[P006] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P03-352] Metal Ion–Directed Self-Assembly of Minimal HIX Peptides into Tunable Hydrogels

○Asuka Inada¹, Kenta Fukumoto¹, Takumi Watanabe¹, Tatsuya Oshima¹ (1. Miyazaki Univ. (Japan))

Keywords:

hydrogel,peptide,self-assembly,metal-ion

[Purpose]Peptide-based hydrogels are promising biomaterials due to their biocompatibility and tunability; however, ultrashort peptides often fail to form ordered networks without external triggers. Here, we investigate metal ion–induced self-assembly as a strategy to overcome this limitation. Inspired by Cu(II)–histidine coordination, a library of His–Ile–X (HIX) tripeptides was designed to examine how side-chain properties influence β-sheet formation and gelation. Structural analyses using CD, FT-IR, and SEM reveal sequence-dependent assembly behavior and establish sequence–structure–function relationships for minimal, stimuli-responsive hydrogels. [Methods]HIX tripeptides were synthesized via Fmoc-based solid-phase peptide synthesis using 17 amino acids (excluding Pro, Cys, and Met). Peptides were dissolved in aqueous buffer (pH 4) and mixed with Cu(II) solutions at defined ratios to evaluate hydrogel formation. Gelation was assessed by vial inversion tests. Secondary structures were analyzed by CD spectroscopy, morphology by SEM, and intermolecular interactions by FT-IR. UV–Vis spectroscopy was used to examine metal coordination. [Results]Cu(II)-induced hydrogelation of HIX peptides produced three outcomes: no gelation, transparent gels, and turbid gels. CD analysis showed that peptides exhibited random coil structures without Cu(II) but formed β-sheet-like structures upon Cu(II) addition. Difference spectra confirmed concentration-dependent structural transitions with isosbestic points indicating a two-state equilibrium. Aromatic residues (Phe, Tyr, Trp) displayed distinct spectral features. Gelation tests revealed that 11 of 17 peptides formed hydrogels, while others remained soluble despite β-sheet signatures. UV–Vis spectra indicated coordination similar to the HIT system. [Consideration]Cu(II) coordination induces β-sheet-like structures in a cooperative, concentration-dependent manner; however, β-sheet formation alone is insufficient for hydrogelation. Non-gelling sequences were attributed to low hydrophobicity (HIG), electrostatic repulsion (HIK, HIR), or excessive chelation (HIH). Aromatic residues enhance assembly via π–π interactions, while HIW exhibits unique behavior due to indole coordination. Concentration-dependent gelation in HIF and HIW highlights the importance of hydrophobic interactions. Overall, gelation depends on a balance of factors including solubility, charge, and coordination behavior, indicating that secondary structure alone does not predict macroscopic gelation. [Conclusion] Cu(II)-induced self-assembly of HIX tripeptides was systematically investigated to elucidate sequence–structure–function relationships in hydrogel formation. While Cu(II) coordination promotes β-sheet-like structures, gelation requires additional factors such as hydrophobicity, electrostatic interactions, and solubility. Aromatic residues further enhance assembly through π–π interactions.