The impact of thermal history on the structure of glycylalanylglycine ethanol/water gels

Abstract

This work revisits several open questions regarding the mechanisms of GAG fibril formation and structure as a function of temperature. The authors recently hypothesized that there is a solubility limit of GAG in ethanol/water that induces self‐assembly. In other words, not all peptides can participate in fibrillization and some fraction is still soluble in solution. We show via FTIR spectroscopy that, indeed, free peptides are still present in solution after fibril formation, strongly supporting the solubility model. Furthermore, previous work showed GAG self‐assembled into right‐handed (phase I) or left‐handed (phase II) chiral structures depending on temperature. In this study, we analyze the crystalline structure of phase I and II gels via WAXS and SAXS to compare their crystalline structures and order. Rheological measurements were used to investigate the response of the fibrillar network to temperature. They reveal that the ability of the peptide to self‐assemble depends on the solubility at a given temperature and not on thermal history. Furthermore, the gel softening point, the linear viscoelastic gel microstructure, and relaxation spectrum are very similar between phase I and phase II. Overall, the temperature only affects the chirality of the fibrils and the formation kinetics.

Short Peptides as Tunable, Switchable, and Strong Gelators

“…The simulated IR and VCD spectra bear a significant similarity with the experimental band profiles (Figure for phase II). Interestingly, recently reported WAXS data of GAG gels would be fully consistent with a canonical β-sheet structure . Hence, our data underscore the notion that sheets with different secondary structure content might exhibit a similar spacing between the incorporated strands and sheets …”

“…Interestingly, recently reported WAXS data of GAG gels would be fully consistent with a canonical β-sheet structure. 65 Hence, our data underscore the notion that sheets with different secondary structure content might exhibit a similar spacing between the incorporated strands and sheets. 60 Recently, we measured the IR spectrum of the gel phase formed by 175 mM GHG upon deprotonation of the imidazole side chain.…”

“…(B) Dynamic frequency sweep of the storage modulus of 200 mM cationic GAG in 55 mol % ethanol/45 mol % water measured after the indicated annealing cycle. Reprinted with permission from ref . Copyright 2021 Wiley & Sons.…”