Histidine–Zinc Interactions Investigated by Isothermal Titration Calorimetry (ITC) and their Application in Self‐Healing Polymers

Histidine–zinc interactions are believed to play a key role in the self‐healing behavior of mussel byssal threads due to their reversible character. Taking this as inspiration, the authors synthesize here histidine‐rich copolymers, as well as model histidine compounds and characterize them using isothermal titration calorimetry (ITC). With this approach, the influence of two different zinc(II) salts and the role in the complex formation of the amine function of the imidazole ring are investigated in detail. The extracted metal–ligand ratios are utilized to design novel self‐healing metallopolymers. For this purpose, n‐lauryl methacrylate is copolymerized with the histidine monomer via reversible addition‐fragmentation chain transfer polymerization. The copolymers are crosslinked using different zinc salts, and the resulting coatings are characterized with Raman spectroscopy to investigate the metal coordination behavior and with scratch healing tests to investigate the self‐healing capacity. Finally, the self‐healing behavior of the different materials is correlated with the metal–ligand binding affinity measured by ITC. The complex behavior of histidine–zinc interactions is investigated in order to determine the thermodynamic parameters as well as the influence of the utilized counter ions. The results are utilized to construct novel self‐healing metallopolymers. These self‐healing coatings are examined in detail with a statistical evaluation and related to the thermodynamic results as well as the mechanical properties.