Assembly and application of diphenylalanine dipeptide nanostructures

Abstract

The self-assembly of biomaterials to form well-ordered hierarchical structures provides great opportunities in biomedical applications. In the past decades, a great many of researches have been focused on self-assembly of peptide molecules owing to their structural simplicity, chemical versatility, biocompatibility, facile synthesis, and widespread applications. Well defined peptide assemblies could be effectively achieved by hydrogen bonding, electrostatic, hydrophobic and π - π stacking interactions. One well-known and the simplest peptide building block is diphenylalanine (FF), the core recognition motif of the Alzheimer’s β -amyloid polypeptide. It is a major building block for the preparation of biological functional nanomaterials. So far, researchers have developed a variety of FF-based micro/nanostructures, such as nanotubes, microtubes, microrods, nanowires, and nanovesicles, etc. However, how to effectively control the shape and size of the self-assembled materials has always been the key concern of the research. In recent years, our group has conducted substantial researches on controlled assembly of FF and its derivatives by simply changing the assembly condition (solvents, peptide concentrations, ultrasonic) or introduction of exogenous small molecules (polyoxometalates, sulfonic azobenzenes, aldehydes). For example, our group obtained hexagonal FF microtubes in water and peony- lower-like mesocrystal in the organic solvent tetrahydrofuran. When the organic solvent was changed to chloroform or toluene, FF organogels were obtained. Moreover, the structural transition from organogels to flower-like microcrystals were observed by changing the components of solvent. Similarly, upon a change in the peptide concentration, reversible shape transition between self-assembled dipeptide nanotubes and vesicle-like structures is achieved. In view of positive charge of cationic dipeptide, negatively charged small molecules (polyoxometalates and sulfonic azobenzenes) were added into the assembly system and colloidal spheres, urchin-like, flower-like and plate-like structures were obtained, respectively. Apart from non-covalent interactions, our group also exploited covalent Schiff’s reaction between the aldehyde group and the primary amine of peptide in the self-assembly of peptides by introducing aldehyde molecules, yielding peptides nanospheres and crystalline platelet structures. These peptide assemblies with diverse structures were successfully applied in drug delivery, optical waveguiding and SERS substrates. These researches not only enrich the FF-based nanomaterials, but also provide new strategy and important experimental basis for the preparation of other peptides-based nanomaterials and biological function materials. With the development of biology and nanotechnology, especially the establishment of the new assemblies or hybrid systems, higher requirements for the experiment, theory and application of biomolecular self-assembly are put forward. Therefore, further study on the assembly structure, the assembly dynamics and effectively control the assembly of peptides and other biological molecules are highly demanded. At the same time, in order to make the materials not only possess academic research significance, but also ultimately realize the social value, the exploitation of the functionalization and application of the materials will also be the focus of future research issues.