Molecular scaffolds that enable the combinatorial synthesis of new supramolecular building blocks are promising targets for the construction of functional molecular systems. Here, we report a ...supramolecular scaffold based on boroxine that enables the formation of chiral and ordered 1D supramolecular polymers, which can be easily functionalized for circularly polarized luminescence. The boroxine monomers are quantitatively synthesized in situ, both in bulk and in solution, from boronic acid precursors and cooperatively polymerize into 1D helical aggregates stabilized by threefold hydrogen‐bonding and π–π stacking. We then demonstrate amplification of asymmetry in the co‐assembly of chiral/achiral monomers and the co‐condensation of chiral/achiral precursors in classical and in situ sergeant‐and‐soldiers experiments, respectively, showing fast boronic acid exchange reactions occurring in the system. Remarkably, co‐condensation of pyrene boronic acid with a hydrogen‐bonding chiral boronic acid results in chiral pyrene aggregation with circularly polarized excimer emission and g‐values in the order of 10−3. Yet, the electron deficiency of boron in boroxine makes them chemically addressable by nucleophiles, but also sensitive to hydrolysis. With this sensitivity in mind, we provide first insights into the prospects offered by boroxine‐based supramolecular polymers to make chemically addressable, functional, and adaptive systems.
Boronic acid self‐condensation provides ready access to boroxine‐based, C3‐symmetrical monomer architectures that can cooperatively assemble into helical supramolecular polymers. The dynamic boroxine scaffold enables fast intermolecular exchange of boronic acid between different monomers and facilitates the introduction of functionality into assembled structures by co‐condensation with functional boronic acids.
Polysaccharides present in the glycocalyx and extracellular matrix are highly important for a multitude of functions. Oligo- and polysaccharides-based biomaterials are being developed to mimic the ...glycocalyx, but the spatial functionalization of these polysaccharides represents a major challenge. In this paper, a series of benzene-1,3,5-tricarboxamide (BTA) based supramolecular monomers is designed and synthesized with mono- (BTA-β-d-glucose; BTA-Glc and BTA-α-d-mannose; BTA-Man) or disaccharides (BTA-β-d-cellobiose; BTA-Cel) at their periphery or a monosaccharide (BTA-OEG4-α-d-mannose; BTA-OEG4-Man) at the end of a tetraethylene glycol linker. These glycosylated BTAs have been used to generate supramolecular assemblies and it is shown that the nature of the carbohydrate appendage is crucial for the supramolecular (co)polymerization behavior. BTA-Glc and BTA-Man are shown to assemble into micrometers long 1D (bundled) fibers with opposite helicities, whereas BTA-Cel and BTA-OEG4-Man formed small spherical micelles. The latter two monomers are used in a copolymerization approach with BTA-Glc, BTA-Man, or ethylene glycol BTA (BTA-OEG4) to give 1D fibers with BTA-Cel or BTA-OEG4-Man incorporated. Consequently, the carbohydrate appendage influences both the assembly behavior and the internal order. Using this approach it is possible to create 1D-fibers with adjustable saccharide densities exhibiting tailored dynamic exchange profiles. Furthermore, hydrogels with tunable mechanical properties can be achieved, opening up possibilities for the development of multicomponent functional biomaterials.
In biology, polymorphism is a well-known phenomenon by which a discrete biomacromolecule can adopt multiple specific conformations in response to its environment. The controlled incorporation of ...polymorphism into noncovalent aqueous assemblies of synthetic small molecules is an important step toward the development of bioinspired responsive materials. Herein, we report on a family of carboxylic acid functionalized water-soluble benzene-1,3,5-tricarboxamides (BTAs) that self-assemble in water to form one-dimensional fibers, membranes, and hollow nanotubes. Interestingly, one of the BTAs with the optimized position of the carboxylic group in the hydrophobic domain yields nanotubes that undergo reversible temperature-dependent dynamic reorganizations. SAXS and Cryo-TEM data show the formation of elongated, well-ordered nanotubes at elevated temperatures. At these temperatures, increased dynamics, as measured by hydrogen–deuterium exchange, provide enough flexibility to the system to form well-defined nanotube structures with apparently defect-free tube walls. Without this flexibility, the assemblies are frozen into a variety of structures that are very similar at the supramolecular level, but less defined at the mesoscopic level.
The cytoskeleton is a highly adaptive network of filamentous proteins capable of stiffening under stress even as it dynamically assembles and disassembles with time constants of minutes. Synthetic ...materials that combine reversibility and strain-stiffening properties remain elusive. Here, strain-stiffening hydrogels that have dynamic fibrous polymers as their main structural components are reported. The fibers form via self-assembly of bolaamphiphiles (BA) in water and have a well-defined cross-section of 9 to 10 molecules. Fiber length recovery after sonication, H/D exchange experiments, and rheology confirm the dynamic nature of the fibers. Cross-linking of the fibers yields strain-stiffening, self-healing hydrogels that closely mimic the mechanics of biological networks, with mechanical properties that can be modulated by chemical modification of the components. Comparison of the supramolecular networks with covalently fixated networks shows that the noncovalent nature of the fibers limits the maximum stress that fibers can bear and, hence, limits the range of stiffening.
Numerous self-assembling molecules have been synthesized aiming at mimicking both the structural and dynamic properties found in living systems. Here we show the application of hydrogen/deuterium ...exchange (HDX) mass spectrometry (MS) to unravel the nanoscale organization and the structural dynamics of synthetic supramolecular polymers in water. We select benzene-1,3,5-tricarboxamide (BTA) derivatives that self-assemble in H
O to illustrate the strength of this technique for supramolecular polymers. The BTA structure has six exchangeable hydrogen atoms and we follow their exchange as a function of time after diluting the H
O solution with a 100-fold excess of D
O. The kinetic H/D exchange profiles reveal that these supramolecular polymers in water are dynamically diverse; a notion that has previously not been observed using other techniques. In addition, we report that small changes in the molecular structure can be used to control the dynamics of synthetic supramolecular polymers in water.
Polar cosolvents are commonly used to guide the self-assembly of amphiphiles in water. Here we investigate the influence of the cosolvent acetonitrile (ACN) on the structure and dynamics of a ...supramolecular polymer in water, which is based on the well-known benzene-1,3,5-tricarboxamide motif. Hydrogen/deuterium exchange mass spectroscopy measurements show that a gradual increase in the amount of ACN results in a gradual increase in the exchange dynamics of the monomers. In contrast, the morphology of the supramolecular polymers remains unchanged up to 15% of ACN, but then an abrupt change occurs and spherical aggregates are formed. Remarkably, this abrupt change coincides with the formation of micro-heterogeneity in the water-ACN mixtures. The results illustrate that in order to completely characterize supramolecular polymers it is important to add time-resolved measurements that probe their dynamic behavior, to the conventional techniques that are used to assess the morphology of the polymers. Subsequently we have used time-resolved measurements to investigate the influence of the concentration of ACN on the polymerization and depolymerization rates of the supramolecular polymers. Polymerization occurs within minutes when molecularly dissolved monomers are injected from ACN into water and is independent of the fraction of ACN up to 15%. In the depolymerization experiments-initiated by mixing equilibrated supramolecular polymers with dissolved monomers-the equilibration of the system takes multiple hours and does depend on the fraction of ACN. Interestingly, the longest equilibration time of the polymers is observed at a critical solvent composition of around 15% ACN. The differences in the timescales detected in the polymerization and depolymerization experiments are likely correlated to the non-covalent interactions involved, namely the hydrophobic effect and hydrogen-bonding interactions. We attribute the observed fast kinetics in the polymerization reactions to the hydrophobic effect, whereas the formation of intermolecular hydrogen bonds is the retarding factor in the equilibration of the polymers in the depolymerization experiments. Molecular dynamics simulations show that the latter is a likely explanation because ACN interferes with the hydrogen bonds and loosens the internal structure of the polymers. Our results highlight the importance of the solution conditions during the non-covalent synthesis of supramolecular polymers, as well as after equilibration of the polymers.
A major challenge in supramolecular polymerization is controlling the stability of the polymers formed, that is, controlling the rate of monomer exchange in the equilibrium between monomer and ...polymer. The exchange dynamics of supramolecular polymers based on benzene‐1,3,5‐tricarboxamide (BTA) can be regulated by copolymerizing molecules with dendronized (dBTA) and linear (nBTA) ethylene glycol‐based water‐soluble side chains. Whereas nBTAs form long nanofibers in water, dBTAs do not polymerize, forming instead small spherical aggregates. The copolymerization of the two BTAs results in long nanofibers. The exchange dynamics of both the BTA monomers in the copolymer are significantly slowed down in the mixed systems, leading to a more stable copolymer, while the morphology and spectroscopic signature of the copolymers are identical to that of nBTA homopolymer. This copolymerization is the supramolecular counterpart of styrene/ maleic anhydride copolymerization.
The exchange dynamics of supramolecular polymers based on benzene‐1,3,5‐tricarboxamide (BTA) can be regulated by copolymerizing molecules with dendronized (dBTA) and linear (nBTA) ethylene glycol‐based water‐soluble side chains. Whereas nBTAs form long nanofibers in water, dBTAs do not polymerize. The copolymerization of the two BTAs results in more stable long nanofibers.
Molecular scaffolds that enable the combinatorial synthesis of new supramolecular building blocks are promising targets for the construction of functional molecular systems. Here, we report a ...supramolecular scaffold based on boroxine that enables the formation of chiral and ordered 1D supramolecular polymers, which can be easily functionalized for circularly polarized luminescence. The boroxine monomers are quantitatively synthesized in situ, both in bulk and in solution, from boronic acid precursors and cooperatively polymerize into 1D helical aggregates stabilized by threefold hydrogen‐bonding and π–π stacking. We then demonstrate amplification of asymmetry in the co‐assembly of chiral/achiral monomers and the co‐condensation of chiral/achiral precursors in classical and in situ sergeant‐and‐soldiers experiments, respectively, showing fast boronic acid exchange reactions occurring in the system. Remarkably, co‐condensation of pyrene boronic acid with a hydrogen‐bonding chiral boronic acid results in chiral pyrene aggregation with circularly polarized excimer emission and g‐values in the order of 10−3. Yet, the electron deficiency of boron in boroxine makes them chemically addressable by nucleophiles, but also sensitive to hydrolysis. With this sensitivity in mind, we provide first insights into the prospects offered by boroxine‐based supramolecular polymers to make chemically addressable, functional, and adaptive systems.
Boronic acid self‐condensation provides ready access to boroxine‐based, C3‐symmetrical monomer architectures that can cooperatively assemble into helical supramolecular polymers. The dynamic boroxine scaffold enables fast intermolecular exchange of boronic acid between different monomers and facilitates the introduction of functionality into assembled structures by co‐condensation with functional boronic acids.
Maleic anhydride (MA) was grafted onto poly(β-hydroxybutyrate) (PHB) chains by using styrene (St) as co-monomer and dicumyl peroxide (DCP) as free-radical initiator. The grafting degree of MA was ...increased from 0.2 wt% to 0.9 wt% with the St/MA ratio up to 2/1. The St-assisted grafting mechanisms are revealed based on titration, thermogravimetric analysis and infrared analysis, i.e. MA is grafted onto PHB chains by way of single monomers and charge-transfer-complex (CTC) at the St/MA ratios of ≤1/1, while St-co-MA oligomers are the dominating grafting pendants when the St/MA ratios ≥2/1. The decomposition temperature (Td-5%) of PHB is raised by approx. 35 °C after grafting of the MA and/or short St/MA pendants, meanwhile higher molecular weight of the PHB is obtained. In addition, the crystallization of PHB is promoted by grafting of the MA or MA-co-St oligomers. The crystallization mechanism of maleated PHB is proposed as well.
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