Chemical fuel-driven living and transient supramolecular polymerization

Mimicking the extracellular world: from natural to fully synthetic matrices utilizing supramolecular biomaterials

The extracellular matrix (ECM) has evolved around complex covalent and non-covalent interactions to create impressive function-from cellular signaling to constant remodeling. A major challenge in the biomedical field is the de novo design and control of synthetic ECMs for applications ranging from tissue engineering to neuromodulation to bioelectronics. As we move towards recreating the ECM's complexity in hydrogels, the field has taken several approaches to recapitulate the main important features of the native ECM (i.e. mechanical, bioactive and dynamic properties). In this review, we first describe the wide variety of hydrogel systems that are currently used, ranging from fully natural to completely synthetic to hybrid versions, highlighting the advantages and limitations of each class. Then, we shift towards supramolecular hydrogels that show great potential for their use as ECM mimics due to their biomimetic hierarchical structure, inherent (controllable) dynamic properties and their modular design, allowing for precise control over their mechanical and biochemical properties. In order to make the next step in the complexity of synthetic ECM-mimetic hydrogels, we must leverage the supramolecular self-assembly seen in the native ECM; we therefore propose to use supramolecular monomers to create larger, hierarchical, co-assembled hydrogels with complex and synergistic mechanical, bioactive and dynamic features.

Unravelling denaturation, temperature and cosolvent-driven chiroptical switching in peptide self-assembly with switchable piezoelectric responses

Herein, we explore the intricate pathway complexity, focusing on the dynamic interplay between kinetic and thermodynamic states, during the supramolecular self-assembly of peptides. We uncover a multiresponsive chiroptical switching phenomenon influenced by temperature, denaturation and content of cosolvent in peptide self-assembly through pathway complexity (kinetic vs. thermodynamic state). Particularly noteworthy is the observation of chiroptical switching during the denaturation process, marking an unprecedented phenomenon in the literature. Furthermore, the variation in cosolvent contents produces notable chiroptical switching effects, emphasizing their infrequent incidence. Such chiroptical switching yields switchable piezoresponsive peptide-based nanomaterials, demonstrating the potential for dynamic control over material properties. In essence, our work pioneers the ability to control piezoresponsive behavior by transforming nanostructures from kinetic to thermodynamic states through pathway complexity. This approach provides new insights and opportunities for tailoring material properties in self-assembled systems.

Repurposing a Catalytic Cycle for Transient Self-Assembly

Life operates out of equilibrium to enable various sophisticated behaviors. Synthetic chemists have strived to mimic biological nonequilibrium systems in such fields as autonomous molecular machines and dissipative self-assembly. Central to these efforts has been the development of new chemical reaction cycles, which drive systems out of equilibrium by conversion of chemical fuel into waste species. However, the construction of reaction cycles has been challenging due to the difficulty of finding compatible reactions that constitute a cycle. Here, we realize an alternative approach by repurposing a known catalytic cycle as a chemical reaction cycle for driving dissipative self-assembly. This approach can overcome the compatibility problem because all steps involved in a catalytic cycle are already known to proceed concurrently under the same conditions. Our repurposing approach is applicable to diverse combinations of catalytic cycles and systems to drive out of equilibrium, which will substantially broaden the scope of out-of-equilibrium systems.

Self-Assembly of Discrete Multi-Chromophoric Systems

Self-assembly of chromophoric systems is a prerequisite to create well-ordered, processable nanomaterials with multiple functionalities. In the past two decades, the field of functional organic materials has primarily focused on systems featuring only one type of dye/π-conjugated unit. Consequently, many reports with mechanistic insights on the self-assembly of the dyes featuring different molecular packing have been reported. Subsequently, we have witnessed several attempts to organize the multi-chromophoric systems in solution and solid-state via different approaches using self-assembly as a tool. Incorporation of more than one dye is important in creating materials with tuneable optoelectronic properties. Consequently, self-assembly of more than one chromophoric systems have been investigated to some extent. This review aims to discuss the self-assembled materials derived from discrete π-conjugated systems comprising more than one dye units connected through covalent bonding (multi-chromophoric systems). Molecular design of various multi-chromophoric systems leading to the formation of crystals, liquid crystals and supramolecular polymers have been correlated with corresponding properties. We envisage that classification of self-assembled multi-chromophoric systems, with a note on tuneable optoelectronic properties, can provide a deeper understanding on the molecular design strategies, which is important in the fabrication of functional organic materials with optimum performances.

Enzymatic Reaction-Coupled, Cooperative Supramolecular Polymerization

Nature employs sophisticated mechanisms to precisely regulate self-assembly and functions within biological systems, exemplified by the formation of cytoskeletal filaments. Various enzymatic reactions and auxiliary proteins couple with the self-assembly process, meticulously regulating the length and functions of resulting macromolecular structures. In this context, we present a bioinspired, reaction-coupled approach for the controlled supramolecular polymerization in synthetic systems. To achieve this, we employ an enzymatic reaction that interfaces with the adenosine triphosphate (ATP)-templated supramolecular polymerization of naphthalene diimide monomers (NSG). Notably, the enzymatic production of ATP (template) plays a pivotal role in facilitating reaction-controlled, cooperative growth of the NSG monomers. This growth process, in turn, provides positive feedback to the enzymatic production of ATP, creating an ideal reaction-coupled assembly process. The success of this approach is further evident in the living-growth characteristic observed during seeding experiments, marking this method as the pioneering instance where reaction-coupled self-assembly precisely controls the growth kinetics and structural aspects of supramolecular polymers in a predictive manner, akin to biological systems.

Self-assembled π-conjugated chromophores: preparation of one- and two-dimensional nanostructures and their use in photocatalysis

Photocatalytic systems have attracted research interest as a clean approach to generate energy from abundant sunlight. In this context, developing efficient and robust photocatalytic structures is crucial. Recently, self-assembled organic chromophores have entered the stage as alternatives to both molecular systems and (in)organic semiconductors. Nanostructures made of self-assembled π-conjugated dyes offer, on the one hand, molecular customizability to tune their optoelectronic properties and activities and on the other hand, provide benefits from heterogeneous catalysis that include ease of separation, recyclability and improved photophysical properties. In this contribution, we present recent achievements in constructing supramolecular photocatalytic systems made of chromophores for applications in water splitting, H2O2 evolution, CO2 reduction, or environmental remediation. We discuss strategies that can be used to prepare ordered photocatalytic systems with an emphasis on the effect of packing between the dyes and the resulting photocatalytic activity. We further showcase supramolecular strategies that allow interfacing the organic nanostructures with co-catalysts, molecules, polymers, and (in)organic materials. The principles discussed here are the foundation for the utilization of these self-assembled materials in photocatalysis.

Controlled Supramolecular Polymerization via Bioinspired, Liquid-Liquid Phase Separation of Monomers

Dynamic supramolecular assemblies, driven by noncovalent interactions, pervade the biological realm. In the synthetic domain, their counterparts, supramolecular polymers, endowed with remarkable self-repair and adaptive traits, are often realized through bioinspired designs. Recently, controlled supramolecular polymerization strategies have emerged, drawing inspiration from protein self-assembly. A burgeoning area of research involves mimicking the liquid-liquid phase separation (LLPS) observed in proteins to create coacervate droplets and recognizing their significance in cellular organization and diverse functions. Herein, we introduce a novel perspective on synthetic coacervates, extending beyond their established role in synthetic biology as dynamic, membraneless phases to enable structural control in synthetic supramolecular polymers. Drawing parallels with the cooperative growth of amyloid fibrils through LLPS, we present metastable coacervate droplets as dormant monomer phases for controlled supramolecular polymerization. This is achieved via a π-conjugated monomer design that combines structural characteristics for both coacervation through its terminal ionic groups and one-dimensional growth via a π-conjugated core. This design leads to a unique temporal LLPS, resulting in a metastable coacervate phase, which subsequently undergoes one-dimensional growth via nucleation within the droplets. In-depth spectroscopic and microscopic characterization provides insights into the temporal evolution of disordered and ordered phases. Furthermore, to modulate the kinetics of liquid-to-solid transformation and to achieve precise control over the structural characteristics of the resulting supramolecular polymers, we invoke seeding in the droplets, showcasing living growth characteristics. Our work thus opens up new avenues in the exciting field of supramolecular polymerization, offering general design principles and controlled synthesis of precision self-assembled structures in confined environments.

Redox-Regulated In Situ Seed-Induced Assembly of Peptides

Morphology-transformational self-assembly of peptides allows for manipulation of the performance of nanostructures and thereby advancing the development of biomaterials. Acceleration of the morphological transformation process under a biological microenvironment is important to efficiently implement the tailored functions in living systems. Herein, we report redox-regulated in situ seed-induced assembly of peptides via design of two co-assembled bola-amphiphiles serving as a redox-resistant seed and a redox-responsive assembly monomer, respectively. Both of the peptides are able to independently assemble into nanoribbons, while the seed monomer exhibits stronger assembling propensity. The redox-responsive monomer undergoes morphological transformation from well-defined nanoribbons to nanoparticles. Kinetics studies validate the role of the assembled inert monomer as the seeds in accelerating the assembly of the redox-responsive monomer. Alternative addition of oxidants and reductants into the co-assembled monomers promotes the redox-regulated assembly of the peptides facilitated by the in situ-formed seeds. The reduction-induced assembly of the peptide could also be accelerated by in situ-formed seeds in cancer cells with a high level of reductants. Our findings demonstrate that through precisely manipulating the assembling propensity of co-assembled monomers, the in situ seed-induced assembly of peptides could be achieved. Combining the rapid assembly kinetics of the seed-induced assembly with the common presence of redox agents in a biological microenvironment, this strategy potentially offers a new method for developing biomedical materials in living systems.

Transient control of lytic activity via a non-equilibrium chemical reaction system

The development of artificial non-equilibrium chemical reaction systems has recently attracted considerable attention as a new type of biomimetic. However, due to the lack of bioorthogonality, such reaction systems could not be linked to the regulation of any biological phenomena. Here, we have newly designed a non-equilibrium reaction system based on olefin metathesis to produce the Triton X-mimetic non-ionic amphiphile as a kinetic product. Using phospholipid vesicles encapsulating fluorescent dyes and red blood cells as cell models, we demonstrate that the developed chemical reaction system is applicable for transient control of the resulting lytic activity.

Cell-Like Synthetic Supramolecular Soft Materials Realized in Multicomponent, Non-/Out-of-Equilibrium Dynamic Systems

Living cells are complex, nonequilibrium supramolecular systems capable of independently and/or cooperatively integrating multiple bio-supramolecules to execute intricate physiological functions that cannot be accomplished by individual biomolecules. These biological design strategies offer valuable insights for the development of synthetic supramolecular systems with spatially controlled hierarchical structures, which, importantly, exhibit cell-like responses and functions. The next grand challenge in supramolecular chemistry is to control the organization of multiple types of supramolecules in a single system, thus integrating the functions of these supramolecules in an orthogonal and/or cooperative manner. In this perspective, the recent progress in constructing multicomponent supramolecular soft materials through the hybridization of supramolecules, such as self-assembled nanofibers/gels and coacervates, with other functional molecules, including polymer gels and enzymes is highlighted. Moreover, results show that these materials exhibit bioinspired responses to stimuli, such as bidirectional rheological responses of supramolecular double-network hydrogels, temporal stimulus pattern-dependent responses of synthetic coacervates, and 3D hydrogel patterning in response to reaction-diffusion processes are presented. Autonomous active soft materials with cell-like responses and spatially controlled structures hold promise for diverse applications, including soft robotics with directional motion, point-of-care disease diagnosis, and tissue regeneration.

Light-regulated morphology control in supramolecular polymers

Stimuli-responsive materials have gained significant recent interest owing to their versatility and wide applications in fields ranging from materials science to biology. In the majority of examples, external stimuli, including light, act as a remote source of energy to depolymerize/deconstruct certain nanostructures or provide energy for exploring their functional features. However, there is little emphasis on the creation and precise control of these materials. Although significant progress has been made in the last few decades in understanding the pros and cons of various directional non-covalent interactions and their specific molecular recognition ability, it is only in the recent past that the focus has shifted toward controlling the dimension, dispersity, and other macroscopic properties of supramolecular assemblies. Control over the morphology of supramolecular polymers is extremely crucial not only for material properties they manifest but also for effective interactions with biological systems for their potential application in the field of biomedicine. This could effectively be achieved using photoirradiation which has been demonstrated by some recent reports. The concept as such offers a broad scope for designing versatile stimuli-responsive supramolecular materials with precise structure-property control. However, there has not yet been a compilation that focuses on the present subject of employing light to impact and regulate the morphology of supramolecular polymers or categorize the functional motif for easy understanding. In this review, we have collated recent examples of how light irradiation can tune the morphology and nanostructures of supramolecular polymers and categorized them based on their chemical transformation such as cis-trans isomerization, cycloaddition, and photo-cleavage. We have also established a direct correlation among the structures of the building blocks, mesoscopic properties and functional behavior of such materials and suggested future directions.

Bio-Inspired Far-From-Equilibrium Hydrogels: Design Principles and Applications

Inspired from dynamic living systems that operate under out-of-equilibrium conditions in biology, developing supramolecular hydrogels with self-regulating and autonomously dynamic properties to further advance adaptive hydrogels with life-like behavior is important. This review presents recent progress of bio-inspired supramolecular hydrogels out-of-equilibrium. The principle of out-of-equilibrium self-assembly for creating bio-inspired hydrogels is discussed. Various design strategies have been identified, such as chemical-driven reaction cycles with feedback control and physically oscillatory systems. These strategies can be coupled with hydrogels to achieve temporal and spatial control over structural and mechanical properties as well as programmable lifetime. These studies open up huge opportunities for potential applications, such as fluidic guidance, information storage, drug delivery, actuators and more. Finally, we address the challenges ahead of us in the coming years, and future possibilities and prospects are identified.

Dynamic supramolecular hydrogels mediated by chemical reactions

Supramolecular self-assembly in a biological system is usually dominated by sophisticated metabolic processes (chemical reactions) such as catalysis of enzymes and consumption of high energy chemicals, leading to groups of biomolecules with unique dynamics and functions in an aqueous environment. In recent years, increasing efforts have been made to couple chemical reactions to molecular self-assembly, with the aim of creating supramolecular materials with lifelike properties and functions. In this feature article, after summarising the work of chemical reaction mediated supramolecular hydrogels, we first focus on a typical example where dynamic self-assembly of molecular hydrogels is activated by in situ formation of a hydrazone bond in water. We discuss how the formation of the hydrazone-based supramolecular hydrogels can be controlled in time and space. After that, we describe transient assembly of supramolecular hydrogels powered by out-of-equilibrium chemical reaction networks regulated by chemical fuels, which show unique properties such as finite lifetime, dynamic structures, and regenerative capabilities. Finally, we provide a perspective on the future investigations that need to be done urgently, which range from fundamental research to real-life applications of dynamic supramolecular hydrogels.

Two-Dimensional Living Supramolecular Polymerization: Improvement in Edge Roughness of Supramolecular Nanosheets by Using a Dummy Monomer

Supramolecular polymers are formed through nucleation (i. e., initiation) and polymerization processes, and kinetic control over the nucleation process has recently led to the realization of living supramolecular polymerization. Changing the viewpoint, herein we focus on controlling the polymerization process, which we expect to pave the way to further developments in controlled supramolecular polymerization. In our previous study, two-dimensional living supramolecular polymerization was used to produce supramolecular nanosheets with a controlled area; however, these had rough edges. In this study, the growth of the nanosheets was controlled by using a 'dummy' monomer to produce supramolecular nanosheets with smoothed edges.

Effect of molar ratio and concentration on the rheological properties of two-component supramolecular hydrogels: tuning of the morphological and drug releasing behaviour

Self-assembled supramolecular hydrogels offer great potential as biomaterials and drug delivery systems. Specifically, peptide-based multicomponent hydrogels are promising materials due to their advantage that their mechanical and physical properties can be tuned to enhance their functionalities and broaden their applications. Herein, we report two-component assembly and formation of hydrogels containing inexpensive complementary anionic, BUVV-OH (A), and cationic, KFFC12 (B), peptide amphiphiles. Individually, neither of these components formed a hydrogel, while mixtures with compositions 1 : 1, 1 : 2, and 2 : 1 (molar ratio) as A : B show hydrogel formation (Milli-Q water, at pH = 6.79). These hydrogels displayed a good shear-thinning behaviour with different mechanical stabilities and nano-fibrous network structures. The 1 : 1 hydrogel shows good cell viability for human embryonic kidney (HEK-293) cells and CHO cells indicating its non-cytotoxicity. The biocompatible, thixotropic 1 : 1 hydrogel with a nanofiber network structure shows the highest mechanical strength with a storage modulus of 3.4 × 103 Pa. The hydrogel is able to encapsulate drugs including antibiotics amoxicillin and rifampicin, and anticancer drug doxorubicin, and it exhibits sustainable release of 76%, 70%, and 81% respectively in vitro after 3 days. The other two mixtures (composition 1 : 2 and 2 : 1) are unable to form a hydrogel when they are loaded with these drugs. Interestingly, it is noticed that with an increase in concentration, the mechanical strength of a 1 : 1 hydrogel is significantly enhanced, showing potential that may act as a scaffold for tissue engineering. The two-component gel offers tunable mechanical properties, thixotropy, injectability, and biocompatibility and has great potential as a scaffold for sustained drug release and tissue engineering.

Controlled Noncovalent Synthesis of Secondary Supramolecular Polymers

Dynamic supramolecular polymers, with their functional similarities to classical covalent polymers and their adaptive and self-repairing nature reminiscent of biological assemblies, have emerged as highly promising systems for the design of smart soft materials. Recent advancements in mechanistic investigations and novel synthetic strategies, such as living supramolecular polymerization, have significantly enhanced our ability to control the primary structure of these supramolecular polymers. However, realizing their full functional potential requires expanding their topological diversity in a manner akin to classical polymers as well as achieving precise molecular organization at higher hierarchical levels of self-assembly. In this paper, we present a remarkable advancement in this field, introducing an unprecedented and controlled synthesis of secondary supramolecular polymers. Our innovative strategy combines chirality-controlled surface-catalyzed secondary nucleation and a bioinspired peptide design, effectively stabilizing higher-order assembly. Furthermore, by harnessing this stereoselective nucleation process, we demonstrate the successful synthesis of racemic supramolecular polymers featuring parallelly stacked conglomerate microstructures─a previously unreported topology in synthetic self-assembled systems. Additionally, we elucidate that the extent of secondary supramolecular polymers can be regulated by modulating the enantiomeric excess of the chiral monomers. Consequently, our study unveils new topologies that exhibit enhanced higher-order structural complexity in the realm of supramolecular polymers.

Engineering metabolic cycle-inspired hydrogels with enzyme-fueled programmable transient volume changes

An enzyme-fueled transient volume phase transition (TVPT) of hydrogels under out-of-equilibrium conditions is reported. The approach takes inspiration from the metabolic cycle, comprising nutrient intake and anabolism/catabolism followed by waste excretion. The incorporation of methacrylic acid and acrylated trypsin in a polymeric hydrogel allowed the TVPT of the gel to be fueled by lysozyme. With the intake of lysozyme as fuel, the construction/destruction of electrostatic cross-linkages induced transient shrinkage/swelling of the gel accompanied by the depletion of lysozyme activity. The system's transient response could be flexibly programmed by adjusting not only the fuel concentration but the chemical composition of materials. The lysozyme-fueled TVPT of the gel could be exploited to transient changes in the mechanical properties of the gel. Our work opens a route toward a new class of stimuli-responsive hydrogels for biomedical applications.

Nanoparticle Self-Assembly: From Design Principles to Complex Matter to Functional Materials

The creation of matter with varying degrees of complexities and desired functions is one of the ultimate targets of self-assembly. The ability to regulate the complex interactions between the individual components is essential in achieving this target. In this direction, the initial success of controlling the pathways and final thermodynamic states of a self-assembly process is promising. Despite the progress made in the field, there has been a growing interest in pushing the limits of self-assembly processes. The main inception of this interest is that the intended self-assembled state, with varying complexities, may not be "at equilibrium (or at global minimum)", rendering free energy minimization unsuitable to form the desired product. Thus, we believe that a thorough understanding of the design principles as well as the ability to predict the outcome of a self-assembly process is essential to form a collection of the next generation of complex matter. The present review highlights the potent role of finely tuned interparticle interactions in nanomaterials to achieve the preferred self-assembled structures with the desired properties. We believe that bringing the design and prediction to nanoparticle self-assembly processes will have a similar effect as retrosynthesis had on the logic of chemical synthesis. Along with the guiding principles, the review gives a summary of the different types of products created from nanoparticle assemblies and the functional properties emerging from them. Finally, we highlight the reasonable expectations from the field and the challenges lying ahead in the creation of complex and evolvable matter.

Autonomic self-regulating systems based on polyelectrolyte microcapsules and microgel particles

Biological systems possess unique non-equilibrium functions, maintaining tight manipulation of their surroundings through inter-communication of multiple components and self-regulatory capability organized over different length scales. However, most artificial materials are incapable of communicating and self-regulating behavior due to their limited number of component and direct responsive modes. Herein, a new integrated self-regulation system is developed utilizing stimuli-responsive polyelectrolyte capsules as building blocks. The combination of stimuli-responsive capsules and enzyme immobilized microgels is designed to mimic life systems and its programmable interactive communications and self-regulation behavior is demonstrated through communication-feedback mechanism. Polyelectrolyte capsules can sense changes of their surrounding, then start the internal communication by releasing energy-rich cargo mimicking the behavior of the cells. The microgel particles subsequently complete closed-loop communication through providing negative feedback on capsules by enzymatic reaction and actuating pH-regulation of the whole system. Different communication modes and pH-regulation behaviors could be achieved by adjusting spatial and kinetic conditions. Proposed intelligent system is highly customizable due to the wide selection of encapsulated cargos, stimuli-responsive blocks and reaction networks, and would have broad influences in areas ranging from medical implants that assist in stabilizing body functions to microreactor system that regulate catalytic reactions.

Self-Regulatory Micro- and Macroscale Patterning of ATP-Mediated Nanobioconjugate

Directional interactions and the assembly of a nanobioconjugate in clusters at a specific location are important for patterning and microarrays in biomedical research. Herein, we report that self-assembly and spatial control in surface patterning of the surfactant-functionalized nanoparticles can be governed in micro- and macroscale environments by two factors, synergistic enzyme-substrate-nanoparticle affinity and the phoretic effect. First, we show that aggregation of cationic gold nanoparticles (GNP) can be modulated by multivalent anionic nanoparticle binding of an adenosine-based nucleotide and enzyme, alkaline phosphatase. We further demonstrate two different types of their autonomous aggregation pattern: (i) by introducing an enzyme gradient that modulates the synergistic nonequilibrium interactivity of the nanoparticle, nucleotide, and enzyme both in microfluidic conditions and at the macroscale; and (ii) the surface deposition pattern from evaporating droplets via the coffee ring effect. Here, temporal control over the width and site of the patterning area inside the microfluidic channel under catalytic and noncatalytic conditions has also been demonstrated. Finally, we show a change in capillary phoresis parameters responsible for the coffee ring due to introduction of ATP-loaded GNP in the blood serum, showing applicability in low-cost disease diagnostics. Overall, an enzyme-actuated surface nanobiopatterning method has been demonstrated that has potential application in controlled micro- and macroscale area patterning with a diverse cascade catalytic surface and spatiotemporal multisensory-based application.

Cumulative Effect of pH and Redox Triggers on Highly Adaptive Transient Coacervates

An intricate synergism between multiple biochemical processes and physical conditions determines the formation and function of various biological self-assemblies. Thus, a complex set of variables dictate the far-from-equilibrium nature of these biological assemblies. Mimicking such systems synthetically is a challenging task. We report multi-stimuli responsive transient coacervation of an aldehyde-appended polymer and a short peptide. The coacervates are formed by the disulphide linkages between the peptide molecules and the imine bond between the polymer and the peptide. Imines are susceptible to pH changes and the disulphide bonds can be tuned by oxidation/reduction processes. Thus, the coacervation is operational only under the combined effect of appropriate pH and oxidative conditions. Taking advantage of these facts, the coacervates are transiently formed under a pH cycle (urea-urease/gluconolactone) and a non-equilibrium redox cycle (TCEP/H₂ O₂ ). Importantly, the system showed high adaptability toward environmental changes. The transient existence of the coacervates can be generated without any apparent change in size and shape within the same system through the sequential application of the above-mentioned nonequilibrium reaction cycles. Additionally, the coacervation allows for efficient encapsulation/stabilisation of proteins. Thus, the system has the potential to be used for protein/drug delivery purposes in the future.

Construction of transient supramolecular polymers controlled by mass transfer in biphasic systems

Inspired by life assembly systems, the construction of transient assembly systems with spatiotemporal control is crucial for developing intelligent materials. A widely adopted strategy is to couple the self-assembly with chemical reaction networks. However, orchestrating the kinetics of multiple reactions and assembly/disassembly processes without crosstalk in homogeneous solutions is not an easy task. To address this challenge, we propose a generic strategy by separating components into different phases, therefore, the evolution process of the system could be easily regulated by controlling the transport of components through different phases. Interference of multiple components that are troublesome in homogeneous systems could be diminished. Meanwhile, limited experimental parameters are involved in tuning the mass transfer instead of the complex kinetic matching and harsh reaction selectivity requirements. As a proof of concept, a transient metallo-supramolecular polymer (MSP) with dynamic luminescent color was constructed in an oil-water biphasic system by controlling the diffusion of the deactivator (water molecules) from the water phase into the oil phase. The lifetime of transient MSP could be precisely regulated not only by the content of chemical fuel, but also factors that affect the efficiency of mass transfer in between phases, such as the volume of the water phase, the stirring rate, and the temperature. We believe this strategy can be further extended to multi-compartment systems with passive diffusion or active transport of components, towards life-like complex assembly systems.

Spatiotemporal Control Over Base-Catalysed Hydrogelation Using a Bilayer System

Controlling the formation and directional growth of hydrogels is a challenge. In this paper, we propose a new methodology to program the gel formation both over space and time, using the diffusion and subsequent hydrolysis of 1,1'-carbonyldiimidazole (CDI) from an immiscible organic solution to the aqueous gel media. This article is protected by copyright. All rights reserved.

Biomacromolecule-Fueled Transient Volume Phase Transition of a Hydrogel

A metabolic cycle-inspired hydrogel which exhibits the biomacromolecule-fueled transient volume phase transition is reported. This hydrogel has the affinity and digestive capacity for a fuel α-poly-L-lysine by incorporating acrylic acid and trypsin. The hydrogel captured fuel and transiently shrank owing to the construction of electrostatic cross-linkages. This process was inherently connected with the digestion of these cross-linkages and the release of oligo-lysine as waste, which induced the reswelling of the hydrogel at equilibrium. The transient volume change of the hydrogel realized the fuel-stimulated transient release of a payload. This study provides a strategy for engineering materials with biomacromolecule-fueled dynamic functions under the out-of-equilibrium condition.

Temporal Stimulus Patterns Drive Differentiation of a Synthetic Dipeptide-Based Coacervate

The fate of living cells often depends on their processing of temporally modulated information, such as the frequency and duration of various signals. Synthetic stimulus-responsive systems have been intensely studied for >50 years, but it is still challenging for chemists to create artificial systems that can decode dynamically oscillating stimuli and alter the systems' properties/functions because of the lack of sophisticated reaction networks that are comparable with biological signal transduction. Here, we report morphological differentiation of synthetic dipeptide-based coacervates in response to temporally distinct patterns of the light pulse. We designed a simple cationic diphenylalanine peptide derivative to enable the formation of coacervates. The coacervates concentrated an anionic methacrylate monomer and a photoinitiator, which provided a unique reaction environment and facilitated light-triggered radical polymerization─even in air. Pulsed light irradiation at 9.0 Hz (but not at 0.5 Hz) afforded anionic polymers. This dependence on the light pulse patterns is attributable to the competition of reactive radical intermediates between the methacrylate monomer and molecular oxygen. The temporal pulse pattern-dependent polymer formation enabled the coacervates to differentiate in terms of morphology and internal viscosity, with an ultrasensitive switch-like mode. Our achievements will facilitate the rational design of smart supramolecular soft materials and are insightful regarding the synthesis of sophisticated chemical cells.

Insights into Chemically Fueled Supramolecular Polymers

Supramolecular polymerization can be controlled in space and time by chemical fuels. A nonassembled monomer is activated by the fuel and subsequently self-assembles into a polymer. Deactivation of the molecule either in solution or inside the polymer leads to disassembly. Whereas biology has already mastered this approach, fully artificial examples have only appeared in the past decade. Here, we map the available literature examples into four distinct regimes depending on their activation/deactivation rates and the equivalents of deactivating fuel. We present increasingly complex mathematical models, first considering only the chemical activation/deactivation rates (i.e., transient activation) and later including the full details of the isodesmic or cooperative supramolecular processes (i.e., transient self-assembly). We finish by showing that sustained oscillations are possible in chemically fueled cooperative supramolecular polymerization and provide mechanistic insights. We hope our models encourage the quantification of activation, deactivation, assembly, and disassembly kinetics in future studies.

Secondary Nucleation-Triggered Physical Cross-Links and Tunable Stiffness in Seeded Supramolecular Hydrogels

Mechanistic understanding and the control of molecular self-assembly at all hierarchical levels remain grand challenges in supramolecular chemistry. Functional realization of dynamic supramolecular materials especially requires programmed assembly at higher levels of molecular organization. Herein, we report an unprecedented molecular control on the fibrous network topology of supramolecular hydrogels and their resulting macroscopic properties by biasing assembly pathways of higher-order structures. The surface-catalyzed secondary nucleation process, a well-known mechanism in amyloid fibrilization and chiral crystallization of small molecules, is introduced as a non-covalent strategy to induce physical cross-links and bundling of supramolecular fibers, which influences the microstructure of gel networks and subsequent mechanical properties of hydrogels. In addition, seed-induced instantaneous gelation is realized in the kinetically controlled self-assembled system under this study, and more importantly, the extent of secondary nucleation events and network topology is manipulated by the concentration of seeds.

Expanding the Scope of Metastable Species in Hydrogen Bonding-Directed Supramolecular Polymerization

We reveal unique hydrogen (H-) bonding patterns and exploit them to control the kinetics, pathways and length of supramolecular polymers (SPs). New bisamide-containing monomers were designed to elucidate the role of competing intra- vs. intermolecular H-bonding interactions on the kinetics of supramolecular polymerization (SP). Remarkably, two polymerization-inactive metastable states were discovered. Contrary to previous examples, the commonly assumed intramolecularly H-bonded monomer does not evolve into intermolecularly H-bonded SPs via ring opening, but rather forms a metastable dimer. In this dimer, all H-bonding sites are saturated, either intra- or intermolecularly, hampering elongation. The dimers exhibit an advantageous preorganization, which upon opening of the intramolecular portion of the H-bonding motif facilitates SP in a consecutive process. The retardation of spontaneous self-assembly as a result of two metastable states enables length control in SP by seed-mediated growth.

Cooperative self-assembling process of core-substituted naphthalenediimide induced by amino-yne click reaction

We report a cooperative (i.e., nucleation-elongation) self-assembling process of a core-substituted naphthalenediimide induced by a catalyst-free amino-yne click reaction at 298 K. The self-assembling process was initiated immediately in the presence of nuclei (seeds). The combination of the click reaction and the seeded self-assembling process paves the way for precise control over supramolecular assemblies of electron-deficient π-systems.

A trefoil knot self-templated through imination in water

The preparation of topologically nontrivial molecules is often assisted by covalent, supramolecular or coordinative templates that provide spatial pre-organization for all components. Herein, we report a trefoil knot that can be self-assembled efficiently in water without involving additional templates. The direct condensation of three equivalents of a tetraformyl precursor and six equivalents of a chiral diamine produces successfully a [3 + 6] trefoil knot whose intrinsic handedness is dictated by the stereochemical configuration of the diamine linkers. Contrary to the conventional wisdom that imine condensation is not amenable to use in water, the multivalent cooperativity between all the imine bonds within the framework makes this trefoil knot robust in the aqueous environment. Furthermore, the presence of water is proven to be essential for the trefoil knot formation. A topologically trivial macrocycle composed of two tetraformyl and four diamino building blocks is obtained when a similar reaction is performed in organic media, indicating that hydrophobic effect is a major driving force behind the scene.

ATP-Induced Emergent Circularly Polarized Luminescence and Encryption

Biomimetic ATP-driven supramolecular assembly is important to understand various biological processes and dissipative systems. Here, we report an ATP-driven chiral assembly exhibiting circularly polarized luminescence (CPL) via the interaction of an achiral terpyridine-based Zn^II complex with nucleotides. It was found that while the metal complexes could co-assemble with the nucleotides to form fluorescent assemblies, only a combination of furan-substituted terpyridine complex and ATP showed an intense CPL with a dissymmetry factor (g_lum ) as high as 0.20. This means that the complex could recognize ATP using CPL as a readout signal, thus providing an example of ATP encryption. Interestingly, when ATP was transferred into ADP or AMP under enzymatic hydrolysis, the CPL decreases or disappears. Addition of ATP generates CPL again, thus producing an ATP-induced CPL system. This work presents the first example of ATP-induced CPL and encryption.

Systems chemistry of peptide-assemblies for biochemical transformations

During the billions of years of the evolutionary journey, primitive polymers, involved in proto metabolic pathways with low catalytic activity, played critical roles in the emergence of modern enzymes with remarkable substrate specificity. The precise positioning of amino acid residues and the complex orchestrated interplay in the binding pockets of evolved enzymes promote covalent and non-covalent interactions to foster a diverse set of complex catalytic transformations. Recent efforts to emulate the structural and functional information of extant enzymes by minimal peptide based assemblies have attempted to provide a holistic approach that could help in discerning the prebiotic origins of catalytically active binding pockets of advanced proteins. In addition to the impressive sets of advanced biochemical transformations, catalytic promiscuity and cascade catalysis by such small molecule based dynamic systems can foreshadow the ancestral catalytic processes required for the onset of protometabolism. Looking beyond minimal systems that work close to equilibrium, catalytic systems and compartments under non-equilibrium conditions utilizing simple prebiotically relevant precursors have attempted to shed light on how bioenergetics played an essential role in chemical emergence of complex behaviour. Herein, we map out these recent works and progress where diverse sets of complex enzymatic transformations were demonstrated by utilizing minimal peptide based self-assembled systems. Further, we have attempted to cover the examples of peptide assemblies that could feature promiscuous activity and promote complex multistep cascade reaction networks. The review also covers a few recent examples of minimal transient catalytic assemblies under non-equilibrium conditions. This review attempts to provide a broad perspective for potentially programming functionality via rational selection of amino acid sequences leading towards minimal catalytic systems that resemble the traits of contemporary enzymes.

Hierarchical self-assembly of aromatic peptide conjugates into supramolecular polymers: it takes two to tango

Supramolecular polymers are self-assembled materials displaying adaptive and responsive "life-like" behaviour which are often made of aromatic compounds capable of engaging in π-π interactions to form larger assemblies. Major advances have been made recently in controlling their mode of self-assembly, from thermodynamically-controlled isodesmic to kinetically-controlled living polymerization. Dynamic covalent chemistry has been recently implemented to generate dynamic covalent polymers which can be seen as dynamic analogues of biomacromolecules. On the other hand, peptides are readily-available and structurally-rich building blocks that can lead to secondary structures or specific functions. In this context, the past decade has seen intense research activity in studying the behaviour of aromatic-peptide conjugates through supramolecular and/or dynamic covalent chemistries. Herein, we review those impressive key achievements showcasing how aromatic- and peptide-based self-assemblies can be combined using dynamic covalent and/or supramolecular chemistry, and what it brings in terms of the structure, self-assembly pathways, and function of supramolecular and dynamic covalent polymers.

Carbodiimide-fueled catalytic reaction cycles to regulate supramolecular processes

Using molecular self-assembly, supramolecular chemists can create Gigadalton-structures with angstrom precision held together by non-covalent interactions. However, despite relying on the same molecular toolbox for self-assembly, these synthetic structures lack the complexity and sophistication of biological assemblies. Those assemblies are non-equilibrium structures that rely on the constant consumption of energy transduced from the hydrolysis of chemical fuels like ATP and GTP, which endows them with dynamic properties, e.g., temporal and spatial control and self-healing ability. Thus, to synthesize life-like materials, we have to find a reaction cycle that converts chemical energy to regulate self-assembly. We and others recently found that this can be done by a reaction cycle that hydrates carbodiimides. This feature article aims to provide an overview of how the energy transduced from carbodiimide hydration can alter the function of molecules and regulate molecular assemblies. The goal is to offer the reader design considerations for carbodiimide-driven reaction cycles to create a desired morphology or function of the assembly and ultimately to push chemically fueled self-assembly further towards the bottom-up synthesis of life.

Spatiotemporal dynamics of self-assembled structures in enzymatically induced agonistic and antagonistic conditions

Predicting and designing systems with dynamic self-assembly properties in a spatiotemporal fashion is an important research area across disciplines ranging from understanding the fundamental non-equilibrium features of life to the fabrication of next-generation materials with life-like properties. Herein, we demonstrate a spatiotemporal dynamics pattern in the self-assembly behavior of a surfactant from an unorganized assembly, induced by adenosine triphosphate (ATP) and enzymes responsible for the degradation or conversion of ATP. We report the different behavior of two enzymes, alkaline phosphatase (ALP) and hexokinase (HK), towards adenosine triphosphate (ATP)-driven surfactant assembly, which also results in contrasting spatiotemporal dynamic assembly behavior. Here, ALP acts antagonistically, resulting in transient self-assemblies, whereas HK shows agonistic action with the ability to sustain the assemblies. This dynamic assembly behavior was then used to program the time-dependent emergence of a self-assembled structure in a two-dimensional space by maintaining concentration gradients of the enzymes and surfactant at different locations, demonstrating a new route for obtaining 'spatial' organizational adaptability in a self-organized system of interacting components for the incorporation of programmed functionality.

Supramolecular fibrillation of peptide amphiphiles induces environmental responses in aqueous droplets

One-dimensional (1D) supramolecular polymers are commonly found in natural and synthetic systems to prompt functional responses that capitalise on hierarchical molecular ordering. Despite amphiphilic self-assembly being significantly studied in the context of aqueous encapsulation and autopoiesis, very little is currently known about the physico-chemical consequences and functional role of 1D supramolecular polymerisation confined in aqueous compartments. Here, we describe the different phenomena that resulted from the chemically triggered supramolecular fibrillation of synthetic peptide amphiphiles inside water microdroplets. The confined connection of suitable dormant precursors triggered a physically autocatalysed chemical reaction that resulted in functional environmental responses such as molecular uptake, fusion and chemical exchange. These results demonstrate the potential of minimalistic 1D supramolecular polymerisation to modulate the behaviour of individual aqueous entities with their environment and within communities.

A Molecular Replication Process Drives Supramolecular Polymerization

Supramolecular polymers are materials in which the connections between monomers in the polymer main chain are non-covalent bonds. This area has seen rapid expansion in the last two decades and has been exploited in several applications. However, suitable contiguous hydrogen-bond arrays can be difficult to synthesize, placing some limitations on the deployment of supramolecular polymers. We have designed a hydrogen-bonded polymer assembled from a bifunctional monomer composed of two replicating templates separated by a rigid spacer. This design allows the autocatalytic formation of the polymer main chain through the self-templating properties of the replicators and drives the synthesis of the bifunctional monomer from its constituent components in solution. The template-directed 1,3-dipolar cycloaddition reaction between nitrone and maleimide proceeds with high diastereoselectivity, affording the bifunctional monomer. The high binding affinity between the self-complementary replicating templates that allows the bifunctional monomer to polymerize in solution is derived from the positive cooperativity associated with this binding process. The assembly of the polymer in solution has been investigated by diffusion-ordered NMR spectroscopy. Both microcrystalline and thin films of the polymeric material can be prepared readily and have been characterized by powder X-ray diffraction and scanning electron microscopy. These results demonstrate that the approach described here is a valid one for the construction of supramolecular polymers and can be extended to systems where the rigid spacer between the replicating templates is replaced by one carrying additional function.

Double diffusion for the programmable spatiotemporal patterning of multi-domain supramolecular gels

To achieve spatial resolution of a multi-component gel, a double diffusion approach is used which enables the precise programming of self-assembled patterned domains with well-defined shapes and sizes. The low-molecular-weight gelators (LMWGs) used in this study are pH-responsive DBS-CO₂H and thermally-responsive DBS-CONHNH₂ (both based on 1,3:2,4-dibenzylidenesorbitol, DBS). A DBS-CONHNH₂ gel was initially assembled in a tray, and then loaded at carefully-selected positions with either basified DBS-CO₂H (i.e. DBS-carboxylate) or an acid. These soluble components subsequently diffuse through the pre-formed gel matrix, and in the domains when/where they mix, protonation of the DBS-carboxylate induces self-assembly of the DBS-CO₂H network, leading to a patterned gel-in-gel object with well-defined shape and dimensions. Using a strong acid achieves fast gelation kinetics, creating smaller, better-defined macroscale objects but with less nanoscale order. Using a weak acid source with slow kinetics, gives slightly larger objects, but on the nanoscale the DBS-CO₂H network formation is better controlled, giving more homogeneous nanoscale structures and stiffer objects. The patterned objects can be further reinforced by the presence of agarose polymer gelator. The shape of the patterning is programmed by both the shape of the central reservoir and the starting geometry in which the reservoirs are organised, with the balance between factors depending on assembly kinetics, as dictated by the choice of acid. This simple methodology therefore enables programming of patterned gels with spatiotemporal control and emergent patterning characteristics.

To achieve spatial resolution of a multi-component gel, a double diffusion approach is used which enables the precise programming of emergent self-assembled patterned domains with well-defined shapes and sizes.

Autonomous DNA nanostructures instructed by hierarchically concatenated chemical reaction networks

Concatenation and communication between chemically distinct chemical reaction networks (CRNs) is an essential principle in biology for controlling dynamics of hierarchical structures. Here, to provide a model system for such biological systems, we demonstrate autonomous lifecycles of DNA nanotubes (DNTs) by two concatenated CRNs using different thermodynamic principles: (1) ATP-powered ligation/restriction of DNA components and (2) input strand-mediated DNA strand displacement (DSD) using energy gains provided in DNA toeholds. This allows to achieve hierarchical non-equilibrium systems by concurrent ATP-powered ligation-induced DSD for activating DNT self-assembly and restriction-induced backward DSD reactions for triggering DNT degradation. We introduce indirect and direct activation of DNT self-assemblies, and orthogonal molecular recognition allows ATP-fueled self-sorting of transient multicomponent DNTs. Coupling ATP dissipation to DNA nanostructures via programmable DSD is a generic concept which should be widely applicable to organize other DNA nanostructures, and enable the design of automatons and life-like systems of higher structural complexity.

Tricomponent Supramolecular Multiblock Copolymers with Tunable Composition via Sequential Seeded Growth

Synthesis of supramolecular block co-polymers (BCP) with small monomers and predictive sequence requires elegant molecular design and synthetic strategies. Herein we report the unparalleled synthesis of tri-component supramolecular BCPs with tunable microstructure by a kinetically controlled sequential seeded supramolecular polymerization of fluorescent π-conjugated monomers. Core-substituted naphthalene diimide (cNDI) derivatives with different core substitutions and appended with β-sheet forming peptide side chains provide perfect monomer design with spectral complementarity, pathway complexity and minimal structural mismatch to synthesize and characterize the multi-component BCPs. The distinct fluorescent nature of various cNDI monomers aids the spectroscopic probing of the seeded growth process and the microscopic visualization of resultant supramolecular BCPs using Structured Illumination Microscopy (SIM). Kinetically controlled sequential seeded supramolecular polymerization presented here is reminiscent of the multi-step synthesis of covalent BCPs via living chain polymerization. These findings provide a promising platform for constructing unique functional organic heterostructures for various optoelectronic and catalytic applications.

Stereoselective Primary and Secondary Nucleation Events in Multicomponent Seeded Supramolecular Polymerization

Bioinspired, kinetically controlled seeded growth has been recently shown to provide length, dispersity, and sequence control on the primary structure of dynamic supramolecular polymers. However, command over the molecular organization at all hierarchical levels for the modulation of higher order structures of supramolecular polymers remains a formidable task. In this context, a surface-catalyzed secondary nucleation process, which plays an important role in the autocatalytic generation of amyloid fibrils and also during the chiral crystallization of small monomers, offers exciting possibilities for topology control in synthetic macromolecular systems by introducing secondary growth pathways compared to the usual primary nucleation-elongation process. However, mechanistic insights into the molecular determinants and driving forces for the secondary nucleation event in synthetic systems are not yet realized. Herein, we attempt to fill this dearth by showing an unprecedented molecular chirality control on the primary and secondary nucleation events in seed-induced supramolecular polymerization. Comprehensive kinetic experiments using in situ spectroscopic probing of the temporal changes of the monomer organization during the growth process provide a unique study to characterize the primary and secondary nucleation events in a supramolecular polymerization process. Kinetic analyses along with various microscopic studies further reveal the remarkable effect of stereoselective nucleation and seeding events on the (micro)structural aspects of the resulting multicomponent supramolecular polymers.

Urea-Urease Reaction in Controlling Properties of Supramolecular Hydrogels: Pros and Cons

Supramolecular hydrogels are useful in many areas such as cell culturing, catalysis, sensing, tissue engineering, drug delivery, environmental remediation and optoelectronics. The gels need specific properties for each application. The properties arise from a fibrous network that forms the matrix. A common method to prepare hydrogels is to use a pH change. Most methods result in a sudden pH jump and often lead to gels that are hard to reproduce and control. The urease-urea reaction can be used to control hydrogel properties by a uniform and controlled pH increase as well as to set up pH cycles. The reaction involves hydrolysis of urea by urease and production of ammonia which increases the pH. The rate of ammonia production can be controlled which can be used to prepare gels with differing properties. Herein, we show how the urease-urea reaction can be used for the construction of next generation functional materials.