Silver-catalyzed C-C bond formation between methane and ethyl diazoacetate in supercritical CO₂

Even in the context of hydrocarbons' general resistance to selective functionalization, methane's volatility and strong bonds pose a particular challenge. We report here that silver complexes bearing perfluorinated indazolylborate ligands catalyze the reaction of methane (CH(4)) with ethyl diazoacetate (N(2)CHCO(2)Et) to yield ethyl propionate (CH(3)CH(2)CO(2)Et). The use of supercritical carbon dioxide (scCO(2)) as the solvent is key to the reaction's success. Although the catalyst is only sparingly soluble in CH(4)/CO(2) mixtures, optimized conditions presently result in a 19% yield of ethyl propionate (based on starting quantity of the diazoester) at 40°C over 14 hours.     

Direct observation and quantification of CO₂ binding within an amine-functionalized nanoporous solid

Understanding the molecular details of CO(2)-sorbent interactions is critical for the design of better carbon-capture systems. Here we report crystallographic resolution of CO(2) molecules and their binding domains in a metal-organic framework functionalized with amine groups. Accompanying computational studies that modeled the gas sorption isotherms, high heat of adsorption, and CO(2) lattice positions showed high agreement on all three fronts. The modeling apportioned specific binding interactions for each CO(2) molecule, including substantial cooperative binding effects among the guest molecules. The validation of the capacity of such simulations to accurately model molecular-scale binding bodes well for the theory-aided development of amine-based CO(2) sorbents. The analysis shows that the combination of appropriate pore size, strongly interacting amine functional groups, and the cooperative binding of CO(2) guest molecules is responsible for the low-pressure binding and large uptake of CO(2) in this sorbent material.     

Ionic liquid-mediated selective conversion of CO₂ to CO at low overpotentials

Electroreduction of carbon dioxide (CO(2))--a key component of artificial photosynthesis--has largely been stymied by the impractically high overpotentials necessary to drive the process. We report an electrocatalytic system that reduces CO(2) to carbon monoxide (CO) at overpotentials below 0.2 volt. The system relies on an ionic liquid electrolyte to lower the energy of the (CO(2))(-) intermediate, most likely by complexation, and thereby lower the initial reduction barrier. The silver cathode then catalyzes formation of the final products. Formation of gaseous CO is first observed at an applied voltage of 1.5 volts, just slightly above the minimum (i.e., equilibrium) voltage of 1.33 volts. The system continued producing CO for at least 7 hours at Faradaic efficiencies greater than 96%.     

How does the arthropod–plant system respond to abrupt and gradual increases in atmospheric CO2?

Global warming caused by elevated carbon dioxide (CO₂) is a major environmental and policy issue.  The current global average temperature has been elevated by 1°C since the industrial revolution, and it is likely to reach a temperature increase of 1.5°C between 2030 and 2052 (IPCC 2018).  Human-caused emission of CO₂ is responsible for the greenhouse effect and the atmospheric CO₂ concentration is higher now than at any other time in the past 500 000 years, and it continues to rise (Lüthi et al. 2008).  Impacts of arthropod–plant interactions on carbon dynamics and the global climate are important but often ignored.  For example, outbreaks of the mountain pine beetle, Dendroctonus ponderosae, in British Columbia during 2000–2020 will cause the release of an estimated 270 Mt carbon and convert the forest from a small carbon sink to a large carbon source (Kurz et al. 2008).   The annual carbon release due to outbreaks of this beetle is almost equivalent to the annual carbon emission from all forest fires occurring in Canada over 1959–1999 (Kurz et al. 2008).Most studies of arthropod–plant interactions have focused on the effects of ambient CO₂ or abruptly increasing CO₂ concentrations.  In general, these studies show that elevated CO₂ has a positive direct effect on plant photosynthesis and photosynthate production (Bezemer and Jones 1998; Kim et al. 2015; Andresen et al. 2018; Thomey et al. 2019).  Most scientists expect C3 plants to benefit from this additional CO₂ and outcompete C4 species, because the efficiency of C3 photosynthesis increases with increasing CO₂ concentration to a far greater extent than it does in C4 photosynthesis (Hovenden and Newton 2018; Reich et al. 2018).  Yan et al. (2020) found that elevated CO₂ increased photosynthetic rate, nodule number, yield and total phenolic content of Medicago truncatula.  Dong et al. (2018a) reported that elevated CO₂ promoted the yield and nutritional quality of cucumber (Cucumis sativus L.).  After conducting a meta-analysis using 57 articles consisting of 1 015 observations, they found that elevated CO₂ increased the concentrations of fructose, glucose, total phenols, and total flavonoids in the edible parts of vegetables by 14.2, 13.2, 8.9, and 45.5%, respectively, but decreased the concentrations of protein and nitrate, by 9.5 and 18.0%, respectively (Dong et al. 2018b).  Robinson et al. (2012) reviewed the evidence from 170 studies and concluded that plant biomass, C:N ratio, total phenolics and flavonoids increase under elevated CO₂, while N-based secondary metabolites and plant terpenoid concentrations decrease.  Being an important limiting factor for phytophagous arthropods, changes in foliar C-based secondary metabolites (e.g., condensed tannins and phenolics) and N-based chemicals may have major effects on arthropod performance.Numerous studies have found that elevated CO₂ indirectly influences arthropod performance via the changes in plant chemical composition (Ge et al. 2010; Xu et al. 2013; Wu 2014; Sun et al. 2018).  Wen et al. (2019) observed a significantly longer larval duration and lower fecundity of Nilaparvata lugens in elevated CO₂.  After analyzing 122 studies, Robinson et al. (2012) concluded that elevated CO₂ increases arthropod survival, abundance and relative consumption rate, but it reduces fecundity, relative growth rate and adult weight.  Many chewing pests, such as cotton bollworm (Helicoverpa armigera) and gypsy moth, exhibited lower fecundity, consumption rate and finite rate under elevated CO₂ (Foss et al. 2013; Liu et al. 2017).  The sucking pests, however, displayed varied responses to elevated CO₂.  For example, in aphids, the responses to elevated CO₂ in terms of fecundity, development and population growth varied between different species, different hosts or even different genotypes of the same host (Sudderth et al. 2005; Gao et al. 2008; Guo et al. 2013).  The studies documented above indicated that the chewing arthropods and sap feeders employ different strategies in response to elevated CO₂.  While it is clear that arthropod–plant interactions are affected by atmospheric CO₂ concentrations, it is currently uncertain whether an abrupt increase in CO₂ causes similar responses as the gradual increase has been observed since the industrial revolution.  A recent study of Bromus inermis (a perennial grass) and its associated arbuscular mycorrhizal fungi (AMF) shows that abrupt and gradual CO₂ change regimes may not elicit the same response (Klironomos et al. 2005).  In a long-term 6-year experiment in which plants were exposed to three CO₂ regimes (ambient CO₂, gradual increase in CO₂, and abrupt increase in CO₂) for 21 successive generations, more AMF taxa were lost when CO₂ was raised abruptly than when a gradual increase of the same magnitude was implemented.  The abrupt change in CO₂ resulted in a significant change in mycorrhizal diversity in the first generation, although little change occurred in subsequent generations.  Species richness of AMF was similar in the gradual and ambient CO₂ treatments but was significantly lower in the abrupt CO₂ change treatment (Klironomos et al. 2005).  It is not known whether these effects would be similar in an intact field experiment where fungal meta-community dynamics may come into play and mediate any local species extinctions.  A comparable long-term 3-year experiment (Wu et al., unpublished data) investigating impacts of abrupt vs. gradual increases in CO₂ on life-history traits of N. lugens feeding on rice over 16 successive generations, indicated that the gradual increase in CO₂ treatment can promote the growth and physiological metabolism of N. lugens relative to the abrupt CO₂ increase treatment.  So, the effects of abrupt and gradual CO₂ change regimes on arthropods, plants and their associated organisms could differ because the changes affecting organisms are initially the greatest for the first subsequent generation in the abrupt regime, while the evolutionary responses of the interacting organisms differ between the two regimes.Current generalizations about the effects of increasing atmospheric CO₂ on arthropod–plant interactions are mainly based on experiments using the abrupt approach.  However, a major assumption of these approaches has not been tested, i.e., whether a single-step increase in CO₂ yields similar responses in arthropod–plant systems as a gradual increase over several decades.  If a sudden increase in CO₂ does not yield a response that is similar to a gradual increase of the same magnitude, some of these generalizations could be affected.  Hovenden and Newton (2018) considered that long-term experiments show unexpected plant responses to elevated CO₂ concentrations.  Therefore, most current research may overestimate the impact of abrupt changes in CO₂ concentrations on the arthropod–plant systems.  We must be cautious when designing experiments and explaining the effects of CO₂ concentrations on the arthropod–plant system, because the magnitudes of responses to environmental changes that are significantly more abrupt may be different than those that would occur in nature.  Therefore, other model systems and intact ecosystems should be used to understand how an increase in atmospheric CO₂ influences interactions between arthropods and their host plants.     

Carbon isotope constraints on the deglacial CO₂ rise from ice cores

The stable carbon isotope ratio of atmospheric CO(2) (δ(13)C(atm)) is a key parameter in deciphering past carbon cycle changes. Here we present δ(13)C(atm) data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in δ(13)C(atm) during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the δ(13)C(atm) evolution. During the Last Glacial Maximum, δ(13)C(atm) and atmospheric CO(2) concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then.     

Massive CO₂ ice deposits sequestered in the south polar layered deposits of Mars

Shallow Radar soundings from the Mars Reconnaissance Orbiter reveal a buried deposit of carbon dioxide (CO(2)) ice within the south polar layered deposits of Mars with a volume of 9500 to 12,500 cubic kilometers, about 30 times that previously estimated for the south pole residual cap. The deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior CO(2) volatile release. If released into the atmosphere at times of high obliquity, the CO(2) reservoir would increase the atmospheric mass by up to 80%, leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling.     

N₂reduction and hydrogenation to ammonia by a molecular iron-potassium complex

The most common catalyst in the Haber-Bosch process for the hydrogenation of dinitrogen (N(2)) to ammonia (NH(3)) is an iron surface promoted with potassium cations (K(+)), but soluble iron complexes have neither reduced the N-N bond of N(2) to nitride (N(3-)) nor produced large amounts of NH(3) from N(2). We report a molecular iron complex that reacts with N(2) and a potassium reductant to give a complex with two nitrides, which are bound to iron and potassium cations. The product has a Fe(3)N(2) core, implying that three iron atoms cooperate to break the N-N triple bond through a six-electron reduction. The nitride complex reacts with acid and with H(2) to give substantial yields of N(2)-derived ammonia. These reactions, although not yet catalytic, give structural and spectroscopic insight into N(2) cleavage and N-H bond-forming reactions of iron.     

Spectroscopic observation of dual catalytic sites during oxidation of CO on a Au/TiO₂ catalyst

The prevailing view of CO oxidation on gold-titanium oxide (Au/TiO(2)) catalysts is that the reaction occurs on metal sites at the Au/TiO(2) interface. We observed dual catalytic sites at the perimeter of 3-nanometer Au particles supported on TiO(2) during CO oxidation. Infrared-kinetic measurements indicate that O-O bond scission is activated by the formation of a CO-O(2) complex at dual Ti-Au sites at the Au/TiO(2) interface. Density functional theory calculations, which provide the activation barriers for the formation and bond scission of the CO-O(2) complex, confirm this model as well as the measured apparent activation energy of 0.16 electron volt. The observation of sequential delivery and reaction of CO first from TiO(2) sites and then from Au sites indicates that catalytic activity occurs at the perimeter of Au nanoparticles.     

The coexistence of superconductivity and topological order in the Bi₂Se₃ thin films

Three-dimensional topological insulators (TIs) are characterized by their nontrivial surface states, in which electrons have their spin locked at a right angle to their momentum under the protection of time-reversal symmetry. The topologically ordered phase in TIs does not break any symmetry. The interplay between topological order and symmetry breaking, such as that observed in superconductivity, can lead to new quantum phenomena and devices. We fabricated a superconducting TI/superconductor heterostructure by growing dibismuth triselenide (Bi(2)Se(3)) thin films on superconductor niobium diselenide substrate. Using scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we observed the superconducting gap at the Bi(2)Se(3) surface in the regime of Bi(2)Se(3) film thickness where topological surface states form. This observation lays the groundwork for experimentally realizing Majorana fermions in condensed matter physics.     

Cloning of Soybean 24 kDa Oleosin Gene and Its Transient Expression asa Carrier for Foreign Protein

The genomic DNA sequence encoding soybean 24 kDa oleosin and its promoter were cloned andanalyzed for investigation of the potentials of the oleosin acted as a carrier for production of recombinant proteins in plant. The -300 box, GA-rich, G-box, SEF-3, SEF-4, RY box, ABA box, CAn and TATA box were found in the upstream region of the soybean oleosin gene, which shows the functional oleosin promoter available. Homology comparison reveals that the soybean 24 kDa oleosin shares the highest identity with the soybean oleosin isoform A (U09118, GenBank), reaching to 98.4% in nucleotide. A soybean oleosinhirudin fusion gene driven by the oleosin promoter was constructed and inserted into plant binary expression vector. The intact tobacco plantlets were transformed by means of vacuum infiltration approach, with the Agrobacterium tumefaciens harboring the above vector. The transient correct expression of oleosin-hirudin fusion gene was identified by SDS/PAGE, western blotting and enterokinase treatment.     

Correlation Analysis of Rice Seed Setting Rate and Weight of 1 000-Grain and Agro-Meteorology over the Middle and Lower Reaches of the Yangtze River, China

The purpose of this study is to reveal the effects of historic climate change on rice yield over the middle and lower reaches of the Yangtze River, China, and to better adapt to climate change in the future. This study presents the relation of temperature and precipitation and rice components from 1981 to 2003 at 48 early rice stations and 30 middle rice stations. It focuses on an analysis of three stages： flowering, pre-milk, and late milk. The results show that mean maximum temperature and mean daily precipitation at the stages of flowering and pre-milk are most related to early rice yield. Yield change of middle rice is mainly because of mean precipitation change at the flowering stage. Furthermore, percentage of undeveloped grain increases as mean maximum temperature rises at the flowering stage. Over-precipitation in the reproductive stage is a major reason for reduction in yield of early rice. Consecutive rainfall and continuous high temperature can have negative effects on middle rice yield. Global warming would affect middle rice more seriously than early rice.     

Experimental and theoretical differential cross sections for a four-atom reaction: HD + OH → H₂O + D

Quantum dynamical theories have progressed to the stage in which state-to-state differential cross sections can now be routinely computed with high accuracy for three-atom systems since the first such calculation was carried out more than 30 years ago for the H + H(2) system. For reactions beyond three atoms, however, highly accurate quantum dynamical calculations of differential cross sections have not been feasible. We have recently developed a quantum wave packet method to compute full-dimensional differential cross sections for four-atom reactions. Here, we report benchmark calculations carried out for the prototypical HD + OH → H(2)O + D reaction on an accurate potential energy surface that yield differential cross sections in excellent agreement with those from a high-resolution, crossed-molecular beam experiment.     

Analysis of Water Resources Supply and Demand and Security of Water Resources Development in Irrigation Regions of the Middle Reaches of the Heihe River Basin, Northwest China

Based on the data for meteorology, hydrology, soil, planting, vegetation, and socio-economic development of the irrigation region in the middle reaches of the Heihe River basin, Northwest China, the model of balance of water supply and demand in the region was established, and the security of water resource was assessed, from which the results that the effects of unified management of water resources in the Heihe River basin between Gansu Province and Inner Mongolia on regional hydrology are significant with a decrease in water supply diverted from Heihe River and an increase in groundwater extracted. In addition, it was found that the groundwater level has been steadily decreasing due to over pumping and decrease in recharges. In present year （2003）, the volume of potential groundwater in the irrigation districts is far small because of the groundwater overdraft; even in the particular regions, there is no availability of groundwater resources for use. By 2003, water supply is not sufficient to meet the water demand in the different irrigation districts, the sustainable development and utilization of water resources are not secured, and the water supply crisis occurs in Pingchuan irrigation district. Achieving water security for the sustainable development of society, agriculture, economy, industry, and livelihoods while maintaining or improving the abilities of the management and planning of water resources, determining of the reasonable percentage between water supply and groundwater utilization and water saving in agricultural irrigation are taken into account. If this does not occur, it is feared that the present performance of water development and planning may further aggravate the problem of scarcities of water resources and further damage the fragile ecological system.     

Soil Properties and Characteristics of Soil Aggregate in Marginal Farmlands of Oasis in the Middle of Hexi Corridor Region, Northwest China

The composition and stability of soil aggregate are closely related to soil quality, soil erosion, and agricultural sustainability. In this study, 49 soil samples at the 0-10 cm surface layer were collected from four soil types (i.e., Ari-Sandic Primosols, Calci-Orthic Aridosols, Siltigi-Otrthic Anthrosols, and Ustic Cambosols) in the marginal farmland in the oasis of the middle Hexi Corridor region and was used to determine the characteristics of soil aggregates. The composition of dry- and wet- sieved aggregates and the physical and chemical properties (including soil particle distribution, soil organic carbon (SOC), calcium carbonate (CaCO3), and oxides of Fe3+ and Al3t) of the selected soils were analyzed. The results show that soil particle size distribution is dominated by fine sand fraction in most of soils except Ustic Cambosols. Soil organic carbon concentration is 5.88±2.52 g kg-1 on average, ranging from 4.75 g kg-1 in Ari-Sandic Primosols to 10.51 g kg-1 in Ustic Cambosols. The soils have high calcium carbonate (CaCO3) concentration, ranging from 84.7 to 164.8 g kg-1, which is increased with soil fine particle and organic carbon content. The percentage of　＞0.25 mm dry aggregates ranges from 65.2% in Ari-Sandic Primosols to 94.6% in Ustic Cambosols, and large dry blocky aggregates (＞5 mm) is dominant in all soils. The mean weight diameter of dry aggregates (DMWD) ranges from 3.2 mm to 5.5 mm. The percentage of ＞0.25 mm water-stable aggregate is from 23.8% to 45.4%. The percentage of aggregate destruction (PAD) is from 52.4% to 66.8%, which shows a weak aggregate stability. Ari-Sandic Primosols has the highest PAD. The distribution and characteristics of soil aggregates are in favor of controlling soil wind erosion. However, the stability of aggregate of all soils is weak and soils are prone to disperse and harden after irrigation. The mass of macro-aggregates and DMWD are positively significantly correlated with the contents of soil clay and silt, soil organic carbon (SOC), CaCO3, and oxides of Fe3+ and A13+. Soil fine silt and clay, SOC and CaCO3 are important agents of aggregation in this region, and the effect of SOC and CaCO3 on aggregate stability is more significant than that of soil silt and clay. Converting cropland to alfalfa forage land can increase SOC concentration, and in turn, enhance the formation of aggregates and stability. For the marginal farmlands in this fragile ecological area, converting cropland to alfalfa grassland or performing crop-grass rotation is an effective and basic strategy to improve soil structure and quality, to mitigate soil wind erosion, and to enhance oasis agricultural sustainability.     

The influence of temperature and moisture content on the longevity of bio-coated rapeseed (Brassica napus L.) during storage

用生物型种衣剂进行包衣处理 ,以未包衣种子作对照 ,把 3种不同含水量的油菜种子分别密封贮藏在高、中、低 3种不同温度条件下 ,分期取样测定种子发芽率的变化 ,结果表明 :含水量为 4 1 %的未包衣种子在所有贮藏温度条件下均能保持较高的发芽率 ,而含水量为 8 6%的在 2 5℃、3 5℃条件贮藏后种子发芽率均有所下降 ,含水量为 1 1 1 %的种子则劣变加快 ,在贮藏温度 3 5℃条件下经 3个月贮藏后发芽率降为 0 生物型种衣剂包衣油菜种子在所有贮藏条件下劣变速度均低于未包衣种子 相对于种子含水量和贮藏温度的提高 ,包衣种子的发芽率下降较慢 ,经 1年贮藏后所有的包衣种子均能保持75 %以上的发芽率 包衣种子的发芽势与发芽指数也均高于未包衣的对照种子     

Advances on the Responses of Root Dynamics to Increased Atmospheric CO2 and Global Climate Change

Plant roots dynamics responses to elevated atmospheric CO2 concentration, increased temperature and changed precipitation can be a key link between plant growth and long-term changes in soil organic matter and ecosystem carbon balance. This paper reviews some experiments and hypotheses developed in this area, which mainly include plant fine roots growth, root turnover, root respiration and other root dynamics responses to elevated CO2 and global climate change. Some recent new methods of studying root systems were also discussed and summarized. It holds herein that the assemblage of information about root turnover patterns, root respiration and other dynamic responses to elevated atmospheric CO2 and global climatic change can help to better understand and explore some new research areas. In this paper, some research challenges in the plant root responses to the elevated CO2 and other environmental factors during global climate change were also demonstrated.     

Sensitivity of Four Yeasts to Fungicides and CO2 Concentrations and Their Antagonistic Ability in Combination with Fungicide to Pathogenic Fungi in vitro

The yeasts Cryptococcus laurentii, Trichosporon pullulans, Rhodotorula glutinis andTrichosporon sp. were used to investigate their sensitivity to four fungicides anddifferent concentrations of CO2, as well as their antagonistic ability to Penicilliumexpansumand Alternaria alternata in vitro when applied with fungicide. There were significantdifferences in sensitivity to the fungicides among the different yeasts(P = 0.05). R.glutinis was more sensitive to Deccocil, Iprodione and Stroby as compared to otheryeasts. Combination antagonistic yeasts with fungicide could more significantly enhancebiocontrol ability of the yeasts against the pathogenic fungi in vitro (P = 0.05). C.laurentii was the most effective antagonist among the four yeasts and could completelycontrol spore germination of P.expansum and A.alternata when combined with Stroby at theconcentration of i00 μL L^-1. The yeasts, except R.glutinis, could grow well on nutrientyeast dextrose agar (NYDA) after 8 d incubation even at 20% CO2 concentration at 25℃.Particularly Trichosporon sp. showeda better adaptability to low temperature as comparedto other antagonists.