Exploring the gel phase of cationic glycylalanylglycine in ethanol/water. I. Rheology and microscopy studies

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

“…After thermal annealing, the phase II fibril network shows a much smaller tan δ at higher frequency, indicating that the network is more homogeneous with less mobility. This supports the observation that slower kinetics lead to more homogeneous networks 26 …”

“…This result suggests that a mixed aggregation mechanism occurs between the kinetic‐limited and diffusion‐limited regimes with a slight dominance of the latter 35 . This conclusion is consistent with the microscopic images shown in Thursch et al, which show regions of percolated fibrils and dense fibril clusters 26 . The reformed fibril networks formed after thermal annealing at 50°C show almost identical power‐law behavior at short times but a much smaller power‐law slope at increased time.…”

“…We now revisit the rheological response of phase I and II gels to test the solubility hypothesis presented by Thursch et al 26 Figure 5 shows the formation kinetics via storage modulus as a function of time for phase I and II gels for different thermal histories. As reported earlier, the sample formed at 5°C shows a higher modulus than the sample formed at 20°C, and this difference is more pronounced for relatively low GAG concentrations (150 mM).…”

“…For example, glycine‐alanine‐glycine (GAG) and glycine‐histidine‐glycine (GHG) self‐assemble into very long microfibrils under the right conditions 19–26 . More specifically, GAG forms fibrils in the presence of a critical fraction of ethanol that depends on peptide concentration 26 . While GHG forms fibrils when the pH of the solution exceeds the pKa of the imidazole side chain 21 …”

“…The storage moduli of GAG gels are considerably high for LMWG and depending on peptide concentration can range from 10 3 to 10 5 Pa 23 . The rate of gel formation depends strongly on the fraction of ethanol and peptide concentration and the optimum gel strength occurs at intermediate rates 26 . The modulus of phase I GAG fibril networks are higher than phase II, but a detailed study regarding the differences of these two phases has not been presented until now.…”