Spatial catalytic acid-base-Pd triple-sites of a hierarchical core-shell structure have been successfully constructed for a three-step reaction, and exhibited excellent catalytic activity and ...stability. A catalytic mechanism has been systematically studied
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single one- and two-step reactions, and possible molecular reactions have been proposed.
We present a hierarchical single catalyst with spatial acid-base-Pd triple-sites showing high catalytic activity and stability for the three-step D-K-H tandem reaction.
Circadian clocks are ubiquitous timing systems that induce rhythms of biological activities in synchrony with night and day. In cyanobacteria, timing is generated by a posttranslational clock ...consisting of KaiA, KaiB, and KaiC proteins and a set of output signaling proteins, SasA and CikA, which transduce this rhythm to control gene expression. Here, we describe crystal and nuclear magnetic resonance structures of KaiB-KaiC, KaiA-KaiB-KaiC, and CikA-KaiB complexes. They reveal how the metamorphic properties of KaiB, a protein that adopts two distinct folds, and the post–adenosine triphosphate hydrolysis state of KaiC create a hub around which nighttime signaling events revolve, including inactivation of KaiA and reciprocal regulation of the mutually antagonistic signaling proteins, SasA and CikA.
Uncovering an efficient and stable photocatalytic system for seawater splitting is a highly desirable but challenging goal. Herein, Cd0.2Zn0.8S@Silicalite-1 (CZS@S-1) composites, in which CZS is ...embedded in the hierarchical zeolite S-1, were prepared and show remarkably high activity, stability and salt resistance in seawater.
Highly efficient and stable supported non-noble metal catalysts to realize the real-time evolution of hydrogen for the promising substitution of fossil fuels are urgently desired but are still ...greatly challenging to achieve. In this work, a highly dispersed ultrafine CoNi nanoalloy has been successfully enclosed within a hierarchically porous carbon which exhibits a unique core-shell metal@carbon structure through an
in situ
carbonized reduction approach by using bimetallic CoNi-MOF-74 as a self-sacrificed template. Note that the all-around interactions between the nanoalloy and carbon within such a unique hierarchically porous core-shell can effectively stabilize and activate the CoNi nanoalloy, meanwhile facilitating the fast mass transfer of substrate molecules. We found that the Co/Ni ratio of the original precursors of MOF-74 and the pyrolysis temperature can significantly meditate the catalytic performance of the derived composite catalysts. In particular, the synthesized catalyst, 10%-CoNi/HPC-400, showed the best catalytic activity and good stability for hydrogen evolution with a turnover frequency value (TOF) of 27.22 min
−1
at 323 K, which is higher than most reported non-noble metal catalysts and even some noble metal catalysts. The outstanding catalytic performance and durability of the composite catalysts were attributed to the synergic effect of the well-dispersed CoNi alloy and the unique hierarchical core-shell structure, which demonstrated the huge potential for AB hydrolysis in hydrogen storage applications.
In situ
synthesis of core-shell carbon enclosed CoNi alloys achieves efficient heterogeneous catalysis.
γ-Valerolactone (GVL) is an important lignocellulosic platform molecule with huge potential for various industrial and chemical applications, which is usually produced using levulinic acid (LA) or ...its esters as raw materials. However, a two-step reaction process in which hydrogenation of the carbonyl groups on metal sites and subsequent lactonization catalyzed by acidic sites over multiple catalysts has generally been needed to realize this synthesis. In this work, a hierarchically multifunctional single catalyst of Ru/phosphotungstic acid/hierarchically porous UiO-66 (Ru/HPW/HP-UiO-66), simultaneously integrated with acidic and metal sites, has been fabricated
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a simple strategy and successfully applied in the one-pot synthesis of GVL using methyl levulinate (ML) as the raw material. The hierarchically porous and nanosized (∼15 nm) HP-UiO-66 can not only provide sufficient space for the mass transfer of substrates but also favors the loading of bulk HPW molecules, which can effectively mediate the catalytic activities and stability of Ru NPs using the confined pore effect of UiO-66 and the strong interaction between HPW and Ru. When applied in the one-pot synthesis of GVL, the hierarchical Ru/HPW/HP-UiO-66 catalyst showed excellent catalytic activity (>97% yield) and stability (maintained after 7 successive cycles) for GVL. More importantly, the hierarchical catalyst also exhibited an extraordinary performance in the hydrogenation of different unsaturated hydrocarbons in aqueous solution. It is expected that our study offers a novel route to biomass upgrades involving metal/acid bifunctional synergistic catalysts.
γ-Valerolactone (GVL) is an important lignocellulosic platform molecule with huge potential for various industrial and chemical applications, which is usually produced using levulinic acid (LA) or its esters as raw materials.
Metal–organic frameworks (MOFs) have great potential for producing photoelectrocatalyzed hydrogen and degrading pollutants, owing to several factors such as high porosity and tunable ...semiconductor-like properties. Wide band gaps, which restrict their use to only UV light induced reactions, and low efficiencies for the separation of photogenerated charge carriers (electrons and holes) pose significant challenges to the widespread applications of MOFs. In this study, a hierarchical hollow Pt@H-UiO-66-NH2/CdS ternary catalyst was designed and synthesized. The immobilized CdS nanoparticles (NPs) in this catalyst endow the MOF H-UiO-66-NH2 with high visible light absorption ability and the Pt NPs serve as electron sinks to improve charge carrier separation. Furthermore, the hierarchical hollow structure of H-UiO-66-NH2 in the composite contributes to boosting light absorption and shortening the distance for charge transfer. As a proof of principle, Pt@H-UiO-66-NH2/CdS catalyzes methylene blue (MB) degradation with a high rate constant of 1.025 × 10−2 and hydrogen production with a rate of 12 810 μmol g−1 h−1, the latter of which is about 2.3, 11.7 and 173 times higher than those of Pt@UiO-66-NH2/CdS, H-UiO-66-NH2/CdS and Pt@H-UiO-66-NH2, respectively.
A stable rod‐like sulfonated viologen (R‐Vi) derivative is developed through a spatial‐structure‐adjustment strategy for neutral aqueous organic redox flow batteries (AORFBs). The obtained R‐Vi ...features four individual methyl groups on the 2,2′,6,6′‐positions of the 4,4′‐bipyridine core ring. The tethered methyls confine the movement of the alkyl chain as well as the sulfonic anion, thus driving the spatial structure from sigmoid to rod shape. The R‐Vi with weak charge attraction and large molecular dimension displays an ultralow membrane permeability that is only 14.7 % of that of typical sigmoid viologen. Moreover, the electron‐donating effect of methyls endows R‐Vi with the lowest redox potential of −0.55 V vs. SHE among one‐electron‐storage viologen‐based AORFBs. The AORFB with the R‐Vi anolyte and a K4Fe(CN)6 catholyte exhibits an energy efficiency up to 87 % and extremely low capacity‐fade rate of 0.007 % per cycle in 3200 continuous cycles.
We report a rod‐like sulfonated viologen (R‐Vi) anolyte for aqueous redox flow batteries (AORFBs). R‐Vi possesses a low membrane‐penetration rate of ≈10−10 cm2 s−1 and the lowest redox potential of −0.55 V vs. SHE among one‐electron‐storage viologens in AORFBs simultaneously. The R‐Vi‐based AORFB exhibits an extremely low capacity‐fade rate of 0.007 % per cycle in 3200 continuous charging–discharging processes.
Organisms are adapted to the relentless cycles of day and night, because they evolved timekeeping systems called circadian clocks, which regulate biological activities with ∼24-hour rhythms. The ...clock of cyanobacteria is driven by a three-protein oscillator composed of KaiA, KaiB, and KaiC, which together generate a circadian rhythm of KaiC phosphorylation. We show that KaiB flips between two distinct three-dimensional folds, and its rare transition to an active state provides a time delay that is required to match the timing of the oscillator to that of Earth's rotation. Once KaiB switches folds, it binds phosphorylated KaiC and captures KaiA, which initiates a phase transition of the circadian cycle, and it regulates components of the clock-output pathway, which provides the link that joins the timekeeping and signaling functions of the oscillator.
Circadian clocks are intracellular systems that orchestrate metabolic processes in anticipation of sunrise and sunset by providing an internal representation of local time. Because the ~24‐h ...metabolic rhythms they produce are important to health across diverse life forms there is growing interest in their mechanisms. However, mechanistic studies are challenging in vivo due to the complex, that is, poorly defined, milieu of live cells. Recently, we reconstituted the intact circadian clock of cyanobacteria in vitro. It oscillates autonomously and remains phase coherent for many days with a fluorescence‐based readout that enables real‐time observation of individual clock proteins and promoter DNA simultaneously under defined conditions without user intervention. We found that reproducibility of the reactions required strict adherence to the quality of each recombinant clock protein purified from Escherichia coli. Here, we provide protocols for preparing in vitro clock samples so that other labs can ask questions about how changing environments, like temperature, metabolites, and protein levels are reflected in the core oscillator and propagated to regulation of transcription, providing deeper mechanistic insights into clock biology.
Signal priority controls have long been viewed as one of the viable strategies to minimize bus delays at intersections so as to reduce the travel time variability or increase headway stability. Such ...control strategies, however, are often not effective for arterials serving heavy bus flows, because frequent signal priority calls will inevitably disrupt the arterial signal plan and incur excessive delays to general traffic. To overcome such deficiencies, this paper presents a bus-based signal progression model for arterials with heavy bus flows as in most major cities in Asia and Europe. The proposed model features its properties of accounting for the impacts of average bus dwell time, its variance, and the bus stop capacity. The impacts of various upstream traffic flow rates and signal plans on the available bus progression band have also been included in computing the optimal bus-progression offsets. Extensive simulation experiments have confirmed the effectiveness of the computed bus progression bands under various traffic congestion levels. The proposed bus-based pre-timed signal system can serve as a base plan for real-time operations of priority control for bus progression if the congestion level on the arterial or dwelling time variance as well as traffic queues have exceeded the operational capacity of the bus-based progression system.
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