No abstract

A T-shaped aromatic amphiphilic molecule based on linear oligo(ethylene oxide) was synthesized. We suggest that its peculiar interfacial behavior at the air-water interface and the structure of the Langmuir-Blodgett monolayer are associated with its peculiar T-shape and competing steric and amphiphilic interactions at different surface pressures. At low surface pressure, uniform and smooth monolayers were formed. Upon compression, the molecular reorganization from spherical to cylindrical transformation occurred, as caused by the submerging of the oligo(ethylene oxide) chains, providing for efficient pi-pi interactions of the central core. At the highest surface pressure, the monolayer collapses into bilayer domains, following a bicontinuous network formation which tends to transform into a perforated film. The unique shape of T-like rigid aromatic cores makes their structural reorganization very peculiar with paired, dimerlike molecular packing dominating in gas and solid states. This paired aggregation is so strong that it is preserved in the course of flipping and formation of vertically oriented backbones.

Stimulierbare Fasern: Aggregate aus Nanofasern mit hydrophilen Oligoethylenoxid‐Dendronen als Hülle gehen beim Erwärmen reversibel in hydrophobe Nanofaserbündel über, da eine Dehydratisierung der dendritischen Ketten auftritt (siehe Schema). Ein thermischer Sol‐Gel‐Phasenübergang ist die Folge.

The a helix is an essential secondary structural motif in proteins. In particular, a helices at the outer surface of proteins play an important role in specific biomolecular recognition events, such as in protein-DNA, protein-RNA, and protein-protein interactions. [1] The a-helical structures are well stabilized in the context of intact proteins. However, an a-helix-forming segment, when isolated from the protein as a short peptide, is rarely helical in solution owing to its inherent thermodynamic instability. [2] Because the stabilization of active folded forms of peptide is important for maintaining the unique functions of protein, extensive research into stabilized a-helical peptides has been carried out. [3] Peptide helix stabilization approaches include the covalent cross-linking of amino acids located at the same face of an a helix, [3a,b] hydrogen-bond surrogates, [2a] metal coordination, [3c] salt bridge formation, [3d] helix nucleation, [3e] helix capping, [3f] and synthetic a-helix receptors. [3g] These minimalist approaches have advantages with regard to simplicity and cost efficiency. However, when considering many a-helix-mediated interactions occurring in a multivalent fashion, [4] the inherent limitation of such monomeric ahelix approaches is that the complex and multivalent biological interactions cannot be effectively targeted.Herein, we describe a simple but effective supramolecular approach in which multiple a-helix-coated artificial proteins can be constructed by the self-assembly of simple peptides. Bottom-up self-assembly of functional supramolecular building blocks is a cost-efficient way of constructing bioactive multivalent structures. [5] To substantiate this goal, a building block was designed in such a way that both an a-helical peptide segment and a self-assembling segment are located within a single macrocyclic structure (peptide 4, Figure 1 a). As the self-assembling segment, a b-sheet peptide with predictable and well-known self-assembly behavior was selected. The a-helix-forming segment is an alanine-based peptide. Lysines are located within the stretch of alanines to increase water solubility and to prevent aggregation. [6] The bsheet peptide segment is a repeat of hydrophobic and of positively or negatively charged amino acids. Such combination of amino acids promotes b-sheet hydrogen bonding and subsequent self-assembly into bilayered ribbon-like fibrous nanostructures. [7] Oligoethylene glycol-based linker segments are placed between the a-helical-and b-sheet-forming sequences to decouple both segments. The peptide macrocycle was designed based on the hypotheses that 1) a cyclic structure will partially stabilize the helical structure by decreasing conformational entropy of the unfolded state, [8] and 2) a self-assembly-induced coil-to-rod transition in the bsheet segment will further constrain and stabilize the helical structure (Figure 1 b). The cyclization reaction was performed while protected peptide was still bound to the resin to achieve a pseudo-dilution ...