New anhydrous lanthanide metal–organic frameworks (MOFs) Pr(tip)1.52n (tip‐Pr), Nd(tip)1.52n (tip‐Nd), Eu(tip)1.52n (tip‐Eu), and Eu(OH)(mip)n (mip‐Eu) (tip=5‐tert‐butylisophthalate anion, ...mip=5‐methylisophthalate ion), have been hydrothermally synthesized and structurally characterized by elemental analyses, FT‐IR spectroscopy, single‐crystal X‐ray diffraction, thermal gravimetric analysis/differential thermal analysis (TG/DTA), and X‐ray powder diffraction (XRPD) techniques. MOFs tip‐Pr, tip‐Nd, and tip‐Eu are isostructural anhydrous compounds, and exhibit an unprecedented 3D microporous structure with hexagonal channel arrays. The selectively prepared MOF mip‐Eu presents an interpenetrated 3D microporous architecture containing the hydroxyl cluster chains. Solid‐state photoluminescence properties at room temperature indicate that both tip‐Eu and mip‐Eu display the characteristic of the Eu3+ ion spectrum dominated by the 5D0→7FJ (J=0‐4) transition. Compared with mip‐Eu, tip‐Eu displays the very high solid‐state quantum yield (0.62±0.03) and longer lifetime value (0.94±0.01 ms), which is due to the absence of the hydroxyl groups from the solid‐state structure of tip‐Eu. More importantly, a new method to directly investigate the potential of solid‐state lanthanide MOFs for ionic sensing in aqueous solutions has been developed, and successfully applied it to study the potential sensing function of tip‐Eu for polyoxometalates (POMs). The possible mechanism for the quenching effect of POMs on the fluorescence of tip‐Eu is elucidated by the strongly competitive absorption of the excited light source energy between POMs and tip ligands. The very promise for the highly sensitive sensing for polyoxometalates, together with the characteristic of the reversible fluorescence response, suggest that solid‐state tip‐Eu can be an excellent candidate for the directly photoluminescent detection of POMs in aqueous solutions.
Tip for detection: New anhydrous 3D microporous lanthanide metal–organic frameworks (MOFs) with hexagonal channel arrays were synthesized based on the 5‐tert‐butylisophthalate ligand (tip; see figure). The potential sensing function of the Eu‐based MOF for polyoxometalates (POMs) in an aqueous solution is investigated for the first time.
Litter crusts are integral components of the water budget in terrestrial ecosystems, especially in arid areas. This innovative study is designed to quantify the ecohydrological effectiveness of ...litter crusts in desert ecosystems. We focus on the positive effects of litter crusts on soil water holding capacity and water interception capacity compared with biocrusts. Litter crusts significantly increased soil organic matter compared to biocrusts and bare lands, by 2.4 times and 3.8 times, respectively. Higher organic matter content resulted in increased soil porosity and decreased soil bulk density. Meanwhile, soil organic matter can help to maintain maximum infiltration rates. Litter crusts significantly increased the water infiltration rate under high water supply. Our results suggested that litter crusts significantly improve soil properties, thereby influencing hydrological processes. Litter crusts play an important role in improving hydrological effectiveness and provide a microhabitat conducive to vegetation restoration in dry sandy ecosystems.
Optical diodes controlling the flow of light are of principal significance for optical information processing. They transmit light from an input to an output, but not in the reverse direction. This ...breaking of time reversal symmetry is conventionally achieved via Faraday or nonlinear effects. For applications in a quantum network, features such as the abilities of all-optical control, on-chip integration, and single-photon operation are important. Here we propose an all-optical optical diode which requires neither magnetic fields nor strong input fields. It is based on a "moving" photonic crystal generated in a three-level electromagnetically induced transparency medium in which the refractive index of a weak probe is modulated by the moving periodic intensity of a strong standing coupling field with two detuned counterpropagating components. Because of the Doppler effect, the frequency range of the crystal's band gap for the probe copropagating with the moving crystal is shifted from that for the counterpropagating probe. This mechanism is experimentally demonstrated in a room temperature Cs vapor cell.
•Artificial forest species and ages had significant effect on soil water storage.•Converting cropland into forest resulted in significant soil water deficit in semi-arid area.•Soil desiccation ...occurred after 12 years of afforestation in the eastern Loess Plateau.
Afforestation as an effective measure to control soil erosion has achieved remarkable effects in northern China. However, large scale of artificial afforestation can increase soil water consumption and induce soil desiccation in arid and semi-arid areas. This study analyzed the variations of soil water storage following the conversion of croplands into forests with different species and stand ages on the Loess Plateau. Three most common artificial forests dominated by Salix matsudana, Populus cathayana, and Sophora japonica with stand ages of 5, 10, and 15 years were investigated to determine the variations in soil water storage. The results showed that soil water storage decreased with increasing afforestation ages and soil depth. Salix matsudana mainly consumed shallow soil water (0–100 cm), P. cathayana mainly consumed deep soil water (100–150 cm), while S. japonica had relatively lower water consumption than the other two species. Converting cropland into forest resulted in a significant water deficit. Soil water deficit in the 0–100 cm soil profiles was significantly higher under S. matsudana than under the other two artificial forests. Severe soil water depletion and obvious soil desiccation occurred after 12 years of afforestation. Therefore, artificial forests with less water consumption, e.g. S. japonica, should be given priority in future afforestation practice. To maintain the sustainability of vegetation, changes in land-use patterns should be considered after 12 years of afforestation.
The CuI‐catalyzed reaction of indoles with N‐tosylhydrazones derived from the ortho‐/para‐hydroxybenzaldhydes affords selectively the C‐3 alkylated products rather than the N‐alkylated products. In ...addition, the I2‐mediated cyclization of the generated C‐3 alkylated products allows the concise synthesis of chromeno2,3‐bindole derivatives.
A copper-catalyzed annulation of oxime acetates and α-amino acid ester derivatives for the easy preparation of 4-pyrrolin-2-ones bearing a 3-amino group has been developed. This process features the ...oxidation of amines with oxime esters as the internal oxidant to produce the active 1,3-dinucleophilic and 1,2-dielectrophilic species concurrently. The subsequent nucleophilic cyclization realizes the efficient construction of 4-pyrrolin-2-one derivatives.
Soil water content (SWC) is a key factor for successful vegetation restoration in arid and semiarid regions, and vegetation has significant influences on the spatial patterns and temporal dynamics of ...SWC. The aim of this study was to investigate the temporal stability of SWC under different restored grasslands in an arid hilly area of Central China. SWC was measured in the 0‐ to 300‐cm soil profile in the natural grassland (Stipa capillata) and three typical planted grasslands (Medicago sativa, Agropyron cristatum, and Caragana korshinskii) over two growing seasons (from June to October 2015 and 2016) under natural rainfall conditions. The results showed that the mean SWC in the natural grassland was approximately 30% higher than those in the planted grasslands. The SWC consumption of the planted legume grasslands in the deepest soil layers (below 200 cm) was higher than that of the natural grassland, owing to the deep root system of the legumes. Both natural and planted grasslands had low SWC temporal stability in the top soil layers (0–50 cm), whereas more stable conditions were gradually observed with increasing the soil depth. The mean value of the mean relative differences of SWC in natural grassland (ca. 15%) was lower than that in the planted grasslands (A. cristatum grasslands) and much lower than that in the scrubland, highlighting the stronger temporal stability of SWC in the natural grassland. In conclusion, natural grassland could maintain higher and stable SWC and is recommended to be used for achieving sustainable vegetation restoration in arid and semiarid regions.
One-step DMAP-catalyzed 3 + 2 and 4 + 2 cycloaddition reactions between C60 and unmodified Morita–Baylis–Hillman adducts in the presence of Ac2O have been developed for the easy preparation of ...cyclopentene- and cyclohexene-fused 60fullerene derivatives. When the MBH adducts bear an alkyl group, two different reaction pathways could be controlled selectively depending on the conditions.
Background and aims
Windblown sand movements, i.e., wind denudation and sand burial, pose a strong selective pressure on dune vegetation. Dune plants commonly receive repeated wind denudation or sand ...burial. Therefore, simultaneously examining the role of sand movement intensity and frequency in shaping dune vegetation is critical for dune biodiversity conservation and ecological restoration. However, studies of this nature are rare.
Methods
We studied the integrated effects of sand movement intensity and frequency on the seedling performance of a dominant semi-shrub,
Artemisia ordosica
, in the Mu Us sandland. We subjected
A. ordosica
seedlings to a total intensity of 10 cm wind denudation or sand burial treatments conducted once, twice or four times.
Key results
We found, given that the total intensity of sand movement remains the same, increasing frequency and decreasing intensity per time largely improved seedling survival. Furthermore, increasing frequency and decreasing intensity per time significantly alleviated the negative effects of wind denudation, although such alleviation effect was not detected for sand burial. Seedlings of
A. ordosica
increased specific leaf area, root length, and biomass allocation to root to adapt to wind denudation, while they developed adventitious roots to adapt to sand burial.
Conclusions
Our results demonstrate that a single heavy sand movement is more detrimental than multiple light ones to the performance of
A. ordosica
seedlings. Our findings suggest that windproof measures to prevent severe sand movements is necessary to allow the establishment of
A. ordosica
during the dune restoration process.
A copper-catalyzed annulation of α,β-unsaturated O-acyl ketoximes with isoquinolinium N-ylides has been developed for the concise synthesis of stable N–H imines with a benzo7,8indolizine core. When ...β-(2-bromoaryl)-α,β-unsaturated O-acyl ketoximes are used as the starting materials, a cascade cyclization occurs to afford the benzo7,8indolizino1,2-cquinolines.
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![DMAP-Catalyzed [3 + 2] and ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0022-3263/small "DMAP-Catalyzed [3 + 2] and [4 + 2] Cycloaddition Reactions between [60]Fullerene and Unmodified Morita–Baylis–Hillman Adducts in the Presence of Ac2O")
