SAXS Analysis of the Order−Disorder Transition and the Interaction Parameter of Polystyrene-<i>block</i>-poly(methyl methacrylate)

SAXS Analysis of the Order−Disorder Transition and the Interaction Parameter of Polystyrene-block-poly(methyl methacrylate

Endogenous Ethanol Affects Biopolyester Molecular Weight in Recombinant <i>Escherichia coli</i>

In biopolyester synthesis, polyhydroxyalkanoate (PHA) synthase (PhaC) catalyzes the polymerization of PHA in bacterial cells, followed by a chain transfer (CT) reaction in which the PHA polymer chain is transferred from PhaC to a CT agent. Accordingly, the frequency of CT reaction determines PHA molecular weight. Previous studies have shown that exogenous alcohols are effective CT agents. This study aimed to clarify the effect of endogenous ethanol as a CT agent for poly­[(<i>R</i>)-3-hydroxybutyrate] [P­(3HB)] synthesis in recombinant <i>Escherichia coli</i>, by comparing with that of exogenous ethanol. Ethanol supplementation to the culture medium reduced P­(3HB) molecular weights by up to 56% due to ethanol-induced CT reaction. NMR analysis of P­(3HB) polymers purified from the culture supplemented with ¹³C-labeled ethanol showed the formation of a covalent bond between ethanol and P­(3HB) chain at the carboxyl end. Cultivation without ethanol supplementation resulted in the reduction of P­(3HB) molecular weight with increasing host-produced ethanol depending on culture aeration. On the other hand, production in recombinant BW25113­(Δ<i>adhE</i>), an alcohol dehydrogenase deletion strain, resulted in a 77% increase in molecular weight. Analysis of five <i>E. coli</i> strains revealed that the estimated number of CT reactions was correlated with ethanol production. These results demonstrate that host-produced ethanol acts as an equally effective CT agent as exogenous ethanol, and the control of ethanol production is important to regulate the PHA molecular weight

One-Pot, Room-Temperature Conversion of CO₂ into Porous Metal–Organic Frameworks

The conversion of CO2 into functional materials under ambient conditions is a major challenge to realize a carbon-neutral society. Metal–organic frameworks (MOFs) have been extensively studied as designable porous materials. Despite the fact that CO2 is an attractive renewable resource, the synthesis of MOFs from CO2 remains unexplored. Chemical inertness of CO2 has hampered its conversion into typical MOF linkers such as carboxylates without high energy reactants and/or harsh conditions. Here, we present a one-pot conversion of CO2 into highly porous crystalline MOFs at ambient temperature and pressure. Cubic [Zn4O­(piperazine dicarbamate)3] is synthesized via in situ formation of bridging dicarbamate linkers from piperazines and CO2 and shows high surface areas (∼2366 m2 g–1) and CO2 contents (>30 wt %). Whereas the dicarbamate linkers are thermodynamically unstable by themselves and readily release CO2, the formation of an extended coordination network in the MOF lattices stabilizes the linker enough to demonstrate stable permanent porosity

Pentiptycene-Based Polyurethane with Enhanced Mechanical Properties and CO₂‑Plasticization Resistance for Thin Film Gas Separation Membranes

The development of thin film composite (TFC) membranes offers an opportunity to achieve the permeability/selectivity requirements for optimum CO2 separation performance. However, the durability and performance of thin film gas separation membranes are mostly challenged by weak mechanical properties and high CO2 plasticization. Here, we designed new polyurethane (PU) structures with bulky aromatic chain extenders that afford preferred mechanical properties for ultra-thin-film formation. An improvement of about 1500% in Young’s modulus and 600% in hardness was observed for pentiptycene-based PUs compared to the typical PU membranes. Single (CO2, H2, CH4, and N2) and mixed (CO2/N2 and CO2/CH4) gas permeability tests were performed on the PU membranes. The resulting TFC membranes showed a high CO2 permeance up to 1400 GPU (10–6 cm3(STP) cm–2 s–1 cmHg–1) and the CO2/N2 and CO2/H2 selectivities of about 22 and 2.1, respectively. The enhanced mechanical properties of pentiptycene-based PUs result in high-performance thin membranes with the similar selectivity of the bulk polymer. The thin film membranes prepared from pentiptycene-based PUs also showed a twofold enhanced plasticization resistance compared to non-pentiptycene-containing PU membranes

Pushing Rubbery Polymer Membranes To Be Economic for CO₂ Separation: Embedment with Ti₃C₂T_<i>x</i> MXene Nanosheets

Sustainable and energy-efficient molecular separation requires membranes with high gas permeability and selectivity. This work reports excellent CO2 separation performance of self-standing and thin-film mixed matrix membranes (MMMs) fabricated by embedding 2D Ti3C2Tx MXene nanosheets in Pebax-1657. The CO2/N2 and CO2/H2 separation performances of the free-standing membranes are above Robeson’s upper bounds, and the performances of the thin-film composite (TFC) membranes are in the target area for cost-efficient CO2 capture. Characterization and molecular dynamics simulation results suggest that the superior performances of the Pebax–Ti3C2Tx membranes are due to the formation of hydrogen bonds between Ti3C2Tx and Pebax chains, leading to the creation of the well-formed galleries of Ti3C2Tx nanosheets in the hard segments of the Pebax. The interfacial interactions and selective Ti3C2Tx nanochannels enable fast and selective CO2 transport. Enhancement of the transport properties of Pebax-2533 and polyurethane when embedded with Ti3C2Tx further supports these findings. The ease of fabrication and high separation performance of the new TFC membranes point to their great potential for energy-efficient CO2 separation with the low cost of $29/ton separated CO2

Polymer-Assisted Construction of Mesoporous TiO₂ Layers for Improving Perovskite Solar Cell Performance

A general polymer, poly­(methyl methacrylate) (PMMA) is utilized as a unique templating agent for forming crack-free mesoporous TiO₂ films by a sol–gel method. The pore morphologies were found to be controllable by varying the amount of PMMA. The PMMA-mediated mesoporous TiO₂ layer has been applied for the first time to perovskite solar cells exhibiting a best power conversion efficiency of ≥14%, which is ca. three times higher than that using a TiO₂ layer prepared by the same sol–gel method without the polymer addition (5.28%). Remarkably, it was superior to the reference device with mesoporous TiO₂ layer prepared with conventional nanoparticle paste (13.1%). Such mesostructure-tuned TiO₂ layers made by the facile sol–gel technique with a commercially available polymer additive has the great potential to contribute significantly toward the development of low-cost, highly efficient perovskite solar cells as well as other functional hybrid devices

Polyhydroxyalkanoate Film Formation and Synthase Activity During In Vitro and In Situ Polymerization on Hydrophobic Surfaces

In vitro and in situ enzymatic polymerization of polyhydroxyalkanoate (PHA) on two hydrophobic surfaces, a highly oriented pyrolytic graphite (HOPG) and an alkanethiol self-assembled monolayer (SAM), was studied by atomic force microscopy (AFM) and quartz crystal microbalance (QCM), using purified Ralstonia eutropha PHA synthase (PhaCRe) as a biocatalyst. (R)-Specific enoyl-CoA hydratase was used to prepare R-enantiomer monomers [(R)-3-hydroxyacyl-CoA] with an acyl chain length of 4−6 carbon atoms. PHA homopolymers with different side-chain lengths, poly[(R)-3-hydroxybutyrate] [P(3HB)] and poly[(R)-3-hydroxyvalerate] [P(3HV)] were successfully synthesized from such R-enantiomer monomers on HOPG substrates. After the reaction, the surface morphologies were analyzed by AFM, revealing a nanometer thick PHA film. The same biochemical polymerization process was observed on an alkanethiol (C18) SAM surface fabricated on a gold electrode using QCM. This analysis showed that a complex sequence of PhaCRe adsorption and PHA polymerization has occurred on the hydrophobic surface. On the basis of these observations, the possible mechanisms of the PhaCRe-catalyzed polymerization reaction on the surface of hydrophobic substrates are proposed

Nanobiomineralization of Carbon Dioxide by Molecularly Engineered Metal–Histidine Complex Nanozymes

Next-generation carbon capture, utilization, and storage (CCUS) technologies will be indispensable elements of global decarbonization efforts. In this context, permanent and rapid sequestration of carbon dioxide (CO2) at high capacities will impact their utility broadly. CO2 mineralization into solid inorganic carbonates is an appealing CCUS approach, which requires fast CO2 hydration for effective implementation. The carbonic anhydrases (CAs) have, thus, gained considerable attention as rate promoters for CO2 hydration. Nevertheless, the poor stability and high cost of CAs limit their practical application prospects. Here, we demonstrate that the molecular size control of histidine-based bolaamphiphiles (HisBolas) is a viable strategy for forming robust nanoarchitectures with unusual CA-like catalytic activity. HisBola molecules self-assemble into nanoparticles (∼40 nm) that fuse into globules in water, and the metal coordination of these supramolecular nanoassemblies results in nanozymes. The developed bioinspired nanozymes boost the CO2 hydration kinetics, thus efficiently catalyzing the mineralization process. Systematically studying the alkyl chain length of HisBolas (HisBola5, 7, and 10), we optimized the catalytic activity of the nanozymes. The nanozyme with the optimum structure, zinc-coordinated HisBola5, showed the highest esterase activity [kcat/Km of ∼33.44 M–1·s–1 and Michaelis constant (Km) of ∼0.29 mM] and CO2 hydration kinetics (kcat.hyd/Km.hyd of ∼30,300 M–1·s–1 and Km.hyd of ∼14 mM) among all metal-coordinated HisBolas screened. Overall, low-molecular-weight HisBolas offer a promising platform for designing metal-coordinated nanozymes with high catalytic activity, outstanding thermal stability, and rapid catalytic CO2 hydration ability for CO2 mineralization. We argue that the alkyl unit-controlled performance manipulation of produced nanozymes offers a new path for engineering supramolecular CA mimics, which share a common trait with proteinaceous enzymes, that is, the supporting role of noncatalytic units in catalytic activity