Search

The electrochemical performance of the deposited PEDOT depends on the water content in the microemulsion (μE).

A Good's buffer ionic liquid (GB-IL) composed of quaternary ammonium cations and Good's buffer anions is first introduced into a microemulsion system as a self-buffering and biocompatible electrolyte. The effects of the constituting ions of a GB-IL and their concentrations on the phase behavior of the anionic surfactant SDBS stabilized n-octane–H2O microemulsion system were studied for the first time using the e–β fish-like phase diagram method. The result indicates that the phase behavior of the above microemulsion system is greatly affected by GB-IL cations with a longer alkyl chain on the cation being more favorable for phase inversion. Compared with NaCl, a GB-IL of the same concentration is more efficient for achieving phase inversion, due to the dual role of an electrolyte and a co-alcohol. In addition to the phase behavior, the stability of horseradish peroxidase (HRP) solubilized in an SDBS stabilized bicontinuous microemulsion is also affected by a GB-IL. It is found that the variation of the cationic alkyl chain has a negligible effect on the microemulsion microstructure, but has a significant influence on the stability of the solubilized HRP. At a fixed concentration of the GB-IL, the quaternary ammonium cation with a longer alkyl chain is better for the stabilization of the HRP activity. For a given GB-IL, a higher level of the GB-IL results in a better HRP stability. More importantly, the GB-IL-buffered microemulsion, at the same level of the buffering salt, is more advantageous than the phosphate-buffered one for the stabilization of the HRP activity. This advantage is more pronounced for higher concentrations of the GB-IL. This difference in the HRP stability, caused by the buffering salts, should be ascribed to the microemulsion microstructure effect as well as the Hofmeister effect. The present study provides a guideline for the construction of a bicontinuous microemulsion with a simplified composition and stabilizing effect on the solubilized enzyme.

In this work, the azobenzene group-containing carboxylic acid salt azobenzene-4,4′-dicarboxylate disodium salt (ADDS) was selected as the dopant for the controlled synthesis of nanostructured polypyrrole (PPy). By controlling the cis-trans configuration of ADDS (via ultraviolet light irradiation) as well as the concentration of divalent ADDS anion (via the medium pH alteration), a series of ADDS-doped PPy hydrogels with different morphologies and electrical properties were prepared accordingly. Under weak alkaline conditions (pH = 8.0), the morphology of the resulting PPy changes from nanofiber (nanobelt) to nanoflake and then to granular structure when the exposure time of ADDS aqueous solution to the UV-light irradiation was extended step by step from 0 to 15 min. This phenomenon is mainly due to the gradual decrease of the trans isomers in ADDS aqueous solution. Under visible light conditions, the morphology of the resulting PPy transforms from nanofiber (nanobelt) to granular structure when the pH of ADDS aqueous solution was varied from pH 8.0 to pH 3.0. This phenomenon is mainly due to the gradual decrease of the divalent doping anions (all trans isomers). Since trans ADDS isomers are co-planar linear molecules, and under weakly alkaline conditions, ADDS exists mainly in the form of divalent anion, the conductivity of PPy doped with all-trans ADDS (10.4 S cm-1) is therefore higher than that of PPy doped with UV-light irradiated ADDS (some trans isomers are transformed to the corresponding cis isomers) (1.0 S cm-1). It can be concluded that the morphologies and the electrical properties of ADDS-doped polypyrrole conducting hydrogels can be tuned just by varying the UV irradiation time and the medium pH, which results in the change of the steric configuration and the existing form of ADDS. The present new strategy is helpful for the controlled synthesis of conducting polymer hydrogels.

In this work, the fishlike phase diagram of the H2O/[Bmim][AOT]/[Bmim][PF6]/n-alcohol as a function of temperature (T) and the mass fraction of [Bmim][AOT] (with or without n-alcohol) in the total mixture (γ) has been observed for the first time at several mass ratios of [Bmim][PF6] to H2O (α) and with different n-alcohols. The larger area of the three-phase region occurs at α ≤ 0.500, and the resulting fish shapes are similar to each other. For a given α, a temperature scan (from lower to higher) at several γ values reveals that the present system forms an upper phase microemulsion first and then a lower phase microemulsion. The formation of hydrophobic ionic liquid-in-water (HIL/W) microemulsion at low temperature and water-in-hydrophobic ionic liquid (W/HIL) microemulsion at high temperature was confirmed by dynamic light scattering and small-angle X-ray scattering techniques. Here, the phase sequence that occurred during the temperature scan is opposite to that of a classic H2O/NaAOT/oil system. At th...

Novel proton-functionalized solid anilinium salts (anilinium hydrochloride ([HANI]Cl) and anilinium nitrate ([HANI]NO3)) are synthesized. Simply mixing proton-functionalized anilinium salt with glycol in appropriate ratios can get deep eutectic solvents (DESs) which are liquid at room temperature. DES system is a new type of ionic liquids (ILs) or IL analogs. Tests show that the resulting DES systems have higher conductivity and lower viscosity which are suitable for electropolymerization. The electropolymerization of aniline in novel liquid DES ([HANI]Cl/(CH2OH)2 and [HANI]NO3/(CH2OH)2) without exogenous protons is first reported. The cyclic voltammograms (CVs) in neat DES show two pairs of redox peaks. Unlike in acidic aqueous solutions, the electropolymerization of aniline in the DES needs no exogenous protons. UV–Vis and FTIR analysis show that the conductive polyaniline (PANI) is obtained. Moreover, the specific capacitance of PANI from the [HANI]Cl/(CH2OH)2 system is ca. 341 F g−1 and that from the [HANI]NO3/(CH2OH)2 is ca. 492 F g−1, which are superior to that of the PANI obtained in an acid medium. The SEM characterization indicates that the resulting PANI on ITO is cross-linked nanoporous polymer membrane, which is benefit for the capacitance performance of PANI.

Via heating first and then cooling, binary ionic liquid (IL) mixture of N-methyl-2-pyrrolidonium methylsulfonate ([HNMP][CH3SO3]) and 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) could form a liquid at room temperature. The glass-transition temperature (Tg) characterized by DSC depends on its composition with Tg being as low as −63 °C. The physicochemical properties of the binary IL mixtures also vary with the composition. With the increase of the mole fraction of [Bmim]Cl, the hydrogen-bond accepting ability (β) of the binary IL mixture increases, but the hydrogen-bond donating ability (α) deceases. In this binary IL mixture, fructose could be effectively converted into 5-hydroxymethylfurfural (HMF) at room temperature. The HMF yields at a given time are found to be well correlated with the physicochemical properties of the binary mixture, especially the α and β values. Under specified conditions, the present IL mixture as medium for fructose dehydration into HMF is comparable to the medium formed by ILs and alcohol, where the alcohols have negative effect on the HMF formation.

A new strategy is proposed here to formulate a bis(2-ethyl-1-hexyl)sulfosuccinate (AOT−) stabilized water-in-ionic liquid microemulsion without any additives. Replacing the inorganic counter ion Na+ by the organic 1-butyl-3-methylimidazolium ([Bmim]+) ion greatly improves the solubility of AOT− in hydrophobic 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim]Tf2N) (IL) and favors the formation of water-in-IL (W/IL) microdroplets. The existence of the W/IL microdroplets has been confirmed by dynamic light scattering, Fourier transform infrared absorption spectroscopy and ultraviolet–visible absorption spectroscopy. Also, presented for the first time are the effects of salts and alcohols on the microstructure and water solubilization capacity of the ternary H2O/[Bmim]AOT/[Bmim]Tf2N system. For inorganic salts, larger concentrations of the salt and higher charge density of the cation result in smaller microdroplet size and weak water solubilization capacity. For 1-hexanol, a high concentration of this alcohol results in small microdroplet size but high water solubilization capacity. Analyses indicate that the salts compress the electric double layers of W/IL microemulsions, decrease the size of the microdroplets and consequently reduce the water solubilization capacity; the alcohol, however, facilitates the aggregation of AOT−, increases the number of W/IL microdroplets, and therefore improves the water solubilization capacity of the system.

The e-β fishlike phase diagram of the system [C16mim]Br/[Omim]Tf2N/water was constructed in the presence of different additives (alcohol and inorganic salt). From the diagram some additive-dependent characteristic physicochemical parameters were obtained. Results show that with the increase of the alkyl chain length of alcohols, the solubility of the alcohol in [Omim]Tf2N, and the optimum solubilization parameter (SP*) decrease, while the maximum alcohol width (△e) for the phase inversion and the mass fraction of the alcohol in the balanced interfacial film (Ain) increase. For inorganic salts, an increase in [NaCl], or an increase of the radius of halides (X–) at constant [NaX], or the substitution of the divalent anion SO42– by the same molar concentration of monovalent anion Cl– makes both SP* and △e increase, but Ain decrease. Overall, the alcohol effect on the phase behavior of the microemulsion is greater than the salt effect, and the composition effect of an inorganic salt is greater than the concen...

In the present work, the sulfobetaine-type zwitterionic surfactant (SB-n) was tried for the first time to construct hydrophobic ionic liquid (HIL)-based bicontinuous microemulsions. The composition-dependent phase behavior of the HIL/water (buffer)/SB-n ternary microemulsion system was determined by the method of T-γ fishlike phase diagram. It is found that the phase inversion temperature increases markedly with the increase of the alkyl chain length (n) of SB-n, but the surfactant efficiency changes little. The HIL greatly affects the phase behavior, depending on the ion structure. It is found that the SB-12 stabilized [C8mim][PF6]-based microemulsion system has moderate phase inversion temperature, and moreover, its surfactant efficiency is the highest among the reported HIL-based bicontinuous microemulsions stabilized by conventional surfactants. The composition-dependent microstructure of the SB-12-stabilized [C8mim][PF6]-based bicontinuous microemulsion was characterized by SAXS technique, and its influence on the catalytic performance of solubilized lipase was also explored. With the increase of the mass ratio of the HIL to water (α), the correlation length (ξ) changes slightly, but the microdomain size (d) decreases steadily. Unlike α, with the increase of the surfactant concentration (γ), the d changes little, but the ξ increases markedly. This abnormal change of ξ with γ should be ascribed to the interface rigidity of the microemulsion. The catalytic efficiency of lipase depends on the rigidity of the interface and its interfacial area. The above original studies not only enrich HIL-based microemulsion systems, but also provide scientific support for lipase-based green synthesis and transformation.

The ionic liquid [HNMP]Cl-catalyzed dehydration of fructose into 5-hydroxymethylfurfural (HMF) in deep eutectic solvents (formed by [Emim]Cl and different alcohols) was investigated. The experimental results indicated that the polarity of an alcohol and its stereostructure were major factors influencing fructose dehydration and that isopropanol was the optimum alcohol for the conversion system. Studies on the mechanism of the alcohol effect indicated that an alcohol could influence the formation of intermediates and their further transformation via the hydrogen bonds formed with [Emim]Cl and [HNMP]Cl. For the normal alcohols, the shorter the chain, the higher is the polarity and the stronger the ability to form the hydrogen bond; as a result, the alcohol with the shortest chain has the greatest negative effect on fructose dehydration. For the branched chain alcohols, the existence of steric hindrance led to their weaker ability to form the hydrogen bond with the ionic liquid so that their negative effects...

Experimental and theoretical studies on the hydrolysis of esters catalyzed by different ionic liquids (ILs) have been made. It is found that the rate of the IL catalyzed hydrolysis of an ester depends not only on the structure of the ester but also on the structure of the ions. For the hydrolysis of p-NPB catalyzed by [Bmim]OAc, spectroscopy and kinetics studies complemented by DFT calculations indicate that the hydrogen bonding formed between the cation/anion of [Bmim]OAc and the reactants (both ester and water) is well correlated with the catalytic efficiency of the IL. The anion OAc− of the catalyst contributes more than its cation [Bmim]+ to the hydrolysis of p-NPB. A joined catalytic effect of [Bmim]+ and OAc− was observed especially in neat [Bmim]OAc. The new evidence provided by present studies helps to fully understand the activation mechanism of an IL toward the hydrolysis of an ester.

To formulate a compatible green medium for the conversion of a hydrophobic substrate by a hydrophilic enzyme, we investigated the phase behavior of pseudo ternary hydrophobic ionic liquid (HIL)/buffer/polyoxyethylene-type nonionic surfactant (CnEm)/n-alcohol system and the effects of the components on the formulation of the HIL-based bicontinuous microemulsion. It is found that small head group of the surfactant, high concentration of n-alcohol (medium/long alkyl chain) and low cohesive energy density of the HIL result in low phase transition temperature. In the CnEm stabilized compatible bicontinuous microemulsion, the kinetics of laccase catalyzed oxidation of 2,6-dimethoxyphenol were also investigated. It is found that in addition to temperature, n-alcohol is the key parameter affecting the catalytic performance of laccase, and the optimum n-alcohol depends on the type of HIL as an oil phase. All the kinetic parameters, such as Km, kcat, kcat/Km, and Ea (apparent activation energy), indicate that the bicontinuous microemulsion consisting of [Omim]NTf2/buffer/CnEm/n-hexanol is a suitable medium for the laccase-catalyzed reaction. To the best of our knowledge, this is the first report on the formulation of HIL-based bicontinuous microemulsion for enzyme catalysis.

A non-aqueous solution of tetra-n-butylammonium fluoride (TBAF) in ethylene glycol has been tried for the first time as a supporting electrolyte for the electropolymerization of 3-aminophenylboronic acid (APBA). Unlike the traditional acidic aqueous solution, the present medium needs no exogenous protons; moreover, the presence of CF3COOH is found to be unfavorable for the polymerization. The protons are in situ generated by the reaction between the boronic acid group on APBA and 1,2-dihydroxyl on ethylene glycol. So, ethylene glycol serves as not only the solvent but also the proton source. As a part of the supporting electrolyte, F(-) is found to be involved in the electrochemical synthesis of poly(3-aminophenylboronic acid) (PAPBA), but it is not indispensable. Studies on the electropolymerization process indicate that the size of the ions in the electrolyte affects the rate of the doping/dedoping process. The smaller the cation, the easier the doping/dedoping process, and the better the stability of the grown film. As demonstrated by Fourier transform infrared spectra, UV-vis spectra, and scanning electron microscopy, the obtained PAPBA is a cross-linked nanoporous polymer membrane that has a good adherence to the glassy carbon electrode.

This report describes a dehydration of fructose into 5-hydroxymethylfurfural (HMF) promoted by ionic liquids [Bmim]Cl and [HNMP][CH3SO3] in ethanol solvent. Two intermediates captured in time-dependent HPLC determinations are identified and structurally characterized by in situ 1H NMR and online ESI(+)-MS/MS. Studies on the influence of the ionic liquids (ILs) on the formation and transformation of the intermediates indicate that [HNMP][CH3SO3] promotes the formation of the intermediates, while [Bmim]Cl promotes their transformation. The contribution of the component ions of the ILs to the dehydration originates from their activation toward the leaving of OH on fructose or the intermediates via the formation of multiple hydrogen bonds. This kind of weak interaction appears only at low temperature. On the basis of the present study and the related literature, we propose a concerted mechanism for the binary IL-promoted conversion of fructose into HMF at room temperature.

The horseradish peroxidase (HRP) mediated synthesis of conducting polyaniline (PANI) was investigated in detail in the bicontinuous microemulsion stabilized by both sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and dodecyl sulfobetaine (SB-12). The addition of zwitterionic surfactant SB-12 not only reduces the phase inversion temperature of the anionic surfactant AOT stabilized microemulsion, but also enhances the catalytic performance of the solubilized HRP. Compared with the previously reported AOT/SDS stabilized bicontinuous microemulsion, the present AOT/SB-12 stabilized bicontinuous microemulsion is much more suitable for the expression of the catalytic activity of HRP; moreover, the conductivity of the resulting PANI improves greatly (a 15-fold increase in conductivity). The present results indicate further that the catalytic activity of HRP and its stability are crucial for the biosynthesis of PANI in bicontinuous microemulsions. To understand the underlying mechanism of the medium effects, electron spin resonance (ESR), UV–vis-NIR and small-angle X-ray scattering (SAXS) spectroscopies were used to investigate the effects of the oil-to-water ratio (α) and the surfactant concentration (γ) of the present bicontinuous microemulsion on the conductivity of resulting PANI. Results show that the bicontinuous microemulsion stabilized by both AOT and SB-12 still has a template role in the biosynthesis of PANI and the PANI conductivity is mainly determined by the microstructure of the template and by the microstructure-dependent activity and stability of the solubilized HRP. Lower α and γ values are beneficial to the enzymatic synthesis of high-quality PANI. The present study is of great help not only to deepen the understanding of the template role of anionic surfactant aggregates in the biosynthesis of conducting PANI, but also to develop new strategies for the biosynthesis of high quality PANI.

A bicontinuous microemulsion system consisting of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), sodium dodecylsulfate (SDS), an aqueous solution (a 0.1 M disodium hydrogenphosphate/citric acid buffer solution of pH = 4.3), and decane was investigated in detail for applications as reaction medium for the horseradish peroxidase (HRP)/hydrogen peroxide-mediated synthesis of the conductive form of polyaniline (PANI). To formulate the optimal single-phase microemulsion with the phase inversion temperature being close to room temperature, the T-γ fishlike phase diagram of the AOT/SDS-buffer-decane pseudoternary system was determined. The effects of the surfactant concentration (γ), the oil-to-water ratio (α) and the temperature (T) on the conductivity of the resulting PANI and the underlying mechanism were investigated using UV–vis-NIR, ESR and small-angle X-ray scattering (SAXS) techniques. Results show that the bicontinuous microemulsion plays a template role in the PANI biosynthesis, and the PANI conductivity also depends on the activity and stability of the solubilized HRP, which are determined by the microdomain size of the microemulsions and the reaction temperature. As far as γ is concerned, it is found that as γ increases, the microdomain size of the bicontinuous microemulsion as well as the activity of the solubilized HRP decreases significantly, leading to a great decrease of the PANI conductivity. Compared with γ, the change of α has small effect on the PANI conductivity. As the α-dependent microdomain size changes little with increasing α, the small change of the PANI conductivity should be ascribed mainly to the HRP activity. For T, over the range of 20 °C–35 °C, it has a slight effect on the microdomain size of the bicontinuous microemulsion, but it has a marked effect on the enzymatic properties of HRP. As the temperature increases, the activity of HRP increases, but its thermal stability decreases greatly. Therefore, the thermal stability of HRP is the major factor causing that the PANI conductivity decreases significantly with increasing T. The present work deepens the understanding of the template effect of anionic surfactant aggregates in the biosynthesis of conducting PANI. To the best of our knowledge, this work is the first study of the use of bicontinuous microemulsions as reaction media for the enzymatic synthesis of a conducting polymer.

In this work, a novel functionalized organic salt − anilinium saccharinate ([HANI][Sac]) was synthesized by the ion exchange method, and its composition and properties were characterized by 1H NMR, 13C NMR, ESI/MS and TG-DSC techniques. [HANI][Sac] can be used as both monomer and supporting electrolyte for efficient electrosynthesis of polyaniline (PANI) in acetonitrile. The obtained PANI has hierarchical porous structure and its doping degree with saccharinate anion ([Sac]-) is as high as 33.5%. The resulting [Sac]--doped-PANI (PANI-[Sac]) can be used as an electrochemically controlled drug delivery system. The in vitro release kinetics of [Sac]- under different potential stimuli conditions showed that, at a given time, the release rate of [Sac]- and its release percentage (ratio of the amount released to that loaded) increase with the negative shift of the applied potential. The amount of [Sac]- loaded and/or released can also be regulated by varying the charge for PANI electropolymerization. The present work provides a new strategy for the facile construction of conducting polymer-based electrochemically controlled drug release system.

The composition-dependent phase behavior of the [Cmmim][PF6]/buffer/[Cnmim][AOT]/n-butanol pseudoternary microemulsion system was investigated by the method of T-γ fishlike phase diagram. It is found that the phase inversion temperature and the surfactant efficiency decrease with the increase of the alkyl chain length (n) of the surfactant counterion and that (m) of the cation of the hydrophobic ionic liquid (HIL). The [C2mim][AOT]-stabilized [Omim][PF6]-based pseudoternary microemulsion system was found to have high surfactant efficiency and moderate phase inversion temperature. The microstructure of bicontinuous microemulsion formed in the pseudoternary system was characterized by SAXS technique, and the influence of microstructure on the catalytic performance of solubilized laccase was also explored. As the mass ratio of HIL to water increases, the microdomain size of the system decreases, and the catalytic efficiency (kcat/Km) of laccase also decreases. When the surfactant content gradually increases, the microdomain size of the system changes little, but its interfacial rigidity increases, and also the interaction between the interface and the solubilized enzyme increases accordingly, resulting in a decrease in the kcat/Km of the solubilized laccase. The variation of temperature over 35 °C–55 °C has little effect on the microdomain size of the system, but it has marked effect on the kcat/Km of the solubilized laccase. The optimal catalytic efficiency of laccase in the present microemulsion is estimated to be ca. 50 °C, which is significantly higher than that (40 °C) in the aqueous medium system, indicating that the bicontinuous microstructure in the system is helpful to improve the thermal stability of laccase. The present study is helpful for the rational formulation of laccase-compatible anionic surfactant-stabilized hydrophobic ionic liquid-based bicontinuous microemulsions, which is suitable for template-assisted biosynthesis of conducting polymers.

In the present study, the lipase-catalyzed hydrolysis of p-nitrophenyl butyrate is used as a model reaction to determine the activity and stability of Candida rugosa lipase in binary ionic liquids (ILs). The binary ILs consist of hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6) and a small amount of hydrophilic 1-butyl-3-methylimidazolium nitrate ([Bmim]NO3) or 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim]CF3SO3) or 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4). The activity and the stability of lipase are first correlated with the physicochemical properties of the binary ILs. In the three binary IL systems, both the hydrophilicity and the polarity of the systems increase with the increase of the content of hydrophilic ILs (HILs). At a fixed concentration of HIL, they vary in a descending order of [Bmim]PF6/[Bmim]NO3>[Bmim]PF6/[Bmim]CF3SO3>[Bmim]PF6/[Bmim]BF4. This order is in contrast with the order of the lipase conformation stability, i.e., the higher the polarity of ILs, the more unstable the lipase conformation. However, both the activity and the stability of lipase depend on the type and the content of the HIL in binary ILs, showing a complex dependency. Analysis shows that the catalytic performance of lipase in the binary ILs is affected not only by the direct influence of the ILs on lipase conformation, but also through their indirect influence on the physicochemical properties of water. The present study helps to explore binary IL mixtures suitable for lipase-based biocatalysis.

A novel proton functionalized room temperature ionic liquid–anilinium acetate ([HANI]Ac) with high ionic conductivity and low viscosity has been synthesized and used for the first time for aniline electropolymerization without any additives. The electropolymerization process reveals that the onset potential for anilinium oxidation (Eonset) in neat [HANI]Ac is +0.45 V vs. SCE, which is lower than those in aqueous and nonaqueous (ionic liquid as solvent/electrolyte) solutions. The control experiments and theoretical calculations indicate that the low Eonset in neat [HANI]Ac should be attributed to charge balancing counter-ion Ac−. Compared with [HANI]Ac/[BMIM]PF6 binary system, the mass transfer resistance of anilinium in neat [HANI]Ac is small, therefore the electropolymerization can be kept on at a high rate in a period. The cyclic voltammograms and Fourier transform infrared spectra demonstrate that the obtained PANI is highly conductive. The PANI has moderate solubility in [HANI]Ac and its adherence to the electrode is poor. During the electropolymerization, the accumulated PANI diffuses from the electrode/solution interface to the bulk phase which leads to different current signals of PANI under different conditions. Stirring slightly increases the oxidation current signal of anilinium but greatly reduces the redox current signal of PANI. Under quiescent conditions, lowering the upper switching potential reduces the redox current signal of PANI. The potential scan rate has great effect not only on the current signal of PANI but also on the redox peak shape. The electropolymerization process of [HANI]Ac in the presence of triethylamine further demonstrates that proton deficiency can result in a significant reduction of the rate of aniline polymerization.

A method is described for in-situ electrochemical preparation of nanoporous gold electrodes (np-GEs) via alloying and dealloying using ethylene glycol (EG) as a solvent. The np-GEs were prepared via cyclic voltammetry from a gold electrode in the presence of ZnCl2 in EG. Effects of temperature, number of scan cycles and scan rate were investigated. It is concluded that the process involves formation of interfacial elemental zinc and the formation of a gold-zinc alloy. At a temperature of 120 °C, the alloy is formed already after the first scan cycle, and ten further cycles do not cause substantial further changes in the morphology. Changes in the morphology were corroborated by data on the electroactivity of the np-GEs. The mechanism of the formation of np-GEs in EG obviously is different from that in other solvents due to the superior smoothing ability of EG for electroplating. This results in more uniform alloy layers and in a more evenly distributed porous structure. The self-supporting np-GE without any further modification displays an amperometric response to catechol (at a working voltage of 420 mV vs. SCE) in the 0.050 to 1.0 mM concentration range, with a detection limit of 1.78 μM (at an S/N of 3), indicating that the np-GE can be applied to convenient and effective determination of catechol.

The phase behavior of the pseudo ternary system 1-tetradecyl-3-methylimidazolium bromide ([C 14 mim]Br)/Triton X-100/H 2 O/1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF 6 ) has been studied at 35 °C. With the increase in the mole fraction of Triton X-100 in the mixed surfactants, the water solubilization capacity increases and the monophasic area enlarges. The H 2 O-in-[Bmim]PF 6 (W/IL) microemulsion was identified via electrical conductivity measurement. The existence of bulk water in the W/IL microemulsion was demonstrated based on the change of the O-D vibration frequency with content of D 2 O added and confirmed using UV–vis technique with CoCl 2 as probe. Laccase can be solubilized in the W/IL microemulsion and exhibits a catalytic activity. The interface of the W/IL microemulsion has an inhibitory effect on the expression of the laccase activity, and the inhibitory effect is varied with the molar ratio of the mixed surfactants.

The laccase-catalyzed polymerization of aniline in sodium dodecyl benzene sulfonate (SDBS) micellar solution was studied in the absence and presence of an ionic liquid tetramethylammonium trifluoromethanesulfonate ([TMA]TfO). It was found that [TMA]TfO was able to lessen the negative effect of SDBS on the laccase activity, especially at high levels, and prevent the association of anilinium cation and SDBS anion. It was also found that low level of [TMA]TfO is beneficial to the synthesis of conducting polyaniline (PANI) probably due to the extension of the lifetime of aniline cation radicals by [TMA]TfO. In the presence of [TMA]TfO, all the polymerization systems were visually clear, and a maximum yield of water-soluble conducting PANI could be obtained at low level of [TMA]TfO and near the critical micelle concentration of SDBS.

The influence of β-cyclodextrin (β-CD) on the laccase-catalyzed aniline polymerization in sodium bis-(2-ethylhexyl)sulfosuccinate (AOT) micellar solution is first presented. Results show that the anionic AOT micelle is compatible with laccase and β-CD also has little negative effect on the expression of the catalytic activity of laccase. β-CD can improve the linearity or conductivity of polyaniline biosynthesized in AOT micellar solution. Component analysis shows that AOT is doped in polyaniline chain while β-CD does not thread on the polyaniline chain. Mechanism analysis indicates that the improvement of the linearity of polyaniline by β-CD is due to steric hindrance close to the ortho-position of aniline, which favors the para-coupled aniline polymerization.

A novel cationic surfactant-based gelling system is presented in this report. The cationic surfactant 1-dodecylpyridinium bromide (DPB) in the mixture of acetone and water can form gels without additive. The gel structure and the gelation mechanism were studied using techniques of rheology, microscopy, FT-IR and 1H NMR spectroscopy. The present results indicate that the DPBs in acetone/water driven by hydrogen bonding, van der Waals force and other non-covalent interactions can self-assemble into rod-like fibers, and the fibers intertwined into a three-dimensional network. Laccase and horseradish peroxidase entrapped in the gel are biologically and/or electrochemically active. In addition, the present gel does not swell in the hydrophobic ionic liquid [Bmim]PF6, showing its great promise in green biocatalysis and biotransformation.

As media for an enzymatic reaction, ionic liquids (ILs) have many advantages over conventional molecular organic solvents, but some drawbacks still remain unsolved. In this review, we focus our attention on the various strategies that have been tried in recent years for improving the enzymatic performance in ILs. For clarity, this review is divided into several parts based on the hydrophilicity/hydrophobicity of ILs. For hydrophobic ILs, we put the emphasis on the construction of new macroscopically homogenous but microscopically heterogenous water-in-IL microemulsion systems and the catalytic performance of solubilized enzymes in them. For hydrophilic ILs, we highlight the enzyme performance related Hofmeister anions or cations series and the surface active effect of ILs.

The ternary system of dodecylpyridinium bromide (DDPB)/acetone/H2O with appropriate composition can form a gel spontaneously and the gel is stable in hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6). Based on the gelation phenomenon we observed, the low molecular weight gelator (LMWG) was first tried to immobilize horseradish peroxidase (HRP) on glassy carbon electrode (GCE). The scanning electron microscope (SEM) images, the UV-Vis spectra and the bioactivity measurement indicate that the gel is suitable for the immobilization of HRP. The direct electrochemistry of the HRP-gel modified GCE (HRP-gel/GCE) in [Bmim]PF6 shows a pair of well-defined and quasi-reversible redox peaks with the heterogeneous electron transfer rate constant (ks) being 14.4 s−1, indicating that the direct electron transfer between HRP and GCE is fast. The HRP-gel/GCE is stable and reproducible. Also the electrode exhibits good electrocatalytic effect on the reduction of trichloroacetic acid (TCA), showing good promise in bioelectrocatalysis.

Aspergillus niger ATCC20611 is one of the most potent filamentous fungi used commercially for production of fructooligosaccharides (FOS), which are prospective components of functional food by stimulating probiotic bacteria in the human gut. However, current strategies for improving FOS yield still rely on production process development. The genetic engineering approach hasn't been applied in industrial strains to increase FOS production level. Here, an optimized polyethylene glycol (PEG)-mediated protoplast transformation system was established in A. niger ATCC 20611 and used for further strain improvement. The pyrithiamine resistance gene (ptrA) was selected as a dominant marker and protoplasts were prepared with high concentration (up to 108g-1 wet weight mycelium) by using mixed cell wall-lysing enzymes. The transformation frequency with ptrA can reach 30-50 transformants per μg of DNA. In addition, the efficiency of co-transformation with the EGFP reporter gene (egfp) was high (approx. 82%). Furthermore, an activity-improved variant of β-fructofuranosidase, FopA(A178P), was successfully overexpressed in A. niger ATCC 20611 by using the transformation system. The transformant, CM6, exhibited a 58% increase in specific β-fructofuranosidase activity (up to 507U/g), compared to the parental strain (320U/g), and effectively reduced the time needed for completion of FOS synthesis. These results illustrate the feasibility of strain improvement through genetic engineering for further enhancement of FOS production level.

Horseradish peroxidase (HRP)/H2O2-triggered polymerization of aniline in sodium bis-(2-ethylhexyl)sulfosuccinate (AOT) micellar solution is first presented. Results show that the critical micelle concentration of AOT in the polymerization system is very low and AOT has small effect on the activity of HRP, so it matches with HRP well for the end. As a template, the AOT micellar solution is essential for the formation of conducting polyaniline. In the present system, AOT also acts as a dopant and a dispersant, leading to the formation of conducting and water soluble polyaniline. Optimization of the pH and the H2O2 concentration results in more conducting polyaniline. During investigation, it was found that HRP itself can induce the formation of chiral polyaniline without any other chiral inducer. In short, with the aid of AOT, one-step biosynthesis of chiral, conducting and water soluble polyaniline using HRP as both catalyst and chiral inducer is realized. Compared with other aniline polymerization systems reported elsewhere, the present system shows many advantages. It needs less templates and no foreign chiral inducer while the synthesized polyaniline has good dispersibility and high electrical conductivity.

BACKGROUND The immobilization of biomacromolecules on carbon nanotubes has attracted considerable attention. Based on the specific affinity between concanavalin A (Con A) and glycosyl, and the ability of alkyl polyglucoside to disperse single-walled carbon nanotubes (SWNTs), a new self-assembly immobilization strategy is developed. RESULTS Using laccase (Lac) and horseradish peroxidase (HRP) as models, it is demonstrated that this new self-assembly immobilization strategy has obvious advantages over the direct adsorption immobilization strategy in enzyme loadings ( 1.34-fold (Lac) and 1.46-fold (HRP) higher) and in the specific activity ( 5.06-fold (Lac) and 4.77-fold (HRP) higher). Circular dichroism (CD) spectra and fluorescence spectra also indicate that the present new indirect immobilization strategy has less impact on the enzyme conformation compared with the direct adsorption strategy. For the catalytic oxidation of dibenzothiophene (DBT), the immobilized HRP prepared using the present self-assembly strategy was more effective than that using the direct adsorption strategy. CONCLUSION Based on these findings, it is concluded that the present self-assembly strategy can greatly improve the enzymatic properties of the immobilized enzymes. © 2013 Society of Chemical Industry

On monolithic nanoporous silver (NPS), via DNA hybridization, we constructed an NPS/DNA-Cy5/silver nanoparticle (Ag NP) sandwich to investigate its SERS effect. In this sandwich, no chemical enhancement contributes to the SERS signal of Cy5. As compared with NPS, the present substrate exhibits particularly strong electromagnetic (EM) field enhancement. At the same Ag NPs surface loading, the SERS intensity decreases exponentially with increasing the length of double-stranded DNA (dsDNA). A larger pore size of NPS leads to weaker EM enhancement within the sandwich, but the relative intensity is not sensitive to the sizes and it is determined by the length of dsDNA.

A new carbon ionic liquid electrode (CILE) has been constructed using a low melting point (39 °C) hydrophobic ionic liquid (IL) 1-propyl-3-methylimidazolium hexafluorophosphate ([Pmim][PF6]) as the binder. Both cyclic voltammetry and electrochemical impedance spectroscopy demonstrate that, in addition to the composition optimization of the IL/graphite composite, heating the composite at a temperature a little higher than the melting point of [Pmim][PF6] can also lower the background current and enhance the mechanical strength of the CILE. The heated CILE is more sensitive than the traditional carbon paste electrode for the detection of H2O2. Glucose oxidase (GOx) can be easily entrapped in the bulk IL/graphite composite. Heating the GOx-modified CILE (GOx-CILE) at the melting point of [Pmim][PF6] does not lower the catalytic activity of GOx. As compared with n-octylpyridinium hexafluorophosphate (melting point 65 °C) as the binder, [Pmim][PF6]-based CILE is much better in signal-to-noise ratio. Under the optimum conditions, the [Pmim][PF6]-based GOx-CILE has a linear amperometric response to glucose over a concentration range of 2.0–26 mM with the detection limit as low as 0.39 mM. It follows that choosing an IL with a melting point of ca. 40 °C as a binder to fabricate enzyme-entrapped CILEs is a good strategy for the enhancement of the performance of the electrode.

In the water-in-[Bmim][PF(6)] microemulsion stabilized by both AOT and Triton X-100, the lipase-catalyzed hydrolysis of 4-nitrophenyl butyrate (p-NPB) was investigated to evaluate the catalytic efficiency of lipase in this novel microemulsion. The structural parameters of the microemulsion and the conditions of the enzymatic reaction affect the catalytic activity of lipase, especially the concentration of Tris-HCl buffer. Under optimum conditions, the catalytic activity of lipase in the present microemulsion is much higher than that in H(2)O saturated [Bmim][PF(6)]. When the partitioning of the substrate in the microemulsion is taken into account, the catalytic efficiency of lipase in this novel microemulsion is 14.3 times that in H(2)O saturated [Bmim][PF(6)] due to the significant decrease of the Michaelis constant in the microemulsion. Due to the large interface, high water activity, and probably the activating effect of the imidazolium cation in the water pool, the present microemulsion is demonstrated to be a promising medium for the lipase-catalyzed hydrolytic reaction. To demonstrate an important biocatalytic application in the IL-based microemulsion, the lipase-catalyzed synthesis of the flavoring agent benzyl acetate via transesterification of vinyl acetate with benzyl alcohol was also studied in the medium. Due to the high dispersion of lipase, large interface and removal of the byproduct, a maximum yield of 94% was obtained, indicating that the novel microemulsion is really important and useful.

We describe a facile electrochemical route for the synthesis of CuO flower-like microspheres (CuO FMs) by anodic dissolution of bulk Cu in sodium hydroxide solution at room temperature and without heating. Scanning electron microscopy and X-ray diffraction revealed that the CuO FMs are phase-pure monoclinic crystallites and comprised of CuO nanoflakes. The concentration of NaOH has a large effect on the size of the CuO FMs. The possible formation mechanism is discussed. The CuO FMs are electrocatalytically active towards the oxidation of H2O2, and this has resulted in a sensor for H2O2. To our knowledge, this is the simplest way to obtain clean CuO FMs.

Sensitive detection of molecules by using the surface-enhanced Raman scattering (SERS) technique depends on the nanostructured metallic substrate and many efforts have been devoted to the preparation of SERS substrates with high sensitivity, stability, and reproducibility. Herein, we report on the fabrication of stable monolithic nanoporous silver (NPS) by chemical dealloying of Ag-Al precursor alloys with an emphasis on the effect of structural evolution on SERS signals. It was found that the dealloying conditions had great influence on the morphology (the ligament/pore size) and the crystallization status, which determined the SERS signal of rhodamine 6G on the NPS. NPS with small pores, low residual Al, and perfect crystallization gave high SERS signals. A high enhancement factor of 7.5 x 10(5) was observed on bare NPS obtained by dealloying Ag(30)Al(70) in 2.5 wt% HCl at room temperature followed by 15 min aging at around 85 degrees C. After coating Ag nanoparticles on the NPS surface, the enhancement factor increased to 1.6 x 10(8) owing to strong near-field coupling between the ligaments and nanoparticles.

In this work, a facile electrochemical route i.e., anodic dissolution of bulk Cu at 2.0 V or more (vs. SCE) in a NaOH solution containing NH 2 OH·HCl, was introduced for the synthesis of clean Cu 2 O microcrystals (Cu 2 O MCs) with morphologies of octahedron, half circular plate, etc. The bulk Cu electrode can be facilely dispersed into Cu(OH) 4 2− in alkaline solutions with the help of intense O 2 releasing. In the presence of reductive NH 2 OH·HCl, Cu(II) was quickly reduced to Cu(I). Due to the concentration gradient of Cu(I) and OH − resulting from the electrochemical reaction and the selective adsorption of OH − on different crystal facets, half circular plate Cu 2 O MCs were for the first time, synthesized. By changing the NaOH concentration or applied potential, octahedron and rectangular plate Cu 2 O MCs could also be obtained. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) techniques, etc. were used to characterize the oxides. The Cu 2 O MCs were phase-pure cubic Cu 2 O. This electrochemical route is simple, basically green and can be used to synthesize Cu 2 O MCs with different morphologies.

Two aptamers that bind separately with exosite I or exosite II of thrombin were studied for better understanding of the binding effect of aptamers on thrombin. CD and intrinsic fluorescence spectra indicated that after binding with aptamers the secondary structure of thrombin seemed unchanged, but the whole conformation of thrombin changed. The binding of aptamers on thrombin also made the catalytic activity of thrombin toward the chromogenic substrate (β-Ala-Gly-Arg-p-nitroanilide diacetate) increased. The present study indicated that the allostery of the two exosites seemed to be independent.

An attempt was made in the present paper to develop a nanoporous gold (NPG)-based electrochemical aptasensor for thrombin detection. The substrate electrode NPG was in situ fabricated by a facile one-step square wave potential pulse (SWPP) treatment. The treatment involved repeated gold oxidation-reduction and intensive H(2) bubbles evolution. After 100min treatment, the active surface area of Au increased greatly (34 times). The electrochemical aptasensor was fabricated using a layer-by-layer assembling strategy. A "sandwich" structure was formed via thrombin connecting the aptamer-modified NPG and the aptamer-modified Au nanoparticles (AuNPs). The AuNPs was modified with two kinds of single strand DNA (ssDNA). One was aptamer of thrombin, but the other was not, reducing the cross-reaction between thrombin and its aptamer on the same AuNP. The electrochemical signal produced by the [Ru(NH(3))(6)](3+) bound to ssDNA via electrostatic interaction was measured by chronocoulometry. Due to the amplification effects of both NPG and AuNPs, this novel NPG-based aptasensor could detect thrombin quantitatively in the range of 0.01-22nM with a detection limit as low as 30fM. The present aptasensor also exhibited excellent selectivity, stability and reusability.

A 3-dimentional (3D) micro-nano hierarchical porous Cu film was fabricated by surface rebuilding of smooth Cu substrates in a blank solution of 1 M NaOH with square wave potential perturbation. The potential step from 0.4 to −2.5 V (vs. SCE) and a frequency of 50 Hz were chosen for the fabrication. The pore formation and Cu nanostructure evolution were characterized by scanning electron microscopy. The fabrication process involved fast Cu electrochemical oxidation–reduction and suitable rate of H2 releasing. During the repeated Cu oxidation–reduction, the Cu atoms were removable, forming dendrite-like structures. At the same time, the formed H2 bubbles acted as a dynamic template to shape the formation of micropores. The effect of H2 bubble as a template on the size of the formed micropores was demonstrated by adding a small amount of surfactant (cetyltrimethylammonium bromide, CTAB) into the basic solution to adjust the size of the bubbles. The as-prepared 3D porous Cu showed high electrocatalytic activity toward the reduction of NO3− and H2O2. The present in situ preparation method was green, convenient and required neither Cu(II) species and additives in solution nor post-treatment for template removal.

Yeast alcohol dehydrogenase (YADH) showed substantial decrease in its catalytic activity due to the strong electrostatic interaction between the head groups of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and YADH in AOT reverse micelles. However, the catalytic activity of YADH in a nonionic reverse micellar interface (GGDE/TX-100) obtained from a functional nonionic surfactant N-gluconyl glutamic acid didecyl ester (GGDE) and Triton X-100 (TX-100) was higher than that in AOT reverse micelle under the respective optimum conditions. A comparison of the kinetic parameters showed that the turnover number kcat in GGDE/TX-100 reverse micelle was 1.4 times as large as that in AOT reverse micelle, but the Michaelis constants in AOT reverse micelle for ethanol K mB was twice and for coenzyme NAD+ K mA was 5 times higher than their counterparts in GGDE/TX-100 reverse micelle. For the conversion of ethanol, the smaller K mB and larger kcat in GGDE/TX-100 reverse micelle resulted in higher catalytic efficiency kcat/K mB. The stability of YADH in GGDE/TX-100 reverse micelle was also found to be better than that in AOT reverse micelle. They were mainly attributed to the absence of electric charge on the head groups of GGDE and TX-100 in the GGDE/TX-100 reverse micelle.

Immobilization of enzymes on porous inorganic materials is very important for biocatalysis and biotransformation. In this paper, nanoporous gold (NPG) was used as a support for lignin peroxidase (LiP) immobilization. NPG with a pore size of 40-50 nm was prepared by dealloying Au/Ag alloy (50:50 wt%) for 17 h. By incubation with LiP aqueous solution, LiP was successfully immobilized on NPG. The optimal temperature of the immobilized LiP was ca. 40, 10 degrees C higher than that of free LiP. After 2h incubation at 45 degrees C, 55% of the initial activity of the immobilized LiP was still retained while the free LiP was completely deactivated. In addition, a high and sustainable LiP activity was achieved via in situ release of H(2)O(2) by a co-immobilized glucose oxidase. The present co-immobilization system was demonstrated to be very effective for LiP-mediated dye decolourization.

Nanoporous gold (NPG), prepared simply by dealloying Ag from Au/Ag alloy, was used in the present study as a carrier for laccase immobilization. Three immobilization strategies, i.e., physical adso...

The laccase-catalyzed conversion of bisphenol A (BPA) in aqueous solutions was studied in the absence and presence of nonionic surfactant Triton X-100. It was found that the addition of Triton X-100 into the reaction system increased the conversion of BPA, especially near the critical micelle concentration of Triton X-100. Also it was found that the stability of laccase was greatly improved in the presence of TritonX-100. Studies on the endogenous fluorescence emission of laccase indicated that there existed an interaction between Triton X-100 and laccase, which was beneficial to folding and stabilizating of laccase. The binding of Triton X-100 to the laccase surface also mitigated the inactivation effect caused by the free radicals and polymerization products. Under otherwise identical conditions, a lower dosage of laccase was needed for the higher conversion of BPA in the presence of Triton X-100.

For hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]), an H(2)O-in-[BMIM][PF(6)] microemulsion could be formed in the presence of nonionic surfactant Triton X-100 (TX-100). In such a medium, both lignin peroxidase (LiP) and laccase could express their catalytic activity with the optimum molar ratio of H(2)O to TX-100 at 8.0 for LiP and20 for laccase, and the optimum pH values at 3.2 for LiP and 4.2 for laccase, respectively. As compared with pure or water saturated [BMIM][PF(6)], in which the two oxidases had negligible catalytic activity due to the strong inactivating effect of [BMIM][PF(6)] on both enzymes, the use of the [BMIM][PF(6)]-based microemulsion had some advantages. Not only the catalytic activities of both fungal oxidases greatly enhanced, but also the apparent viscosity of the medium decreased.