Stereochemical insights into enantioselective antiplasmodial lignanamides from the twigs and leaves of Solanum erianthum.

Stereochemical investigations on the twigs and leaves of Solanum erianthum afforded five pairs of lignanamide enantiomers and a previously undescribed phenolic amide (3). Particularly, two pairs of previously undescribed lignanamide racemates (1a/1b-2a/2b) represent the first case of natural products that feature an unreported 5/5-fused N/O-biheterocyclic core. Their structures, including the absolute configurations, were determined unambiguously by using spectroscopic analyses and electronic circular dichroism calculations. A speculative biogenetic pathway for 1-3 was proposed. Interestingly, these lignanamides exhibited enantioselective antiplasmodial activities against drug-sensitive Plasmodium falciparum 3D7 strain and chloroquine-resistant Plasmodium falciparum Dd2 strain, pointing out that chirality plays an important role in drug development.

Nonlinear Optical Properties of 2D Materials and their Applications.

2D materials are a subject of intense research in recent years owing to their exclusive photoelectric properties. With giant nonlinear susceptibility and perfect phase matching, 2D materials have marvelous nonlinear light-matter interactions. The nonlinear optical properties of 2D materials are of great significance to the design and analysis of applied materials and functional devices. Here, the fundamental of nonlinear optics (NLO) for 2D materials is introduced, and the methods for characterizing and measuring second-order and third-order nonlinear susceptibility of 2D materials are reviewed. Furthermore, the theoretical and experimental values of second-order susceptibility χ(2) and third-order susceptibility χ(3) are tabulated. Several applications and possible future research directions of second-harmonic generation (SHG) and third-harmonic generation (THG) for 2D materials are presented.

Asymmetric Total Syntheses of ent-Stachybotrin C and Its Congener.

The asymmetric total syntheses of ent-stachybotrin C and its congener have been accomplished through a convergent approach in the longest linear sequence of 12 steps from commercially available materials, respectively. Noteworthy transformation of the synthesis involved a cascade Knoevenagel condensation/Hantzsch ester reduction/epoxide ring-opening/transetherification to construct the core pyran ring with two adjacent stereocenters.

Sesquiterpenoids and Cytochalasins with Immunosuppressive Activity from Sonchus wightianus.

The plant species, Sonchus wightianus DC., was historically used in China for both medicinal and dietary uses. In present study, seven new guaiane sesquiterpenoids (1-7) and one cytochalasin (8), along with five known guaianes (9-13) and two known cytochalasins (14 and 15), were isolated from the whole plants of S. wightianus. These guaianes showed structural variations in the substituents at C-8 and/or C-15, and compounds 6 and 7 are two sesquiterpenoid glycoside derivatives. Their structures were determined by extensive analysis of spectroscopic, electronic circular dichroism, and X-ray diffraction data, and chemical method. Biological tests revealed that compounds 5 and 8 are potent and selective immunosuppressive reagents.

Temporal and vertical dynamics of carbon accumulation potential under grazing-excluded grasslands in China: The role of soil bulk density.

Despite the progress made in understanding relevant carbon dynamics under grazing exclusion, previous studies have underestimated the role of soil bulk density (BD), and its implications for potential accumulation of soil organic carbon (SOC), especially at regional scale over long term. In this study, we first constructed a database covering a vast majority of the grasslands in northwestern China based on 131 published literatures. A synthesis was then conducted by analyzing the experimental data to comprehensively investigate the mechanisms of vegetation recovery, carbon-nitrogen coupling, and the importance of changed soil BD in evaluating SOC sequestration potential. The results showed that although the recovery of vegetation height and cover were both critical for improving vegetation biomass, vegetation height required a longer recovery period. While the SOC accumulation was found to be greater in surface layers than deeper ones, it exhibited a reduced capacity for carbon sequestration and an increased risk of SOC loss. Grazing exclusion significantly reduced soil BD across different soil profiles, with the rate of change influenced by soil depth, time, geographical and climatic conditions. The potential for SOC accumulation in the top 30 cm of soil based on data of 2003-2022 was 0.78 Mg ha-1 yr-1 without considering BD effects, which was significantly underestimated compared to that of 1.16 Mg ha-1 yr-1 when BD changes were considered properly. This suggests that the efficiency of grazing exclusion in carbon sequestration and climate mitigation may have been previously underreported. Furthermore, mean annual precipitation represented the most relevant environmental factor that positively correlated to SOC accumulation, and a wetter climate may offer greater potential for carbon accumulation. Overall, this study implies grazing exclusion may play an even more critical role in carbon sequestration and climate change mitigation over long-term than previously recognized, which provides essential scientific evidence for implementing stepwise ecological restoration in grasslands.

Total Syntheses of Uncommon C30 Terpenoids: Chamaecydin and Isochamaecydin.

(-)-Chamaecydin and (-)-isochamaecydin, two uncommon C30 terpenoids comprising abietane-type diterpenes and thujane-type monoterpenes, were achieved from ß-pinene with (-)-sabinene in 18 and 20 steps, respectively. Key steps include a Claisen-Ireland rearrangement to establish the all-carbon quaternary center, a Rh catalyzed C-H bond insertion reaction to install a spiro-five-membered ring and a Lewis acid promoted cyclization of polyenes to construct the two six-membered rings.

Total Synthesis of Guajavadimer A via Lewis Acid-Catalyzed Cascade Double Hetero-Diels-Alder Reactions.

The first total synthesis of guajavadimer A, a dimeric caryophyllene-derived meroterpenoid featuring an unprecedented 4-9-6-6-6-9-4-fused ring system, is reported. Key to the approach is the construction of the pyrano[4,3,2-de]chromene core via a cascade of double hetero-Diels-Alder reactions. Practically, a 4-substituted-2,6-dihydroxybenzaldehyde dimethyl acetal serves as an effective surrogate for ortho-quinone methide, which is generated from the corresponding aldehyde and trimethyl orthoformate, with ß-caryophyllene undergoing cycloaddition to generate pyrano[4,3,2-de]chromene derivatives with excellent regioselectivity and stereoselectivity in one pot under mild conditions.

Spatiotemporal evolution and influencing factors of China's economic development performance under carbon emission constraints.

BACKGROUND: China's high-quality economic development depends on achieving sustainable economic development, reaching peak carbon emissions, achieving carbon neutrality, and intensifying the development of an industrial and energy structure that saves resources and protects the environment. This study used the data envelopment analysis (DEA) model and the Malmquist productivity index to measure the economic development performance of mainland China under carbon emission constraints. Then, it described the spatiotemporal evolution of economic development performance and analyzed its influencing factors using the Tobit model. RESULTS: The results revealed that there were obvious differences in the trends of the static and dynamic performance of economic development. On the one hand, the static performance of economic development exhibited an upward trend from 2008 to 2020. Its distribution characteristics were dominant in the higher and high-level areas. On the other hand, the dynamic performance had a downward trend from 2008 to 2016 and then an upward trend from 2016 to 2020. In most provinces, the dynamic performance was no longer constrained by technological progress but rather by scale efficiency. It was found that the main factors influencing economic development performance were urbanization level, energy efficiency, vegetation coverage, and foreign investment, while other factors had no significant influence. CONCLUSIONS: This study suggests that China should improve its economic development performance by increasing the use of clean energy, promoting human-centered urbanization, increasing carbon absorption capacity, and absorbing more foreign capital in the future.

Carbon allowance allocation based on comprehensive performance of carbon emissions: Case of typical industries in Zhengzhou.

Studying the comprehensive performance of industrial carbon emission has profound significance for improving carbon allowance allocation scheme and achieving the carbon neutrality target. The paper selects 181 enterprises in Zhengzhou as the case, a comprehensive carbon emission performance indicator system and a carbon allowance allocation model were established, and compared with other allocation schemes (historical/baseline method). The results showed that the overall differences in the comprehensive performance evaluation indicator of carbon emissions in typical industries in Zhengzhou were obvious, and there was a correlation with the characteristics of industrial production activities. The overall emission reduction of Zhengzhou was 244.33×103t, and the emission reduction ratio was 7.94% by simulating carbon allowance allocation under the comprehensive performance. The carbon allowance allocation method based on the comprehensive performance has the strongest restraint on the "high emission, low performance" industry, which is more equitable and more conducive to carbon emission reduction. In the future, it will be recommended to give full play to the leading role of the government, implement industrial carbon allowance allocation based on the comprehensive performance evaluation of carbon emissions, to achieve multi-objectives of resource conservation, environmental pollution abatement, and carbon reduction.

Improved Luminous Efficiency of AgInS2 Quantum Dots and Zeolitic Imidazolate Framework-70 Composite for White Light Emitting Diode Applications.

The application of multiple quantum dots (QDs) in the field of white light emitting diodes (WLEDs) is still an important challenge due to their low luminous efficiency and quenching phenomenon. In this paper, we prepared AgInS2 QDs/zeolitic imidazolate framework-70 (AIS/ZIF-70) composite by a microwave hydrothermal method. Owing to the high porosity and stability of ZIF-70, it could effectively prevent quenching issues due to the aggregation of QDs. Since the ZIF-70 and QDs were chemically bonded, the formation of the ZnS layer could effectively passivate the surface defect and thus the quantum yield reached 21.49 % in aqueous solution. The luminous efficiency (LE) of the assembled AIS/ZIF-based WLED was reinforced by 6.8 times with a molar ratio of AgIn/Zn=18, i. e. at 5.26 % molar fraction of ZIF-70. Moreover, the color rendering index (CRI) and correlated color temperature (CCT) of AIS/ZIF-based WLED were 84.3 and 3631 K, respectively, indicating its potential application in solid-state lighting.

Detection of spatiotemporal changes in ecological quality in the Chinese mainland: Trends and attributes.

Global climate change and revegetation programs have significantly changed the ecological quality (EQ) in the Chinese mainland after 1999. Monitoring and assessing the changes in the regional EQ and analyzing their drivers are crucial for ensuring ecological restoration and rehabilitation. However, it is challenging to carry out a long-term and large-scale quantitative assessment of the EQ of a region based on traditional field investigations and experiment methods alone; notably, in previous studies, the effects of carbon and water cycles and human activities on the variations in EQ have not been studied comprehensively. Therefore, in addition to remote sensing data and principal component analysis, we used the remote sensing-based ecological index (RSEI), to assess the EQ changes in the Chinese mainland during 2000-2021. Additionally, we also analyzed the impacts of carbon and water cycles and anthropological activities on the changes in the RSEI. The main conclusions of this study were: since the beginning of the 21st century, we observed a fluctuating upward trend in the EQ changes in the Chinese mainland and eight climatic regions. From 2000 to 2021, in terms of the EQ, North China (NN) portrayed the highest increase rate (2.02 × 10-3 year-1, P < 0.05). There was a breaking point in 2011, the EQ in the region experienced a change, from a downward trend to an upward one. Northwest China, Northeast China, and NN portrayed an overall significant increasing trend in the RSEI, whereas the southwest part of the Southwest Yungui Plateau (YG) and a part of the plain region of the Changjiang (Yangtze) River (CJ) river region portrayed a significant decreasing trend in the EQ. Overall, the carbon and water cycles and human activities played a pivotal role in determining the spatial patterns and trends of the EQ in the Chinese mainland. In particular, the self-calibrating Palmer Drought Severity Index, actual evapotranspiration (AET), gross primary productivity (GPP), and soil water content (Soil_w) were identified as the key drivers of the RSEI. In the central and western Qinghai-Tibetan Plateau (QZ) and the northwest region of NW, the changes in RSEI were dominated by AET; however, in central NN, southeastern QZ, northern YG, and central NE, the changes were driven by GPP, and in the southeast region of NW, south region of NE, northern region of NN, middle YG region, and a part of the middle CJ region, the changes were driven by Soil_w. The population-density-related change in the RSEI was positive in the northern regions (NN and NW) but negative in the southern regions (SE), whereas the RSEI change related to ecosystem services was positive in the NE, NW, QZ, and YG regions. These results are beneficial for the adaptive management and protection of the environment and the realization of green and sustainable developmental strategies in the Chinese mainland.

The impact of irrigation modes on agricultural water-energy­carbon nexus.

Despite the tremendous contribution of irrigated agriculture in addressing global food security, there is still confusion for farmers and governments about the choice of irrigation mode owing to the drastic environmental impacts of irrigation, including water shortage, energy crisis, and global warming. Exploring the agricultural water-energy­carbon (WEC) nexus under different irrigation modes helps to accomplish the multi-objective of water & energy saving and carbon emission reduction. In this paper, a conceptual framework was nominated to evaluate the water & energy consumption and carbon emissions for winter wheat irrigation at township level and quantitatively discuss the complex interaction by the coupling coordination degree (CCD) of the WEC system under different irrigation modes in Henan Province, China. We discovered that irrigation modes profoundly affect water and energy consumption and carbon emissions in agriculture, as well as the spatial distribution of CCD from WEC system. Townships under irrigation mode with diversion and irrigation projects as the primary method (WDI) clustered together in the north and east with highest water consumption and carbon emissions, while townships under irrigation mode with rain-fed agriculture as the primary method (PI) accumulated in the west and south with lower water consumption and carbon emissions. Meanwhile, the CCD of the WEC nexus system was in basic coordination (0.40) and showed an unbalanced spatial distribution pattern with high in the southeast and low in the northwest. By comparing four irrigation modes, the coupling level of the WEC nexus system under irrigation mode with groundwater irrigation as the primary method (GI) was better and PI mode was the least ideal. This study helps to further understand agricultural WEC nexus under different irrigation modes and provide references for local governments in selecting appropriate irrigation modes to realize water-energy saving and carbon emission reduction in agricultural activities.

A Review of Influencing Factors on Spatial Spread of COVID-19 Based on Geographical Perspective.

The COVID-19 outbreak is a manifestation of the contradiction between man and land. Geography plays an important role in epidemic prevention and control with its cross-sectional characteristics and spatial perspective. Based on a systematic review of previous studies, this paper summarizes the research progress on factors influencing the spatial spread of COVID-19 from the research content and method and proposes the main development direction of geography in epidemic prevention and control research in the future. Overall, current studies have explored the factors influencing the epidemic spread on different scales, including global, national, regional and urban. Research methods are mainly composed of quantitative analysis. In addition to the traditional regression analysis and correlation analysis, the spatial lag model, the spatial error model, the geographically weighted regression model and the geographic detector have been widely used. The impact of natural environment and economic and social factors on the epidemic spread is mainly reflected in temperature, humidity, wind speed, air pollutants, population movement, economic development level and medical and health facilities. In the future, new technologies, new methods and new means should be used to reveal the driving mechanism of the epidemic spread in a specific geographical space, which is refined, multi-scale and systematic, with emphasis on exploring the factors influencing the epidemic spread from the perspective of spatial and behavioral interaction, and establish a spatial database platform that combines the information of residents' cases, the natural environment and economic society. This is of great significance to further play the role of geography in epidemic prevention and control.

Scalable Total Synthesis of (+)- and (-)-Codonopiloneolignanin A via Ti(IV)/NHC Cooperative Control Highly Enantioselective Dimerization of Multisubstituted Cinnamaldehyde.

The first gram-scale asymmetric total synthesis of (+)- and (-)-codonopiloneolignanin A has been achieved from multisubstituted cinnamaldehyde in four steps with 37% overall yield. The synthetically challenging tricyclic [5, 3, 0, 03,8] decane skeleton was efficiently constructed via a highly enantioselective dimerization of multisubstituted cinnamaldehyde, followed by a sequence of cascade reactions including Prins cyclization, cation mediated cyclization, and deprotection. Furthermore, the scope of NHC-catalyzed/Ti(IV)-mediated synergistic control multisubstituted cinnamaldehyde dimerization was investigated. Significantly, the bioactivity of codonopiloneolignanin A and its enantiomer, particularly scarce in nature, was tested and showed good anticancer activity.

Exploring the influence of human mobility factors and spread prediction on early COVID-19 in the USA.

BACKGROUND: COVID-19 is still spreading rapidly around the world. In this context, how to accurately predict the turning point, duration and final scale of the epidemic in different countries, regions or cities is key to enabling decision makers and public health departments to formulate intervention measures and deploy resources. METHODS: Based on COVID-19 surveillance data and human mobility data, this study predicts the epidemic trends of national and state regional administrative units in the United States from July 27, 2020, to January 22, 2021, by constructing a SIRD model considering the factors of "lockdown" and "riot". RESULTS: (1) The spread of the epidemic in the USA has the characteristics of geographical proximity. (2) During the lockdown period, there was a strong correlation between the number of COVID-19 infected cases and residents' activities in recreational areas such as parks. (3) The turning point (the point of time in which active infected cases peak) of the early epidemic in the USA was predicted to occur in September. (4) Among the 10 states experiencing the most severe epidemic, New York, New Jersey, Massachusetts, Texas, Illinois, Pennsylvania and California are all predicted to meet the turning point in a concentrated period from July to September, while the turning point in Georgia is forecast to occur in December. No turning points in Florida and Arizona were foreseen for the forecast period, with the number of infected cases still set to be growing rapidly. CONCLUSIONS: The model was found accurately to predict the future trend of the epidemic and can be applied to other countries. It is worth noting that in the early stage there is no vaccine or approved pharmaceutical intervention for this disease, making the fight against the pandemic reliant on non-pharmaceutical interventions. Therefore, reducing mobility, focusing on personal protection and increasing social distance remain still the most effective measures to date.

Total Synthesis of (±)-Spiroaxillarone A.

Spiroaxillarone A, a novel and unique spirocyclic dinaphthalene natural product with significant antimalarial activity, was regioselectively synthesized from tetrahydrocurcumin in five steps with an overall 10% yield. Key features of the synthesis involved an oxidized free radical cycloaddition to build the spiro ring central skeleton and an oxidized dehydrogenation to introduce two double bonds via enol silicon ether from diketones.

The Spatio-Temporal Characteristics and Influencing Factors of Covid-19 Spread in Shenzhen, China-An Analysis Based on 417 Cases.

The global pandemic of COVID-19 has made it the focus of current attention. At present, the law of COVID-19 spread in cities is not clear. Cities have long been difficult areas for epidemic prevention and control because of the high population density, high mobility of people, and high frequency of contacts. This paper analyzed case information for 417 patients with COVID-19 in Shenzhen, China. The nearest neighbor index method, kernel density method, and the standard deviation ellipse method were used to analyze the spatio-temporal characteristics of the COVID-19 spread in Shenzhen. The factors influencing that spread were then explored using the multiple linear regression method. The results show that: (1) The development of COVID-19 epidemic situation in Shenzhen occurred in three stages. The patients showed significant hysteresis from the onset of symptoms to hospitalization and then to diagnosis. Prior to 27 January, there was a relatively long time interval between the onset of symptoms and hospitalization for COVID-19; the interval decreased thereafter. (2) The epidemic site (the place where the patient stays during the onset of the disease) showed an agglomeration in space. The degree of agglomeration constantly increased across the three time nodes of 31 January, 14 February, and 22 February. The epidemic sites formed a "core area" in terms of spatial distribution and spread along the "northwest-southeast" direction of the city. (3) Economic and social factors significantly impacted the spread of COVID-19, while environmental factors have not played a significant role.

Spatial and temporal differentiation of COVID-19 epidemic spread in mainland China and its influencing factors.

This paper uses the exploratory spatial data analysis and the geodetector method to analyze the spatial and temporal differentiation characteristics and the influencing factors of the COVID-19 (corona virus disease 2019) epidemic spread in mainland China based on the cumulative confirmed cases, average temperature, and socio-economic data. The results show that: (1) the epidemic spread rapidly from January 24 to February 20, 2020, and the distribution of the epidemic areas tended to be stable over time. The epidemic spread rate in Hubei province, in its surrounding, and in some economically developed cities was higher, while that in western part of China and in remote areas of central and eastern China was lower. (2) The global and local spatial correlation characteristics of the epidemic distribution present a positive correlation. Specifically, the global spatial correlation characteristics experienced a change process from agglomeration to decentralization. The local spatial correlation characteristics were mainly composed of the'high-high' and 'low-low' clustering types, and the situation of the contiguous layout was very significant. (3) The population inflow from Wuhan and the strength of economic connection were the main factors affecting the epidemic spread, together with the population distribution, transport accessibility, average temperature, and medical facilities, which affected the epidemic spread to varying degrees. (4) The detection factors interacted mainly through the mutual enhancement and nonlinear enhancement, and their influence on the epidemic spread rate exceeded that of single factors. Besides, each detection factor has an interval range that is conducive to the epidemic spread.

Ionic liquid assisted preparation and modulation of the photoluminescence kinetics for highly efficient CsPbX3 nanocrystals with improved stability.

CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) are competitive fluorescent materials for lighting and displays owing to their excellent photophysical properties. However, the stability and optoelectronic performance of the perovskite NCs are severely limited by the highly dynamic binding feature of the present ligand strategy. Herein, a facile approach was employed to synthesize CsPbBr3 NCs with the assistance of the ionic liquid (IL) 1-butyl-3-methylimidazolium bromide ([Bmim]Br). By strictly controlling the addition dose of [Bmim]Br (nIL/nPb = 0.125) into the reaction precursor, it is possible to obtain the desired cube-shaped and monodisperse CsPbBr3 NCs with simultaneous enhancement of the storage and irradiation stability as well as photoluminescence quantum yields (PLQYs, ∼91%). Stability tests show that the emission intensity of the parent CsPbBr3 NCs drops to 50% of its initial emission intensity after storage under an open atmosphere for 91 days, while the sample prepared with the assistance of [Bmim]Br can maintain 82% of the PL intensity. Meanwhile, the modified CsPbBr3 NCs also present superior photo-stability, and still maintain 81% of the original PL intensity after continuous illumination under an ultraviolet lamp for 24 h, but the intensity of the parent CsPbBr3 NCs reduces to 35% of the original intensity. Through the morphology, composition, and luminescence kinetics evolution of CsPbBr3 NCs, these benefits were attributed to the modulation by [Bmim]Br, which could effectively provide Br ions for the formation and growth of NCs, resulting in the reduction of surface traps. Moreover, [Bmim]Br exhibited strong interactions with NCs, and the deprotonation of oleic acid (OA) was inhibited, resulting in the effective passivation of surface defects. Finally, CsPbX3 NCs with different compositions were obtained via a facile anion exchange reaction, leading to the tunable emission in the range of 462-665 nm and a wide colour gamut (129.65% NTSC standard). This work opens a new avenue for modulating the surface properties of CsPbX3 NCs, which will create opportunities for their application in the photoelectric field.

Total Synthesis of Nominal ent-Chlorabietol B.

The nominal enantiomer of chlorabietol B was regio- and stereoselectively synthesized from (-)-abietic acid in 13 steps. Key features of the synthesis involved an oxidative [3+2] cycloaddition to install the dihydrobenzofuran moiety and an Aldol reaction, followed by elimination and reduction steps to introduce the long chain with three cis double bonds. However, obvious differences in the NMR spectra of the synthetic and natural samples suggested that the proposed structure of chlorabietol B should be revised carefully.