Determination of the Water/AOT/Isooctane Reverse Micelles Size Parameters from Their Refractive Index Data

The present paper aims to study the proprieties of water confined in water/AOT/isooctane reverse micelles from their refractive indices at 298.5 K. The refractive indices of the microemulsions were investigated at increasing water concentration and at different micellar volume fractions, Φ _d. The refractive index of micellar water was deduced for a large water to AOT molar ratio, W ₀. The refractive index of interfacial water was also calculated. Then, the molar faction of interfacial water, α, was deduced for different W ₀ values and compared with those measured by NMR as reported in the literature. The results show qualitative agreement. Finally, the average aggregation number, n _agg, the area per surfactant headgroup, σ, as well as the interfacial thickness, d _i, of the reverse micelles were determined for the W ₀ values studied. The values of these structural parameters also show good qualitative agreement with NMR and small angle X-ray scattering data reported in the literature. Thus, the refractive index method can be a cheap and fast alternative for these two methods.     

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.     

Aggregation Behaviors of Tricarbocyanine Dye in Water and in AOT Reverse Micelles

The photophysical property of the tricarbocyanine dye IR144 has been extensively studied in non‐aqueous solvents. However, as a potential near‐infrared biomedical imaging probe, the photophysical property of IR144 in water is still little known. So, the aggregation behaviors of IR144 in water with steady‐state absorption spectroscopy and integrated polarization dependent femtosecond pump‐probe spectroscopy were investigated. Through comparing the absorption spectral bandshape of IR144 in water and in water pool of AOT reverse micelles, It is found that IR144 form dimer aggregates in water even at very low concentration (<1.0×10^?7 mol·L^?1). And the absorption spectrum of the IR144 aggregates always displays a bimodal feature, which is independent of the dye concentration ranging from 1.0×10^?7 to 1.0×10^?4 mol·L^?1. For better understanding the aggregation behaviors of IR144 in water, we measured the ground state recovery kinetics and the reorientation kinetics of IR144 in water and in water pool of AOT reverse micelles (W₀=[H₂O]/[AOT], W₀=40). It is found that the fluorescence quantum yield of IR144 in water is lower than that in water pool of AOT reverse micelles, and the reorientation time of IR144 in water is slower than that in water pool of AOT reverse micelles. Those kinetic measurements also verify that IR144 exists as dimer aggregates in water.     

Effects of Alkylamines on the Percolation Phenomena in Water/AOT/Isooctane Microemulsions

We carried out an investigation on the influence of several alkylamines, frequently present in reactions carried out in microemulsions, on the properties of the water/AOT/isooctane system. The presence of alkylamines has an important effect on the electrical percolation phenomena. This effect of amines on the electrical percolation of microemulsions of AOT/isooctane/water can be explained by taking into account the ability of these substrates to associate with the AOT film in the microemulsion, the basicity of the amine, and the different solubility of the amine in the three pseudophases of the system. Copyright 2000 Academic Press.     

Analysis of the Amino Acids of Soy Globulins by AOT Reverse Micelles and Aqueous Buffer

The 7S and 11S globulins from soybean proteins using reverse micelle and aqueous buffer extraction methods were characterized by using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and scanning electron microscope (SEM), and their amino acid compositions were also evaluated. SDS-PAGE did not show electrophoretic differences between 7S and 11S globulin subunits with two extraction methods. SEM analysis showed that the AOT reverse micelle processing of 7S and 11S globulins induced a reduction of droplet size. Some individual amino acid contents of 7S and 11S globulins using two extraction methods were different, some were similar. In all the samples, the glutamic acid, aspartic acid, and leucine were the dominant amino acids while the cystine and methionine were the first-limiting amino acids. The proportion of essential amino acids to the total amino acids (E/T) of the 7S globulin from aqueous buffer and reverse micelles was similar. While significant differences were obtained in the proportion of E/T of the 11S globulin.     

The Dynamics and Energetics of Percolation of Water/AOT/Isooctane Microemulsions upon the Addition of Tween Nonionic Surfactants

The temperature‐induced percolation of water/AOT/isooctane microemulsions was studied in the presence of the Tween series of polyoxyethylated nonionic surfactants employing conductometry. Percolation temperatures were determined utilizing the Sigmoidal‐Boltzmann equation procedure. The results were analyzed in terms of the percolation temperature, scaling parameters, activation energy, and thermodynamics of the clustering process. It was observed that the Tween series of surfactants aided the percolation process, and the percolation parameters were found to be independent of the hydrophobic chain length of these additives. The percolation temperature was found to be dependent on the concentration of the Tweens. It was concluded that the influence of the Tween series of surfactants on the percolation phenomenon was due to the number of ethylene oxide moieties in the head groups region of the additive. The effects of these additives was described in terms of modifications in the microemulsion's interfacial layer, outer oil layer, viscosity of the water micropool, and interactions between the anionic head groups of AOT.     

Immunoassay for the Determination of 7-Hydroxycoumarin in Serum Using 'Real-Time' Biosensor Analysis

ABSTRACT

An inhibition immunoassay for the determination of total 7-hydroxycoumarin (7-OHC) in human serum samples using the BIACORE biosensor is described. 7-OHC-BSA was immobilised onto BIACORE sensor chips and 7-OHC was premixed with a polyclonal anti-7-OHC antibody and injected over this surface. Excess antibody bound to the immobilised conjugate, generating a binding response that was inversely proportional to the amount of 7-OHC in the sample. The sample buffer was formulated to minimise non-specific binding of serum components to the sensor surface. Regeneration of the sensor surface was optimised such that the conjugate-coated surface retained acceptable antibody-binding capacity over 64 binding-regeneration cycles. The recovery of free drug from samples spiked with 7-hydroxycoumarin-glucuronide (7-OHCG) approximated 100%, while the inter- and intra-day coefficients of variation for the assay were less than 8.76% for 5 replicates. The assay had a measuring range of 0.5 – 80 μg/ml. This BIACORE-based immunoassay for 7-OHC could be performed using crude samples and both the reproducibility and sensitivity compared well to established methods of analysis.     

Determination of AOT by Adsorptive Stripping Tensammetry in Connection to the Biopolimers Extractin by Reversed Micelles

Abstract

Bis(2ethylexyl) sodium sulfosuccinate (AOT) can be determined using Adsorptive Stripping Differential Pulse Tensammetry (ASDP) in concentration range 5 10^?7 ? 5 10^?6 M. Higher concentrations can be determined by direct Differential Pulse Polarography.

The method is fit for determining AOT in reversed micelles and in water, a problem that is closely bound to the use of water-in-oil microemulsions for the selective extraction of biopolimers and their recovery in biotechnology.     

Investigations of Water Morphology in Reverse Micelles: Mesoscopic Simulation and IR Spectral Analysis

Abstract

A simple model, i.e., sodium bis(2‐ethylhexyl) sulfosuccinate [Aerosol OT (AOT)] represented by one‐head and two‐tail beads tied together by a harmonic spring and water or isooctane by one bead, was put forward via dissipative particle dynamics (DPD) simulation method. According to the experimental AOT/water/isooctane system, the aggregates of simulated reverse micelle can be obtained in the three‐dimensional cell. Three types of water morphology, such as bound water, trapped water, and bulky water, were distinguished using the water isodensity slice in DPD simulation. The IR spectra experiment also showed three types of water in the same system. One conclusion is that DPD simulation can be considered as an adjunct to experiments and provide other valuable information for the experiment.     

Application of a Multiple Linear Regression Model to Fixed Bands IR Detector Data in GPC-IR Analysis of Polyolefins

Summary: An infrared detector based on a set of narrow band optical filters was coupled to a high temperature Gel Permeation Chromatograph (GPC) producing continuous chromatograms of absorbance after the molar mass fractionation. A multiple linear regression (MLR) model was established to relate the measured absorbance to the average octene weight percent in industrial ethylene-octene copolymer samples. This method is compared to univariate and multivariate band ratio models. The application of these models to produce molar mass compositional distributions is also outlined.     

Spectrophotometric Determination of Dissociation Constants of Thiovioluric Acid and the Stability Constant of its Fe(II) Complex

Spectrophotometric studies of Fe(II)-thiovioluric acid system indicates the presence of a 1:2 complex in the pH range 4.0–6.5. The apparent equilibrium constant (K′₁) has been determined by general absorbance-extinction concentration scheme. The first and second dissociation constants of the acid have been studied at an ionic strength of 0.1 M while the third dissociation constant has been determined at I = 1 M. The effects of sudden pH change and buffer compositions on the dissociations have also been investigated. The stability constant of the complex has been calculated from the apparent equilibrium constant at ionic strength of 0.1 M. The stability constant works out to be 15.67 at pH 5.5.     

Dissociation Constant of Acetic Acid in (N,N-Dimethylformamide + Water) Mixtures at the Temperature 298.15 K

In the present work the thermodynamic dissociation constants of acetic acid were determined in (N,N-dimethylformamide (DMF) + water) mixtures over the DMF mole fraction range from 0 to 0.65 at the temperature 298.15 K by the potentiometric titration method. The dissociation constant in pure DMF was obtained by extrapolation and comparative calculation methods. The dependence of the acetic acid dissociation constant on the mixed solvent composition was fitted with linear multiple regression of the solvatochromic parameters of (DMF + water) mixtures at every studied composition.     

多波长线性回归导数分光光度法同时测定饮料中糖精钠和苯甲酸

测定了同时测定两组分的多波多线性回归导数分光光度法,无需进行化学分离。方法用于模拟样品和饮料样品中糖精钠和苯甲酸的同时测定,回收率为９８％￣１０１％,相对标准偏差〈３．０％。     

AOT/异辛烷/水微乳液中结晶紫与AOT相互作用的热力学研究

用紫外-可见分光光度法在不同温度下测定了结晶紫(CV)在双-2-乙基己基硫代琥珀酸钠(气溶胶OT或AOT)为表面活性剂的W/O微乳液中的吸光度. 根据结晶紫和AOT在微乳液水滴界面缔合的模型对实验数据进行处理, 结果表明, 随着微乳液中水与AOT的摩尔比w的减小和温度的升高, 结晶紫缔合度增大, 根据不同温度下的缔合平衡常数计算了反应的热力学函数, Δ_rG_m, Δ_rH_m和Δ_rS_m     

比值导数波谱-多波长最小一乘回归分光光度法同时测定饮料中糖精钠、苯甲酸和山梨酸

提出了比值导数波谱－多波长最小一乘回归分光光度法。该法能同时测定三组分混合物而毋需零交点波长和等吸收点，且回归稳健性好．可消除异常点的影响。方法用于合成样品和饮料中糖精钠、苯甲酸和山梨酸的同时测定，相对误差＜± ３． ５％，回收率为 ９６． ６％～１０４．４％，相对标准偏差为２．０％～３．１％．     

An Experimental Study on the Relationship between the Physical Properties of CTAB/Hexanol/Water Reverse Micelles and ZrO2-Y2O3 Nanoparticles Prepared

Based on the studies of their physical properties such as aqueous solution uptake, electric conductivity, and microstructure, CTAB/hexanol/water reverse micelles (CTAB, cetyltrimethyl ammonium bromide) were used to prepare ZrO2-Y2O3 nanoparticles. The relationship between the micelle microstructure and size, morphology, and aggregate properties of particles prepared was also investigated. It has been found that with high CTAB concentration ([CTAB] > 0.8 mol/l), the reverse micelles can solubilize a sufficient amount of aqueous solution with high metallic ion concentration ( approximately 1.0 mol/L), while the microstructure of the reverse micelles keeps unchanged. The most important factor affecting the size and shape of reverse micelles was found to be the water content w0 (w0, molar ratio of water to surfactant used). When both the CTAB concentration and the w0 values are low, the diameters of reverse micelles are below 20 nm, and the ZrO2-Y2O3 particles prepared are also very small. However, the powders obtained were found to form a lot of aggregates after drying and calcination. High CTAB concentration, high w0 value, and high metallic ion concentration in the aqueous phase for high powder productivity were found to be the suitable compositions of reverse micelles for preparing high-quality ZrO2-Y2O3 nanoparticles. Under these conditions, the reverse micelles are still spherical in shape even the reverse micellar system is nearly saturated with aqueous solutions. These reverse micelles were found to have a diameter of between 60 and 150 nm and the ZrO2-Y2O3 particles prepared therefrom range from 30 to 70 nm with spherical shape and not easy to form aggregates. Copyright 1999 Academic Press.     

GC/MS中保留指数和保留温度回归分析应用于单萜烯结构确认

GC／MS定性分析中,由于同分异构体的质谱图相似,常常出现结构鉴定错误．同分异构体化合物的保留行为具有较大地差别,采用文献保留指数和保留温度测定值回归分析方法对2篇已发表论文进行了研究,发现了对单萜烯类同分异构体结构鉴定中存在的错误,并提出可能的正确结构．文献保留指数和保留温度测定值回归分析方法可以简化GC／MS色谱峰的定性分析过程,提高定性分析的准确性,在样品定性分析中具很强的使用价值．     

Application of Artificial Neural Network and Multiple Linear Regression Retention Models for Optimization of Separation in Ion Chromatography by Using Several Criteria Functions

This work focuses on problems regarding empirical retention modelling and optimization of separation in ion chromatography. Influences of eluent flow rate and concentration of eluent competing ion (OH^–) on separation of seven inorganic anions (fluoride, chloride, nitrite, sulphate, bromide, nitrate, and phosphate) were investigated. Artificial neural networks and multiple linear regression retention models in combination with several criteria functions were used and compared in global optimization process. It can be seen that general recommendations for optimization of separation in ion chromatography is application of chromatography exponential function criterion in combination with artificial neural networks retention model.