Comparative studies on the interaction of [C4mim]Br, and [C8mim]Br with β-casein micelles

Do Ionic Liquids Exhibit the Required Characteristics to Dissolve, Extract, Stabilize, and Purify Proteins? Past-Present-Future Assessment

Proteins are highly labile molecules, thus requiring the presence of appropriate solvents and excipients in their liquid milieu to keep their stability and biological activity. In this field, ionic liquids (ILs) have gained momentum in the past years, with a relevant number of works reporting their successful use to dissolve, stabilize, extract, and purify proteins. Different approaches in protein-IL systems have been reported, namely, proteins dissolved in (i) neat ILs, (ii) ILs as co-solvents, (iii) ILs as adjuvants, (iv) ILs as surfactants, (v) ILs as phase-forming components of aqueous biphasic systems, and (vi) IL-polymer-protein/peptide conjugates. Herein, we critically analyze the works published to date and provide a comprehensive understanding of the IL-protein interactions affecting the stability, conformational alteration, unfolding, misfolding, and refolding of proteins while providing directions for future studies in view of imminent applications. Overall, it has been found that the stability or purification of proteins by ILs is bispecific and depends on the structure of both the IL and the protein. The most promising IL-protein systems are identified, which is valuable when foreseeing market applications of ILs, e.g., in "protein packaging" and "detergent applications". Future directions and other possibilities of IL-protein systems in light-harvesting and biotechnology/biomedical applications are discussed.

Interaction Mechanism of Different Surfactants with Casein: A Perspective on Bulk and Interfacial Phase Behavior

Understanding the interaction mechanism between proteins and surfactants is conducive to the application of protein/surfactant mixtures in the food industry. The present study investigated the interaction mechanism of casein with cationic Gemini surfactant (BQAS), anionic Gemini surfactant (SGS), anionic single-chain surfactant (sodium dodecyl sulfate [SDS]), and two biosurfactants (rhamnolipid [RL] and lactone sophorolipid [SL]) at the interface and in bulk phase. BQAS/casein and SDS/casein mixtures exhibit a strong synergistic effect on the surface activity. For SGS, RL, and SL, the formation of surfactant/casein complexes caused no improvement in surface activity. Dilational elasticity results indicate the displacement of casein by SGS, RL, and SL at the surface. However, the BQAS/casein complexes manifested varying dilational properties from pure casein surface. The strong electrostatic interaction between BQAS and casein produced large-size precipitate particles. For other surfactants, no precipitate particles formed. Determination of ζ-potential, UV-vis absorption spectra, and fluorescence spectra demonstrated the stronger interaction of BQAS and SDS with casein than that of SGS, RL, and SL. Addition of BQAS initially increased and then decreased the α-helix structure of casein. For SGS, RL, and SL, no noticeable change occurred in the casein structure. However, the formation of SDS/casein complexes was conducive to the casein structure. In conclusion, the interaction between BQAS and casein is similar to that of cationic single-chain surfactant. Furthermore, SGS exhibits a significantly different interaction mechanism from the corresponding monomer (SDS), possibly resulting from its excellent interfacial activity, low critical micelle concentration values, and strong self-assembly capability. For RL and SL, the weak interaction is attributed to the relatively complicated structure and less charged degree of hydrophilic headgroups.

Ionic liquids in protein amyloidogenesis: a brief screenshot of the state-of-the-art

Ionic liquids (ILs) are a vast class of organic non-aqueous electrolytes whose interaction with biomolecules is receiving great attention for potential applications in bio-nano-technology. Recently, it has been shown that ILs can affect protein amyloidogenesis. Whereas some ILs favour the aggregation of proteins into amyloids, others inhibit their formation. Moreover, ILs can dissolve mature fibrils and restore the protein biochemical function. In this letter, we present a brief state-of-the-art summary of this emerging field that holds the promise of important developments both in basic science and in applications from bio-medicine to material science, and bio-nano-technology. The huge variety of ILs offers a vast playground for future studies and potential applications.

Heteroassembly Ability of Dicationic Ionic Liquids and Neutral Active Pharmaceutical Ingredients

Extensive investigation of interactions and aggregation properties of IL + API systems is necessary to apply ionic liquids (ILs) with different hydrophobic characteristics to drug delivery or in active pharmaceutical ingredient (API) formulations. Therefore, this study aims to investigate the heteroassembly between dicationic ILs ([BisOct(MIM)₂][2X], in which X is Br or BF₄, and [BisOct(BnIM)₂][2Br]), both in the absence and the presence of neutral APIs (salicylic acid, ibuprofen, and paracetamol) with different functional groups. Isothermal titration calorimetry results demonstrate that IL-API associations occur at very low concentrations of IL. These results were reinforced by electrospray ionization mass spectrometry with variable collision-induced dissociation, in which the IL dication interactions with APIs were detected. The strength of the dication-API interaction was determined from E _cm,1/2 data. The aggregation parameters (cac, ΔG _agg ^°, and K) between ILs and APIs were evaluated by conductivity. The ¹H NMR data showed that differences in chemical shifts provided relevant insights about interaction sites in both components.

Effect of the submicellar concentration of bile salts on structural alterations of β-casein micelles

The role of bile salts, sodium deoxycholate (NaDC) and sodium cholate (NaCh), on the self-assembly behavior of β-casein micelles (β-CMs) was investigated using various fluorescence techniques.

Aggregation behavior and total miscibility of fluorinated ionic liquids in water

In this work, novel and nontoxic fluorinated ionic liquids (FILs) that are totally miscible in water and could be used in biological applications, where fluorocarbon compounds present a handicap because their aqueous solubility (water and biological fluids) is in most cases too low, have been investigated. The self-aggregation behavior of perfluorosulfonate-functionalized ionic liquids in aqueous solutions has been characterized using conductometric titration, isothermal titration calorimetry (ITC), surface tension measurements, dynamic light scattering (DLS), viscosity and density measurements, and transmission electron microscopy (TEM). Aggregation and interfacial parameters have been computed by conductimetry, calorimetry, and surface tension measurements in order to study various thermodynamic and surface properties that demonstrate that the aggregation process is entropy-driven and that the aggregation process is less spontaneous than the adsorption process. The novel perfluorosulfonate-functionalized ILs studied in this work show improved surface activity and aggregation behavior, forming distinct self-assembled structures.