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Carbon dioxide is considered an inert gas that rarely participates in atmospheric chemical reactions. Nonetheless, we show here that CO2 is involved in some important photo-oxidation reactions in the atmosphere through the formation of carbonate radicals (CO3⚫-). This potentially active intermediate CO3⚫- is routinely overlooked in atmospheric chemistry concerning its effect on sulfate formation. The present work demonstrates that the SO2 uptake coefficient is enhanced by 17 times on mineral dust particles driven by CO3⚫-. Importantly, upon irradiation, mineral dust particles are speculated to produce gas-phase carbonate radical ions when the atmospherically relevant concentration of CO2 presents, thereby potentially promoting external sulfate aerosol formation and oxidative potential in the atmosphere. Employing a suite of laboratory investigations of sulfate formation in the presence of carbonate radicals on the model and authentic dust particles, ground-based field measurements of sulfate and (bi)carbonate ions within ambient PM, together with density functional theory (DFT) calculations for single electron transfer processes in terms of CO3⚫--initiated S(IV) oxidation, a novel role of carbonate radical in atmospheric chemistry is elucidated.

Both iodic acid (HIO3, IA) and methanesulfonic acid (CH3S(O)2OH, MSA) have been identified by field studies as important precursors of new particle formation (NPF) in marine areas. However, the mechanism of NPF in which IA and MSA are jointly involved is still unclear. Hence, we investigated the IA-MSA nucleation system under different atmospheric conditions and uncovered the corresponding nucleating mechanism at the molecular level for the first time, using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that the pure-IA nucleation rate was much lower than the results of CLOUD (Cosmics Leaving Outdoor Droplets) experiments. MSA can promote IA cluster formation through stabilizing IA via both hydrogen and halogen bonds, especially under conditions with lower temperatures, sparse IA, and rich MSA. However, the nucleation rate of the IA-MSA mechanism is much lower than that of field observations, indicating that the effect of additional nucleation precursors needs to be considered (e.g., H2SO4, HIO2, NH3, and amines). The IA-MSA nucleation mechanism revealed in this study may help to gain insight into the joint effect of marine sulfur- and iodine-containing components on marine NPF.

The role of pyruvic acid (PA), one of the most abundant α-keto carboxylic acids in the atmosphere, was investigated both in the SO3 hydrolysis reaction to form sulfuric acid (SA) and in SA-based aerosol particle formation using quantum chemical calculations and a cluster dynamics model. We found that the PA-catalyzed SO3 hydrolysis is a thermodynamically driven transformation process, proceeding with a negative Gibbs free-energy barrier, ca. −1 kcal mol−1 at 298 K, ∼ 6.50 kcal mol−1 lower than that in the water-catalyzed SO3 hydrolysis. Results indicated that the PA-catalyzed reaction can potentially compete with the water-catalyzed SO3 reaction in SA production, especially in dry and polluted areas, where it is found to be ∼ 2 orders of magnitude more efficient that the water-catalyzed reaction. Given the effective stabilization of the PA-catalyzed SO3 hydrolysis product as SA⚫PA cluster, we proceeded to examine the PA clustering efficiency in a sulfuric-acid–pyruvic-acid–ammonia (SA-PA-NH3) system. Our thermodynamic data used in the Atmospheric Cluster Dynamics Code indicated that under relevant tropospheric temperatures and concentrations of SA (106 molec.cm-3), PA (1010 molec.cm-3) and NH3 (1011 and 5 × 1011 molec.cm-3), PA-enhanced particle formation involves clusters containing at most one PA molecule. Namely, under these monomer concentrations and 238 K, the (SA)2⚫PA⚫(NH3)2 cluster was found to contribute by ∼ 100 % to the net flux to aerosol particle formation. At higher temperatures (258 and 278 K), however, the net flux to the particle formation is dominated by pure SA-NH3 clusters, while PA would rather evaporate from the clusters at high temperatures and not contribute to the particle formation. The enhancing effect of PA was examined by evaluating the ratio of the ternary SA-PA-NH3 cluster formation rate to binary SA-NH3 cluster formation rate. Our results show that while the enhancement factor of PA to the particle formation rate is almost insensitive to investigated temperatures and concentrations, it can be as high as 4.7 × 102 at 238 K and [NH3] = 1.3 × 1011 molec.cm-3. This indicates that PA may actively participate in aerosol formation, only in cold regions of the troposphere and highly NH3-polluted environments. The inclusion of this mechanism in aerosol models may reduce uncertainties that prevail in modeling the aerosol impact on climate.

In comparison with iodic acid, iodous acid is a potentially important nucleation precursor in marine regions.

A cheap and easily available ZnEt2 is an effective precatalyst, which can be used for the hydroboration reaction of various organic carbonates and esters with HBpin.

Tetranuclear Cp4M4(CO)4 clusters have been synthesized for iron and vanadium but not for the intermediate first-row transition metals manganese and chromium. All of the low-energy structures of these "missing" Cp4M4(CO)4 (M = Mn, Cr) species are shown by density functional theory to consist of a central M4 tetrahedron with each of the four faces capped by a μ3-CO group. The individual low-energy structures differ in their spin states and in their formal metal-metal bond orders along the six edges of their central M4 tetrahedra. The two low-energy Cp4Mn4(μ3-CO)4 structures are a triplet structure with all Mn-Mn single bonds and a singlet structure with one Mn≡Mn triple bond and five Mn-Mn single bonds along the six tetrahedral edges. Related low-energy Cp4Cr4(μ3-CO)4 structures include a quintet structure with all Cr-Cr single bonds and a singlet structure with two Cr≡Cr triple bonds and four Cr-Cr single bonds. However, the potential energy surface of the Cp4Cr4(CO)4 system is complicated by three other structures of comparable energies including two triplet structures and one quintet structure with various combinations of single, double, and triple chromium-chromium bonds in the central Cr4 tetrahedron.

Carbon capture and storage (CCS) is an effective means of mitigating anthropogenic CO2 emissions in the atmosphere. However, it is important to consider the risks of CO2 leakage from storage sites and their potential impacts on near-surface ecosystems. We explored the impact of increased soil CO2 concentrations on sunflowers (Helianthus annuus Linn.), a main oil crop, using pot experiments. The results indicate that the crude fat content of the sunflowers decreased by 3.62%, whereas the crude protein content and linoleic acid contents increased by 4.12% and 13.98%, respectively; sunflower yields remain unchanged under 1500 g m−2 day−1 CO2 leakage. We confirmed that the sunflower oil content decreased because of higher soil CO2. A decrease in sunflower oil production rates will reduce their commercial value. The elevated crude protein and linoleic acid contents increased the nutrients in sunflower meal and edible oil, indicating that increased CO2 in soil caused by CCS leakage can improve the quality of sunflower oil to some extent. Considering the tolerance of sunflowers to CO2 leakage, planting sunflowers in CCS project areas is a feasible solution for addressing CO2 leakage.

Graphite is useful as a low-cost and high-voltage cathode of dual-ion batteries (DIBs) to allow anion (de-)intercalation, yet its practical applications are hindered by low Coulombic efficiencies (...

Despite the high abundance in the atmosphere, alcohols in general and methanol in particular are believed to play a small role in atmospheric new particle formation (NPF) largely due to the weak binding abilities of alcohols with the major nucleation precursors, e.g., sulfuric acid (SA) and dimethylamine (DMA). Herein, we identify a catalytic reaction that was previously overlooked, namely, the reaction between methanol and SO3, catalyzed by SA, DMA, or water. We found that alcohols can have unexpected quenching effects on the NPF process, particularly in dry and highly polluted regions with high concentrations of alcohols. Specifically, the catalytic reaction between methanol and SO3 can convert methanol into a less-volatile species-methyl hydrogen sulfate (MHS). The latter was initially thought to be a good nucleation agent for NPF. However, our simulation results suggest that the formation of MHS consumes an appreciable amount of atmospheric SO3, disfavoring further reactions of SO3 with H2O. Indeed, we found that MHS formation can cause a reduction of SA concentration up to 87%, whereas the nucleation ability of MHS toward new particles is not as good as that of SA. Hence, a high abundance of methanol in the atmosphere can lower the particle nucleation rate by as much as two orders of magnitude. Such a quenching effect suggests that the recently identified catalytic reactions between alcohols and SO3 need to be considered in atmospheric modeling in order to predict SA concentration from SO2, while also account for their potentially negative effect on NPF.

Starting soon after discovery, we carried out a programme of continuous observations for the active comet C/2017 K2 (PANSTARRS) using the Lijiang 2.4 m telescope from 2017 September 8 to 2018 June 18 with a Johnson R filter. Three fixed linear apertures of ra1 = 6.4 x 104 km, ra2 = 7.7 x 104 km and ra3 = 9.6 x 104 km were chosen to measure the brightness of C/2017 K2 respectively, and the instrumental magnitudes were then converted into the PS1 r system. During the period of observation, the cross-section area increased at rates of 22.0, 28.5 and 44.1 km2 d(-1) relative to the different linear photometry apertures, and the corresponding mass-loss rates were 63.8 kg s(-1), 82.6 kg s(-1) and 127.5 kg s(-1), assuming that the dust-particle size is (a) over bar = 0.5 mm and the density is. = 500 kgm(3). The size of the C/2017 K2 nucleus is estimated as 1.2 less than or similar to rn less than or similar to 2.5 km for CO sublimation and 3.1 less than or similar to rn less than or similar to 183.9 km for CO2 with an aperture of 9.6 x 10(4) km; meanwhile the grain size of K2 is ac less than or similar to 9 mm for CO and a(c) less than or similar to 0.8 mm for CO2. The long-term monitoring data provided in this paper will be very valuable and helpful for studying the activity mechanism of C/2017 K2.

Different landscapes in a river basin make different contributions to non-point source pollution according to the source–sink theory. Changes in landscape pattern have a considerable impact on river water quality. Precise predictions of the future landscape pattern provide strong support for manipulating land use patterns, which is beneficial for sustainable development in the watershed. The Jiulong River Basin in south-eastern China was selected as the study area. The Random Forest classifier, which combined textural characteristics with spectral information, was applied to interpret the landscapes from Landsat images acquired in 1995, 2005 and 2015 in this paper. The overall classification accuracy reached 86%, and the Kappa index was higher than 0.83, which was better than the accuracy of classifiers based on the exclusive use of spectral information. We used a hybrid cellular automaton–Markov (CA–Markov) model to simulate the landscape pattern of the Jiulong River Basin in 2015 and verified the accuracy according to the interpreted landscape classification map in 2015. The pixels that were predicted to the correct landscape account for 88.35% of total pixels, and the Kappa coefficient was 0.88, indicating that the CA–Markov model was credible for predicting the future landscape pattern in the Jiulong River Basin. The CA–Markov model was applied to forecast the landscape pattern of this watershed in 2025, and the transition area matrix from 2015 to 2025 was obtained. The predicted results demonstrated the imbalanced migration of source–sink landscapes in the future, which indicated the deterioration of water quality in the study area. Hence, government regulators need rational manipulation of the landscape pattern for sustainable development in the Jiulong River Basin.

Amino acids are recognized as significant components of atmospheric aerosols. However, their potential role in atmospheric new particle formation (NPF) is poorly understood, especially aspartic acid (ASP), one of the most abundant amino acids in the atmosphere. It has not only two advantageous carboxylic acid groups but also one amino group, both of which are both effective groups enhancing NPF. Herein, the participation mechanism of ASP in the formation of new particle involving sulfuric acid (SA)–ammonia (A)-based system has been studied using the Density Functional Theory (DFT) combined with the Atmospheric Clusters Dynamic Code (ACDC). The results show that the addition of ASP molecules in the SA–A-based clusters provides a promotion on the interaction between SA and A molecules. Moreover, ACDC simulations indicate that ASP could present an obvious enhancement effect on SA–A-based cluster formation rates. Meanwhile, the enhancement strength R presents a positive dependence on [ASP] and a negative dependence on [SA] and [A]. Besides, the enhancement effect of ASP is compared with that of malonic acid (MOA) with two carboxylic acid groups (Chemosphere, 2018, 203, 26–33), and ASP presents a more obvious enhancement effect than MOA. The mechanism of NPF indicates that ASP could contribute to cluster formation as a “participator” which is different from the “catalytic” role of MOA at 238 K. These new insights are helpful to understand the mechanism of NPF involving organic compounds with multiple functional groups, especially the abundant amino acids, such as the ASP, in the urban/suburban areas with intensive human activities and industrial productions and therefore the abundant sources of amino acids. Furthermore, the NPF of the SA–A-based system involving amino acid should be considered when assessing the environmental risk of amino acid.

Rodent focal ischemia models are widely used to mimic and examine human strokes. To the best of our knowledge, no investigation has systematically examined the expression changes of microRNA (miR)-449a and Amphiregulin (AREG) as well as their biological relationship during middle cerebral artery occlusion (MCAO) and oxygen and glucose deprivation/reperfusion (OGD/R). The present study examined the histological and behavioral outcomes of MCAO and the function of miR-449a and AREG in cerebral ischemic injury. Rats were subjected to 2 h MCAO, which was followed by reperfusion. miR-449a and AREG were examined in the injury tissues of MCAO rats and the OGD/R cell line by reverse transcription-quantitative polymerase chain reaction. Protein expressions of AREG in the injury tissues of MCAO rats was measured using an immunohistochemistry and the protein expression levels of AREG, epidermal growth factor receptor (EGFR), phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (Akt) and the phosphorylation level of Akt (p-Akt) were analyzed by western blotting. Cell apoptosis was examined following the knock down and subsequent overexpression of AREG in a human OGD/R neuronal cell line by small interfering RNAs (siRNAs) and plasmid transfection. Luciferase reporter assays were used to validate the target of miR-449a. The expression changes and regulatory mechanisms of miR-449a and AREG in an ischemia/reperfusion (I/R) injury model were examined in vivo and in vitro. The neurological deficit score, brain edema volume, cerebral infarct area, and the number of apoptosis cells in ischemic rats were all markedly elevated, than that in the control rats. The expression of miR-449a was decreased and AREG was increased in the MCAO rats and human OGD/R neuronal cell line. miR-449a inhibition or AREG overexpression in OGD/R cells resulted in a significant decrease in apoptotic cells, and AREG was revealed to be one of the direct targets of miR-449a. Molecular recovery was observed following transfection with miR-449a mimics and AREG knockdown in an OGD/R model in vitro. The present study demonstrated that miR-449a was downregulated while AREG was upregulated in cerebral ischemic injury, and the recovery of neurological function can be obtained following the overexpression of miR-449a and the knockdown of AREG in an I/R injury model. miR-449a functions in ischemic stroke via directly targeting AREG. These findings suggest a novel mechanism involving in cerebral I/R injury model and may aid investigators in gaining a deeper understanding of strokes in a clinical setting.

Organosulfur compounds are being of increasing interest in the atmospheric environment and climate because of their profound impacts on the formation of secondary organic aerosol. However, their role in the initial step of new particle formation (NPF) is still unclear. Here, using Density Functional Theory (DFT) calculation combined with the Atmospheric Clusters Dynamic Code (ACDC) model, we study the enhancement effect of hydroxymethanesulfonic acid (HMSA) - one of the most important organosulfur compounds - on sulfuric acid (SA) - dimethylamine (DMA) molecular clustering and the underlying mechanism. The results show that HMSA can enhance cluster formation rates at room temperature with the enhancement strength ranging from zero to four orders of magnitude. The comparison of the enhancement effect between HMSA and MSA shows that the enhancement strength of HMSA could be up to 3.97 times stronger than that of MSA, indicating that HMSA may be a more potential stabilizer. Meanwhile, different from the “bridge” role of α-hydroxyl acids, HMSA acts as “stabilizer” directly participating in NPF. Both of its enhancement strength on cluster formation rate and the corresponding contribution to the growth pathway present a negative dependence on SA concentration. All those could, to some extent, help to explain the missing sources of NPF between field observation and currently cognition, as well as to assist us to better understand atmospheric organosulfur chemistry.

Research on the “source–sink” landscape pattern of nonpoint source pollution is of great significance to natural resource management, environmental protection, water quality improvement, nonpoint source pollution prevention and control, and ecological security pattern construction. Remote sensing has proven by many scholars as a practical and effective technique to study landscape patterns and nonpoint source pollution. However, there are still many obstacles to the application of remote sensing technology, such as classification errors, scale effects and the issue, whereby landscape metrics cannot describe the landscape information comprehensively. In view of the characteristics of the macroscale and multi-scale of remote sensing, the analysis of landscape patterns is the basis for the study of the relationship research between patterns and ecological processes, and it is also the key to the study of landscape dynamics and functions. This paper attempts to summarize the representative results and the challenges of remote sensing in the study of the source and sink landscape of the nonpoint source pollution landscape and provide corresponding solutions as a reference for future research.

The structures and energetics of the binuclear dimethylphosphido vanadium carbonyls (Me2P)2V2(CO)n (n = 10, 9, 8, 7, 6) have been examined using density functional theory. The experimentally known (Me2P)2V2(CO)8 with two bridging Me2P groups and all terminal CO groups is found to be the lowest energy structure by a substantial margin. The predicted V V distance in this structure of 2.696 A is close to the experimental distance of 2.733 A as determined by X-ray crystallography. The Wiberg bond index (WBI) of 0.94 supports the formulation of this V V interaction as a formal double bond, consistent with the 18-electron rule. Decarbonylation of (Me2P)2V2(CO)8 is predicted to give a singly CO-bridged (Me2P)2V2(CO)6(µ-CO) structure with a shorter V V distance of 2.374 A corresponding to a WBI of 1.30 and suggesting a formal triple bond. Further decarbonylation to (Me2P)2V2(CO)6 is predicted to lead to structures with four-electron donor bridging η2-µ-CO groups rather than structures with formal V V quadruple bonds. For the carbonyl-richer system (Me2P)2V2(CO)9 the lowest energy structure retains two bridging Me2P ligands and all terminal CO groups. Its V V distance of 3.138 A coupled with a WBI value of 0.23 suggests the formal single bond required by the 18-electron rule. The lowest energy (Me2P)2V2(CO)10 structure has a similar V V single bond. However, only one of its Me2P ligands bridges the central V V bond; the other Me2P group is a terminal ligand bonded to a single vanadium atom. Structures with intact Me2P-PMe2 ligands having direct P P bonds are very high energy structures relative to their isomers with two separate Me2P units lacking a direct P P bond.

Sulfate is one of the most important components in the aerosol due to its key role in air pollution and global climate change. Recent work has suggested that reactive nitrogen chemistry in aqueous water can explain the missing source of sulfate in the aqueous water. Herein, we have mapped out the energy profile of the oxidization process of SO2 leading from NO2 and two feasible three-step mechanisms have been proposed. For the oxidation of HOSO2− and HSO3− by the dissolved NO2 in weakly acidic and neutral aerosol (pH ≤ 7), the main contribution to the missing sulfate production comes from the oxidation of HOSO2−. The whole process is a self-sustaining process. For the oxidation of SO32− in alkaline aerosol (pH > 7), the third step - decomposition step of H2O or hydrolysis of SO3 step which are two parallel processes are the rate-limiting steps. The present results are of avail to better understand the missing source of sulfate in the aerosol and hence may lead to better science-based solutions for resolving the severe haze problems in China.

Spontaneous Ca2+ oscillation is a special kind of astrocyte signal that is crucial in several brain functions. However, the underlying mechanism of its initiation is still unclear. Experimental investigations reveal quite different results of the contribution of Ca2+ influxes from the extracellular space. We developed a new biophysical model, which includes two kinds of extracellular Ca2+ influx: through voltage gated Ca2+ channels and through capacitative Ca2+ entry. Besides, two stochastic models are constructed to discuss the influence of channel noise in voltage gated influx and stochastic IP3 receptor dynamics on the contribution of Ca2+ fluxes. Simulation results reveal that the contribution of a given flux can be considerably strengthened or weakened by special cellular states, such as the change of membrane potential, inter-flux feedback; the special cellular condition (e.g. endoplasmic reticulum depletion, other flux inhibition). In stochastic environment, the contribution of fluxes may be strongly altered and the respond of different fluxes varies qualitatively. Our results may help to understand the different results obtained in experiments.

Marine aerosols have significant impacts on the global radiation balance and climate. New particle formation (NPF) is an essential source of aerosol formation. Sulfur-containing acids (sulfuric acid (SA), methanesulfonic acid (MSA), and methanesulfinic acid (MSIA)) oxidized from ocean-emitted dimethyl sulfide (DMS), have been identified as nucleation precursors in marine NPF. Given their homology, these sulfur species are likely to contribute jointly to the NPF. However, the joint effects of such sulfur acids on NPF and the nucleating mechanism remain unknown. Hence, the first quaternary SA-MSA-MSIA-DMA nucleation system was systematically investigated under different conditions using density functional theory (DFT) combined and Atmospheric Cluster Dynamic Code (ACDC). The results indicate that MSA and MSIA can synergistically enhance the formation rates of SA-dimethylamine (DMA) clusters, especially in regions with low temperatures, sparse SA and DMA. In the mid-latitude oceans, MSA and MSIA can jointly promote nucleation by forming SA-MSA-DMA and SA-MSIA-DMA clusters like ‘division of cooperation’. While in the cold polar regions, MSA and MSIA can synergistically enhance clustering via forming stable MSA-MSIA-based clusters like ‘hand in hand’. The proposed quaternary SA-MSA-MSIA-DMA mechanism manifests itself more effectively in the nucleation process, and such a multi-component nucleation model may help us to understand the frequent marine NPF more comprehensively.

The rational design and synthetic route to fabricate hybrid materials with desirable electrocatalytic functionalities remain critical but still challenging for sustainable energy devices. Here, we constructed a tungsten trioxide nano-lamellae chemically anchored with pyridinic-N-dominated doped CNT/graphene frameworks (W-NCG) via a general solution-based synthesis method. The detailed results indicated that this hybrid structure is composed of vacancy-defect abundant WO3 porous nanoflakes anchoring through or onto a 3D N-doped carbon matrix. After a facile post-annealing treatment, the W-NCG sample is utilized as a bi-functional catalyst for rechargeable lithium-oxygen batteries. The optimized sample with a large BET surface exhibits unprecedented ORR/OER activity in the cell, and satisfying specific capacity (∼7850 mA h g-1) and cycling stability. This excellent electrochemical performance can be ascribed to the pseudo 3D structure with sufficient microspace and good electrical conductivity, which facilitate the high dispersion of active components and effectivly relieve the formation of large/irreversible Li2O2. As such, this porous W-NCG framework is a prospective high-performance cathode material for Li-O2 batteries.

Nitric acid, an air pollutant with strong acidity and oxidizability, can be found in considerable quantities in the gas and aerosol phase. Understanding the role of nitric acid in atmospheric new particle formation is essential to study the complicated nucleation mechanism. Using density functional theory combined with the Atmospheric Clusters Dynamic Code (ACDC), the role of nitric acid in the formation of new particles has been investigated under different atmospheric conditions (different precursor concentrations and temperatures). The results show that nitric acid can form clusters with sulfuric acid and ammonia by hydrogen bond or even proton-transfer interactions. The concentrations of clusters involving nitric acid can be comparable with those of sulfuric acid-ammonia-based clusters, considering the thermodynamic stability combined with the realistic atmospheric concentrations of precursors. Within the atmospheric concentration range, nitric acid can enhance the formation rates of sulfuric acid-ammonia clusters, especially at low temperature, low sulfuric acid concentration and high ammonia concentration. In addition, the new particle formation mechanism indicates that nitric acid can contribute to the cluster formation and the role of nitric acid in the cluster formation pathway is as a "bridge" connecting the smaller and larger clusters.

We use SiO2 as a template and dopamine as a carbon source to synthesize a hollow C shell, and we load Co and Ru nanoparticles onto it to obtain a Co–Ru@C shell composite. The diameter and thickness of the C shell are 100 nm and 5–10 nm, respectively, and numerous holes of different sizes exist on the C shell. Meanwhile, numerous C shells stack together to form macropores, thereby forming a hierarchical porous structure in the material. Brunauer–Emmett–Teller surface area analysis reveals that the specific surface area and pore volume of the Co–Ru@C shell are 631.57 m2 g−1 and 2.20 cc g−1, respectively, which can result in many three-phase interfaces and provide more space for the deposition of discharge products. Compared with Co@C shell and C shell electrodes, the obtained Co–Ru@C shell-based electrodes exhibit the highest discharge capacity, the lowest oxygen reduction reaction/oxygen evolution reaction overpotential and the best cycle stability, indicating the excellent catalytic ability of the Co–Ru@C shell.

The structure and thermochemistry of the triads of binuclear chromium carbonyl complexes [(Me2P)2CH2]Cr2(CO)n (n = 10, 9, 8), [(Me2P)2CH2]2Cr2(CO)n (n = 8, 7, 6) and [(Me2P)2CH2]3Cr2(CO)n (n = 6, 5, 4) have been investigated using density functional theory. The lowest-energy structures of the carbonyl-richest triad members [(Me2P)2CH2]Cr2(CO)10, [(Me2P)2CH2]2Cr2(CO)8, and [(Me2P)2CH2]3Cr2(CO)6 have long Cr⋯Cr distances indicating the absence of direct chromium bonds. The lowest energy structures of the intermediate triad members [(Me2P)2CH2]2Cr2(CO)7 and [(Me2P)2CH2]3Cr2(CO)5 systems have Cr–Cr single bonds of lengths of 3.13 and 3.39 A, respectively, and intact diphosphine ligands. However, in the lowest energy [(Me2P)2CH2]Cr2(CO)9 structure, one of the terminal CO groups is converted into a four-electron donor bridging η2-μ-CO group, retaining a long non-bonding Cr⋯Cr distance of 4.80 A. The lowest energy structure of the carbonyl-poorest [(Me2P)2CH2]Cr2(CO)8, [(Me2P)2CH2]2Cr2(CO)6, and [(Me2P)2CH2]3Cr2(CO)4 members of each triad show different features. In the lowest energy [(Me2P)2CH2]Cr2(CO)8 structure the ligand splits into separate Me2P and Me2PCH2 units, both of which bridge a Cr–Cr bond of length 3.06 A. The lowest energy [(Me2P)2CH2]2Cr2(CO)6 structure has a four-electron donor bridging η2-μ-CO group and a Cr–Cr single bond of length 2.91 A. The lowest energy [(Me2P)2CH2]3Cr2(CO)4 structure is a triplet structure with a Cr–Cr single bond of length 3.03 A.

As the simplest and the most abundant dicarboxylic acids in the atmosphere, oxalic acid (OA) not only plays a key role in aerosol nucleation, but also acts as a prototypical compound for the investigation of intra- and intermolecular hydrogen bonding interactions. In this work, a systematic theoretical study on the hydrated OA dimers were carried out using density functional theory (DFT) at the M06-2X/6-311++G(3df, 2p) level. The properties of the hydrogen bonds in clusters were inspected through topological analysis using atoms in molecules (AIM) theory. The most stable OA dimer involves a cyclic structure with two intermolecular hydrogen bonds. Our calculations show that one H2O has slightly effect on the hydrogen bonds, while two water molecules weaken and three water molecules even break the two intermolecular hydrogen bonds between OAs. Furthermore, there are no hydrogen bond interactions between OAs in almost all stable clusters when the H2O number increases to four and five. Additionally, the ionization and the isomerization of OA through water-assisted proton transfer phenomena were observed in tetrahydrates and pentahydrates. Our work has provided new insights into the conversion process of anhydrous OA to hydrated clusters, which are helpful for further understanding the atmospheric nucleation process and the nature of hydrogen bond.

It is well established that oxidation products of volatile organic compounds (VOCs) play a major role in atmospheric new-particle formation (NPF). However, the mechanism of their effect and the corresponding influence under various atmospheric conditions remain unclear. Meanwhile, considering the difficulty of experiment in determining the water content of the cluster and performing at low temperature, we combine Density Functional Theory (DFT) and Atmospheric Clusters Dynamic Code (ACDC) model to investigate a multicomponent system involving lactic acid (LA) and atmospheric nucleation precursors (sulfuric acid (SA), dimethylamine (DMA), water (W)) under a wide range of atmospheric conditions (relative humidity (RH) from 20% to 100%, temperature (T) from 220 K to 300 K). Conformational analysis shows that LA could enhance NPF in two direction due to its two highly oxidized function groups. Then, the results from ACDC simulation present a direct evidence of its enhancement effect on NPF when the concentration of LA is larger than 10 10 molecules cm − 3 . The corresponding enhancement strength presents a positive dependence on its concentrations and a negative dependence on RH and T, respectively. Besides, LA·nW (n = 0–1) reflect their enhancement effect on the cluster growth paths by acting as “bridge”, which contributes to pure SA-DMA-W-based clusters by evaporating LA contained clusters. The corresponding contribution presents a positive dependence on the concentration of LA, RH and T, respectively. We hope our study could provide theoretical clues to better understand the characteristic of NPF in polluted area, where NPF commonly involves oxidized organics, sulfuric acid, amine and water.

Binuclear chromium carbonyl complexes of the general type [MeN(PF2)2]mCr2(CO)n, including the experimentally known [MeN(PF2)2]3Cr2(CO)n (n = 6, 5) species, have been studied by density functional theory (DFT) methods. The lowest energy structures for the three series of [MeN(PF2)2]mCr2(CO)n (m = 1, 2, 3) structures can be grouped into three triads, namely [MeN(PF2)2]Cr2(CO)n (n = 10, 9, 8), [MeN(PF2)2]2Cr2(CO)n (n = 8, 7, 6), and [MeN(PF2)2]3Cr2(CO)n (n = 6, 5, 4). The carbonyl richest structures of each triad, namely [MeN(PF2)2]Cr2(CO)10, [MeN(PF2)2]2Cr2(CO)8, and [MeN(PF2)2]3Cr2(CO)6 have all terminal carbonyl groups, no chromium–chromium bond, and the MeN(PF2)2 ligands bridging the pair of chromium atoms. However, for [MeN(PF2)2]3Cr2(CO)6 a structure with two of the three MeN(PF2)2 ligands chelating to single chromium atoms are energetically competitive. Low-energy singlet spin state structures for the intermediate and carbonyl poorest members of each triad can incorporate a variety of features such as chromium–chromium single and double bonds, MeN(PF2)2 ligands split into bridging MeNPF2 + PF2 groups, and four-electron donor bridging η2-μ-CO groups as required to give each chromium atom the favored 18-electron configuration. Such four-electron donor bridging η2-μ-CO groups are not found in low-energy structures of related binuclear carbonyl complexes [MeN(PF2)2]mM2(CO)n (M = Fe, Ni; m = 1, 2) of the later transition metals iron and nickel.

Gas-phase simulations of nitric acid–amine chemistry suggest that the fundamental acid–base interaction between HNO3 and NH3 results in a variety of HNO3–NH3-based complexes, such as (HNO3)3·(NH3)2, (HNO3)3·(NH3)3, and (HNO3)4·(NH3)3, that can be formed. The formation of these complexes in the gas phase follow different growth mechanisms under different relative humidity conditions. On the other hand, at the air–water interface, Born–Oppenheimer molecular dynamics simulations suggest that the formation of the fundamental NO3–··(R1)(R2)NH2+ [for NH3, R1 = R2 = H; CH3NH2, R1 = H, R2 = CH3; and (CH3)2NH, R1 = R2 = CH3] ion pairs require the formation of the HNO3··(R1)(R2)NH complexes in the gas-phase prior to their adsorption on the water surface. Ion-pair formation at the water surface involves proton transfer from HNO3 to (R1)(R2)NH and occurs within a few femtoseconds of the simulation. The NO3–··(R1)(R2)NH2+ ion pairs preferentially remain at the interface over the picosecond time scale, where they are s...