Novel functions emerge from novel structures. To develop efficient catalytic systems for challenging chemical transformations, chemists often seek inspirations from enzymatic catalysis. A large ...number of iron complexes supported by nitrogen‐rich multidentate ligands have thus been developed to mimic oxo‐transfer reactivity of dioxygen‐activating metalloenzymes. Such efforts have significantly advanced our understanding of the reaction mechanisms by trapping key intermediates and elucidating their geometric and electronic properties. Critical to the success of this biomimetic approach is the design and synthesis of elaborate ligand systems to balance the thermodynamic stability, structural adaptability, and chemical reactivity. In this Concept article, representative design strategies for biomimetic atom‐transfer chemistry are discussed from the perspectives of “ligand builders”. Emphasis is placed on how the primary coordination sphere is constructed, and how it can be elaborated further by rational design for desired functions.
Designer ligands for biomimetic chemistry: A judicious combination of donor atoms, ligand denticity, and backbone topology dictates the stereochemistry and reactivity of iron complexes to mimic non‐heme enzymes, which reductively activate dioxygen to catalyze oxidative transformations of organic molecules.
Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust ...tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m
) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.
Abstract
Mechanically tough and self-healable polymeric materials have found widespread applications in a sustainable future. However, coherent strategies for mechanically tough self-healing polymers ...are still lacking due to a trade-off relationship between mechanical robustness and viscoelasticity. Here, we disclose a toughening strategy for self-healing elastomers crosslinked by metal–ligand coordination. Emphasis was placed on the effects of counter anions on the dynamic mechanical behaviors of polymer networks. As the coordinating ability of the counter anion increases, the binding of the anion leads to slower dynamics, thus limiting the stretchability and increasing the stiffness. Additionally, multimodal anions that can have diverse coordination modes provide unexpected dynamicity. By simply mixing multimodal and non-coordinating anions, we found a significant synergistic effect on mechanical toughness ( > 3 fold) and self-healing efficiency, which provides new insights into the design of coordination-based tough self-healing polymers.
Hydrogen bonding-assisted polarization is an effective strategy to promote bond-making and bond-breaking chemical reactions. Taking inspiration from the catalytic triad of serine protease active ...sites, we have devised a conformationally well-defined benzimidazole platform that can be systematically functionalized to install multiple hydrogen bonding donor (HBD) and acceptor (HBA) pairs in a serial fashion. We found that an increasing number of interdependent and mutually reinforcing HBD-HBA contacts facilitate the bond-forming reaction of a fluorescence-quenching aldehyde group with the cyanide ion, while suppressing the undesired Brønsted acid-base reaction. The most advanced system, evolved through iterative rule-finding studies, reacts rapidly and selectively with CN
−
to produce a large (>180-fold) enhancement in the fluorescence intensity at
λ
max
= 450 nm.
Biomimetic cascade hydrogen bonds promote covalent capture of a nucleophile by polarizing the electrophilic reaction site, while suppressing non-productive acid-base chemistry as the competing reaction pathway.
Enzymes have evolved over billions of years to meet specific functional demands. The extraordinary efficiency and selectivity of such biological catalysts continue to inspire the design and synthesis ...of their small‐molecule surrogates. In the relatively short history of synthetic bioinorganic chemistry, designer ligands have also been evolved from simple classical Werner‐type ligands. As an illustrative example that showcases the design thought process, in their Concept article on page 5916 ff., H. Park and D. Lee build “taxonomic trees” for the synthetic mimics of O2‐activating non‐heme iron enzymes. Primary emphasis is placed on how the combination of ligand donor groups, denticity, and backbone topology collectively dictate the coordination chemistry of the metal center of immediate relevance to the oxidation/oxygenation reactivity.
An elastic printed circuit board (E-PCB) is a conductive framework used for the facile assembly of system-level stretchable electronics. E-PCBs require elastic conductors that have high conductivity, ...high stretchability, tough adhesion to various components, and imperceptible resistance changes even under large strain. We present a liquid metal particle network (LMP
) assembled by applying an acoustic field to a solid-state insulating liquid metal particle composite as the elastic conductor. The LMP
conductor satisfies all the aforementioned requirements and enables the fabrication of a multilayered high-density E-PCB, in which numerous electronic components are intimately integrated to create highly stretchable skin electronics. Furthermore, we could generate the LMP
in various polymer matrices, including hydrogels, self-healing elastomers, and photoresists, thus showing their potential for use in soft electronics.
Modulating lithium metal deposition is vital for the realization of stable and energy‐dense Li–metal batteries. Ionic liquid (IL) has been regarded as a promising electrolyte additive for a uniform ...Li deposition because its cation moiety forms a lithiophobic protective layer on Li protuberant tips. Despite recent advances in ILs for Li metal batteries, rational designs for IL additives are still in their infancy, and further improvement is required. Here, a new class of self‐assembled protective layer based on the design of a new IL molecule enabling high‐performance Li–metal batteries is reported. For the first time, symmetric design of lithiophobic side chains is introduced to the IL cations. This symmetric design creates a self‐assembled lithiophobic protective layer on Li protuberant tips, resulting in the smooth deposition of Li. Thus, the symmetric IL enables stable cycling of Li–LiFePO4 and Li–LiNi0.6Co0.2Mn0.2O2 (NCM622) batteries with an average Coulombic efficiency of ≈99.8% over 600 cycles. In addition, the symmetric IL enables a practical thin Li (40 µm)‐NCM622 cell with an energy density of ≈658 Wh kg‐1 based on the cathode mass in a coin‐type battery. This work proposes a design protocol for IL‐based additives and provides a prospective way to highly efficient, long‐lasting Li–metal batteries.
A novel ionic liquid (IL) modified by symmetric alkyl chains is employed as an electrolyte additive to control Li deposition. The symmetric alkyl chains to IL cation mitigate the self‐agglomeration and create a densely assembled lithiophobic layer on protuberance tips. This compact protection layer formed by symmetric ILs effectively controls the smooth Li deposits, enabling long‐lasting, practical, and full‐cell batteries.
Achieving a circular plastics economy is one of our greatest environmental challenges, yet conventional mechanical recycling remains inadequate for thermoplastics and incompatible with thermosets. ...The next generation of plastic materials will be designed with the capacity for degradation and recycling at end-of-use. To address this opportunity in the burgeoning technologies of 3D printing and photolithography, we report a modular system for the production of degradable and recyclable thermosets
via
photopolymerization. The polyurethane backbone imparts robust, elastic, and tunable mechanical properties, while the use of hemiacetal ester linkages allows for facile degradation under mild acid. The synthetic design based on hemiacetal esters enables simple purification to regenerate a functional polyurethane diol.
We develop a platform for recyclable polyurethane-based thermosets fabricated by photopolymerization. Tunable mechanical properties and 3D printing are demonstrated, with mild acid-catalyzed degradation enabled by hemiacetal linkages.
Abstract Dielectric elastomer actuators (DEAs) offer versatile applications including haptics, soft robotics and smart lenses. However, due to the lack of conductive electrodes with low modulus and ...high stretchability, their use is limited by nonsolid electrodes, hindering integration with other systems. In this study, transparent and patternable solid electrodes, achieving actuation performance comparable to a commonly used non‐solid counterpart (e.g., carbon grease), with a stretchable and patternable conducting polymer composed of PEDOT:PSS and PEG‐PPG‐PEG diacrylate (P123DA) are reported. Varying the ratio of P123DA to PEDOT:PSS enables optimization of electrical and mechanical properties to achieve compliant solid electrodes in static and dynamic actuation. The ratio of P123DA to PEDOT:PSS is found to impact PEDOT:PSS nanofiber formation and the associated electrical and mechanical properties. Moreover, the resulting P123DA/PEDOT:PSS‐based solid electrode shows excellent optical transmittance exceeding 95%. This work highlights the potential of tuning different solid electrode properties to realize transparent, patternable, and stretchable solid electrodes, enhancing their applicability in diverse fields.
Achieving a circular plastics economy is one of our greatest environmental challenges, yet conventional mechanical recycling remains inadequate for thermoplastics and incompatible with thermosets. ...The next generation of plastic materials will be designed with the capacity for degradation and recycling at end-of-use. To address this opportunity in the burgeoning technologies of 3D printing and photolithography, we report a modular system for the production of degradable and recyclable thermosets via photopolymerization. The polyurethane backbone imparts robust, elastic, and tunable mechanical properties, while the use of hemiacetal ester linkages allows for facile degradation under mild acid. The synthetic design based on hemiacetal esters enables simple purification to regenerate a functional polyurethane diol.
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