Abstract
Diphenylalanine (FF) represents the simplest peptide building block that self-assembles into ordered nanostructures with interesting physical properties. Among self-assembled peptide structures, FF nanotubes display notable stiffness and piezoelectric parameters (Young’s modulus = 19–27 GPa, strain coefficient d33 = 18 pC/N). Yet, inorganic alternatives remain the major materials of choice for many applications due to higher stiffness and piezoelectricity. Here, aiming to broaden the applications of the FF motif in materials chemistry, we designed three phenyl-rich dipeptides based on the β,β-diphenyl-Ala-OH (Dip) unit: Dip-Dip, cyclo-Dip-Dip, and tert-butyloxycarbonyl (Boc)-Dip-Dip. The doubled number of aromatic groups per unit, compared to FF, produced a dense aromatic zipper network with a dramatically improved Young’s modulus of ∼70 GPa, which is comparable to aluminum. The piezoelectric strain coefficient d33 of ∼73 pC/N of such assembly exceeds that of poled polyvinylidene-fluoride (PVDF) polymers and compares well to that of lead zirconium titanate (PZT) thin films and ribbons. The rationally designed π–π assemblies show a voltage coefficient of 2–3 Vm/N, an order of magnitude higher than PVDF, improved thermal stability up to 360 °C (∼60 °C higher than FF), and useful photoluminescence with wide-range excitation-dependent emission in the visible region. Our data demonstrate that aromatic groups improve the rigidity and piezoelectricity of organic self-assembled materials for numerous applications.
Highlights
Diphenylalanine (FF) represents the simplest peptide building block that self-assembles into ordered nanostructures with interesting physical properties
Dipeptides with a higher content of aromatic groups may self-assemble into highly rigid, strongly piezoelectric structures that may provide high-performance materials for piezoMEMS.[16,26−28]. Aiming to explore this hypothesis, we designed three short, highly aromatic dipeptides based on the β,β-diphenylAla-OH (Dip)[29] motif, namely, Dip-Dip, cyclo-Dip-Dip, and tert-butyloxycarbonyl (Boc)-Dip-Dip, each containing four aromatic groups
Our results demonstrate that chemical densification of phenyl groups strengthens the supramolecular packing in the aromatic zipper structure, resulting in the fabrication of organic materials with highly improved electromechanical performance with potential application in the development of eco-friendly miniaturized devices
Summary
Diphenylalanine (FF) represents the simplest peptide building block that self-assembles into ordered nanostructures with interesting physical properties. Hierarchical self-assembly, a ubiquitous process in biological systems, is the guiding principle of bottomup nanotechnology, harnessed to generate highly ordered functional superstructures from simple building units.[1−4] Of these, self-assembled bioinspired peptide-based nanostructures have been intensely studied due to their biocompatible and biodegradable nature.[5−14] One widely applied building block is the aromatic dipeptide diphenylalanine (FF), the core recognition motif of the Alzheimer’s βamyloid polypeptide.[15−19] FF-based molecular assemblies, in particular nanotubes, possess extreme physical and chemical stability along with interesting mechanical, optical, and piezoelectric properties.[5,15,16,20−22] One of the interesting properties of FF-based peptide nanotubes is their mechanical rigidity, with Young’s modulus values of 19−27 GPa.[23,24] Density functional theory (DFT) calculations show that the high mechanical strength is the result of a aromatic zipper present in the nanotubes.[25] The strong π−π interactions within the assemblies coupled with the extensive hydrogen bond network leads to strong piezoelectricity (d33 = 17.9 pC/N and d15 = 60 pC/N).[26] dipeptides with a higher content of aromatic groups may self-assemble into highly rigid, strongly piezoelectric structures that may provide high-performance materials for piezoMEMS.[16,26−28]. Our results demonstrate that chemical densification of phenyl groups strengthens the supramolecular packing in the aromatic zipper structure, resulting in the fabrication of organic materials with highly improved electromechanical performance with potential application in the development of eco-friendly miniaturized devices
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