Direct electrochemistry and electrocatalysis of myoglobin immobilized in hyaluronic acid and room temperature ionic liquids composite film

A novel biocomposite film based on hyaluronic acid (HA) and hydrophilic room temperature ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMIM][BF₄]) was explored. Here, HA was used as a binder to form [EMIM][BF₄]-HA composite film and help [EMIM][BF₄] to attaching on glass carbon electrode (GCE) surface, while doping [EMIM][BF₄] in HA can effectively reduce the electron transfer resistance of HA. The composite film can be readily used as an immobilization matrix to entrap myoglobin (Mb). A pair of well-defined and quasi-reversible redox peaks of Mb was obtained at the Mb-[EMIM][BF₄]-HA composite film modified GCE (Mb-[EMIM][BF₄]-HA/GCE) through direct electron transfer between Mb and the underlying electrode. The Mb-[EMIM][BF₄]-HA/GCE showed an excellent electrocatalytic activity toward the reduction of H₂O₂. Based on the [EMIM][BF₄]-HA biocomposite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Using ionic liquid [EMIM][CH3COO] as an enzyme-‘friendly’ co-solvent for resolution of amino acids

An ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate [EMIM][CH₃COO], was used in 0–4.0 M (∼60% IL, v/v), as a nonvolatile organic medium for the enzymatic resolution of amino acids. When dl-phenylalanine methyl ester was studied as a model substrate, high enantiomeric excesses (ee) of l-amino acid were obtained in all ionic concentrations; however, lower yields were observed at high IL concentrations. This IL is more enzyme-‘friendly’ than the hydrophilic organic solvent acetonitrile and those ILs containing chaotropic anions (such as [EMIM][OTs]). Among three proteases and two lipases investigated, lyophilized Bacillus licheniformis protease exhibited the best enantioselectivity and activity. Highly enantioselective resolutions were also produced for several other amino acids in 2.0 M IL. Interestingly, high ee were also found in deuterium oxide (D₂O) rather than in ordinary water, and a further enhancement was achieved with the co-existence of [EMIM][CH₃COO]. The heavy water effect was explained in terms of protein stabilization by D₂O. The secondary structural changes of enzyme in various media were interpreted by the second derivatives of FT-IR spectra.     

Physical Vapor Deposition of [EMIM][Tf2N]: A New Approach to the Modification of Surface Properties with Ultrathin Ionic Liquid Films

Ultrathin films of the ionic liquid (IL) 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][Tf₂N], are prepared on a glass substrate by means of an in situ thermal‐evaporation/condensation process under ultrahigh‐vacuum conditions. By using X‐ray photoelectron spectroscopy (XPS), it is demonstrated that the first layer of the IL film grows two dimensionally, followed by the three‐dimensional growth of successive layers. The first molecular layer consists of a bilayer, with the [EMIM]⁺ cations in contact to the surface and the [Tf₂N]^? anions at the vacuum side. The ultrathin IL films are found to be stable under ambient conditions.     

Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

Isobaric vapor–liquid equilibrium (VLE) data for ethanol–water systems containing ionic liquids (ILs) 1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) at atmospheric pressure (101.32 kPa) were measured with a circulation still. The results showed that the VLE of ethanol–water systems in the presence of different ILs was obviously different from that of the IL-free system. All ILs studied showed a salting-out effect, which gave rise to a change of the relative volatility of ethanol, and even to an elimination of the azeotropic point. It was found that the salting-out effect followed the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆] and [MMIM][DMP] > [EMIM][DEP], which was ascribed to the preferential solvation ability of the ions resulting from the dissociation of the IL.     

The thermochemistry of solvation of imidazolium-based ionic liquids in benzene

ABSTRACT

The present work is devoted to the thermochemical study of solvation of ionic liquids (IL) in benzene. The solution enthalpies of 1-ethyl-3-methylimidazolium tricyanomethanide [EMIM][C(CN)₃], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄], 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF₆], 1-octyl-3-methylimidazolium tetrafluoroborate [OMIM][BF₄], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][NTf₂], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTf₂] and 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][TfO] in benzene were measured. The solvation enthalpies of imidazolium-based IL were calculated. Molar refractions of imidazolium-based IL form literature data on density and refractive indexes of IL were also calculated. The linear correlation between solvation enthalpy and molar refraction of IL was observed. This correlation can be used to calculate the vaporization enthalpy of imidazolium-based IL from solution calorimetry data.     

Effect of anions on static orientational correlations, hydrogen bonds, and dynamics in ionic liquids: a simulational study

Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and PAdua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM+ is studied in the presence of three different anions, namely, chloride Cl-, tetrafluoroborate BF(4)(-), and bis((trifluoromethyl)sulfonyly)imide TF2N-. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF4] to [EMIM][TF2N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF2N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM][BF4] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.     

The performance of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid as mobile phase additive in HPLC‐based lipophilicity assessment

Ionic liquids have been widely used as green alternative mobile phase additives to shield the residuals silanols groups and modify the stationary/mobile phase HPLC systems. The present study aimed to evaluate the performance of the ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM][BF4]) in producing extrapolated logk_w indices suitable to substitute for octanol–water logP or logD values. The effect of [EMIM][BF4] was investigated for a set of basic and neutral drugs using two different columns, BDS and ABZ⁺. [EMIM][BF4] was added simply alone or in combination with n‐octanol and was compared with the conventional masking agent n‐decylamine. [EMIM][BF4] reduced the retention by suppressing silanophilic interactions, althoug to a lower extent than n‐decylamine. Addition of n‐octanol further decreased the retention by shielding silanol sites on BDS and/or interacting with polar groups through hydrogen bonding on ABZ⁺. Logk_w/logD_7.4 relationships proved moderate compared with those derived upon addition of n‐decylamine. They were considerably improved upon the introduction of protonated fraction F⁺ in the correlation, reflecting ion pair formation between the chaotropic anion [BF4]^‐ and the protonated basic compounds. In this aspect, the ionic liquid [EMIM][BF4], although efficient as a masking agent, cannot be recommended as mobile phase additive to reproduce octanol–water partitioning. Copyright © 2010 John Wiley & Sons, Ltd.     

Study on the Conductivities of Pure and Aqueous Bromide-Based Ionic Liquids at Different Temperatures

Electrical conductivities were measured for the pure ionic liquids [C₆mim][Br] (1-hexyl-3-methylimidazolium bromide) and [C₈mim][Br] (1-octyl-3-methylimidazolium bromide) at 0.1 MPa from 293.15 to 333.15 K. Conductivity measurements were also made for the binary water + [C₆mim][Br] and water + [C₈mim][Br] systems and their ternary water + [C₆mim][Br] + [C₈mim][Br] system at 0.1 MPa and 293.15, 298.15, and 303.15 K. The conductivity data of the pure ionic liquids were correlated by the VFT (Vogel-Tamman-Fulcher) equation, and the fitting parameters and mean absolute deviations were determined. New explanations are presented for the molality-dependent behavior of the conductivity of the binary water + [C₆mim][Br] and water + [C₈mim][Br] systems. The generalized Young’s rule and the semi-ideal solution theory for conductivity were used to predict the conductivities of the ternary water + [C₆mim][Br] + [C₈mim][Br] system from the conductivities of its corresponding binary water + [C₆mim][Br] and water + [C₈mim][Br] subsystems. The predictions are in good agreement with the measured values.     

The Electrochemical Surface Forces Apparatus: The Effect of Surface Roughness, Electrostatic Surface Potentials, and Anodic Oxide Growth on Interaction Forces, and Friction between Dissimilar Surfaces in Aqueous Solutions

We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with μN resolution), and distances (with ? resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force-distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with ?-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal-ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg-Healy-Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force-distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)(3) phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction forces while tuning electrochemical surface potentials.     

Supercrystal structures of polyhedral PbS nanocrystals

We analyzed the interaction between chemically grafted polysaccharide layers in aqueous solutions. To fabricate such layers, an end-terminated dextran silane coupling agent was synthesized and the polydextran was grafted to oxidized silicon wafers and to silica particles. This resulted in the formation of a 28 nm thick layer (in air) and a grafted amount of 40 mg/m(2) as determined by ellipsometry. The physical properties of the grafted layer were investigated in aqueous solutions by atomic force microscope imaging and colloidal probe force measurements. Surface and friction forces were measured between one bare and one polydextran coated silica surface. A notable feature was a bridging attraction due to affinity between dextran and the silica surface. Surface interactions and friction forces were also investigated between two surfaces coated with grafted polydextran. Repulsive forces were predominant, but nevertheless a high friction force was observed. The repulsive forces were enhanced by addition of sodium dodecyl sulfate (SDS) that associates with the tethered polydextran layers. SDS also decreased the friction force. Our data suggests that energy dissipation due to shear-induced structural changes within the grafted layer is of prime importance for the high friction forces observed, in particular deformation of protrusions in the surface layer.     

Assembly of a Novel Dumbbell‐type Dinuclear Copper(II) Complex: Synthesis,Structure and Properties

A new dumbbell‐type 4,4′‐bipy‐bridged dinuclear copper(II) complex, [Cu₂(4,4′‐bipy)L₂(H₂O)₂](ClO₄)₄ · 8CH₃OH · 10H₂O, where L = 1‐[bis(3‐aminopropyl)amino]‐2‐ propanol and bipy = bipyridine, has been synthesized and characterized, X‐ray crystallographic analysis shows that the [Cu₂(4,4′‐bipy)L₂(H₂O)₂]⁴⁺ cations and water molecules generate layer structures extending parallel to bc planes through hydrogen bonding interactions of O–H ··· O and C–H ··· O. The layers are also connected by hydrogen bonding interactions involving methanol, water, and perchlorate anions. These interactions lead to the formation of rectangular channels of 12.3 Å × 6.0 Å along the crystallographic c axis. Perchlorate anions fill in each channel in a sandwich‐like packing mode, they are joined with the adjacent layers by water heptamers. Magnetic susceptibility measurements show that the magnetic exchange interaction is weak although it has a regular π‐type electron transfer pathway. Furthermore, the electrochemical and thermogravimetric properties of the complex were also investigated.     

Glass transition behaviour of the quaternary ammonium type ionic liquid, {[DEME][I] + H2O} mixtures

By a simple DTA system, the glass transition temperatures of the quaternary ammonium type ionic liquid, {N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium iodide, [DEME][I] + H₂O} mixtures after quick pre-cooling were measured as a function of water concentration (x mol% H₂O). Results were compared with the previous results of {[DEME][BF₄] + H₂O} mixtures in which double glass transitions were observed in the water concentration region of (16.5 to 30.0) mol% H₂O. Remarkably, we observed the double glass transition phenomenon in {[DEME][I] + H₂O} mixtures too, but the two-T_gs regions lie towards the water-rich side of (77.5 to 85.0) mol% H₂O. These clearly reflect the difference in the anionic effect between ${\text{BF}}_4^{-}$ and I^? on the water structure. The end of the glass-formation region of {[DEME][I] + H₂O} mixtures is around x = 95.0 mol% H₂O, and this is comparable to that of {[DEME][BF₄] + H₂O} mixtures (x = 96.0 mol% H₂O).     

Spontaneous phase transfer of thermosensitive hairy particles between water and an ionic liquid

This article describes the temperature-induced phase transfer behavior of a series of thermosensitive polymer brush-grafted particles between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). Six samples were made by surface-initiated atom transfer radical polymerization: silica particles grafted with poly(methoxypoly(ethylene glycol) methacrylate) (PPEGMMA) with two different molecular weights, poly(methoxytri(ethylene glycol) methacrylate) (PTEGMMA), poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA), and two copolymers of PEGMMA and TEGMMA with different compositions (P(PEGMMA-co-TEGMMA)-82 and P(PEGMMA-co-TEGMMA)-74). The cloud points of free PPEGMMA with M(n,SEC) of 23 and 40 kDa, P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA in [EMIM][TFSI]-saturated water were 95, 94, 80, 72, and 43 °C, respectively. PDEGMMA was not soluble in the ionic liquid-saturated water. PPEGMMA brush-grafted particles moved spontaneously and completely from water to the [EMIM][TFSI] phase upon heating at 80 °C. When cooled to 22 °C, all particles returned to the water layer. From UV-vis absorbance measurements, the transfer temperature (T(tr)) of PPEGMMA-grafted particles from water to the ionic liquid was 42 °C. Thermodynamic analysis showed that the particle transfer was an entropically driven process. P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA brush-grafted particles also underwent reversible and quantitative transfer between the two phases upon heating at 70 °C and cooling at 0 °C; their transfer temperatures from water to [EMIM][TFSI] were 36, 30, and 16 °C, respectively. T(tr) was a linear function of the cloud point of the corresponding free polymer in ionic liquid-saturated water. In contrast, PDEGMMA-grafted particles moved spontaneously to the ionic liquid layer upon heating but did not return to water even after prolonged stirring at 0 °C.     

Ionothermal synthesis and characterization of two new heteropolytungstates with 1-ethyl-3-methylimidazolium bromide ionic liquid as solvent

In this article, we have synthesized two new heteropolytungstate-based compounds [EMIM]₄[SiW₁₂O₄₀] (1) and [EMIM]₆[P₂W₁₈O₆₂] · 4H₂O (2) using the ionic liquid (IL) [EMIM]Br (EMIM = 1-ethyl-3-methylimidazolium) as a solvent and characterized them by infrared (IR) and ultraviolet (UV) spectra, thermogravimetric (TG) and elemental analyses, electrochemistry, and single-crystal X-ray analyses. Compound 1 is constructed from one [SiW₁₂O₄₀]^4? and four [EMIM]⁺. In the structure, [SiW₁₂O₄₀]^4? and [EMIM]⁺ are connected by hydrogen bonds with the surface oxygens of the polyoxoanion to form a 3-D supramolecular framework. The heteropolyanion of 2 is a classical Dawson-type structure [P₂W₁₈O₆₂]^6? and connected with six cations through hydrogen bonds. The structures of these two heteropolyanions are consistent with those synthesized by traditional methods, indicating that ionothermal synthesis is an effective method for the preparation of heteropolyoxometalates. The photocatalytic properties of these compounds have also been investigated.     

1-乙基-3-甲基咪唑L-乳酸盐作为手性配体用于氨基酸的手性拆分

基于手性配体交换机理,研究了以手性离子液体1-乙基-3-甲基咪唑L-乳酸盐([EMIM][L-Lac])为手性配体拆分色氨酸对映体(Trys)、苯丙氨酸对映体(Phes)和酪氨酸对映体(Tyrs)的方法。实验考察了背景电解质和中心离子种类、手性配体与中心离子的浓度及比例、运行缓冲液pH等因素对Trys、Phes和Tyrs手性拆分的影响。研究发现,当运行缓冲液为40.0 mmol/L [EMIM][L-Lac]、20.0 mmol/L氯化铜(pH 4.5)时,3对对映体均能得到良好的手性拆分。为了验证[EMIM][L-Lac]的良好性能,实验进一步将L-乳酸(L-Lac)作为手性配体用于Trys的手性拆分。对比实验发现,单独使用L-乳酸,DL-Try只能得到部分拆分,加入离子液体1-乙基-3-甲基咪唑醋酸盐(EMIM-Ace)后,DL-Try分离情况得到了很大改善,但出峰时间延长至30 min以上。而使用[EMIM][L-Lac]时,Trys的出峰时间均在15 min以内。实验最后还对手性拆分机理做了进一步讨论。实验结果表明:在EMIM-Ace辅助L-Lac体系中,EMIM-Ace仅被用于抑制电渗流,并未参与手性配体交换反应;而在[EMIM][L-Lac]体系中,参与手性配体交换反应的主要是未解离的[EMIM][L-Lac],而不是解离后的L-乳酸根离子形成的L-乳酸。     

Revealing the influence of the strength of coulomb interactions on the viscosity and interfacial tension of ionic liquid cosolvent mixtures

Within this work, viscosity and interfacial tension of selected ionic liquid cosolvent mixtures, [EMIM][EtOSO3] (1-ethyl-3-methyl-immidazolium ethyl sulfate) with water and ethanol, were studied as a function of composition by surface light scattering (SLS) and the pendant drop method in a consistent manner, allowing a close insight into the nature of interactions. Here, we show that the viscosity behavior clearly reflects the bulk structure of the ionic liquid cosolvent mixtures and correlates to the fluid structure at the phase boundary. In contrast to former work, we found the viscosity of ionic liquid [EMIM][EtOSO3] to be decreasing the stronger by small amounts of the cosolvents and the lower their dielectric constant. Furthermore, two distinct trends for the dependence of the viscosity on the cosolvent concentration were resolved. These were assigned to ion-dipole interactions dominating in the salt-rich region and to dipole-dipole interactions in the diluted one. A crossover between both regions is reflected by the interfacial tension data, where it seems that up to a "critical" concentration almost no cosolvent is present at the phase boundary.     

Thermodynamic analysis for solubility of pimelic acid in ionic liquids

Based on the solubilities of pimelic acid in ionic liquids [EMIM][HSO₄], [PMIM]Br, [i-PMIM][HSO₄], [BMIM]Br, and [BMIM][HSO₄], dissolution enthalpy and dissolution entropy at different temperatures have been calculated. The experimental data of solubilities are correlated with the modified Apelblat equation. The thermodynamic properties of pimelic acid in ionic liquids were discussed. The solubilities correlated by the model are in good agreement with experimental data.     

Synthesis of coumarin derivatives in a microfluidic flow system employing the Pechmann condensation: A case study

For the synthesis of coumarin derivatives using the Pechmann condensation scheme, an acidic ionic liquid catalyst, abbreviated as [EBsImH][HSO ₄ ] , was prepared from the ring opening of 1,4-butanesultone by 1-ethylimidazole, followed by the addition of 1 equiv. H₂SO₄(c). The [EBsImH][HSO ₄ ] -catalyzed Pechmann condensation reactions proceeded smoothly in a batch setup, with recyclable [EBsImH][HSO ₄ ] showing great catalytic activity. The acidic ionic liquid catalyst [EBsImH][HSO ₄ ] was recovered from EtOAc/H₂O extraction of the product mixture, where the H₂O layer was worked up and dried for reuse in consecutive runs of the Pechmann condensation reactions, maintaining >85% conversion for four times. The catalytic reactions were also carried out in a microfluidic flow setup. The flow parameters, the reactant molar amounts, and the additional H₂SO₄ as a modifying acid catalyst were optimized in the current case study. A minimum conversion rate of 2.8 g/hr of coumarin derivatives was demonstrated.     

Thermodynamic study of interfacial tension between oil and aqueous phases composed of ionic liquids and brine

The first fundamental step in determining the physicochemical properties of an equilibrium system is to determine the activity coefficient of electrolyte and non-electrolyte ions. Based on understanding the importance of activity coefficient in thermodynamic systems in this study, in order to predict interfacial tension between oil and aqueous phases composed of ionic liquids and brine, a modified thermodynamic equation based on concentration and coefficient of activity of ionic liquids is defined. For this study, the Extended UNIQUAC model is desired and its adjustable parameters are optimized with Genetic + PSO algorithm. The modified model has practical features such as investigating the effect of concentrations of salts in the water of oil fields formation on the interfacial tension of the system, investigating the effect of concentrations of various organic compounds such as ionic liquids on the interfacial tension of the system and investigating the interaction energy between organic and inorganic ions. In this study, the optimization of the modified thermodynamic equation to predict the interfacial tension of solutions containing [C₈Py][Cl], [C₁₈Py][Cl], [C₁₂mim][Cl] and [C₁₈mim][Cl] with the presence of brine and distilled water is investigated. Also, the effect of ionic strength of the solution in 32 equilibrium systems on interfacial tension is investigated. According to the optimization results of this study, the design of a computer program can be considered to predict the interfacial tension with the presence of ionic liquids and salts.