Reversible Chemistry Research Articles

Multilevel Dynamic System as Molecular Morning-After Timer.

Systems chemistry aims to develop molecular systems that display emerging properties arising from their network and absent in their individual constituents. Employing reversible chemistry under thermodynamic control represents a valuable tool for generating dynamic combinatorial libraries of interconverting molecules, which may exhibit intriguing collective behaviour. A simple dynamic combinatorial library was prepared using dithioacetal / thiol / disulfide exchanges. Because of the relative reactivities of these reversible reactions, the library constitutes a two-layer dynamic system with one layer active in an acid medium (thiol/dithioacetal exchange) and one layer active in a basic medium (thiol/disulfide exchange). This property enables the system to respond to momentary changes in acidity of the medium by activating different network regions, channeling some building blocks from one layer to another through shared thiol reagents (nodes). This momentaneous change in wiring affects the final steady state composition of the library, measured the next day, even though the event that caused it vanishes without leaving any residue. Therefore, the final composition of this dynamic system provides information about this transient past perturbation in the environment such as: when it occurred, how long it was, or how intense it was.

Healable Supracolloidal Nanocomposite Water-Borne Coatings.

Water-borne coatings often contain nanofillers to enhance their mechanical or optical properties. The aggregation of these fillers may, however, lead to undesired effects such as brittle and opaque coatings, reducing their performance and lifetime. By controlling the distribution and structural arrangement of the nanofillers in the coatings and inserting reversible chemical bonds, both the elasticity and strength of the coatings may be effectively improved, while healing properties, via the reversible chemistry, extend the coating's lifetime. Aqueous dispersions of polymer-core/silica-corona supracolloidal particles were used to prepare water-borne coatings. Polymer and silica nanoparticles were prefunctionalized with thiol/disulfide groups during the supracolloid assembly. Disulfide bridges were further established between a cross-linker and the supracolloids during drying and coating formation. The supracolloidal nanocomposite coatings were submitted to intentional (physical) damages, i.e., blunt and sharp surface scratches or cut through into two pieces, and subsequently UV irradiated to induce the recovery of the damage(s). The viscoelasticity and healing properties of the coatings were examined by dynamic, static, and surface mechanical analyses. The nanocomposite coatings showed a great extent of interfacial restoration of cut damage and surface scratches. The healing properties are strongly related to the coating's viscoelasticity and interfacial (re)activation of the disulfide bridges. Nanocomposite coatings with silica concentrations below their critical volume fraction show higher in situ healing efficiency, as compared to coatings with higher silica concentration. This work provides insights into the control of nanofillers distribution in water-borne coatings and strategies to increase the coating lifetime via mechanical damage recovery.

Thermoreversible [2 + 2] Photodimers of Monothiomaleimides and Intrinsically Recyclable Covalent Networks Thereof.

The development of intrinsically recyclable cross-linked materials remains challenged by the inherently unfavorable chemical equilibrium that dictates the efficiency of the reversible covalent bonding/debonding chemistry. Rather than having to (externally) manipulate the bonding equilibrium, we here introduce a new reversible chemistry platform based on monosubstituted thiomaleimides that can undergo complete and independent light-activated covalent bonding and on-demand thermal debonding above 120 °C. Specifically, repeated bonding/debonding of a small-molecule thiomaleimide [2 + 2] photodimer is demonstrated over five heat/light cycles with full conversion in both directions, thereby regenerating its initial monothiomaleimide constituents. This motivated the synthesis of multifunctional thiomaleimide reagents as precursors for the design of covalently cross-linked networks that display intrinsic switching between a monomeric and polymeric state. The resulting materials are shown to covalently dissociate and depolymerize upon heating both in solution and in bulk, thus transforming the densely photo-cross-linked material back into a viscous liquid. Temperature-regulated photorheology evidenced the intrinsic recyclability of the thiomaleimide-based thermosets during multiple cycles of UV cross-linking and thermal de-cross-linking. The thermally reversible photodimerization of thiomaleimides presents a new addition to the designer playground of dynamic polymer networks, providing interesting opportunities for the reprocessing and closed-loop recycling of covalently cross-linked materials.

A review on realizing rechargeable batteries based on SOCl2/SO2 electrolyte systems

AbstractAs representative high‐energy density primary batteries, Li‐SOCl2 and Li‐SO2 batteries possess superiorities including high working potential, long temperature range, low self‐discharge rate and high safety compared with other conventional primary batteries. In spite of the high energy features, these devices have only been applied for single discharge rather than achieved energy cyclic utilization via recharge. Various modifying strategies have been put out concerning the two electrolyte systems to liberate theoretical energy storage capability as much as possible over decades. Nevertheless, reversible chemistry is also urgently required nowadays for these sulfur‐based electrolyte primary batteries to achieve transformation and upgrading. In the review, we collect some of the modification works for Li‐SOCl2 and Li‐SO2 primary batteries since their invention and successively introduce some of the opening research studies of secondary batteries, designed technologies of which are demonstrated through aspects through anode interface, cathode materials, and electrolyte composition. Finally, it is aiming to look further into the future development of the reversibility of the unique electrolyte systems.

Use of covalent dynamic networks as binders on epoxy‐based carbon fiber composites: Effect on properties, processing, and recyclability

AbstractComposites are gaining widespread market interest due to their outstanding mechanical properties and light weight. However, this growth is hindered by the lack of sustainable recycling solutions. This research aims to integrate reversible chemistries to advanced carbon fiber‐reinforced composite materials for recycling in a so‐called eco‐design, circular approach. Diene and dienophile reactions are generated at the surface of the carbon fiber allowing a bond–debond interaction with the epoxy matrix. The application of the Diels–Alder adduct on the fiber modifies its polarity and structure. This research assesses a biobased and synthetic epoxy equivalent and demonstrates that this newly developed interphase chemistry has a direct impact on the crosslinking efficiency of the resin, as well as on their interlaminar properties. Furthermore, it has been observed that depending on the type of resin, these changes can have differing impacts on final properties of the composite, reducing the crosslinking density up to 50% in some modifications while in others the Tg remains constant.

Phosphorus fluoride exchange: Multidimensional catalytic click chemistry from phosphorus connective hubs

Phosphorus Fluoride Exchange (PFEx) represents a cutting-edge advancement in catalytic click-reaction technology. Drawing inspiration from Nature's phosphate connectors, PFEx facilitates the reliable coupling of P(V)-F loaded hubs with aryl alcohols, alkyl alcohols, and amines to produce stable, multidimensional P(V)-O and P(V)-N linked products. The rate of P-F exchange is significantly enhanced by Lewis amine base catalysis, such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). PFEx substrates containing multiple P-F bonds are capable of selective, serial exchange reactions via judicious catalyst selection. In fewer than four synthetic steps, controlled projections can be deliberately incorporated along three of the four tetrahedral axes departing from the P(V) central hub, thus taking full advantage of the potential for generating three-dimensional diversity. Furthermore, late-stage functionalization of drugs and drug fragments can be achieved with the polyvalent PFEx hub, hexafluorocyclotriphosphazene (HFP), as has been demonstrated in prior research.

Synthesis of Renewable, Recyclable, Degradable Thermosets Endowed with Highly Branched Polymeric Structures and Reinforced with Carbon Fibers

This paper demonstrates the molecular design of renewable polymer thermosets that are chemically recyclable yet degradable on demand. In this design, the thermosets comprise a limonene-based highly branched polymer, which has been synthesized via the regioselective thiol–ene reaction between natural limonene and multifunctional thiol, and a Meldrum’s acid derivative for the click/declick reaction of thiol groups that are deliberately positioned on the outer surface of the branched polymer. Thus, the accessible thiols expedite the covalent bond exchange reaction and enable the formation of a network and bulk recycling of the entire network; the labile cross-linkers enable molecular degradation or repurposing of the materials under benign conditions. The thermosets can be also reinforced with the addition of carbon fibers. Thus, reversible deformation or self-lamination of the resultant carbon composites, which are degradable and recyclable, was achieved owing to the thermosets, which act as a matrix or binder. We envision that the renewable materials presented here would be advanced by introducing diverse biomolecules or reversible chemistry to develop disposable bio-based platforms that can be further upcycled at the end of their lifecycles.

Reversible adhesives and debondable joints for fibre-reinforced plastics: Characteristics, capabilities, and opportunities

Fibre reinforced polymer (FRP) materials are well established in both the wind energy and aerospace industries, with the adoption of FRPs beginning to grow significantly in the automotive sector due to their favourable mechanical and physical properties. Their increased usage, coupled with the inherent complexity of forming FRP–FRP joints, has led to an increase in adhesives as a typical joining method. However, such adhesive joints pose a challenge when undertaking repair or at end-of-life (EoL). Separating the joint to facilitate recycling of the high-value FRP can be extremely labour- and time-intensive.Therefore, the introduction of debondable and reversible technologies into conventional structural adhesives such as acrylics, epoxies and polyurethanes has begun to attract interest within academia and industry which can overcome this challenge by demonstrating reversibility. Nevertheless, such adhesives are at various stages of technology readiness. The next step in adhesive materials development aims to meet current requirements and deliver an evolutionary advantage by enabling repair (when necessary), recycling, and transition towards a circular economy for FRP materials. For example, the use of reversible chemistries such as Diels-Alder or Covalent Adaptable Networks.This comprehensive review considers the latest literature for current debonding technologies including mechanical and thermal debonding, thermally expanding microspheres, induction heating, foaming agents and chemical degradation as well as a variety of reversible chemistries that could be introduced into adhesives for potential use in FRP-FRP joints, including how such reversibility might be activated and any consequences for practical application. The aim is to give readers a deeper understanding of their properties and potential application.

Room-Temperature Liquid-Metal Coated Zn Electrode for Long Life Cycle Aqueous Rechargeable Zn-Ion Batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are potential candidates for grid-scale energy storage applications. In addition to its reversible chemistry in aqueous electrolytes, Zn metal is stable in water and air. However, there are critical challenges, such as non-uniform plating, hydrogen evolution, corrosion, and the formation of a passivation layer, which must be addressed before practical applications. In this study, the surface of Zn metal was coated with room-temperature bulk liquid-metal and liquid-metal nanoparticles to facilitate the uniform plating of Zn–ions during cycling. A simple probe ultrasonication method was used to prepare the liquid-metal nanoparticles, and a nanoparticle suspension film was formed through spin coating. At an areal capacity and current density of 0.5 mAh cm−2 and 0.5 mA cm−2, respectively, symmetric cells composed of bare Zn metal electrodes were prone to short-circuiting after ~45 h of deposition/striping cycles. However, under the same operating conditions, symmetric cells employing the room-temperature liquid-metal-coated electrodes operated stably for more than 500 h. Compared to the symmetric cell with bare Zn, the symmetric cell with the bulk liquid-metal coated electrode exhibited a significant reduction in the initial nucleation barrier, with respective values of 113.2 and 10.1 mV. Electrochemical characterization of practical full cells also showed significant improvements in the capacity and cycling performance derived from the room-temperature liquid-metal coating.

Photocycloadditions for the Design of Reversible Photopolymerizations

The quest for circular designs and ways to reuse polymer materials demands further advances in the development of reversible chemistries. Stimuli-responsive systems incorporated into polymer materials that enable the formation and cleavage of covalent bonds, hold great potential to reversibly decompose materials into their original building blocks. [2π+2π] photocycloadditions, for which the addition and reversion mechanism can be triggered by disparate wavelengths, stand as an attractive platform for triggering such controlled and reversible photoligation towards achieving renewable polymer materials. This perspective highlights the potential of this type of photochemistry to incorporate solid polymer materials and generate reversible polymerizations. The design of effective photoresponsive materials with specific functions requires the consideration of a number of parameters. Following a bottom-up approach – from molecular chemistry to macromolecular functionality – this perspective provides a recipe of the key aspects to consider in the design of such advanced renewable materials. Furthermore, examples of the state of the art in the field are highlighted and an overview of the fundamental challenges that remain is provided. Finally, an outlook on the next frontiers to cross is proposed.

Eugenol-derived Organic Liquids as an In-Situ CO2 Capturing and Conversion System for Eugenol-based Polycarbonate Synthesis.

The significant development of catalytic biomass conversion has provided a large library of chemicals ready for subsequent upgrading to polymerisable monomers for the design and preparation of sustainable polymers. In this study, hydroxyethylation of eugenol by using green ethylene carbonate as alkylation reagent and cheap tetrabutylammonium iodide ionic liquids as green solvents and catalysts produced 2-(4-allyl-2-methoxyphenoxy)ethan-1-ol with a 85% yield, which could be used to construct an in situ CO2 capture and conversion system by taking the reversible chemistry of alcoholic compounds with CO2 in the presence of superbases, on which α,ω-diene functionalized carbonate monomers were successfully prepared and were applied in thiol-ene click and acyclic diene metathesis polymerisation (ADMET), producing a series of poly(thioether carbonate)s and unsaturated aromatic aliphatic polycarbonates with moderate molecular weights and satisfactory thermal properties. The structures of the formed CO2 reversible ILs, the polymerisable monomers and the corresponding polymers were fully characterized by various technologies.

Exponential decay toward equilibrium via log convexity for a degenerate reaction-diffusion system

We consider a system of two reaction-diffusion equations coming out of reversible chemistry. When the reaction happens on the totality of the domain, it is known that exponential convergence to equilibrium holds (with explicit rate). We show in this paper that this exponential convergence also holds when the reaction happens only on a given open set of a ball, thanks to an observation estimate deduced by logarithmic convexity.

Self-Healing Injectable Hydrogels for Tissue Regeneration.

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

Low-Cost and Sustainable Direct Recycling of Battery Materials

The development of next-generation energy storage devices and systems for electric vehicles (EVs) relies on materials with significantly improved performance and lower cost. The increasing amount of lithium-ion battery (LIBs) consumption will result in the resource shortage and price increase of lithium and precious transition metals (Co, Ni etc.) that are critical for making high-performance LIBs. Also, future batteries that mainly use low-cost materials (Na, Fe, Mn) will have limited economic benefits to recycle even though the wastes generated from disposal of used batteries can cause severe environment pollution. In this context, design of low-cost and energy-efficient recycling and regeneration process for spent batteries is attracting growing interest. From a reversible chemistry point of view, this talk will focus on a potential strategy to directly recycle and regenerate spent LIBs using a “non-destructive” approach, which will lead to new electrode materials that can show the same level of performance as the native materials. We will show successful recycling of various battery materials, including cathode (LiMO2, LiMn2O4, and LiFePO4) and anode (graphite) using the direct regeneration approach. Such a strategy combines fundamental understanding and process optimization for remanufacturing of energy materials. Therefore, it can potentially offer a sustainable solution for future energy storage.

Recyclable cell-surface chemical tags for repetitive cancer targeting.

Metabolic glycan labeling provides a facile yet powerful tool to install chemical tags to the cell membrane via metabolic glycoengineering processes of unnatural sugars. These cell-surface chemical tags can then mediate targeted conjugation of therapeutic agents via efficient chemistries, which has been extensively explored for cancer-targeted treatment. However, the commonly used in vivo chemistries such as azide-cyclooctyne and tetrazine-cyclooctene chemistries only allow for one-time use of cell-surface chemical tags, posing a challenge for long-term, continuous cell targeting. Here we show that cell-surface ketone groups can be recycled back to the cell membrane after covalent conjugation with hydrazide-bearing molecules, enabling repetitive targeting of hydrazide-bearing agents. Upon conjugation to ketone-labeled cancer cells via a pH-responsive hydrazone linkage, Alexa Fluor 488-hydrazide became internalized and entered endosomes/lysosomes where ketone-sugars can be released and recycled. The recycled ketone groups could then mediate targeted conjugation of Alexa Fluor 647-hydrazide. We also showed that doxorubicin-hydrazide can be targeted to ketone-labeled cancer cells for enhanced cancer cell killing. This study validates the recyclability of cell-surface chemical tags for repetitive targeting of cancer cells with the use of a reversible chemistry, which will greatly facilitate future development of potent cancer-targeted therapies based on metabolic glycan labeling.

Water-Based Dynamic Depsipeptide Chemistry: Building Block Recycling and Oligomer Distribution Control Using Hydration-Dehydration Cycles.

The high kinetic barrier to amide bond formation has historically placed narrow constraints on its utility in reversible chemistry applications. Slow kinetics has limited the use of amides for the generation of diverse combinatorial libraries and selection of target molecules. Current strategies for peptide-based dynamic chemistries require the use of nonpolar co-solvents or catalysts or the incorporation of functional groups that facilitate dynamic chemistry between peptides. In light of these limitations, we explored the use of depsipeptides: biorelevant copolymers of amino and hydroxy acids that would circumvent the challenges associated with dynamic peptide chemistry. Here, we describe a model system of N-(α-hydroxyacyl)-amino acid building blocks that reversibly polymerize to form depsipeptides when subjected to two-step evaporation–rehydration cycling under moderate conditions. The hydroxyl groups of these units allow for dynamic ester chemistry between short peptide segments through unmodified carboxyl termini. Selective recycling of building blocks is achieved by exploiting the differential hydrolytic lifetimes of depsipeptide amide and ester bonds, which we show are controllable by adjusting the solution pH, temperature, and time as well as the building blocks’ side chains. We demonstrate that the polymerization and breakdown of the depsipeptides are facilitated by cyclic morpholinedione intermediates, and further show how structural properties dictate half-lives and product oligomer distributions using multifunctional building blocks. These results establish a cyclic mode of ester-based reversible depsipeptide formation that temporally separates the polymerization and depolymerization steps for the building blocks and may have implications for prebiotic polymer chemical evolution.

Reconstructed covalent organic frameworks

Covalent organic frameworks (COFs) are distinguished from other organic polymers by their crystallinity1–3, but it remains challenging to obtain robust, highly crystalline COFs because the framework-forming reactions are poorly reversible4,5. More reversible chemistry can improve crystallinity6–9, but this typically yields COFs with poor physicochemical stability and limited application scope5. Here we report a general and scalable protocol to prepare robust, highly crystalline imine COFs, based on an unexpected framework reconstruction. In contrast to standard approaches in which monomers are initially randomly aligned, our method involves the pre-organization of monomers using a reversible and removable covalent tether, followed by confined polymerization. This reconstruction route produces reconstructed COFs with greatly enhanced crystallinity and much higher porosity by means of a simple vacuum-free synthetic procedure. The increased crystallinity in the reconstructed COFs improves charge carrier transport, leading to sacrificial photocatalytic hydrogen evolution rates of up to 27.98 mmol h−1 g−1. This nanoconfinement-assisted reconstruction strategy is a step towards programming function in organic materials through atomistic structural control.

(Invited) Leveraging Reversible Chemistry for Materials Sustainability in Energy Storage

The development of next-generation energy storage devices and systems for electric vehicles (EVs) relies on materials with significantly improved performance and lower cost. The increasing amount of lithium-ion battery (LIBs) consumption will result in the resource shortage and price increase of lithium and precious transition metals (Co, Ni etc.); the wastes generated from disposal of used batteries can cause severe environment pollution. In this context, design of energy-efficient recycling and regeneration process for spent batteries is attracting growing interest. From a reversible chemistry point of view, this talk will introduce a potential strategy to directly recycle and regenerate spent LIBs using a “non-destructive” approach, which will lead to new electrode materials that can show the same level of performance as the native materials. Such a strategy combines fundamental understanding and process optimization for remanufacturing of energy materials. Therefore, it can potentially offer a sustainable solution for future energy storage.

Preparation of De-emulsifier of Gemini Surfactant & it's Application in Oil Industry

A Gemini surfactants (GS) which are bis quaternary ammonium salt. It is prepared from tetramethyl ethylene diamine (TMEDA) with cetyl bromide, while an ordinary surfactant (OS),which is quaternary ammonium salt, is prepared from trimethyl amine (TMA) and cetyl bromide. They were identified by elemental analysis and IR spectroscopy.
 Comparing the GS,OS and the commercial surfactants, the Gemini surfactant shows an interesting properties and have a variety of uses, such as a De-emulsifier.
 Adopting the composition ratios found in the study of reverse chemistry of commercial De-emulsifier, Rp 6000, which is usually use in the south and north oil companies in Iraq. The prepares active gradients were characterized by various techniques, IR spectroscopy, elemental analysis, melting point, solubility, flash point and functional group analysis.
 
 The efficiency of the prepared De-emulsifier was examined by standard methods and compared with the efficiency of commercial Rp 6000 based on the same wet crude oil sources.

Reversible and Stable Hemiaminal Hydrogels from Polyvinylamine and Highly Reactive and Selective Bis(N-acylpiperidone)s.

Water-soluble bis(N-acylpiperidone)s with aldehyde-like reactivity are reported to react rapidly with polyvinylamine at room temperature, providing unprecedented clean reaction products. Unlike most amine/ketone reactions that result in arbitrary mixtures of imines, aminals, hemiaminals, or hydrates, in the present study hemiaminals, aminals, or hemiaminal/aminal mixtures are exclusively found. Detailed NMR spectroscopy of solutions, gels, and solids, aided by model reactions, reveals that the hemiaminal/aminal ratio depends on pH, water content, and cross-linking density. Network formation is fully reversible upon changes in pH, with the resulting moduli from rheology spanning almost 3 orders of magnitude. The self-healing ability of the system is probed by rheology as well, demonstrating maintained material properties of fractured and healed samples. The unusually clean, fast, and reversible chemistry highlights bispiperidones as a class of efficient building blocks with unprecedented possibilities in dynamic covalent chemistry.