Summary
The continuing nitrogen (N) deposition observed worldwide alters ecosystem nutrient cycling and ecosystem functioning. Litter decomposition is a key process contributing to these changes, but ...the numerous mechanisms for altered decomposition remain poorly identified.
We assessed these different mechanisms with a decomposition experiment using litter from four abundant species (Achnatherum sibiricum, Agropyron cristatum, Leymus chinensis and Stipa grandis) and litter mixtures representing treatment‐specific community composition in a semi‐arid grassland under long‐term simulation of six different rates of N deposition.
Decomposition increased consistently with increasing rates of N addition in all litter types. Higher soil manganese (Mn) availability, which apparently was a consequence of N addition‐induced lower soil pH, was the most important factor for faster decomposition. Soil C : N ratios were lower with N addition that subsequently led to markedly higher bacterial to fungal ratios, which also stimulated litter decomposition.
Several factors contributed jointly to higher rates of litter decomposition in response to N deposition. Shifts in plant species composition and litter quality played a minor role compared to N‐driven reductions in soil pH and C : N, which increased soil Mn availability and altered microbial community structure. The soil‐driven effect on decomposition reported here may have long‐lasting impacts on nutrient cycling, soil organic matter dynamics and ecosystem functioning.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Conversion of naturally abundant nitrogen to ammonia is a key (bio)chemical process to sustain life and represents a major challenge in chemistry and biology. Electrochemical reduction is emerging as ...a sustainable strategy for artificial nitrogen fixation at ambient conditions by tackling the hydrogen- and energy-intensive operations of the Haber-Bosch process. However, it is severely challenged by nitrogen activation and requires efficient catalysts for the nitrogen reduction reaction. Here we report that a boron carbide nanosheet acts as a metal-free catalyst for high-performance electrochemical nitrogen-to-ammonia fixation at ambient conditions. The catalyst can achieve a high ammonia yield of 26.57 μg h
mg
and a fairly high Faradaic efficiency of 15.95% at -0.75 V versus reversible hydrogen electrode, placing it among the most active aqueous-based nitrogen reduction reaction electrocatalysts. Notably, it also shows high electrochemical stability and excellent selectivity. The catalytic mechanism is assessed using density functional theory calculations.
Developing Type‐I photosensitizers is considered as an efficient approach to overcome the deficiency of traditional photodynamic therapy (PDT) for hypoxic tumors. However, it remains a challenge to ...design photosensitizers for generating reactive oxygen species by the Type‐I process. Herein, we report a series of α,β‐linked BODIPY dimers and a trimer that exclusively generate superoxide radical (O2−.) by the Type‐I process upon light irradiation. The triplet formation originates from an effective excited‐state relaxation from the initially populated singlet (S1) to triplet (T1) states via an intermediate triplet (T2) state. The low reduction potential and ultralong lifetime of the T1 state facilitate the efficient generation of O2−. by inter‐molecular charge transfer to molecular oxygen. The energy gap of T1‐S0 is smaller than that between 3O2 and 1O2 thereby precluding the generation of singlet oxygen by the Type‐II process. The trimer exhibits superior PDT performance under the hypoxic environment.
Heavy‐atom‐free boron dipyrromethene (BODIPY)‐based photosensitizers generate ROS exclusively by the Type‐I process upon near‐infrared light illumination for tumor ablation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Atomically ordered intermetallic nanoparticles are promising for catalytic applications but are difficult to produce because the high-temperature annealing required for atom ordering inevitably ...accelerates metal sintering that leads to larger crystallites. We prepared platinum intermetallics with an average particle size of <5 nanometers on porous sulfur-doped carbon supports, on which the strong interaction between platinum and sulfur suppresses metal sintering up to 1000°C. We synthesized intermetallic libraries of small nanoparticles consisting of 46 combinations of platinum with 16 other metal elements and used them to study the dependence of electrocatalytic oxygen-reduction reaction activity on alloy composition and platinum skin strain. The intermetallic libraries are highly mass efficient in proton-exchange-membrane fuel cells and could achieve high activities of 1.3 to 1.8 amperes per milligram of platinum at 0.9 volts.
An organic crystal of 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (pCBP) exhibits time‐dependent afterglow color from blue to orange over 1 s. Both experimental and computational data confirm that the color ...evolution results from well‐separated, long‐persistent thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) with different but comparable decay rates. TADF is enabled by a small S1–T1 energy gap of 0.7 kcal mol−1. The good separation of TADF and RTP is due to a 11.8 kcal mol−1 difference in the S0 energies of the S1 and T1 structures, indicating that apart from the excited‐state properties, tuning the ground state is also important for luminescence properties. This afterglow color evolution of pCBP allows its applications in anticounterfeiting and data encryption with high security levels.
Organic sunset: A time‐dependent afterglow color in a single‐component organic molecular crystal was observed. It originates from well‐separated, long‐persistent thermally activated delayed fluorescence and room‐temperature phosphorescence with different but comparable decay rates.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Ultrathin and ultralong: Highly uniform, ultrathin (diameter 5–7 nm), and ultralong (aspect ratio >104) PtPdTe nanowires (NWs) were synthesized by using a facile method employing Te NWs as both ...sacrificial templates and reducing agents. Fine‐tuning of the molar ratios of Pt and Pd precursors afforded PtPdTe NWs with different compositions and enhanced electroactivity in the methanol oxidation reaction in comparison with a commercial Pt/C catalyst.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A free‐standing Pt‐nanowire membrane fabricated via a multistep templating process is used as an electrocatalyst for the oxygen reduction reaction (ORR). It exhibits remarkably high stability and ...good catalytic activity due to its unique nanowire‐network structure.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Hedgehog (Hh) has been known as the only cholesterol-modified morphogen playing pivotal roles in development and tumorigenesis. A major unsolved question is how Hh signaling regulates the activity of ...Smoothened (SMO). Here, we performed an unbiased biochemical screen and identified that SMO was covalently modified by cholesterol on the Asp95 (D95) residue through an ester bond. This modification was inhibited by Patched-1 (Ptch1) but enhanced by Hh. The SMO(D95N) mutation, which could not be cholesterol modified, was refractory to Hh-stimulated ciliary localization and failed to activate downstream signaling. Furthermore, homozygous SmoD99N/D99N (the equivalent residue in mouse) knockin mice were embryonic lethal with severe cardiac defects, phenocopying the Smo−/− mice. Together, the results of our study suggest that Hh signaling transduces to SMO through modulating its cholesterylation and provides a therapeutic opportunity to treat Hh-pathway-related cancers by targeting SMO cholesterylation.
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•SMO is covalently modified by cholesterol on the Asp95 (D95) residue•Cholesterol modification of SMO is inhibited by Ptch1 and enhanced by Hh•SMO cholesterylation is essential for Hh signaling and embryonic development
Xiao et al. identify that SMO is covalently modified by cholesterol. This modification is regulated by Ptch1 and Hh and is essential for Hh signaling. It suggests that Hh signaling transduces to SMO through modulating its cholesterylation and that targeting SMO cholesterylation may provide a therapeutic approach to treat Hh-pathway-related cancers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Haber–Bosch process for industrial-scale NH3 production suffers from high energy consumption and serious CO2 emission. Electrochemical N2 reduction is an attractive carbon-neutral alternative for ...NH3 synthesis but is severely restricted due to N2 activation needing efficient electrocatalysts for the N2 reduction reaction (NRR) under ambient conditions. Here, we report that Ti3C2Tx (T = F, OH) MXene nanosheets act as high-performance 2D NRR electrocatalysts for ambient N2-to-NH3 conversion with excellent selectivity. In 0.1 M HCl, such catalysts achieve a large NH3 yield of 20.4 µg h−1 mgcat.−1 and a high faradic efficiency of 9.3% at −0.4 V vs. reversible hydrogen electrode, with high electrochemical and structural stability. Density functional theory calculations reveal that N2 chemisorbed on Ti3C2Tx experiences elongation/weakness of the N≡N triple bond facilitating its catalytic conversion to NH3 and the distal NRR mechanism is more favorable with the final reaction of *NH2 to NH3 as the rate-limiting step.
Thiothymidine has a potential application as a photosensitizer in cancer photodynamic therapy (PDT). As the chromophore of thiothymidine, 2-thiothymine exhibits ultrahigh quantum yield of intersystem ...crossing to the lowest triplet state T(1) (ca. 100%), which contrasts with the excited-state behavior of the natural thymine that dissipates excess electronic energy via ultrafast internal conversion to the ground state. In this work, we employed high-level complete-active space self-consistent field and its second-order perturbation methods to explore the photophysical mechanism of a 2-thiothymine model. We have optimized the minimum energy structures in the low-lying seven electronic states, as well as ten intersection points. On the basis of the computed potential energy profiles and spin-orbit couplings, we proposed three competitive, efficient nonadiabatic pathways to the lowest triplet state T(1) from the initially populated singlet state S(2). The suggested mechanistic scenario explains well the recent experimental phenomena. The origin responsible for the distinct photophysical behaviors between thymine and 2-thiothymine is ascribed to the heavy-atom effect, which is significantly enhanced in the latter. Additionally, this heavy-atom effect is found to be state-specific, which could in principle be used to tune the photophysics of 2-thiothymine. The present high-level electronic structure calculations also contribute to understand the working mechanism of thiothymidine in PDT.
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