Metal-Mediated Self-Assembled Architectures of Structured Peptides

Abstract

Metalloproteins, a fascinating class of biomolecules, incorporate metal ions into their structures to perform critical functions such as catalyzing reactions, transferring electrons, and transporting oxygen. Inspired by the intricate designs and functionalities of metalloproteins, significant efforts have been invested in the literature in emulating their structures and activities. These efforts involve the utilization of both natural and non-natural amino acid building blocks and their intricate interactions with diverse metal ions. Metal-ion-coordinated supramolecular architectures of peptides have attracted considerable attention in recent years due to their close resemblance to metalloproteins and also en route to creating artificial enzymes and catalysts. In the present work, we explored structured peptides as metal coordination templates to understand the supramolecular architectures of protein secondary structure mimetics. The designed short tripeptide 3₁₀-helices terminated by the pyridyl groups displayed remarkably diverse networks upon coordinating with the silver ion. The analysis revealed the anions of silver salts also play a significant role in the formation of diverse networks of 3₁₀-helices and silver ions. The inherent dipoles of the helical peptides in silver-coordinated networks were further explored for the second harmonic generation response. Further, we observed a subtle change in the sequences of peptides that leads to a transformation from helix into beta-turns upon metal coordination. In contrast to 3₁₀-helical structures from α-peptides, the alpha, gamma, alpha-hybrid tripeptides, composed of saturated gamma-amino acids, exhibit stable C12 helical structures both in single crystals and the solution state. We further examined the utility of C12-helices in the design of metal-helix networks. Utilizing Ag+, Zn2+, Cd2+, and lanthanide ions (Tb3+ and Eu3+), we elucidated the organization of helical structures. In the presence of Tb3+ and Eu3+ ions, the peptides showed photoluminescence properties. Instructively, the same tripeptide helices form gels in active methylene solvents. Overall, the presented research elucidates a novel avenue for the exploration of short helices as innovative tools in the design and development of peptide-based biomaterials and porous networks.