Designer Peptide Amphiphiles: Self-Assembly to Applications

Peptide amphiphiles (PAs) are extremely attractive as molecular building blocks, especially in the bottom-up fabrication of supramolecular soft materials, and have potential in many important applications across various fields of science and technology. In recent years, we have designed and synthesized a large group of peptide amphiphiles. This library of PAs has the ability to self-assemble into a variety of aggregates such as fibers, nanosphere, vesicles, nanosheet, nanocups, nanorings, hydrogels, and so on. The mechanism behind the formation of such a wide range of structures is intriguing. Each system has its individual method of aggregation and results in assemblies with important applications in areas including chemistry, biology, and materials science. The aim of this feature article is to bring together our recent achievements with designer PAs with respect to their self-assembly processes and applications. Emphasis is placed on rational design, mechanistic aspects of the self-assembly processes, and the applications of these PAs. We hope that this article will provide a conceptual demonstration of the different approaches taken toward the construction of these task-specific PAs.

Unorthodox Combination of Cation-π and Charge-Transfer Interactions within a Donor-Acceptor Pair

Cation-π and charge-transfer (CT) interactions are ubiquitous in nature and involved in several biological processes. Although the origin of both the interactions in isolated pairs has extensively been studied, CT interactions are more prominent in supramolecular chemistry. Involvement of cation-π interactions in the preparation of advanced functional soft materials is uncommon. Moreover, a combination of these two interactions within a pair of electron donor (D) and acceptor (A) is uncharted. Here, we present a rational design to incorporate a combination of these two interactions within a D-A pair. A pyrene-peptide conjugate exhibits a combination of cation-π and CT interactions with a cationic naphthalenediimide (NDI) molecule in water. Nuclear Overhauser effect spectroscopy NMR along with other techniques and density functional theory calculations reveal the involvement of these interactions. The π-planes of pyrene and NDI adopt an angle of 56° to satisfy both the interactions, whereas β-sheet formation by the peptide sequence facilitates self-assembly. Notably, the binary system forms a self-supporting hydrogel at a higher concentration. The hydrogel shows efficient self-healing and injectable property. The hydrogel retains its thixotropic nature even at an elevated temperature. Broadly, we demonstrate a pathway that should prove pertinent to various areas, ranging from understanding biological assembly to peptide-based functional soft materials.