High‐Temperature Self‐Assembly of Peptides into Vertically Well‐Aligned Nanowires by Aniline Vapor

Abstract

The self-assembly of peptide-based building blocks into nanostructures is an attractive route for fabricating novel bio-inspired materials because of their capacity for molecular recognition and functional flexibility as well as the mild conditions required in the fabrication process.[1-4] Among various peptide-based building blocks forming nanostructures, the simplest building blocks are aromatic dipeptides like diphenylalanine, which can readily self-assemble into nanotubes in aqueous solutions at ambient conditions. [2,[5][6][7] According to literature, the peptide nanotubes could be used in versatile applications for casting conducting metal nanowires, [8] enhancing the sensitivity of electrochemical detection of biomolecules, [9] and fabricating nano-fluidic channels [10] or peptide liquid crystals.[11]Although the self-assembly of peptides into nanostructured materials had been extensively studied, little progress had been made in the alignment and positioning of peptide nanostructures on a solid surface. Major obstacles include the complexity of current 'solution-based' approaches to peptide nanofabrication, causing dispersion and agglomeration problems, [6] which also require the chemical modification of surface and peptide nanostructures. [12] In the present study, we report a novel solid-phase growth of crystalline peptide nanowires at high temperatures driven by aniline vapor under anhydrous conditions. The formation of vertically well-aligned peptide nanowires on a solid surface were investigated through multiples tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), matrix-assisted laser desorption/ ionization time-of-flight (MALDI-TOF) mass spectrometry, and thermal analytical tools like the differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). We prepared an amorphous peptide thin film by drying a drop of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution containing diphenylalanine on a Si substrate. We conducted the experiment under strictly anhydrous conditions in a vacuum desiccator because water vapor could affect the final surface structure of the peptide thin film.[13] We could control the thickness of the film from a few mm down to $50 nm precisely by simply changing the diphenylalanine concentration in HFIP solution. According to our SEM and XRD analysis, the thin peptide film exhibited no surface features ( Fig. 1) and no characteristic diffraction peaks (Fig. 2), which indicate the 'amorphous' nature of the film. From the amorphous peptide film as a starting point, we were able to successfully grow vertically well-aligned peptide nanowires by aging the film at temperatures above 100 8C with aniline vapor. Figure 1 shows the electron micrographs of vertically wellaligned, rigid peptide nanowires. Peptide nanowires were uniformly formed over the entire region of the whole surface (10 mm  10 mm). The average diameter of the nanowires measured by SEM was found to be about 150 nm, but if we consider the effect of conductive coating for SEM, the act...

Ostwald’s rule of stages governs structural transitions and morphology of dipeptide supramolecular polymers

“…The diphenylalanine (FF) structural motif and its derivatives are among the most widely studied minimal building blocks that allow the formation of ordered polymer-like assemblies at the nano-scale [17][18][19][20] . This class of molecular species exhibits effective self-assembly properties, and has been shown to generate a rich variety of ultrastructures, with functional physical and chemical properties, including piezoelectricity 21,22 , luminescence 23 and robust mechanical characteristics [24][25][26][27][28][29] . Moreover, it is becoming increasingly clear that the ability to control the structures of self-assembled peptides at interfaces has great potential for a multitude of future applications 30 .…”

Patterned Growth of Vertically Aligned Organic Nanowire Waveguide Arrays

“…17Ϫ20 However, vertical growth of organic nanowires has been rarely reported. 21,22 Site-selective growth of nanowires in predefined patterns has been proved to be able to simplify the device fabrication. 23,24 Owing to the relatively weak molecular interaction in organic nanostructures, their vapor transport can be done at relatively lower temperature.…”

Bio-Inspired Synthesis of Electrode Materials for Lithium Rechargeable Batteries

“…The duplications of the nanostructure of the biomaterials offers new possibilities for biomaterials in a broad range of research fields beyond the conventional bio-applications by enabling the synthesis of various functional materials in complex forms. (Brachmann & Cagan, 2003), (c) well-aligned peptide nanowires (Ryu & Park, 2008), and (d) polyaniline-naphthol blue black nanotubes (Xia et al, 2004). Fig.…”

“…Figure 2 illustrates various shapes of self-assembled biomaterials formed naturally and artificially. They exhibit exclusive structures from nanoscale to macroscale (Brachmann & Cagan, 2003;Ryu & Park, 2008;Xia et al, 2004). Recently, it has been widely demonstrated that self-assembled biomaterials can serve as structural motifs for non-biological nanostructured materials (Sanchez et al, 2005).…”