Diphenylalanine nanotubes

AB3 dendritic platform 23 functioned as an efficient carrier for the controlled formation of diphenylalanine nanotubes (Fig. 5.19). First, it prevented the formation of any organized structures when the peptides were attached. Second, the three units of diphenylalanine were rapidly released upon cleavage of the trigger. Finally, the platform allowed control of the release of the end units through a variety of triggering agents. 

The diphenylalanine nanotube sensors were based on the observation that peptide nanotubes improve the electrochemical properties of graphite and gold electrodes when deposited directly onto the electrode surface (Yemini et al., 2005b). The high surface area of the nanotubes and the potential alignment of aromatic residues are thought to contribute to the observed increase in conductivity. This property makes nanotube-coated electrodes and hydrophobin-coated electrodes suitable for use as amperometric biosensors that produce a current in response to an electrical potential across two electrodes. 

Other research has focused on the interaction of cells with peptide structures that assemble via aromatic interactions. Cells have been grown on the surface of gels formed by Fluorenylmethoxycarbonyl (FMOC) modified diphenylalanine nanotubes (Mahler et al., 2006). Although cells were only grown for short time frames (24 h), the cells were viable on these scaffolds. 

F. 15 Morphological transitirai of diphenylalanine nanotubes to vesicular structures on erniju-gatirai of a 12-mer oligonueleotide sequence [93] (figpre reproduced with pmnissirm of Royal Society of Chemistry)... 

FIGURE 5.17 TEM micrographs of diphenylalanine peptide nanotubes self-assembled after the enzymatic cleavage, (a) TEM images of 22 prior to the enzymatic cleavage, (b and c) TEM images of 22 after the enzymatic cleavage. 

FIGURE 5.19 Controlled formation of diphenylalanine peptide nanotubes. 

Figure 7 Scanning electron microscopy image of vertically aligned diphenylalanine-based peptide nanotubes assembled on a glass surface. The scale bar is 10 lm in length. Reprinted by permission from Macmillan Publishers Ltd., Nature Nanotechnology (Reches and Gazit, 2006), copyright 2006 (http //www.nature.com/nnano/index.html).

Larger patterned surfaces can also be achieved using inkjet printing. This technique has been used to create micron-sized letters of the alphabet containing diphenylalanine peptide nanotubes [tertbutoxycarbonyl-Phe-Phe-OH (Boc-Phe-Phe-OH)] on either transparent foil or indium-tin oxide (Adler-Abramovich and Gazit, 2008) as shown in Figure 13. This later... 

Figure 18 Schematic of a glucose biosensor assembled from diphenylalanine peptide nanotubes. The enzyme GOX has been cross-linked to these nanotubes, which are further linked to the gold (Au) electrode and immobilized in a polyethyleneimine (PEI) matrix. The nanofibers act in two ways they immobilize the sensing enzyme and enhance the transducer. Reprinted in part with permission from Yemini et al. (2005a) (copyright 2005 American Chemical Society).

Gorbitz, C.H. The structure of nanotubes formed by diphenylalanine, the core recognition motif of Alzheimer s j8-amyloid polypeptide, ChemComm. 22 (2006) 2332-2334. 

Reches M, Gazit E (2005) Self-assembly of peptide nanotubes and amyloid-like structures by charged-termini-capped diphenylalanine peptide analogues. Isr J Chem 45(3) 363-371... 

Peptide-based self-assembly is capable of synthesizing nanomaterials with various microstructures from tubes to spheres. Dipeptides, probably the simplest building blocks with a versatility in controlling microstructures, can form tubular, spherical, fibrous, or bundle, and array structures by modifying motifs on the dipeptides and/or altering synthesis conditions (Figure 6.4a). For example, the Alzheimer s p-amyloid peptide with diphenylalanine motif forms multiwaUed nanotubes when the peptide is... 

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