Folding-driven synthesis of oligomers

New multiple-layered 3D polymers showing aggregation-induced emission and polarization

An exceptional achiral and chiral multilayer 3D polymer has been created and controlled by uniform and distinct aromatic chromophore units that are multiply sandwiched by naphthyl berths. In order to put together this assembly, it was necessary to search for new catalytic Suzuki-Miyaura polycouplings among various catalytic systems, monomers, and catalysts. Gel Permeation Chromatography (GPC) was able to verify the presence of many framework layers. The resulting achiral and chiral polymers displayed notable optical characteristic.

Complexation-driven assembly of imine-linked helical receptors showing adaptive folding and temperature-dependent guest selection

The development of synthetic receptors capable of selectively binding guests with diverse structures and multiple functional groups poses a significant challenge. Here, we present the efficient assembly of foldamer-based receptors for monosaccharides, utilising the principles of complexation-induced equilibrium shifting and adaptive folding. Diimine 4 can be quantitatively assembled from smaller components when D-galactose is added as a guest among monosaccharides we examined. During this assembly, dual complexation-induced equilibrium shifts toward both the formation of diimine 4 and the conversion of D-galactose into α-D-galactofuranose are observed. Diimine 6 is quantitatively assembled in the presence of two different guests, methyl β-D-glucopyranoside and methyl β-D-galactopyranoside, resulting in the formation of two dimeric complexes: (6-MP)2⊃(methyl β-D-glucopyranoside)2 and (6-MM)2⊃(methyl β-D-galactopyranoside∙2H2O)2, respectively. These two complexes exhibit distinct folding structures with domain-swapping cavities depending on the bound guest and temperature. Interestingly, (6-MM)2⊃(methyl β-D-galactopyranoside∙2H2O)2 is exclusively formed at lower temperatures, while (6-MP)2⊃(methyl β-D-glucopyranoside)2 is only formed at higher temperatures.

Dynamic covalent synthesis

Dynamic covalent synthesis aims to precisely control the assembly of simple building blocks linked by reversible covalent bonds to generate a single, structurally complex, product. In recent years, considerable progress in the programmability of dynamic covalent systems has enabled easy access to a broad range of assemblies, including macrocycles, shape-persistent cages, unconventional foldamers and mechanically-interlocked species (catenanes, knots, etc.). The reversibility of the covalent linkages can be either switched off to yield stable, isolable products or activated by specific physico-chemical stimuli, allowing the assemblies to adapt and respond to environmental changes in a controlled manner. This activatable dynamic property makes dynamic covalent assemblies particularly attractive for the design of complex matter, smart chemical systems, out-of-equilibrium systems, and molecular devices.

Four-layer folding framework: design, GAP synthesis, and aggregation-induced emission

The design and synthesis of a type of [1 + 4 + 2] four-layer framework have been conducted by taking advantage of Suzuki-Miyaura cross-coupling and group-assisted purification (GAP) chemistry. The optimized coupling of double-layer diboronic esters with 1-bromo-naphth-2-yl phosphine oxides resulted in a series of multilayer folding targets, showing a broad scope of substrates and moderate to excellent yields. The final products were purified using group-assisted purification chemistry/technology, achieved simply by washing crude products with 95% EtOH without the use of chromatography and recrystallization. The structures were fully characterized and assigned by performing X-ray crystallographic analysis. UV-vis absorption, photoluminescence (PL), and aggregation-induced emission (AIE) were studied for the resulting multilayer folding products.

(Re-)Directing Oligomerization of a Single Building Block into Two Specific Dynamic Covalent Foldamers through pH

Dynamic foldamers are synthetic folded molecules which can change their conformation in response to an external stimulus and are currently at the forefront of foldamer chemistry. However, constitutionally dynamic foldamers, which can change not only their conformation but also their molecular constitution in response to their environment, are without precedent. We now report a size- and shape-switching small dynamic covalent foldamer network which responds to changes in pH. Specifically, acidic conditions direct the oligomerization of a dipeptide-based building block into a 16-subunit macrocycle with well-defined conformation and with high selectivity. At higher pH the same building block yields another cyclic foldamer with a smaller ring size (9mer). The two foldamers readily and repeatedly interconvert upon adjustment of the pH of the solution. We have previously shown that addition of a template can direct oligomerization of the same building block to yet other rings sizes (including a 12mer and a 13mer, accompanied by a minor amount of 14mer). This brings the total number of discrete foldamers that can be accessed from a single building block to five. For a single building block system to exhibit such highly diverse structure space is unique and sets this system of foldamers apart from proteins. Furthermore, the emergence of constitutional dynamicity opens up new avenues to foldamers with adaptive behavior.

Fluorescent Dynamic Covalent Polymers for DNA Complexation and Templated Assembly

Dynamic covalent polymers (DCPs) offer opportunities as adaptive materials of particular interest for targeting, sensing and delivery of biological molecules. In this view, combining cationic units and fluorescent units along DCP chains is attractive for achieving optical probes for the recognition and delivery of nucleic acids. Here, we report on the design of acylhydrazone-based DCPs combining cationic arginine units with π-conjugated fluorescent moieties based on thiophene-ethynyl-fluorene cores. Two types of fluorescent building blocks bearing neutral or cationic side groups on the fluorene moiety are considered in order to assess the role of the number of cationic units on complexation with DNA. The (chir)optical properties of the building blocks, the DCPs, and their complexes with several types of DNA are explored, providing details on the formation of supramolecular complexes and on their stability in aqueous solutions. The DNA-templated formation of DCPs is demonstrated, which provides new perspectives on the assembly of fluorescent DCP based on the nucleic acid structure.

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.

Asymmetric Catalytic Assembly of Triple-Columned and Multiple-Layered Chiral Folding Polymers Showing Aggregation-Induced Emission (AIE)

The first chiral multi-layer 3D folding polymers have been assembled and regulated by both uniformed and differentiated aromatic chromophoric units between naphthyl piers. Screening catalysts, catalytic systems and monomers was proven to be crucial for asymmetric catalytic Suzuki-Miyaura poly-couplings for this assembly. X-ray crystallography of corresponding dimers and trimers revealed the absolute stereochemistry and the intermolecular packing pattern. Up to 61,960 M w /41,900 M n and m / z = 4317 for polymers and oligomers as confirmed by GPC and MALDI-TOF MS indicated that the present frameworks were composed of multiple layers stacked. The resulting multiple π-assemblies exhibited remarkable optical properties in aggregated states (PL in solids and AIE in solutions), as well as reversible redox properties in electrochemical performance.

Supramolecular helices from helical building blocks via head-to-tail intermolecular interactions

Supramolecular helices from helical building blocks represent an emerging analogue of the α-helix. In cases where the helicity of the helical building block is well propagated, the head-to-tail intermolecular interactions that lead to the helix could be enhanced to promote the formation and the stability of the supramolecular helix, wherein homochiral elongation dominates and functional helical channel structures could also be generated. This feature article outlines the supramolecular helices built from helical building blocks, i.e., helical aromatic foldamers and helical short peptides that are held together by intermolecular π-π stacking, hydrogen/halogen/chalcogen bonding, metal coordination, dynamic covalent bonding and solvophobic interactions, with emphasis on the influence of efficient propagation of helicity during assembly, favouring homochirality and channel functions.

Subtle Modification of Imine-linked Helical Receptors to Significantly Alter their Binding Affinities and Selectivities for Chiral Guests

Aromatic helical receptors P-1 and P-2 were slightly modified by aerobic oxidation to afford new receptors P-7 and P-8 with right-handed helical cavities. This subtle modification induced significant changes in the binding properties for chiral guests. Specifically, P-1 was reported to bind d-tartaric acid (K_a =35500 M^-1 ), used as a template, much strongly than l-tartaric acid (326 M^-1 ). In contrast, its modified receptor P-7 exhibited significantly reduced affinities for d-tartaric acid (3600 M^-1 ) and l-tartaric acid (125 M^-1 ). More dramatic changes in the affinities and selectivities were observed for P-2 and P-8 upon binding of polyol guests. P-2 was determined to selectively bind d-sorbitol (52000 M^-1 ) over analogous guests, but P-8 showed no binding selectivity: d-sorbitol (1890 M^-1 ), l-sorbitol (3330 M^-1 ), d-arabitol (959 M^-1 ), l-arabitol (4970 M^-1 ) and xylitol (4960 M^-1 ) in 5% (v/v) DMSO/CH₂ Cl₂ at 25±1 °C. These results clearly demonstrate that even subtle post-modifications of synthetic receptors may significantly alter their binding affinities and selectivities, in particular for guests of long and flexible chains.

Two Sides of the Same Coin: Emergence of Foldamers and Self-Replicators from Dynamic Combinatorial Libraries

The ability of molecules and systems to make copies of themselves and the ability of molecules to fold into stable, well-defined three-dimensional conformations are of considerable importance in the formation and persistence of life. The question of how, during the emergence of life, oligomerization reactions become selective and channel these reactions toward a small number of specific products remains largely unanswered. Herein, we demonstrate a fully synthetic chemical system where structurally complex foldamers and self-replicating assemblies emerge spontaneously and with high selectivity from pools of oligomers as a result of forming noncovalent interactions. Whether foldamers or replicators form depends on remarkably small differences in building block structures and composition and experimental conditions. We also observed the dynamic transformation of a foldamer into a replicator. These results show that the structural requirements/design criteria for building blocks that lead to foldamers are similar to those that lead to replicators. What determines whether folding or replication takes place is not necessarily the type of noncovalent interaction, but only whether they occur intra- or intermolecularly. This work brings together, for the first time, the fields of replicator and foldamer chemistry.

Triple-Columned and Multiple-Layered 3D Polymers: Design, Synthesis, Aggregation-Induced Emission (AIE), and Computational Study

Conjugated polymers and oligomers have great potentials in various fields, especially in materials and biological sciences because of their intriguing electronic and optoelectronic properties. In recent years, the through-space conjugation system has emerged as a new assembled pattern of multidimensional polymers. Here, a novel series of structurally condensed multicolumn/multilayer 3D polymers and oligomers have been designed and synthesized through one-pot Suzuki polycondensation (SPC). The intramolecularly stacked arrangement of polymers can be supported by either X-ray structural analysis or computational analysis. In all cases, polymers were obtained with modest to good yields, as determined by GPC and ¹H-NMR. MALDI-TOF analysis has proven the speculation of the step-growth process of this polymerization. The computational study of ab initio and DFT calculations based on trimer and pentamer models gives details of the structures and the electronic transition. Experimental results of optical and AIE research confirmed by calculation indicates that the present work would facilitate the research and applications in materials.

Autonomous helical propagation of active toroids with mechanical action

Self-assembly in nature is fundamentally dynamic, existing in out-of-equilibrium state in which the systems have the ability to autonomously respond to environmental changes. However, artificial systems exist in a global minimum state, which are incapable of conducting such complex functions. Here we report that input of thermal energy can trigger fixed, artificial toroids to spontaneously nucleate helical growth. The helical polymerization undergoes reversible and repeatable cycles with subsequent energy input. When the toroids are located inside lipid vesicles, the polymerization-depolymerization cycle is accompanied by reversible elongation of spherical vesicles. Such liberation from a global minimum state will pave the way to create emergent structures with functions as complex as those of living systems.

Self-assembly in nature is dynamic and exists in out-of-equilibrium state and thus systems have the ability to autonomously respond to environmental changes. Here the authors report that input of thermal energy can trigger fixed, artificial toroids to spontaneously nucleate helical growth.

Complex Molecules That Fold Like Proteins Can Emerge Spontaneously

Folding can bestow macromolecules with various properties, as evident from nature's proteins. Until now complex folded molecules are the product either of evolution or of an elaborate process of design and synthesis. We now show that molecules that fold in a well-defined architecture of substantial complexity can emerge autonomously and selectively from a simple precursor. Specifically, we have identified a self-synthesizing macrocyclic foldamer with a complex and unprecedented secondary and tertiary structure that constructs itself highly selectively from 15 identical peptide-nucleobase subunits, using a dynamic combinatorial chemistry approach. Folding of the structure drives its synthesis in 95% yield from a mixture of interconverting molecules of different ring sizes in a one-step process. Single-crystal X-ray crystallography and NMR reveal a folding pattern based on an intricate network of noncovalent interactions involving residues spaced apart widely in the linear sequence. These results establish dynamic combinatorial chemistry as a powerful approach to developing synthetic molecules with folding motifs of a complexity that goes well beyond that accessible with current design approaches. The fact that such molecules can form autonomously implies that they may have played a role in the origin of life at earlier stages than previously thought possible.

Template-promoted self-replication in dynamic combinatorial libraries made from a simple building block

We report dynamic combinatorial libraries made from a simple building block that is on the verge of enabling self-assembly driven self-replication. Adding a template provides a sufficient additional push yielding self-replication. Self-assembly and self-replication can emerge with building blocks that are considerably smaller than those reported thus far.

pH-Responsive Dipeptide-Based Dynamic Covalent Chemistry Systems Whose Products and Self-Assemblies Depend on the Structure of Isomeric Aromatic Dialdehydes

Facile control over preparation of organic building blocks and self-assembled aggregations to construct the desired materials remains challenges. This article reports selective dynamic covalent bonds formation and the corresponding self-assembly behaviors by using a dipeptide, glycylglycine (GlyGly), reacting with isomeric aromatic dialdehydes o-phthalaldehyde (OPA), p-phthalaldehyde (PPA), and m-phthalaldehyde (MPA) to demonstrate diversified aggregation forms caused by structure topology variations. Under alkaline condition, the aldehyde groups of phthalaldehydes can be connected with the amino groups of GlyGly by imine bonds as the dynamic chemical bonds. Owing to the fact that formation and dissociation of the imine bonds were reversibly pH-responsive, the reactions and aggregates assembled by their products were also reversibly controlled by changing pH. Three products, including two-armed product (OPGG, in which two GlyGly molecules were connected with one OPA molecule), single-armed product (PPG, in which only one GlyGly molecule was connected with a PPA molecule), and a mixture product (MPGG and MPG), as well as their different self-assembly behaviors, were obtained from OPA/GlyGly, PPA/GlyGly, and MPA/GlyGly systems, respectively, at the same condition of pH 8.6 in 90% methanol aqueous solution. However, for OPA/GlyGly system, another different type of product with benzopyrrole structure (OPG) was obtained by nucleophilic substitution via mixing OPA and GlyGly in water, which generated organic nanoparticles. Based on the results above, we conjectured the differences in dynamic covalent bond formation and supramolecular assembly clearly were influenced by the structure topologies of phthalaldehydes (OPA, PPA, and MPA). The experimental phenomenon verified the hypothesis as well, which may guide us to realize facile construction of selective reaction products and intelligent reversibly responsive materials with diverse morphologies and functions.

Reversible fabrication and self-assembly of a gemini supra-amphiphile driven by dynamic covalent bonds

A smart gemini supra-amphiphile behaving with pH/CO2 dual-sensitive hierarchical self-assembly was fabricated under the effect of dynamic covalent bonds. In the presence of an amino-functionalized cation, water-insoluble terephthalaldehyde, and an amphiphilic anion, the benzoic imine bond can initiate the transformation from a single-tailed supra-amphiphile to a gemini supra-amphiphile with increasing pH, followed by the subsequent evolution from micelles to vesicles. Reversible self-assembly and disassembly of the gemini supra-amphiphile can be realized via CO2/N2 treatment, thus inducing the fission and reversion of vesicles. Interestingly, the flexible nature of supra-amphiphiles allows for the hierarchical assembly of vesicles, leading to the formation of aqueous two-phase systems. Multiple responsive supra-amphiphiles have useful applications in the fabrication of smart supra-molecular materials, including self-healing materials, nanocarriers and chemosensors.

Templated Self-Assembly of Dynamic Peptide Nucleic Acids

Template-directed macromolecule synthesis is a hallmark of living systems. Inspired by this natural process, several fundamentally novel mechanisms for template-directed assembly of nucleic acid analogues have been developed. Although these approaches have broad significance, including potential applications in biotechnology and implications for the origins of life, there are unresolved challenges in how to characterize in detail the complex assembly equilibria associated with dynamic templated reactions. Here we describe mechanistic studies of template-directed dynamic assembly for thioester peptide nucleic acid (tPNA), an informational polymer that responds to selection pressures under enzyme-free conditions. To overcome some of the inherent challenges of mechanistic studies of dynamic oligomers, we designed, synthesized, and implemented tPNA-DNA conjugates. The DNA primer region affords a high level of control over the location and register of the tPNA backbone in relation to the template strand. We characterized the degree and kinetics of dynamic nucleobase mismatch correction at defined backbone positions. Furthermore, we report the fidelity of dynamic assembly in tPNA as a function of position along the peptide backbone. Finally, we present theoretical studies that explore the level of fidelity that can be expected for an oligomer having a given hybridization affinity in dynamic templated reactions and provide guidance for the future development of sequence self-editing polymers and materials. As our results demonstrate, the use of molecular conjugates of constitutionally static and dynamic polymers establishes a new methodology for expediting the characterization of the complex chemical equilibria that underlie the assembly of dynamic informational polymers.

An aryl-triazole foldamer containing a 1,8-naphthalimide fluorescent motif for monitoring and enhancing the anion-induced folding

A 1,8-naphthalimide fluorescent motif was found to facilitate folding and to largely enhance halogen anion binding for an aryl-triazole foldamer.

Supramolecular catalysis in the methylation of meta-phenylene ethynylene foldamer containing N,N-dimethylaminopyridine

DFT investigations show that the methylation reaction of N,N-dimethylaminopyridine (DMAP)-modified meta-phenylene ethynylene foldamer can be catalyzed by the noncovalent interactions between the foldamer and the methyl sulfonate esters.

Dynamic covalent polymers

This Highlight presents an overview of the rapidly growing field of dynamic covalent polymers. This class of polymers combines intrinsic reversibility with the robustness of covalent bonds, thus enabling formation of mechanically stable, polymer-based materials that are responsive to external stimuli. It will be discussed how the inherent dynamic nature of the dynamic covalent bonds on the molecular level can be translated to the macroscopic level of the polymer, giving access to a range of applications, such as stimuli-responsive or self-healing materials. A primary distinction will be made based on the type of dynamic covalent bond employed, while a secondary distinction will be based on the consideration whether the dynamic covalent bond is used in the main chain of the polymer or whether it is used to allow side chain modification of the polymer. Emphasis will be on the chemistry of the dynamic covalent bonds present in the polymer, in particular in relation to how the specific (dynamic) features of the bond impart functionality to the polymer material, and to the conditions under which this dynamic behavior is manifested. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3551-3577.

Dynamic control of chirality and self-assembly of double-stranded helicates with light

Helicity switching in biological and artificial systems is a fundamental process that allows for the dynamic control of structures and their functions. In contrast to chemical approaches to responsive behaviour in helicates, the use of light as an external stimulus offers unique opportunities to invert the chirality of helical structures in a non-invasive manner with high spatiotemporal precision. Here, we report that unidirectional rotary motors with connecting oligobipyridyl ligands, which can dynamically change their chirality upon irradiation, assemble into metal helicates that are responsive to light. The motor function controls the self-assembly process as well as the helical chirality, allowing switching between oligomers and double-stranded helicates with distinct handedness. The unidirectionality of the light-induced motion governs the sequence of programmable steps, enabling the highly regulated self-assembly of fully responsive helical structures. This discovery paves the way for the future development of new chirality-dependent photoresponsive systems including smart materials, enantioselective catalysts and light-driven molecular machines.

Facile Stimuli-Responsive Transformation of Vesicle to Nanofiber to Supramolecular Gel via ω-Amino Acid-Based Dynamic Covalent Chemistry

This paper reports an interesting type of self-assembly systems based on dynamic covalent bonds. The systems are pH-responsible and reversible, which could be utilized for controlling the morphology transformation of the assemblies. In alkaline conditions, the amine group of 11-aminoundecanoic acid (AUA) can connect with the aldehyde group of benzaldehyde (BA) or 1-naphthaledhyde (NA) by dynamic covalent bond to form a small organic building block accompanied by the morphological transformation from vesicles to fibers. When pH is lowered to a neutral value, the dynamic covalent bonds (imine bonds) can be hydrolyzed, leading to the dissociation of fibers and appearance of spherical aggregates. The transformation was confirmed reversible as fibers appeared again when the pH was changed back to alkaline value. In addition, a reversibly controlled gel was designed based on the nanofiber formation. NaCl, which is capable of greatly enhance the nanofiber density and cross-linking, was used to induce the growth of free-standing gel from free-flowing nanofiber system, and the resultant gel was proven to be pH-reversible.

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

Photoinduced heterodisulfide metathesis for reagent-free synthesis of polymer nanoparticles

Reagent-free synthetic methods are of great interest because of their simplicity and implications in green chemistry. We have taken advantage of photoinduced heterodisulfide metathesis to generate crosslinked polymer nanoparticles. The method of development and the mechanistic basis for the synthetic approach are outlined in this communication.

Dynamic combinatorial/covalent chemistry: a tool to read, generate and modulate the bioactivity of compounds and compound mixtures

Reversible covalent bond formation under thermodynamic control adds reactivity to self-assembled supramolecular systems, and is therefore an ideal tool to assess complexity of chemical and biological systems. Dynamic combinatorial/covalent chemistry (DCC) has been used to read structural information by selectively assembling receptors with the optimum molecular fit around a given template from a mixture of reversibly reacting building blocks. This technique allows access to efficient sensing devices and the generation of new biomolecules, such as small molecule receptor binders for drug discovery, but also larger biomimetic polymers and macromolecules with particular three-dimensional structural architectures. Adding a kinetic factor to a thermodynamically controlled equilibrium results in dynamic resolution and in self-sorting and self-replicating systems, all of which are of major importance in biological systems. Furthermore, the temporary modification of bioactive compounds by reversible combinatorial/covalent derivatisation allows control of their release and facilitates their transport across amphiphilic self-assembled systems such as artificial membranes or cell walls. The goal of this review is to give a conceptual overview of how the impact of DCC on supramolecular assemblies at different levels can allow us to understand, predict and modulate the complexity of biological systems.

Assembly-driven synthesis of hybrid molecular capsules controlled by chiral sorting

Chiral capsules with polar interiors (reversed capsules) undergo heterochiral sorting and exhibit positive mutalism - both hemispheres mutually benefit from the association. This feature can be coupled with partial reversibility of the formation reaction and utilized to amplify synthesis of hybrid capsules made of hemispheres that cannot be formed independently.

Recycling of informational units leads to selection of replicators in a prebiotic soup

Prebiotic chemical reactions would have been greatly aided by a process whereby living materials could have been recycled under conditions of limiting resources. Recombination of RNA fragments is a viable means of recycling but has not been demonstrated. Using systems based on the Azoarcus group I intron ribozyme, computational Monte Carlo studies indicate that a moderate level of recycling activity, spontaneous or catalyzed, leads to the most robust selection scenarios. It is interesting that recycling leads to a threshold effect where a dominant species suddenly jumps to fixation. In conjunction, laboratory studies with the Azoarcus ribozyme corroborate these results, showing that mixtures of scrambled and/or deleteriously mutated molecules can recycle their component fragments to generate fully functional recombinase ribozymes. These studies highlight the importance of recombination and recycling jointly in the advent of living systems.

Toward self-constructing materials: a systems chemistry approach

To design the next generation of so-called "smart" materials, researchers will need to develop chemical systems that respond, adapt, and multitask. Because many of these features occur in living systems, we expect that such advanced artificial systems will be inspired by nature. In particular, these new materials should ultimately combine three key properties of life: metabolism, mutation, and self-replication. In this Account, we discuss our endeavors toward the design of such advanced functional materials. First, we focus on dynamic molecular libraries. These molecular and supramolecular chemical systems are based on mixtures of reversibly interacting molecules that are coupled within networks of thermodynamic equilibria. We will explain how the superimposition of combinatorial networks at different length scales of structural organization can provide valuable hierarchical dynamics for producing complex functional systems. In particular, our experimental results highlight why these libraries are of interest for the design of responsive materials and how their functional properties can be modulated by various chemical and physical stimuli. Then, we introduce examples in which these dynamic combinatorial systems can be coupled to kinetic feedback loops to produce self-replicating pathways that amplify a selected component from the equilibrated libraries. Finally, we discuss the discovery of highly functional self-replicating supramolecular assemblies that can transfer an electric signal in space and time. We show how these wires can be directly incorporated within an electronic nanocircuit by self-organization and functional feedback loops. Because the network topologies act as complex algorithms to process information, we present these systems in this order to provide context for their potential for extending the current generation of responsive materials. We propose a general description for a potential autonomous (self-constructing) material. Such a system should self-assemble among several possible molecular combinations in response to external information (input) and possibly self-replicate to amplify its structure. Ultimately, its functional response (output) can drive the self-assembly of the system and also serve a mechanism to transfer this initial information. Far from equilibrium, such synergistic processes could give rise to evolving, "information gaining" systems which become increasingly complex because internal self-organization rapidly reduces the potential energy surrounding the system.

H-shaped supra-amphiphiles based on a dynamic covalent bond

The imine bond, a kind of dynamic covalent bond, is used to bind two bolaform amphiphiles together with spacers, yielding H-shaped supra-amphiphiles. Micellar aggregates formed by the self-assembly of the H-shaped supra-amphiphiles are observed. When pH is tuned down from basic to slightly acidic, the benzoic imine bond can be hydrolyzed, leading to the dissociation of H-shaped supra-amphiphiles. Moreover, H-shaped supra-amphiphiles have a lower critical micelle concentration than their building blocks, which is very helpful in enhancing the stability of the benzoic imine bond being hydrolyzed by acid. The surface tension isotherms of the H-shaped supra-amphiphiles with different spacers indicate their twisty conformation at a gas-water interface. The study of H-shaped supra-amphiphiles can enrich the family of amphiphiles, and moreover, the pH-responsiveness may make them apply to controlled or targetable drug delivery in a biological environment.

Biodynamers: self-organization-driven formation of doubly dynamic proteoids

Polypeptide-type dynamic biopolymers (biodynamers) have been generated by polycondensation via acylhydrazone and imine formation of amino-acid-derived components that polymerize driven by self-organization. They have been characterized as globular particles, reminiscent of folded proteins, by cryo-TEM, LS, DOSY NMR, and SANS studies. The reversible polymers obtained show remarkably low dispersity and feature double covalent dynamics allowing for fine-tuning of both exchange and incorporation processes through pH control. In the course of build-up, they perform a selection of the most suitable building block, as indicated by the preferential incorporation of the more hydrophobic amino-acid component with increased rate and higher molecular weight of the polymer formed. The system described displays nucleation-elongation behavior driven by hydrophobic effects and represents a model for the operation of adaptation processes in the evolution of complex matter.