Effect of 1-Ethyl-3-methylimidazolium Tetrafluoroborate and Acetate Ionic Liquids on Stability and Amyloid Aggregation of Lysozyme

Conformational Properties of Aβ Peptide Oligomers in Aqueous Ionic Liquid Solution: Insights from Molecular Simulation Studies

Alzheimer's disease is a progressive irreversible neurological disorder with abnormal extracellular deposition of amyloid β (Aβ) peptides in the brain. We have carried out atomistic molecular dynamics simulations to investigate the size-dependent conformational properties of aggregated Aβ oligomers of different orders, namely, pentamer [O(5)], decamer [O(10)], and hexadecamer [O(16)] in aqueous solutions containing the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). The calculations revealed reduced peptide conformational fluctuations in O(5) and O(10) in the presence of the IL. In contrast, the higher order oligomer [O(16)] has been found to exhibit greater structural distortion due to enhanced flexibilities of its peptide units in the presence of the IL. Based on the distributions of the solvent (water) and the cosolvent (IL) components, it is demonstrated that exchange of water by the IL ion pairs at the exterior surface of the oligomers primarily occurs beyond the first layer of surface-bound water molecules. Importantly, a reduced number of relatively weaker peptide salt bridges have been found in O(16) in binary water-IL solution as compared to the other two smaller-sized oligomers [O(5) and O(10)]. Such differential influence of the IL on peptide salt bridges results in less favorable binding free energies of peptide monomers to O(16), which leads to its greater structural distortion and reduced stability compared to those of O(5) and O(10).

Deciphering the Role of Anions of Ionic Liquids in Modulating the Structure and Stability of ct-DNA in Aqueous Solutions

Stabilizing biomolecules under ambient conditions can be extremely beneficial for various biological applications. In this context, the utilization of ionic liquids (ILs) in enhancing the stability and preservation of nucleic acids in aqueous solutions is found to be promising. While the role of the cationic moiety of ILs in the said event has been thoroughly explored, the importance of the anionic moiety in ILs, if any, is rather poorly understood. Herein, we examine the function of anions of ILs in nucleic acid stabilization by examining the stability and structure of calf thymus-DNA (ct-DNA) in the presence of various ILs composed of a common 1-ethyl-3-methylimidazolium cations (Emim+) and different anions, which includes Cl-, Br-, NO 3 - , Ac - , HS O 4 - and B F 4 - by employing various spectroscopic techniques as well as Molecular Dynamics (MD) simulation studies. Analysis of our data suggests that the chemical nature of anions including polarity, basicity, and hydrophilicity become an important factor in the overall DNA-IL interaction event. At lower concentrations, the interplay of intermolecular interaction between the IL anions with their respective cations and the solvent molecules becomes a very crucial factor in inducing their stabilizing effect on ct-DNA. However, at higher concentrations of ILs, the ct-DNA stabilization is additionally governed by specific-ion effect. MD simulation studies have also provided valuable insights into molecular-level understanding of the DNA-IL interaction event. Overall, the present study clearly demonstrated that along with the cationic moiety of ILs, the anions of ILs can play a significant role in deciding the stability of duplex DNA in aqueous solution. The findings of this study are expected to enhance our knowledge on understanding of IL-DNA interactions in a better manner and will be helpful in designing optimized IL systems for nucleic acid based applications.

Modulation of Insulin Amyloid Fibrillization in Imidazolium-Based Ionic Liquids with Hofmeister Series Anions

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.

Application of Amyloid-Based Hybrid Membranes in Drug Delivery

The properties of amyloid fibrils, e.g., unique structural characteristics and superior biocompatibility, make them a promising vehicle for drug delivery. Here, carboxymethyl cellulose (CMC) and whey protein isolate amyloid fibril (WPI-AF) were used to synthesize amyloid-based hybrid membranes as vehicles for the delivery of cationic and hydrophobic drugs (e.g., methylene blue (MB) and riboflavin (RF)). The CMC/WPI-AF membranes were synthesized via chemical crosslinking coupled with phase inversion. The zeta potential and scanning electron microscopy results revealed a negative charge and a pleated surface microstructure with a high content of WPI-AF. FTIR analysis showed that the CMC and WPI-AF were cross-linked via glutaraldehyde and the interacting forces between membrane and MB or RF was found to be electrostatic interaction and hydrogen bonding, respectively. Next, the in vitro drug release from membranes was monitored using UV-vis spectrophotometry. Additionally, two empirical models were used to analyze the drug release data and relevant rate constant and parameters were determined accordingly. Moreover, our results indicated that in vitro drug release rates depended on the drug–matrix interactions and transport mechanism, which could be controlled by altering the WPI-AF content in membrane. This research provides an excellent example of utilizing two-dimensional amyloid-based materials for drug delivery.

Unprecedented enhancement and preservation of the peroxidase activity of cytochrome-c packaged with ionic liquid-modified gold nanoparticles by offsetting temperature and time stresses

Inspired by the biocompatibility of ionic liquids and their dexterousness for the preservation of enzyme structure and activity, herein, the interactions of Cyt-c with naked AuNPs and four IL-mediated AuNPs, which were formed by the fabrication of ILs with common cation 1-ethyl-3-methyl-imidazolium (EMIM) and different anions, to obtain AuNP-IL1 [(BF4)^-1 anion], AuNP-IL2 [(CH₃OSO₃)^-1 anion], AuNP-IL3 [(CH₃CH₂OSO₃)^-1 anion], and (AuNP-IL4) [Cl^-1 anion], were studied. Through this work, the peroxidase activity observed in the presence of a lower concentration IL-AuNPs is exceptionally increased (16 fold). IL-AuNPs preferentially counteract the temperature gradient change and long-term solvent preservation effects while persistently maintaining the Cyt-c peroxidase activity without much depreciation. The hydrodynamic diameter (d_H) of the Cyt-c-AuNP system was obtained, which supported the TEM results. Furthermore, to evaluate the effect of Cyt-c interaction with the AuNPs, a Zeta potential analysis was performed. Taken together, the binding of IL-AuNPs with Cyt-c, diameter size analysis, zeta potential, structural integrity evaluation using the DichroWeb software and morphology results suggest the interaction order of the IL-AuNPs to be in a sequence of AuNP-IL2 > AuNP-IL3 > AuNP- IL4 > AuNP-IL1 > Naked AuNPs. Moreover, results indicate that the IL anions play a dominating role in the modulation of interactions between IL-mediated AuNPs and Cyt-c. The study strongly supports the promising character of sulfur-containing IL-mediated AuNPs for Cyt-c immobilization simultaneously opening new avenues for the application of greener and biocompatible nanoparticles with drug delivery and therapeutic applications.

Controlling Amyloid Fibril Properties Via Ionic Liquids: The Representative Case of Ethylammonium Nitrate and Tetramethylguanidinium Acetate on the Amyloidogenesis of Lysozyme

Protein aggregation into amyloid fibrils has been observed in several pathological conditions and exploited in nanotechnology. It is also key in several biochemical processes. In this work, we show that ionic liquids (ILs), a vast class of organic electrolytes, can finely tune amyloid properties, opening a new landscape in basic science and applications. The representative case of ethylammonium nitrate (EAN) and tetramethyl-guanidinium acetate (TMGA) ILs on lysozyme is considered. First, atomic force microscopy has shown that the addition of EAN and TMGA leads to thicker and thinner amyloid fibrils of greater and lower electric potential, respectively, with diameters finely tunable by IL concentration. Optical tweezers and neutron scattering have shed light on their mechanism of action. TMGA interacts with the protein hydration layer only, making the relaxation dynamics of these water molecules faster. EAN interacts directly with the protein instead, making it mechanically unstable and slowing down its relaxation dynamics.

Amyloid Formation in Nanoliter Droplets

Processes that monitor the nucleation of amyloids and characterize the formation of amyloid fibrils are vital to medicine and pharmacology. In this study, we observe the nucleation and formation of lysozyme amyloid fibrils using a facile microfluidic system to generate nanoliter droplets that can control the flow rate and movement of monomer-in-oil emulsion droplets in a T-junction microchannel. Using a fluorescence assay, we monitor the nucleation and growth process of amyloids based on the volume of droplets. Using the microfluidic system, we demonstrate that the lag phase, which is vital to amyloid nucleation and growth, is reduced at a lower droplet volume. Furthermore, we report a peculiar phenomenon of high amyloid formation at the edge of a bullet-shaped droplet, which is likely due to the high local monomer concentration. Moreover, we discovered that amyloid fibrils synthesized in the nanoliter droplets are shorter and thicker than fibrils synthesized from a bulk solution via the conventional heating method. Herein, a facile procedure to observe and characterize the nucleation and growth of amyloid fibrils using nanoliter droplets is presented, which is beneficial for investigating new features of amyloid fibril formation as an unconventional synthetic method for amyloid fibrils.