Structurally Dynamic Gelatin-Based Hydrogels with Self-Healing, Shape Memory, and Cytocompatible Properties for 4D Printing

Three-dimensional (3D) printable hydrogels with a shape memory effect have emerged as a new class of 4D printing materials recently and found wide applications in various fields. However, synergistically endowing such materials with good mechanical strength and biocompatibility for biomedical uses remains challenging. In this study, a series of multiresponsive hydrogels have been prepared through a dynamic covalent imine/Diels-Alder network from biocompatible starting materials of modified gelatin and poly(ethylene glycol)-based polymers. By further secondary crosslinking with a hyperbranched triethoxysilane reagent (HPASi) that contains multiple supramolecular hydrogen bonding, the hydrogels presented a strengthened self-healing and temperature-responsive shape memory effect. With the additional features of superior stretchability (elongation at break up to 523%), good cytocompatibility, and 3D printable properties, these multifunctional hydrogels showed great potential for broad biomedical applications.

Using a dual-emission Sm(iii)-macrocycle as the perceptive lab-on-a-molecule chemosensor toward selective and discriminative detection of nitroaromatic explosives

A dual-emission Sm(iii)-macrocycle Sm-2l is designed as the perceptive lab-on-a-molecule toward selective and discriminative detection of nitroaromatic explosives by statistical analysis.

A Twisted Chiral Cavitand with 5-Fold Symmetry and Its Length-Selective Binding Properties

Controlling bottom-up syntheses from chiral seeds to construct architectures with specific chiralities is currently challenging. Herein, a twisted chiral cavitand with 5-fold symmetry was constructed by bottom-up synthesis using corannulene as the chiral seed and pillar[5]arene as the chiral wall. After docking between the seed and the wall, their dynamic chiralities (M and P) are fixed. Moreover, the formed hedges also exhibit M and P chirality. Through dynamic covalent bonding, the thermodynamically stable product is obtained selectively as a pair of enantiomers (MMM and PPP), where all three subcomponents, i.e., the corannulene, hedges, and pillar[5]arene, are tilted in the same direction. Furthermore, the twisted cavitand exhibits length-selective binding to alkylene dibromides, with three maximum binding constants being unexpectedly observed.

Tunable Construction of Sandwich-Type Double-[1 + 1] and Half-Folded [2 + 2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects

The first-row transition-metal ions Mn²⁺-Cu²⁺ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn²⁺-Cu²⁺ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co²⁺ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H₂pdd precursor and the [1 + 1] Cu²⁺ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H₂hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.

Influence of the solvent in the self-assembly and binding properties of [1 + 1] tetra-imine bis-calix[4]pyrrole cages

We report the self-assembly of shape-persistent [1 + 1] tetra-imine cages 1 based on two different tetra-α aryl-extended calix[4]pyrrole scaffolds in chlorinated solvents and in a 9 : 1 CDCl₃ : CD₃CN solvent mixture. We show that the use of a bis-N-oxide 4 (4,4'-dipyridyl-N,N'-dioxide) as template is not mandatory to induce the emergence of the cages but has a positive effect on the reaction yield. We use ¹H NMR spectroscopy to investigate and characterize the binding properties (kinetic and thermodynamic) of the self-assembled tetra-imine cages 1 with pyridine N-oxide derivatives. The cages form kinetically and thermodynamically stable inclusion complexes with the N-oxides. For the bis-N-oxide 4, we observe the exclusive formation of 1 : 1 complexes independently of the solvent used. In contrast, the pyridine-N-oxide 5 (mono-topic guest) produces inclusion complexes displaying solvent dependent stoichiometry. The bis-N-oxide 4 is too short to bridge the gap between the two endohedral polar binding sites of 1 by establishing eight ideal hydrogen bonding interactions. Nevertheless, the bimolecular 4⊂1 complex results as energetically favored compared to the 5₂⊂1 ternary counterpart. The inclusion of the N-oxides, 4 and 5, in the tetra-imine cages 1 is significantly faster in chlorinated solvents (minutes) than in the 9 : 1 CDCl₃ : CD₃CN solvent mixture (hours). We provide an explanation for the similar energy barriers calculated for the formation of the 4⊂1 complex using the two different ternary counterparts 5₂⊂1 and (CD₃CN)₂⊂1 as precursors. We propose a mechanism for the in-out guest exchange processes experienced by the tetra-imine cages 1.

2,5-Furandicarboxaldehyde as a bio-based crosslinking agent replacing glutaraldehyde for covalent enzyme immobilization

In the quest for a bio-based and safer substitute for glutaraldehyde, we have investigated 2,5 diformylfuran (DFF) as bifunctional crosslinking agent for the covalent immobilization of glucoamylase on amino-functionalized methacrylic resins. Immobilization experiments and systematic comparison with glutaraldehyde at four different concentrations for the activation step showed that DFF leads to comparable enzymatic activities at all tested concentrations. Continuous flow experiment confirms a similar long term stability of the immobilized formulations obtained with the two crosslinkers. The NMR study of DFF in aqueous solution evidenced a much simpler behaviour as compared to glutaraldehyde, since no enolic forms can form and only a mono-hydrated form was observed. Unlike in the case of glutaraldehyde, DFF reacts covalently with the primary amino groups via imine bond formation only. Nevertheless, the stability of the covalent immobilization was confirmed also at acidic pH (4.5), most probably because of the higher stability of the imine bonds formed with the aromatic aldehydes. In terms of toxicity DFF has the advantage of being poorly soluble in water and, more importantly, poorly volatile as compared to glutaraldehyde, which displays severe respiratory toxicity. We have performed preliminary ecotoxicity assays using Aliivibrio fischeri, a marine bacterium, evidencing comparable behaviour (below the toxicity threshold) for both dialdehydes at the tested concentrations.

Multicolor emission based on a N, N'-Disubstituted dihydrodibenzo [a, c] phenazine crown ether macrocycle

Dynamic fluorophore 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) affords a new platform to produce diverse emission outputs. In this paper, a novel DPAC-containing crown ether macrocycle D-6 is synthesized and characterized. Host-guest interactions of D-6 with different ammonium guests produced a variety of fluorescence with hypsochromic shifts up to 130 nm, which are found to be affected by choice of solvent or guest and host/guest stoichiometry. Formation of supramolecular complexes were confirmed by UV-vis titration, ¹H NMR and HRMS spectroscopy.

Mucus-Inspired Dynamic Hydrogels: Synthesis and Future Perspectives

Mucus hydrogels at biointerfaces are crucial for protecting against foreign pathogens and for the biological functions of the underlying cells. Since mucus can bind to and host both viruses and bacteria, establishing a synthetic model system that can emulate the properties and functions of native mucus and can be synthesized at large scale would revolutionize the mucus-related research that is essential for understanding the pathways of many infectious diseases. The synthesis of such biofunctional hydrogels in the laboratory is highly challenging, owing to their complex chemical compositions and the specific chemical interactions that occur throughout the gel network. In this perspective, we discuss the basic chemical structures and diverse physicochemical interactions responsible for the unique properties and functions of mucus hydrogels. We scrutinize the different approaches for preparing mucus-inspired hydrogels, with specific examples. We also discuss recent research and what it reveals about the challenges that must be addressed and the opportunities to be considered to achieve desirable de novo synthetic mucus hydrogels.

Noncooperative guest binding by metal-free [2 + 2] Schiff-base macrocycles

Salphen-based [n + n] macrocycles have been widely explored for their unique chemical and topological properties following metal ion coordination. Despite having vastly different reactivity than their coordinated counterparts, fewer studies have focused on metal-free salphen macrocycles. We investigated the binding of [2 + 2] Schiff-base macrocycle host 3, which contains a central 18-crown-6-like cavity and two N₂O₂ moieties. This macrocycle strongly binds to spherical cationic guests (K₁₁ ≈ 10³-10⁴ M^-1, DCM/MeCN). The most robust binding was shown for K⁺ and Na⁺, followed by Li⁺ and Rb⁺. More sterically demanding cationic guests like dibenzylammonium (DBA⁺) showed almost no binding. The binding pocket in 3 is slightly smaller than 18-crown-6, resulting in binding outside the cavity, which provides a scaffold appropriate for 2 : 1 complexes, where two host molecules sandwich the guest. All host-guest complexes follow a 2 : 1 noncooperative binding model, where each successive binding event is less likely than the previous, unlike coordinated versions of 3, where most binding is 1 : 1.

Isoniazid Linked to Sulfonate Esters via Hydrazone Functionality: Design, Synthesis, and Evaluation of Antitubercular Activity

Isoniazid (INH) is one of the key molecules employed in the treatment of tuberculosis (TB), the most deadly infectious disease worldwide. However, the efficacy of this cornerstone drug has seriously decreased due to emerging INH-resistant strains of Mycobacterium tuberculosis (Mtb). In the present study, we aimed to chemically tailor INH to overcome this resistance. We obtained thirteen novel compounds by linking INH to in-house synthesized sulfonate esters via a hydrazone bridge (SIH1-SIH13). Following structural characterization by FTIR, ¹H NMR, ¹³C NMR, and HRMS, all compounds were screened for their antitubercular activity against Mtb H37Rv strain and INH-resistant clinical isolates carrying katG and inhA mutations. Additionally, the cytotoxic effects of SIH1-SIH13 were assessed on three different healthy host cell lines; HEK293, IMR-90, and BEAS-2B. Based on the obtained data, the synthesized compounds appeared as attractive antimycobacterial drug candidates with low cytotoxicity. Moreover, the stability of the hydrazone moiety in the chemical structure of the final compounds was confirmed by using UV/Vis spectroscopy in both aqueous medium and DMSO. Subsequently, the compounds were tested for their inhibitory activities against enoyl acyl carrier protein reductase (InhA), the primary target enzyme of INH. Although most of the synthesized compounds are hosted by the InhA binding pocket, SIH1-SIH13 do not primarily show their antitubercular activities by direct InhA inhibition. Finally, in silico determination of important physicochemical parameters of the molecules showed that SIH1-SIH13 adhered to Lipinski's rule of five. Overall, our study revealed a new strategy for modifying INH to cope with the emerging drug-resistant strains of Mtb.

Polymeric Emissive Materials Based on Dynamic Covalent Bonds

Dynamic covalent polymers, composed of dynamic covalent bonds (DCBs), have received increasing attention in the last decade due to their adaptive and reversible nature compared with common covalent linked polymers. Incorporating the DCBs into the polymeric material endows it with advanced performance including self-healing, shape memory property, and so forth. However, the emissive ability of such dynamic covalent polymeric materials has been rarely reviewed. Herein, this review has summarized DCBs-based emissive polymeric materials which are classified according to the different types of DCBs, including imine bond, acylhydrazone bond, boronic ester bond, dynamic C-C bond, as well as the reversible bonds based on Diels–Alder reaction and transesterification. The mechanism of chemical reactions and various stimuli-responsive behaviors of DCBs are introduced, followed by typical emissive polymers resulting from these DCBs. By taking advantage of the reversible nature of DCBs under chemical/physical stimuli, the constructed emissive polymeric materials show controllable and switchable emission. Finally, challenges and future trends in this field are briefly discussed in this review.

Dynamic covalent chemistry with azines

Dynamic covalent chemistry is used in many applications that require both the stability of covalent bonds and the possibility to exchange building blocks. Here we present azines as a dynamic covalent functional group that combines the best characteristics of imines and acylhydrazones. We show that azines are stable in the presence of water and that dynamic combinatorial libraries of azines and aldehydes equilibrate in less than an hour.

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.

Controllable Construction of Amino-Functionalized Dynamic Covalent Porous Polymers for High-Efficiency CO2 Capture from Flue Gas

The design of high-efficiency CO₂ adsorbents with low cost, high capacity, and easy desorption is of high significance for reducing carbon emissions, which yet remains a great challenge. This work proposes a facile construction strategy of amino-functional dynamic covalent materials for effective CO₂ capture from flue gas. Upon the dynamic imine assembly of N-site rich motif and aldehyde-based spacers, nanospheres and hollow nanotubes with spongy pores were constructed spontaneously at room temperature. A commercial amino-functional molecule tetraethylenepentamine could be facilely introduced into the dynamic covalent materials by virtue of the dynamic nature of imine assembly, thus inducing a high CO₂ capacity (1.27 mmol·g^-1) from simulated flue gas at 75 °C. This dynamic imine assembly strategy endowed the dynamic covalent materials with facile preparation, low cost, excellent CO₂ capacity, and outstanding cyclic stability, providing a mild and controllable approach for the development of competitive CO₂ adsorbents.

Synthesis and Processing of Dynamic Covalently Crosslinked Polydextran/Carbon Dot Nanocomposite Hydrogels with Tailorable Microstructures and Properties

Using functionalized nanoparticles to crosslink hydrophilic polymers is a growing theme of directly constructing nanocomposite (NC) hydrogels. Employing dynamic covalent chemistry at the nanoparticle-polymer interface is particularly attractive due to the spontaneous formation and reversible manner of dynamic covalent bonds. However, the structure and property modulation of the dynamic covalently crosslinked NC hydrogels has not been thoroughly discussed. Here, we fabricated NC hydrogels by using amine-functionalized carbon dots (CDs) to crosslink polydextran aldehyde (PDA) polymers through imine bond formation. The role of PDA with different oxidation degrees (i.e., PDA10, PDA30, and PDA50) in affecting the microstructures and properties of PDA@CD hydrogels was systematically investigated, showing that the PDA50@CD hydrogel presented the densest structure and the highest mechanical strength among the three PDA@CD hydrogels. The pH-responsiveness, 3D printing, electrospinning, and biocompatibility of PDA@CD hydrogels were also demonstrated, showing the great promise of using PDA@CD hydrogels for applications in biomedicine and biofabrication.

Tuning the selectivity of amino acid recognition with dynamic covalent bond constrained fluorophores in aqueous media

The recognition and discrimination of amino acids are generating continuous interest due to their importance. Herein we developed a series of dynamic covalent reaction constrained aldehyde-derived fluorescent probes for the binding of amino acids with tunable selectivity. Diverse emission behaviors were obtained via pH triggered movement of ring-chain tautomerization equilibrium of aldehyde probes. By taking advantage of the distinct pK_a and reactivity of aldehyde probes and amino acids, unique fluorescence signaling patterns were generated, and the selectivity for amino acid recognition was further modulated. The selective recognition of Cys/Hcy was attained at pH 7.4 as a result of thiazolidine formation. The manipulation of the reactivity at pH 10 enabled the realization of high selectivity for His and Cys, respectively. Moreover, pH and redox stimuli-responsive dynamic covalent networks were constructed for the regulation of amino acid recognition. The strategies and results described should be appealing in many aspects, including dynamic assemblies, molecular sensing, biological labeling, and smart materials.

Dissipative Formation of Covalent Basket Cages

Living systems use chemical fuels to transiently assemble functional structures. As a step toward constructing abiotic mimics of such structures, we herein describe dissipative formation of covalent basket cage CBC 5 by reversible imine condensation of cup-shaped aldehyde 2 (i.e., basket) with trivalent aromatic amine 4. This nanosized [4+4] cage (V=5 nm3 , Mw =6150 Da) has shape of a truncated tetrahedron with four baskets at its vertices and four aromatic amines forming the faces. Importantly, tris-aldehyde basket 2 and aliphatic tris-amine 7 undergo condensation to give small [1+1] cage 6. The imine metathesis of 6 and aromatic tris-amine 4 into CBC 5 was optimized to bias the equilibrium favouring 6. Addition of tribromoacetic acid (TBA) as a chemical fuel perturbs this equilibrium to result in the transient formation of CBC 5, with subsequent consumption of TBA via decarboxylation driving the system back to the starting state.

Degradable polyprodrugs: design and therapeutic efficiency

Prodrugs are developed to increase the therapeutic properties of drugs and reduce their side effects. Polyprodrugs emerged as highly efficient prodrugs produced by the polymerization of one or several drug monomers. Polyprodrugs can be gradually degraded to release therapeutic agents. The complete degradation of polyprodrugs is an important factor to guarantee the successful disposal of the drug delivery system from the body. The degradation of polyprodrugs and release rate of the drugs can be controlled by the type of covalent bonds linking the monomer drug units in the polymer structure. Therefore, various types of polyprodrugs have been developed based on polyesters, polyanhydrides, polycarbonates, polyurethanes, polyamides, polyketals, polymetallodrugs, polyphosphazenes, and polyimines. Furthermore, the presence of stimuli-responsive groups, such as redox-responsive linkages (disulfide, boronate ester, metal-complex, and oxalate), pH-responsive linkages (ester, imine, hydrazone, acetal, orthoester, P-O and P-N), light-responsive (metal-complex, o-nitrophenyl groups) and enzyme-responsive linkages (ester, peptides) allow for a selective degradation of the polymer backbone in targeted tumors. We envision that new strategies providing a more efficient synergistic therapy will be developed by combining polyprodrugs with gene delivery segments and targeting moieties.

Strain Release Behaviour during Crack Growth of a Polymeric Beam under Elastic Loads for Self-Healing

The response of polymeric beams made of Acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) in the form of 3D printed beams is investigated to test their elastic and plastic responses under different bending loads. Two types of 3D printed beams were designed to test their elastic and plastic responses under different bending loads. These responses were used to develop an origami capsule-based novel self-healing mechanism that can be triggered by crack propagation due to strain release in a structure. Origami capsules of TPU in the form of a cross with four small beams, either folded or elastically deformed, were embedded in a simple ABS beam. Crack propagation in the ABS beam released the strain, and the TPU capsule unfolded with the arms of the cross in the direction of the crack path, and this increased the crack resistance of the ABS beam. This increase in the crack resistance was validated in a delamination test of a double cantilever specimen under quasi-static load conditions. Repeated test results demonstrated the effect of self-healing on structural crack growth. The results show the potential of the proposed self-healing mechanism as a novel contribution to existing practices which are primarily based on external healing agents.

Synthesis, physico-chemical characterization, and environmental applications of meso porous crosslinked poly (azomethine-sulfone)s

To develop innovative mesoporous crosslinked poly(azomethine- sulfone)s with environmental applications, a simple Schiff base condensation technique based on barbituric acid BA or condensed terephthaldehyde barbituric acid TBA in their structures as monomeric units are applied. Different analysis methodologies and viscosity measurements identify them as having stronger heat stability and an amorphous structure. The photophysical features of the multi stimuli response MSR phenomenon are observable, with white light emission at higher concentrations and blue light emission at lower concentrations. Their emission characteristics make them an excellent metal ions sensor through diverse charge transfer methods. They can have a better inhibition efficiency and be employed as both mixed-type and active corrosion inhibitors according to their fluorescence emission with metals, demonstrating their capacity to bind with diverse metals. The adsorption of two distinct dye molecules, Methylene blue MB cationic and sunset yellow SY anionic, on the mesoporous structures of the polymers is investigated, revealing their selectivity for MB dye adsorption. Quantum studies support these amazing discoveries, demonstrating a crab-like monomeric unit structure for the one that is heavily crosslinked.

Thermodynamic, kinetic, and mechanistic studies of the thermal guanidine metathesis reaction

We describe studies of the thermal guanidine metathesis (TGM) reaction, a reversible transformation that results in exchange of N-substituents of the guanidine functional group. By comparing the effects of discrete structural variations, we find that steric congestion is an important factor in determining both the equilibrium guanidine composition and the reaction kinetics. The alkyl versus aryl nature of N-substitution also plays an essential role in the reaction rate, up to the point that minimal TGM reactivity is observed when the guanidine contains wholly alkyl substituents. Furthermore, we demonstrate that TGM occurs under thermodynamic control and present evidence that it proceeds by a dissociative mechanism, supported by direct observation of a carbodiimide intermediate.

Fast, strong, and reversible adhesives with dynamic covalent bonds for potential use in wound dressing

Adhesives typically fall into two categories: those that have high but irreversible adhesion strength due to the formation of covalent bonds at the interface and are slow to deploy, and others that are fast to deploy and the adhesion is reversible but weak in strength due to formation of noncovalent bonds. Synergizing the advantages from both categories remains challenging but pivotal for the development of the next generation of wound dressing adhesives. Here, we report a fast and reversible adhesive consisting of dynamic boronic ester covalent bonds, formed between poly(vinyl alcohol) (PVA) and boric acid (BA) for potential use as a wound dressing adhesive. Mechanical testing shows that the adhesive film has strength in shear of 61 N/cm² and transcutaneous adhesive strength of 511 N/cm², generated within 2 min of application. Yet the film can be effortlessly debonded when exposed to excess water. The mechanical properties of PVA/BA adhesives are tunable by varying the cross-linking density. Within seconds of activation by water, the surface boronic ester bonds in the PVA/BA film undergo fast debonding and instant softening, leading to conformal contact with the adherends and reformation of the boronic ester bonds at the interface. Meanwhile, the bulk film remains dehydrated to offer efficient load transmission, which is important to achieve strong adhesion without delamination at the interface. Whether the substrate surface is smooth (e.g., glass) or rough (e.g., hairy mouse skin), PVA/BA adhesives demonstrate superior adhesion compared to the most widely used topical skin adhesive in clinical medicine, Dermabond.

Teaching an Old Compound New Tricks: Reversible Transamidation in Maleamic Acids

Dynamic combinatorial chemistry is a method widely used for generating responsive libraries of compounds, with applications ranging from chemical biology to materials science. It relies on dynamic covalent bonds that are able to form in a reversible manner in mild conditions, and therefore requires the discovery of new types of these bonds in order to progress. Amides, due to their high stability, have been scarcely used in this field and typically require an external catalyst or harsh conditions for exchange. Compounds able to undergo uncatalysed transamidation at room temperature are still rare exceptions. In this work, we describe reversible amide formation and transamidation in a class of compounds known as maleamic acids. Due to the presence of a carboxylic acid in β-position, these compounds are in equilibrium with their anhydride and amine precursors in organic solvents at room temperature. First, we show that this equilibrium is responsive to external stimuli: by alternating the additions of a Brønsted acid and a base, we can switch between amide and anhydride several times without side-reactions. Next, we prove that this equilibrium provides a pathway for reversible transamidation without any added catalyst, leading to thermodynamic distributions of amides at room temperature. Lastly, we use different preparation conditions and concentrations of Brønsted acid to access different library distributions, easily controlling the transition between kinetic and thermodynamic regimes. Our results show that maleamic acids can undergo transamidation in mild conditions in a reversible and tunable way, establishing them as a new addition to the toolbox of dynamic combinatorial chemistry.

Dynamic combinatorial libraries of a dimercapto-pillar[5]arene

We report the synthesis and dynamic covalent chemistry (DCvC) of an A1/A2-dimercapto-functionalized pillar[5]arene (Di-SH-P5). The introduction of thiol moieties into this macrocyclic host makes it an effective building block for making a dynamic combinatorial library (DCL), giving rise to a set of cyclic trimers with intriguing host-guest properties as the dominant constituents.

Anisotropic Compartmentalization of the Liquid-Liquid Interface using Dynamic Imine Chemistry

The liquid-liquid interface offers a fascinating avenue for generating hierarchical compartments. Herein, the dynamic imine chemistry is employed at the oil-water interface to investigate the effect of dynamic covalent bonds for modulating the droplet shape. The imine bond formation between oil-soluble aromatic aldehydes and water-soluble polyethyleneimine greatly stabilized the oil-water interface by substantially lowering the interfacial tension. The successful jamming of imine-mediated assemblies was observed when a compressive force was applied to the droplet. Thus, the anisotropic compartmentalization of the liquid-liquid interface was created, and it was later altered by changing the pH of the surrounding environment. Finally, a proof-of-concept demonstration of a pH-triggered cargo release across the interfacial membrane confirmed the feasibility of stimuli-responsive behavior of dynamic imine assemblies.

Tandem Imine Formation and Alkyne Metathesis Enabled by Catalyst Choice

Three-rung molecular ladder 8 was prepared in one pot via tandem imine condensation and alkyne metathesis. Catalyst VI is demonstrated to successfully engender the metathesis of imine-bearing substrate 7, while catalyst III does not. The susceptibility of catalyst VI to deactivation by hydrolysis and ligand exchange is demonstrated. Assembly and disassembly of ladder 8 in one pot were demonstrated in the presence and absence of a Lewis acid catalyst.

Imine- and Amine-Type Macrocycles Derived from Chiral Diamines and Aromatic Dialdehydes

The condensation of aromatic dialdehydes with chiral diamines, such as 1,2-trans-diaminocyclohexane, leads to various enantiopure or meso-type macrocyclic Schiff bases, including [2 + 2], [3 + 3], [4 + 4], [6 + 6] and [8 + 8] condensation products. Unlike most cases of macrocycle synthesis, the [3 + 3] macrocycles of this type are sometimes obtained in high yields by direct condensation without a metal template. Macrocycles of other sizes from this family can often be selectively obtained in high yields by a suitable choice of metal template, solvent, or chirality of the building blocks. In particular, the application of a cadmium(II) template results in the expansion of the [2 + 2] macrocycles into giant [6 + 6] and [8 + 8] macrocycles. These imine macrocycles can be reduced to the corresponding macrocyclic amines which can act as hosts for the binding of multiple cations or multiple anions.

Self-Healing Chitosan Hydrogels: Preparation and Rheological Characterization

The paper aims at the preparation of chitosan self-healing hydrogels, designed as carriers for local drug delivery by parenteral administration. To this aim, 30 hydrogels were prepared using chitosan and pyridoxal 5-phosphate (P5P), the active form of vitamin B6 as precursors, by varying the ratio of glucosamine units and aldehyde on the one hand and the water content on the other hand. The driving forces of hydrogelation were investigated by nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction, and polarized light microscopy (POM) measurements. NMR technique was also used to investigate the stability of hydrogels over time, and their morphological particularities were assessed by scanning electron microscopy (SEM). Degradability of the hydrogels was studied in media of four different pH, and preliminary self-healing ability was visually established by injection through a syringe needle. In-depth rheological investigation was conducted in order to monitor the storage and loss moduli, linear viscoelastic regime, and structural recovery capacity. It was concluded that chitosan crosslinking with pyridoxal 5-phosphate is a suitable route to reach self-healing hydrogels with a good balance of mechanical properties/structural recovery, good stability over time, and degradability controlled by pH.

Toward in Silico Modeling of Dynamic Combinatorial Libraries

Dynamic combinatorial libraries (DCLs) display adaptive behavior, enabled by the reversible generation of their molecular constituents from building blocks, in response to external effectors, e.g., protein receptors. So far, chemoinformatics has not yet been used for the design of DCLs-which comprise a radically different set of challenges compared to classical library design. Here, we propose a chemoinformatic model for theoretically assessing the composition of DCLs in the presence and the absence of an effector. An imine-based DCL in interaction with the effector human carbonic anhydrase II (CA II) served as a case study. Support vector regression models for the imine formation constants and imine-CA II binding were derived from, respectively, a set of 276 imines synthesized and experimentally studied in this work and 4350 inhibitors of CA II from ChEMBL. These models predict constants for all DCL constituents, to feed software assessing equilibrium concentrations. They are publicly available on the dedicated website. Models rationally selected two amines and two aldehydes predicted to yield stable imines with high affinity for CA II and provided a virtual illustration on how effector affinity regulates DCL members.

Design, Synthesis and Characterization of Vitrimers with Low Topology Freezing Transition Temperature

Vitrimers are crosslinked polymeric materials that behave like fluids when heated, regulated by the kinetics of internal covalent bond-exchange that occurs rapidly at or above the topology freezing transition temperature (T_v) of the vitrimer, making these materials readily reprocessable and recyclable. We report two novel multiphase vitrimeric materials prepared by the cross-linking of two polymers, namely poly(triethylene glycol sebacate) and poly(2-hydroxyethyl acrylate), using zinc acetate or tin(II) 2-ethylhexanoate as catalysts, which exhibit significantly low T_v temperatures of 39 °C and 29 °C, respectively. The transesterification reactions allow rapid and pronounced stress relaxation at high temperatures, following the Arrhenius law. The lower T_v of these vitrimers could be attributable to the flexible long chains of these polymers and the significant excess of OH moieties present along the main chain of the polymer. The design of such multiphase vitrimers is not only useful for the practical application of vitrimers to reduce plastic waste but could also facilitate further development of functional polymer materials that can be reprocessed at low temperatures.

Access to ortho-Hydroxyphenyl Ketimines via Imine Anion-Mediated Smiles Rearrangement

We have achieved a facile access to N-(2-halophenyl)-2-hydroxyphenylimine derivatives via imine anion-mediated Smiles rearrangement. When 2-(2-halophenoxy)benzonitriles were treated with 1.2-1.4 equiv of organolithium reagents, nucleophilic addition to the nitrile group followed by Smiles rearrangement occurred to give various N-(2-halophenyl)-2-hydroxyphenylimine derivatives, which are sometimes difficult to synthesize by the conventional acid-promoted condensation reaction between carbonyl compounds and aniline derivatives, in good to excellent chemical yields (up to 91%).

A double-decker cage for allosteric encapsulation of ATP

In this work, we describe the preparation of double-decker cage [1-H₆]⁶⁺ comprising two binding pockets, each with three ammonium and three amide hydrogen bonding sites. This novel host possesses a high affinity for trapping two molecules of ATP in an allosteric fashion, with both experiments and theory suggesting the synergistic action of charged hydrogen bonds and π-π stacking in the encapsulation.

Dynamic reversible adhesives based on crosslinking network via Schiff base and Michael addition

It is of practical interest to obtain polymers with complex material properties in a simplified synthetic manner for a broader range of practical applications. In this work, we constructed a dynamic reversible adhesive based on branched polyamine (PA) and p-formylphenyl acrylate (FPA) by simultaneously performing Michael addition reaction and Schiff base reaction. Branched polyamines provide a large number of amino groups as reaction sites that can react with both carbon-carbon double bonds and aldehyde groups. This enables the branched polymeric adhesive system to have a large number of Schiff base bonds within it, an important property of Schiff base bonds is that they are dynamically reversible. This allows us to prepare adhesives with hyperbranched crosslinking networks and recycling properties, and we have verified that FPA-PA adhesives do not exhibit significant fatigue after multiple recycling through the gluing-destruction-gluing process. The resulting FPA-PA adhesives produce tough bonding on multi-substrates such as steel, aluminum, glass, PVC, PTFE, birch and moso bamboo, which exhibited by lap shear strength of 2.4 MPa, 1.7 MPa, 1.4 MPa, 1.3 MPa, 0.4 MPa, 1.6 MPa, and 1.8 MPa, respectively. The feasibility of the synthesis idea of simultaneous Michael addition reaction and Schiff base reaction was demonstrated, as well as the excellent performance and great application potential of FPA-PA adhesives to be recyclable on multi-substrates.

Rapid Stress Relaxation, Multistimuli-Responsive Elastomer Based on Dual-Dynamic Covalent Bonds and Aniline Trimer

Covalent adaptable networks (CANs) are an emerging kind of smart materials in which cross-links are reversible upon some stimuli and then provide malleability and a stimuli-responsive ability to the materials. There is a trend to endow CANs with multistimuli-responsive capabilities and rapid stress relaxation to pursue more advanced applications. To integrate these two features into one material, here, dual-dynamic covalent bonds (imines and boronic esters) and aniline trimer (ACAT) were incorporated into the styrene butadiene elastomer as dynamic cross-links. The obtained CANs were demonstrated with rapid stress relaxation and a relatively low activation energy of 36 ± 1 kJ mol^-1, resulting from the synergistic effect of dual-dynamic covalent bonds to rearrange the network at a faster rate than for either imines or boronic esters. Because of the dynamic nature of imines or boronic esters, the elastomer can be recycled upon heat. Moreover, the appearance and configuration of the elastomer could also be manipulated by pH and light because of the inclusion of ACAT. All in all, the coupled multistimuli-responsive behavior and rapid stress relaxation in one single elastomer would potentially be applicable for sensors and actuators with good recyclability.