Hierarchical Assembly of Hemin-Peptide Catalytic Systems on Graphite Surfaces

The formation of molecular hybrid systems with cofactors and peptides on graphite electrodes has recently been demonstrated. The design of peptide sequences is crucial for forming robust catalytic molecular systems on electrodes. However, the relationship between peptide sequences, molecular structure, and catalytic performance has not been fully explored. In this study, we employed peptides with simple dipeptide repeats, which effectively immobilize hemin, to construct a stable catalytic system and investigated the molecular basis of their self-assembly and catalytic activity by varying the sequence. Among peptides containing the dipeptide sequences (YH, VH, and LH), YH demonstrated the most efficient immobilization of hemin, which is catalytically active in electrochemical reactions. Using advanced molecular visualization techniques, specifically frequency modulation atomic force microscopy (FM-AFM), we characterized the well-ordered structures of these peptides on graphite electrodes, revealing their molecular-scale organization. Our findings in electrochemical characterizations include a quantitative evaluation of the surface density of hemin immobilized by self-assembled peptides and the catalytic activity of the peptide-hemin hybrid system under electrochemical conditions in the presence of H₂O₂. The strong peptide-peptide and peptide-hemin interactions, facilitated by π-π interactions of tyrosine residues, contribute to the system's stability and efficiency. The dipeptide repeats serve as a useful platform to investigate the role of important amino acids, beyond histidine, in stably immobilizing cofactors. These results highlight the potential for developing durable and efficient catalytic interfaces in electrochemical applications.