Loss Of N2 Research Articles

Azide Radical Initiated Ring Opening of Cyclopropenes Leading to Alkenyl Nitriles and Polycyclic Aromatic Compounds

AbstractWe report herein a radical‐mediated amination of cyclopropenes. The transformation proceeds through a cleavage of the three‐membered ring after the addition of an azide radical on the strained double bond and leads to tetrasubstituted alkenyl nitrile derivatives upon loss of N2. With 1,2‐diaryl substituted cyclopropenes, this methodology could be extended to a one‐pot synthesis of highly functionalized polycyclic aromatic compounds (PACs). This transformation allows the synthesis of nitrile‐substituted alkenes and aromatic compounds from rapidly accessed cyclopropenes using only commercially available reagents.

Azide Radical Initiated Ring Opening of Cyclopropenes Leading to Alkenyl Nitriles and Polycyclic Aromatic Compounds.

We report herein a radical-mediated amination of cyclopropenes. The transformation proceeds through a cleavage of the three-membered ring after the addition of an azide radical on the strained double bond and leads to tetrasubstituted alkenyl nitrile derivatives upon loss of N2 . With 1,2-diaryl substituted cyclopropenes, this methodology could be extended to a one-pot synthesis of highly functionalized polycyclic aromatic compounds (PACs). This transformation allows the synthesis of nitrile-substituted alkenes and aromatic compounds from rapidly accessed cyclopropenes using only commercially available reagents.

Site of Azido Substitution in the Sugar Moiety of Azidopyrimidine Nucleosides Influences the Reactivity of Aminyl Radicals Formed by Dissociative Electron Attachment.

In this work, electron-induced site-specific formation of neutral π-type aminyl radicals (RNH·) and their reactions with pyrimidine nucleoside analogs azidolabeled at various positions in the sugar moiety, e.g., at 2'-, 3'-, 4'-, and 5'- sites along with a model compound 3-azido-1-propanol (3AZPrOH), were investigated. Electron paramagnetic resonance (EPR) studies confirmed the site and mechanism of RNH· formation via dissociative electron attachment-mediated loss of N2 and subsequent facile protonation from the solvent employing the 15N-labeled azido group, deuterations at specific sites in the sugar and base, and changing the solvent from H2O to D2O. Reactions of RNH· were investigated employing EPR by warming these samples from 77 K to ca. 170 K. RNH· at a primary carbon site (5'-azido-2',5'-dideoxyuridine, 3AZPrOH) facilely converted to a σ-type iminyl radical (R═N·) via a bimolecular H-atom abstraction forming an α-azidoalkyl radical. RNH· when at a secondary carbon site (e.g., 2'-azido-2'-deoxyuridine) underwent bimolecular electrophilic addition to the C5═C6 double bond of a proximate pyrimidine base. Finally, RNH· at tertiary alkyl carbon (4'-azidocytidine) underwent little reaction. These results show the influence of the stereochemical and electronic environment on RNH· reactivity and allow the selection of those azidonucleosides that would be most effective in augmenting cellular radiation damage.

On the methylacetylene abundance and nitrogen isotope ratio in Pluto’s atmosphere

To bring our photochemical model of Pluto’s atmosphere and ionosphere (Krasnopolsky, 2020) into agreement with the recent detection of 5 ​× ​1015 ​cm−2 methylacetylene C3H4 (Steffl et al., 2020), rate coefficients of the three key reactions of C3H4 production and loss have been changed to values calculated by Vuitton et al. (2019). This change reduces the abundance of cyanoacetylene HC3N close to the measured ALMA upper limit (Lellouch et al., 2017), increases the model abundances of H2 and C3H8 by factors of 1.3, and reduces the abundances of H and C4H2 by factors of 1.3, while other species are changed less than 5% in the model. The predicted abundance of atomic hydrogen agrees with that derived from the observed Lyman-beta emission by Steffl et al. (2020).The observed HC14N/HC15N ​> ​125 on Pluto (Lellouch et al., 2017) looks puzzling compared to HC14N/HC15N ​= ​60 on Titan. Our analysis confirms the predissociation of N2 at 80–100 ​nm as the main process of nitrogen isotope fractionation. The observed twofold difference is partially caused by the diffusive depletion of the heavy isotope in HCN and in the predissociation of N2. On Pluto, the mean altitudes of HCN and predissociation of N2 are 500 and 860 ​km, well above the homopause at 96 ​km. On Titan, observations of HC14N/HC15N refer to 90–460 ​km (Vinatier et al., 2007), the predissociation occurs near 985 ​km, both below the homopause at 1000 ​km, and diffusive depletion does not occur. Therefore the observed limit corresponds to 14N/15N ​> ​253 for N2 in the lower atmosphere and 14N/15N ​> ​228 in the upper layers of the N2 ice. These limits reflect the conditions on Pluto in the last two million years, which is the lifetime of N2 in Pluto’s atmosphere with the current N2 loss of 37.5 ​g ​cm−2 Byr−1 primarily for photodestruction. The calculated isotope fractionation factor of 1.96 accounts for the formation and condensation of nitriles, diffusive separation, and fractionation in thermal escape. Variations of 14N/15N in the N2 ice are related to the evolution of the solar EUV, mixing processes in the N2 ice, and possible periods of hydrodynamic escape, which are poorly known and not considered here.

Machine Learning Analysis of Direct Dynamics Trajectory Outcomes for Thermal Deazetization of 2,3-Diazabicyclo[2.2.1]hept-2-ene.

Experimentally, the thermal gas-phase deazetization of 2,3-diazabicyclo[2.2.1]hept-2-ene (1) results in the loss of N2 and the formation of bicyclo products 3 (exo) and 4 (endo) in a nonstatistical ratio, with preference for the exo product. Here, we report unrestricted M06-2X quasiclassical trajectories initialized from the concerted N2 ejection transition state that were able to replicate the experimental preference to form 3. We found that the 3:4 ratio results from the relative amounts of very fast (ballistic) exotype trajectories versus trajectories that lead to the 1,3-diradical intermediate 2. These quasiclassical trajectories provided a set of transition-state vibrational, velocity, momenta, and geometric features for the machine learning analysis. A selection of popular supervised classification algorithms (e.g., random forest) provided poor prediction of trajectory outcomes based on only transition-state vibrational quanta and energy features. However, these machine learning models provided more accurate predictions using atomic velocities and atomic positions, attaining ∼70% accuracy using initial conditions and between 85 and 95% accuracy at later reaction time steps. This increased accuracy allowed the feature importance analysis to reveal that, at the later-time analysis, the methylene bridge out-of-plane bending is correlated with trajectory outcomes for the formation of either the exo product or toward the diradical intermediate. Possible reasons for the struggle of machine learning algorithms to classify trajectories based on transition-state features is the heavily overlapping feature values, the finite but very large possible vibrational mode combinations, and the possibility of chaos as trajectories propagate. We examined this chaos by comparing a set of nearly identical trajectories that differed by only a very small scaling of the kinetic energies resulting from the transition-state reaction coordinate.

Autocatalytic Carbonyl Arylation through In Situ Release of Aryl Nucleophiles from N-Aryl-N'-Silyldiazenes.

A method for the catalytic generation of functionalized aryl alkali metals is reported. These highly reactive intermediates are liberated from silyl‐protected aryl‐substituted diazenes by the action of Lewis basic alkali metal silanolates, resulting in desilylation and loss of N2. Catalytic quantities of these Lewis bases initiate the transfer of the aryl nucleophile from the diazene to carbonyl and carboxyl compounds with superb functional‐group tolerance. The aryl alkali metal can be decorated with electrophilic substituents such as methoxycarbonyl or cyano as well as halogen groups. The synthesis of a previously unknown cyclophane‐like [4]arene macrocycle from a 1,3‐bisdiazene combined with a 1,4‐dialdehyde underlines the potential of the approach.

Flow and heat transfer characteristics in slip regime for an annulus of evacuated collector tube subjected to non-uniform solar flux boundary condition

Due to the accumulation of residual gas, vacuum failure may occur in the annulus of evacuated collector tube in solar trough thermal power system, resulting in the changes of flow and heat transfer mechanism and characteristics. In this paper, based on the actual situation of solar radiation in summer of Chongqing, China, the flow and heat transfer characteristics of the annulus in slip regime were numerically studied. The effects of gas pressure, gas types (N2, H2 and He), heat transfer fluid temperature were analyzed and discussed. The results show that the temperature jump under lower gas pressure directly affects the heat loss and temperature distribution of the annulus. The temperature jump is most obvious for the residual gas of H2 at gas pressure of 130Pa, while it basically disappears for N2 and He (the corresponding Knudsen numbers Kn are 0.0019 and 0.0040; 0.0022 and 0.0046; 0.0026 and 0.0052 respectively under heat transfer fluid temperatures of 473.15 K, 573.15 K and 673.15 K). The heat loss and the outer wall temperature of glass envelope rise with the increasing of heat transfer fluid temperature and gas pressure, and are related to the thermo-physical properties and thermal adaptation coefficient of gas. For gas pressure being less than 70Pa (Kn > 0.0048) or greater than 20000Pa (continuous gas flow regime), the heat loss of N2 keeps increasing with gas pressure, and the heat losses of H2 and He are even more than 1200 W·m−1 under heat transfer fluid temperature of 673.15 K. When the temperature of heat transfer fluid is 573.15 K and the pressure increases from 1.83Pa to 130Pa, the declining relative values of first law efficiency (thermal efficiency) and second law efficiency (exergic efficiency) for N2, H2 and He are 1.59%, 10.07% and 8.48% respectively.

A trigold carbide cation stabilized as a labile pyridine adduct

Auration of trimethylsilyldiazomethane by an (N-heterocyclic carbene)gold alkoxide affords a stable (silyldiazoalkyl)gold complex. The reaction of this species with a gold(I) fluoride, more efficient in the presence of an added gold cation equivalent, results in auration, desilylation, and N2 loss. The putative trigold carbide cation was isolated as its pyridine adduct, a stable N-(triauromethyl)pyridinium ion. Reaction of the cationic pyridine adduct with carbon monoxide breaks the CN bond, forming the stable trigold ketenylidene cation. DFT studies suggest substantial negative charge at the bridging carbon in the methylpyridinium analogue and in two possible intermediates, the trigold carbide cation and the pyridine adduct of a neutral digold carbide.

Synthesis of polyheterocyclic 1,1-diboryltriazenes by γ-nitrogen insertion of azides into activated B-B single bonds.

The γ-nitrogen insertion of arylazides into the B-B bond of electron-rich cyclic μ-hydridodiboranes stabilised by one N-heterocyclic carbene (NHC) ligand leads to the expansion of the central C3B2 ring, yielding unsymmetrical polyheterocyclic 1,1-diboryltriazenes. The 2-benzyl-bridged analogues undergo further NHC ring expansion and thermally induced loss of N2.

Consecutive N2 loss from a uranium diphosphazide complex.

A new 'diphosphazidosalen' ligand was synthesized and successfully transferred to uranium using salt metathesis strategies. The resultant 8-coordinate uranium(iv) diphosphazide complex [κ6-1,2-{(N3)PPh2(2-O-C6H4)}2C6H4]UCl2 (1) is unstable to consecutive N2 loss, affording the asymmetric species [κ5-1-{(N3)PPh2(2-O-C6H4)}-2-{N=PPh2(2-O-C6H4)}C6H4)]UCl2 (2), defined by a phosphazide-phosphinimine mixed-ligand framework, and ultimately, the uranium(iv) phosphasalen complex [κ4-1,2-{N=PPh2(2-O-C6H4)}2C6H4]UCl2(THF) (3).

Lewis acid capping of a uranium(v) nitride via a uranium(iii) azide molecular square.

Reaction of (CpiPr4)2UI with NaN3 resulted in formation of tetrameric uranium(iii) azide-bridged 'molecular square' [(CpiPr4)2U(μ-η1:η1-N3)]4 (1). Addition of B(C6F5)3 to 1 induced loss of N2 at room temperature, yielding the uranium(v) borane-capped nitrido (CpiPr4)2U(μ-N)B(C6F5)3 (2).

Photodegradation of bis(1H-tetrazol-5-yl)amine (H2BTA), a high nitrogen content tetrazole-based energetic compound in water

Tetrazoles have wide industrial applications, notably in the pharmaceutical industry. Tetrazole derivatives such as bis(1H-tetrazol-5-yl)amine (H2BTA) have recently been considered by the defense industry as high nitrogen composite propellants. Photodegradation studies under solar simulating conditions showed that H2BTA was partially degraded in water, while it was completely degraded under UV light at 254 nm. When H2BTA (0.35 mM) was irradiated with simulated sunlight at pH 3.65, there was a 1-day lag phase before the chemical started to degrade, reaching 43.5% degradation after 7 d. However, when pH increased to 5.76, it degraded without lag phase, suggesting that an HBTA− anion was involved in the initial degradation of the chemical. 5-Aminotetrazole (5-AT) was identified as a final degradation product and N-(1H-tetrazol-5-yl)formamide(T(5 yl)FA) and 1H-tetrazol-5-ylcarbamic acid (T(5 yl)CA) as intermediate products. At λ = 254 nm, H2BTA disappeared rapidly, resulting in the loss of 94% after 65 min. 5-AT was detected together with several transient products including N-(1H-tetrazol-5-yl)carbamohydrazonic acid (T(5 yl)CHA) and T(5 yl)FA. Kinetic studies and products analysis revealed that H2BTA photodegraded via two initial routes. One route (a) marked by the initial loss of HN3 and another (b) marked by the initial loss of N2. Route a) was characteristics for irradiation with simulated sunlight; however, routes a) and b) proceeded simultaneously under UV light. 5-AT eventually degraded to presumably give N2 and/or HN3 under UV light. Understanding the photodegradation pathway of H2BTA under simulated sunlight can help in providing the basis for natural attenuation assessment of the chemical in contaminated aquatic environments.

Reactivity Modes of Cp*M-Type Half-Sandwich Dichalcogenolate Complexes with 2,6-Disubstituted Aryl Azides: The Effects of the Metal Center, Chalcogen, and Ligand Moiety on Product Formation

Cp*M-type half-sandwich dichalcogenolate complexes bearing either carborane or benzene moieties show diverse reactivity patterns toward two selected 2,6-disubstituted aryl azides under thermal or photolytic conditions. The chalcogen (S and Se) has little effect on the formation of final products. However, the effects of both the metal center and the ligand moiety of the metal precursor on the reactions were significant. Compared to iridium precursor Cp*IrS2C2B10H10 (1a), rhodium and cobalt analogues (1b: Cp*RhS2C2B10H10, 1c: Cp*CoS2C2B10H10) demonstrated no reactivity toward aryl azides. The reaction of Cp*IrSe2C2B10H10 (1d) with 2,6-Me2C6H3N3 led to the clean formation of complex 2 with C(sp3)–H activation of one methyl group of the Cp* ligand and loss of N2 along with the rearrangement of the benzene ring of the original azide ligand, whereas the treatment of Cp*IrS2C6H4 (1e) with 2,6-Me2C6H3N3 under the same reaction conditions gave a 16-electron half-sandwich complex 5 featuring C–N coupling on one methyl group from the Cp* ligand. When 2-Me-6-NO2C6H3N3 was employed, the same reaction patterns for forming products (3 and 6) with the nitro group migrating to the para-position versus the original aryl azide were observed. In addition, the reaction with metal precursor 1d generated another product 4 featuring the exchange of nitro and azido groups, while the reaction with 1e afforded another complex 7 with the formation of the N–NO2 moiety. All new complexes were characterized by spectroscopy methods, and single-crystal X-ray analyses were performed for complexes 2 and 5–7. Furthermore, radical mechanisms for the formation of complexes 2–7 were proposed.

Intramolecular C-H Functionalization Followed by a [2σ + 2π] Addition via an Intermediate Nickel-Nitridyl Complex.

Irradiation of a disphenoidal Ni(II) azido complex, [Cz tBu(Pyr iPr)2NiN3] (1), revealed an unprecedented nickel complex, [Cz tBu(Pyr iPr)(NH2-Pyr iPr)] (2), in >90% isolated yield. As evidenced by single-crystal X-ray diffraction, 2 is produced by double intramolecular C-H activation of a putative nickel-nitridyl intermediate, [Cz tBu(Pyr iPr)2Ni-⃛N•]. Calculations support the generation of an intermediate with significant nitridyl radical character after the loss of N2, which, in turn, undergoes tandem C-H activations, leading to functionalized intermediates and products. This is an unprecedented example of transient Ni-⃛N•-promoted intramolecular C-H functionalization, followed by a [2σ + 2π] addition, yielding bis-metallacyclic product 2. Complex 2 is also observed from the reaction of Ni(I) precursor Cz tBu(Pyr iPr)2Ni (3) and Me3SiN3, suggesting a unique thermal route toward a masked nickel-nitridyl intermediate.

Dinitrogen emissions: an overlooked key component of the N balance of montane grasslands

While emissions of nitric oxide (NO), ammonia (NH3) and nitrous oxide (N2O) from grassland soils have been increasingly well constrained, soil dinitrogen (N2) emissions are poorly understood. However, N2 losses might dominate total gaseous nitrogen (N) losses. Knowledge on N losses is key for the development of climate-adapted management that balances agronomic and environmental needs. Hence, we quantified all gaseous N losses from a montane grassland in Southern Germany both for ambient climatic conditions and for a climate change treatment (+ 2 °C MAT, − 300 mm MAP). Monthly measurements of soil N2 emissions of intact soil cores revealed that those exceeded by far soil N2O emissions and averaged at 350 ± 101 (ambient climate) and 738 ± 197 µg N m−2 h−1 (climate change). Because these measurements did not allow to quantify emission peaks after fertilization, an additional laboratory experiment was deployed to quantify the response of NH3, NO, N2O, and N2 emissions in sub daily temporal resolution to a typical slurry fertilization event (51 kg N ha−1). Our results revealed that total N gas losses amounted to roughly half of applied slurry-N. Surprisingly, N2 but not NH3 dominated fertilizer N losses, with N2 emissions accounting for 16–21 kg or 31–42% of the applied slurry-N, while NH3 volatilization (3.5 kg), N2O (0.2–0.5 kg) and NO losses (0–0.2 kg) were of minor importance. Though constraining annual N2 loss remained uncertain due to high spatiotemporal variability of fluxes, we show that N2 losses are a so far overlooked key component of the N balance in montane grasslands, which needs to be considered for developing improved grassland management strategies targeted at increasing N use efficiency.

Designing Reactions with Post-Transition-State Bifurcations: Asynchronous Nitrene Insertions into C–C σ Bonds

Summary Discoveries of chemical reactions with potential energy surfaces with post-transition-state bifurcations are increasing in frequency. Although such potential energy surface features are often discovered accidentally, we demonstrate here that they can be designed rationally. We describe a process for designing such reactions and apply it to the design of a nitrene addition/alkyl-shift reaction with a post-transition state bifurcation. We examine substituent effects on this reaction and propose a dynamics-based model for selectivity control.

Tracing denitrification in the Canada Basin: N2 loss to the atmosphere on the Chukchi Shelf and benthic inputs in deep waters

The global marine fixed nitrogen budget acts as a strong control on oceanic primary productivity, and the Arctic plays a disproportionately large role in the sink terms for this budget. This paper aims to quantify the impact of nitrogen cycling on the Canada Basin, utilizing two tracers of denitrification: N2/Ar, a dissolved gas tracer, and N*, a nutrient ratio tracer. In the Pacific Winter Water (PWW), which forms in the Chukchi Sea, we observe a disconnect between N2/Ar and N*, where the excess N2 expected from N* observations is far larger than the N2 excess we measure. We show that loss of N2 to the atmosphere through ventilation on the Chukchi Shelf likely accounts for this disparity, highlighting the importance of using N2/Ar as a denitrification tracer only in isolated water masses. We additionally observe increasing N2/Ar and decreasing N* in the old deep waters of the Canada Basin, suggesting benthic denitrification has been operating in the deep sediments over the 500-year age of this water mass. We use a one-dimensional vertical reaction-diffusion model to estimate denitrification rates of 0.0053–0.0130 mmol-N m−2 d−1, or 0.04–0.1 Tg N y−1 integrated over the whole basin, which is about half the rates estimated for other deep basins, in-line with lower remineralization rates in the deep Canada Basin. Further measurements of these tracers in the Arctic, particularly directly in the Chukchi Sea, will help constrain the relative importance of physical vs. biological processes on N2 in this region.

Probing arginine-phosphopeptide interactions in non-covalent peptide-peptide ion complexes using gas-phase cross-linking and Born-Oppenheimer molecular dynamics calculations

We report a study of non-covalent complexes of phosphopeptides pXAAAA and N-Ac-pXAAAA (X = Ser, Thr, Tyr) with arginine-containing peptides carrying diazirine 4,4-azipentyl tags at the N-terminus, *LGG(A)nR, or in the photoleucine residue, L*GG(A)nR (n = 3–5). Complexes with *LGG(A)nR were successfully generated as singly charged ions in the gas phase in 0.6–3.5% yields. In contrast, complexes with L*GG(A)nR were formed in negligible (<0.1%) yields. Selective photodissociation at 355 nm of the diazirine ring in [*LGG(A)nR + pXAAAA + H]+ ions resulted in loss of N2, producing large (75–95%) fractions of non-dissociating complexes that were further probed by collision-induced dissociation tandem mass spectrometry (CID-MS3). Covalent cross-links in the complexes produced by photoinduced carbene insertion were identified by specific CID-MS3 dissociations involving H3PO4 transfer and backbone fragmentations. N-acetylation in the phosphopeptides was found to have a substantial negative effect on the formation of covalent cross-links. Amongst the phosphorylated amino acid residues, pTyr showed the highest tendency (up to 92%) to form covalent cross-links. The fractions of covalent cross-links substantially increased with the length of the photopeptide chain. Born-Oppenheimer molecular dynamics (BOMD) calculations of canonical and zwitterionic protomers of the (pYAAAA + *LGGAAAR + H)+ complex indicated multiple close contacts between the incipient carbene of the diazirine ring and the XH bonds (XC, N, O) in the phosphopeptide. BOMD in combination with structural analysis by density functional theory calculations were used to interpret the experimental data and explain the cross-linking efficiencies.

Cobalt Pincer Complexes in Catalytic C-H Borylation: The Pincer Ligand Flips Rather Than Dearomatizes.

The mechanism for the borylation of an aromatic substrate by a cobalt pincer complex was investigated by density functional theory calculations. Experimental observations identified trans-(iPrPNP)CoH2(BPin) as the resting state in the borylation of five-membered heteroarenes, and 4-BPin-(iPrPNP)Co(N2)BPin as the resting state in the catalytic borylation of arene substrates. The active species, 4-R-(iPrPNP)CoBPin (R=H, BPin), were generated by reductive elimination of H2 in the former, through Berry pseudorotation to the cis isomer, and N2 loss in the latter. The catalytic mechanism of the resulting Co(I) complex was computed to involve three main steps: C-H oxidative addition of the aromatic substrate (C6H6), reductive elimination of PhBPin, and regeneration of the active complex. The oxidative addition product formed through the most favorable pathway, where the breaking C-H bond of C6H6 is parallel to a line between the two phosphine atoms, leaves the complex with a distorted PNP ligand, which rearranges to a more stable complex via dissociation and re-association of HBPin. Alternative pathways, σ-bond metathesis and the oxidative addition in which the breaking C-H bond is parallel to the Co-B bond, are predicted to be unlikely for this Co(I) complex. The thermodynamically favorable formation of the product PhBPin via reductive elimination drives the reaction forward. The active species regenerates through the oxidative addition of B2Pin2 and reductive elimination of HBPin. In the overall reaction, the flipping (refolding) of the five-membered phosphine rings, which connects the species with two phosphine rings folded in the same direction and that with them folded in different directions, is found to play an important role in the catalytic process, as it relieves steric crowding within the PNP ligand and opens Co coordination space. Metal-ligand cooperation based on the ligand's aromatization/dearomatization, a common mechanism for heavy-metal pincer complexes, and the dissociation of one phosphine ligand, do not apply in this system. This study provides guidance for understanding important features of pincer ligands with first-transition-row metals that differ from those in heavier metal complexes.

Effects of long-term increased N deposition on tropical montane forest soil N2 and N2O emissions

Nitrogen (N) deposition is projected to substantially increase in the tropics over the coming decades, which is expected to lead to enhanced N saturation and gaseous N emissions from tropical forests (via NO, N2O, and N2). However, it is unclear how N deposition in tropical forests influences both the magnitude of gaseous loss of nitrogen and its partitioning into the N2 and N2O loss mechanisms. Here, for the first time, we employed the acetylene inhibition technique and the 15N-nitrate labeling method to quantify N2 and N2O emission rates for long-term experimentally N-enriched treatments in primary and secondary tropical montane forest. We found that during laboratory incubation under aerobic conditions long-term increased N addition of up to 100 kg N ha−1 yr−1 at Jianfengling forest, China, did not cause a significant increase in either N2O or N2 emissions, or N2O/N2. However, under anaerobic conditions, N2O emissions decreased and N2 emissions increased with increasing N addition in the secondary forest. These changes may be attributed to substantially greater N2O reduction to N2 during denitrification, further supported by the decreased N2O/N2 ratio with increasing N addition. No such effects were observed in the primary forest. In both forests, N addition decreased the contribution of denitrification while increasing the contribution of co-denitrification and heterotrophic nitrification to N2O production. Denitrification was the predominant pathway to N2 production (98–100%) and its contribution was unaffected by N addition. Despite the changes in the contributions of denitrification to N2O gas emissions, we detected no change in the abundance of genes associated with denitrification. While the mechanisms for these different responses are not yet clear, our results indicate that the effects of N deposition on gaseous N loss were ecosystem-specific in tropical forests and that the microbial processes responsible for the production of N gases are sensitive to N inputs.