Exploring the Heterogeneous Dynamical Environment at the Interface of Aβ Peptide in Aqueous Ionic Liquid Solution.

In this study, we have investigated the heterogeneous dynamical environment around an ensemble of full-length amyloid-β (Aβ) peptide monomers in binary aqueous solution containing the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF] as a co-solvent. Atomistic molecular dynamics (MD) simulations have been employed with the aim of understanding the effect of the IL on the distribution of water molecules and IL components around distinct segments of the peptide. As compared to pure aqueous medium, locally heterogeneous restricted water motions at the interface have been spotted in the presence of the IL. Our calculations revealed faster diffusion of water molecules hydrating hydrophilic segments (N-term and turn) as opposed to that around hydrophobic segments (hp1, hp2, and C-term). The extent of non-uniform restriction on the center-of-mass motions as well as the reorientation of water molecules and IL ions have been similarly affected in the binary IL-water solution. The effects of IL on the formation of hydrogen bond networks have been evident from the longer hydrogen bond relaxation time scales of peptide-water, with only a small fraction of peptide-anion hydrogen bonds contributing to the structural relaxation. Due to the size and shape factors, the increasingly sluggish dynamics of the IL components in the solvation shell can be attributed to a longer time scale for the onset of maximum dynamic heterogeneity. Interestingly, the water molecules around the polar segments of the peptide take longer to attain dynamic heterogeneity, which intensifies in the presence of IL. These calculations clearly suggest that electrostatic interaction plays a crucial role in water-mediated peptide-IL interaction, thereby shielding the surface from hydrophobic collapse and preventing possible further growth of the monomers into fibrils at higher peptide concentrations.