Hierarchical Self-Assembly of Halogen-Bonded Block Copolymer Complexes into Upright Cylindrical Domains

Self-assembly of block copolymers into well-defined, ordered arrangements of chemically distinct domains is a reliable strategy for preparing tailored nanostructures. Microphase separation results from the system, minimizing repulsive interactions between dissimilar blocks and maximizing attractive interactions between similar blocks. Supramolecular methods have also achieved this separation by introducing small-molecule additives binding specifically to one block by noncovalent interactions. Here, we use halogen bonding as a supramolecular tool that directs the hierarchical self-assembly of low-molecular-weight perfluorinated molecules and diblock copolymers. Microphase separation results in a lamellar-within-cylindrical arrangement and promotes upright cylindrical alignment in films upon rapid casting and without further annealing. Such cylindrical domains with internal lamellar self-assemblies can be cleaved by solvent treatment of bulk films, resulting in separated and segmented cylindrical micelles stabilized by halogen-bond-based supramolecular crosslinks. These features, alongside the reversible nature of halogen bonding, provide a robust modular approach for nanofabricatio

Supramolecular amplification of amyloid self-assembly by iodination

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents

Oberflächen passen sich an - bürstenartige Polymermoleküle an Oberflächen mit schaltbaren Eigenschaften

It is the surface which in many cases determines the appearance and application-relevant properties of a material. Thin films of polymer brushes just a few nanometres in thickness can change the surface properties significantly and may provide even switching capabilities, where the thin film will for instance take up or repel water. Polymer brushes of two largely different polymer materials must in this case be tightly attached at one end to a solid substrate and will then occupy alternatively the upper or lower surface layer, depending on external conditions. In this way, either one or the other polymer material will be exposed and influence the surface properties. This purely physical switching process can be controlled by external triggers (selective or non-selective solvents, pH value, temperature, etc.). The physico- chemical surface properties (wettability, functionality etc.) switch between values established by the properties of the polymer materials involved.Oberflächen bestimmen in vielen Fällen das Erscheinungsbild und wichtige Gebrauchseigenschaften von Materialen. Bereits wenige Nanometer dünne Polymerfilme können diese Eigenschaften signifikant verändern und erlauben es, diese Eigenschaften sogar zu schalten, sodass ein Film beispielsweise Wasser abweisen oder aufnehmen kann. Hierzu werden Polymerbürsten aus zwei sehr verschiedenen Polymeren mit dem einen Ende fest an ein Substrat gebunden. In Abhängigkeit von den äußeren Bedingungen können sie sich dann wechselseitig an der Oberfläche anreichern, sodass die Oberflächeneigenschaften jeweils durch das eine oder andere Polymer bestimmt werden. Dieser rein physikalische Schaltprozess kann durch externe Stimuli (selektive oder nichtselektive Lösungsmittel, pH-Wert, Temperatur etc.) initiiert werden, wobei die physiko-chemischen Oberflächeneigenschaften (Benetzbarkeit, Funktionalität etc.) zwischen den durch die Eigenschaften der verwendeten Polymere bestimmten Extremwerten hin und her schalten können

Supramolecular amplification of amyloid self-assembly by iodination

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents

Gas phase synthesis of non-bundled, small diameter single-walled carbon nanotubes with near-armchair chiralities

We present a floating catalyst synthesis route for individual, i.e., non-bundled, small diameter single-walled carbon nanotubes (SWCNTs) with a narrow chiral angle distribution peaking at high chiralities near the armchair species. An ex situ spark discharge generator was used to form iron particles with geometric number mean diameters of 3–4 nm and fed into a laminar flow chemical vapour deposition reactor for the continuous synthesis of long and high-quality SWCNTs from ambient pressure carbon monoxide. The intensity ratio of G/D peaks in Raman spectra up to 48 and mean tube lengths up to 4 μm were observed. The chiral distributions, as directly determined by electron diffraction in the transmission electron microscope, clustered around the (n,m) indices (7,6), (8,6), (8,7), and (9,6), with up to 70% of tubes having chiral angles over 20°. The mean diameter of SWCNTs was reduced from 1.10 to 1.04 nm by decreasing the growth temperature from 880 to 750 °C, which simultaneously increased the fraction of semiconducting tubes from 67% to 80%. Limiting the nanotube gas phase number concentration to ∼10 exp 5 cm exp −3 prevented nanotube bundle formation that is due to collisions induced by Brownian diffusion. Up to 80% of 500 as-deposited tubes observed by atomic force and transmission electron microscopy were individual. Transparent conducting films deposited from these SWCNTs exhibited record low sheet resistances of 63 Ω/□ at 90% transparency for 550 nm light.Peer reviewe

Superfluorinated Ionic Liquid Crystals Based on Supramolecular, Halogen-Bonded Anions

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [CnF2n+1-I···I···I-CnF2n+1]- are reported. The material system is unique in many ways, demonstrating for the first time 1)ionic, halogen-bonded liquid crystals, and 2)imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation

Adsorption and Grafting of Polyelectrolytes at Solid-Liquid Interfaces

A novel strategy for fabrication of responsive functional polymer films is based on grafting of several different functional polymers onto a solid substrate at high grafting density, resulting in varied types of polymer brushes. Such an arrangement suggests many interesting applications of the multicomponent polymer brushes, regarding their versatile adaptive surfaces, capable for responding to changes of solvent polarity, pH, temperature, electromagnetic field and other stimuli, generally by reversible swelling. Mixed amphiphilic polystyrene-poly(2-vynil pyridine) (PS-P2VP) brushes are an example for responsive class of smart materials, which can switch between hydrophilic and hydrophobic energetic state upon changes in the quality of surrounding media. The switching of wettability was found to operate in a broad range and was selectively controlled in organic solvents and in aqueous solutions. Another example for an adaptive/switching behavior is addressed to a polymer brush with a remarkable response to the pH and the ionic strength variations of the aqueous solutions. Combination of weak polyacrylic acid, PAA, and weak polybase, P2VP, in the anchored layer allowed one with a small shift of the pH, to obtain a significant effect on the surface and the interfacial properties of the material. Both type of polymer brushes were examined as adsorbing materials for nanoparticles and charged synthetic- and bio-macromolecules. Their adaptive properties were successively linked to the results of the adsorption experiments. The simplest case was adsorption of nano-particles, functionalised with strong ionic groups, onto binary, PAA-P2VP, polyelectrolyte brushes. Maintaining a constant charge density of the adsorbing component (strong polyelectrolyte effect), allowed one to cause and manipulate a privileged swelling of one of the weak polyelectrolyte brush layers, without affecting the adsorbate properties, and to regulate the thickness of adsorbed layer only by the pH signal. In the case of adsorption of macromolecules with tuneable electrical charge (polyampholytes and proteins), the system became more complicated, regarding their environmentally responsive properties, similar to that exhibited by the polymer brushes. The driving forces were regulated by the switching performance of the brush, simply by adjusting the pH and/or ionic strength conditions. The adsorbed amount and morphological changes of polyampholyte layers were investigated as function of pH and was performed on mixed amphiphilic and binary polyelectrolyte brushes. A special emphasis was set on the binary brush capability to take the control over the interfacial performance of attaching proteins. It was found, that the sharp environmental response of the adsorbent (the polymer brush) strongly influences the morphology of adsorbed protein layers, their thickness and properties. Changing the polarity of the substrate allowed one to regulate the adsorption processes qualitatively and quantitatively. The significant aggregation of protein molecules on PS-P2VP brush and their disassembly on PAA-P2VP brush at the same solvent conditions, we devote to the hydrophobic-hydrophilic transition, occurred at the surface by replacing PS with PAA. The protein aggregates, monitored on the surface of PS-P2VP, sufficiently decrease their size, when switching the brush energetic state from hydrophobic to hydrophilic by adjusting the pH of the media. This effect was found to be well controlled by the brush switching phenomenon in hydrophilic-hydrophobic direction and vice versa. In conclusion, we showed how the structural reorganization in thin polymer brush layers of different type may dramatically affect their surface properties. The adaptive behavior in response of external stimuli was found to be a basis for highly specific interactions, depending on geometric factors, conformational state and environment

Complexation-Driven Mutarotation in Poly(l-proline) Block Copolypeptides

Novel poly(l-lysine)-block-poly(l-proline) (PLL-b-PLP)-based materials with all PLP helical conformers, i.e., PLP II and the rare PLP I are here reported. Electrostatic supramolecular complexation of the adjacent cationic PLL with anionic molecules bearing DNA analogue H-bonding functionalities, such as deoxyguanosine monophosphate (dGMP), preserves the extended PLP II helix, and the complexed molecule is locked and held in position by orthogonal shape-persistent hydrogen-bonded dGMP ribbons and their extended π-stacking. The branched anionic surfactant dodecylbenzenesulfonic acid (DBSA) on the other hand, introduces periodicity frustration and interlayer plasticization, leading to a reversed mutarotation to the more compact PLP I helix by complexation, without external stimuli, and is here reported for the first time. We foresee that our findings can be used as a platform for novel molecularly adaptive functional materials, and could possibly give insight in many proline-related transmembrane biological functions. © 2015 American Chemical Society