Comparison of peroxidase activities of hemin, cytochrome c and microperoxidase-11 in molecular solvents and imidazolium-based ionic liquids

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Ionic liquids and deep eutectic solvents for the recovery of phenolic compounds: effect of ionic liquids structure and process parameters

Water pollution is a severe and challenging issue threatening the sustainable development of human civilization. Besides other pollutants, waste fluid streams contain phenolic compounds. These have an adverse effect on the human health and marine ecosystem due to their toxic, mutagenic, and carcinogenic nature. Therefore, it is necessary to remove such phenolic pollutants from waste stream fluids prior to discharging to the environment. Different methods have been proposed to remove phenolic compounds from wastewater, including extraction using ionic liquids (ILs) and deep eutectic solvent (DES), a class of organic salts having melting point below 100 °C and tunable physicochemical properties. The purpose of this review is to present the progress in utilizing ILs and DES for phenolic compound extraction from waste fluid streams. The effects of IL structural characteristics, such as anion type, cation type, alkyl chain length, and functional groups will be discussed. In addition, the impact of key process parameters such as pH, phenol concentration, phase ratio, and temperature will be also described. More importantly, several ideas for addressing the limitations of the treatment process and improving its efficiency and industrial viability will be presented. These ideas may form the basis for future studies on developing more effective IL-based processes for treating wastewaters contaminated with phenolic pollutants, to address a growing worldwide environmental problem.

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.

The study and application of biomolecules in deep eutectic solvents

Deep eutectic solvents offer stimulating possibilities for biomolecular stabilization and manipulation, biocatalysis, bioextraction, biomass processing, and drug delivery and therapy.

Recent advances in ionic liquids and nanotechnology for drug delivery

In drug discovery and drug development, it is estimated that around 40% of commercialized and 90% of under-study drugs have inadequate pharmaceutical properties, severely impairing its therapeutic efficacy. Thus, there is a strong demand to find strategies to enhance the delivery of such drugs. Ionic liquids are a novel class of liquids composed of a combination of organic salts that are of particular interest alone or in combination with drug delivery systems. This review is focused on the recent efforts using ionic liquids in drug solubility, formulation and drug delivery with specific emphasis on nanotechnology. The latest developments using hybrid delivery systems obtained upon the combination of drug delivery systems and ionic liquids will also be addressed.

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.

Salt bridges govern the structural heterogeneity of heme protein interactions and porphyrin networks: microperoxidase-11

In this work, a proteolytic digest of cytochrome c (microperoxidase 11, MP-11) was used as a model to study the structural aspects of heme protein interactions and porphyrin networks. The MP-11 structural heterogeneity was studied as a function of the starting pH (e.g., pH 3.1-6.1) and concentration (e.g., 1-50 μM) conditions and adduct coordination. Trapped ion mobility spectrometry coupled to mass spectrometry (TIMS-MS) showed the MP-11 structural dependence of the charge state distribution and molecular ion forms with the starting pH conditions. The singly charged (e.g., [M]+, [M - 2H + NH4]+, [M - H + Na]+ and [M - H + K]+) and doubly charged (e.g., [M + H]2+, [M - H + NH4]2+, [M + Na]2+ and [M + K]2+) molecular ion forms were observed for all solvent conditions, although the structural heterogeneity (e.g., number of mobility bands) significantly varied with the pH value and ion form. The MP-11 dimer formation as a model for heme-protein protein interactions showed that dimer formation is favored toward more neutral pH and favored when assisted by salt bridges (e.g., NH4 +, Na+ and K+ vs. H+). Inspection of the dimer mobility profiles (2+ and 3+ charge states) showed a high degree of structural heterogeneity as a function of the solution pH and ion form; the observation of common mobility bands suggest that the different salt bridges can stabilize similar structural motifs. In addition, the salt bridge influence on the MP-11 dimer formations was measured using collision induced dissociation and showed a strong dependence with the type of salt bridge (i.e., a CE50 of 10.0, 11.5, 11.8 and 13.0 eV was observed for [2M + H]3+, [2M - H + NH4]3+, [2M + Na]3+ and [2M + K]3+, respectively). Measurements of the dimer equilibrium constant showed that the salt bridge interactions increase the binding strength of the dimeric species.

Reliable method for the detection of horseradish peroxidase activity and enzyme kinetics

Enzyme-catalyzed reactions are complicated and their kinetics depend on various chemical and physical factors. In a simple enzyme-catalyzed reaction, the enzyme kinetics often involve two or more substrates. However, this complexity is often ignored when studying enzyme kinetics or determining enzyme activity. Such an example is horseradish peroxidase (HRP), whose activity and kinetics in the reduction of H₂O₂ are usually detected and studied using spectroanalysis, with guaiacol (GA) as the hydrogen donor. In this process, the concentrations of two substrates, GA and H₂O₂, both change, which makes the practical detection, based on determination of the GA oxydate, GA(O), totally wrong. In this study, we introduce a new electrochemical method for detecting the specific activity (SA) and studying the enzyme kinetics of HRP. This electrochemical method was used to directly detect one substrate (H₂O₂) while the concentration of the other substrate (GA) was kept constant by adding ascorbic acid to the system to reduce GA(O) and regenerate GA. For the first time, this HRP-catalyzed reaction, including the mechanism and kinetics, was investigated precisely using a simple electrochemical method. The maximum SA and reaction rate constant k₁ were reliably detected and calculated. The proposed method indicated that the SA of commercially available HRP (300 U mg^-1 detected by spectroanalysis) was 1228.8 U mg^-1 at a GA concentration of 4.5 mM, and up to 2049.9 U mg^-1 as the GA concentration tended toward infinity. Our results suggest that reported methods for detecting enzyme activity and/or kinetics should be re-examined according to the catalytic mechanism of the enzyme.

Structural changes in cellular membranes induced by ionic liquids: From model to bacterial membranes

Ionic liquids (ILs) have generated considerable attention recently because of their cytotoxicity and application as antibiotics. However, the mechanism of how they damage cell membranes is not currently well understood. In this paper, the antibacterial activities of two imidazolium-based ILs, namely 1-butyl- 3-methylimidazolium tetrafluroborate ([BMIM][BF4]) and 1-ethyl- 3-methylimidazolium tetrafluroborate ([EMIM][BF4]) have been investigated. The activity of [BMIM][BF4] on gram negative bacteria E. coli is observed to be stronger compared with the short chained [EMIM][BF4]. To explain this observation, the effects of these ILs on the self-assembled structures of model cellular membranes have been investigated. The in-plane elasticity of a monolayer formed at air-water interface by 1,2-dipalmitoyl- sn-glycero- 3-phosphocholine (DPPC) lipids was reduced in the presence of the ILs. The x-ray reflectivity studies on polymer supported lipid bilayer have shown the bilayer to shrink and correspondingly exhibit an increase in electron density. The presence of a certain mol% of negatively charged lipid, 1,2-dipalmitoyl-rac-glycero-3-phospho-L-serine (DPPS), in DPPC mono- and bi-layers enhances the effect considerably.

Choline-Based Amino Acid ILs-Collagen Interaction: Enunciating Its Role in Stabilization/Destabilization Phenomena

Given the potential of productive interaction between choline-based amino acid ionic liquids (CAAILs) and collagen, we investigated the role of four CAAILs, viz., choline serinate, threoninate, lysinate, and phenylalaninate, and the changes mediated by them in the structure of collagen at different hierarchical orderings, that is, at molecular and fibrillar levels. The rheological, dielectric behavior and the secondary structural changes signify the alteration in the triple helical structure of collagen at higher concentrations of CAAILs. A marginal swelling and slight decrease in the thermal stability of rat tail tendon collagen fibers were observed for choline serinate and threoninate, albeit distortions in banding patterns were noticed for choline lysinate and phenylalaninate, suggesting chaotropicity of the ions at the fibrillar level. This signifies the changes in the hydrogen-bonding environment of collagen with increasing concentrations of CAAILs, which could be due to competitive hydrogen bonding between the carbonyl group of amino acid ionic liquids and the hydroxyl groups of collagen.

Thermodynamics of interaction of ionic liquids with lipid monolayer

Understanding the interaction of ionic liquids with cellular membrane becomes utterly important to comprehend the activities of these liquids in living organisms. Lipid monolayer formed at the air-water interface is employed as a model system to follow this interaction by investigating important thermodynamic parameters. The penetration kinetics of the imidazolium-based ionic liquid 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM][BF4]) into the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid layer is found to follow the Boltzmann-like equation that reveals the characteristic time constant which is observed to be the function of initial surface pressure. The enthalpy and entropy calculated from temperature-dependent pressure-area isotherms of the monolayer show that the added ionic liquids bring about a disordering effect in the lipid film. The change in Gibbs free energy indicates that an ionic liquid with longer chain has a far greater disordering effect compared to an ionic liquid with shorter chain. The differential scanning calorimetric measurement on a multilamellar vesicle system shows the main phase transition temperature to shift to a lower value, which, again, indicates the disordering effect of the ionic liquid on lipid membrane. All these studies fundamentally point out that, when ionic liquids interact with lipid molecules, the self-assembled structure of a cellular membrane gets perturbed, which may be the mechanism of these molecules having adverse effects on living organisms.

An activity transition from NADH dehydrogenase to NADH oxidase during protein denaturation

A decrease in the specific activity of an enzyme is commonly observed when the enzyme is inappropriately handled or is stored over an extended period. Here, we reported a functional transition of an FMN-bound diaphorase (FMN-DI) that happened during the long-term storage process. It was found that FMN-DI did not simply lose its β-nicotinamide adenine diphosphate (NADH) dehydrogenase activity after a long-time storage, but obtained a new enzyme activity of NADH oxidase. Further mechanistic studies suggested that the alteration of the binding strength of an FMN cofactor with a DI protein could be responsible for this functional switch of the enzyme.

Proteins in Ionic Liquids: Current Status of Experiments and Simulations

In the last two decades, while searching for interesting applications of ionic liquids as potent solvents, their solvation properties and their general impact on biomolecules, and in particular on proteins, gained interest. It turned out that ionic liquids are excellent solvents for protein refolding and crystallization. Biomolecules showed increased solubilities and stabilities, both operational and thermal, in ionic liquids, which also seem to prevent self-aggregation during solubilization. Biomolecules can be immobilized, e.g. in highly viscous ionic liquids, for particular biochemical processes and can be designed to some extent by the proper choice of the ionic liquid cations and anions, which can be characterized by the Hofmeister series.

A biomimetic enzyme modified electrode for H2O2 highly sensitive detection

An efficient catalyst based on artificial bionic peroxidase was synthesized for electrocatalysis. A poly(ethyleneimine)/Au nanoparticle composite (PEI-AuNP) was prepared and it was then linked to hemin via a coupling reaction between carboxyl groups in hemin and amino groups in PEI without the activation of a carboxyl group by carbodiimide. Fourier transform infrared (FTIR) spectroscopy verified the formation of amido bonds within the structure. The presence of AuNPs contributed greatly in establishing the amido bonds within the composite. Transmission electron microscopy (TEM) and UV-visible spectroscopy were also used to characterize the PEI-AuNP-hemin catalyst. PEI-AuNP-hemin exhibited intrinsic peroxidase-like catalytic activities. The PEI-AuNP-hemin deposited on a glass carbon electrode had strong sensing for H2O2 with a well-defined linear relationship between the amperometric response and H2O2 concentration in the range from 1 μM to 0.25 mM. The detection limit was 0.247 nM with a high sensitivity of 0.347 mA mM(-1) cm(-2). The peroxidase-like catalytic activity of PEI-AuNP-hemin is discussed in relation to its microstructure. The study suggests that PEI-AuNP-hemin may have promising application prospects in biocatalysis and bioelectronics.

Unusually high thermal stability and peroxidase activity of cytochrome c in ionic liquid colloidal formulation

All ionic liquid-based colloidal formulation as a thermally stable medium for enzyme biocatalysis.

Hydrogen-bond acidity of ionic liquids: an extended scale

One of the main drawbacks comprising an appropriate selection of ionic liquids (ILs) for a target application is related to the lack of an extended and well-established polarity scale for these neoteric fluids. Albeit considerable progress has been made on identifying chemical structures and factors that influence the polarity of ILs, there still exists a high inconsistency in the experimental values reported by different authors. Furthermore, due to the extremely large number of possible ILs that can be synthesized, the experimental characterization of their polarity is a major limitation when envisaging the choice of an IL with a desired polarity. Therefore, it is of crucial relevance to develop correlation schemes and a priori predictive methods able to forecast the polarity of new (or not yet synthesized) fluids. In this context, and aiming at broadening the experimental polarity scale available for ILs, the solvatochromic Kamlet-Taft parameters of a broad range of bis(trifluoromethylsulfonyl)imide-([NTf2](-))-based fluids were determined. The impact of the IL cation structure on the hydrogen-bond donating ability of the fluid was comprehensively addressed. Based on the large amount of novel experimental values obtained, we then evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond acidity of ILs. A three-parameter model based on the cation-anion interaction energies was found to adequately describe the experimental hydrogen-bond acidity or hydrogen-bond donating ability of ILs. The proposed three-parameter model is also shown to present a predictive capacity and to provide novel molecular-level insights into the chemical structure characteristics that influence the acidity of a given IL. It is shown that although the equimolar cation-anion hydrogen-bonding energies (EHB) play the major role, the electrostatic-misfit interactions (EMF) and van der Waals forces (EvdW) also contribute, admittedly in a lower extent, towards the hydrogen-bond acidity of ILs. The new extended scale provided for the hydrogen-bond acidity of ILs is of high value for the design of new ILs for task-specific applications.

Direct extraction of genomic DNA from maize with aqueous ionic liquid buffer systems for applications in genetically modified organisms analysis

To date, the extraction of genomic DNA is considered a bottleneck in the process of genetically modified organisms (GMOs) detection. Conventional DNA isolation methods are associated with long extraction times and multiple pipetting and centrifugation steps, which makes the entire procedure not only tedious and complicated but also prone to sample cross-contamination. In recent times, ionic liquids have emerged as innovative solvents for biomass processing, due to their outstanding properties for dissolution of biomass and biopolymers. In this study, a novel, easily applicable, and time-efficient method for the direct extraction of genomic DNA from biomass based on aqueous-ionic liquid solutions was developed. The straightforward protocol relies on extraction of maize in a 10 % solution of ionic liquids in aqueous phosphate buffer for 5 min at room temperature, followed by a denaturation step at 95 °C for 10 min and a simple filtration to remove residual biopolymers. A set of 22 ionic liquids was tested in a buffer system and 1-ethyl-3-methylimidazolium dimethylphosphate, as well as the environmentally benign choline formate, were identified as ideal candidates. With this strategy, the quality of the genomic DNA extracted was significantly improved and the extraction protocol was notably simplified compared with a well-established method.

Insights into the denaturation of bovine serum albumin with a thermo-responsive ionic liquid

Influence of bovine serum albumin on the phase transition behavior of the synthetic ionic liquid tetrabutylphosphonium styrenesulfonate ([P(4),(4),(4),(4)][SS]) together with the interactions between [P(4),(4),(4),(4)][SS] and bovine serum albumin (BSA) was investigated by differential scanning calorimetry (DSC), turbidity measurements, FT-IR, in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2DCOS). Our results reveal that the addition of BSA would increase the phase transition temperature but weaken the transition behavior of [P(4),(4),(4),(4)][SS] solution. DSC and turbidity data show us that the transition temperature of a ternary system with 20 wt% BSA added is 3 °C higher than that with 20% (w/v) [P(4),(4),(4),(4)][SS] solution. Interactions between [P(4),(4),(4),(4)][SS] and BSA together with the phase transition behavior of [P(4),(4),(4),(4)][SS] are responsible for the denaturation of BSA upon heating. PCMW determined the obvious distinctions in LCST of different chemical groups manifesting their various response sequences in the phase separation and denaturation upon heating. Finally, 2DCOS was employed to elucidate the sequential order of chemical group motions during heating. It is worth noting that the appearance of the isosbestic point in the C[double bond, length as m-dash]O groups of FTIR spectra indicates the direct transformation of the conformation of α-helix, random coil to β-sheet and β-turn without an intermediate transition state. Additionally, the phase separation process of ionic liquid is able to recover to the original state before heating while the denaturation of BSA is irreversible after a cooling process.

Does the stability of proteins in ionic liquids obey the Hofmeister series?

Understanding the behavior of Hofmeister anions of ionic liquids (ILs) on protein stability helps to shed light on how the anions interact with proteins in aqueous solution and is a long standing object for chemistry and biochemistry. Ions effects play a major role in understanding the physicochemical and biological phenomenon that undertakes the protein folding/unfolding and refolding process. Despite the generality of these effects, our understanding of ions at the molecular-level is still limited. This review offers a tour through past successful investigations and presents a challenge in current research in the field to reassess the possibilities of ions and to apply new strategies. This review highlights on the stability behavior of the proteins and also comparisons of our past research work in the Hofmeister series of ILs. Furthermore, we specifically focus on the critical discussion on the recent findings with existing results and their implications, along with our understanding of the Hofmeister series of anions of ILs on biomolecular stability. A detailed examination of the difference between selective proteins can provide a better understanding of the molecular mechanism of protein folding/unfolding in the presence of the Hofmeister series of ions of ILs.

Selective isolation of hemoglobin by use of imidazolium-modified polystyrene as extractant

Ionic liquids have attracted much attention in the analysis of a variety of species. The functional groups in ionic liquids can result in highly efficient separation and enrichment and, because of their typical lack of volatility, they are environmentally benign. We grafted imidazole cations onto the surface of chloromethyl polystyrene, denoted PS-CH2-[MIM](+)Cl(-), and this modified polymer was used to selectively extract the protein hemoglobin (Hb). The prepared extractant PS-CH2-[MIM](+)Cl(-), containing 2 mmol immobilized imidazole groups per gram polymer, was characterized by FT-IR, surface charge analysis, and elemental analysis. The adsorption efficiency was 91%. The adsorption capacity of the PS-CH2-[MIM](+)Cl(-) for Hb was 23.6 μg mg(-1), and 80% of the retained Hb could be readily recovered by use of 0.5% (m/v) aqueous sodium dodecyl sulfate (SDS) solution as eluate. The activity of the eluted Hb was approximately 90%. The prepared imidazole-containing solid phase polymer was used for direct adsorption of Hb without use of any other solid matrix as support of the ionic liquid. The material was used in practice to isolate Hb from human whole blood.

Thermodynamic studies of ionic hydration and interactions for amino acid ionic liquids in aqueous solutions at 298.15 K

Amino acid ionic liquids are a special class of ionic liquids due to their unique acid-base behavior, biological significance, and applications in different fields such as templates in synthetic chemistry, stabilizers for biological macromolecules, etc. The physicochemical properties of these ionic liquids can easily be altered by making the different combinations of amino acids as anion along with possible cation modification which makes amino acid ionic liquids more suitable to understand the different kinds of molecular and ionic interactions with sufficient depth so that they can provide fruitful information for a molecular level understanding of more complicated biological processes. In this context, volumetric and osmotic coefficient measurements for aqueous solutions containing 1-ethyl-3-methylimidazolium ([Emim]) based amino acid ionic liquids of glycine, alanine, valine, leucine, and isoleucine are reported at 298.15 K. From experimental osmotic coefficient data, mean molal activity coefficients of ionic liquids were estimated and analyzed using the Debye-Hückel and Pitzer models. The hydration numbers of ionic liquids in aqueous solutions were obtained using activity data. Pitzer ion interaction parameters are estimated and compared with other electrolytes reported in the literature. The nonelectrolyte contribution to the aqueous solutions containing ionic liquids was studied by calculating the osmotic second virial coefficient through an application of the McMillan-Mayer theory of solution. It has been found that the second osmotic virial coefficient which includes volume effects correlates linearly with the Pitzer ion interaction parameter estimated independently from osmotic data as well as the hydrophobicity of ionic liquids. The enthalpy-entropy compensation effect, explained using the Starikov-Nordén model of enthalpy-entropy compensation, and partial molar entropy analysis for aqueous [Emim][Gly] solutions are made by using experimental Gibb's free energy data and literature enthalpy data. This study highlights that the hydrophobic interaction persists even in the limit of infinite dilution where the hydration effects are usually dominant, implying importance of hydrophobic hydration. Analysis of the results further shows that the hydration of amino acid ionic liquids occurs through the cooperative H-bond formation with the kosmotropic effect in contrast to the usual inorganic salts or hydrophobic salts like tetraalkylammonium halides.

Isopropylammonium formate as a mobile phase modifier for liquid chromatography

Isopropylammonium formate (IPAF), a new alkylammonium formate (AAF) room temperature ionic liquid, has been synthesized from isopropylamine and formic acid and characterized as an organic solvent mobile phase replacement for reversed-phase liquid chromatography (LC). Characterization of IPAF solvent properties in water such as pH, conductivity, and viscosity, as well as its synthesis, is described. The LC polarity (P') and the solvent strength (S) parameters are determined to be 6.0 and 2.4, respectively, similar to those same parameters for methanol and acetonitrile. Application of this RTIL is demonstrated as an organic solvent replacement for reversed-phase LC to separate a test mixture of niacinamide, acetophenone and p-nitroaniline. The van Deemter plot profile for several columns of different dimensions, particle size, pore size and stationary phase are compared using an IPAF-water mobile phase. At flow rates above 2 mL/min, on-line mixing of the viscous IPAF with water appears not to be uniform. A flattening of the van Deemter profile is noted for particularly short (50 mm) wide bore (4.6 mm) columns packed with larger particles (10 µm). Small particle longer columns likely facilitated mixing at the beginning of the column generating typical linearly increasing van Deemeter curves. IPAF has been further shown as a function of temperature to be a non-denaturing modifier solvent for the separation of the protein cytochrome c from tryptophan compared to methanol. This is important to show, because the semi-preparative separation of native proteins using AAF mobile phases is the long-term goal of this research program.

Flavins secreted by bacterial cells of Shewanella catalyze cathodic oxygen reduction

On Her Majesty's Secrete Service: Oxygen reduction is an important process for microbial fuel cells (MFCs) and microbiologically-influenced corrosion (MIC). We demonstrate that flavins secreted by anode-respiring Shewanella cells can catalyze cathodic oxygen reduction via adsorption on the cathode. The findings will provide new insight for developing methods to improve MFC performance and to prevent MIC.

Peroxide-dependent analyte conversion by the heme prosthetic group, the heme Peptide "microperoxidase-11" and cytochrome C on chitosan capped gold nanoparticles modified electrodes

In view of the role ascribed to the peroxidatic activity of degradation products of cytochrome c (cyt c) in the processes of apoptosis, we investigate the catalytic potential of heme and of the cyt c derived heme peptide MP-11 to catalyse the cathodic reduction of hydrogen peroxide and to oxidize aromatic compounds. In order to check whether cyt c has an enzymatic activity in the native state where the protein matrix should suppress the inherent peroxidatic activity of its heme prosthetic group, we applied a biocompatible immobilization matrix and very low concentrations of the co-substrate H₂O₂. The biocatalysts were entrapped on the surface of a glassy carbon electrode in a biocompatible chitosan layer which contained gold nanoparticles. The electrochemical signal for the peroxide reduction is generated by the redox conversion of the heme group, whilst a reaction product of the substrate oxidation is cathodically reduced in the substrate indication. The catalytic efficiency of microperoxidase-11 is sufficient for sensors indicating HRP substrates, e.g., p-aminophenol, paracetamol and catechol, but also the hydroxylation of aniline and dehalogenation of 4-fluoroaniline. The lower limit of detection for p-aminophenol is comparable to previously published papers with different enzyme systems. The peroxidatic activity of cyt c immobilized in the chitosan layer for catechol was found to be below 1 per mill and for p-aminophenol about 3% as compared with that of heme or MP-11.

Stimuli responsive ionogels for sensing applications-an overview

This overview aims to summarize the existing potential of "Ionogels" as a platform to develop stimuli responsive materials. Ionogels are a class of materials that contain an Ionic Liquid (IL) confined within a polymer matrix. Recently defined as "a solid interconnected network spreading throughout a liquid phase", the ionogel therefore combines the properties of both its solid and liquid components. ILs are low melting salts that exist as liquids composed entirely of cations and anions at or around 100 °C. Important physical properties of these liquids such as viscosity, density, melting point and conductivity can be altered to suit a purpose by choice of the cation/anion. Here we provide an overview to highlight the literature thus far, detailing the encapsulation of IL and responsive materials within these polymeric structures. Exciting applications in the areas of optical and electrochemical sensing, solid state electrolytes and actuating materials shall be discussed.

Applications of Ionic Liquids in Electrochemical Sensors and Biosensors

Ionic liquids (ILs) are salt that exist in the liquid phase at and around 298 K and are comprised of a bulky, asymmetric organic cation and the anion usually inorganic ion but some ILs also with organic anion. ILs have attracted much attention as a replacement for traditional organic solvents as they possess many attractive properties. Among these properties, intrinsic ion conductivity, low volatility, high chemical and thermal stability, low combustibility, and wide electrochemical windows are few. Due to negligible or nonzero volatility of these solvents, they are considered “greener” for the environment as they do not evaporate like volatile organic compounds (VOCs). ILs have been widely used in electrodeposition, electrosynthesis, electrocatalysis, electrochemical capacitor, lubricants, plasticizers, solvent, lithium batteries, solvents to manufacture nanomaterials, extraction, gas absorption agents, and so forth. Besides a brief discussion of the introduction, history, and properties of ILs the major purpose of this review paper is to provide an overview on the advantages of ILs for the synthesis of conducting polymer and nanoparticle when compared to conventional media and also to focus on the electrochemical sensors and biosensors based on IL/composite modified macrodisk electrodes. Subsequently, recent developments and major strategies for enhancing sensing performance are discussed.

Enzyme-catalyzed crosslinkable hydrogels: emerging strategies for tissue engineering

State-of-the-art bioactive hydrogels can easily and efficiently be formed by enzyme-catalyzed mild-crosslinking reactions in situ. Yet this cell-friendly and substrate-specific method remains under explored. Hydrogels prepared by using enzyme systems like tyrosinases, transferases and lysyl oxidases show interesting characteristics as dynamic scaffolds and as systems for controlled release. Increased attention is currently paid to hydrogels obtained via crosslinking of precursors by transferases or peroxidases as catalysts. Enzyme-mediated crosslinking has proven its efficiency and attention has now shifted to the development of enzymatically crosslinked hydrogels with higher degrees of complexity, mimicking extracellular matrices. Moreover, bottom-up approaches combining biocatalysts and self-assembly are being explored for the development of complex nano-scale architectures. In this review, the use of enzymatic crosslinking for the preparation of hydrogels as an innovative alternative to other crosslinking methods, such as the commonly used UV-mediated photo-crosslinking or physical crosslinking, will be discussed. Photo-initiator-based crosslinking may induce cytotoxicity in the formed gels, whereas physical crosslinking may lead to gels which do not have sufficient mechanical strength and stability. These limitations can be overcome using enzymes to form covalently crosslinked hydrogels. Herewith, we report the mechanisms involved and current applications, focusing on emerging strategies for tissue engineering and regenerative medicine.