Synthesis and Stabilization of Gold Nanoparticles in Reverse Micelles of Aerosol OT and Triton X-100

Mechanisms of the formation and stabilization of gold nanoparticles in reverse micelles of micro-emulsions based on Triton X-100 (TX-100) and Aerosol OT (AOT) are studied. The instability of AOT-based microemulsions is shown to be caused by the oxidative degradation of gold nanoparticles in micelle water pools. Methods are proposed for the stabilization of these microemulsions. It is revealed that the mean size of gold nanoparticles synthesized in TX-100 reverse micelles in the presence of sodium sulfite is markedly smaller than that of particles prepared in AOT reverse micelles. This is explained by the fact that gold clusters are formed in the micelle shell rather than in the water pool. In the shell, the clusters are stabilized by oxyethylene groups of TX-100 molecules.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 534–540.Original Russian Text Copyright © 2005 by Spirin, Brichkin, Razumov.     

Stabilization of the AgI Nanocrystal Size with Thiols in Reverse Micelles

The stabilization of AgI nanocrystals with dodecanethiol (DDT) and thioglycerol (TGC) in AOT reverse micelles was studied. It was established that water-soluble TGC stabilizes nanocrystals in micelle water pools, while hydrophobic DDT, in organic phase of micellar solution. Optimal values of [Ag⁺]/[thiol] molar ratio needed to synthesize the nanocrystals with minimal size were determined: this value varied from 1 : 10 to 1 : 50 in the case of DDT and was equal to 1 : 0.3 in the case of TGC. It was found that final nanocrystal size depended both on the amount of thiol and on the moment of its addition to microemulsion. Variations in these parameters made it possible to synthesize nanocrystals of various sizes. It was shown that AgI nanocrystals stabilized with thiol could be separated from micelles with no changes in their size.     

Synthesis of Barium Lithium Fluoride Nanocrystals Using Reverse Micelles as Microemulsion

Barium lithium fluoride nanocrystals were synthesized in cetyltrimethylammonium bromide (CTAB)/2-octanol/water microemulsion systems. The impurity peaks in XRD patterns were not determined. The result of SEM confirmed that the average sizes and shape of the BaLiF3 nanocrystals. The formation of BaLiF3 and particles size were strongly affected by water content. With increasing water content and reaction times, the size of the particle increases.Meanwhile, the solvent was also found to play a key role in the synthesis of the BaLiF3 nanocrystals.     

MnOOH纳米棒的反胶束法制备及表征

采用水溶液/CTAB/正丁醇/庚烷四组分组成的反相胶束体系,制备了MnOOH纳米棒,并用透射电镜(TEM)、高分辨透射电镜(HRTEM)和X射线粉末衍射(XRD)进行了表征.结果显示所得MnOOH为单斜晶系,直径约为10 nm、长度约为200 nm.实验表明,不同的反应时间所得纳米棒的长度不同,但直径可以保持不变.     

Specific Behavior of Hydrogen Peroxide in a System of AOT Reverse Micelles

It is revealed that, in contrast to organic hydroperoxides, hydrogen peroxide (H₂O₂) is rapidly decomposed in a system of reverse micelles of sodium bis(2-ehylhexyl)sulfosuccinate (AOT) in n-decane. The yield of free radicals upon the decomposition of H₂O₂ in a system of reverse micelles upon the interaction between AOT and cobalt acetyl acetonate (Co(acac)₂) is studied by the inhibitor method using an original spin trap. It is established that the interaction between H₂O₂ and AOT proceeds with no radical formation. Co(acac)₂ catalyses the radical decomposition of H₂O₂ in an aqueous solution. In micellar AOT solutions in n-decane, H₂O₂ and Co(acac)₂ in practice do not react, because H₂O₂ is localized in a micelle water pool, Co(acac)₂ and the spin trap, in the organic phase. In this case, the generation of radicals is not observed.     

Phenidone Oxidation during Photoinitiated Chemical Reduction of AgBr Nanocrystals in Water Pools of Reverse Micelles

Photoinitiated chemical reduction of AgBr nanocrystals (synthesized in water pools of reverse micelles of Aerosol OT and sodium dodecyl sulfate) with phenidone was shown to yield 1-phenyl-3-hydroxypyrazole along with reduced silver. This becomes possible because of irreversible oxidation of phenidone (1-phenyl-3-pyrazolidone) used as a reducing agent, and the rate of 1-phenyl-3-hydroxypyrazole accumulation significantly increases in the presence of a silver halogenide. The formation of the dissociated form of 1-phenyl-3-hydroxypyrazole becomes more probable with decreasing diameter of the water pool of reverse micelles formed by both surfactants.     

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     

溶剂对反胶束法合成CdS纳米粒子粒径的影响

以磺基琥珀酸二辛酯钠盐(AOT)为保护剂,利用反胶束法在不同烷烃溶液中合成了CdS纳米粒子.采用紫外-可见光谱、透射电子显微镜、荧光光谱法对其进行表征.研究表明:在不同烷烃溶液中合成的CdS纳米粒子,其粒子大小和荧光强度都随溶剂而改变.     

Nucleotide Coupling in Reverse Micelles

Nucleotide coupling was investigated in reverse micelles formed by (cetyl)trimethylammonium bromide (CTAB), in hexane/pentan-1-o1. In particular, the coupling of 2′ -deoxy-5′-O-methylcytidine 3′ O-phosphate, prepared by phosphoramidite chemistry, with 5′-amino-5-deoxythymidine was studied in the presence of a H₂O-soluble carbodiimide at (w_o) = 11 and 22 (w_o=[H₂O]/[CTAB]). The effect of w_o on the reaction rate was investigated. A solid-phase strategy was developed for the synthesis of 2′-deoxy-5′O-methyl-cytidyl-(3′-5′)-5′-amino-5′deoxythymidine. The nucleotide coupling yieldig the expected product occurred readily in reverse micelles. Nucleotide coupling is thus possible in reverse micelles, and this is discussed in connection with the micellar self-replication program.     

反相胶束微乳液法制备氧化钇纳米微晶

纳米结晶;反相胶束微乳液法制备氧化钇纳米微晶     

Protein Stability in Reverse Micelles

The N‐terminal SH3 domain of the Drosophila signal transduction protein drk was encapsulated in reverse micelles. Both the temperature of maximum stability and the melting temperature decreased on encapsulation. Dissecting the temperature‐dependent stability into enthalpic and entropic contributions reveals a stabilizing enthalpic and a destabilizing entropic contribution. These results do not match the expectations of hard‐core excluded volume theory, nor can they be wholly explained by interactions between the head groups in the reverse micelle and the test protein. We suggest that geometric constraints imposed by the reverse micelles need to be considered.     

Solution behaviour of Aerosol OT in non-polar solvents

The aggregational behaviour of Aerosol OT in non-polar solvents and the applications of these systems in various areas have been reviewed. Aerosol OT forms reverse micelles in oils without using any cosurfactant and the reverse micellar solution can dissolve large amounts of water with the formation of discrete droplet microemulsion or bicontinuous microemulsions. Due to their simplicity in the sense of the smallest number of components in the reverse micellar systems, these systems have been widely studied and have also been divergently applied. This review gives a detailed account of various aspects of Aerosol OT reverse micelles namely their aggregational, structural, conformational, dynamic and applications reported in the literature to date.     

Self-Replication of Oligonucleotides in Reverse Micelles

The coupling between the tri(deoxynucleotides) d[(MeO)C-G-Ap] ( 1 ) and d[(NH₂)T_d5′-C-G-] ( 2 ) to yield the phosphoramidate-linked (hexadeoxy-nucleotide) d[(MeO)C-G-Anh⁵′T_d5′-C-G] ( 3 ) was investigated both in aqueous solution and in reverse micelles constituted of CTAB (cetyl(trimethyl)ammonium bromide) in hexane/pentan-1-ol 9:1. No siginificant difference was found concerning the yield and the kinetics of the reaction in the two systems. The coupling between 1 and 2 was also carried out in the presence of the template d[(MeO)C-G-A-T-C-G] ( 4 ), an analogue of 3 , so as to reproduce the conditions of template-directed self replication. It was shown that the trinucleotide coupling in the presence of a template obeys the so-called square-root law both in H₂O and in reverse micelles. No significant difference of the time course of the reaction in H₂O and in reverse micelles was observed. This shows that self-replication of oligonucleotides occurs within geometrically bounded structures, which represents a step forward in the mimicking of minimal life processes.     

Specific Features in Measuring Particle Size Distributions in Highly Disperse Aerosol Systems

The distribution of highly dispersed aerosols is studied. Particular attention is given to the diffusion dynamic approach, as it is the best way to determine particle size distribution. It shown that the problem can be divided into two steps: directly measuring particle penetration through diffusion batteries and solving the inverse problem (obtaining a size distribution from the measured penetrations). No reliable way of solving the so-called inverse problem is found, but it can be done by introducing a parametrized size distribution (i.e., a gamma distribution). The integral equation is therefore reduced to a system of nonlinear equations that can be solved by elementary mathematical means. Further development of the method requires an increase in sensitivity (i.e., measuring the dimensions of molecular clusters with radioactive sources, along with the activity of diffusion battery screens).     

反胶束体系中水团的笼效应

在反胶束体系中研究了菁染料的吸收光谱以及ω值对菁染料荧光光谱的影响.讨论了不同粒径的AgCl纳米粒子对反胶束体系中菁染料的吸附状态及J-聚集体形成的影响.特别研究了反胶束水团空间限定效应对菁染料荧光量子产率及J-聚集体的影响.     

Transport of charged Aerosol OT inverse micelles in nonpolar liquids

Surfactants such as Aerosol OT (AOT) are commonly used to stabilize and electrically charge nonpolar colloids in devices such as electronic ink displays. The electrical behavior of such devices is strongly influenced by the presence of charged inverse micelles, formed by excess surfactant that does not cover the particles. The presence of charged inverse micelles results in increased conductivity of the solution, affecting both the energy consumption of the device and its switching characteristics. In this work, we use transient current measurements to investigate the electrical properties of suspensions of the surfactant Aerosol OT in dodecane. No particles are added, to isolate the effect of excess surfactant. The measured currents upon application of a voltage step are found to be exponentially decaying, and can be described by an analytical model based on an equivalent electric circuit. This behavior is physically interpreted, first by the high generation rate of charged inverse micelles giving the suspension resistor like properties, and second by the buildup of layers of charged inverse micelles at both electrodes, acting as capacitors. The model explains the measurements over a large range of surfactant concentrations, applied voltages, and device thicknesses.     

反相胶束中辣根过氧化物酶的停流光谱研究

用停流光谱法研究了HRP在AOT、CTAB和SDS反相胶束中的吸收光谱和反应动力学，实验结果显示在AOT反相胶束中，HRP的吸收峰位置与水相中相同；而另外两种反相胶束对HRP的分子结构产生了较大影响，快速反应动力学研究显示在反相胶束中HRP形成化合物Ⅰ的速率常数远远高于化合物Ⅰ形成HRP—Ⅱ的反应速率常数，推测这是反相胶束的特殊性质造成的结果。     

Incorporation of substituted acrylamides to the lamellar mesophase of Aerosol OT

The structure and stability of the lamellar liquid crystal formed by the surfactant sodium bis-2ethylhexyl sulfosuccinate (AOT) in water is perturbed by small amounts of the substituted acrylamides N-isopropyl, N,N-diethyl, N-acryloylmorpholine, and N,N-dimethyl methacrylamide, as revealed by small angle X-ray scattering (SAXS), deuterium NMR, and microscopy. These molecules are water soluble and stay mostly in the water layers between lamellae, but a small fraction of them (5-19%) are incorporated into the AOT bilayers, thereby producing dramatic changes. Both, the degree of anisotropy in the water molecules hydrating AOT (quadrupolar splitting in (2)H NMR) and the long period spacing between lamellae (SAXS), decrease with addition of this molecules at low concentrations, which is attributed to the lower average headgroup density at the AOT/water interface when the acrylamide is incorporated. The strength of these perturbations depends on the acrylamide, and goes in parallel with the hydrophobic character of the alkyl side groups in its molecule, which suggests that the acrylamides incorporated to the bilayer enter into contact with the lipophilic tails of the AOT molecule. An interaction with the hydrated heads of AOT is also suggested in the particular case of N-isopropylacrylamide. On increasing the molecule concentration an incipient melting of the lamellar phase towards an isotropic solution takes place, first at the microscopic level, then macroscopic. Near this phase transition, the ordered domains lose the random orientation prevailing at lower acrylamide concentrations, and adopt a preferred orientation, perpendicular to the magnetic field.     

反胶束中的酶催化研究进展

评述酶在反胶束中的定位和结构、动力学特性、催化活性和稳定性，反胶束作为酶催化反应介质的优点，反胶束中酶催化反应的类型及其应用。     

Computer Simulation of Luminophore Solubilization in Reverse Micelles

The solubilization of ionic (sodium naphthalene-2,6-disulfonate) and nonionic (diethyl 2,5-dihydroxyterephthalate) organic luminophores in water–isooctane–NaАОТ (sodium 1,4-bis[(2-ethylhexyl) oxy]-1,4-dioxybutane-2-sulfonate) reverse micelles is simulated by the molecular dynamics method. In a stationary state, the localization of luminophore molecules in a micelle appears to be the same irrespective of their initial positions in the system. The position and orientation of solubilized luminophores relative to a reverse micelle depend on the hydrophobicity and the capability for dissociation of the functional groups of their molecules, the size of the reverse micelle, and the structure of its electrical double layer.