Ewoud

Nature, Published online: 13 October 2023; doi:10.1038/d41586-023-03238-5

The fact that artificial intelligence can do much of the work makes a mockery of the process. It’s time to make it easier for scientists to ask for research funding.

This minireview provides insights into up-conversion of lignin, which is a major byproduct of paper and pulp industries and has highly polyphenolic structure. Lignin can be functionalized through chemical and enzymatic routes to develop value-added chemicals for industries. Further, cross-linking strategies lead to the development of functional materials such as polymeric resins, bioplastics, hydrogels, nanocarriers and carbon fibers.

Abstract

Lignin, a complex and abundant biopolymer derived from plant cell walls, has emerged as a promising feedstock for sustainable material development. Due to the high abundance of phenylpropanoid units, aromatic rings, and hydroxyl groups, lignin is an ideal candidate for being explored in various material applications. Therefore, the demand on lignin valorization for development of value-added products is significantly increasing. This mini-review provides an overview of lignin upconversion, focusing on its functionalization through chemical and enzymatic routes, and its application in lignin-based polymer resins, hydrogels, and nanomaterials. The functionalization of lignin molecules with various chemical groups offers tailored properties and increased compatibility with other materials, expanding its potential applications. Additionally, the formation of lignin-based networks, either through cross-linking or blending with polymers, generates novel materials with improved mechanical, thermal, and barrier properties. However, challenges remain in optimizing functionalization techniques, preserving the innate complexity of lignin, and achieving scalability for industrial implementation. As lignin‘s potential continues to be unlocked, it is poised to contribute significantly to the shift towards more eco-friendly and resource-efficient industries.

Sustainable strategies inspired by the innate structural features of lignin were developed for the synthesis of diverse biologically active compounds, including tetrahydroisoquinolines, quinazolinones, dopamine and the natural product tetrahydropapaveroline. The synthetic approach enabled the rapid assessment of relevant biological activities through in vitro and in vivo studies and computational similarity searches, with multiple promising hits identified.

Abstract

Deriving active pharmaceutical agents from renewable resources is crucial to increasing the economic feasibility of modern biorefineries and promises to alleviate critical supply-chain dependencies in pharma manufacturing. Our multidisciplinary approach combines research in lignin-first biorefining, sustainable catalysis, and alternative solvents with bioactivity screening, an in vivo efficacy study, and a structural-similarity search. The resulting sustainable path to novel anti-infective, anti-inflammatory, and anticancer molecules enabled the rapid identification of frontrunners for key therapeutic indications, including an anti-infective against the priority pathogen Streptococcus pneumoniae with efficacy in vivo and promising plasma and metabolic stability. Our catalytic methods provided straightforward access, inspired by the innate structural features of lignin, to synthetically challenging biologically active molecules with the core structure of dopamine, namely, tetrahydroisoquinolines, quinazolinones, 3-arylindoles and the natural product tetrahydropapaveroline. Our diverse array of atom-economic transformations produces only harmless side products and uses benign reaction media, such as tunable deep eutectic solvents for modulating reactivity in challenging cyclization steps.

Synlett
DOI: 10.1055/a-2159-4369

A strategy for the Ni-catalyzed decarbonylation of α-oxyacetic acid thioesters is described, providing a new pathway for the synthesis of monosulfide acetals, and further proving that oxygen atoms can stabilize an α-carbocation and promote a decarbonylation reaction. This method has good functional-group compatibility and can tolerate a wide range of electron-withdrawing, electron-neutral, and electron-donating substituents. In addition, this method complements the conventional cross-coupling reactions.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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Nature, Published online: 26 September 2023; doi:10.1038/d41586-023-02997-5

In some areas of social science, around half of studies can’t be replicated. A new test-fast, fail-fast initiative aims to show what research is hot — and what’s not.

The synthesis and purification of pectin-based 2,5-furandicarboxylic acid methyl esters from gram-scale to kilogram-scale enables the valorisation of agricultural side streams into fully renewable polyesters.

Abstract

2,5-Furandicarboxylic acid (FDCA) is one of the most attractive emerging renewable monomers, which has gained interest especially in polyester applications, such as the production of polyethylene furanoate (PEF). Recently, the attention has shifted towards FDCA esters due to their better solubility as well as the easier purification and polymerisation compared to FDCA. In our previous work, we reported the synthesis of FDCA butyl esters by dehydration of aldaric acids as stable intermediates. Here, we present the synthesis of FDCA methyl esters in high yields from pectin-based galactaric acid using a solid acid catalyst. The process enables high substrate concentrations (up to 20 wt %) giving up to 50 mol % FDCA methyl esters with total furancarboxylates yields of up to 90 mol %. The synthesis was successfully scaled up from gram-scale to kilogram-scale in batch reactors showing the feasibility of the process. The stability of the catalyst was tested in re-use experiments. Purification of the crude product by vacuum distillation and precipitation gave furan-2,5-dimethylcarboxylate with a 98 % purity.

Nature Communications, Published online: 17 August 2023; doi:10.1038/s41467-023-40702-2

Efficient production of dopamine direct from lignin is a highly desirable target but extremely challenging. Here, we report an innovative strategy for the sustainable production of dopamine hydrochloride from softwood lignin with a mass yield of 6.4 wt.%.

Proceedings of the National Academy of Sciences, Volume 120, Issue 32, August 2023.

The mechanism for residual solid (char) formation in lignin depolymerization is proposed. The results demonstrate that the lignin-char is composed of a multiplicate layer of alternate lignin and coke. During the lignin conversion, residual solid is generated from the G and S units in phenolic oligomer via the pathways of alkyl aryl ether rearrangement, α-hydroxyl coupling reaction, and aldol condensation.

Abstract

Current techniques of lignin conversion are challenged by the low carbon utilization efficiency resulting from the severe generation of residual solid (char). Therefore, a better understanding of pathway for char formation is significant and highly desired for lignin valorization. In this work, we propose a fundamental mechanistic insight into char formation in lignin depolymerization, using hydrothermal decomposition as model reaction. The results demonstrate that the char featuring a multi-layer construction of coke and oligomer contains mainly G units, primarily generated from native G-lignin and demethoxylation of S-lignin. Instead, H-lignin contributes to the formation of volatile monophenols. Furthermore, new methylene bridges form between the benzene rings in lignin, which consequently results in the formation of recalcitrant char. Based on these observations, a plausible mechanism for char formation is proposed and verified by the density functional theory calculation.

Within the context of the development of phosphorus-based Lewis acids, we report herein the synthesis of four fluorophosphonium organic Lewis acids, with tetracarbonyl cobaltate as counter-anion: [R3PF]+[Co(CO)4]- (with R = o-Tol, Cy, iPr, and tBu). These novel ion pairs were fully characterized by NMR and IR spectroscopy, elemental analysis, and, for three of them, X-ray diffraction. The catalytic activities of these ion pairs were investigated for the carbonylation of β lactones to succinic anhydrides. [tBu3PFCo(CO)4] IV (3 mol%) afforded 91 % of succinic anhydride after 16 h at 80 °C, at a very mild pressure of 2 bar of carbon monoxide. To our knowledge, this work is the first report on using fluorophosphoniums as main-group Lewis acids in a transition metal-catalyzed reaction.

The utilization of water as a sustainable reaction medium has important advantages over traditional organic solvents. Hydroxypropyl methylcellulose has emerged as a biomass-based polymeric additive that enables organic reactions in water through hydrophobic effects. However, such conditions imply slurries as reaction mixtures, where the efficacy of mass transfer and mixing decreases with increasing vessel size. In order to circumvent this limitation and establish an effectively scalable platform for performing hydroxypropyl methylcellulose-mediated aqueous transformations, we utilized oscillatory plug flow reactors that feature a smart dimensioning design principle across different scales. Using nucleophilic aromatic substitutions as valuable model reactions, rapid parameter optimization was performed first in a small-scale instrument having an internal channel volume of 5 mL. The optimal conditions were then directly transferred to a 15 mL reactor, achieving a three-fold scale-up without re-optimizing any reaction parameters. By precisely fine-tuning the oscillation parameters, the system achieved optimal homogeneous suspension of solids, preventing settling of particles and clogging of process channels. Ultimately, this resulted in a robust and scalable platform for performing multiphasic reactions under aqueous conditions.

Polymer networks functionalized with dual-cleavable imine and acetal bonds are developed to enable efficient chemical recycling. These poly(imine-acetal)s facilitate depolymerization into primary building blocks, offering ample design spaces for various polymer types. Furthermore, this innovative approach allows straightforward compound separation, leading to the conservation of chemical resources and promoting closed-loop recycling scheme.

Abstract

Chemical recycling offers a promising solution for the end-of-life treatment of synthetic polymers. However, the efficient recovery of well-defined recycled building blocks continues to be a major challenge, especially for crosslinked thermosets. Here, we developed vanillin-based polymer networks functionalized with dual-cleavable imine and acetal bonds that facilitate chemical recycling to primary building blocks and their convenient separation at the molecular level. A library of crosslinked poly(imine-acetal)s was synthesized by combining the in-bulk synthesized liquid di-vanillin acetal monomer (DVA) with commercially available liquid di- and triamines under solvent-free conditions. These thermosets showed tailor-made thermal and mechanical properties along with outstanding chemical recyclability. Under aqueous acidic conditions, poly(imine-acetal)s selectively and completely disintegrate into small molecules. During the polymer design stage, these compounds were carefully selected to enable facile separation without tedious techniques. As a result, the primary building blocks were isolated in high yields and purity and immediately reused to produce fresh polymers with identical thermomechanical properties. Since our “design for recycling” concept aims at obtaining the primary building blocks rather than monomers after depolymerization, a plethora of possibilities are unlocked to utilize these chemical resources, including closed-loop recycling as portrayed.

Science, Volume 381, Issue 6656, Page 398-404, July 2023.

Technology for the rapid scale-up of synthetic organic electrochemistry from milligrams to multi-grams or multi-100 gram quantities is highly desirable. Traditional parallel plate flow electrolysis cells can produce large quantities of material, but transfer from batch to this flow technology requires re-optimization of the reaction conditions and fully homogeneous reaction mixtures. Moreover, single-pass processing is often difficult to accomplish due to gas generation and the low flow rates typically used in continuous mode. Herein we present a novel reactor design, based on a rotating cylinder electrode concept, that enables seamless scale up from small scale batch experimentation to gram and even multi-kilogram per day quantities. The device can operate in batch and flow mode and it is able to easily process slurries without clogging of the system or fouling of the electrodes. Continuous operation is also demonstrated using three reactors in series that act as a continuous stirred electrochemical reactor cascade, providing kilogram per day productivities in a single pass.

To be or not to be burnt: that's the question. Read more about kraft lignin: the potential, the chemistry of how it is formed, and stateof-the-art applications in both fuels and materials. A technoeconomic discussions discloses two important economic incentives to recover lignin from pulp production.

Abstract

Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this Review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.

Nature, Published online: 26 July 2023; doi:10.1038/d41586-023-02409-8

Atomic bomb historian Richard Rhodes talks to Nature about how researchers fare in the film, and what it gets right and wrong.

Sustainable covalent adaptable networks (CANs): Vinylogous urethane CANs were developed according to green chemistry principles, from organosolv lignin using solvent-free reactions and non-toxics compounds. Structure-property relationship as well as the vitrimer behavior of the cross-linked materials was fully investigated. The recyclable materials also exhibited healing ability, improving their lifecycle and sustainability.

Abstract

During the two last decades, covalent adaptable networks (CANs) have proven to be an important new class of polymer materials combining the main advantages of thermoplastics and thermosets. For instance, materials can undergo reprocessing cycles by incorporating dynamic covalent bonds within a cross-linked network. Due to their versatility, renewable resources can be easily integrated into these innovative systems to develop sustainable materials, which can be related to the context of the recent development of a circular bioeconomy. Lignins, the main renewable sources of aromatic structures, are major candidates in the design of novel and biobased stimuli-responsive materials such as vitrimers due to their high functionality and specific chemical architectures. In the aim of developing recyclable lignin-based vinylogous urethane (VU) networks, an innovative strategy was elaborated in which lignin was first modified into liquid polyols and then into polyacetoacetates. Resulting macromonomers were integrated into aromatic VU networks and fully characterized through thermal, mechanical, and rheological experiments. Viscoelastic behaviors of the different aromatic vitrimers exhibited fast stress-relaxations (e. g., 39 s at 130 °C) allowing easy and fast mechanical reprocessing. A thermomechanical recycling study was successfully performed. Then, the developed strategy enabled the fabrication of healable biobased aromatic vitrimers with tunable structures and properties.

The refinement of biomass, particularly lignin, for the production of chemicals as a solution to the energy crisis, has been substantiated as a potentially promising technology. The effective amalgamation of photocatalytic technology with biomass refining has received considerable attention recently. Nonetheless, the current research landscape is heavily concentrated on lignin molecular models, with little attention being paid to the study of actual lignin. This Review highlights recent progress in the photoreforming of actual lignin for the production of energy or chemicals.

Abstract

Photoreforming of lignocellulosic biomass to simultaneously produce gas fuels and value-added chemicals has gradually emerged as a promising strategy to alleviate the fossil fuels crisis. Compared to cellulose and hemicellulose, the exploitation and utilization of lignin via photoreforming are still at the early and more exciting stages. This Review systematically summarizes the latest progress on the photoreforming of lignin-derived model components and “real” lignin, aiming to provide insights for lignin photocatalytic valorization from fundamental to industrial applications. Considering the complexity of lignin physicochemical properties, related analytic methods are also introduced to characterize lignin photocatalytic conversion and product distribution. We finally put forward the challenges and perspective of lignin photoreforming, hoping to provide some guidance to valorize biomass into value-added chemicals and fuels via a mild photoreforming process in the future.

Flow processing offers many opportunities to optimize reactions in a rapid and automated manner, yet often requires relatively large quantities of input materials. To combat this, we report the use of a flexible droplet flow reactor, equipped with two analytical instruments, for low-volume optimization experiments. A Buchwald-Hartwig amination toward the drug olanzapine, with 6 independent optimizable variables, was optimized using three different automated approaches: self-optimization, design of experiments and kinetic modeling. These approaches are complementary and provide differing information on the reaction: pareto optimal operating points, response surface models and mechanistic models, respectively. The results were achieved using <10% of the material that would be required for standard flow operation. Finally, a chemometric model was built utilizing automated data handling and three subsequent validation experiments demonstrated good agreement between the droplet flow reactor and a standard (larger scale) flow reactor.

Nature, Published online: 12 July 2023; doi:10.1038/d41586-023-02007-8

Samples from the surface of Jezero Crater on Mars have been analysed by the SHERLOC instrument aboard NASA’s Perseverance rover. Signatures from these samples are consistent with the presence of organic molecules and, together with earlier measurements, could constitute the first in situ detection of organic molecules on another planet.

Nature, Published online: 07 July 2023; doi:10.1038/d41586-023-02218-z

By designing an autonomous system that fed prompts to the chatbot, researchers produced a paper that was fluent and insightful. Yet they still have concerns.