Bio-Inspired Photosensory Artificial Synapse Based on Functionalized Tellurium Multiropes for Neuromorphic Computing

Nanomaterials like graphene and transition metal dichalcogenides are being explored for developing artificial photosensory synapses with low-power optical plasticity and high retention time for practical nervous system implementation. However, few studies are conducted on Tellurium (Te)-based nanomaterials due to their direct and small bandgaps. This paper reports the superior photo-synaptic properties of covalently bonded Tellurium sulfur oxide (TeSOx) and Tellurium selenium oxide (TeSeOx)nanomaterials, which are fabricated by incorporating S and Se atoms on the surface of Te multiropes using vapor deposition. Unlike pure Te multiropes, the TeSOx and TeSeOx multiropes exhibit controllable temporal dynamics under optical stimulation. For example, the TeSOx multirope-based transistor displays a photosensory synaptic response to UV light (λ = 365 nm). Furthermore, the TeSeOx multirope-based transistor exhibits photosensory synaptic responses to UV-vis light (λ = 365, 565, and 660 nm), reliable electrical performance, and a combination of both photodetector and optical artificial synaptic properties with a maximum responsivity of 1500 AW-1 to 365 nm UV light. This result is among the highest reported for Te-heterostructure-based devices, enabling optical artificial synaptic applications with low voltage spikes (1 V) and low light intensity (21 µW cm-2), potentially useful for optical neuromorphic computing.

Unexpected diselenide metathesis in selenocysteine-substituted biologically active peptides

Substitution of disulfide bonds with a diselenide bonds in peptides and proteins is an often-used strategy to increase the stability of naturally occurring peptides and proteins. In this paper, diselenide metathesis between model diselenide dimer peptides, as well as that in diselenide(s)-substituted biologically active peptides, were analyzed. Surprisingly, depending on the tertiary structure of the peptides, we observed that the metathesis reaction occurs under physiological conditions even in the absence of reducing agents, light and heating.

Visible Light-Induced Templated Metathesis of Peptide-Nucleic Acid Conjugates with a Diselenide Bridge

The use of template molecules as chemical scaffolds that significantly influence the course of the reaction has recently been intensively studied. Peptide nucleic acids (PNA) are molecules that mimic natural nucleic acids. They are a promising matrix in such reactions because they possess high affinity and specificity in their interactions. The manner of PNA interaction is predictable based on sequence complementarity. Recently, we report the visible light-induced metathesis reaction in peptides containing a diselenide bond. Herein, we present an efficient and straightforward method of the visible light-driven diselenide-based metathesis of peptide-nucleic acid conjugates. Compared to a similar photochemical transformation in peptides, a significant increase in the metathesis efficiency was obtained due to the template effect.

Merging the Interfaces of Different Shape-Shifting Polymers Using Hybrid Exchange Reactions

Sophisticated shape-shifting structures and integration of advanced functions often call for different-chemistry-based polymers (such as epoxy and polyurethane) in a unified system. However, permanent cross-links pose crucial obstacles to be seamless. Here, merging interfaces via hybrid exchange reactions among different dynamic covalent bonds (including ester, urethane, thiourethane, boronic-ester, and oxime-ester linkages) is proposed, breaking the long-lasting restriction that these widely used bonds only undergo self-exchange reactions. Model compound studies are conducted to verify that hybrid exchange reactions occur. As demonstrations, different liquid crystal elastomers are tenaciously joined into coherent assemblies, with the desired biomimetic structures (e.g., flying fish containing stiff and flexible parts) and rare deformation modes (e.g., flower blooming upon both heating and cooling). Besides connecting polymers, hybrid exchange reactions also facilitate the creation of new materials through cross-fusion of different polymers. In addition to the polymers used in this work, hybrid exchange reactions can be adapted to other polymers based on similar mechanisms and beyond. Besides shape-shifting-related areas (e.g., soft robots, flexible electronics, and biomedical devices), it may also foster innovation in other fields involving general polymers, as well as promote deeper understanding of dynamic covalent chemistry.

Dynamic Covalent Hydrogels: Strong yet Dynamic

Hydrogels are crosslinked polymer networks with time-dependent mechanical response. The overall mechanical properties are correlated with the dynamics of the crosslinks. Generally, hydrogels crosslinked by permanent chemical crosslinks are strong but static, while hydrogels crosslinked by physical interactions are weak but dynamic. It is highly desirable to create synthetic hydrogels that possess strong mechanical stability yet remain dynamic for various applications, such as drug delivery cargos, tissue engineering scaffolds, and shape-memory materials. Recently, with the introduction of dynamic covalent chemistry, the seemingly conflicting mechanical properties, i.e., stability and dynamics, have been successfully combined in the same hydrogels. Dynamic covalent bonds are mechanically stable yet still capable of exchanging, dissociating, or switching in response to external stimuli, empowering the hydrogels with self-healing properties, injectability and suitability for postprocessing and additive manufacturing. Here in this review, we first summarize the common dynamic covalent bonds used in hydrogel networks based on various chemical reaction mechanisms and the mechanical strength of these bonds at the single molecule level. Next, we discuss how dynamic covalent chemistry makes hydrogel materials more dynamic from the materials perspective. Furthermore, we highlight the challenges and future perspectives of dynamic covalent hydrogels.

Advances and Challenges of Self-Healing Elastomers: A Mini Review

In the last few decades, self-healing polymeric materials have been widely investigated because they can heal the damages spontaneously and thereby prolong their service lifetime. Many ingenious synthetic procedures have been developed for fabricating self-healing polymers with high performance. This mini review provides an impressive summary of the self-healing polymers with fast self-healing speed, which exhibits an irreplaceable role in many intriguing applications, such as flexible electronics. After a brief introduction to the development of self-healing polymers, we divide the development of self-healing polymers into five stages through the perspective of their research priorities at different periods. Subsequently, we elaborated the underlying healing mechanism of polymers, including the self-healing origins, the influencing factors, and direct evidence of healing at nanoscopic level. Following this, recent advance in realizing the fast self-healing speed of polymers through physical and chemical approaches is extensively overviewed. In particular, the methodology for balancing the mechanical strength and healing ability in fast self-healing elastomers is summarized. We hope that it could afford useful information for research people in promoting the further technical development of new strategies and technologies to prepare the high performance self-healing elastomers for advanced applications.

A review on room-temperature self-healing polyurethane: synthesis, self-healing mechanism and application

Polyurethanes have been widely used in many fields due to their remarkable features such as excellent mechanical strength, good abrasion resistance, toughness, low temperature flexibility, etc. In recent years, room-temperature self-healing polyurethanes have been attracting broad and growing interest because under mild conditions, room-temperature self-healing polyurethanes can repair damages, thereby extending their lifetimes and reducing maintenance costs. In this paper, the recent advances of room-temperature self-healing polyurethanes based on dynamic covalent bonds, noncovalent bonds and combined dual or triple dynamic bonds are reviewed, focusing on their synthesis methods and self-healing mechanisms, and their mechanical properties, healing efficiency and healing time are also described in detial. In addition, the latest applications of room-temperature self-healing polyurethanes in the fields of leather coatings, photoluminescence materials, flexible electronics and biomaterials are summarized. Finally, the current challenges and future development directions of the room-temprature self-healing polyurethanes are highlighted. Overall, this review is expected to provide a valuable reference for the prosperous development of room-temperature self-healing polyurethanes.

Graphical abstract

Multicomponent Reaction of Isocyanide, Ditelluride, and Mn(III) Carboxylate: Synthesis of N-Acyl Tellurocarbamate

A multicomponent reaction of isocyanides, ditellurides and manganese(III) carboxylates under mild reaction conditions leads to the synthesis of various N-acyl tellurocarbamates. This method demonstrates good functional tolerance and broad substrate scope and, as a result, is especially suitable for the postfunctionalization of complicated molecules such as drugs. The given method can be further extended to the synthesis of selenocarbamates.

Copper-Selenocysteine Quantum Dots for NIR-II Photothermally Enhanced Chemodynamic Therapy

Chemodynamic therapy has been appealing for effective cancer treatment. Particularly, Fenton-like reactions catalyzed by Cu²⁺-based nanoparticles showed promising prospects. Herein, we fabricated copper-selenocysteine quantum dots (Cu-Sec QDs) with the majority of Cu⁺ by a facile and robust thermal titration process. No high temperature or pressure is needed for this synthetic route of QDs. The selenocysteine functioned as the reducing agent as well as the stabilizer, circumventing the poor water solubility and stability, leading to enhanced biocompatibility. The existence of Cu⁺ endowed the QDs the ability to catalyze the Fenton-like reaction without an extra reduction reaction of Cu²⁺ to Cu⁺. Moreover, the strong absorption in the near-infrared-II region (1000-1300 nm) of the final Cu-Sec QDs is in great favor of the chemodynamic therapy via the photothermally enhanced Fenton-like reaction. And the Cu-Sec QDs exhibited obvious cytotoxicity to various cancer cell lines. We believe that this facile and robust synthetic approach could open up another method for the fabrication of quantum dots toward the potential Fenton-like reaction-based applications in biological fields.

Heterometathesis of diphosphanes (R2P–PR2) with dichalcogenides (R'E–ER', E = O, S, Se, Te)

The reactions of R2P–PR2 with R'E–ER', (where E = Se, S, O, Te) to give R2P–ER' have been explored experimentally and computationally. The reaction of Ph2P–PPh2 with PhSe–SePh gives Ph2P–SePh...

Disulfide metathesis via sulfur⋯iodine interaction and photoswitchability

The idea of constitutional dynamic chemistry (CDC) and dynamic combinatorial chemistry (DCC) is widespread in the literature using the chemistry of disulfides. The synthesis of unsymmetrical diaryl disulfides is challenging due to the presence of a weak S-S bond. We report herein the synthesis of unsymmetrical diaryl disulfides from two symmetrical disulfides via a cross-metathesis reaction which was controlled by a weak sulfur⋯iodine (S⋯I) interaction. The unsymmetrical disulfides were stable in acetonitrile solution in the presence of N-iodosuccinimide (NIS), and found to be reversibly photoswitchable to the symmetrical disulfides under visible light irradiation.

Recent developments in selenium-containing polymeric micelles: prospective stimuli, drug-release behaviors, and intrinsic anticancer activity

Selenium is capable of forming a dynamic covalent bond with itself and other elements and can undergo metathesis and regeneration reactions under optimum conditions. Its dynamic nature endows selenium-containing polymers with striking sensitivity towards some environmental alterations. In the past decade, several selenium-containing polymers were synthesized and used for the preparation of oxidation-, reduction-, and radiation-responsive nanocarriers. Recently, thioredoxin reductase, sonication, and osmotic pressure triggered the cleavage of Se-Se bonds and swelling or disassembly of nanostructures. Moreover, some selenium-containing nanocarriers form oxidation products such as seleninic acids and acrylates with inherent anticancer activities. Thus, selenium-containing polymers hold promise for the fabrication of ultrasensitive and multifunctional nanocarriers of radiotherapeutic, chemotherapeutic, and immunotherapeutic significance. Herein, we discuss the most recent developments in selenium-containing polymeric micelles in light of their architecture, multiple stimuli-responsive properties, emerging immunomodulatory activities, and future perspectives in the delivery and controlled release of anticancer agents.

Radical-initiated P,P-metathesis reactions of diphosphanes: evidence from experimental and computational studies

By combining the diphosphanes Ar2P-PAr2, where Ar = C6H5, 4-C6H4Me, 4-C6H4OMe, 3,5-C6H3(CF3)2, it has been shown that P,P-metathesis generally occurs rapidly under ambient conditions. DFT calculations have shown that the stability of unsymmetrical diphosphanes Z2P-PZ'2 is a function of the difference between the Z and Z' substituents in terms of size and electronegativity. Of the mechanisms that were calculated for the P,P-metathesis, the most likely was considered to be one involving Ar2P˙ radicals. The observations that photolysis increases the rate of the P,P-metatheses and TEMPO inhibits it, are consistent with a radical chain process. The P,P-metathesis reactions that involve (o-Tol)2P-P(o-Tol)2 are anomalously slow and, in the absence of photolysis, were only observed to take place in CHCl3 and CH2Cl2. The role of the chlorinated solvent is ascribed to the formation of Ar2PCl which catalyses the P,P-metathesis. The slow kinetics observed with (o-Tol)2P-P(o-Tol)2 is tentatively attributed to the o-CH3 groups quenching the (o-Tol)2P˙ radicals or inhibiting the metathesis reaction sterically.

Photoresponsive dynamic covalent bond based on addition–fragmentation chain transfer of allyl selenides

A new dynamic covalent bond allyl selenide that can undergo a reversible addition–fragmentation chain transfer reaction under ultraviolet irradiation.

Fabrication of Core Crosslinked Polymeric Micelles as Nanocarriers for Doxorubicin Delivery: Self-Assembly, In Situ Diselenide Metathesis and Redox-Responsive Drug Release

Polymeric micelles (PMs) have been used to improve the poor aqueous solubility, slow absorption and non-selective biodistribution of chemotherapeutic agents (CAs), albeit, they suffer from disassembly and premature release of payloads in the bloodstream. To alleviate the thermodynamic instability of PMs, different core crosslinking approaches were employed. Herein, we synthesized the poly(ethylene oxide)-b-poly((2-aminoethyl)diselanyl)ethyl l-aspartamide)-b-polycaprolactone (mPEG-P(LA-DSeDEA)-PCL) copolymer which self-assembled into monodispersed nanoscale, 156.57 ± 4.42 nm, core crosslinked micelles (CCMs) through visible light-induced diselenide metathesis reaction between the pendant selenocystamine moieties. The CCMs demonstrated desirable doxorubicin (DOX)-loading content (7.31%) and encapsulation efficiency (42.73%). Both blank and DOX-loaded CCMs (DOX@CCMs) established appreciable colloidal stability in the presence of bovine serum albumin (BSA). The DOX@CCMs showed redox-responsive drug releasing behavior when treated with 5 and 10 mM reduced glutathione (GSH) and 0.1% H2O2. Unlike the DOX-loaded non-crosslinked micelles (DOX@NCMs) which exhibited initial burst release, DOX@CCMs demonstrated a sustained release profile in vitro where 71.7% of the encapsulated DOX was released within 72 h. In addition, the in vitro fluorescent microscope images and flow cytometry analysis confirmed the efficient cellular internalization of DOX@CCMs. The in vitro cytotoxicity test on HaCaT, MDCK, and HeLa cell lines reiterated the cytocompatibility (≥82% cell viability) of the mPEG-P(LA-DSeDEA)-PCL copolymer and DOX@CCMs selectively inhibit the viabilities of 48.85% of HeLa cells as compared to 15.75% of HaCaT and 7.85% of MDCK cells at a maximum dose of 10 µg/mL. Overall, all these appealing attributes make CCMs desirable as nanocarriers for the delivery and controlled release of DOX in tumor cells.

Tunable Structural Color Patterns Based on the Visible-Light-Responsive Dynamic Diselenide Metathesis

Structural color materials with reversible stimuli-responsiveness to external environment have been widely used in sensors, encryption, display, and other fields. Compared with other stimuli, visible light is highly controllable both temporally and spatially with less damage to materials, which is more suitable for structural color patterning. Herein, a new diselenide-containing shape memory material is prepared and used for creating patterns via visible light stimulus. In this system, the structural color originates from birefringence of stretched materials, whose shapes can be fixed while maintaining the mechanical stress. The fixed stress can be released by diselenide metathesis under visible light irradiation. By regulating the wavelength or irradiation time with a commercial projector, the pattern with tunable structural colors is realized and the structural color pattern can be erased and rewritten arbitrarily. During the patterning process, the optical signal is first stored as mechanical signal and then transformed back to optical signal. It is a new method for preparing visible-light-responsive structural color material and has great potential in display devices, anticounterfeiting labels, and data storage.

Wavelength-Controlled Light-Responsive Polymer Vesicle Based on Se-S Dynamic Chemistry

Wavelength-controlled Se-S dynamic chemistry was put forward recently as a convenient way to regulate the balance of a selenide sulfide exchange reaction. In this paper, we synthesized an asymmetric polymeric amphiphile linked with a Se-S bond and then induced it to self-assemble into vesicles in water. When the visible light was applied to the assembly solution with addition of toluene, Se-S bonds containing vesicles were ruptured. Thus, the wavelength-controlled light responses of relatively stable polymer assembly were accomplished by introduction of the Se-S dynamic covalent bond, and the response mechanism of the Se-S bond in the vesicle was explored by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and X-ray photoelectron spectroscopy (XPS). The results indicated that fracture of the Se-S bond led to the dissociation of assembly. Introduction of Se-S dynamic chemistry into the molecular assembly area enriched the light-responsive polymer systems and would bring many potential applications in the future.

Achieving Fast Self-Healing and Reprocessing of Supertough Water-Dispersed "Living" Supramolecular Polymers Containing Dynamic Ditelluride Bonds under Visible Light

It is very challenging to achieve polymers that are mechanically robust and fast self-healable at ambient conditions, which are highly desirable for smart materials of the next-generation. Herein, combining dynamic ditelluride bonds and 2-ureido-4[1H]-pyrimidinone (UPy) moieties in the main chains, a novel type of visible-light-induced self-healing water-dispersed supramolecular polymers (DTe-WSPs) with outstanding healing properties were developed. The prepared DTe-WSPs emulsions showed excellent emulsion stability, and highly transparent DTe-WSPs films obtained from these emulsions exhibited much improved mechanical properties and fast recoverability after the incorporation of UPy groups, owing to the physical cross-links formed by quadruple hydrogen-bonded UPy moieties. Supertoughness (105.2 MJ m^-3) and fast self-healability under visible light (healing efficiency of 85.6% within 10 min) could be achieved simultaneously with the adjustment of the ditelluride content and the UPy content, and the toughness of our polymers is higher than those of the reported ambient temperature self-healable polymers. The visible-light-induced ditelluride metathesis is a predominant factor in the healing process of DTe-WSPs, and the ditelluride metathesis triggered by photothermy and hydrogen bonding could also afford the ultimate healing result. Meanwhile, DTe-WSPs can be reprocessed using visible light, providing a facile way to process polymers at mild conditions. To our surprise, the "living" DTe-WSPs exhibited the ability to initiate the polymerization of vinyl monomers under visible light, which is first reported for water-dispersed self-healing polymers. We considered the elaborated design philosophy, based on the readily available, clean, safe, and easily manipulated visible light, which can not only provide inspiration for preparing fast ambient temperature self-healing and reprocessing polymer materials with robust mechanical properties but also develop a new macroinitiator to initiate the ambient temperature polymerization of vinyl monomers.

A photochemical transformation of cyclic peptides leading to formation of selenolanthionine bridges

Peptides with diselenide bridge under UV irradiation eliminate one selenium atom forming selenoether bond with good yield.

Organoselenium chemistry-based polymer synthesis

Novel synthesis of selenium containing polymers with pre-determined structures and applications thereof.

The molecular mechanisms underlying mussel adhesion

Marine mussels are able to firmly affix on various wet surfaces by the overproduction of special mussel foot proteins (mfps). Abundant fundamental studies have been conducted to understand the molecular basis of mussel adhesion, where the catecholic amino acid, l-3,4-dihydroxyphenylalanine (DOPA) has been found to play the major role. These studies continue to inspire the engineering of novel adhesives and coatings with improved underwater performances. Despite the fact that the recent advances of adhesives and coatings inspired by mussel adhesive proteins have been intensively reviewed in literature, the fundamental biochemical and biophysical studies on the origin of the strong and versatile wet adhesion have not been fully covered. In this review, we show how the force measurements at the molecular level by surface force apparatus (SFA) and single molecule atomic force microscopy (AFM) can be used to reveal the direct link between DOPA and the wet adhesion strength of mussel proteins. We highlight a few important technical details that are critical to the successful experimental design. We also summarize many new insights going beyond DOPA adhesion, such as the surface environment and protein sequence dependent synergistic and cooperative binding. We also provide a perspective on a few uncharted but outstanding questions for future studies. A comprehensive understanding on mussel adhesion will be beneficial to the design of novel synthetic wet adhesives for various biomedical applications.

Light-Driven Diselenide Metathesis in Peptides

Peptides containing selenocysteine moieties are susceptible to non-catalytic reactions of diselenide bonds metathesis induced by visible light. In contrast to previously reported radical metathesis of disulfide bridges in cysteine derivatives, this newly developed reaction is fast and clean, and proceeds without decomposition of peptides and without formation of side products. The diselenide bond in peptides was reported in literature to be more stable than the disulfide one and also less susceptible to metathesis induced by thiols and reducing reagents. We demonstrated that visible light induces fast metathesis of Se-Se bonds in peptides. This reaction is important for the folding of peptides containing selenocysteine residues and may find application in designing dynamic combinatorial libraries of peptides responsive to external influence.