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Amines at typical atmospheric concentrations of a only few molecules per trillion air molecules combine with sulphuric acid to form highly stable aerosol particles at rates similar to those observed in the lower atmosphere. Atmospheric chemistry of anthropogenic amines Amines emitted into the atmosphere from anthropogenic sources are thought to enhance nucleation from trace atmospheric vapours, stimulate particle formation and influence the development and properties of clouds. Direct evidence for this under atmospheric conditions has been lacking; however, this study, using the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN, demonstrates that amines at atmospherically relevant concentrations can sufficiently increase nucleation rates to be able to account for the particle formation rates observed in the atmospheric environment. Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei 1 . Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes 2 . Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases 2 . However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere 3 . It is thought that amines may enhance nucleation 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid–amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid–dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.

Atmospheric aerosols formed by nucleation of vapors affect radiative forcing and therefore climate. However, the underlying mechanisms of nucleation remain unclear, particularly the involvement of organic compounds. Here, we present high-resolution mass spectra of ion clusters observed during new particle formation experiments performed at the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research. The experiments involved sulfuric acid vapor and different stabilizing species, including ammonia and dimethylamine, as well as oxidation products of pinanediol, a surrogate for organic vapors formed from monoterpenes. A striking resemblance is revealed between the mass spectra from the chamber experiments with oxidized organics and ambient data obtained during new particle formation events at the Hyytiälä boreal forest research station. We observe that large oxidized organic compounds, arising from the oxidation of monoterpenes, cluster directly with single sulfuric acid molecules and then form growing clusters of one to three sulfuric acid molecules plus one to four oxidized organics. Most of these organic compounds retain 10 carbon atoms, and some of them are remarkably highly oxidized (oxygen-to-carbon ratios up to 1.2). The average degree of oxygenation of the organic compounds decreases while the clusters are growing. Our measurements therefore connect oxidized organics directly, and in detail, with the very first steps of new particle formation and their growth between 1 and 2 nm in a controlled environment. Thus, they confirm that oxidized organics are involved in both the formation and growth of particles under ambient conditions.

Recent research [Wang et al., Nature 581, 184–189 (2020)] indicates nitric acid (NA) can participate in sulfuric acid (SA)–ammonia (NH₂) nucleation in the clean and cold upper free troposphere, whereas NA exhibits no obvious effects at the boundary layer with relatively high temperatures. Herein, considering that an SA–dimethylamine (DMA) nucleation mechanism was detected inmegacities [Yao et al., Science 361, 278–281 (2018)], the roles of NA in SA-DMA nucleation are investigated. Different from SA-NH₂ nucleation, we found that NA can enhance SA-DMA–based particle formation rates in the polluted atmospheric boundary layer, such as Beijing in winter, with the enhancement up to 80-fold. Moreover, we found that NA can promote the number concentrations of nucleation clusters (up to 27-fold) and contribute 76% of cluster formation pathways at 280 K. The enhancements on particle formation by NA are critical for particulate pollution in the polluted boundary layer with relatively high NA and DMA concentrations.

In recent years, the detection of nitrosamine precursors has become an important issue for regulatory authorities such as the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). The present study provides a pre-column derivatization method for the analysis of dimethylamine (DMA) and diethylamine (DEA) in pharmaceutical products using HPLC and a fluorescence detector. Appropriate chromatographic parameters, including mobile phase composition (organic solvent, buffer, pH), elution type, flow rate, temperature, and λexcitation/emission, were investigated. Analysis was performed at λexcitation = 450 nm and λemission = 540 nm on a C18 column (at 40 °C) using gradient elution as a mobile phase with Eluent A: Phosphoric Acid Buffer (20 mM, pH = 2.8) and Eluent B: methanol, with a flow of 0.8 mL/min. The method was validated according to ICH specifications in terms of linearity (0.5–10 ng/mL for DMA and 5–100 ng/mL for DEA), specificity, and robustness, as well as repeatability, intermediate precision (%RSD < 2.9), and accuracy (% recovery 98.2–102.0%). The derivatization process was optimized using the “Crossed D-Optimal” experimental design procedure, where one mixture component was cross-correlated with two factors. The stability of the samples was studied over a period of one month. To process the samples (pharmaceuticals), various purification techniques were tried using solid/liquid or liquid/liquid extraction with dichloromethane. Finally, a straightforward solid-phase extraction (SPE, C18) method was chosen prior to derivatization. The method was successfully applied, since the extraction recoveries were >81.6% for DMA (0.5 ppm) and >81.1% for DEA (5 ppm). Based on the results obtained and the available literature, the scientific community seeks, by proposing flexible analytical methods, to delimit the problem of nitrosamines.

Platinum and ruthenium nanoparticles stabilised by an amine modified polymer immobilised ionic liquid (MNP@NH 2 -PEGPIILS, M = Pt, Ru) catalyse the hydrolytic liberation of hydrogen from dimethylamine borane (DMAB), ammonia borane (AB) and NaBH 4 under mild conditions. While RuNP@NH 2 -PEGPIILS and PtNP@NH 2 -PEGPIILS catalyse the hydrolytic evolution of hydrogen from NaBH 4 with comparable initial TOFs of 6,250 molesH 2 .molcat −1 .h −1 and 5,900 molesH 2 .molcat −1 .h −1 , respectively, based on the total metal content, RuNP@NH 2 -PEGPIILS is a markedly more efficient catalyst for the dehydrogenation of DMAB and AB than its platinum counterpart, as RuNP@NH 2 -PEGPIILS gave initial TOFs of 8,300 molesH 2 .molcat −1 .h −1 and 21,200 molesH 2 .molcat −1 .h −1 , respectively, compared with 3,050 molesH 2 .molcat −1 .h −1 and 8,500 molesH 2 .molcat −1 .h −1 , respectively, for PtNP@NH 2 -PEGPIILS. Gratifyingly, for each substrate tested RuNP@NH 2 -PEGPIILS and PtNP@NH 2 -PEGPIILS were markedly more active than commercial 5wt % Ru/C and 5wt% Pt/C, respectively. The apparent activation energies of 55.7 kJ mol −1 and 27.9 kJ mol −1 for the catalytic hydrolysis of DMAB and AB, respectively, with RuNP@NH 2 -PEGPIILS are significantly lower than the respective activation energies of 74.6 kJ mol −1 and 35.7 kJ mol −1 for its platinum counterpart, commensurate with the markedly higher initial rates obtained with the RuNPs. In comparison, the apparent activation energies of 44.1 kJ mol −1 and 46.5 kJ mol −1 , for the hydrolysis NaBH 4 reflect the similar initial TOFs obtained for both catalysts. The difference in apparent activation energies for the hydrolysis of DMAB compared with AB also reflect the higher rates of hydrolysis for the latter. Stability and reuse studies revealed that RuNP@NH 2 -PEGPIILS recycled efficiently as high conversions for the hydrolysis of DMAB were maintained across five runs with the catalyst retaining 97% of its activity. Graphical Abstract

Hydrolysis of N 2 O 5 under tropospheric conditions plays a critical role in assessing the fate of O 3 , OH, and NO x in the atmosphere. However, its removal mechanism has not been fully understood, and little is known about the role of entropy. Herein, we propose a removal path of N 2 O 5 on the water clusters/droplet with the existence of amine, which entails a low free-energy barrier of 4.46 and 3.76 kcal/mol on a water trimer and droplet, respectively, at room temperature. The free-energy barrier exhibits strong temperature dependence; a barrierless hydrolysis process of N 2 O 5 at low temperature (≤150 K) is observed. By coupling constrained ab initio molecular dynamics (constrained AIMD) simulations with thermodynamic integration methods, we quantitively evaluated the entropic contributions to the free energy and compared NH 3 -, methylamine (MA)-, and dimethylamine (DMA)-promoted hydrolysis of N 2 O 5 on water clusters and droplet. Our results demonstrate that methylation of NH 3 stabilizes the product state and promotes hydrolysis of N 2 O 5 by reducing the free-energy barriers. Furthermore, a quantitative analysis of the internal coordinate distribution of the reaction center and the relative position of surrounding species reveals that the significant entropic contribution primarily results from the ensemble effect of configurations observed in the AIMD simulations. Such an ensemble effect becomes more significant with more water molecules included. Lowering the temperature effectively minimizes the entropic contribution, making the hydrolysis more exothermic and barrierless. This study sheds light on the importance of the promoting effect of amines and the entropic effect on gas-phase hydrolysis reactions, which may have far-reaching implications in atmospheric chemistry.

Chronic kidney disease (CKD) remains a major health threat worldwide which is associated with elevated blood level of dimethylamine (DMA) and unbalanced platelet functions. Dimethylamine, a simple aliphatic amine, is abundantly found in human urine as well as other body fluids like plasma. However, the relation between dimethylamine and platelet activation is unclear. This study aims to unravel the mechanism of DMA and platelet function in chronic kidney disease. Through in vitro platelet characterization assay and in vivo CKD mouse model, the level of DMA, platelet activity and renal function were assessed by established methods. PKCδ and its downstream kinase MEK1/2 were examined by immunoblotting analysis of human platelet extract. Rescue experiments with PKCδ inhibitor or choline deficient diet were also conducted. DMA level in plasma of mouse CKD model was elevated along with enhanced platelet activation and comprised renal function. DMA can activate platelet in vitro and in vivo. Inhibition of PKCδ could antagonize the effect of DMA on platelet activation. When choline as the dietary source of DMA was deprived from CKD mouse, the level DMA was reduced and platelet activation was attenuated. Our results demonstrate that dimethylamine could enhance platelet activation in CKD model, potentially through activation of PKCδ.

The geometrical structures and photophysical properties of Ir(4,6-dFppy)2(pic) (FIrpic) and its derivative (o-FIr, m-FIr, p-FIr) with dimethylamine substituted at the picolinic acid (N∧O) ligand were fully investigated by density functional theory and time-dependent density functional theory. The simulated electronic structure, as well as absorption and emission spectra of FIrpic are in good agreement with the experimental observations. The introduction of dimethylamine at the N∧O ligand at different positions is beneficial to extend the π-electron delocalization, increase HOMO energy levels, and hence improve the hole injection and transfer ability compared with those of FIrpic. Furthermore, o-FIr, m-FIr, and p-FIr have large absorption intensity and participation of metal-to-ligand charge transfer (MLCT) contribution in the main absorption spectra, which would be useful to improve the intersystem crossing (ISC) from the singlet to triplet excited state. More importantly, the high quantum yield of o-FIr (which is explained based on the detailed analysis of triplet energy, ET1), participation of 3MLCT contribution in the phosphorescent spectra, and energy difference between 3MLCT and triplet metal centered (3MC) d-d excited state compared with m-FIr and p-FIr indicate that o-FIr is expected to be an excellent blue phosphorescence emitter with high efficiency.

For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus. Significance A significant fraction of atmospheric aerosols is formed from the condensation of low-volatility vapors. These newly formed particles can grow, become seeds for cloud particles, and influence climate. New particle formation in the planetary boundary layer generally proceeds via the neutral channel. However, unambiguous identification of neutral nucleating clusters has so far not been possible under atmospherically relevant conditions. We explored the system of sulfuric acid, water, and dimethylamine in a well-controlled laboratory experiment and measured the time-resolved concentrations of neutral clusters. Clusters containing up to 14 sulfuric acid and 16 dimethylamine molecules were observed. Our results demonstrate that a cluster containing as few as two sulfuric acid and one or two dimethylamine molecules is already stable against evaporation.

Increasing evidence has shown that fecal microbiota transplantation (FMT) could be a promising treatment option for Crohn’s disease (CD). However, the frequency of FMT for CD treatment remains unclear. This study aimed to evaluate the optimal timing for administering the second course of FMT to maintain the long-term clinical effects from the first FMT for patients with CD. Sixty-nine patients with active CD who underwent FMT twice and benefited from the first FMT were enrolled in this study. Clinical response, stool microbiota, and urine metabolome of patients were assessed during the follow-up. The median time of maintaining clinical response to the first FMT in total 69 patients was 125 days (IQR, 82.5–225.5). The time of maintaining clinical response to the second FMT in 56 of 69 patients was 176.5 days (IQR, 98.5–280). The fecal microbiota composition of each patient post the first FMT was closer to that of his/her donor. Compared to that of the baseline, patients prior to the second course of FMT showed significant differences in urinary metabolic profiles characterized by increased indoxyl sulfate, 4-hydroxyphenylacetate, creatinine, dimethylamine, glycylproline, hippurate, and trimethylamine oxide (TMAO). This study demonstrated that patients with CD could be administered the second course of FMT less than 4 months after the first FMT for maintaining the clinical benefits from the first FMT. This was supported by the host–microbial metabolism changes in patients with active CD. Trial registration : ClinicalTrials.gov , NCT01793831. Registered 18 February 2013. https://clinicaltrials.gov/ct2/show/NCT01793831?term=NCT01793831&rank=1