Selenium Embedded in Metal–Organic Framework Derived Hollow Hierarchical Porous Carbon Spheres for Advanced Lithium–Selenium Batteries

Metal–organic framework derived hollow hierarchical porous carbon spheres (MHPCS) have been fabricated via a facile hydrothermal method combined with a subsequent annealing treatment. Such MHPCS are composed of masses of small hollow carbon bubbles with a size of ∼20 nm and shells of ∼5 nm thickness interconnected to each other. MHPCS/Se composite is developed as a cathode for Li–Se cells and delivers an initial specific capacity up to 588.2 mA h g^–1 at a current density of 0.5 C, exhibiting an outstanding cycling stability over 500 cycles with a decay rate even down to 0.08% per cycle. This material is capable of retaining up to 200 mA h g^–1 even after 1000 cycles at a current density of 1 C. Such good electrochemical performance may be ascribed to the distinct hollow structure of the carbon spheres and a large amount of Se wrapped within small carbon bubbles, thus not only enhancing the electronic/ionic transport but also providing additional buffer space to adjust volume changes of Se during charge/discharge processes

Selenium Encapsulated into Metal–Organic Frameworks Derived N‑Doped Porous Carbon Polyhedrons as Cathode for Na–Se Batteries

The substitution of Se for S as cathode for rechargeable batteries, which confine selenium in porous carbon, attracts much attention as a potential area of research for energy storage systems. To date, there are no reports about metal–organic frameworks (MOFs) to use for Na–Se batteries. Herein, MOFs-derived nitrogen-doped porous carbon polyhedrons (NPCPs) have been obtained via facile synthesis and annealing treatment. Se is encapsulated into the mesopores of carbon polyhedrons homogeneously by melt-diffusion process to form Se/NPCPs composite, using as cathode for advanced Na–Se batteries. Se/NPCPs cathode exhibits excellent rate capabilities of 351.6 and 307.8 at 0.5C and 2C, respectively, along with good cycling performance with high Coulombic efficiency of 99.7% and slow decay rate of 0.05% per cycle after 1000 cycles at 2C, which result from the NPCPs having a unique porous structure to accommodate volumetric expansion of Se during discharge–charge processes. Nitrogen doping could enhance the electrical conductivity of carbon matrix and facilitate rapid charge transfer

Construction, Model-Based Analysis, and Characterization of a Promoter Library for Fine-Tuned Gene Expression in <i>Bacillus subtilis</i>

Promoters are among the most-important and most-basic tools for the control of metabolic pathways. However, previous research mainly focused on the screening and characterization of some native promoters in <i>Bacillus subtilis</i>. To develop a broadly applicable promoter system for this important platform organism, we created a <i>de novo</i> synthetic promoter library (SPL) based on consensus sequences by analyzing the microarray transcriptome data of <i>B. subtilis</i> 168. A total of 214 potential promoters spanning a gradient of strengths was isolated and characterized by a green fluorescence assay. Among these, a detailed intensity analysis was conducted on nine promoters with different strengths by reverse-transcription polymerase chain reaction (RT-PCR) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Furthermore, reconstructed promoters and promoter cassettes (tandem promoter cluster) were designed via statistical model-based analysis and tandem dual promoters, which showed strength that was increased 1.2- and 2.77-fold compared to that of promoter P43, respectively. Finally, the SPL was employed in the production of inosine and acetoin by repressing and over-expressing the relevant metabolic pathways, yielding a 700% and 44% increase relative to the respective control strains. This is the first report of a <i>de novo</i> synthetic promoter library for <i>B. subtilis</i>, which is independent of any native promoter. The strategy of improving and fine-tuning promoter strengths will contribute to future metabolic engineering and synthetic biology projects in <i>B. subtilis</i>

The distribution and new functions of PKs.

(A) The distribution of PKs across the tree of life, as referenced in Jillian F. Banfield’s study [38]. The blue color in pie chart represents species with PKs present in all genome sequenced species. (B) The catalytic activity of PKs from different species on different substrates. The displayed 7 PKs not only exhibited activity on F6P or Xu5P, but also demonstrated the ability to convert short-chain ketoses into AcP. The corresponding table on the right represents the catalytic activity of these 7 candidate PKs on 6 classes of ketose or ketose phosphate. Each color represents to a specific enzyme activity (U/mg). Detailed catalytic activity data are shown in S1 Table. The raw data was listed in S1 Data. AcP, acetyl-phosphate; F6P, fructose-6-phosphate; PK, phosphoketolase; Xu5P, xylulose-5-phosphate.</p

High-throughput screening of BbPK for glycolaldehyde (GALD).

The x-axis labels represent the selected location in the BbPK. The y-axis labels represent the relative catalytic activities of the different mutants. Relative activity was defined as the ratio of the reduction of substrate for mutants to that of the wild type. The raw data was listed in S1 Data. (TIF)</p

The raw image for S19 Fig.

The canonical glycolysis pathway is responsible for converting glucose into 2 molecules of acetyl-coenzyme A (acetyl-CoA) through a cascade of 11 biochemical reactions. Here, we have designed and constructed an artificial phosphoketolase (APK) pathway, which consists of only 3 types of biochemical reactions. The core enzyme in this pathway is phosphoketolase, while phosphatase and isomerase act as auxiliary enzymes. The APK pathway has the potential to achieve a 100% carbon yield to acetyl-CoA from any monosaccharide by integrating a one-carbon condensation reaction. We tested the APK pathway in vitro, demonstrating that it could efficiently catabolize typical C1-C6 carbohydrates to acetyl-CoA with yields ranging from 83% to 95%. Furthermore, we engineered Escherichia coli stain capable of growth utilizing APK pathway when glycerol act as a carbon source. This novel catabolic pathway holds promising route for future biomanufacturing and offering a stoichiometric production platform using multiple carbon sources.</div

Calculated energy profiles for the forming process of 2-α, β-dihydroxyethylidene-ThDP (DHEThDP) from short-chain ketoses.

(A) The energy profiles for 1,3-dihydroxyacetone. (B) The energy profiles for D-erythrulose. (C) The energy profiles for L-erythrulose. Energies are given in kilocalories per mole. Note: After adding the large basis set, solvation, and zero-point energy corrections, the energies of TS2 for 1, 3-dihydroxyacetone and D-erythrulose were calculated to be lower than those of int1. Therefore, intramolecular proton transfer of 1,3-dihydroxyacetone and D-erythrulose can be assumed to be barrierless or to occur with very low barriers. (TIF)</p

Energies and energy corrections for the forming process of DHEThDP from DHA.

Energies and energy corrections for the forming process of DHEThDP from DHA.</p

Activity of PKs from different species on different substrates.

Activity of PKs from different species on different substrates.</p

The phosphoketolase (PK) pathway in nature.

Fructose-6-phosphate (F6P) and xylulose-5-phosphate (Xu5P) are converted into D-erythorse-4-phosphate/glyceraldehyde-3-phosphate (E4P/G3P) and acetyl-phosphate (AcP), which not only can be converted into acetyl-CoA by phosphate acetyltransferase (PTA), but also can be converted to ATP and acetate by acetate kinase (AK). (TIF)</p