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. 2014 Jul 22;8(7):7220-8.
doi: 10.1021/nn502240r. Epub 2014 Jun 23.

Seamless metallic coating and surface adhesion of self-assembled bioinspired nanostructures based on di-(3,4-dihydroxy-L-phenylalanine) peptide motif

Affiliations

Seamless metallic coating and surface adhesion of self-assembled bioinspired nanostructures based on di-(3,4-dihydroxy-L-phenylalanine) peptide motif

Galit Fichman et al. ACS Nano. .

Abstract

The noncoded aromatic 3,4-dihydroxy-L-phenylalanine (DOPA) amino acid has a pivotal role in the remarkable adhesive properties displayed by marine mussels. These properties have inspired the design of adhesive chemical entities through various synthetic approaches. DOPA-containing bioinspired polymers have a broad functional appeal beyond adhesion due to the diverse chemical interactions presented by the catechol moieties. Here, we harnessed the molecular self-assembly abilities of very short peptide motifs to develop analogous DOPA-containing supramolecular polymers. The DOPA-containing DOPA-DOPA and Fmoc-DOPA-DOPA building blocks were designed by substituting the phenylalanines in the well-studied diphenylalanine self-assembling motif and its 9-fluorenylmethoxycarbonyl (Fmoc)-protected derivative. These peptides self-organized into fibrillar nanoassemblies, displaying high density of catechol functional groups. Furthermore, the Fmoc-DOPA-DOPA peptide was found to act as a low molecular weight hydrogelator, forming self-supporting hydrogel which was rheologically characterized. We studied these assemblies using electron microscopy and explored their applicative potential by examining their ability to spontaneously reduce metal cations into elementary metal. By applying ionic silver to the hydrogel, we observed efficient reduction into silver nanoparticles and the remarkable seamless metallic coating of the assemblies. Similar redox abilities were observed with the DOPA-DOPA assemblies. In an effort to impart adhesiveness to the obtained assemblies, we incorporated lysine (Lys) into the Fmoc-DOPA-DOPA building block. The assemblies of Fmoc-DOPA-DOPA-Lys were capable of gluing together glass surfaces, and their adhesion properties were investigated using atomic force microscopy. Taken together, a class of DOPA-containing self-assembling peptides was designed. These nanoassemblies display unique properties and can serve as multifunctional platforms for various biotechnological applications.

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Figures

Figure 1
Figure 1
DOPA-containing self-assembling peptides form ordered assemblies. (a) Chemical structure of the DOPA-containing designed peptides. (b,c) TEM micrographs of DOPA–DOPA dipeptide assemblies; (d–f) TEM micrographs of the hydrogel-forming Fmoc–DOPA–DOPA assemblies; (g) E-SEM micrograph of the Fmoc–DOPA–DOPA hydrogel after gradual dehydration.
Figure 2
Figure 2
Rheological and structural properties of the Fmoc–DOPA–DOPA hydrogelator. Strain sweep (a) and frequency sweep (b) characterization of 5 mg/mL in situ-formed hydrogel at 25 °C. (c) Gelation kinetics of Fmoc–DOPA–DOPA at different concentrations at 25 °C. (d) Gelation kinetics of 5 mg/mL Fmoc–DOPA–DOPA at different temperatures. (e) Kinetics of absorbance at 405 nm at two concentrations and macroscopic visualization of the preparation. (f) HR-SEM micrographs of the turbid peptide solution immediately after inducing the assembly process (left and center panels) and of the semitransparent gel after 2 h of incubation (right panel).
Figure 3
Figure 3
Silver reduction by preprepared Fmoc–DOPA–DOPA hydrogel. (a) Macroscopic visualization and UV–vis spectra of assemblies at 5 mg/mL taken after 5 days of incubation. (b) TEM micrographs of the formation of silver particles after 1 day of incubation of assemblies at 2.5 mg/mL (bottom panels) and a control gel with no addition of silver nitrate (top panel). (c) TEM micrographs of the assemblies at 5 mg/mL after 3 days of incubation. The arrows indicate noncoated peptide assemblies. In all micrographs, negative staining was not applied.
Figure 4
Figure 4
Characterization of Fmoc–DOPA–DOPA–Lys assemblies. (a) Chemical structure and TEM analysis of 1.25 wt % (17.2 mM) Fmoc–DOPA–DOPA–Lys assemblies prepared in either 12.5% ethanol or 12.5% DMSO. (b) Adhesion force map and corresponding histogram of 1.25 wt % Fmoc–DOPA–DOPA–Lys prepared in ethanol and water. (c) Adhesion force map and corresponding histogram of 1.25 wt % Fmoc–DOPA–DOPA–Lys prepared in DMSO and water. (d) AFM images of the exposed area of the bottom (left and center panels) and top (right) glass surfaces after peeling two glass slides that were adhered overnight by an aliquot of 1.25 wt % Fmoc–DOPA–DOPA–Lys in 12.5% ethanol. (e) AFM images of the exposed area of the bottom (left and center panels) and top (right panel) glass surfaces after peeling two glass slides that were adhered overnight by a preparation of 1.25 wt % Fmoc–DOPA–DOPA–Lys in 12.5% DMSO.

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