Extended Biocatalytic Halogenation Cascades Involving a Single‐Polypeptide Regeneration System for Diffusible FADH2

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Extended Biocatalytic Halogenation Cascades Involving a Single-Polypeptide Regeneration System for Diffusible FADH2

A bifunctional fusion enzyme with phosphite dehydrogenase and flavin reductase activities has been constructed and characterised. Co-expression of this single polypeptide regeneration system with tryptophan halogenases and carrier-free immobilisation in combiCLEAs facilitates preparative-scale synthesis of halotryptophan from a single cultivation. Extension of the catalytic cascade with a specific dioxygenase enables single cultivation one-pot synthesis of l-4-Cl-kynurenine on a preparative scale.


Abstract

Flavin-dependent halogenases have attracted increasing interest for aryl halogenation at unactivated C−H positions because they are characterised by high regioselectivity, while requiring only FADH2, halide salts, and O2. Their use in combined crosslinked enzyme aggregates (combiCLEAs) together with an NADH-dependent flavin reductase and an NADH-regeneration system for the preparative halogenation of tryptophan and indole derivatives has been previously described. However, multiple cultivations and protein purification steps are necessary for their production. We present a bifunctional regeneration enzyme for two-step catalytic flavin regeneration using phosphite as an inexpensive sacrificial substrate. This fusion protein proved amenable to co-expression with various flavin-dependent Trp-halogenases and enables carrier-free immobilisation as combiCLEAs from a single cultivation for protein production and the preparative synthesis of halotryptophan. The scalability of this system was demonstrated by fed-batch fermentation in bench-top bioreactors on a 2.5 L scale. Furthermore, the inclusion of a 6-halotryptophan-specific dioxygenase into the co-expression strain further converts the halogenation product to the kynurenine derivative. This reaction cascade enables the one-pot synthesis of l-4-Cl-kynurenine and its brominated analogue on a preparative scale.

Thermomechanical Modeling of the Stabilization Process for Carbon Fiber Production

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Thermomechanical Modeling of the Stabilization Process for Carbon Fiber Production

A hybrid semi-parametric model for the continuous oxidative thermal stabilization of polyacrylonitrile precursor fibers is described. Process temperature, residence time, fiber stretching, and the fiber density of the precursor are considered as influencing parameters. The model may be a first step for cheaper tailored fibers and offers a novel plant-transferable optimization solution.


Abstract

Within carbon fiber manufacturing, the stabilization process is the most time- and energy-intensive process due to the complexity of chemical structure transformation. Therefore, optimization is strictly required to enable cost-efficient stabilization processes. For the first time, a hybrid semi-parametric model for continuous stabilization is developed to prognose stabilization progress and density of the stabilized fiber. The proposed model takes the process parameters like dwell time, stabilization temperature, and fiber stretching as well as precursor properties, such as fiber density, into account. Finally, the proposed hybrid semi-parametric model offers a novel plant-transferable optimization solution for model-based energy optimization in the stabilization process.

Bacterial J‐Domains with C‐Terminal Tags Contact the Substrate Binding Domain of DnaK and Sequester Chaperone Activity

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Bacterial J-Domains with C-Terminal Tags Contact the Substrate Binding Domain of DnaK and Sequester Chaperone Activity

J-proteins are cofactors that assist molecular chaperones in cellular protein folding. We have found that short C-terminal tags added to the N-terminal domains of J-proteins (J-domains) can promote interactions with multiple domains of DnaK, including the substrate binding domain. These modified J-domains are capable of disrupting DnaK chaperone activity in vitro, and recovery following proteotoxic stress in cells. This work highlights the importance of C-terminal sequences in J-protein function.


Abstract

Functional interactions between the molecular chaperone DnaK and cofactor J-proteins (DnaJs), as well as their homologs, are crucial to the maintenance of proteostasis across cell types. In the bacterial pathogen Mycobacterium tuberculosis, DnaK–DnaJ interactions are essential for cell growth and represent potential targets for antibiotic or adjuvant development. While the N-terminal J-domains of J-proteins are known to form important contacts with DnaK, C-terminal domains have varied roles. Here, we have studied the effect of adding C-terminal tags to N-terminal J-domain truncations of mycobacterial DnaJ1 and DnaJ2 to promote additional interactions with DnaK. We found that His6 tags uniquely promote binding to additional sites in the substrate binding domain at the C-terminus of DnaK. Other C-terminal tags attached to J-domains, even peptides known to interact with DnaK, do not produce the same effects. Expression of C-terminally modified DnaJ1 or DnaJ2 J-domains in mycobacterial cells suppresses chaperone activity following proteotoxic stress, which is exaggerated in the presence of a small-molecule DnaK inhibitor. Hence, this work uncovers genetically encodable J-protein variants that may be used to study chaperone–cofactor interactions in other organisms.

ZIF‐8 Incorporated in an Optimized Pebax®1657/PES Membrane for Pure and Mixed CO2/CH4 Gas Separation

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ZIF-8 Incorporated in an Optimized Pebax®1657/PES Membrane for Pure and Mixed CO2/CH4 Gas Separation

A novel optimized mixed-matrix membrane (MMM) of Pebax/polyethersulfone filled with ZIF-8 nanoparticles was fabricated and investigated for pure CO2, CH4, and N2 gases and CO2/CH4 binary gas mixtures. The MMM offered higher permeability and selectivity in comparison with the neat membrane and exceeded Robeson's upper bound.


Abstract

Synthesized ZIF-8 (zeolitic imidazolate framework-8) nanoparticles were embedded in Pebax®1657/polyethersulfone (PES) to construct a mixed-matrix membrane. The membrane was characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and tensile tests. The separation performance of CO2 from CH4 and N2 was also measured at feed pressures of 4, 8, and 12 bar at room temperature. The results indicated that adding nanoparticles and glassy polymer into the Pebax®1657 matrix led to improved thermal and mechanical stabilities of the membrane and an 88 % increase in CO2 permeance (at 30 wt % ZIF-8 in Pebax®1657/PES-10 %). The Pebax®1657/PES/ZIF-8 membrane exceeded Robeson's trade-off upper bound.

Improved Cytotoxicity and Induced Apoptosis in HeLa Cells by Co‐loading Vitamin E Succinate and Curcumin in Nano‐MIL‐88B‐NH2

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Improved Cytotoxicity and Induced Apoptosis in HeLa Cells by Co-loading Vitamin E Succinate and Curcumin in Nano-MIL-88B-NH2

Fe-MIL-88B-NH2 has been co-loaded with α-tocopheryl succinate (TOS) and curcumin (CCM). The incorporation of TOS into the structure of Fe-MIL-88B-NH2 improves cytotoxicity and apoptosis induction in the HeLa cell line.


Abstract

One of the strategies for improved therapeutic effects in cancer therapy is combination chemotherapy. In this study, a flexible nano-MOF (Fe-MIL-88B-NH2) was synthesized in a sonochemical process, then co-loaded with α-tocopheryl succinate (TOS) and curcumin (CCM). The anticancer activity of co-loaded Fe-MIL-88B-NH2 (Fe-MIL-88B-NH2/TOS@CCM) against the HeLa cells was compared with that of the single-loaded counterpart (Fe-MIL-88B-NH2@CCM). MTT analysis indicates improved cytotoxicity of Fe-MIL-88B-NH2/TOS@CCM. The data from the cell apoptosis assay indicated more apoptosis in the case of the co-loaded nano-MOF. This study indicates the positive effect of the presence of TOS on enhancing the anticancer effect of Fe-MIL-88B-NH2@CCM to prepare a more efficient drug delivery nanosystem.

Applying the bioisosterism strategy to obtain lead compounds against SARS‐CoV‐2 cysteine proteases: An in‐silico approach

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Applying the bioisosterism strategy to obtain lead compounds against SARS-CoV-2 cysteine proteases: An in-silico approach

Employing the bioisosterism strategy enables the conception of new drug candidates from biologically active molecules whose safety and efficacy are already established. In this sense, gaining selectivity to SARS-CoV-2 cysteine proteases is a powerful step towards creating a chemical arsenal against COVID-19, especially when drug resistance is in vogue.


Abstract

SARS-CoV-2 cysteine proteases are essential nonstructural proteins due to their role in the formation of the virus multiple enzyme replication-transcription complex. As a result, those functional proteins are extremely relevant targets in the development of a new drug candidate to fight COVID-19. Based on this fact and guided by the bioisosterism strategy, the present work has selected 126 out of 1050 ligands from DrugBank website. Subsequently, 831 chemical analogs containing bioisosteres, some of which became structurally simplified, were created using the MB-Isoster software, and molecular docking simulations were performed using AutoDock Vina. Finally, a study of physicochemical properties, along with pharmacokinetic profiles, was carried out through SwissADME and ADMETlab 2.0 platforms. The promising results obtained with the molecules encoded as DB00549_BI_005, DB04868_BI_003, DB11984_BI_002, DB12364_BI_006 and DB12805_BI_004 must be confirmed by molecular dynamics studies, followed by in vitro and in vivo empirical tests that ratify the advocated in-silico results.

Predicting Degradation Mechanisms in Lithium Bistriflimide “Water‐In‐Salt” Electrolytes For Aqueous Batteries

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Predicting Degradation Mechanisms in Lithium Bistriflimide “Water-In-Salt” Electrolytes For Aqueous Batteries

Degradation mechanisms in LiTFSI/water solutions, which are well-known water-in-salt electrolytes (WISEs), are evidenced through an accelerated radiolysis approach. Aging mechanisms depend strongly on the molality of the salt and on the interactions and competition between the reactivities of water and the anions. The main aging products determined by radiolysis are consistent with the ones observed electrochemically.


Abstract

Aqueous solutions are crucial to most domains in biology and chemistry, including in energy fields such as catalysis and batteries. Water-in-salt electrolytes (WISEs), which extend the stability of aqueous electrolytes in rechargeable batteries, are one example. While the hype for WISEs is huge, commercial WISE-based rechargeable batteries are still far from reality, and there remain several fundamental knowledge gaps such as those related to their long-term reactivity and stability. Here, we propose a comprehensive approach to accelerating the study of WISE reactivity by using radiolysis to exacerbate the degradation mechanisms of concentrated LiTFSI-based aqueous solutions. We find that the nature of the degradation species depends strongly on the molality of the electrolye, with degradation routes driven by the water or the anion at low or high molalities, respectively. The main aging products are consistent with those observed by electrochemical cycling, yet radiolysis also reveals minor degradation species, providing a unique glimpse of the long-term (un)stability of these electrolytes.

Molybdenum Tricarbonyl Complexes Supported by Linear PNP Ligands: Influence of P‐ and N‐Substituents on Relative Stability, Stereoisomerism and on the Activation of Small Molecules

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Molybdenum Tricarbonyl Complexes Supported by Linear PNP Ligands: Influence of P- and N-Substituents on Relative Stability, Stereoisomerism and on the Activation of Small Molecules

Molybdenum tricarbonyl complexes supported by PNPhP ligands with terminal alkyl substituents were synthesized. Surprisingly, all of these complexes are found in the fac configuration, irrespective of the steric demand of the alkyl substituents. This is due to the fact that mer-fac isomerization is hindered.


Abstract

Series of linear tridentate PNPhPR-ligands (R=Me, Et, Pln, Ph, Cyp, iPr, Cy, tBu) and molybdenum tricarbonyl complexes [Mo(CO)3PNPhPR] (R=Ph, Et, Cyp, iPr, Cy,) were synthesized and characterized using NMR-, IR-, and Raman spectroscopy as well as X-ray crystallography. The influence of the different phosphine donor groups of the PNPhPR ligands on the bonding and activation of CO ligands is investigated. Importantly, all complexes are found to adopt a fac geometry, both in solution and in the solid state. This is in contrast to analogous complexes supported by PNHP ligands. DFT calculations reveal that the phenyl ring at the central amine function is the cause of the preferred geometry, hindering isomerization to a mer geometry.