Physicochemical investigation of cobalt–iron cyanide nanoparticles synthesized by a novel solid–solid reaction in confined space

Cobalt–iron cyanide (Co_x[Fe(CN)₆]) nanoparticles have been synthesized by a novel solid–solid reaction in the confined space of dry sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles dispersed in n-heptane. The reaction has been carried out by mixing two dry AOT/n-heptane solutions containing CoCl₂ and K₄Fe(CN)₆ or K₃Fe(CN)₆ nanoparticles in the micellar core, respectively. By UV-Vis spectroscopy it was ascertained that, after the mixing process, the formation of stable nanoparticles is fast and complete. Microcalorimetric measurements of the thermal effect due to the Co_x[Fe(CN)₆] nanoparticle formation allowed the determination of the stoichiometric ratio (x) and of the molar enthalpy of reaction in the core of AOT reversed micelles. The observed behavior suggests the occurrence of confinement effects and surfactant adsorption on the nanoparticle surface. Further structural information was achieved by small-angle X-ray scattering (SAXS) measurements. From all liquid samples, interesting salt/AOT composites were prepared by simple evaporation of the apolar solvent. Size, crystal structure, and electronic properties of Co_x[Fe(CN)₆] nanoparticles containing composites were obtained by wide-angle X-ray scattering (WAXS) and X-ray photoelectron spectroscopy (XPS).     

Kinetic Studies on of Veratryl the Lignin Peroxidase Catalyzed Oxidation Alcohol by H2O2 in AOT/Isooctane/ Toluene/Water Reverse Micelles

The steady state kinetics of the lignin peroxidase （LIP） catalyzed oxidation of veratryl alcohol （VA） by H2O2 in a sodium bis（2-ethylhexyl） sulfosuccinate （AOT）/isooctane/toluene/water reverse micellar medium was studied and a comparison with the corresponding aqueous medium was made to understand the effect of the reverse micellar medium on the catalytic mechanism and kinetic parameters. Results indicated that the model reaction in the AOT reverse micelle followed the ping-pong mechanism with true kcat, Km,VA and KmH2O2 being 59.6min^-1, 13.9 mmol· L^-1 and 94.8 μmol·L^-1, respectively; inhibition of high level of H2O2 on LiP followed the reversible competitive pattern with Ki being 0.140 mmol·L^-1. The reaction mechanism and inhibition pattern in the AOT reverse micellar medium were the same as those in bulk aqueous medium, but the kinetic parameters except KmH2O2 were greatly different in the two media. The kcat and Ki values in the reverse micelle were approximately 2 and 20 times smaller than the corresponding values in the aqueous solution, but the Michaelis constant of VA was approximately 100 times greater than that in the aqueous solution. The above mentioned differences in the kinetic parameters were caused by the microheterogeneity and the interface of the AOT reverse micelle, which resulted in the partitioning of VA and H2O2, and by the changes of the conformation of LiP and the reactivity of the substrates.     

Specific interactions in reversed micelles: Oxidation of Fe(bpy)32+ by S2O82− in AOT-oil-water microemulsions

The oxidation of Fe(bpy)₂²⁺ by peroxodisulphate (bpy = 2,2′-bipyridine) has been studied in a variety of sodium bis(2-ethylhexyl)sulfosuccinate(aerosol-OT or AOT)-oil-water microemulsions by changing the nature of the oil phase, the surfactant concentration, and the molar ratio w = [H₂O]/[AOT]. Kinetic results show that the influence of surfactant concentration is due to a dilution effect. On the other hand, the comparison between the reaction rate in conventional aqueous solution with that in AOT w/o microemulsions seems to indicate that the iron(II) species is distributed between the aqueous phase and the interphase. © 1995 John Wiley & Sons, Inc.     

Calorimetric investigation of reaction Ca(NO3)2 + Na3PO4 in water and microemulsions saturated with CO2

The reactions of Ca(NO₃)₂ + Na₃PO₄ in water and water/sodium bis(2‐ethylhexyl) sulfosuccinate (AOT)/hydrocarbon microemulsions saturated CO₂ with various molar ratios of water to surfactant R, oil phases, and surfactant concentrations were investigated by isothermal titration calorimetry. The product of the reaction was confirmed to be sodium‐and‐carbonate‐substituted hydroxyapatite (NaCO₃HAP) by Fourier transform infrared spectra (FTIR), energy dispersive spectrometry (EDS), and X‐ray diffraction (XRD). From calorimetric measurements, the molar enthalpies of solution of water in the AOT/n‐dodecane system, and the molar enthalpies, the rate constants, and the activation energies of the reactions were determined. It was found that the enthalpy of solution of water in AOT/n‐dodecane micells and the molar enthalpy of the reaction in the microemulsions increased with the decreases of R until R = 7; below that they kept almost constant. It may be attributed to the increase of the ratio of the bound water to the free water with the decrease of R until there was no free water when R < 7. However, the reaction rate constant k₁ was affected by the ionic strength of the medium and log k₁ showed a linear dependence on 1/R in the whole range of R we investigated. It was also observed that the rate constant and the enthalpy of the reaction remained almost unchanged when the surfactant concentration and the nature of oil phase varied. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 322–330, 2011     

Kinetics of the Oxidation of Phenylhydrazine by [Fe(CN)6]3− in Water‐in‐Oil Microemulsions

The oxidation reaction of phenyl hydrazine (Phh) by hexacyanoferrate ([Fe(CN)₆]^3?) has been studied in water‐in‐oil (w/o) microemulsion media. The kinetic profile of the reaction was investigated as a function of [Phh], droplet size, and droplet concentration. Comparison of the kinetic profiles of the reaction in microemulsion, water‐urea, and water‐AOT‐urea media indicates that the kinetic profile of the reaction in microemulsion shows a behavior similar to that of the reaction in water‐AOT‐urea medium at 4 M urea. An initial increase and then a decrease in k_obs is observed with increasing molar ratio, W_o(=[H₂O]/[AOT]) at constant [AOT] (=0.4 M), whereas k_obs decreases upon increasing the AOT concentration at constant molar ratio.     

Structural and catalytic aspects of cutinase in w/o microemulsions

 Structural and catalytic properties of cutinase were studied in bis(2-ethylhexyl) sodium sulfo-succinate (AOT)-isooctane microemulsion systems. The effect of the water content of the microemulsions on the cutinase activity on an esterification reaction of lauric acid with pentanol showed that cutinase followed a bell-shaped profile presenting a maximum at w _o=9, with w _o=[H₂O]/[AOT]. Kinetic studies allowed the determi-nation of the apparent parameters K _m and V _max. Electron paramagnetic resonance (EPR) spectroscopy studies of active site labeled cutinase in microemulsions with varying w _o values showed that in all microemulsions, the mobility of the label is higher than in the aqueous solution. Furthermore, it was found that the maximum of the enzyme activity did not correspond to a reduced active site mobility. Up to w _o=9 there was an increase of both activity and active site mobility. As the water content of the system became higher, the mobility of the bound spin label further increased whereas the enzymatic activity dropped considerably. Received: 20 December 1996 Accepted: 24 February 1997     

Effect of AOT on enzymatic activity of the organic solvent resistant tyrosinase from Streptomyces sp. REN-21 in aqueous solutions and water-in-oil microemulsions

The effect of AOT (sodium-bis(2-ethylhexyl sulfosuccinate)) on enzymatic activity of the organic solvent resistant tyrosinase (OSRT) in aqueous phosphate buffer solutions and in water-in-oil microemulsions of the water/AOT/isooctane system has been investigated. In contrast to mushroom tyrosinase, AOT does not activate OSRT in aqueous solutions, altering its activity very little at concentrations lower than 2 mM. Increasing contents of AOT in isooctane reduce the observed initial reaction rates of oxidation of t-butylcatechol (tBC) and 4-methylcatechol (4-MC). Similarly to mushroom tyrosinase, the effect has been described using an equation based on preferential binding of the substrates by surfactant interface layers. The apparent Michaelis-Menten substrate binding constants increase linearly with AOT concentration (with slopes of 0.12+/-0.02 and 0.051+/-0.006 for tBC and 4-MC, respectively), and the effective enzyme turnover number in the microemulsions remains practically constant.     

Study of the alkaline fading of phenolphthalein in microemulsions

The reactions of the alkaline fading of phenolphthalein (PN) have been studied in water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane microemulsions by monitoring the absorbance changes of PN in the system with the time and the results compared with those found for the same reactions in aqueous solutions. It was found that the values of the equilibrium constants and the forward reaction rate constants in the microemulsions were significantly larger than that in aqueous solutions and decreased with increasing the molar ratio of water to AOT (ω), except for that with low ω. The temperature dependence of the reaction rate constant was analyzed to obtain the values of free energy, enthalpy, and entropy of activation, which suggests the existence of an isokinetic relationship and a common mechanism for the reactions occurring in the microemulsions with different ω. It was also observed that the competition between the reactions of the alkaline fading of PN and the hydrolyzation of AOT in water/AOT/isooctane microemulsions when the reaction time was sufficiently long.     

AOT/Triton X-100混合反胶束体系的导电性能

采用聚乙二醇辛基苯基醚(TritonX-100)和二(2-乙基己基)琥珀酸磺酸钠(AOT)双表面活性剂,与正己烷、正己醇和水构成混合反胶束体系;研究了表面活性剂质量比、助表面活性剂含量、水油体积比和温度等因素对反胶束体系导电性能的影响,同时采用循环伏安法研究了K3Fe(CN)6/K4Fe(CN)6在该体系中的电化学行为.结果表明:由两种表面活性剂构成的反胶束体系电导率σ明显大于单一表面活性剂反胶束体系电导率;体系电导率随AOT与TritonX-100的质量比w(w=mAOT∶mTritonX-100)的变化而变化,w为0-0.4时,电导率随w增大而线性增大,之后增加趋势变缓;w=0.96时,σ达到稳定值576μS·cm-1.混合体系电导率随溶水量的增大及温度的上升而提高;而增加助表面活性剂可显著降低体系的电导率.在所研究体系中,Fe(CN)36-/Fe(CN)46-电化学反应对的氧化还原峰电位几乎不随扫描速率变化,峰电位差约为75mV,峰电流的比值约为1,氧化峰电流与扫描速率的平方根成正比,说明K3Fe(CN)6/K4Fe(CN)6在混合反胶束体系中显示出良好的氧化还原可逆性,反应由扩散步骤控制.     

Chemical and Electrochemical Syntheses of Benzo[b](1,4)‐diazepine‐7,8‐diones

Electrochemical and chemical syntheses of benzodiazepinediones were carried out from the reaction of catechols with N,N′‐dialkylproylenediamine in aqueous solution at room temperature, using CV and controlled‐potential coulometry with K₃Fe(CN)₆ as an oxidant.     

Mechanisms involved in chemical vapor generation by aqueous tetrahydroborate(III) derivatization : Role of hexacyanoferrate(III) in plumbane generation

The role played by K₃Fe(CN)₆ (0.08 or 1.5 g l^− 1) in producing strong enhancement factors in the generation efficiency of plumbane in the reaction of NaBH₄ (10 or 40 g l^− 1) with Pb(II) (50 μg l^− 1) in 0.1 M HCl solution, was investigated by using continuous flow chemical vapor generation coupled with atomic fluorescence spectrometry (CF-CVG-AFS). Different mixing sequences and reaction times of reagents were tested using different chemifold setups. Part of CF-CVG-AFS experiments were performed using the on-line, delayed addition of Pb(II) to a K₃Fe(CN)₆ + NaBH₄ reaction mixture. Kinetic calculations estimating the concentration of K₃Fe(CN)₆ remaining in the K₃Fe(CN)₆ + NaBH₄ reaction mixture before it merged with Pb(II) solution were also performed. Batch experiments measuring the amount of hydrogen evolved (pressure of H₂ vs time) and pH variation during K₃Fe(CN)₆ + NaBH₄ + HCl reaction were performed in order to have a correct estimation of the concentration of K₃Fe(CN)₆ remaining in the reaction system. The comparison of CF-CVG-AFS experiments with kinetic calculations indicates that strong enhancement factors of plumbane generation can be obtained without any interaction of K₃Fe(CN)₆ with Pb(II). The key role of K₃Fe(CN)₆ is recognized in its reaction with NaBH₄ to give “special” borane complex intermediates, which are highly effective in the generation of plumbane from Pb(II).     

Investigation on the basic hydrolysis of crystal violet in mixed reverse micelles formed with AOT and nonionic surfactants

 The kinetics and thermodynamics of the basic hydrolysis of crystal violet (CV) in mixed reverse micelles formed with anionic surfactant AOT and nonionic surfactants have been investigated. It was found that the mixed reverse micelles had inhibitory effects on CV hydrolysis compared with the normal aqueous solution, and the equilibrium constant K of the reaction in mixed reverse micellar systems is smaller than that in pure water. The influence of water content and surfactant composition in reverse micelles on the second-order rate constant k ₁ of the positive reaction, on the first-order rate constant k _-1 of the reverse reaction, as well as on the equilibrium constant K of the reaction has been studied, and the results obtained were interpreted in terms of the nature of surfactants and the properties of microenvironment where the reaction took place. Received: 24 October 1997 Accepted: 18 March 1998     

Kerr Effect in Systems Containing TiO2 Nanoparticles

Abstract

Kerr effect measurements as a function of the relation [water]/[alkoxide] concentration (h) were performed. These systems were prepared from water/AOT/isooctane microemulsions by adding titanium (IV) butoxide. From a certain h value it was observed that Kerr constant values change abruptly. This behaviour is indicative of the beginning of the sol -gel transition. The influence of the overall alkoxide concentration is discussed.     

Determination of Riboflavin Using Flow Injection Inhibitory Chemiluminescence

ABSTRACT

A new flow injection method for the determination of riboflavin based on the inhibition of the intensity of chemiluminescence (CL) from the luminol-K₃Fe(CN)₆ system is described. While riboflavin mixed with K₃Fe(CN)₆, by the fast oxidation reaction between riboflavin and K₃Fe(CN)₆, K₄Fe(CN)₆ was generated, which then inhibited the CL reaction of K₃Fe(CN)₆ and luminol in alkaline aqueous solution. The CL emission was correlated with the riboflavin concentration in the range from 0.032 to 100 μg·ml?¹, and the detection limit was 0.01 μg·ml?¹ (3σ). A complete analysis could be performed in 2 min with a relative standard deviation of less than 2.2%. The influence of foreign species was studied and the method has been applied successfully to the determination of riboflavin in pharmaceutical samples, the recovery was from 98.0% to 102%.     

Electron transport membrane: Preparation of polypeptide membrane with spacers between the polymer matrix and viologen moiety and their application to an electron transfer reaction

Polypeptide membranes with several lengths of spacers [? (CH₂)_n? ; n = 3, 6, 12] between the polymer matrix and viologen moiety as a functional group were prepared. Reduction of K₃Fe(CN)₆ with Na₂S₂O₄ across the obtained membrane in aqueous media were carried out and reduction rate of K₃Fe(CN)₆ across the membrane of n = 6 was faster than that of n = 3. However, the reduction of the membrane (n = 12) did not proceed chemically and electrochemically at all.     

Preparation of57Fe enriched K4[Fe(CN)6] and K3[Fe(CN)6]

A simple method to prepare⁵⁷Fe enriched K₄[Fe(CN)₆] and K₃[Fe(CN)₆] is described. The yields of the products are much better than those reported in the literature so far. The enrichment is essential for⁵⁷Fe Mössbauer investigation in a variety of Prussiate type complexes and other inorganic compounds which are conveniently prepared from K₄[Fe(CN)₆] and K₃[Fe(CN)₆]. K₄[Fe(CN)₆] was obtained by reacting freshly prepared Fe(OH)₃ with glacial acetic acid and treating with iron acetate in boiling aqueous solution of KCN. The novel feature of the procedure to obtain K₃[Fe(CN)₆] is that the oxidation of K₄[Fe(CN)₆] has been carried out in the solid state by passing chlorine gas over the powdered specimen. K₃[Fe(CN)₆] was crystallised from alkaline solution of this oxidised powder. The compounds were characterised by Mössbauer spectroscopy.     

A new method for preparation of silica potassium cobalt hexacyanoferrate composite ion exchanger from silica sol

A new method for the preparation of porous silicapotassium cobalt hexacyanoferrate (SiO₂ ^.KCoFC) composite from silica sol is described. Silica sol was first gelled with K₄Fe(CN)₆ solution. Then the resulting hydrogel, SiO₂ ^.K₄Fe(CN)₆ was reacted with Co(NO₃)₂ solution in acetone to give the composite SiO₂ ^.KCoFC hydrogel. The empirical formula of KCoFC in the composite was found to be K₁.₆₉Co _0.93Fe(CN)₆. The removal efficiency of the composite for Cs was judged by measuring its distribution coefficient, K _d in 1M HCl solution containing 10 ppm Cs. The K _d of Cs was found to be 5.73^.10⁵ ml/g-composite.     

Laccase behavior in the microenvironment of water core within a biosurfactant‐based reversed micelles system rhamnolipid/n‐hexanol/isooctane/water

Compared with synthetic surfactants (cetyltrimethyl ammonium bromide, sodium bis(2‐ethylhexyl) sulfosuccinate and Tween‐80), the properties of the aqueous core as well as the microenvironment behavior were investigated in water‐in‐oil microemulsions, which are formed by water and biosurfactant rhamnolipid (RL) in the solvent of isooctane/n‐hexanol (1:1, v/v). Besides, as a typical substrate of lignocellulose, guaiacol was used to detect the laccase activity in reversed micelles (RMs). The results were eventually confirmed that RL‐based RM system has higher solubilization ability, more friendly environmental compatibility and milder reaction microenvironment than the others. In this study, triangle phase diagram of surfactant/n‐hexanol/isooctane/water was constructed to analyze the variation of phase behavior between each RM system. For the RL‐based RM system, the effect of the molar ratio of water to surfactant (ω₀) on enzyme hydrolytic activity was also determined to be shown as a bell‐shaped curve and presented a maximum at ω₀ = 19; the O―H stretching vibrations of water in aqueous core was also studied by analyzing the IR spectrum over the region of 3050–3750 cm ^{? 1}. Moreover, kinetic studies showed that the catalytic efficiency of the laccase in RL‐based RM system was lower than in aqueous solution. Nevertheless, the RM system obtained the highest hydrolysis rate at RL concentration of 1.0CMC, which is 0.055 mM. Copyright © 2015 John Wiley & Sons, Ltd.     

Droplet Exchange Kinetics in Microemulsions

The dynamic behavior of water-in-oil microemulsions (w/o), stabilized by sodium bis (2-ethyl-hexyl) sulphosuccinate (AOT), has been studied by means of stop flow method using spectroscopic detection. Kinetic model based on the ferroferric reaction was developed. Interdroplet exchange rate constant, k _ex , associated with the exchange of materials upon collisions between droplets in w/o microemulsions system has been determined. k _ex increases with increase in the chain length of linear alkanes and decreases with the water to surfactant molar concentration ratio (w ₀ = [H ₂ O]/[AOT]) and decreases in presence of viscosity modifier.     

Spectrometric study of AOT-hydrolysis reaction in water/AOT/isooctane microemulsions using phenolphthalein as a chemical probe

The kinetics of the alkaline hydrolysis of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in water/AOT/isooctane microemulsions has been studied by monitoring the absorbance change of the phenolphthalein in the system with time. The apparent first-order rate constant k(obs) has been obtained and found to be dependent on both the molar ratio of water to AOT ω and the temperature. The dependences of k(obs) on ω have been analyzed by a pseudophase model which gives the true rate constants k(i) of the AOT-hydrolysis reaction on the interface and the partition coefficients K(wi) for the distribution of OH(-) between aqueous and interface pseudophases at various temperatures; the latter is almost independent of the temperature and ω. The temperature dependences of the reaction rate constants k(obs) and k(i) have been analyzed to obtain enthalpy ΔH(≠), entropy ΔS(≠), and energy E(a) of activation, which indicate that the distribution of OH(-) between aqueous and interface pseudophases increases ΔS(≠) but makes no contribution to E(a) and ΔH(≠). The influence of the overall concentration of AOT in the system on the rate constant has been examined and found to be negligible. It contradicts with what was reported by García-Río et al. (1) but confirms that the first-order reaction of the AOT-hydrolysis takes place on the surfactant interface. The study of the influence of AOT-hydrolysis on the kinetics of the alkaline fading of crystal violet or phenolphthalein in the water/AOT/isooctane microemulsions suggests that corrections for the AOT-hydrolysis in these reactions are required.