A nanohybridization strategy is presented for the fabrication of high performance lithium ion batteries based on redox‐active organic molecules. The rearrangement of electroactive aromatic molecules ...from bulk crystalline particles into molecular layers is achieved by non‐covalent nanohybridization of active molecules with conductive scaffolds. As a result, nanohybrid organic electrodes in the form of a flexible self‐standing paper–free of binder/additive and current collector–are synthesized, which exhibit high energy and power densities combined with excellent cyclic stability.
Governing the fundamental reaction in lithium–oxygen batteries is vital to realizing their potentially high energy density. Here, novel oxygen reduction reaction (ORR) catalysts capable of mediating ...the lithium and oxygen reaction within a solution‐driven discharge, which promotes the solution‐phase formation of lithium peroxide (Li2O2), are reported, thus enhancing the discharge capacity. The new catalysts are derived from mimicking the biological redox mediation in the electron transport chain in Escherichia coli, where vitamin K2 mediates the oxidation of flavin mononucleotide and the reduction of cytochrome b in the cell membrane. The redox potential of vitamin K2 is demonstrated to coincide with the suitable ORR potential range of lithium–oxygen batteries in aprotic solvent, thereby enabling its successful functioning as a redox mediator (RM) triggering the solution‐based discharge. The use of vitamin K2 prevents the growth of film‐like Li2O2 even in an ether‐based electrolyte, which has been reported to induce surface‐driven discharge and early passivation of the electrode, thus boosting the discharge capacity by ≈30 times. The similarity of the redox mediation in the biological cell and lithium–oxygen “cell” inspires the exploration of redox active bio‐organic compounds for potential high‐performance RMs toward achieving high specific energies for lithium–oxygen batteries.
A new redox mediator (RM), vitamin K2, for oxygen reduction reaction of lithium–oxygen batteries is developed, which is enabled by the inspiration from biological respiration system. Vitamin K2 surprisingly enhances the discharge capacity of lithium–oxygen cell by converting the reaction pathway of oxygen reduction. Successeful utilization of vitamin K2 shows validity of exploiting biological knowledge to discover high‐performance RM.
Metformin, a first-line drug used to treat type 2 diabetes, has also been shown to have anticancer effects against a variety of malignancies, including colorectal cancer. Although inhibition of the ...mTOR pathway is known to be the most important mechanism for the antitumor effects of metformin, other mechanisms remain unclear. The purpose of this study was to identify the antitumor mechanism of metformin in colorectal cancer using high-throughput data, and then test the mechanism experimentally. We identified the gene signature of metformin-treated colon cancer cells. This signature was processed for prediction using colon adenocarcinoma patient data from the Cancer Genome Atlas to classify the patients showing a gene expression pattern similar to that in metformin-treated cells. This patient group showed better overall and disease-free survival. Furthermore, pathway analysis revealed that the metformin-predicted group was characterized by decreased interleukin (IL)-6 pathway signaling, epithelial-mesenchymal transition, and colon cancer metastatic signaling. We induced epithelial-mesenchymal transition in colon cancer cell lines via IL-6 treatment, which increased cell motility and promoted invasion. However, these effects were blocked by metformin. These findings suggest that blockade of IL-6-induced epithelial-mesenchymal transition is an antitumor mechanism of metformin.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dark current density (Jdark) is the most important factors determining signal‐to‐noise ratio, linear dynamic range and detectivity (D*) of organic photodetectors (OPDs). However, the ...solution‐processed OPDs generally suffer from high Jdark under bias because the origin of Jdark still remains unclear and related to complicate factors. In this work, the effect of fluorinated alkyl side chain (FAC) of conjugated polymers (CPs) on the OPD performance is systematically investigated according to the number of fluorine atom. The OPDs, comprising the CPs with a FAC (CP‐FAC), exhibit at least two orders lower Jdark (≈3.73 × 10‐10 A cm‐2 at ‐2 V) compared to that without FAC while significantly maintaining high external quantum efficiency (≈78%). This is because the side chain fluorination leads to the formation of a more ordered molecular structure of the CPs, which reduces the trap density and energetic disorder, thus resulting in the effective suppression of Jdark and in the enhancement of charge carrier mobility. The CP‐FAC based OPD exhibits an exceptionally high D* (≈3.39 × 1013 cm Hz1/2 W‐1 at ‐2 V) and a reasonable response speed (f‐3db = ≈56.31 kHz). Furthermore, a photoplethysmography sensor comprising the CP‐FAC based OPD in a transmission mode is demonstrated.
The suppression of dark current density directly affects the detectivity of organic photodetectors. This study demonstrates that the fluorination of the alkyl side chains of conjugated polymers can lead to the formation of closely and evenly stacked molecular structures that decreases the number of trap states and degree of energetic disorder, thereby effectively suppressing the dark current density.
Enzymes are thought to have evolved highly specific catalytic activities from promiscuous ancestral proteins. By analyzing a genome-scale model of Escherichia coli metabolism, we found that 37% of ...its enzymes act on a variety of substrates and catalyze 65% of the known metabolic reactions. However, it is not apparent why these generalist enzymes remain. Here, we show that there are marked differences between generalist enzymes anf specialist enzymes, known to catalyze a single chemical reaction on one particular substrate in vivo. Specialist enzymes (i) are frequently essential, (ii) maintain higher metabolic flux, and (iii) require more regulation of enzyme activity to control metabolic flux in dynamic environments than do generalist enzymes. Furthermore, these properties are conserved in Archaea and Eukarya. Thus, the metabolic network context and environmental conditions influence enzyme evolution toward high specificity.
Biocatalytic cyclization is highly desirable for efficient synthesis of biologically derived chemical substances, such as the commodity chemicals ε-caprolactam and δ-valerolactam. To identify ...biocatalysts in lactam biosynthesis, we develop a caprolactam-detecting genetic enzyme screening system (CL-GESS). The Alcaligenes faecalis regulatory protein NitR is adopted for the highly specific detection of lactam compounds against lactam biosynthetic intermediates. We further systematically optimize the genetic components of the CL-GESS to enhance sensitivity, achieving 10-fold improvement. Using this highly sensitive GESS, we screen marine metagenomes and find an enzyme that cyclizes ω-amino fatty acids to lactam. Moreover, we determine the X-ray crystal structure and catalytic residues based on mutational analysis of the cyclase. The cyclase is also used as a helper enzyme to sense intracellular ω-amino fatty acids. We expect this simple and accurate biosensor to have wide-ranging applications in rapid screening of new lactam-synthesizing enzymes and metabolic engineering for lactam bio-production.
Multiplex control of metabolic pathway genes is essential for maximizing product titers and conversion yields of fuels, chemicals, and pharmaceuticals in metabolic engineering. To achieve this goal, ...artificial transcriptional regulators, such as clustered regularly interspaced short palindromic repeats (CRISPR) interference (CRISPRi), have been developed to specifically repress genes of interest.
In this study, we deployed a tunable CRISPRi system for multiplex repression of competing pathway genes and, thus, directed carbon flux toward production of molecules of interest in Escherichia coli. The tunable CRISPRi system with an array of sgRNAs successfully repressed four endogenous genes (pta, frdA, ldhA, and adhE) individually and in double, triple, or quadruple combination that are involved in the formation of byproducts (acetate, succinate, lactate, and ethanol) and the consumption of NADH in E. coli. Single-target CRISPRi effectively reduced the amount of each byproduct and, interestingly, pta repression also decreased ethanol production (41%), whereas ldhA repression increased ethanol production (197%). CRISPRi-mediated multiplex repression of competing pathway genes also resulted in simultaneous reductions of acetate, succinate, lactate, and ethanol production in E. coli. Among 15 conditions repressing byproduct-formation genes, we chose the quadruple-target CRISPRi condition to produce n-butanol in E. coli as a case study. When heterologous n-butanol-pathway enzymes were introduced into E. coli simultaneously repressing the expression of the pta, frdA, ldhA, and adhE genes via CRISPRi, n-butanol yield and productivity increased up to 5.4- and 3.2-fold, respectively.
We demonstrated the tunable CRISPRi system to be a robust platform for multiplex modulation of endogenous gene expression that can be used to enhance biosynthetic pathway productivity, with n-butanol as the test case. CRISPRi applications potentially enable the development of microbial "smart cell" factories capable of producing other industrially valuable products.
Graphene encapsulation is an attractive surface‐coating technology that can simultaneously improve the rate capability and cycle stability of nickel‐rich LiNixCoyMn1−x−yO2 (NCM). Here, carbon ...encapsulation with the addition of polyethylenimine (PEI) and polyhedral oligomeric silsesquioxane (POSS), which can effectively suppress access to and generation of harmful factors in the electrolyte to maximize the rate performance and cycle stability of nickel‐rich NCM, is described. The PEI‐POSS/carbon layer not only facilitates electron and lithium‐ion transport on the NCM surface but also inhibits side reactions with the electrolyte during repeated electrochemical reactions. In addition, it provides mechanical support that suppresses the formation of microcracks related to anisotropic volume change of nickel‐rich NCM secondary particles and inhibits irreversible phase transitions on surface structures by mitigating electrolyte wettability. As a result, PEI‐POSS/carbon‐encapsulated NCM exhibits a higher rate capability (84 mAh g−1 at 5 C) and cycle stability (93.5% for 100 cycles at 1 C) compared with bare NCM (0 mAh g−1 at 5 C and 78.4% for 100 cycles at 1 C). In a cycle test at 45 °C, it achieves a capacity retention of 72.6% for 100 cycles at 1 C, which is a 323% improvement in performance over that of bare NCM (22.5%).
Uniform and multifunctional polyethylenimine (PEI)‐polyhedral oligomeric silsesquioxane (POSS)/carbon encapsulation is successfully proposed for the nickel‐rich LiNixCoyMn1−x−yO2 (NCM) cathode materials. The proposed carbon‐encapsulated NCM achieves superior electrochemical performance because the carbon layer acts as an electron conductor and protective film. Further, PEI and POSS added to the carbon layer can improve the protective function of the carbon layer by inhibiting access to harmful factors.
The galvanostatic lithiation/sodiation voltage profiles of hard carbon anodes are simple, with a sloping drop followed by a plateau. However, a precise understanding of the corresponding redox sites ...and storage mechanisms is still elusive, which hinders further development in commercial applications. Here, a comprehensive comparison of the lithium‐ and sodium‐ion storage behaviors of hard carbon is conducted, yielding the following key findings: 1) the sloping voltage section is presented by the lithium‐ion intercalation in the graphitic lattices of hard carbons, whereas it mainly arises from the chemisorption of sodium ions on their inner surfaces constituting closed pores, even if the graphitic lattices are unoccupied; 2) the redox sites for the plateau capacities are the same as those for the closed pores regardless of the alkali ions; 3) the sodiation plateau capacities are mostly determined by the volume of the available closed pore, whereas the lithiation plateau capacities are primarily affected by the intercalation propensity; and 4) the intercalation preference and the plateau capacity have an inverse correlation. These findings from extensive characterizations and theoretical investigations provide a relatively clear elucidation of the electrochemical footprint of hard carbon anodes in relation to the redox mechanisms and storage sites for lithium and sodium ions, thereby providing a more rational design strategy for constructing better hard carbon anodes.
A comprehensive comparison of the lithium‐ and sodium‐ion storage behaviors of hard carbon is conducted, yielding the key findings: the sloping voltage section is presented by the lithium‐ion intercalation in the graphitic lattices of hard carbons, whereas it mainly arises from the chemisorption of sodium ions. The intercalation preference and the plateau capacity have an inverse correlation.
Countries around the world have taken control measures to mitigate the spread of COVID-19, including Korea. Social distancing is considered an essential strategy to reduce transmission in the absence ...of vaccination or treatment. While interventions have been successful in controlling COVID-19 in Korea, maintaining the current restrictions incurs great social costs. Thus, it is important to analyze the impact of different polices on the spread of the epidemic. To model the COVID-19 outbreak, we use an extended age-structured SEIR model with quarantine and isolation compartments. The model is calibrated to age-specific cumulative confirmed cases provided by the Korea Disease Control and Prevention Agency (KDCA). Four control measures-school closure, social distancing, quarantine, and isolation-are investigated. Because the infectiousness of the exposed has been controversial, we study two major scenarios, considering contributions to infection of the exposed, the quarantined, and the isolated. Assuming the transmission rate would increase more than 1.7 times after the end of social distancing, a second outbreak is expected in the first scenario. The epidemic threshold for increase of contacts between teenagers after school reopening is 3.3 times, which brings the net reproduction number to 1. The threshold values are higher in the second scenario. If the average time taken until isolation and quarantine reduces from three days to two, cumulative cases are reduced by 60% and 47% in the first scenario, respectively. Meanwhile, the reduction is 33% and 41%, respectively, for rapid isolation and quarantine in the second scenario. Without social distancing, a second wave is possible, irrespective of whether we assume risk of infection by the exposed. In the non-infectivity of the exposed scenario, early detection and isolation are significantly more effective than quarantine. Furthermore, quarantining the exposed is as important as isolating the infectious when we assume that the exposed also contribute to infection.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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