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Nitrogen fertilization in agriculture has serious environmental consequences, including production of the greenhouse gas nitrous oxide (N2O), pollution of groundwater with nitrate (NO3–), and river eutrophication. Nitrogen use efficiency can be increased by amending fertilizers with inhibitors to slow microbial nitrification processes, which transform ammonia to NO3–. Unfortunately, commercial inhibitors have failed to perform reliably across various agroecosystems for reasons not well understood. Using a combination of bacterial studies and soil incubations, we demonstrate here that 4-methyl-1-(prop-2-yn-1-yl)-1H-1,2,3-triazole (MPT) exhibits superior nitrification inhibitory properties. Unlike the commercial reversible inhibitors, MPT acts as a mechanistic, irreversible inhibitor of the key enzyme ammonia monooxygenase, enabling effective retention of ammonium (NH4+) and suppression of NO3– and N2O production over 21 days in several agricultural soils with pH values ranging from 4.7 to 7.5. A bacterial viability stain and a suite of freshwater and terrestrial ecotoxicity tests did not indicate any acute or chronic toxicity. Real-time quantitative polymerase chain reaction (qPCR) analysis revealed an enhanced inhibitory effect of MPT on both ammonia-oxidizing bacteria and archaea. Thus, MPT outperforms currently available nitrification inhibitors and has great potential for broad application in various agricultural settings.

The presence of alkene moieties in fatty acids of (phospho)lipids and cholesterol derivatives makes them highly susceptible to damage by nitrate radicals (NO3⋅), potentially formed through simultaneous exposure to the environmental air pollutants nitrogen dioxide (NO2⋅) and ozone (O3). Absolute rate coefficients derived from reactions with simplified model systems range from 4 to 8×109 M−1 s−1 in acetonitrile, ranking among the highest determined for NO3⋅ reactions with biomolecules in solution to date. Alkenes featuring an electron‐withdrawing carbonyl substituent also display notable reactivity with k values of (2.5±1.0)×108 M−1 s−1. Calculations suggest that these reactions are initiated by oxidative electron transfer (ET) involving the C=C bond, followed by recombination of the resulting alkene radical cation with nitrate anion (NO3−) to form the nitrate adduct radical as the kinetically controlled product. Conversely, saturated fatty acid derivatives and cholestanol react with NO3⋅ through hydrogen atom transfer (HAT) with rate coefficients of 106–107 M−1 s−1, indicating that biomolecules with a considerable number of non‐ or moderately activated sp3 C−H bonds are also highly susceptible to NO3⋅ attack. These findings underscore the potential health hazards associated with exposure to combined NO2⋅ and O3 gases.

Optimizing nitrogen (N) availability to plants is crucial for achieving maximum crop yield and quality. However, ensuring the appropriate supply of N to crops is challenging due to the various pathways through which N can be lost, such as ammonia (NH3) volatilization, nitrous oxide emissions, denitrification, nitrate (NO3−) leaching, and runoff. Additionally, N can become immobilized by soil minerals when ammonium (NH4+) gets trapped in the interlayers of clay minerals. Although synchronizing N availability with plant uptake could potentially reduce N loss, this approach is hindered by the fact that N loss from crop fields is typically influenced by a combination of management practices (which can be controlled) and weather dynamics, particularly precipitation, temperature fluctuations, and wind (which are beyond our control). In recent years, the use of urease and nitrification inhibitors has emerged as a strategy to temporarily delay the microbiological transformations of N-based fertilizers, thereby synchronizing N availability with plant uptake and mitigating N loss. Urease inhibitors slow down the hydrolysis of urea to NH4+ and reduce nitrogen loss through NH3 volatilization. Nitrification inhibitors temporarily inhibit soil bacteria (Nitrosomonas spp.) that convert NH4+ to nitrite (NO2−), thereby slowing down the first and rate-determining step of the nitrification process and reducing nitrogen loss as NO3− or through denitrification. This review aims to provide a comprehensive understanding of urease and nitrification inhibitor technologies and their profound implications for plants and root nitrogen uptake. It underscores the critical need to develop design principles for inhibitors with enhanced efficiency, highlighting their potential to revolutionize agricultural practices. Furthermore, this review offers valuable insights into future directions for inhibitor usage and emphasizes the essential traits that superior inhibitors should possess, thereby paving

Nitrification inhibitors have been coformulated with nitrogen fertilizers since the 1970s to modulate the microbiological conversion of nitrogen in agricultural soils. 3,4-Dimethyl-1H-pyrazole (DMP) and dicyandiamide (DCD) are currently the most used commercial nitrification inhibitors, but their mode of action is not well understood. This work seeks to fill this void by assessing for the first time in detail their mechanism of inhibition, efficacy, and acute toxicity with pure cell cultures of Nitrosomonas europaea. Bacterial assays based on the quantification of the nitrite (NO2–) production showed that both inhibitors reversibly target ammonia monooxygenase (AMO), which catalyzes the first step of the nitrification process. Michaelis–Menten kinetics suggest that both DMP and DCD act as uncompetitive inhibitors. Real-time measurements of the oxygen (O2) consumption confirmed the nonmechanistic mode of inhibition and showed that DMP reduced the O2 uptake rate by AMO much more at considerably lower concentrations than DCD, in line with the lower inhibitory efficiency of the latter. Acute toxicity tests revealed that DCD has a 10% higher toxicity than DMP when comparing treatments at the same inhibition efficacy (i.e., DMP at 10 ppm, DCD at 100 ppm), indicating that the inhibition of the nitrification process cannot simply be achieved by increasing the inhibitor concentration. The methods presented in this study could assist the development of more reliable nitrification inhibitors in the future.

Utilization of coal tailings (CTs) to enable ammonia (NH3) capture is of interest from pollution control and waste management perspectives. In this work, CTs were surface modified by air oxidation at different temperatures and varying duration to increase the uptake of NH3. The CTs treated at 300 and 250 °C for 5 h achieved an NH3 uptake of 52.5 and 45.3 mg g−1, respectively, which was significantly higher than that of the untreated CT (2.1 mg g−1). A linear relationship between NH3 uptake and concentration of acidic surface functional groups was found (R2 = 0.99). Spectroscopic analysis showed that NH3 can be retained on the oxidized CT through chemisorption involving carboxylic groups, leading to the formation of amides. Kinetic studies in the temperature range of 200–300 °C revealed an activation energy of 50.2 kJ mol−1 for the formation of acidic surface functional groups on CTs. These comparably mild conditions for the oxidative surface modification make CTs versatile and readily available materials for reducing agricultural NH3 emissions.

Nitrogen losses in agricultural systems can be reduced through enhanced-efficiency fertilizers (EEFs), which control the physicochemical release from fertilizers and biological nitrogen transformations in soils. The adoption of EEFs by farmers requires evidence of consistent performance across soils, crops and climates, paired with information on the economic advantages. Here we show that the benefits of EEFs due to avoided social costs of nitrogen pollution considerably outweigh their costs—and must be incorporated in fertilizer policies. We outline new approaches to the design of EEFs using enzyme inhibitors with modifiable chemical structures and engineered, biodegradable coatings that respond to plant rhizosphere signalling molecules.

The rate of oxidative damage of aliphatic amino acids and dipeptides by the environmental pollutant nitrate radical (NO3·) in an aqueous acidic environment was studied by laser flash photolysis. The reactivity dropped by a factor of about four for amino acid residues with secondary amide bonds and by a factor of up to nearly 20 for amino acid residues with tertiary amide bonds, compared with that in acetonitrile. According to density functional theory studies, the lower reactivity is due to protonation of the amide moiety, whereas in neutral water, hydrogen bonding with the amide should have little impact on the absolute reaction rate compared with that in acetonitrile. This finding can be rationalized by the high reactivity and broad reaction pattern of NO3·. Although hydrogen bonding involving the amide group raises the energies associated with some electron transfer processes, alternative low-energy pathways remain available so that the overall reaction rate is barely affected. The undiminished high reactivity of NO3· toward aliphatic amino acid residues in a neutral aqueous environment highlights the health-damaging potential of exposure to the combined air pollutants nitrogen dioxide (NO2·) and ozone (O3).

Methionine, cysteine and cystine, which were acetylated at the N‐terminus and methylated at the C‐terminus, react rapidly with the environmental nitrate radical (NO3.) with rate coefficients of 7.7×109, 3.4×109 and 2.0×109 M−1 s−1, respectively, in acetonitrile. Methionine (Ac−Met−OMe) is successively oxidized via the sulfoxide (Ac−MetO−Me) to the sulfone (Ac−MetO2−OMe), with the latter step being also extremely fast with a rate coefficient of 1.2×109 M−1 s−1. Computations predict formation of an initial charge transfer complex between NO3. and the S or SO moiety in Ac‐Met‐OMe, Ac‐MetO‐OMe and cystine (Ac−Cys(S−S)Cys‐OMe), respectively, which is followed by simultaneous S−O bond formation and NO2. expulsion. Calculations for the reaction of cysteine (Ac‐Cys‐OMe) with NO3. revealed side‐chain oxidation to give a thiyl radical or a sulfenic acid as likely pathways. These findings highlight the potential harmful impact of NO2./O3 pollution on S‐containing amino acid residues in peptides.

Nitrogen fertilizers amended with nitrification inhibitors (NIs) are used to increase nitrogen use efficiencies in agricultural systems. 3,4-Dimethylpyrazole phosphate (DMPP) is the most successful commercial NI to date but has a highly variable efficacy. To explore whether degradation could contribute to its inconsistent performance, incubation studies were performed with DMPP and 3,4-dimethylpyrazole glycolate (DMPG) in two alkaline clay soils that were treated with the fertilizer ammonium sulfate ((NH4)2SO4). Analysis of the soil extracts revealed a qualitative correlation between the amount of NI present in the soil and inhibition efficiency as well as several degradation products resulting from the oxidation of a methyl side chain and dimerization. A similar outcome was obtained for the degradation in sterilized soil and in accelerated weathering studies in the absence of soil. Our data suggest that chemical and not microbiological pathways are primarily responsible for the degradation of this inhibitor, which could potentially be initiated by reactive oxygen species (ROS) resulting from both biotic and abiotic processes in soils.

Nitrogen (N) fertilisers amended with nitrification inhibitors can increase nitrogen use efficiencies in agricultural systems but the effectiveness of existing commercial inhibitor products, including 3,4-dimethylpyrazole phosphate (DMPP), is strongly influenced by climatic and edaphic factors. With increasing pressure to reduce the environmental impact of large-scale agriculture it is important to develop new nitrogen-stabilising products that can give reliable and consistent results, particularly for warmer climatic conditions. We synthesised a library of 17 compounds featuring a substituted 1,2,3-triazole motif and performed laboratory incubations in two south-eastern Australian soils. In the neutral (pH 7.3) soil, the compounds N002, N013, N016 and N017, which possess short non-polar alkyl or alkynyl substituents at the triazole ring, retained NH4+-N concentrations at 35 °C soil temperature to a better extent (P < 0.001) than DMPP. In the alkaline soil (pH 8.8) N013 performed better with regards to NH4+-N retention (P = 0.004) than DMPP at 35 °C soil temperature. Overall, our data suggest that substituted 1,2,3-triazoles, which can be synthesized with good yields and excellent atom economy through 1,3-dipolar cycloaddition from readily available starting materials, are promising nitrification inhibitors performing similar to, or better than DMPP, particularly at elevated soil temperatures.

Pyrimidine cyclobutane dimers are hazardous DNA lesions formed upon exposure of DNA to UV light, which can be repaired through oxidative electron transfer (ET). Laser flash photolysis and computational studies were performed to explore the role of configuration and constitution at the cyclobutane ring on the oxidative repair process, using the nitrate radical (NO3•) as oxidant. The rate coefficients of 8–280 × 107 M−1 s−1 in acetonitrile revealed a very high reactivity of the cyclobutane dimers of N,N’-dimethylated uracil (DMU), thymine (DMT), and 6-methyluracil (DMU6-Me) towards NO3•, which likely proceeds via ET at N(1) as a major pathway. The overall rate of NO3• consumption was determined by (i) the redox potential, which was lower for the syn- than for the anti-configured dimers, and (ii) the accessibility of the reaction site for NO3•. In the trans dimers, both N(1) atoms could be approached from above and below the molecular plane, whereas in the cis dimers, only the convex side was readily accessible for NO3•. The higher reactivity of the DMT dimers compared with isomeric DMU dimers was due to the electron-donating methyl groups on the cyclobutane ring, which increased their susceptibility to oxidation. On the other hand, the approach of NO3• to the dimers of DMU6-Me was hindered by the methyl substituents adjacent to N(1), making these dimers the least reactive in this series.

In nature, proteins serve as media for long-distance electron transfer (ET) to carry out redox reactions in distant compartments. This ET occurs either by a single-step superexchange or through a multi-step charge hopping process, which uses side chains of amino acids as stepping stones. In this study we demonstrate that Phe can act as a relay amino acid for long-distance electron hole transfer through peptides. The considerably increased susceptibility of the aromatic ring to oxidation is caused by the lone pairs of neighbouring amide carbonyl groups, which stabilise the Phe radical cation. This neighbouring-amide-group effect helps improve understanding of the mechanism of extracellular electron transfer through conductive protein filaments (pili) of anaerobic bacteria during mineral respiration.

The mechanism of the recently described N→C direction peptide synthesis through silver-promoted coupling of N-protected amino acids with thioacetylated amino esters was explored by using density functional theory. Calculation of the potential energy surfaces for various pathways revealed that the reaction proceeds through silver-assisted addition of the carboxylate to the thioamide, which is followed by deprotonation and silver-mediated extrusion of sulfur as Ag2 S. The resulting isoimide is the key intermediate, which subsequently rearranges to an imide through a concerted pericyclic [1,3]-acyl shift (O-sp(2) N 1,3-acyl migration). The proposed mechanism clearly emphasises the requirement of two equivalents of Ag(I) and basic reaction conditions, which is in full agreement with the experimental findings. Alternative rearrangement pathways involving only one equivalent of Ag(I) or through O-sp(3) N 1,3-acyl migration can be excluded. The computations further revealed that peptide couplings involving thioformamides require significant conformational changes in the intermediate isoformimide, which slow down the rearrangement process.

Acetaminophen (paracetamol, APAP) is a safe and widely used analgesic medication when taken at therapeutic doses. However, APAP can cause potentially fatal hepatotoxicity when taken in overdose or in patients with metabolic irregularities. The production of the electrophilic and putatively toxic compound N-acetyl-p-benzoquinone imine (NAPQI), which cannot be efficiently detoxicated at high doses, is implicated in APAP toxicity. Numerous studies have identified that excess NAPQI can form covalent linkages to the thiol side chains of cysteine residues in proteins; however, the reactivity of NAPQI toward other amino acid side chains is largely unexplored. Here, we report a survey of the reactivity of NAPQI toward 11 N-acetyl amino acid methyl esters and four peptides. (1)H NMR analysis reveals that NAPQI forms covalent bonds to the side-chain functional groups of cysteine, methionine, tyrosine, and tryptophan residues. Analogous reaction products were observed when NAPQI was reacted with synthetic model peptides GAIL-X-GAILR for X = Cys, Met, Tyr, and Trp. Tandem mass spectrometry peptide sequencing showed that the NAPQI modification sites are located on the "X" residue in each case. However, when APAP and the GAIL-X-GAILR peptide were incubated with rat liver microsomes that contain many metabolic enzymes, NAPQI formed by oxidative metabolism reacted with GAIL-C-GAILR exclusively. For the peptides where X = Met, Tyr, and Trp, competing reactions between NAPQI and alternative nucleophiles precluded arylation of the target peptide by NAPQI. Although Cys residues are favorably targeted under these conditions, these data suggest that NAPQI can, in principle, also damage proteins at Met, Tyr, and Trp residues.

The photophysical behaviour of the isolated retinal protonated n-butylamine Schiff base (RPSB) is investigated in the gas phase using a combination of ion mobility spectrometry and laser spectroscopy. The RPSB cations are introduced by electrospray ionisation into an ion mobility mass spectrometer where they are exposed to tunable laser radiation in the region of the S1 ← S0 transition (420-680 nm range). Four peaks are observed in the arrival time distribution of the RPSB ions. On the basis of predicted collision cross sections with nitrogen gas, the dominant peak is assigned to the all-trans isomer, whereas the subsidiary peaks are assigned to various single, double and triple cis geometric isomers. RPSB ions that absorb laser radiation undergo photoisomerization, leading to a detectable change in their drift speed. By monitoring the photoisomer signal as a function of laser wavelength an action spectrum, extending from 480 to 660 nm with a clear peak at 615 ± 5 nm, is obtained. The photoisomerization action spectrum is related to the absorption spectrum of isolated retinal RPSB molecules and should help benchmark future electronic structure calculations.

Manufactured polymer materials are used in increasingly demanding applications, but their lifetime is strongly influenced by environmental conditions. In particular, weathering and ageing leads to dramatic changes in the properties of the polymers, which results in decreased service life and limited usage. Despite the heavy reliance of our society on polymers, the mechanism of their degradation upon exposure to environmental oxidants is barely understood. In this work, model systems of important structural motifs in commercial high-performing polyesters were used to study the reaction with the night-time free radical oxidant NO3 (•) in the absence and presence of other radical and non-radical oxidants. Identification of the products revealed 'hot spots' in polyesters that are particularly vulnerable to attack by NO3 (•) and insight into the mechanism of oxidative damage by this environmentally important radical. It is suggested that both intermediates as well as products of these reactions are potentially capable of promoting further degradation processes in polyesters under environmental conditions.