Enzymatic activity and thermal stability of metallo proteins in hydrated ionic liquids

Factor defining the effects of tetraalkylammonium chloride on stability, folding, and dynamics of horse cytochrome c

This article describes the molecular mechanism by which tetraalkylammonium chloride ([R4N]Cl: R- = methyl (Me), ethyl (Et), propyl (Pr),butyl (Bu)) modulates the stability, folding, and dynamics of cytochrome c (Cyt c). Analysis of [R4N]Cl effects on thermal/chemical denaturations, millisecond refolding/unfolding kinetics, and slow CO-association kinetics of Cyt c without and with denaturant providing some significant results: (i) [R4N]Cl decreasing the unfolding free energy estimated by thermodynamic and kinetic analysis of thermal/chemical denaturation curves and kinetic chevrons (Log kobs-[GdmCl]) of Cyt c, respectively (ii) hydrophobicity of R-group of [R4N]Cl, preferential inclusion of [R4N]Cl at the protein surface, and destabilizing enthalpic attractive interactions of [Me4N]Cl and steric entropic interactions of [Et4N]Cl,[Pr4N]Cl and [Bu4N]Cl with protein contribute to [R4N]Cl-induced decrease thermodynamic stability of Cyt c (iii) [R4N]Cl exhibits an additive effect with denaturant to decrease thermodynamic stability and refolding rates of Cyt c (iv) low concentrations of [R4N]Cl (≤ 0.5 M) constrain the motional dynamics while the higher concentrations (>0.75 M [R4N]Cl) enhance the structural-fluctuations that denture protein (v) hydrophobicity of R-group of [R4N]Cl alters the [denaturant]-dependent conformational stability, refolding-unfolding kinetics, and CO-association kinetics of Cyt c. Furthermore, the MD simulations depicted that the addition of 1.0 M of [R4N]Cl increased the conformational fluctuations in Cyt c leading to decreased structural stability in the order [Me4N]Cl < [Et4N]Cl < [Pr4N]Cl < [Bu4N]Cl consistent with the experimental results.

Low-Frequency Spectra of Hydrated Ionic Liquids with Kosmotropic and Chaotropic Anions

In this study, we investigated the water concentration dependence of the intermolecular vibrations of two hydrated ionic liquids (ILs), cholinium dihydrogen phosphate ([ch][dhp]) and cholinium bromide ([ch]Br), using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES). The anions of the former and latter hydrated ILs are kosmotropic and chaotropic, respectively. We found that the spectral peak of ∼50 cm-1 shifted to the low-frequency side in hydrated [ch][dhp], indicating the weakening of its intermolecular interactions. In contrast, no change in the peak frequency of the low-frequency band at ∼50 cm-1 was observed with increasing water concentration in hydrated [ch]Br. The vibrational density of states (VDOS) spectra generated from molecular dynamics (MD) simulations were in qualitative agreement with the experimental results. Decomposition analysis of the VDOS spectra for each component revealed that the red shift of the low-frequency band in the hydrated [ch][dhp] upon water addition was essentially due to the contributions of anions and water rather than that of the cholinium cation. We also found from the low-frequency spectra of the two hydrated ILs that they differed in the concentration dependence of the 180 cm-1 band, which is assigned as a hindered translational motion of water molecules combined to form O···O stretching motions. From the relationship between the peak frequency of the low-frequency band and the bulk parameter, which is the square root of the surface tension divided by the density, we found that the peak frequency in the hydrated IL with kosmotropic [dhp]- depends on the bulk parameter, similar to the case for an aqueous solution of the typical deep eutectic solvent reline. However, the peak frequency of the hydrated IL with chaotropic Br- is constant with the bulk parameter.

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.

Hydrated Ionic Liquids: Perspective for Bioscience

Hydrated ionic liquid (IL) is a simple mixture of IL and water. Unique aqueous electrolyte solution can be designed by mixing IL with limited amount of water. In most hydrated ILs, there are no free water and all are strongly interacted with ions. The properties of hydrated ILs, such as polarity, viscosity, ion mobility, and hydrogen bonding ability, can therefore be controlled simply by water content. This mixture is expected to provide similar environment to that of living cell, and is desired to be effective solvents for biomolecules. In this account, we would like to survey the basic properties, recent results, and future aspects of the hydrated ILs.

Impact of an Ionic Liquid on Amino Acid Side Chains: A Perspective from Molecular Simulation Studies

Ionic liquids (ILs) are known to modify the structural stability of proteins. The modification of the protein conformation is associated with the accumulation of ILs around the amino acid (AA) side chains and the nature of interactions between them. To understand the microscopic picture of the structural arrangements of ILs around the AA side chains, room temperature molecular dynamics (MD) simulations have been carried out in this work with a series of hydrophobic, polar and charged AAs in aqueous solutions containing the IL 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]) at 2 M concentration. The calculations revealed distinctly nonuniform distribution of the IL components around different AAs. In particular, it is demonstrated that the BMIM⁺ cations preferentially interact with the aromatic AAs through favorable stacking interactions between the cation imidazolium head groups and the aromatic AA side chains. This results in preferential parallel alignments and enhanced population of the cations around the aromatic AAs. The potential of mean force (PMF) calculations revealed that such favorable stacking interactions provide greater stability to the contact pairs (CPs) formed between the aromatic AAs and the IL cations as compared to the other AAs. It is further quantified that for most of the AAs (except the cationic ones), a favorable enthalpy contribution more than compensates for the entropy cost to form stable CPs with the IL cations. These findings are likely to provide valuable fundamental information toward understanding the effects of ILs on protein conformational stability.

Structure and Function of Redox-Sensitive Superfolder Green Fluorescent Protein Variant

Aims: Genetically encoded green fluorescent protein (GFP)-based redox biosensors are widely used to monitor specific and dynamic redox processes in living cells. Over the last few years, various biosensors for a variety of applications were engineered and enhanced to match the organism and cellular environments, which should be investigated. In this context, the unicellular intraerythrocytic parasite Plasmodium, the causative agent of malaria, represents a challenge, as the small size of the organism results in weak fluorescence signals that complicate precise measurements, especially for cell compartment-specific observations. To address this, we have functionally and structurally characterized an enhanced redox biosensor superfolder roGFP2 (sfroGFP2). Results: SfroGFP2 retains roGFP2-like behavior, yet with improved fluorescence intensity (FI) in cellulo. SfroGFP2-based redox biosensors are pH insensitive in a physiological pH range and show midpoint potentials comparable with roGFP2-based redox biosensors. Using crystallography and rigidity theory, we identified the superfolding mutations as being responsible for improved structural stability of the biosensor in a redox-sensitive environment, thus explaining the improved FI in cellulo. Innovation: This work provides insight into the structure and function of GFP-based redox biosensors. It describes an improved redox biosensor (sfroGFP2) suitable for measuring oxidizing effects within small cells where applicability of other redox sensor variants is limited. Conclusion: Improved structural stability of sfroGFP2 gives rise to increased FI in cellulo. Fusion to hGrx1 (human glutaredoxin-1) provides the hitherto most suitable biosensor for measuring oxidizing effects in Plasmodium. This sensor is of major interest for studying glutathione redox changes in small cells, as well as subcellular compartments in general. Antioxid. Redox Signal. 37, 1-18.

Roles of Surfactants in Oriented Immobilization of Cellulase on Nanocarriers and Multiphase Hydrolysis System

Surfactants, especially non-ionic surfactants, play an important role in the preparation of nanocarriers and can also promote the enzymatic hydrolysis of lignocellulose. A broad overview of the current status of surfactants on the immobilization of cellulase is provided in this review. In addition, the restricting factors in cellulase immobilization in the complex multiphase hydrolysis system are discussed, including the carrier structure characteristics, solid-solid contact obstacles, external diffusion resistance, limited recycling frequency, and nonproductive combination of enzyme active centers. Furthermore, promising prospects of cellulase-oriented immobilization are proposed, including the hydrophilic-hydrophobic interaction of surfactants and cellulase in the oil-water reaction system, the reversed micelle system of surfactants, and the possible oriented immobilization mechanism.

Protein aggregation and crystallization with ionic liquids: Insights into the influence of solvent properties

Ionic liquids (ILs) have been used in solvents for proteins in many applications, including biotechnology, pharmaceutics, and medicine due to their tunable physicochemical and biological properties. Protein aggregation is often undesirable, and predominantly occurs during bioprocesses, while the aggregation process can be reversible or irreversible and the aggregates formed can be native/non-native and soluble/insoluble. Recent studies have clearly identified key properties of ILs and IL-water mixtures related to protein performance, suggesting the use of the tailorable properties of ILs to inhibit protein aggregation, to promote protein crystallization, and to control protein aggregation pathways. This review discusses the critical properties of IL and IL-water mixtures and presents the latest understanding of the protein aggregation pathways and the development of IL systems that affect or control the protein aggregation process. Through this feature article, we hope to inspire further advances in understanding and new approaches to controlling protein behavior to optimize bioprocesses.

Contrasting Effects of Ionic Liquids of Varying Degree of Hydrophilicity on the Conformational and Interfacial Properties of a Globular Protein

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 (PF₆^-), ethyl sulfate (ETS^-), acetate (OAc^-), chloride (Cl^-), dicyanamide (DCA^-), and nitrate (NO₃^-) . 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.

Effects of Ionic Liquids on Metalloproteins

In the past decade, innovative protein therapies and bio-similar industries have grown rapidly. Additionally, ionic liquids (ILs) have been an area of great interest and rapid development in industrial processes over a similar timeline. Therefore, there is a pressing need to understand the structure and function of proteins in novel environments with ILs. Understanding the short-term and long-term stability of protein molecules in IL formulations will be key to using ILs for protein technologies. Similarly, ILs have been investigated as part of therapeutic delivery systems and implicated in numerous studies in which ILs impact the activity and/or stability of protein molecules. Notably, many of the proteins used in industrial applications are involved in redox chemistry, and thus often contain metal ions or metal-associated cofactors. In this review article, we focus on the current understanding of protein structure-function relationship in the presence of ILs, specifically focusing on the effect of ILs on metal containing proteins.

Use of Ionic Liquids in Protein and DNA Chemistry

Ionic liquids (ILs) have been receiving much attention as solvents in various areas of biochemistry because of their various beneficial properties over the volatile solvents and ILs availability in myriad variants (perhaps as many as 108) owing to the possibility of paring one cation with several anions and vice-versa as well as formulations as zwitterions. Their potential as solvents lies in their tendency to offer both directional and non-directional forces toward a solute molecule. Because of these forces, ionic liquids easily undergo intermolecular interactions with a range of polar/non-polar solutes, including biomolecules such as proteins and DNA. The interaction of genomic species in aqueous/non-aqueous states assists in unraveling their structure and functioning, which have implications in various biomedical applications. The charge density of ionic liquids renders them hydrophilic and hydrophobic, which retain intact over long-range of temperatures. Their ability in stabilizing or destabilizing the 3D-structure of a protein or the double-helical structure of DNA has been assessed superior to the water and volatile organic solvents. The aptitude of an ion in influencing the structure and stability of a native protein depends on their ranking in the Hofmeister series. However, at several instances, a reverse Hofmeister ordering of ions and specific ion-solute interaction has been observed. The capability of an ionic liquid in terms of the tendency to promote the coiling/uncoiling of DNA structure is noted to rely on the basicity, electrostatic interaction, and hydrophobicity of the ionic liquid in question. Any change in the DNA's double-helical structure reflects a change in its melting temperature (T m), compared to a standard buffer solution. These changes in DNA structure have implications in biosensor design and targeted drug-delivery in biomedical applications. In the current review, we have attempted to highlight various aspects of ionic liquids that influence the structure and properties of proteins and DNA. In short, the review will address the issues related to the origin and strength of intermolecular interactions, the effect of structural components, their nature, and the influence of temperature, pH, and additives on them.

Predicting Entropic Effects of Water Mixing with Ionic Liquids Containing Anions of Strong Hydrogen Bonding Ability: Role of the Cation

Ionic liquids (ILs) such as choline dihydrogen phosphate exhibit an extraordinary solubilizing ability for proteins such as cytochrome C when mixed with 20 wt % water. Most widely used imidazolium-based ionic liquids coupled with dihydrogen phosphate do not exhibit the same solubilizing properties, suggesting that a multifunctional cation such as choline might play a key role in enhancing these properties of ionic liquid mixtures with water. In this theoretical work, we compare intermolecular interactions between the water molecule and ionic liquid ions in two ion-paired clusters of choline- and 1-butyl-3-methyl-imidazolium-based ionic liquids coupled with acetate, dihydrogen phosphate, and mesylate. Gibbs free energy (GFE) of solvation of water in these ionic liquids was calculated. Incorporation of a water molecule into ionic liquid clusters was accompanied by negative GFEs of solvation in both types of cations. These results were in good agreement with previously reported experimental GFEs of solvation of water in ILs. Compared to imidazolium-based clusters, strong interionic interactions of choline ionic liquids resulted in more negative GFEs due to their smaller deformation upon the addition of a water molecule, with dihydrogen phosphate and mesylate predicting the lowest GFEs of -30.1 and -43.5 kJ/mol^-1, respectively. Lower GFEs of solvation of water in choline-based clusters were also accompanied with smaller entropic penalties, suggesting that water easily incorporates itself into the existing ionic network. Analysis of the intramolecular bonds within the water molecule showed that the choline hydroxyl group donates electron density to the neighboring water molecule, leading to additional polarization. The predicted infrared spectra of clusters of ionic liquids with water showed a pronounced red shift due to strongly polarized O-H bonds, in excellent agreement with the experimentally measured infrared spectra of ionic liquid mixtures with water. Increased polarization of water in choline-based ionic liquids undoubtedly creates more effective solvents for stabilizing biological molecules such as proteins.

What do we learn from enzyme behaviors in organic solvents? - Structural functionalization of ionic liquids for enzyme activation and stabilization

Enzyme activity in nonaqueous media (e.g. conventional organic solvents) is typically lower than in water by several orders of magnitude. There is a rising interest of developing new nonaqueous solvent systems that are more "water-like" and more biocompatible. Therefore, we need to learn from the current state of nonaqueous biocatalysis to overcome its bottleneck and provide guidance for new solvent design. This review firstly focuses on the discussion of how organic solvent properties (such as polarity and hydrophobicity) influence the enzyme activity and stability, and how these properties impact the enzyme's conformation and dynamics. While hydrophobic organic solvents usually lead to the maintenance of enzyme activity, solvents carrying functional groups like hydroxys and ethers (including crown ethers and cyclodextrins) can lead to enzyme activation. Ionic liquids (ILs) are designable solvents that can conveniently incorporate these functional groups. Therefore, we systematically survey these ether- and/or hydroxy-functionalized ILs, and find most of them are highly compatible with enzymes leading to high activity and stability. In particular, ILs carrying both ether and tert-alcohol groups are among the most enzyme-activating solvents. Future direction is to learn from enzyme behaviors in both water and nonaqueous media to design biocompatible "water-like" solvents.

Development of a novel cellulose solvent based on pyrrolidinium hydroxide and reliable solubility analysis

Cellulose processing remains a challenge as it is insoluble in water and common organic solvents. Ionic liquids (ILs) are organic salts with a melting point below 100 °C and are known for their excellent solvent properties. Unlike common organic solvents, which can form toxic or flammable vapours due to their high volatility, ILs can be considered as more environmentally friendly due to their negligible vapour pressure and flame retardant properties. We found that N-butyl-N-methylpyrrolidinium hydroxide enables rapid dissolution of up to 20 wt% Avicel® cellulose at 25 °C in aqueous solution (50 wt% water), making it the first pyrrolidinium-based salt capable of dissolving cellulose. Furthermore, solubility studies are currently carried out mainly with the naked eye, microscopy or spectroscopy. The former is a subjective method because it depends on the observer, and particles at the micro-level cannot be seen with the human eye. Microscopic and spectroscopic analyses are suitable for the verification of solubility; however, the acquisition costs of the instruments are high, and sample preparation is time-consuming. We propose that turbidity is a suitable measure for solubility, and investigated a simple and fast method to evaluate cellulose solubility in aqueous N-butyl-N-methylpyrrolidinium hydroxide by employing a turbidimeter which was compared with microscopy and ocular (eye) observation. In this study, we have not only found a promising new solvent for cellulose processing, but also offer a reliable solubility analysis.

[C₄mpyr][OH] enables rapid dissolution of up to 20 wt% Avicel® cellulose at 25 °C in aqueous solution (50 wt% water), making it an attractive new solvent for cellulose processing. Three solubility analysis methods were investigated and compared.

Mechanical Stabilization of Deoxyribonucleic Acid Solid Films Based on Hydrated Ionic Liquid

Solid films of deoxyribonucleic acid (DNA) containing a hydrated ionic liquid, choline dihydrogen phosphate (CDP), were prepared by a solvent-casting method. Thermal properties, aggregation structure, thermal molecular motion, and tensile properties of CDP-containing DNA films were examined by thermogravimetry (TG), wide-angle X-ray diffraction (WAXD) measurement, dynamic mechanical analysis (DMA), and tensile tests, respectively. The water retentivity of the films at room temperature was much improved with CDP. The packing density of DNA helical chains clearly depended on the amount of CDP in the film. A small amount of CDP contributed to the suppression of the B_I → B_II conformational transition and the cooperative motion of the DNA duplex in the film. The tensile properties of the film drastically changed in the presence of CDP. When the amount of hydrated CDP in the film increased, the mechanical response of the film changed from glassy-like to rubbery-like via a semicrystalline-like state. The above results make it clear that CDP plays two major roles as a water absorber and plasticizer in the DNA film. Thus, it can be concluded that the use of an ionic liquid as an additive significantly increases the possibility of using a DNA solid film as a structural material.

Strategic planning of proteins in ionic liquids: future solvents for the enhanced stability of proteins against multiple stresses

Ionic liquids (ILs) present a vast number of solvents capable of replacing toxic organic solvents in chemical, biotechnology and biomedical applications. ILs are inexpensive and environmentally friendly as the materials can be recycled conveniently. Chemists use a variety of cation and anion combinations to produce an IL that fits the requirements of the sustainable future through the pursuit of greener chemical processes. As such, the development of various types of ILs has been recognized as the emergence of environmentally friendly solvents to attain enhanced protein stability in vitro. The literature survey reveals that there exist a large number of scholarly articles as well as elegant reviews on protein stability in ILs. Biomolecules have adapted to antagonistic environmental stresses that normally denature proteins, and the mechanism of adaptation that protects the cellular components against denaturation involves the intracellular concentration of co-solvents. In this regard, recent experimental results distinctly demonstrated that ILs are stabilizing proteins against denaturing stresses, and their presence in the cells does not alter protein functional activities. However, a review focusing particularly on the refolding and counteracting effects of the ILs against denatured proteins by multiple stresses is still missing. This perspective unveils the studies that have been conducted to improve protein stabilities with ILs as well as the refolding and counteracting abilities of these ILs against the denatured proteins under the influence of multiple stresses. We believe that ILs can provide significant environmental and economic advantages for biochemical processes in the near future. Essentially, numerous investigations are required to allow us to further explore the stabilizing properties of ILs over proteins.

Silk Fibroin Bending Actuators as an Approach Toward Natural Polymer Based Active Materials

This work reports on the development of ionic liquid (IL)/silk fibroin (SF) composite films as electroactive polymers actuators. Different contents (20, 40, and 60% wt) of 1-butyl-3-methylimidazolium tricyanomethanide ([Bmim][C(CN₃)]) and choline dihydrogen phosphate ([Ch][DHP]) ILs were incorporated into the SF polymer matrix. Due to IL-SF interactions, morphological changes such as globule-like nanostructures are induced in the samples. High concentrations of IL promote SF β-sheet formation above 65%. Further, an increase in the thermal stability of the SF was observed through the incorporation of [Bmim][C(CN₃)]. IL type and content allow tuning of the electrical response as well as achieving bending actuation. [Bmim][C(CN3)]/SF samples allow bending responses up to 0.5 at an applied voltage of 3 V. In conclusion, this work demonstrates the ability of IL/SF composites to act as electroactive polymer actuators and opens new perspectives in the application of natural resources for smart materials.

Water-Induced Breaking of the Coulombic Ordering in a Room-Temperature Ionic Liquid Metal Complex

Control of ion arrangements in ionic liquids represents a major challenge owing to the presence of the predominant coulombic interactions between cationic and anionic ion species that forms the coulombic ordering. Here, water-induced ion rearrangement in a room-temperature ionic liquid (RT-IL) metal complex, (1-ethyl-3-methylimidazolium)₂ [MnN(CN)₄ ], is demonstrated through coordinative interactions between anions. Solidification occurred, which was associated with the formation of a "separated" structure consisting of cation columns and anionic cyanide-bridged one-dimensional coordination polymers. The energy diagram is in accord with the resultant RT-IL incorporating mononuclear [MnN(CN)₄ ]^2- molecules being a kinetic phase stabilized by inter-ion repulsions of the anionic divalent metal complex moieties. Water acts to decrease the coulombic interactions, including repulsion, giving rise to breaking of the coulombic ordering arising from coordination bond formation in the IL phase.

Preparation of lysozyme-imprinted nanoparticles on polydopamine-modified titanium dioxide using ionic liquid as a stabilizer

Molecular imprinting of proteins has evolved into an efficient approach for protein recognition and separation. However, maintaining the structural stability of proteins during the preparation process of molecularly imprinted polymers (MIPs) remains challenging. Ionic liquids (ILs), being capable of maintaining the stability of proteins, might enable effective imprinting and accurate recognition of proteins. In this study, lysozyme (Lyz)-imprinted titanium dioxide (TiO₂) nanoparticles, TiO₂@Lyz-MIPs, have been successfully prepared for selective recognition and separation of Lyz. This was achieved by the free radical polymerization of hydroxyethyl acrylate (HEA) and poly(ethylene glycol) dimethacrylate (PEGDMA) on polydopamine (PDA)-modified TiO₂ nanoparticles using an IL, choline dihydrogen phosphate (chol dhp), as the stabilizer of Lyz. It was found that both PDA modification of TiO₂ and the use of chol dhp as stabilizer improved the adsorption capacity of TiO₂@Lyz-MIPs toward Lyz. When the concentration of HEA was 7 mg mL⁻¹, the ratio of monomer to crosslinker was 20 : 1, and the concentration of chol dhp was 12.5 mg mL⁻¹, the highest imprinting factor of 4.40 was achieved. TiO₂@Lyz-MIPs exhibited relatively high adsorption capacity with the maximum adsorption capacity up to 120 mg g⁻¹, which was more than four times higher than that of the non-imprinted polymers (NIPs) counterpart, TiO₂@Lyz-NIPs. The adsorption rate of Lyz by TiO₂@Lyz-MIPs was also much higher than that of TiO₂@Lyz-NIPs. TiO₂@Lyz-MIPs could successfully separate Lyz from diluted egg white, a complex mixture of proteins. Findings from this study indicate that effective recognition cavities toward Lyz were formed on the surface of Lyz-imprinted TiO₂ nanoparticles prepared using IL as the template stabilizer. This approach may facilitate the development of MIPs for efficient protein recognition and separation.

Molecular imprinting of proteins has evolved into an efficient approach for protein recognition and separation.

Using Thermodynamics to Assess the Molecular Interactions of Tetrabutylphosphonium Carboxylate–Water Mixtures

Densities, ρ, viscosities, η, and enthalpies of mixing, , of binary [P4 4 4 4][CnCOO]–water mixtures (with n=1, 2 or 7) were determined at atmospheric pressure as a function of temperature. The excess, , apparent, , and partial, , molar volumes were deduced from experimental data, as well as fragilities, m*, and excess Gibbs free energies of activation of viscous flow, . exhibited predominantly negative deviation from ideality, with a minimum at approximately ~0.8 for all three systems, indicating strong hydrogen-bonding interactions. All three binary systems were found to be fragile, with [P4 4 4 4][C7COO] showing the smallest deviations in fragility with the addition of water. values of the systems were exothermic over the entire composition range, having the following trend: [P4 4 4 4][C2COO]&gt;[P4 4 4 4][C7COO]&gt;[P4 4 4 4][C1COO].

Hydration States of Cholinium Phosphate-Type Ionic Liquids as a Function of Water Content

We investigated the hydration states of cholinium phosphate-type ionic liquids (ILs) in relation to ion structure, focusing on the influence of the hydroxyl group of the cation and the alkyl chain length of the anion. Water activity measurements provided information on the macroscopic hydration states of the hydrated ILs, while NMR measurements and molecular dynamics simulations clearly showed the microscopic interactions and coordination of the water molecules. The hydrogen bonding networks in these ILs were influenced by the anion structure and water content, and the mobility of water molecules was influenced by the number of hydroxyl groups in the cation and anion.

Hydrated ionic liquids enable both solubilisation and refolding of aggregated concanavalin A

Dissolution and refolding of aggregated concanavalin A were demonstrated in hydrated ionic liquids.

Design and properties of functional zwitterions derived from ionic liquids

A zwitterion, an ion pair where cation and anion are covalently tethered, is known to be a type of salt. These ions have not been recognised as interesting, but they are physicochemically unique and fascinating ions. In the present review, some functional zwitterions derived from ionic liquids are mentioned to emphasise the usefulness of the tethering of the component cations and anions of ionic liquids. Basic properties, advantages and disadvantages after the functional design of zwitterions, and some applications are summarised.

Biological and nanotechnological applications using interactions between ionic liquids and nucleic acids

Nucleic acids have emerged as powerful biological and nanotechnological tools. In biological and nanotechnological experiments, methods of extracting and purifying nucleic acids from various types of cells and their storage are critical for obtaining reproducible experimental results. In nanotechnological experiments, methods for regulating the conformational polymorphism of nucleic acids and increasing sequence selectivity for base pairing of nucleic acids are important for developing nucleic acid-based nanomaterials. However, dearth of media that foster favourable behaviour of nucleic acids has been a bottleneck for promoting the biology and nanotechnology using the nucleic acids. Ionic liquids (ILs) are solvents that may be potentially used for controlling the properties of the nucleic acids. Here, we review researches regarding the behaviour of nucleic acids in ILs. The efficiency of extraction and purification of nucleic acids from biological samples is increased by IL addition. Moreover, nucleic acids in ILs show long-term stability, which maintains their structures and enhances nuclease resistance. Nucleic acids in ILs can be used directly in polymerase chain reaction and gene expression analysis with high efficiency. Moreover, the stabilities of the nucleic acids for duplex, triplex, and quadruplex (G-quadruplex and i-motif) structures change drastically with IL cation-nucleic acid interactions. Highly sensitive DNA sensors have been developed based on the unique changes in the stability of nucleic acids in ILs. The behaviours of nucleic acids in ILs detailed here should be useful in the design of nucleic acids to use as biological and nanotechnological tools.

Aqueous ionic liquids in comparison with standard co-solutes : Differences and common principles in their interaction with protein and DNA structures

Ionic liquids (ILs) are versatile solvents for a broad range of biotechnological applications. Recent experimental and simulation results highlight the potential benefits of dilute ILs in aqueous solution (aqueous ILs) in order to modify protein and DNA structures systematically. In contrast to a limited number of standard co-solutes like urea, ectoine, trimethylamine-N-oxide (TMAO), or guanidinium chloride, the large amount of possible cation and anion combinations in aqueous ILs can be used to develop tailor-made stabilizers or destabilizers for specific purposes. In this review article, we highlight common principles and differences between aqueous ILs and standard co-solutes with a specific focus on their underlying macromolecular stabilization or destabilization behavior. In combination with statistical thermodynamics theories, we present an efficient framework, which is used to classify structure modification effects consistently. The crucial importance of enthalpic and entropic contributions to the free energy change upon IL-assisted macromolecular unfolding in combination with a complex destabilization mechanism is described in detail. A special focus is also set on aqueous IL-DNA interactions, for which experimental and simulation outcomes are summarized and discussed in the context of previous findings.

Aqueous ionic liquids and their influence on peptide conformations: denaturation and dehydration mechanisms

Low concentrated aqueous ionic liquids (ILs) and their influence on protein structures have attracted a lot of interest over the last few years. This can be mostly attributed to the fact that aqueous ILs, depending on the ion species involved, can be used as protein protectants or protein denaturants. Atomistic molecular dynamics (MD) simulations are performed in order to study the influence of different aprotic ILs on the properties of a short hairpin peptide. Our results reveal distinct binding and denaturation effects for 1-ethyl-3-methylimidazolium (EMIM) in combination with different anions, namely, chloride (CL), tetrafluoroborate (BF4) and acetate (ACE). The simulation outcomes demonstrate that the studied ILs with larger anions reveal a more pronounced accumulation behavior of the individual ion species around the peptide, which is accomplished by a stronger dehydration effect. We can relate these findings to the implications of the Kirkwood-Buff theory, which provides a thermodynamic explanation for the denaturation strength in terms of the IL accumulation behavior. The results for the spatial distribution functions, the binding energies and the local/bulk partition coefficients are in good agreement with metadynamics simulations in order to determine the energetically most stable peptide conformations. The free energy landscapes indicate a decrease of the denaturation strength in the order EMIM/ACE, EMIM/BF4 and EMIM/CL, which coincides with a decreasing size of the anion species. An analysis of the potential binding energies reveals that this effect is mainly of enthalpic nature.

"Solvent-in-salt" systems for design of new materials in chemistry, biology and energy research

Inorganic and organic "solvent-in-salt" (SIS) systems have been known for decades but have attracted significant attention only recently. Molten salt hydrates/solvates have been successfully employed as non-flammable, benign electrolytes in rechargeable lithium-ion batteries leading to a revolution in battery development and design. SIS with organic components (for example, ionic liquids containing small amounts of water) demonstrate remarkable thermal stability and tunability, and present a class of admittedly safer electrolytes, in comparison with traditional organic solvents. Water molecules tend to form nano- and microstructures (droplets and channel networks) in ionic media impacting their heterogeneity. Such microscale domains can be employed as microreactors for chemical and enzymatic synthesis. In this review, we address known SIS systems and discuss their composition, structure, properties and dynamics. Special attention is paid to the current and potential applications of inorganic and organic SIS systems in energy research, chemistry and biochemistry. A separate section of this review is dedicated to experimental methods of SIS investigation, which is crucial for the development of this field.

Effect of Ionic Liquids on the Hatching of Artemia salina Cysts

We investigated the effect of six ionic liquids (ILs), and dimethylsulfoxide (DMSO) as a typical molecular liquid (organic solvent), on the hatching of Artemia salina cysts. The effect of an IL on the hatching of Artemia salina strongly depends on the specific combination of cation and anion. Of the ILs tested, choline acetate and choline chloride had a significantly lower toxicity. The level of inhabitation followed the order [chl][dhp] > [bmim][NO3] > [MAN][NO3] > [bmim][Ac] > DMSO > [chl][Ac] ≥ [chl][Cl].

Long-term protein packaging in bio-ionic liquids: Improved catalytic activity and enhanced stability of cytochrome C against multiple stresses

There is a considerable interest in the use of structurally stable and catalytically active enzymes, such as cytochrome C (Cyt C), in the pharmaceutical and fine chemical industries. However, harsh process conditions, such as temperature, pH, and presence of organic solvents, are the major barriers to the effective use of enzymes in biocatalysis. Herein, we demonstrate the suitability of bio-based ionic liquids (ILs) formed by the cholinium cation and dicarboxylate-based anions as potential media for enzymes, in which remarkable enhanced activity and improved stability of Cyt C against multiple stresses were obtained. Among the several bio-ILs studied, an exceptionally high catalytic activity (> 50-fold) of Cyt C was observed in aqueous solutions of cholinium glutarate ([Ch][Glu]; 1g/mL) as compared to the commonly used phosphate buffer solutions (pH 7.2), and > 25-fold as compared to aqueous solutions of cholinium dihydrogen phosphate ([Ch][Dhp]; 0.5g/mL) -the best known IL for long term stability of Cyt C. The catalytic activity of the enzyme in presence of bio-ILs was retained against several external stimulus, such as chemical denaturants (H2O2 and GuHCl), and temperatures up to 120 °C. The observed enzyme activity is in agreement with its structural stability, as confirmed by UV-Vis, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopies. Taking advantage of the multi-ionization states of di/tri-carboxylic acids, the pH was switched from acidic to basic by the addition of the corresponding carboxylic acid and choline hydroxide, respectively. The activity was found to be maximum at a 1:1 ratio of [Ch][carboxylate], with a pH in the range from 3 to 5.5. Moreover, it was found that the bio-ILs studied herein protect the enzyme against protease digestion and allow long-term storage (at least for 21 weeks) at room temperature. An attempt by molecular docking was also made to better understand the efficacy of the investigated bio-ILs towards the enhanced activity and long term stability of Cyt C. The results showed that dicarboxylates anions interact with the active site's amino acids of the enzyme through H-bonding and electrostatic interactions, which are responsible for the observed enhancement of the catalytic activity. Finally, it is demonstrated that Cyt C can be successfully recovered from the aqueous solution of bio-ILs and reused without compromising its yield, structural integrity and catalytic activity, thereby overcoming the major limitations in the use of IL-protein systems in biocatalysis.

Aqueous ionic liquids and their effects on protein structures: an overview on recent theoretical and experimental results

Ionic liquids (ILs) are used in a variety of technological and biological applications. Recent experimental and simulation results reveal the influence of aqueous ionic liquids on the stability of protein and enzyme structures. Depending on different parameters like the concentration and the ion composition, one can observe distinct stabilization or denaturation mechanisms for various ILs. In this review, we summarize the main findings and discuss the implications with regard to molecular theories of solutions and specific ion effects. A preferential binding model is introduced in order to discuss protein-IL effects from a statistical mechanics perspective. The value of the preferential binding coefficient determines the strength of the ion influence and indicates a shift of the chemical equilibrium either to the native or the denatured state of the protein. We highlight the role of water in order to explain the self-association behavior of the IL species and discuss recent experimental and simulation results in the light of the observed binding effects.

Quantitative assessment of kosmotropicity of hydrated ionic liquids by nuclear magnetic resonance

The NMR chemical shift variation of H₂O varied with the component ion and reflected the kosmotropicity quantitatively in hydrated ionic liquids.