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

Abstract

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 selfhealing behavior of the different materials is correlated with the metal-ligand binding affinity measured by ITC. 2 (2.5 g, 5.52 mmol) was dissolved in 40 mL dry dichloromethane. Triethylamine (1.53 mL, 11.06 mmol) and acetic anhydride (0.52 mL, 5.52 mmol) was added dropwise. After complete conversion, which was monitored by thin layer chromatography (TLC), the solvent and the triethylamine were evaporated in vacuo. The residue was dissolved in 50 mL chloroform and washed with 0.1 m NaHCO 3 solution and afterward with deionized water. The organic layer was dried over Na 2 SO 4 . Finally, the crude product was purified by silica gel chromatography (MeOH/CHCl 3 1:9, R f = 0.5).Yield: 2.0 g (4.04 mmol) of a white solid, 73%. Melting point: 76-77 °C. 1 H NMR (300 MHz, CDCl 3 ): δ = 0.85-0.89 (t, 3H, CH 3 ), 1.22-1.46 (m, 4H, CH 2 CH 2 CH 3 ), 1.93-2.04 (m, 4H, CH 3 Macromol. Chem. Phys. , , 1600458 M. Enke et al.

Polymeric Photoacids Based on Naphthols—Design Criteria, Photostability, and Light‐Mediated Release

“…The post‐polymerization modification was carried out using a fivefold excess of the functional amines NOeA or NAmeA with respect to the incorporated FMA units, and an equimolar amount of trimethylamine and HO‐Dhbt as coupling reagent according to a literature procedure (Figure A) . The reaction was conducted in DMF at 70 °C for two days to ensure full conversion, and 1 H NMR spectroscopy was used to characterize the final functionalized copolymers (Figure D).…”

“…The post-polymerization modification was carried out using af ivefold excess of the functional amines NOeA or NAmeA with respectt ot he incorporated FMA units, and an equimolar amount of trimethylamine and HO-Dhbt as coupling reagent accordingt oaliterature procedure ( Figure 2A). [38] The reaction was conducted in DMF at 70 8Cfor two days to ensure full conversion, and 1 HNMR spectroscopy wasu sed to characterize the final functionalized copolymers ( Figure 2D). The appearance of aromatic signals corresponding to the 1-naphthol protons indicated as uccessful functionalization and the actual composition of both P[MEO 9 MA x -co-NOeMAm y ]a nd P[MEO 9 MA x -co-NAmeMAm y ]c ould be calculated and were 28 and 35 %, respectively.T of urther evaluate the extento ff unctionalization, 19 FNMR spectroscopy was carried out and ar epresentative 19 Fs pectra for P[MEO 9 MA x -co-NOeMAm y ]i ss hown in Figure 2E (the respective 19 FNMR spectra of P[MEO 9 MA x -co-NAmeMAm y ]c an be found in the SupportingI nformation, Figure S6).…”

“…Post‐polymerization modification of P[MEO 9 MA x ‐ co ‐PFMA y ] : The synthetic procedure was adapted and modified from a literature recipe . The respective copolymers were mixed together with 5 equiv.…”

Remendable polymers via reversible Diels–Alder cycloaddition of anthracene‐containing copolymers with fullerenes

“…This finding is caused by the lower conversion of the anthracene units with fullerene moieties in contrast to the maleimide/furan system. Nevertheless, a fullerene‐containing polymer film could be obtained, which is stable at room temperature and feature better mechanical performance compared to pure PLMA films, which are too soft to be measured with the nanoindenter . Furthermore, CP1F is much harder than CP2F, which should also have an influence on the self‐healing properties of the samples.…”

Mussel Byssus Structure‐Function and Fabrication as Inspiration for Biotechnological Production of Advanced Materials

“…Initial efforts to produce mussel‐inspired materials took a minimalist approach, reducing the complexity of the byssal proteins to single amino acid moieties . In particular, there has been a strong focus on harnessing metal coordination chemistry mediated via Histidine and DOPA moieties toward synthetic production of wet adhesives and self‐healing materials . This reductionist synthetic approach has been highly successful; however, the details are well reviewed elsewhere and lie outside the scope of the current review.…”