Conspectus Catalytic hydrogenation using molecular hydrogen represents a green and practical approach for reductions of all kinds of organic chemicals. Traditionally, in the majority of these ...processes the presence of transition metal catalysts is required. In this regard, noble-metal-based catalysts have largely been implemented, such as the application of iridium, palladium, rhodium, ruthenium, and others. Recently, the employment of earth-abundant 3d metals has emerged to replace the utilization of scarce noble metals because of their availability, lower cost, and often reduced toxicity. In this respect, several cobalt complexes, in the form of either molecularly well-defined or in situ-formed complexes, are receiving increasing attention from the scientific community. Importantly, the stability and reactivity of the complexes have greatly been supported by multidentate ligands under steric and/or electronic influences. For instance, tridentate or tetradentate phosphine ligands indirectly tune the reactivity of the metal center to accelerate the overall process, whereas direct participation of the ligand in pincer-type complexes through ligand–metal cooperation regulates the elementary steps in the catalytic cycle. In this Account, we emphasize specifically the advancements in cobalt-catalyzed hydrogenations using molecular hydrogen accomplished in our group. A variety of substrate classes ranging from simple molecules (e.g., carbon dioxide) to complex compounds were explored under the mild and efficient catalytic conditions. Notable examples include the reduction of carbon dioxide to afford either formates using a Co(BF4)2·6H2O/Tetraphos catalyst system or methanol employing a Co(acac)3/Triphos complex in the presence of HNTf2. As interesting examples of the synthesis of fine chemicals, cobalt-promoted hydrogenations of nitriles to primary amines and reductive alkylations of indoles using carboxylic acids as alkylating agents are highlighted. Moreover, highly selective hydrogenations of N-heteroarenes under additive-free conditions were possible by the application of specific cobalt complexes. More recently, a set of carboxylic esters could be hydrogenated to the corresponding alcohols with high efficiency by the use of a well-defined cobalt–PNP pincer catalyst. In particular, the decent reactivity of cobalt catalysts enabled high selectivity and functional group tolerance to be achieved. Throughout our studies, it was found that the pairing of a suitable cobalt precursor and an appropriate tridentate or tetradentate phosphine ligand plays a crucial role harnessing the desired reactivity, while other monodentate and bidentate phosphine ligands showed no reactivity in these investigations. Our developments could provide supervisory information for the future exploration of cobalt-catalyzed hydrogenation reactions and other types of reactions involving cobalt catalysis. Furthermore, relevant contributions from other groups, remaining challenges, and future perspectives in this research area are also presented.
Versatile ruthenium catalysts allowed for efficient direct oxygenations of aryl carbamates under remarkably mild reaction conditions. In addition to chelation-assisted C–H activation, the optimized ...ruthenium catalyst proved amenable to para-selective hydroxylations of anisoles without Lewis basic directing groups.
Point cloud is a widely used 3D data form, which can be produced by depth sensors, such as Light Detection and Ranging (LIDAR) and RGB-D cameras. Being unordered and irregular, many researchers ...focused on the feature engineering of the point cloud. Being able to learn complex hierarchical structures, deep learning has achieved great success with images from cameras. Recently, many researchers have adapted it into the applications of the point cloud. In this paper, the recent existing point cloud feature learning methods are classified as point-based and tree-based. The former directly takes the raw point cloud as the input for deep learning. The latter first employs a k-dimensional tree (Kd-tree) structure to represent the point cloud with a regular representation and then feeds these representations into deep learning models. Their advantages and disadvantages are analyzed. The applications related to point cloud feature learning, including 3D object classification, semantic segmentation, and 3D object detection, are introduced, and the datasets and evaluation metrics are also collected. Finally, the future research trend is predicted.
Rainfall-induced landslide hazard warning, which refers to the prediction of the spatial-temporal probability of landslide occurrence in a certain area under the conditions of continuous rainfall ...processes, can be established based on landslide susceptibility mapping and critical rainfall threshold calculations. However, it is difficult to determine appropriate machine learning models for mapping landslide susceptibility. Additionally, it is significant to consider the influences of early effective rainfall on landslide instability in the critical rainfall threshold methods. Furthermore, the uncertainties of the critical rainfall threshold values generated by different calculation methods have not been well explored. To overcome these three drawbacks, first, frequency ratio analysis-based logistic regression (LR), support vector machine (SVM) and random forest (RF) models are adopted to predict landslide susceptibility for machine learning model comparison. Second, three different types of critical rainfall threshold methods, namely, cumulative effective rainfall-duration (EE-D), effective rainfall intensity-duration (EI-D) and cumulative effective rainfall-effective rainfall intensity (EE-EI) models, are proposed to calculate the temporal probabilities of landslide occurrence under rainfall conditions based on the concept of effective rainfall. The accuracies and uncertainties of these three critical rainfall threshold methods are discussed. Finally, the landslide susceptibility maps and the critical rainfall threshold values are coupled to predict the rainfall-induced landslide hazards. Xunwu County in China is selected as the study area, and several rainfall-induced landslides are used as the test samples of the proposed landslide hazard warning model. The results show that the RF model has remarkably higher susceptibility prediction accuracy than the SVM and LR models, and the prediction performance of the temporal probabilities of landslide occurrence using the EI-D values are higher than those of EE-D and EE-EI values. Furthermore, rainfall-induced landslide hazard warning is effectively implemented based on the coupling of the susceptibility map and EI-D model.
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•Rainfall-induced landslide hazard warning is examined by landslide susceptibility mapping and critical rainfall threshold.•Various machine learning models are compared for predicting landslide susceptibility.•Uncertainties of different critical rainfall threshold models for landslide hazard warning are explored.•Effective rainfall intensity-duration threshold model has the highest accuracy than other models.
Given its wide distribution in the natural environment and global transport potential, mercury (Hg) is regarded as a ubiquitous pollutant. In this study, we carried out nation-wide sampling campaigns ...across China to investigate the distribution of Hg in agricultural soils. Concentrations of Hg in the soils collected in 2011 and 2016 ranged from 0.04 to 0.69 and 0.06–0.78 mg kg−1, respectively. Based on the data from 2016, the reserve of Hg in the surface arable soils (0–20 cm) in China was 4.1 × 104 metric tons and Chinese cultivated soils accounted for 63.4–364 metric tons of Hg released to the global atmosphere. The soil Hg concentrations were significantly higher than the reference background level, highlighting the impacts of anthropogenic activities. The vertical distribution pattern showed a clear enrichment at the surface and a decrease with depth of the soils. Comparison of calculated geo-accumulation indexes among individual provinces showed that Northwest China had higher levels of Hg contamination than other regions of China, likely due to long-term energy related combustions in the area. Soil Hg level showed strong positive correlations with organic matter contents of soil, as well as the mean annual precipitation and temperature of the sampling locations. The non-carcinogenic human health risks of soil Hg were below the threshold level, but the general risk to the ecosystem was considerable. The increases in Hg accumulation from 2011 to 2016 at provincial level were found to relate to coal combustion, power generation and per capita GDP. This examination of energy consumption and socioeconomic drivers for China's soil Hg reserve increase is critical for direct Hg control by guiding policy-making and targets of technology development in era of rapid economic growth.
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•Nation-wide mercury concentration, distributions, and potential risks in agricultural soils in China were determined.•Temporal accumulation trend of soil Hg was identified and the increases were closely related to anthropogenic activities.•Correlations between Hg and soil properties as well as meteorological parameters were estimated.
CH/NO functionalizations by cobalt(III) catalysis allowed the expedient synthesis of a broad range of isoquinolines. Thus, internal and challenging terminal alkynes proved to be viable substrates ...for an isohypsic annulation, which was shown to proceed by a facile CH cobaltation.
Versatile cobalt(III) catalysis enabled alkyne annulations in the absence of external oxidants, allowing the synthesis of a broad range of isoquinolines. The robust CH/NO functionalization strategy proceeded by facile CH activation in high yields within 15 min.
The extensive utilization of phthalate-containing products has lead to ubiquitous contamination of phthalate esters (PAEs) in various matrices. However, comprehensive knowledge of their pollution in ...Chinese farmland and associated risks is still limited. In this study, 15 PAEs were determined in soils from agricultural fields throughout the Mainland China. The concentrations of Σ15PAEs were in the range of 75.0-6369 μg kg(-1). Three provinces (i.e., Fujian, Guangdong and Xinjiang, China) showed the highest loadings of PAEs. Bis(2-Ethylhexyl) phthalate (DEHP) was found as the most abundant component and contributed 71.5% to the ∑15PAEs. The major source of PAEs in arable soils was associated with the application of agricultural plastic films, followed by the activities for soil fertility. Furthermore, the non-cancer and carcinogenic risks of target PAEs were estimated. The hazard indexes (HIs) of PAEs in all samples were below 1 and the carcinogenic risk levels were all within 10(-4). Results from this study will provide valuable information for Chinese agricultural soil management and risk avoidance.
The prevalence and proliferation of antibiotic resistance genes (ARGs) have been identified as an emerging contaminant of concern and a crucial threat to public health worldwide. In this study, we ...carried out a nation-wide sampling campaign across China to investigate the distribution and abundances of 8 major ARGs in agricultural soils. The levels of sulfonamide (sul) and tetracycline (tet) resistance genes in China's agricultural soils ranged from 10−6–10−2 to 10−8–10−2 gene copies/16S rRNA gene copies, respectively. Northeast China is the hot-spot of ARGs, likely due to long-term wastewater irrigation in the area. Redundancy analysis was further performed to assess the influences of environmental variables on ARG abundances. Sulfonamide resistance genes displayed strong correlations with meteorological parameters (mean annual precipitation and temperature), and decreased from north to south. In comparison, tetracycline resistance genes were more closely related to soil organic matter and pH. Co-selection between heavy metals and ARGs was significant among Cu, Hg and sulfonamide resistance genes. This study highlighted the current status of ARG contamination and their influencing factors in China's agricultural soils. Findings are valuable to identify effective management options for reducing the release of antibiotics and control ARG spread in the agriculture sector across the world.
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•The nation-wide occurrence, abundance, distribution and potential sources of sulfonamide and tetracycline resistance genes in agricultural soils in China were determined.•Comprehensive analyses were performed to estimate the correlations between ARGs and soil properties, meteorological parameters, and heavy metals.
•Prenatal and neonatal exposure to PFASs occur globally but differ among countries.•PFOS and PFOA exceed some major environmental toxins in maternal and cord blood.•Exposure to PFOS and PFOA has ...declined since 2000 while trends for others differ.•Biomonitoring and research at isomeric and enantiomeric levels are essential.•We prefer whole blood over plasma and serum in using blood to assess PFAS exposure.
Per- and polyfluoroalkyl substances (PFASs) are ubiquitous in the environment, making it inevitable for humans to be exposed to these pollutants. The exposure begins while in utero and continues in infancy, during the potentially most sensitive early stages of life. This review summarizes the current knowledge on pre- and neo-natal exposures based on more than 200 articles published from 2000 to date. All relevant biological matrices used in the cited studies were included, such as maternal blood, umbilical cord blood, breast milk, placenta, amniotic fluid, fetal organs, newborns’ dried blood spots, and infant serum. We show that such exposures are geographically global with significant discrepancies among countries and continents, and that while the levels of major legacy PFASs (PFOS and PFOA) have declined since 2000, those of others may have not. We also show that levels of PFOS and PFOA exceed those of some major environmental toxins, such as p,p′-DDE, BDE-47, PCB-153, PBB-153, and OH-PBDEs in maternal blood. Given that the behavior and potential effects have an origin in molecular structure, biomonitoring and research at the levels of isomers and enantiomers are critically important. Through critical analysis of these works, we summarize the major achievements, consensus, and the deficiencies of existing research. To our knowledge, this is the first review on the overall internal exposure status of mothers and infants to PFASs during pregnancy and lactation.
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