of subsoil processes of paddy soils.