Association of self-assembled structures and their material function: the way by which this class of building blocks bears the potential for diverse applications.

Rationally designed materials that exploit specific, directional, tunable and reversible non-covalent interactions offer unprecedented advantages: they enable modular and generalizable platforms with tunable mechanical, chemical and biological properties. Indeed, the reversible nature of supramolecular interactions gives rise to biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signalling. Self-assembly is defined as the ability of a molecule, without guidance of external factors, to associate through non-covalent interactions to form highly ordered 3-dimensional structures. One of the main driving forces of self-assembly is molecular amphiphilicity, which can drive formation of complex and stable nanostructures. Self-assembling of peptide and peptide conjugates have attracted great attention due to their biocompatibility, biodegradability and biofunctionality. Understanding assembly mechanism enables the better design of peptides which may form useful and functional nanostructures. On the other hand, the design of peptides able to fold into β-hairpin or β-sheet has been much less satisfactory, mainly because of their high tendency to aggregate and low solubility. Both disadvantages are due to the amphipathic character of the β-structure and to the high content of hydrophobic residues, the ones with highest β-sheet propensities. Similar to β-sheet structure, short helical peptides have been recently discovered to possess a diverse set of functionalities with the potential to fabricate artificial self-assembly materials. Here we outline the functional roles of self-assembled peptides and their potential as artificial materials. The peptides here presented are: i synthetic homologues of natural, metabolically stable bioactive sequences and, therefore, able to form specific secondary structures; ii composed of hydrophobic amino acid with specific non-covalent interactions (hydrogen bonds, hydrophobic interactions); iii used as building blocks in order to build oligopeptides which assume new, regular secondary structure. The understanding of sequence-to-structure relationship of the observed peptides and their functional roles opens a new direction of molecular engineering and development of future functional materials.