Chiral Recognition of Self-Assembled Peptides on MoS2 via Lattice Matching.

Chiral recognition of peptides on solid surfaces has been studied for a better understanding of their assembly mechanism toward its applications in stereochemistry and enantioselective catalysis. However, moving from small peptides such as dipeptides, understanding the chiral recognition of larger biomolecules such as oligopeptides or peptides with a larger sequence is challenging. Furthermore, their intrinsic mechanism for chiral recognition in liquid conditions was poorly investigated experimentally. Here, we used in/ex situ atomic force microscopy (AFM) to investigate the chiral recognition of self-assembled structures of l/d-type peptides on molybdenum disulfide (MoS2). We chose single-layer MoS2 with a triangular shape as a substrate for the self-assembly of peptides. The facet edges of MoS2 were utilized as a landmark to identify the crystallographic orientation of their ordered structures. We found both peptide enantiomers formed nanowires on MoS2 with a mirror symmetry according to the facet edges of MoS2. From in situ AFM measurements, we found a dimension of a unit cell in the self-assembled structure and proposed a model of lattice matching between peptides and MoS2 lattice. The lattice matching for chiral recognition was further investigated by changing peptide sequences and surface lattice from MoS2 to graphite. This work further deepened the understanding of biomolecular chiral recognition and will lead us to rationally design specific morphologies and conformations of chiral self-assembled structures of peptides with expected functions in the future.

Fibroin-like Peptides Self-Assembling on Two-Dimensional Materials as a Molecular Scaffold for Potential Biosensing.

Self-assembled peptides have revealed uniform ordering on two-dimensional (2D) materials such as mica, graphene, and MoS2 so far. These peptides are expected to be utilized as a molecular scaffold for biosensing based on 2D materials. However, the stability of the peptide structures on 2D materials under liquid has not been evaluated, and some of the previously reported peptides may have instability under water. In this work, by mimicking an amino-acid sequence of silk protein, we successfully developed peptide sequences that can maintain ordered nanostructures even after rinsing with deionized water. The structural stability was also proven under electrochemical bias, which is crucial as a biomolecular scaffold for practical biosensing with 2D materials. The stability probably arises from its ß-sheet-like structures with improved intermolecular interactions and binding to the surface of 2D materials, resulting in the formation of stable domains of ordered peptide structures. Our peptides showed their ability to immobilize probe molecules for biosensing and inhibit nonspecific adsorption through their co-assembly process. Interestingly, we found two structural phases in the self-assembled structures, where only one of the phases reveals a binding affinity to target molecules.