Proteins in Ionic Liquids: Reactions, Applications, and Futures (original) (raw)
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Insights into Protein-Ionic Liquid Interactions Aiming at Macromolecule Delivery Systems
Journal of the Brazilian Chemical Society, 2018
Over the last few years, researchers have started to explore a particular class of compounds defined as ionic liquids (ILs) in attempts to use their unique characteristics. Since ILs have a very low vapor pressure, these fascinating compounds hold great potential as high performance chemicals for several applications in the (bio)pharmaceutical industry. In general, and unlike common organic solvents with comparable polarities, ILs are quite compatible with enzymes (enhancing their structural and chemical stability) and other proteins, since they can promote higher selectivities, faster reaction rates and greater enzyme stabilities in biocatalytic reactions providing, at the same time, a path for the structural and functional stabilization of protein entities. ILs appear to enhance the delivery of macromolecules, particularly protein entities, and their interactions with ILs will be tackled in detail in this review paper.
Communications Chemistry
Ionic liquids offer exciting possibilities for biocatalysis as solvent properties provide rare opportunities for customizable, energy-efficient bioprocessing. Unfortunately, proteins and enzymes are generally unstable in ionic liquids and several attempts have been made to explain why; however, a comprehensive understanding of the ionic liquid–protein interactions remains elusive. Here, we present an analytical framework (circular dichroism (CD), fluorescence, ultraviolet-visible (UV/Vis) and nuclear magnetic resonance (NMR) spectroscopies, and small-angle X-ray scattering (SAXS)) to probe the interactions, structure, and stability of a model protein (green fluorescent protein (GFP)) in a range (acetate, chloride, triflate) of pyrrolidinium and imidazolium salts. We demonstrate that measuring protein stability requires a similar holistic analytical framework, as opposed to single-technique assessments that provide misleading conclusions. We reveal information on site-specific ionic ...
Innovative aspects of protein stability in ionic liquid mixtures
Biophysical reviews, 2018
Mixtures of ionic liquids (ILs) have attracted our attention because of their extraordinary performances in extraction technologies and in absorbing large amount of CO gas. It has been observed that when two or more ILs are mixed in different proportions, a new solvent is obtained which is much better than that of each component of ILs from which the mixture is obtained. Within a mixture of ILs, several unidentified interactions occur among several ions which give rise to unique solvent properties to the mixture. Herein, in this review, we have highlighted the utilization of the advantageous properties of the IL mixtures in protein stability studies. This approach is exceptional and opens new directions to the use of ILs in biotechnology.
CrystEngComm, 2012
We have performed experiments on the crystallization of two low molecular weight, positively charged proteins, lysozyme and ribonuclease A, using ionic liquids as either crystallization additives or, in particular cases, as precipitating agents. The ionic liquids (ILs) have been ordered according to their salting-in/out ability and the relative position of these ionic liquids in this ranking has been rationalized by considering their hydration properties (positive-negative, hydrophobichydrophilic). The ability to screen the effective charge of cationic proteins and aid protein nucleation (salting-out) has been shown to be superior for large polarizable anions with low charge density, negatively hydrated-Cl 2 , Br 2 , [SCN] 2 , methane-[C 1 SO 3 ] 2 and ethanesulfonates [C 2 SO 3 ] 2 , than for anions with a relatively stable hydration shell, positively hydrated-lactate [Lac] 2 , butylsulfonate [C 4 SO 3 ] 2 and acetate [Ac] 2. Upon increasing the background salt concentration, where electrostatic interactions are already effectively screened, the ability of the IL ions to stabilize proteins in solution (salting-in) has been shown to increase as the ions are likely to migrate to the non-polar protein surface and lower protein-water interfacial tension. This tendency is enhanced as the focus moves from those ions with positively hydrated hydrophilic compartments (e.g. [Ac] 2) to those with negatively hydrated groups (e.g. [C 1 SO 3 ] 2) and the prevailing hydrophobic hydration (e.g. [C 4 SO 3 ] 2). The observed inversion in the relative effect of ILs on protein crystallization with increasing ionic strength of the aqueous media has been interpreted as the differing effects of ion adsorption: charge screening and interfacial tension modification. Moreover, this work can further help in our understanding of the influence of ionic liquids on conformational changes of biomacromolecules in solution. Identification of the specific incorporation sites for choline and acetate ions, localized in two lysozyme crystals grown in pure IL solutions without any buffer or inorganic precipitant, can give us some insight into the role of the ionic liquid ions in protein structure development.
Recent advances in exploiting ionic liquids for biomolecules: Solubility, stability and applications
Biotechnology Journal, 2016
The technological utility of biomolecules (e.g. proteins, enzymes and DNA) can be significantly enhanced by combining them with ionic liquids (ILs)-potentially attractive "green" and "designer" solvents-rather than using in conventional organic solvents or water. In recent years, ILs have been used as solvents, cosolvents, and reagents for biocatalysis, biotransformation, protein preservation and stabilization, DNA solubilization and stabilization, and other biomolecule-based applications. Using ILs can dramatically enhance the structural and chemical stability of proteins, DNA, and enzymes. This article reviews the recent technological developments of ILs in protein-, enzyme-, and DNA-based applications. We discuss the different routes to increase biomolecule stability and activity in ILs, and the design of biomolecule-friendly ILs that can dissolve biomolecules with minimum alteration to their structure. This information will be helpful to design ILbased processes in biotechnology and the biological sciences that can serve as novel and selective processes for enzymatic reactions, protein and DNA stability, and other biomolecule-based applications.
Microscopic Understanding of the Effect of Ionic Liquid on Protein from Molecular Simulation Studies
We have performed molecular dynamics (MD) simulations of the protein α-lactalbumin in aqueous solution containing the ionic liquid (IL) 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF 4 ]) as the cosolvent at different concentrations. Attempts have been made to obtain quantitative understanding of the effects of the IL on the conformational features of the protein as well as the distributions of the IL and water around it. The calculations revealed enhanced rigidity of the protein with reduced conformational fluctuations and increasingly correlated local motions in the presence of the IL. Nonuniform relative population of the BMIM + and BF 4 − ions at the protein surface with respect to that in the bulk solution has been observed. It is demonstrated that exchange of water by the IL around the protein results in rearrangement of the hydrogen bond network at the interface with breaking of protein−water hydrogen bonds and formation of protein−IL hydrogen bonds. Importantly, it is found that the protein forms increased number of stronger salt bridges in the presence of IL. This shows that the formation of a greater number of such stronger salt bridges is the origin behind the enhanced rigidity of the protein in the presence of the IL.
Thermodynamic Contribution of Amino Acids in Ionic Liquids Towards Protein Stability
Current Biochemical Engineering, 2014
Amino acids (AA s ) combine to form a three-dimensional protein structure and are of very much importance in understanding the biophysical properties of biomolecules. Basically, the nature and the arrangement of the AA s in a protein backbone is only responsible for the individual characteristics of the macromolecule. The AA s in a protein backbone are influenced by the solvent molecules hence, it is very important to have a clear idea on the solubility, stability, and thermodynamic properties of these AA s in various solvents and co-solvents. A basic level of quantifying protein-solvent interactions involve the use of transfer free energies, G tr from water to solvents. The values of G tr for side chains and peptide backbone quantify the thermodynamic consequences of solvating a protein species in a co-solvent solution relative to pure water. Based on the transfer model and experimental G tr for these AA s , it has been proposed that these cosolvents exert their effect on protein stability primarily via the protein backbone. The G tr of AA s from water to another solvent system will be either favorable or unfavorable. By definition, an unfavorable transfer free energy, G tr > 0, means that the protein becomes solvophobic on transfer to a solvent, whereas a favorable transfer free energy, G tr < 0, represents that the protein becomes solvophilic on transfer to a solvent. The sign and magnitude of the measured G tr quantifies the protein response to changes in solvent quality. Therefore, this review will provide the basis of a universal mechanism for co-solvent-mediated (that includes the new novel biocompatible ionic liquids (ILs)) protein stabilization and destabilization as the protein backbone is shared by all proteins, regardless of side chain sequence.
Ionic liquids (ILs), depending on their cation−anion combinations, are known to influence the conformational properties and activities of proteins in a nonuniform manner. To obtain microscopic understanding of such influence, it is important to characterize protein−IL interactions and explore the modified solvation environment around the protein. In this work, molecular dynamics (MD) simulations of the globular protein α-lactalbumin have been carried out in aqueous IL solutions containing 1-butyl-3-methylimidazolium cations (BMIM +) in combination with a series of anions with varying degree of hydrophilicity, namely, hexafluorophosphate (PF 6 −), ethyl sulfate (ETS −), acetate (OAc −), chloride (Cl −), dicyanamide (DCA −), and nitrate (NO 3 −). The calculations revealed that ILs with hydrophobic and hydrophilic anions have contrasting influence on conformational flexibility of the protein. It is further observed that the BMIM + cations exhibit site-specific orientations at the interface depending on the hydrophilicity of the anion component. Most importantly, the results demonstrated enhanced propensity of hydrophilic ILs to replace relatively weaker protein−water hydrogen bonds by stronger protein−IL hydrogen bonds at the protein surface as compared to the hydrophobic ILs. Such breaking of protein−water hydrogen bonds at a greater extent leads to greater loss of water hydrating the protein in the presence of hydrophilic ILs, thereby reducing the protein's stability.