Self‐Supporting Elastic Film without Covalent Linkages as a Hierarchically Integrated β‐Sheet Assembly

Abstract

In general, an amphiphilic molecule that can form an aggregate in a certain medium, especially an aqueous bilayer aggregate, forms a self-supporting film when the solution is cast onto an appropriate substrate then air dried.[1] The orderly molecular alignment within the cast film is useful for forming an ultrathin layer or coating with few defects. However, the supramolecular cast film has neither mechanical strength nor elasticity. Our aim in the present study is to improve the mechanical strength of the cast film, and to form an elastic supramolecular film that has the elastic properties of a macromolecular film. The prominent advantages of macromolecular films, namely, strength and elasticity, are ascribed to the covalent linkage that constitutes a sequence of the lowest unit molecule, the monomer. Therefore, an alternative interaction is needed to replace the covalent linkage to obtain an elastic supramolecular film. By using multiple H bonding as an alternative, Meijer and co-workers have demonstrated a supramolecular polymer.[2] The monomer of the supramolecular polymer has two sets of H-bonding blocks, for example, pyrimidon, at both edges of the molecule, which links the other molecules by multiple H bonding. The bora-type monomers yield a highly viscous, resinlike liquid. A similar substance has also been reported by Rebek, Jr. and coworkers.[3] Furthermore, the research group of Hutchison demonstrated that the self-assembled monolayer of a glycylglycine-containing amphiphile was stabilized by 3D networks of H bonding.[4] On the other hand, multiple H bonding has been observed as a b-sheet structure in the cast films of the tripeptide-containing amphiphiles.[5] These amphiphiles produce a self-supporting transparent film, but they are extremely brittle. This result means that another interaction that immobilizes the b-sheets will be needed for improving the mechanical strength of the supramolecular film. Thus, we attempted to use the side chains of the peptide part. Because the side chains of the adjacent amino-acid residues locate in opposite directions across the b-sheet plane, [6] the side chains could interlock with counterparts of the other b-sheet planes. This specific interdigitated structure should fasten the b-sheet planes when the peptide part contains at least three consecutive leucine residues as illustrated in Figure 1, which is similar to a zipper or a fastener. To reduce the confusion with the leucine zipper peptides, we prefer to call the aforementioned structure "leucine fastener". The leucine fastener will not be formed if a b-sheet structure is absent. Emphasis is placed on this hierarchy. However, until now, such hierarchic integration has not yet been realized. We demonstrate herein the hierarchic integration of supramolecular monomers, and aim to form a self-supporting elastic film without covalent linkage between the monomers.The supramolecular monomers used in the study are leucine-containing amphiphiles (N + C 11 (Leu) n Glu(OC 12 ) 2 ; n = 2, 3, 4). These amphiphiles dissolve i...

Binding Mechanisms in Supramolecular Complexes

“…Deviations from the increments are to be anticipated if the acidity or basicity of the groups involved changes considerably. [359] The production of nanoscale materials from DNA double strands and the corresponding quadruplexes also rests on such complementary hydrogen bonds. [353] Generally speaking, additivity appears to be better preserved with stronger associations.…”

“…[357] Nucleic acids themselves represent building blocks for the construction of higher molecular weight associates through numerous D-A combinations, [358] as well as for the development of new materials through selfassociation. [359] The production of nanoscale materials from DNA double strands and the corresponding quadruplexes also rests on such complementary hydrogen bonds. [360] Such D-A arrays are particularly well-suited to the noncovalent binding of fullerenes to electron-donor units in redox-or photoactivatable systems.…”

Bindungsmechanismen in supramolekularen Komplexen

“…[357] Nucleinsäuren selber dienen als Bausteine für die Konstruktion höhermolekularer Assoziate über zahlreiche D-A-Kombinationen, [358] auch für die Ent-wicklung neuer Materialien durch Selbstassoziation. [359] Auch die Herstellung nanoskaliger Materialien aus DNA-Doppelsträngen und entsprechenden Quadruplexen beruht auf solchen komplementären Wasserstoffbrücken. [360] Solche D-A-Arrays eignen sich besonders für die nichtkovalente Verbindung von Fullerenen zu Elektronendonoreinheiten in redoxoder photoaktivierbaren Systemen.…”

Langmuir Films of Unusual Components

“…Cast films of the same peptide-amphiphile were also prepared. 136 Surprisingly, self-standing thin films prepared by simple casting can be manipulated using tweezers, and can be folded without breaking despite the fact that the constituent molecules are not covalently bonded. Another biomolecule attractive for use as structural design component is DNA.…”