Complexation of Al(III) by 8-Hydroxyquinoline and Drastic Fluorescence Enhancement in Reverse Micelles

Complexation of Al^IIIby 8-hydroxyquinoline and fluorescence behavior of the quinolinate(s) were studied in reverse micellar systems at low water content, and compared to aqueous media. Two surfactants were used: one was cationic (CTAC: cetyltrimethylammonium chloride) and the other was anionic (AOT: sodium bis(2-ethylhexyl)sulfosuccinate). The results obtained in the CTAC/dichloromethane system (W= [H₂O]/[surfactant] = 0.9) showed that complexation occurred very likely in the oil phase and no micellar effect was observed. On the contrary, in the presence of AOT, specific micellar effects were observed due to the presence of the anionic polar heads: stabilization of the positively charged 1:1 and 1:2 chelates, at the expense of the neutral water-insoluble 1:3 chelate which is formed in aqueous solutions under similar conditions;drastic fluorescence enhancement factorsof 120 and 100 in AOT/heptane (W= 1.5) and AOT/dichloromethane (W= 1.6), respectively. Such factors have never been reported so far in either hydroorganic or direct micellar systems. In return, the length of time for the production of the complex(es) is increased because of the microheterogeneity of the medium and the small sizes of the water pools.     

Calorimetric study on the solubilization of some primary alcohols by reversed AOT micelles

A calorimetric method to evaluate, at the same time, the distribution constant and the standard enthalpy of transfer of a solute partitioned between organic phase and reversed micelles is proposed. The method was applied to the partition of methanol, 1-propanol and 1-pentanol between n-heptane and AOT reversed micelles containing water at 25°C. The results show that the distribution constant decreases as the alcohol alkyl chain length increases and that the solubilization site can change as the water content of reversed AOT micelles increases. In particular, at sufficiently high water content, methanol seems to be preferably solubilized in the aqueous pseudophase whereas 1-pentanol prefers always the palisade layer as site of solubilization.In part from Doctor in Biology thesis of F. Pinio, University of Palermo, Italy.     

Autocatalytic oxidation of Fe(Phen)3 2+ by bromate in water-in-oil reverse micelles of AOT

Autocatalytic oxidation of ferroin by bromate in water-in-oil reverse micelles of AOT has been studied experimentally and theoretically. The simplest models for this process have been constructed. Analytical solutions for these models were found for some limiting cases. It has been shown that the autocatalytic reaction runs much more slowly in reverse micelles than in water. The dependencies of the maximum reaction rate, _max, the exponent of the increase in ferriin concentration, , and induction period, , on micelle concentration have been obtained at =[H₂O]/[AOT]=4.6. It was found that there is only one theoretical model which can explain the experimental data. The values of the elementary reaction rate constantsk _i were estimated on the basis of the theoretical dependencies of _max and on the constantsk _i . All elementary rate constants turned out to be two or three orders of magnitude smaller than the corresponding constants for the reaction proceeding in water. The decrease in the rate constants is explained by the increase in viscosity and pH in a micellar water core at low .Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1401–1407, August, 1993.This work was supported by the Russian Foundation for Fundamental Investigations through Research Grant 93-03-4090.     

Refractive index of water-AOT-n-heptane microemulsions

Refractive index measurements on water/AOT/n-heptane microemulsions as a function of the volume fraction of the dispersed phase (water plus AOT) and of the water/AOT molar ratio R have been performed at 25°C. The refractive index was found to vary monotonically with without any change in rate during the crossover of the percolation threshold. Such a behavior suggested that, well above the percolation threshold, the water-AOT-n-heptane microemulsions are still formed by water-containing AOT reversed micelles dispersed in the oil phase. The analysis of the experimental data allowed an evaluation the fraction of the water molecules bonded to the AOT head group as a function of R.     

Salinity Controlled Vesicle Formation and Growth in Aqueous Mixture of Aerosol OT/Triton X‐100

Mixed vesicles can be formed spontaneously from aqueous mixture of the double‐tailed anionic surfactant sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) and the nonionic surfactant octylphenoxypolyethoxyethanol (Triton X‐100) under the inducement of salt, the formation mechanism of which should be attributed to the compression of salt on the electric bilayers of the head groups. The stability and the polydispersity of the vesicles are superior to single‐component AOT vesicles, which can be proved by the TEM image and visual observation. The vesicle region was presented in a pseudo‐ternary diagram of AOT/TX‐100/brine. The size of the vesicle was measured using dynamic light scattering. It is found that the vesicle size increases with the salinity but decreases with the content of TX‐100 in the mixture at the same salinity. Especially, the vesicle size is independent of the surfactant concentration at fixed salinity.     

Electrophoretic mobility and stability of SiO2 nanoparticles in the solutions of AOT in n-hexadecane-chloroform mixtures

Electrophoretic mobility of SiO₂ nanoparticles in a n-hexadecane-chloroform mixture depending on AOT concentration and chloroform content was determined. It was shown that an increase in chloroform content and a decrease in AOT concentration cause a growth in electrophoretic mobility. The use of the values of Debye lengths (characteristic thickness) of the diffuse part of the electric double layer (EDL) that were determined previously allowed us to calculate the electrokinetic potential and to evaluate the stability of organosols. The obtained data were in good correlation with the dynamics of temporal changes of hydrodynamic radius and the intensity of light scattering. Organosols may be used for heteroaggregation (sorption) of Au and Ag nanoparticles on SiO₂.     

Volumetric and transport properties of aerosol-OT reversed micelles containing light and heavy water

Densities and viscosities of sodium bis(2-ethylhexyl) sulfosuccinate (AOT in-heptane system containing light and heavy water, as a function of the molar ratio R (R=[H₂O or D₂O]/[AOT]) were measured at 0, 5, 25 and 40°C. At low R values, the apparent molar volume of deuterium oxide is smaller than that of light water. The difference is related to the strength of the hydrogen bonding H₂O and D₂O. The viscosities of both H₂O-AOT-n-heptane and D₂O-AOT-n-heptane systems were explained in terms of intermicellar interactions mainly governed by hydration of the head groups of AOT.     

Gas phase charged aggregates of bis(2-ethylhexyl)sulfosuccinate (AOT) and divalent metal ions: first evidence of AOT solvated aggregates

Assembling and chelating properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) towards divalent metal ions have been investigated in the gas phase by electrospray ionization mass spectrometry. A variety of positively charged monometallated and mixed metal aggregates are formed. Interestingly, several ions contain solvent (MeOH, H(2)O) molecules and constitute the most abundant AOT cationic aggregates not containing sodium. These species are the first example of solvated AOT-metal ion aggregates in the gas phase. By increasing the surfactant aggregation number, the abundance of solvated species becomes lower than that of unsolvated ones. Decompositions of ionic species have been studied by tandem mass spectrometry, and their stability has been determined through energy resolved mass spectrometry. In contrast with positively charged AOT-alkaline metal ion aggregates, whose decompositions are dominated by the loss of individual surfactant molecules, AOTNa-divalent ion aggregates mainly dissociate through the cleavage of the AOT H(2)C-O bond followed by further intramolecular fragmentations. This finding, that is consistent with an enhanced chelation of divalent ions with AOT(-) head groups, has been taken as an indication that such aggregates are characterized by a reverse micelle-like organization with a ionic core formed by the metal cations interacting with the negatively charged surfactant polar heads, whereas the surfactant alkyl chains point outside.     

聚乙烯吡咯烷酮存在时反相微乳液中水的状态

运用傅立叶变换红外光谱（FTIR）研究不同分子量的聚乙烯吡咯烷酮（PVP）存在时,十二烷基甜菜碱(C12BE)/正庚烷 /正戊醇 /水（Ⅰ）及二（2 乙基）己基磺化琥珀酸钠（AOT）/正庚烷 /水（Ⅱ） 反相微乳液中水的存在状态.采用计算机分峰技术将微乳液中水分子的O－H伸缩振动进行曲线拟合, （Ⅰ）得到三个子峰,分别位于(3560±20)cm－1,(3430±10)cm－1,(3280±10)cm－1附近; （Ⅱ）得到四个子峰,分别位于3618 cm－1, 3550 cm－1, 3446 cm－1和3292 cm－1处.尽管PVP均增溶于W/O型微乳液中表面活性剂分子的极性基团附近,却没有引起长链间自由水的变化.但由于两体系的差异,PVP的存在,导致微乳液（Ⅰ）的本体水减少,结合水增多,却使体系（Ⅱ）的结合水减少,本体水增多.由于W/O型微乳液中水与生物膜中水相似,这些研究有助于理解生物膜界面上的生物化学和生物物理现象.     

AOT/水/甲苯微乳体系的第二维里系数和液滴间的相互作用

在一系列温度下通过对水与丁二酸双(2-乙基己基)酯磺酸钠(AOT)摩尔比为12、不同浓度的AOT/水/甲苯微乳液进行静态光散射测量, 获得液滴的相对分子质量、AOT的聚集数、液滴半径和不同温度下的第二维里系数. 利用第二维里系数与温度的关系获得液滴的相互作用焓和熵, 分别为-4.03×10⁴ J·mol^-1和-139.8 J·mol^-1·K^-1, 说明AOT/水/甲苯微乳液滴间表面活性剂疏水链相互交叉渗透的能量变化为负值, 交叉渗透为焓驱动.