Hydrocarbon Backbone Research Articles

Enzymatic oxidation of polyethylene by Galleria mellonella intestinal cytochrome P450s

Polyethylene is widely used but highly resistant to biodegradation, owing to its composition of only a hydrocarbon backbone. For biodegradation to occur, oxidation within the polymer needs to be initiated. Galleria mellonella was the first insect discovered to autonomously oxidize polyethylene without the aid of gut microbes. However, the specific enzyme remains unidentified. Here, we identified for the first time two polyethylene oxidation enzyme candidates of cytochrome P450 (CYP), 6B2-GP04 and CYP6B2-13G08, from the G. mellonella midgut. Both candidate clones oxidized polyethylene efficiently, generating short-chain aliphatic compounds, with CYP6B2-GP04 exhibiting higher activity than CYP6B2-13G08 in yeast and insect cells. In silico structural modeling approaches revealed that the CYP6B2-GP04 Phe118 was essential for interacting with hydrocarbons, which was further validated by mutating it to glycine. Furthermore, directed enzyme evolution led to the identification of an enzyme variant with significantly increased oxidation efficiency. Our findings offer promising enzyme-based solutions for polyethylene biodegradation, potentially mitigating polyethylene-driven plastic pollution.

High Molecular Weight Semicrystalline Substituted Polycyclohexene From Alternating Copolymerization of Butadiene and Methacrylate and Its Ambient Depolymerization.

Cyclohexene cannot be polymerized via ring-opening polymerization under any conditions due to its lack of ring strain. A hypothetical polycyclohexene would therefore have a strong thermodynamic driving force to depolymerize to monomer if a metathesis catalyst were provided while otherwise having thermal and hydrolytic stability under normal conditions because of its hydrocarbon backbone. We envisioned access to this otherwise unattainable family of polymers via the alternating polymerization of a diene and an alkene. Ethyl aluminum chloride was found to promote highly alternating polymerization of butadiene and methacrylate when radically initiated at room temperature, resulting in formal polycyclohexene structures. Ultrahigh molecular weight (up to 1750 kDa) polymers can be synthesized at the decagram scale in high monomer conversions. The resulting presumably atactic copolymers exhibited semicrystallinity, leading to high toughness. In the presence of a small amount of the Grubbs catalyst, the generated polycyclohexene can be fully depolymerized at ambient temperatures into pure constituent cyclohexene. The strategy of using orthogonal chemistry for the polymerization and depolymerization processes allows access to polymer structures with subambient ceiling temperatures without using ultralow temperature synthesis or relying on the monomer-polymer equilibrium.

Influence of the backbone chemistry and ionic functional groups of five pairs of oppositely charged polyelectrolytes on complex coacervation

Complex coacervation plays an important role in various fields. Here, the influences of the backbone chemistry and ionic functional groups of five pairs of oppositely charged polyelectrolytes on complex coacervation were investigated. These pairs include synthetic polymers with aliphatic hydrocarbon backbones, peptides with amide bonds, and carbohydrates with glycosidic linkages. Despite sharing identical charged groups, specific pairs displayed distinct liquid/liquid and liquid/solid phase separations depending on the polyelectrolyte mixing ratio, buffer, and ionic strength. The coacervate phase boundary broadened in the orders: glycosidic linkages > amide backbone > aliphatic hydrocarbon backbone, and Tris-phosphate > Tris-acetate > Tris-chloride buffers. Coacervates prepared from polyelectrolytes with lower solubilities in water resisted disassembly at high salt concentrations, and their merge rate was slow. These observations suggest that the hydrophobic segments in polyelectrolytes interfere with the formation of complex coacervates; however, following coacervate formation, the hydrophobic segments render the coacervates stable and elastic.

Mechanochemical Backbone Editing for Controlled Degradation of Vinyl Polymers.

The chemically inert nature of fully saturated hydrocarbon backbones endows vinyl polymers with desirable durability, but it also leads to their significant environmental persistence. Enhancing the sustainability of these materials requires a pivotal yet challenging shift: transforming the inert backbone into one that is degradable. Here, we present a versatile platform for mechanochemically editing the fully saturated backbone of vinyl polymers towards degradable polymer chains by integrating cyclobutene-fused succinimide (CBS) units along backbone through photo-iniferter reversible addition-fragmentation chain-transfer (RAFT) copolymerization. Significantly, the evenly insertion of CBS units does not compromise thermal or chemical stability but rather offers a means to adjust the properties of polymethylacrylate (PMA). Meanwhile, reactive acyclic imide units can be selectively introduced to the backbone through mechanochemical activation (pulse ultrasonication or ball-milling grinding) when required. Subsequent hydrolysis of the acyclic imide groups enables efficient degradation, yielding telechelic oligomers. This approach holds promise for inspiring the design and modification of more environmentally friendly vinyl polymers through backbone editing.

Mechanochemical Backbone Editing for Controlled Degradation of Vinyl Polymers

AbstractThe chemically inert nature of fully saturated hydrocarbon backbones endows vinyl polymers with desirable durability, but it also leads to their significant environmental persistence. Enhancing the sustainability of these materials requires a pivotal yet challenging shift: transforming the inert backbone into one that is degradable. Here, we present a versatile platform for mechanochemically editing the fully saturated backbone of vinyl polymers towards degradable polymer chains by integrating cyclobutene‐fused succinimide (CBS) units along backbone through photo‐iniferter reversible addition‐fragmentation chain‐transfer (RAFT) copolymerization. Significantly, the evenly insertion of CBS units does not compromise thermal or chemical stability but rather offers a means to adjust the properties of polymethylacrylate (PMA). Meanwhile, reactive acyclic imide units can be selectively introduced to the backbone through mechanochemical activation (pulse ultrasonication or ball‐milling grinding) when required. Subsequent hydrolysis of the acyclic imide groups enables efficient degradation, yielding telechelic oligomers. This approach holds promise for inspiring the design and modification of more environmentally friendly vinyl polymers through backbone editing.

Chemically recyclable rosin-based polymers

The pursuit of next-generation sustainable polymers with chemical recyclability and resource renewability has become a priority in materials science. Rosin, a widely available renewable natural biomass, holds promise in this regard. In this study, dehydroabietic acid was incorporated into a cyclooctene monomer structure as pendant groups. This tailored monomer with low ring strain possesses the ability to efficiently undergo ring-opening metathesis polymerization (ROMP), resulting in the synthesis of rosin-based unsaturated polymers with a fully hydrocarbon backbone. The molecular weight of these polymers, ranging from 50 kDa to 160 kDa, can be easily modulated by varying the monomer-to-catalyst feeding ratio. Remarkably, these amorphous polymers exhibit exceptional thermostability, with a decomposition temperature exceeding 400 °C. This type of polymer exhibits excellent acid and alkali resistance within a pH range of 3 to 11. Upon exposure to Grubbs catalyst under mild conditions, these polymers undergo depolymerization back to the native monomer in a highly efficient manner, achieving a remarkable recovery ratio of approximately 95 %. It is evident that this innovative approach is not only relevant for the development of rosin-based polymers but also holds promise for informing the design of other renewable polymers with superior thermostability and enhanced chemical recyclability.

Using a Tunable Triblock Cationic Polymer to Unravel Performance and Durability Effects in Anion Exchange Membrane Based Electrolysis

The use of anion exchange membranes (AEMs) as the polymer electrolyte membrane and related cationic polymers as ionomers in the electrodes of water splitting electrolyzers could lead to significant advantages including the elimination of precious metal electrocatalysts. Because oxygenated radicals in base have a very much lower half life than in acid these materials can be based on hydrocarbon backbones. This leads to an enormous possible variation in polymer chemistry and, while exciting from the point of view of the creation of new polymer chemistries, has led to a lack of detail in determining exactly how all of these many polymers really behave in terms of performance and durability. All of the new materials that are currently being commercialized are designed to be free standing films that are chemically stable to attack by the strongly nucleophilic hydroxide anion. Often these polymers have excessive swelling and poor mechanical properties and lack easy variation enabling their modification to the properties required for an ionomer. Studies where the effect of film processing on performance or durability are also lacking. There is a chronic lack of knowledge in how cationic polymers interact with catalyst particles, charge carrier and the AEM in electrodes. Further complicating these studies is whether the device is operated in water, carbonate or hydroxide solution. The first of which give unexpectedly low performance but may be more amenable to long durability and latter of which gives high performance and low durability.We have developed a triblock co-polymer, with polychlorostyrene blocks that can be quaternized to give a hydrophilic phase and a central hydrophobic polyethylene (pE) block that gives the material good mechanical properties. This seemingly simple system can show tremendous variations. We can control the polymer block lengths and overall molecular weight of the polymer. The material can be suspension cast or melt processed to obtain uniform films. The films are post-quaternized and we can control the degree of functionalization and the nature of the cation. What is interesting about these materials is that for all anions that we have studied their conductivity behavior indicates that they are fully dissociated. We hypothesize that the pE content of the films localizes the water, this has the effect of both promoting anion conduction and also not wetting much of the polymer and so improving the durability and mechanical properties. In a series of films where we systematically increase the pE content, the materials swell less but do not necessarily loose performance. They do however show durability improvements, where a material that is 50% pE will thin in an electrolysis test giving rise to a degradation rate of -23 mV/h, a material with 80% pE will show a degradation rate of +400mV/h, at 500 μA/cm2. Further understanding of these materials is likely to result in further durability improvements. Performance and durability can also be varied by the method by which the film is processed.By using an unsaturated version of the cationic triblock co-polymer in electrode formulations and post hydrogenating we can insolubilize the polymer (by creating an insoluble pE containing polymer insitu) as the ionomer in the electrode. This allows us to study, ionomer loading and to begin to control the positioning of the ionomer. We have baselined these materials using Ni supports, and studied Membrane electrode assemblies on our optimized membranes. These ionomers are surprisingly durable as they contain aromatic groups, leading to further speculation that the localization of the water in the material again gives performance and durability advantages. In this talk we will also show how ionomer chemistry can be used to improve the performance and durability of electrolysis electrodes with either silver, cobalt oxide, or manganese oxide.

Discovery of Class I Diterpene Cyclases Producing a Tetracyclic Cephalotene Skeleton in Plum Yews

The cephalotane diterpenoids (e.g., harringtonolide, cephanolides) from plum yews (Cephalotaxus) represent a rare class of tetracyclic C20 and C19 natural products with intriguing bioactivities. Here, we report the discovery and functional characterization of multiple diterpene synthases (diTPSs) from Cephalotaxus harringtonia and Cephalotaxus hainanensis. In addition to diTPSs responsible for ent-kaurene and biformene biosynthesis, two class I cephalotene synthases (CSs) were found to directly cyclize geranylgeranyl diphosphate (GGPP) into a unique cephalot-12-ene skeleton, which is a crucial step in the biogenesis of cephalotane diterpenoids. A plausible biosynthetic mechanism en route to tetracyclic ring formation was proposed based on an isotope labeling experiment combined with quantum chemical calculations. Site-directed mutagenesis indicated that residue F625 in CS is a key switch of diversifying the hydrocarbon backbone to bicyclic verticillene and tricyclic taxadiene. Altogether this report provides insight into the carbocation cascade reaction driven by active sites in class I diTPSs, promotes our understanding of how chemical diversity originates and evolves in gymnosperms, and lays a solid foundation for future investigation of Cephalotaxus diterpene metabolites.

Introducing Novel Materials with Diffuse Electrons for Applications in Redox Catalysis and Quantum Computing via Theoretical Calculations

Diamond-like structures, where carbon atoms have been replaced with Li+ and C–C bonds with diamines, have currently been introduced as new materials, which can host diffuse electrons in the periphery of each lithium tetra-amine center. These materials display a diverse range of properties behaving as metals or semiconductors depending on the diamine chain length. Multi-reference wavefunction and density functional theory calculations were employed to study the electronic structure of these materials. Initially, gas phase calculations are performed on isolated (NH3)3LiNH2(CH2)1–10H2NLi(NH3)3 molecular strings. One diffuse electron surrounds the periphery of each −NH2Li(NH3)3 terminus. The two terminal electrons couple into a triplet and open-shell singlet states, which are nearly degenerate for long chains and as closed shell singlets for short. At intermediate lengths, the wavefunction of the ground-state singlet state mixes both open- and closed-shell configurations raising doubts about which configuration should be considered for density functional theory calculations. Observations from gas phase calculations accurately predict properties from the condense phase density functional theory calculations carried out for proposed crystalline Li-diamine materials, offering an avenue for further development and insight. Spin-polarized and unpolarized calculations are performed for the whole range of hydrocarbon sizes reporting geometrical and electronic band structures, spin density contours, and density of states. Diffuse electrons can be used for redox reactions or can serve as qubits for quantum computing. Future work will focus on decorating the hydrocarbon backbone with functional groups and/or bulky units, in order to facilitate or block the association between neighboring electrons for more controlled quantum computing applications and propose materials for selective redox catalysis.

Steam cracking of methyl ester: A modeling study on the influence of the hydrocarbon backbone

Biodiesel can be used to produce clean platform chemicals for the chemical industry, as an alternative to or blend with conventional steam cracking feedstocks. Research on the decomposition chemistry of biodiesel is crucial for understanding their combustion, aging and potential as source for base chemical production. Three methyl esters are studied with varying hydrocarbon chain length and a different degrees of saturation to evaluate the impact of these structural differences on the decomposition chemistry and the decomposition product composition. A new kinetic model is developed with the automatic kinetic model generation tool Genesys for the pyrolysis of methyl butanoate, methyl decanoate and methyl dec-4-enoate. New ab initio calculations are carried out for the pyrolysis of methyl butanoate and for retro-ene reactions in unsaturated hydrocarbons and methyl esters, because of their importance in the secondary decomposition chemistry. The first-principles based kinetic model is validated using in-house experimental data gathered in a tubular reactor and against literature experimental data gathered in a jet-stirred reactor for methyl decanoate pyrolysis. A rate of production analysis reveals the main channels towards the pyrolysis products. The presence of the double bond in the hydrocarbon chain leads to a higher production of aromatic species, at the cost of a lower ethylene and propylene production. The high selectivity to aromatics is caused by the fast formation of 1,3-cyclopentadiene from the unsaturated, resonantly stabilized radicals formed during the decomposition.

Surface viscosities of lipid bilayers determined from equilibrium molecular dynamics simulations

Lipid membrane viscosity is critical to biological function. Bacterial cells grown in different environments alter their lipid composition in order to maintain a specific viscosity, and membrane viscosity has been linked to the rate of cellular respiration. To understand the factors that determine the viscosity of a membrane, we ran equilibrium all-atom simulations of single component lipid bilayers and calculated their viscosities. The viscosity was calculated via a Green-Kubo relation, with the stress-tensor autocorrelation function modeled by a stretched exponential function. By simulating a series of lipids at different temperatures, we establish the dependence of viscosity on several aspects of lipid chemistry, including hydrocarbon chain length, unsaturation, and backbone structure. Sphingomyelin is found to have a remarkably high viscosity, roughly 20 times that of DPPC. Furthermore, we find that inclusion of the entire range of the dispersion interaction increases viscosity by up to 140%. The simulated viscosities are similar to experimental values obtained from the rotational dynamics of small chromophores and from the diffusion of integral membrane proteins but significantly lower than recent measurements based on the deformation of giant vesicles.

Surface viscosities of several lipids determined from equilibrium molecular dynamics simulations.

Lipid membrane viscosity is critical to biological function. Bacterial cells grown in different environments have been shown to alter their lipid composition in order to maintain a viscosity in a narrow range,1 and membrane viscosity has been shown to control the rate of cellular respiration.2 In order to understand the factors which determine membrane viscosity, we ran equilibrium all-atom simulations of single component lipid bilayers and calculated their viscosities. The viscosity was calculated via a Green-Kubo relation, with the stress tensor autocorrelation function fit to a stretched exponential function. By simulating a series of lipids at different temperatures, we establish the dependence of viscosity on several aspects of lipid chemistry, including hydrocarbon chain length, unsaturation and backbone structure. Sphingomyelin is found to have a remarkably high viscosity, roughly twenty times that of DPPC. Including the full range of the dispersion increases the membrane viscosity by up to 140%, alleviating some of the discrepancy between simulated and experimental viscosity measurements, although the simulated viscosities remain significantly lower than recent experimental values reported for a series of lipids.3

Highly durable, perfluorinated Q(PFBE-co-VBC) and PVDF blend anion exchange membranes with interconnected morphological features for electrochemical energy conversion systems

Alkaline anion exchange membrane that possesses fluorocarbon and hydrocarbon backbones demonstrates high stability in electrochemical energy conversion systems.

Direct Correlation between the Secondary Structure of an Amphiphilic Polymer and Its Prominent Antiviral Activity.

An amphiphilic segmented polyurethane (F-PU-S), with pendant sulfate groups and a flexible hydrocarbon backbone, exhibits intrachain H-bonding-reinforced folding and hierarchical assembly, producing an anionic polymersome with efficient display of sulfate groups at the surface. It shows an excellent antiviral activity against Sendai virus (SV) by inhibiting its entry to the cells. Mechanistic investigation suggests fusion of the SV and the polymersome to produce larger particles in which neither the folded structure of the polymer nor the fusogenic property of the SV exists anymore. In sharp contrast, a structurally similar polymer R-PU-S, in which the chain folding pathway is blocked by replacing the flexible C6 chain with a rigid cyclohexane chain in the backbone, cannot form a similar polymersome structure and hence does not exhibit any antiviral activity. On the other hand, the third polymer (F-PU-C), which is similar to F-PU-S except for the pendant anionic groups (carboxylate instead of sulfate), also fails to exhibit any antiviral activity against SV, confirming the essential role of the chain folding as well as the pendant sulfate groups for the fusion-induced antiviral activity of F-PU-S, which provides an important structural guideline for developing new antiviral polymers.

Bioactive Aurones, Indanones, and Other Hemiindigoid Scaffolds: Medicinal Chemistry and Photopharmacology Perspectives.

Hemiindigoids comprise a range of natural and synthetic scaffolds that share the same aromatic hydrocarbon backbone as well as promising biological and optical properties. The encouraging therapeutic potential of these scaffolds has been unraveled by many studies over the past years and uncovered representants with inspiring pharmacophoric features such as the acetylcholinesterase inhibitor donezepil and the tubulin polymerization inhibitor indanocine. In this review, we summarize the last advances in the medicinal potential of hemiindigoids, with a special attention to molecular design, structure-activity relationship, ligand-target interactions, and mechanistic explanations covering their effects. As their strong fluorogenic potential and photoswitch behavior recently started to be highlighted and explored in biology, giving rise to the development of novel fluorescent probes and photopharmacological agents, we also discuss these properties in a medicinal chemistry perspective.

Facile biosynthesis of taxadiene by a newly constructed Escherichia coli strain fusing enzymes taxadiene synthase and geranylgeranyl pyrophosphate synthase

Taxadiene has received extensive attention as the hydrocarbon backbone of a well-known anti-cancer drug, Paclitaxel. In this study, a de novo pathway for taxadiene biosynthesis from cheap carbon sources was newly constructed using Escherichia coli BL21 (DE3) as a chassis cell. The total biosynthesis pathway of taxadiene was divided into upstream and downstream modules for respective optimization. To facilitate the cyclization of the diterpene substrate geranylgeranyl pyrophosphate, two of the key downstream module enzymes, taxadiene synthase and geranylgeranyl pyrophosphate synthase, were genetically expressed in the form of fusion protein. After a series of optimization, the best recombinant strain, designated as E. coli strain ECU5008, achieved a titer of 93.5 mg/L taxadiene in shake flask cultivation. In addition, a commercially available macroporous adsorption resin was employed for the extraction and purification of taxadiene, in which each gram of resin Hz-816 could adsorb about 13.2 mg of taxadiene from the methanol extract of the cultured E. coli cells. The application of macroporous adsorption resin effecctively improved the isolation yield of taxadiene from fermentation broth. Availability data and materialsAll data generated or analyzed during this study are included in this article and its Supplementary information file.

How differences in the molecular structure of monohydroxy alcohols affect the tendency to crystallization

The tendency to crystallize was studied in the selected monohydroxy alcohols: 1-chloro-2-methyl-2-propanol, 1-chloro-2-propanol, 3-chloro-1-propanol, and 8-chloro-1-octanol. Performed calorimetric measurements have proved that the differences in structures of tested alcohols influence the tendency to crystallization. At a sufficiently fast heating rate, no crystallization was observed in the case of 1-chloro-2-propanol and 3-chloro-1-propanol, contrary to other two alcohols. The obtained results suggest that elongation of the alkyl chain or adding a methyl group to the hydrocarbon backbone increases the susceptibility to crystallization.

Theoretical Study on the Gas‐Phase Oxidation Mechanism of Ethylene by Nitrous Oxide

AbstractThe application of nitrous oxide (N2O) as a candidate oxidant provides a new opportunity for green propellants and propulsion systems. In this study, reaction paths are calculated by the DFT method in the B3LYP/6‐31++G** approximation for direct oxidation of ethylene with nitrous oxide. The results indicate that the reaction between N2O and C2H4 proceeds by a chain reaction mechanism. The reaction prefers the mechanism including 1,3‐dipolar cycloaddition of N2O to the double bond with the formation of unstable 4,5‐dihydro‐[1,2,3] oxadiazole intermediate via a transition state with an activation energy barrier of 102.54 kJ/mol, which is far below than that of N2O or C2H4 decomposition. Subsequently, the next step is the decomposition of these intermediates through hydrogen transfer within the hydrocarbon backbone and the formation of the final products.

The molecular mechanism of constructive remodeling of a mechanically-loaded polymer

Large or repeated mechanical loads usually degrade polymers by accelerating fragmentation of their backbones but rarely, they can cause new backbone bonds to form. When these new bonds form faster than the original bonds break, mechanical degradation may be arrested or reversed in real time. Exploiting such constructive remodeling has proven challenging because we lack an understanding of the competition between bond-forming and bond-breaking reactions in mechanically-stressed polymers. Here we report the molecular mechanism and analysis of constructive remodeling driven by the macroradical products of mechanochemical fragmentation of a hydrocarbon backbone. By studying the changing compositions of a random copolymer of styrene and butadiene sheared at 10 °C in the presence of different additives we developed an approach to characterizing this growth/fracture competition, which is generalizable to other underlying chemistries. Our results demonstrate that constructive remodeling is achievable under practically relevant conditions, requires neither complex chemistries, elaborate macromolecular architectures or free monomers, and is amenable to detailed mechanistic interrogation and simulation. These findings constitute a quantitative framework for systematic studies of polymers capable of autonomously counteracting mechanical degradation at the molecular level.

Solid-State Pathway Control via Reaction-Directing Heteroatoms: Ordered Pyridazine Nanothreads through Selective Cycloaddition.

Nanothreads are one-dimensional nanomaterials composed of a primarily sp3 hydrocarbon backbone, typically formed through the compression of small molecules to high pressures. Although nanothreads have been synthesized from a range of precursors, controlling reaction pathways to produce atomically precise materials remains a difficult challenge. Here, we show how heteroatoms within precursors can serve as "thread-directing" groups by selecting for specific cycloaddition reaction pathways. By using a less-reactive diazine group within a six-membered aromatic ring, we successfully predict and synthesize the first carbon nanothread material derived from pyridazine (1,2-diazine, C4H4N2). Compared with previous nanothreads, the synthesized polypyridazine, shows a predominantly uniform chemical structure with exceptional long-range order, allowing for structural characterization using vibrational spectroscopy and X-ray diffraction. The results demonstrate how thread-directing groups can be used for reaction pathway control and the formation of chemically precise nanothreads with a high degree of structural order.