Reversible covalent polymers are able to change their bond arrangement and structure via reversible reaction triggered by external stimuli including heating, light and pH, while retaining the ...stability of irreversible covalent polymers in the absence of the stimuli. In recent years, more and more research has been devoted to utilization of reversible covalent bonds in synthesizing new materials, which not only overcomes disadvantages of permanent covalent polymers, but also brings in new functionalities. More importantly, a series of novel techniques dedicated to polymerized products with features such as properties regulation, self-healing, reprocessing, solid state recycling, and controllable degradation are developed, heralding the opportunity of upgrading of traditional polymer engineering. Although the exploration of this emerging topic is still in its infancy, the advances so far are encouraging and clearly directed to large scale applications. This review systematically outlines this promising trend, following a bottom-up strategy, taking into account both theoretical and experimental achievements. It mainly consists of four parts, involving design and preparation: (i) the basis of reversible covalent chemistry, (ii) rheology of reversible covalent polymers, (iii) methods of construction of reversible covalent polymers, and (iv) smart, adaptive properties offered by reversible covalent chemistry. The key elements for realizing reorganization of polymers containing reversible covalent bonds are covered. The advantages and weaknesses of representative reaction systems are analyzed, while the challenges and opportunities to engineering application of the equilibrium control based on reversible covalent chemistry for producing end-use polymers are summarized. In this way, the readers may grasp both the overall situation as well as insight into future work.
Stimuli‐responsive polymers built by reversible covalent bonds used to possess unbalanced mechanical properties. Here, a crosslinked polyurethane containing aromatic pinacol as a novel reversible CC ...bond provider is synthesized, whose tensile strength and failure strain are tunable from 27.3 MPa to as high as 115.2 MPa and from 324% to 1501%, respectively, owing to the relatively high bond energy of the CC bond of pinacol as well as the hydrogen bond between hard segments and semicrystalline soft segments. Moreover, the dynamic equilibrium of pinacol enables self‐healing and recycling of the polymer. Interestingly, the dynamic exchange among macromolecules, for the first time, successfully cooperates with solid‐state drawing that applies to thermoplastics, realizing strengthening of thermoset. Meanwhile, the radicals derived from homolysis of pinacol can repeatedly initiate polymerization of vinyl monomers. The fruitful outcomes of this work may create a series of promising new techniques.
The CC bond of pinacol is dynamically reversible at moderate temperature. A crosslinked polyurethane carrying pinacol unit is synthesized, which can be self‐healed, reprocessed, and recycled via the catalyst‐free reversible homolysis/radicals recombination of the CC bond. Moreover, its strength can be greatly improved by solid‐state drawing. The radicals created during homolysis are enabled to repeatedly initiate polymerization of vinyl monomers.
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•A reduced graphene oxide/polyacrylamide 3D porous anode is successfully fabricated.•High specific area and hydrophilicity greatly promote bacterial loading capacity.•Bionic soft ...surface ensure affinitive contact between anode and microbial biofilms.•Hydrogel properties effectively reduce the polarization resistance of anode.•Orientation of graphene further improves the conductivity and maximum power density.
In this study, a reduced graphene oxide/polyacrylamide (rGO/PAM) three-dimensional (3D) composite hydrogel coupled with current collector graphite brush (GB) was developed as anode for microbial fuel cells (MFCs). The rGO/PAM was fabricated through in-situ polymerization of acrylamide in graphene oxide dispersion, followed by reduction with ascorbic acid. The resulting macro-porous scaffold with high surface area and biocompatibility was benefit for both mass diffusion of the culture medium, microbial colonization and electron mediators. As a result, the GB/rGO/PAM anode produces a remarkably high maximum power density and volumetric power density of 758 mW m−2 and 53 W m−3 at the stable state of power generation, respectively. Moreover, the orientated rGO/PAM (O-rGO/PAM) with higher conductivity could further improve the maximum power density of MFCs, achieving 782 mW m−2. The above results are substantially higher than those of traditional GB, plain carbon cloth (CC), and the control GB/GO/PAM and CC/rGO/PAM based electrodes measured under the same conditions. The new 3D composite hydrogel electrode shows great promise for improving the power generation of MFCs devices.
Oxidative coupling and oxidative rearrangement are two of the most common biosynthetic strategies to form diaryl ethers. In contrast, enzymatic diaryl ether generation that proceeds in a nonoxidative ...manner has not been characterized thus far. Here, we discovered a versatile thioesterase (TE) domain from the nonreducing polyketide synthase (nrPKS) AN7909, which catalyzes diaryl ether formation through a series of successive steps involving esterification, a Smiles rearrangement, and hydrolysis. Further mutations and biochemical analyses with synthetic mimic substrates provide insight into the proposed catalytic process of the TE domain.
Atherosclerosis (AS) is chronic pathological process based on the inflammatory reaction associated with factors including vascular endothelial dysfunction, inflammation, and autoimmunity. ...Inflammasomes are known to be at the core of the inflammatory response. As a pattern recognition receptor of innate immunity, the NLRP3 inflammasome mediates the secretion of inflammatory factors by activating the Caspase-1, which is important for maintaining the immune system and regulating the gut microbiome, and participates in the occurrence and development of AS. The intestinal microecology is composed of a large number of complex structures of gut microbiota and its metabolites, which play an important role in AS. The gut microbiota and its metabolites regulate the activation of the NLRP3 inflammasome. Targeting the NLRP3 inflammasome and regulating intestinal microecology represent a new direction for the treatment of AS. This paper systematically reviews the interaction between the NLRP3 inflammasome and gut microbiome in AS, strategies for targeting the NLRP3 inflammasome and gut microbiome for the treatment of AS, and provides new ideas for the research and development of drugs for the treatment of AS.
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Atramycin C (1), one new angucycline bearing an O‐6 rhamnose side chain, along with one new highly hydroxylated angucyclinone emycin G (2), and ten known analogs (3–12) were isolated from the ...marine‐derived Streptomyces sp. strain BHB‐032. Their structures were assigned by spectroscopic analysis and comparison with literature data. The absolute configuration of the sugar unit of 1 was assigned as 6‐O‐α‐l‐rhamnoside, based on the analysis of the coupling constants and chemical derivatization, whereas the absolute configuration of 2 was determined by X‐ray diffraction. Furthermore, the stereochemistry of saccharothrixin A (3) and SNA‐8073‐A (4) was established unequivocally by X‐ray crystallography for the first time. Compounds 1 and 2 exhibited moderate antimicrobial activities with minimum inhibitory concentration (MIC) values ranging from 16 to 64 μg/ml.
One new angucycline bearing a rare O‐6 rhamnose side chain (1), along with one new highly hydroxylated angucyclinone emycin G (2), and ten known analogs were isolated from the marine‐derived Streptomyces sp. strain BHB‐032. Compounds 1 and 2 exhibited moderate antimicrobial activities with MIC values ranging from 16 to 64 μg/ml.
To impart self-healing polymers largely adjustable dynamicity and mechanical performance, here we develop libraries of catalyst-free reversible polythioureas directly from commodity 1,4-phenylene ...diisothiocyanate and amines via facile click chemistry based modular assembly. By using the amine modules with various steric hindrances and flexibilities, the reversible thiourea units acquire triggering temperatures from room temperature to 120 °C. Accordingly, the derived self-healable, recyclable and controlled degradable dynamically crosslinked polythioureas can take effect within wide temperature range. Moreover, mechanical properties of the materials can be tuned covering plastics, elastomers and fibers using (i) different assemble modules or (ii) solid-state stretching. Particularly, unidirectional stretching leads to the record-high tensile strength of 266 MPa, while bidirectional stretching provides the materials with biaxial strengths up to over 120 MPa. The molecular mechanism and technological innovations discussed in this work may benefit promotion and application of self-healing polymers towards greatly diverse demands and scenarios.
The present paper is devoted to preparation of intrinsic self-healing polymeric materials used for structural applications. The authors introduced a novel healing chemistry based on dynamically ...reversible C–ON bonds, which imitates natural healing in living bodies without affecting their operations. To verify its feasibility, alkoxyamine moieties served as intermolecular links in polystyrene. Upon heating, covalent bond fission and radical recombination synchronously took place among alkoxyamine moieties. Cracked parts were thus reconnected repeatedly, without losing integrity and load bearing ability of the material even above T g.
(±)‐Pratenone A (1), the first representative of natural 3‐(1‐naphthyl)‐2‐benzofuran‐1(3H)‐one polyketides, was isolated from a marine‐derived Streptomyces pratensis strain KCB‐132 together with ...three other new analogues (2−4). Its structure was assigned by spectroscopic analysis, and the absolute configurations of the two enantiomers separated by high‐performance liquid chromatography were determined by single‐crystal X‐ray diffraction and electronic circular dichroism calculations. The solvent‐induced racemization of 1 and a proposed biogenetic pathway to 1−4 from the co‐isolated angucyclinone precursor, as well as their biological activity, are also discussed.
Pratenone A (1), the first representative of natural 3‐(1‐naphthyl)‐2‐benzofuran‐1(3H)‐one polyketides, was isolated from a marine‐derived Streptomyces pratensis strain KCB‐132 in racemic form. After chiral separation, the two enantiomers appeared to be interconvertible when stored in solution. Pratenone A exhibited selective antimicrobial activity against S. aureus CMCC 26003 with an MIC value of 8 μg/mL.
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