Amyloid fibrils draw attention as potential novel biomaterials due to their high stability, strength, elasticity or resistance against degradation. Therefore, the controlled and fast fibrillization process is of great interest, which raises the demand for effective tools capable of regulating amyloid fibrillization. Ionic liquids (ILs) were identified as effective modulators of amyloid aggregation. The present work is focused on the study of the effect of 1-ethyl-3-methyl imidazolium-based ILs with kosmotropic anion acetate (EMIM-ac) and chaotropic cation tetrafluoroborate (EMIM-BF₄) on the kinetics of lysozyme amyloid aggregation and morphology of formed fibrils using fluorescence and CD spectroscopy, differential scanning calorimetry, AFM with statistical image analysis and docking calculations. We have found that both ILs decrease the thermal stability of lysozyme and significantly accelerate amyloid fibrillization in a dose-dependent manner at concentrations of 0.5%, 1% and 5% (v/v) in conditions and time-frames when no fibrils are formed in ILs-free solvent. The effect of EMIM-BF₄ is more prominent than EMIM-ac due to the different specific interactions of the anionic part with the protein surface. Although both ILs induced formation of amyloid fibrils with typical needle-like morphology, a higher variability of fibril morphology consisting of a different number of intertwining protofilaments was identified for EMIM-BF_4.

Amyloid fibrils have immense potential to become the basis of modern biomaterials. The formation of amyloid fibrils in vitro strongly depends on the solvent properties. Ionic liquids (ILs), alternative solvents with tunable properties, have been shown to modulate amyloid fibrillization. In this work, we studied the impact of five ILs with 1-ethyl-3-methylimidazolium cation [EMIM⁺] and anions of Hofmeisterseries hydrogen sulfate [HSO₄⁻], acetate [AC⁻], chloride [Cl⁻], nitrate [NO₃⁻], and tetrafluoroborate [BF₄⁻] on the kinetics of insulin fibrillization and morphology, and the structure of insulin fibrils when applying fluorescence spectroscopy, AFM and ATR-FTIR spectroscopy. We found that the studied ILs were able to speed up the fibrillization process in an anion- and IL-concentration-dependent manner. At an IL concentration of 100 mM, the efficiency of the anions at promoting insulin amyloid fibrillization followed the reverse Hofmeister series, indicating the direct binding of ions with the protein surface. At a concentration of 25 mM, fibrils with different morphologies were formed, yet with similar secondary structure content. Moreover, no correlation with the Hofmeister ranking was detected for kinetics parameters. IL with the kosmotropic strongly hydrated [HSO₄⁻] anion induced the formation of large amyloid fibril clusters, while the other kosmotropic anion [AC⁻] along with [Cl⁻] led to the formation of fibrils with similar needle-like morphologies to those formed in the IL-free solvent. The presence of the ILs with the chaotropic anions [NO₃⁻] and [BF₄⁻] resulted in longer laterally associated fibrils. The effect of the selected ILs was driven by a sensitive balance and interplay between specific protein–ion and ion–water interactions and non-specific long-range electrostatic shielding.

Conformational transitions of horse heart ferricytochromec(ferricytc) have been investigated in the presence of strong inorganic acids and their salts by optical absorption spectroscopy, magnetic circular dichroism and circular dichroism. In the presence of acids (HClO₄or H₂SO₄, pH 2) or their salts (1 M NaClO₄or Na₂SO₄, pH 2, 25 °C), the three ligation states of ferricytcheme were identified. One is the high-spin state: His18-Fe-H₂O (40-50%), and two are the low-spin states: His18-Fe-Met80 (30-25%) and His18-Fe-His (30-25%). Under these conditions low temperatures facilitate native heme coordination of ferricytc. Transition from low-spin to high-spin heme coordination of ferricytcis complete in 1 M HClO₄or 3 M H₂SO₄. At the concentration of HClO₄and H₂SO₄above 3 M, different behavior in spectral transitions of ferricytcnear the heme is observed. High-spin pentacoordinated ferricytcwith the heme ligand of His18-Fe is formed in 8 M H₂SO₄. This state is unstable at higher concentration of H₂SO₄and porphyrin ferricytcis formed. At HClO₄concentration higher than 3 M, the new, until this time not observed heme coordination structure of ferricytcoriginates.