Potential enthalpic energy of water in oils exploited to control supramolecular structure

Energetics of Competing Chiral Supramolecular Polymers

Chirality can have unexpected consequences including on properties other than spectroscopic. We show herein that a racemic mixture of bis-urea stereoisomers forms thermodynamically stable supramolecular polymers that result in a more viscous solution than for the pure stereoisomer. The origin of this macroscopic property was probed by characterizing the structure and stability of the assemblies. Both racemic and non-racemic bis-urea stereoisomers form two competing helical supramolecular polymers in solution: a double and a single helical structure at low and high temperature, respectively. The transition temperature between these assemblies, as probed by spectroscopic and calorimetric analyses, is strongly influenced by the composition (by up to 70 °C). A simple model that accounts for the thermodynamics of this system, indicates that the stereochemical defects (chiral mismatches and helix reversals) affect much more the stability of single helices. Therefore, the heterochiral double helical structure predominates over the single helical structure (whilst the opposite holds for the homochiral structures), which explains the aforementioned higher viscosity of the racemic bis-urea solution. This rationale constitutes a new basis to tune the macroscopic properties of the increasing number of supramolecular polymers reported to exhibit competing chiral nanostructures.

Acid Catalysis with Alkane/Water Microdroplets in Ionic Liquids

Ionic liquids are composed of an organic cation and a highly delocalized perfluorinated anion, which remain tight to each other and neutral across the extended liquid framework. Here we show that n-alkanes in millimolar amounts enable a sufficient ion charge separation to release the innate acidity of the ionic liquid and catalyze the industrially relevant alkylation of phenol, after generating homogeneous, self-stabilized, and surfactant-free microdroplets (1-5 μm). This extremely mild and simple protocol circumvents any external additive or potential ionic liquid degradation and can be extended to water, which spontaneously generates microdroplets (ca. 3 μm) and catalyzes Brönsted rather than Lewis acid reactions. These results open new avenues not only in the use of ionic liquids as acid catalysts/solvents but also in the preparation of surfactant-free, well-defined ionic liquid microemulsions.

Engineering the Nanoscaled Morphologies of Linear DNA Homopolymers

Supramolecular polymers have unique characteristics such as self-healing and easy processing. However, the scope of their structures is limited to mostly either flexible, random coils or rigid, straight chains. By broadening this scope, novel properties, functions, and applications can be explored. Here, DNA is used as a model system to engineer innovative, nanoscaled morphologies of supramolecular polymers. Each polymer chain consists of multiple copies of the same short (38-46 nucleotides long) DNA strand. The component DNA strands first dimerize into homo-dimers, which then further assemble into long polymer chains. By subtly tuning the design, a range of polymer morphologies are obtained; including straight chains, spirals, and closed rings with finite sizes. Such structures are confirmed by AFM imaging and predicted by molecular coarse simulation.

Overtemperature-protection intelligent molecular chiroptical photoswitches

Stimuli-responsive intelligent molecular machines/devices are of current research interest due to their potential application in minimized devices. Constructing molecular machines/devices capable of accomplishing complex missions is challenging, demanding coalescence of various functions into one molecule. Here we report the construction of intelligent molecular chiroptical photoswitches based on azobenzene-fused bicyclic pillar[n]arene derivatives, which we defined as molecular universal joints (MUJs). The Z/E photoisomerization of the azobenzene moiety of MUJs induces rolling in/out conformational switching of the azobenzene-bearing side-ring and consequently leads to planar chirality switching of MUJs. Meanwhile, temperature variation was demonstrated to also cause conformational/chiroptical inversion due to the significant entropy change during the ring-flipping. As a result, photo-induced chiroptical switching could be prohibited when the temperature exceeded an upper limit, demonstrating an intelligent molecular photoswitch having over-temperature protection function, which is in stark contrast to the low-temperature-gating effect commonly encountered.

Realizing overtemperature protection with a molecular device is challenging. Here, the authors demonstrate an overtemperature protection function by integrating thermo- and photoresponsive functions into a pillar[6]arene based pseudocatanene.

Supramolecular Depolymerization in the Mixture of Two Poor Solvents: Mechanistic Insights and Modulation of Supramolecular Polymerization of Ionic π-Systems

Solvents are fundamentally essential for the synthesis and processing of soft materials. Supramolecular polymers (SPs), an emerging class of soft materials, are usually stable in single and mixtures of poor solvents. In contrast to these preconceived notions, here we report the depolymerization of SPs in the mixture of two poor solvents. This surprising behavior was observed for well-known cationic perylene diimides (cPDIs) in the mixtures of water and amphiphilic organic solvents such as isopropanol (IPA). cPDIs form stable SPs in water and IPA but readily depolymerize into monomers in 50-70 vol% IPA containing water. This is due to the selective solvation of the π-surface of cPDIs by alkyl chains of IPA and ionic side chains by water, as evidenced by molecular dynamic simulations. Moreover, by systematically changing the ratio between water and amphiphilic organic solvent, we could achieve an unprecedented supramolecular polymerization both by increasing and decreasing the solvent polarity.

Mechanistic insights of evaporation-induced actuation in supramolecular crystals

Water-responsive materials undergo reversible shape changes upon varying humidity levels. These mechanically robust yet flexible structures can exert substantial forces and hold promise as efficient actuators for energy harvesting, adaptive materials and soft robotics. Here we demonstrate that energy transfer during evaporation-induced actuation of nanoporous tripeptide crystals results from the strengthening of water hydrogen bonding that drives the contraction of the pores. The seamless integration of mobile and structurally bound water inside these pores with a supramolecular network that contains readily deformable aromatic domains translates dehydration-induced mechanical stresses through the crystal lattice, suggesting a general mechanism of efficient water-responsive actuation. The observed strengthening of water bonding complements the accepted understanding of capillary-force-induced reversible contraction for this class of materials. These minimalistic peptide crystals are much simpler in composition compared to natural water-responsive materials, and the insights provided here can be applied more generally for the design of high-energy molecular actuators.

Pathway and Length Control of Supramolecular Polymers in Aqueous Media via a Hydrogen Bonding Lock

Programming the organization of π-conjugated systems into nanostructures of defined dimensions is a requirement for the preparation of functional materials. Herein, we have achieved high-precision control over the self-assembly pathways and fiber length of an amphiphilic BODIPY dye in aqueous media by exploiting a programmable hydrogen bonding lock. The presence of a (2-hydroxyethyl)amide group in the target BODIPY enables different types of intra- vs. intermolecular hydrogen bonding, leading to a competition between kinetically controlled discoidal H-type aggregates and thermodynamically controlled 1D J-type fibers in water. The high stability of the kinetic state, which is dominated by the hydrophobic effect, is reflected in the slow transformation to the thermodynamic product (several weeks at room temperature). However, this lag time can be suppressed by the addition of seeds from the thermodynamic species, enabling us to obtain supramolecular polymers of tuneable length in water for multiple cycles.

Competition between chiral solvents and chiral monomers in the helical bias of supramolecular polymers

Solute-solvent interactions are key for the assembly and proper functioning of biomacromolecules and play important roles in many fields of organic and polymer chemistry. Despite numerous reports describing the effects of (chiral) solvents on helical conformations of (supramolecular) polymers, the combination of chiral solvents and chiral monomers is unexplored. Here we report diastereomeric differences in the supramolecular polymerization of enantiomers of chiral triphenylene-2,6,10-tricarboxamides in chiral chlorinated solvents. Competition between the preferences induced by the stereocentres of the assembled monomers and those present in the solvent molecules results in unforeseen temperature-dependent solvation effects. By combining experiments and mathematical modelling, we show that the observed differences between enantiomers originate from the combined additive entropic effects of stereocentres present in the monomer and in the solvent. Remarkably, copolymerizations show that the chiral solvent can bias the copolymer helicity and thereby overrule the helical preference of the monomers. Our results highlight the importance of cumulative solvation effects in supramolecular polymerizations.

Biasing the Screw-Sense of Supramolecular Coassemblies Featuring Multiple Helical States

By enchaining a small fraction of chiral monomer units, the helical sense of a dynamic polymer constructed from achiral monomer units can be disproportionately biased. This phenomenon, known as the sergeants-and-soldiers (S&S) effect, has been found to be widely applicable to dynamic covalent and supramolecular polymers. However, it has not been exemplified with a supramolecular polymer that features multiple helical states. Herein, we demonstrate the S&S effect in the context of the temperature-controlled supramolecular copolymerization of chiral and achiral biphenyl tetracarboxamides in alkanes. The one-dimensional helical structures presented in this study are unique because they exhibit three distinct helical states, two of which are triggered by coassembling with monomeric water that is codissolved in the solvent. The self-assembly pathways are rationalized using a combination of mathematical fitting and simulations with a thermodynamic mass-balance model. We observe an unprecedented case of an "abnormal" S&S effect by changing the side chains of the achiral soldier. Although the molecular structure of these aggregates remains elusive, the coassembly of water is found to have a profound impact on the helical excess.

Solute-Solvent Interactions in Modern Physical Organic Chemistry: Supramolecular Polymers as a Muse

Interactions between solvents and solutes are a cornerstone of physical organic chemistry and have been the subject of investigations over the last century. In recent years, a renewed interest in fundamental aspects of solute-solvent interactions has been sparked in the field of supramolecular chemistry in general and that of supramolecular polymers in particular. Although solvent effects in supramolecular chemistry have been recognized for a long time, the unique opportunities that supramolecular polymers offer to gain insight into solute-solvent interactions have become clear relatively recently. The multiple interactions that hold the supramolecular polymeric structure together are similar in strength to those between solute and solvent. The cooperativity found in ordered supramolecular polymers leads to the possibility of amplifying these solute-solvent effects and will shed light on extremely subtle solvation phenomena. As a result, many exciting effects of solute-solvent interactions in modern physical organic chemistry can be studied using supramolecular polymers. Our aim is to put the recent progress into a historical context and provide avenues toward a more comprehensive understanding of solvents in multicomponent supramolecular systems.

Control of self-assembly pathways toward conglomerate and racemic supramolecular polymers

Homo- and heterochiral aggregation during crystallization of organic molecules has significance both for fundamental questions related to the origin of life as well as for the separation of homochiral compounds from their racemates in industrial processes. Herein, we analyse these phenomena at the lowest level of hierarchy – that is the self-assembly of a racemic mixture of (R,R)- and (S,S)-PBI into 1D supramolecular polymers. By a combination of UV/vis and NMR spectroscopy as well as atomic force microscopy, we demonstrate that homochiral aggregation of the racemic mixture leads to the formation of two types of supramolecular conglomerates under kinetic control, while under thermodynamic control heterochiral aggregation is preferred, affording a racemic supramolecular polymer. FT-IR spectroscopy and quantum-chemical calculations reveal unique packing arrangements and hydrogen-bonding patterns within these supramolecular polymers. Time-, concentration- and temperature-dependent UV/vis experiments provide further insights into the kinetic and thermodynamic control of the conglomerate and racemic supramolecular polymer formation.

Homo- and heterochiral aggregation is a process of interest to prebiotic and chiral separation chemistry. Here, the authors analyze the self-assembly of a racemic mixture into 1D supramolecular polymers and find homochiral aggregation into conglomerates under kinetic control, while under thermodynamic control a racemic polymer is formed.

Long-Lived Charge-Transfer State from B-N Frustrated Lewis Pairs Enchained in Supramolecular Copolymers

The field of supramolecular polymers is rapidly expanding; however, the exploitation of these systems as functional materials is still elusive. To become competitive, supramolecular polymers must display microstructural order and the emergence of new properties upon copolymerization. To tackle this, a greater understanding of the relationship between monomers' design and polymer microstructure is required as well as a set of functional monomers that efficiently interact with one another to synergistically generate new properties upon copolymerization. Here, we present the first implementation of frustrated Lewis pairs into supramolecular copolymers. Two supramolecular copolymers based on π-conjugated O-bridged triphenylborane and two different triphenylamines display the formation of B-N pairs within the supramolecular chain. The remarkably long lifetime and the circularly polarized nature of the resulting photoluminescence emission highlight the possibility to obtain an intermolecular B-N charge transfer. These results are proposed to be the consequences of the enchainment of B-N frustrated Lewis pairs within 1D supramolecular aggregates. Although it is challenging to obtain a precise molecular picture of the copolymer microstructure, the formation of random blocklike copolymers could be deduced from a combination of optical spectroscopic techniques and theoretical simulation.

Hydrogen-bonded host-guest systems are stable in ionic liquids

We show that H-bonded host–guest systems associate in ionic liquids (ILs), pure salts with melting point below room temperature, in which dipole–dipole electrostatic interactions should be negligible in comparison with dipole-charge interactions. Binding constants (K_a) obtained from titrations of four H-bonded host–guest systems in two organic solvents and two ionic liquids yield smaller yet comparable K_a values in ionic liquids than in organic solvents. We also detect the association event using force spectroscopy, which confirms that the binding is not solely due to (de)solvation processes. Our results indicate that classic H-bonded host–guest supramolecular chemistry takes place in ILs. This implies that strong H-bonds are only moderately affected by surroundings composed entirely of charges, which can be interpreted as an indication that the balance of Coulombic to covalent forces in strong H-bonds is not tipped towards the former.

Morphology control in metallosupramolecular assemblies through solvent-induced steric demand

Controlling the supramolecular self-assembly of π-conjugated systems into defined morphologies is a prerequisite for the preparation of functional materials. In recent years, the development of sophisticated sample preparation protocols and modulation of various experimental conditions (solvent, concentration, temperature, etc.) have enabled precise control over aggregation pathways of different types of monomer units. A common method to achieve pathway control consists in the combination of two miscible solvents in defined proportions - a "poor" and "good" solvent. However, the role of solvents of opposed polarity in the self-assembly of a given building block still remains an open question. Herein, we unravel the effect of aggregation-inducing solvent systems of opposed polarity (aqueous vs. non-polar media) on the supramolecular assembly of a new bolaamphiphilic Pt(ii) complex. A number of experimental methods show a comparable molecular packing in both media driven by a synergy of solvophobic, aromatic and weak hydrogen-bonding interactions. However, morphological analysis of the respective aggregates in aqueous and non-polar media reveals a restricted aggregate growth in aqueous media into spherical nanoparticles and a non-restricted 2D-nanosheet formation in non-polar media. These findings are attributed to a considerably more efficient solvation and, in turn, increased steric demand of the hydrophilic chains in aqueous media than in nonpolar media, which can be explained by the entrapment of water molecules in the hydrophilic aggregate shell via hydrogen bonds. Our findings reveal that the different solvation of peripheral solubilizing groups in solvents of opposed polarity is an efficient method for morphology control in self-assembly.

Illuminating the Impact of Submicron Particle Size and Surface Chemistry on Interfacial Position and Pickering Emulsion Type

Pickering emulsions are increasingly applied in the production of medicines, cosmetics, and in food technology. To apply Pickering emulsions in a rational manner it is insufficient to examine properties solely on a macroscopic scale, as this does not elucidate heterogeneities in contact angles (θ) of individual particles, which may have a profound impact on stability and microstructure. Here, we apply the super-resolution technique iPAINT to elucidate for the first time the microscopic origins of macroscopically observed emulsion phase inversions induced by a variation in particle size and aqueous phase pH. We find θ of single carboxyl polystyrene submicron particles (CPS) significantly decreases due to increasing aqueous phase pH and particle size, respectively. Our findings confirm that θ of submicron particles are both size- and pH-dependent. Interestingly, for CPS stabilized water-octanol emulsions, this enables tuning of emulsion type from water-in-oil to oil-in-water by adjustments in either particle size or pH.

How Water in Aliphatic Solvents Directs the Interference of Chemical Reactivity in a Supramolecular System

Water is typically considered to be insoluble in alkanes. Recently, however, monomerically dissolved water in alkanes has been shown to dramatically impact the structure of hydrogen-bonded supramolecular polymers. Here, we report that water in methylcyclohexane (MCH) also determines the outcome of combining a Michael reaction with a porphyrin-based supramolecular system. In dry conditions, the components of the reaction do not affect or destabilize the supramolecular polymer, whereas in ambient or wet conditions the polymers are rapidly destabilized. Although spectroscopic investigations show no effect of water on the molecular structure of the supramolecular polymer, light scattering and atomic force microscopy experiments show that water increases the flexibility of the supramolecular polymer and decreases the polymer length. Through a series of titrations, we show that a cooperative interaction, involving the coordination of the amine catalyst to the porphyrin and complexation of the substrates to the flexible polymers invokes the depolymerization of the aggregates. Water crucially stabilizes these cooperative interactions to cause complete depolymerization in humid conditions. Additionally, we show that the humidity-controlled interference in the polymer stability occurs with various substrates, indicating that water may play a ubiquitous role in supramolecular polymerizations in oils. By controlling the amount of water, the influence of a covalent chemical process on noncovalent aggregates can be mediated, which holds great potential to forge a connection between chemical reactivity and supramolecular material structure. Moreover, our findings highlight that understanding cooperative interactions in multicomponent noncovalent systems is crucial to design complex molecular systems.

Modulation of the Self-Assembly of π-Amphiphiles in Water from Enthalpy- to Entropy-Driven by Enwrapping Substituents

Depending on the connectivity of solubilizing oligoethylene glycol (OEG) side chains to the π-cores of amphiphilic naphthalene and perylene bisimide dyes, self-assembly in water occurs either upon heating or cooling. Herein, we show that this effect originates from differences in the enwrapping capability of the π-cores by the OEG chains. Rylene bisimides bearing phenyl substituents with three OEG chains attached directly to the hydrophobic π-cores are strongly sequestered by the OEG chains. These molecules self-assemble at elevated temperatures in an entropy-driven process according to temperature- and concentration-dependent UV/Vis spectroscopy and calorimetric dilution studies. In contrast, for rylene bisimides in which phenyl substituents with three OEG chains are attached via a methylene spacer, leading to much weaker sequestration, self-assembly originates upon cooling in an enthalpy-driven process. Our explanation for this controversial behavior is that the aggregation in the latter case is dictated by the release of "high energy water" from the hydrophobic π-surfaces as well as dispersion interactions between the π-scaffolds which drive the self-assembly in an enthalpically driven process. In contrast, for the former case we suggest that in addition to the conventional explanation of a dehydration of hydrogen-bonded water molecules from OEG units it is in particular the increase in conformational entropy of back-folded OEG side chains upon aggregation that provides the pronounced gain in entropy that drives the aggregation process. Thus, our studies revealed that a subtle change in the attachment of solubilizing substituents can switch the thermodynamic signature for the self-assembly of amphiphilic dyes in water from enthalpy- to entropy-driven.

Solvent Water Controls Photocatalytic Methanol Reforming

Understanding the role of different solvent molecules for practical solid-liquid heterogeneous photocatalytic reactions is critical for determining the pathway of the reaction. In this study, the operando nuclear magnetic resonance (NMR) method, combined with density functional theory (DFT) calculations, was employed to evaluate the control effect of solvent water in the photocatalytic reforming mechanism of methanol with a Pt-TiO₂ catalyst. Results indicate that the presence of water effectively promotes the formation of the HCHO intermediate but inhibits the H₂ evolution originating from the switch of the hydrogen source of the H₂ formation from CH₃OH to H₂O. More interestingly, as detected directly in the ab initio molecular dynamics simulation, a small amount of H₂O can dissociate, and the evolved -OH species at Ti_5c site can greatly reduce the C-H activation barrier of -CH₃O, contributing to the formation of oxidation products (e.g., HOCH₂OH and CH₃OCH₂OH) on the Pt-TiO₂ surface.

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

Synchrotron radiation provides insight into spectroscopy and dynamics in clusters and nanoparticles.

Thermodynamic insights into the entropically driven self-assembly of amphiphilic dyes in water

Self-assembly of amphiphilic dyes and π-systems are more difficult to understand and to control in water compared to organic solvents due to the hydrophobic effect. Herein, we elucidate in detail the self-assembly of a series of archetype bolaamphiphiles bearing a naphthalene bisimide (NBI) π-core with appended oligoethylene glycol (OEG) dendrons of different size. By utilizing temperature-dependent UV-vis spectroscopy and isothermal titration calorimetry (ITC), we have dissected the enthalpic and entropic parameters pertaining to the molecules' self-assembly. All investigated compounds show an enthalpically disfavored aggregation process leading to aggregate growth and eventually precipitation at elevated temperature, which is attributed to the dehydration of oligoethylene glycol units and their concomitant conformational changes. Back-folded conformation of the side chains plays a major role, as revealed by molecular dynamics (MD) and two dimensional NMR (2D NMR) studies, in directing the association. The sterical effect imparted by the jacketing of monomers and dimers also changes the aggregation mechanism from isodesmic to weakly anti-cooperative.

Steering the Self-Assembly Outcome of a Single NDI Monomer into Three Morphologically Distinct Supramolecular Assemblies, with Concomitant Change in Supramolecular Polymerization Mechanism

Noncovalent self-assembly creates an effective route to highly sophisticated supramolecular polymers with tunable properties. However, the outcome of this assembly process is highly dependent on external conditions. In this work, a monomeric naphthalene diimide (NDI), designed to allow solubility in a wide range of solvents, can assemble into three distinct noncovalent supramolecular species depending on solvent composition and temperature. Namely, while the self-assembly in chlorinated solvents yields relatively short, hydrogen-bonded nanotubes, the reduction of solvent polarity changes the assembly outcome, yielding π-π stacking polymers, which can further bundle into a more complex aggregate. The obtained polymers differ not only in their global morphology but-more strikingly-also in the thermodynamics and kinetics of their supramolecular self-assembly, involving isodesmic or two-stage cooperative assembly with kinetic hysteresis, respectively. Ultimately, three distinct assembly states can be accessed in a single experiment.

A Competing Hydrogen Bonding Pattern to Yield a Thermo-Thickening Supramolecular Polymer

Introduction of competing interactions in the design of a supramolecular polymer (SP) creates pathway complexity. Ester-bis-ureas contain both a strong bis-urea sticker that is responsible for the build-up of long rod-like objects by hydrogen bonding and ester groups that can interfere with this main pattern in a subtle way. Spectroscopic (FTIR and CD), calorimetric (DSC), and scattering (SANS) techniques show that such ester-bis-ureas self-assemble into three competing rod-like SPs. The previously unreported low-temperature SP is stabilized by hydrogen bonds between the interfering ester groups and the urea moieties. It also features a weak macroscopic alignment of the rods. The other structures form isotropic dispersions of rods stabilized by the more classical urea-urea hydrogen bonding pattern. The transition from the low-temperature structure to the next occurs reversibly by heating and is accompanied by an increase in viscosity, a rare feature for solutions in hydrocarbons.

Assembling a Natural Small Molecule into a Supramolecular Network with High Structural Order and Dynamic Functions

Programming the hierarchical self-assembly of small molecules has been a fundamental topic of great significance in biological systems and artificial supramolecular systems. Precise and highly programmed self-assembly can produce supramolecular architectures with distinct structural features. However, it still remains a challenge how to precisely control the self-assembly pathway in a desirable way by introducing abundant structural information into a limited molecular backbone. Here we disclose a strategy that directs the hierarchical self-assembly of sodium thioctate, a small molecule of biological origin, into a highly ordered supramolecular layered network. By combining the unique dynamic covalent ring-opening-polymerization of sodium thioctate and an evaporation-induced interfacial confinement effect, we precisely direct the dynamic supramolecular self-assembly of this simple small molecule in a scheduled hierarchical pathway, resulting in a layered structure with long-range order at both macroscopic and molecular scales, which is revealed by small-angle and wide-angle X-ray scattering technologies. The resulting supramolecular layers are found to be able to bind water molecules as structural water, which works as an interlayer lubricant to modulate the material properties, such as mechanical performance, self-healing capability, and actuating function. Analogous to many reversibly self-assembled biological systems, the highly dynamic polymeric network can be degraded into monomers and reformed by a water-mediated route, exhibiting full recyclability in a facile, mild, and environmentally friendly way. This approach for assembling commercial small molecules into structurally complex materials paves the way for low-cost functional supramolecular materials based on synthetically simple procedures.

Equilibrium Model for Supramolecular Copolymerizations

The coassembly of different building blocks into supramolecular copolymers provides a promising avenue to control their properties and to thereby expand the potential of supramolecular polymers in applications. However, contrary to covalent copolymerization which nowadays can be well controlled, the control over sequence, polymer length, and morphology in supramolecular copolymers is to date less developed, and their structures are more determined by the delicate balance in binding free energies between the distinct building blocks than by kinetics. Consequently, to rationalize the structures of supramolecular copolymers, a thorough understanding of their thermodynamic behavior is needed. Though this is well established for single-component assemblies and over the past years several models have been proposed for specific copolymerization cases, a generally applicable model for supramolecular cooperative copolymers is still lacking. Here, we provide a generalization of our earlier mass-balance models for supramolecular copolymerizations that encompasses all our earlier models. In this model, the binding free energies of each pair of monomer types in each aggregate type can be set independently. We provide scripts to solve the model numerically for any (co)polymerization of one or two types of monomer into an arbitrary number of distinct aggregate types. We illustrate the applicability of the model on data from literature as well as on new experimental data of triarylamine triamide-based copolymers in three distinct solvents. We show that apart from common properties such as the degree of polymerization and length distributions, our approach also allows us to investigate properties such as the copolymer microstructure, that is, the internal ordering of monomers within the copolymers. Moreover, we show that in some cases, also intriguing analytical approximations can be derived from the mass balances.

From prebiotic chemistry to supramolecular oligomers: urea-glyoxal reactions

A fundamental question in origin-of-life studies and astrochemistry concerns the actual processes that initiate the formation of reactive monomers and their oligomerization. Answers lie partly in the accurate description of reaction mechanisms compatible with environments plausible on early Earth as well as cosmological scenarios in planetary factories. Here we show in detail that reactions of urea-as archetypal prebiotic substance-and reactive carbonyls-exemplified by glyoxal-lead to a vast repertoire of oligomers, in which different five- and six-membered non-aromatic heterocycles self-assemble and insert into chains or dendritic-like structures with masses up to 1000 Da. Such regular patterns have been interpreted by experimental and computational methods. A salient conclusion is that such processes most likely occur through SN-type mechanisms on hydrated or protonated species. Remarkably, such supramolecular oligomeric mixtures can be easily isolated from organic solvents, thus opening the door to the generation of novel urea-containing polymers with potential applications in materials chemistry and beyond.

One-pot universal initiation-growth methods from a liquid crystalline block copolymer

The construction of hierarchical nanostructures with precise morphological and dimensional control has been one of the ultimate goals of contemporary materials science and chemistry, and the emulation of tailor-made nanoscale superstructures realized in the nature, using artificial building blocks, poses outstanding challenges. Herein we report a one-pot strategy to precisely synthesize hierarchical nanostructures through an in-situ initiation-growth process from a liquid crystalline block copolymer. The assembly process, analogous to living chain polymerization, can be triggered by small-molecule, macromolecule or even nanoobject initiators to produce various hierarchical superstructures with highly uniform morphologies and finely tunable dimensions. Because of the high degree of controllability and predictability, this assembly strategy opens the avenue to the design and construction of hierarchical structures with broad utility and accessibility.

Super-resolution microscopy on single particles at fluid interfaces reveals their wetting properties and interfacial deformations

Solid particles adsorbed at fluid interfaces are crucial for the mechanical stability of Pickering emulsions. The key parameter which determines the kinetic and thermodynamic properties of these colloids is the particle contact angle, θ. Several methods have recently been developed to measure the contact angle of individual particles adsorbed at liquid-liquid interfaces, as morphological and chemical heterogeneities at the particle surface can significantly affect θ. However, none of these techniques enables the simultaneous visualization of the nanoparticles and the reconstruction of the fluid interface to which they are adsorbed, in situ. To tackle this challenge, we utilize a newly developed super-resolution microscopy method, called iPAINT, which exploits non-covalent and continuous labelling of interfaces with photo-activatable fluorescent probes. Herewith, we resolve with nanometer accuracy both the position of individual nanoparticles at a water-octanol interface and the location of the interface itself. First, we determine single particle contact angles for both hydrophobic and hydrophilic spherical colloids. These experiments reveal a non-negligible dependence of θ on particle size, from which we infer an effective line tension, τ. Next, we image elliptical particles at a water-decane interface, showing that the corresponding interfacial deformations can be clearly captured by iPAINT microscopy.

Future of Supramolecular Copolymers Unveiled by Reflecting on Covalent Copolymerization

Supramolecular copolymers are an emerging class of materials, and in the last years their potential has been demonstrated on a broad scale. Implementing noncovalent polymers with multiple components can bring together useful features such as dynamicity and new functionalities. However, mastering and tuning the microstructure of these systems is still an open challenge. In this Perspective, we aim to trace the general principles of supramolecular copolymerization by analyzing them through the lens of the well-established field of covalent copolymerization. Our goal is to delineate guidelines to classify and analyze supramolecular copolymers in order to create a fruitful platform to design and investigate new multicomponent systems.

Vinyl Triflimides-A Case of Assisted Vinyl Cation Formation

A new concept for selectivity control in carbocation-driven reactions has been identified which allows for the chemo-, regio-, and stereoselective addition of nucleophiles to alkynes-assisted vinyl cation formation-enabled by a Li⁺ -based supramolecular framework. Mechanistic analysis of a model complex (Li₂ NTf₂ ⁺ ⋅3 H₂ O) confirms that solely the formation of a complex between the incoming nucleophile and the transition state of the alkyne protonation is responsible for the resulting selective N addition to the vinyl cation. Into the bargain, a general, operationally simple synthetic procedure to previously inaccessible vinyl triflimides is provided.

Temperature-controlled helical inversion of asymmetric triphenylamine-based supramolecular polymers; difference of handedness at the micro- and macroscopic levels

The M-helicity of asymmetric N-triphenylamine-based supramolecular polymers was inverted to the P-helicity during heating.