This review discusses one-dimensional supramolecular polymers that form in aqueous media. First, naturally occurring supramolecular polymers are described, in particular, amyloid fibrils, actin filaments, and microtubules. Their structural, thermodynamic, kinetic, and nanomechanical properties are highlighted, as well as their importance for the advancement of biologically inspired supramolecular polymer materials. Second, five classes of synthetic supramolecular polymers are described: systems based on (1) hydrogen-bond motifs, (2) large π-conjugated surfaces, (3) host-guest interactions, (4) peptides, and (5) DNA. We focus on recent studies that address key challenges in the field, providing mechanistic understanding, rational polymer design, important functionality, robustness, or unusual thermodynamic and kinetic properties.

Enzymes are a source of inspiration for chemists attempting to create versatile synthetic catalysts. In order to arrive at a polymeric chain carrying catalytic units separated spatially, it is a prerequisite to fold these polymers in water into well-defined compartmentalized architectures thus creating a catalytic core. Herein, we report the synthesis, physical properties, and catalytic activity of a water-soluble segmented terpolymer in which a helical structure in the apolar core is created around a ruthenium-based catalyst. The supramolecular chirality of this catalytic system is the result of the self-assembly of benzene-1,3,5-tricarboxamide side chains, while the catalyst arises from the sequential ruthenium-catalyzed living radical polymerization of the different monomers followed by ligand exchange. The polymers exhibit a two-state folding process and show transfer hydrogenation in water.

A challenging target in the noncovalent synthesis of nanostructured functional materials is the formation of uniform features that exhibit well-defined properties, e.g., precise control over the aggregate shape, size, and stability. In particular, for aqueousbased one-dimensional supramolecular polymers, this is a daunting task. Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing out attractive noncovalent forces within the hydrophobic core of the polymerizing building blocks with electrostatic repulsive interactions on the hydrophilic rim we managed to switch from elongated, rod-like assemblies to small and discrete objects. Intriguingly this rod-tosphere transition is expressed in a loss of cooperativity in the temperature-dependent self-assembly mechanism. The aggregates were characterized using circular dichroism, UV and 1H-NMR spectroscopy, small angle X-ray scattering, and cryotransmission electron microscopy. In analogy to many systems found in biology, mechanistic details of the self-assembly pathways emphasize the importance of cooperativity as a key feature that dictates the physical properties of the produced supramolecular polymers.aqueous self-assembly | controlled architecture | supramolecular polymerization | dynamic materials M olecular self-assembly has emerged as a fascinating area in its own right (1, 2). A toolbox initially developed by supramolecular chemists quickly expanded into an interdisciplinary field aiming at the manipulation of matter at the molecular scale (3, 4). Up until recently self-assembly in dilute aqueous environments has predominantly dealt with linear amphiphiles that form closed structures (5-9), such as spherical micelles, cylindrical or rod-like micelles, and vesicles using, for example, phospholipids (10, 11), synthetic block copolymers (12, 13), or dendrimers (14). Morphological control in objects of defined size or shape, and transitions between different morphologies are increasingly well understood (15)(16)(17)(18). Surprisingly, however, the generality of these concepts has not been translocated into another area of increasing interest, namely, the self-assembly of one-dimensional arrays. In that context the development of discotic monomers has proven to be a valuable route to allow for the synthesis of rod-like supramolecular polymers (19), whose potential applications in functional soft matter include electronics, biomedical engineering, and sensors (20)(21)(22)(23)(24)(25)(26). Considering the enormous interest in such systems, it is surprising that efforts to control the size and shape of nano-and micrometer size one-dimensional objects are rare (27-29); successful strategies rely on the use of templates (30, 31), end cappers (32), or selective solvent techniques (33).In order to control the growth of aqueous one-dimensional supramolecular polymers, we propose to utilize electrostatic repulsive contributions in analogy to surfactant...

β-sheet-encoded anionic and cationic dendritic peptide amphiphiles form supramolecular copolymers when self-assembled in a 1:1 feed ratio of the monomers. These ampholytic materials have been designed for on-off polymerization in response to pH triggers. The cooperative supramolecular self-assembly process is switched on at a physiologically relevant pH value and can be switched off by increasing or decreasing the pH value.

The self-assembly into supramolecular polymers is a process driven by reversible non-covalent interactions between monomers, and gives access to materials applications incorporating mechanical, biological, optical or electronic functionalities. Compared to the achievements in precision polymer synthesis via living and controlled covalent polymerization processes, supramolecular chemists have only just learned how to developed strategies that allow similar control over polymer length, (co)monomer sequence and morphology (random, alternating or blocked ordering). This highlight article discusses the unique opportunities that arise when coassembling multicomponent supramolecular polymers, and focusses on four strategies in order to control the polymer architecture, size, stability and its stimuli-responsive properties: (1) endcapping of supramolecular polymers, (2) biomimetic templated polymerization, (3) controlled selectivity and reactivity in supramolecular copolymerization, and (4) living supramolecular polymerization. In contrast to the traditional focus on equilibrium systems, our emphasis is also on the manipulation of selfassembly kinetics of synthetic supramolecular systems. V C 2016

A multistimuli-responsive transient supramolecular polymerization of β-sheet-encoded dendritic peptide monomers in water is presented. The amphiphiles, which contain glutamic acid and methionine, undergo a glucose oxidase catalyzed, glucose-fueled transient hydrogelation in response to an interplay of pH and oxidation stimuli, promoted by the production of reactive oxygen species (ROS). Adjusting the enzyme and glucose concentration allows tuning of the assembly and the disassembly rates of the supramolecular polymers, which dictate the stiffness and transient stability of the hydrogels. The incorporation of triethylene glycol chains introduces thermoresponsive properties to the materials. We further show that repair enzymes are able to reverse the oxidative damage in the methionine-based thioether side chains. Since ROS play an important role in signal transduction cascades, our strategy offers great potential for applications of these dynamic biomaterials in redox microenvironments.

The combination of attractive supramolecular interactions of a hydrophobic Au-metallopeptide with the shielding effect of flexible oligoethylene glycol chains provides access to a stepwise self-assembly of a Au-metalloamphiphile in water. Kinetic control of the supramolecular polymer morphology is achieved using a temperature-dependent assembly protocol, which yields low dispersity supramolecular polymers (metastable state I) or helical bundled nanorods (state II).

To develop fluorescent organic nanoparticles with tailored properties for imaging and sensing, full control over the size, fluorescence, stability, dynamics, and supramolecular organization of these particles is crucial. We have designed, synthesized, and fully characterized 12 nonionic fluorene co-oligomers that formed self-assembled fluorescent nanoparticles in water. In these series of molecules, the ratio of hydrophilic ethylene glycol and hydrophobic alkyl side chains was systematically altered to investigate its role on the above-mentioned properties. The nanoparticles consisting of π-conjugated oligomers containing polar ethylene glycol side chains were less stable and larger in size, while nanoparticles self-assembled from oligomers containing nonpolar pendant chains were more stable, smaller, and generally had a higher fluorescence quantum yield. Furthermore, the dynamics of the molecules between the nanoparticles was enhanced if the number of hydrophilic side chains increased. Energy transfer studies between naphthalene and benzothiadiazole fluorene co-oligomers with the same side chains showed no exchange of molecules between the particles for the apolar molecules. For the more polar systems, the exchange of molecules between nanoparticles took place at room temperature or after annealing. Self-assembled nanoparticles consisting of π-conjugated oligomers having different side chains caused self-sorting, resulting either in the formation of domains within particles or the formation of separate nanoparticles. Our results show that we can control the stability, fluorescence, dynamics, and self-sorting properties of the nanoparticles by simply changing the nature of the side chains of the π-conjugated oligomers. These findings are not only important for the field of self-assembled nanoparticles but also for the construction of well-defined multicomponent supramolecular materials in general.