Self-assembly of diphenylalanine backbone homologues and their combination with functionalized carbon nanotubes.

Bhimareddy Dinesh,Paolo Samorì,Cécilia Ménard-Moyon,Alberto Bianco,Marco A. Squillaci

doi:10.1039/c5nr04665c

Abstract

The integration of carbon nanotubes (CNTs) into organized nanostructures is of great interest for applications in materials science and biomedicine. In this work we studied the self-assembly of β and γ homologues of diphenylalanine peptides under different solvent and pH conditions. We aimed to investigate the role of peptide backbone in tuning the formation of different types of nanostructures alone or in combination with carbon nanotubes. In spite of having the same side chain, β and γ peptides formed distinctively different nanofibers, a clear indication of the role played by the backbone homologation on the self-assembly. The variation of the pH allowed to transform the nanofibers into spherical structures. Moreover, the co-assembly of β and γ peptides with carbon nanotubes covalently functionalized with the same peptide generated unique dendritic assemblies. This comparative study on self-assembly using diphenylalanine backbone homologues and of the co-assembly with CNT covalent conjugates is the first example exploring the capacity of β and γ peptides to adopt precise nanostructures, particularly in combination with carbon nanotubes. The dendritic organization obtained by mixing carbon nanotubes and peptides might find interesting applications in tissue engineering and neuronal interfacing.

Highlights

To assess the stability and the lifetime of these assemblies, the peptide solutions were stored at room temperature for 30 days and their assemblies were found unaltered as shown by scanning electron microscopic (SEM) analysis (Fig. S1†), revealing their long time stability towards ageing
A well-mixed peptide solution was immediately drop cast and after the solvent evaporation, the transmission electron microscopy (TEM) images (Fig. S2†) allowed to observe nanofibers with almost similar morphology to those obtained in 50% ethanol solution (Fig. 2)
We have found that β peptide Bocβ3(R)Phe-β3(R)Phe-OH and γ peptide Boc-γ4(R)Phe-γ4(R)Phe-OH self-assemble to generate fibers of different dimensions and shapes, which undergo morphological changes at acidic pH

Summary

Introduction

The structure and the function of peptides are the resultant of their amino acid composition They can be altered by applying strategic modifications at the level of each amino acid residues. These modifications may include alterations made on the backbone or on the side chain of the residues.[14,15] The peptides with such modified parts display enhanced biological stability toward proteolysis.[16,17] Besides this, the use of backbone homologated amino acids bearing proteinogenic side chains has emerged as a successful approach to generate secondary structural motifs in peptidomimetics, called foldamers.[14,18,19] The additional methylene groups on the backbone of the peptide provides several degrees of conformational space resulting in various secondary structures. Further investigations using exact analogues of backbone homologated diphenylalanines will allow to better explore the characteristics of the assemblies originated by the backbone extensions, alone or in combination with nanomaterials, and to expand their applications

Objectives

Results

Conclusion