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Polyhydroxyalkanoates (PHAs) have been reported with agricultural and medical applications in virtue of their biodegradable and biocompatible properties. Here, we systematically engineered three modules for the enhanced biosynthesis of medium-chain-length polyhydroxyalkanoate (mcl-PHA) in Pseudomonas chlororaphis HT66. The phzE, fadA, and fadB genes were deleted to block the native phenazine pathway and weaken the fatty acid β-oxidation pathway. Additionally, a PHA depolymerase gene phaZ was knocked out to prevent the degradation of mcl-PHA. Three genes involved in the mcl-PHA biosynthesis pathway were co-overexpressed to increase carbon flux. The engineered strain HT4Δ::C1C2J exhibited an 18.2 g/L cell dry weight with 84.9 wt % of mcl-PHA in a shake-flask culture, and the 3-hydroxydodecanoate (3HDD) monomer was increased to 71.6 mol %. Thermophysical and mechanical properties of mcl-PHA were improved with an enriched ratio of 3HDD. This study demonstrated a rational metabolic engineering approach to enhance the production of mcl-PHA with the enriched dominant monomer and improved material properties.

Natural phenazines are a class of multifunctional secondary metabolites of bacteria that play an important role in the biocontrol of plant pathogens. In this paper, a novel bioactive phenazine derivative was isolated from Streptomyces lomondensis S015 through silica gel chromatography and preparative high-performance liquid chromatography (HPLC). The structure was identified as 1-carboxyl-6-formyl-4,7,9-trihydroxy-phenazine (CFTHP) by NMR spectroscopy in combination with ultraperformance liquid chromatography & mass spectrometry (UPLC-MS). CFTHP could inhibit Pythium ultimum, Rhizoctonia solani, Septoria steviae, and Fusarium oxysporum f. sp. niveum with minimal inhibitory concentration (MIC) values of 16, 32, 16, and 16 μg/mL, respectively. A global regulatory gene phoP could positively regulate CFTHP biosynthesis since its production was 3.0-fold enhanced by phoP overexpression and inhibited by phoP deletion in Streptomyces lomondensis S015. These studies illustrated the potential of CFTHP as a promising biopesticide and provided a reference for phenazine production improvement.

An efficient oxygen reduction reaction (ORR) can be achieved by accelerating the movement of electrons, ions, reactants, and products. Here, we prepared core–shell nanohybrids with Fe0.8Zn0.2 nanop...

Two-dimensional materials with intrinsic long-range ordered magnetic moments have drawn a lot of attention. However, for practical applications, whether or not the magnetism is stable in their nanostructures has not been revealed. Here, based on the recently proposed magnetic penta-hexa-graphene, we study the electronic and magnetic properties of its nanoribbons (named PHGNRs). The results show that the PHGNRs have intrinsic robust magnetic moments that are different from zigzag graphene nanoribbons, where the magnetic moments caused by the edge effect are vulnerable. Moreover, the magnetic ground states, namely, ferromagnetic (FM) or antiferromagnetic (AFM), can be transformed by changing the width of PHGNRs. Most interestingly, under the FM ground state, the spin-polarized electronic properties reveal that the zigzag PHGNRs transform from spin-gapless semiconductors (SGSs) to half-metals, as the width of nanoribbons increases, while all the armchair PHGNRs are magnetic semiconductors. Furthermore, by considering different edge effects caused by the residual carbon atoms on the edges, the PHGNRs can further derive different types of SGSs, as well as half-metals. Our work suggests that the PHGNRs possessing intrinsic robust magnetic moments have potential applications in the field of spintronic devices.

Aiming to explore novel oxygen reduction reaction (ORR) catalysts with advanced electrochemical performance and economical and long-term stability is crucial to fuel cells or metal-air batteries. Herein, ordered Pt–Fe intermetallic with an ultralow Pt loading is facilely achieved via the thermal treatment of Pt nanocrystals anchored to the Fe, N-codoped surface-functioned carbon derived from zeolitic imidazolate frameworks. Benefiting from the ordered Pt–Fe intermetallic formed by the rationally applied calcination treatment, the optimized catalyst shows a larger mass activity and better long-term durability compared with Pt/C. Besides, when the optimized sample is applied in the configuration of a zinc-air battery system, it has a higher maximum power density, a better specific capacity as well as a longer discharge time, surpassing those of the Pt/C catalyst.

The development of proton-exchange membrane fuel cell (PEMFC) technology will give rise to a great evolution toward a more sustainable and eco-friendly life by powering clean electric vehicles or stations. However, several vital problems still hinder the commercialization of PEMFCs. The foremost issue is the high cost compared to the contenders, deriving from both the high consumption of Pt catalysts and low service life under practical operations. In this review, deeper investigations on how to further lower the cost of PEMFCs show the importance of understanding and engineering the multiphase transport processes in the membrane electrode assembly (MEA). The definitions, rules, numerical simulations, and experimental validations of various mass transfer processes across the MEA are introduced to provide a holistic evaluation and enable optimization to improve the cell performance and reliability. In addition, because the sluggish oxygen reduction reaction in the cathode catalyst layer (CCL) requires most of the Pt catalysts, the oxygen/water-related multiphase transfer in CCLs is taken as a focus for detailed analysis. Several successful strategies, such as triple-phase boundary engineering, graded design, and novel ordered three-dimensional structure construction, are proven to be promising in greatly reducing the Pt consumption in the CCL and facilitating the microscopic multiphase transfer processes of the MEA. With optimized engineering of the electrode structure and configuration inside the MEA, the mass transfer resistances can be minimized to give the best operating conditions for electrochemical reactions to occur in the catalyst layers. Finally, the main challenges and some perspectives for developing advanced MEAs with lower cost in high-performance and reliable PEMFCs are provided.

Sodium ion batteries (SIBs) are considered one of the most promising alternatives for large-scale energy storage due largely to the abundance and low cost of sodium. However, the lack of high-performance cathode materials at low cost represents a major obstacle toward broad commercialization of SIB technology. In this work, we report a green route strategy that allows cost-effective fabrication of carbon-coated Na2FePO4F cathode for SIBs. By using vitamin C as a green organic carbon source and environmentally friendly water-based polyacrylic latex as the binder, we have demonstrated that the Na2FePO4F phase in the as-derived Na2FePO4F/C electrode shows a high reversible capacity of 117 mAh g–1 at a cycling rate of 0.1 C. More attractively, excellent rate capability is achieved while retaining outstanding cycling stability (∼85% capacity retention after 1000 charge–discharge cycles at a rate of 4 C). Further, in operando X-ray diffraction has been used to probe the evolution of phase structures during the ...

The first example of living cationic isomerization polymerization of β-pinene was achieved with an initiating system that consists of the HCl−2-chloroethyl vinyl ether adduct [1a; CH3CH(OCH2CH2Cl)Cl] and isopropoxytitanium trichloride [TiCl3(OiPr)] in the presence of tetra-n-butylammonium chloride (nBu4NCl) in CH2Cl2 at −40 and −78 °C. The number-average molecular weight of the polymers (Mn ≤ 5 × 103) increased in direct proportion to monomer conversion, and the molecular weight distribution of the polymers was relatively narrow (Mw/Mn ∼ 1.3). The living nature of the polymerization was further demonstrated by monomer-addition experiments. A similar living polymerization was also feasible with the HCl−styrene adduct or 1-phenylethyl chloride [1b; CH3CH(Ph)Cl] in conjunction with TiCl3(OiPr) and nBu4NCl. 1H NMR analysis of the polymers from 1a showed that 1a serves as an initiator and generates poly(β-pinene) chains consisting of the 1-(2-chloroethoxy)ethyl head group, a tert-chloride tail group, and is...