The Dipole Moment of Reverse Micelles according to Computer Simulation Data

Sodium 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxybutane-2-sulfonate (Aerosol OT) reverse micelles in isooctane have been simulated, and the mean-square dipole moment has been calculated. The formed isolated micelles have been classified according to aggregate radius and surface area per one surfactant molecule. It has been shown that, for micelles with a constant surface density of surfactant anion charges, the meansquare dipole moment rises with the aggregate size faster than the squared radius does. Dipole moment values obtained within the atomistic model for a reverse micelle are much higher than the values presented in the literature for the primitive model.     

NPES/AOT反胶束增溶体系及性质研究

该文以壬基酚聚氧乙烯醚硫酸钠(NPES)与琥珀酸二(2-乙基己基)酯磺酸钠(AOT)复配体系为主表面活性剂,正丁醇为助表面活性剂,以柴油为油相,研究了反胶束增溶体系的粘度和电导率等物理化学性质;利用脉冲核磁共振图谱中水的T2弛豫时间分布曲线,研究了反胶束溶液中水的结合状态和分布,采用正规溶液理论计算了NPES/AOT的相互作用参数β值(-7.78),研究结果表明二者存在较强的协同效应,从理论上解释了二者在反胶束溶液中的最佳比例和协同增效作用.     

Micellar Solubilization of Biopolymers in Hydrocarbon Solvents III. Empirical Definition of an Acidity Scale in Reverse Micelles

This paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pH_wp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pH_wp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale. An empirical acidity scale for water pools in reverse micelles of bis (2-ethyl-hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the ³¹P-chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pH_wp and the pH of the starting buffer in bulk water (which we define as pH_st). However, this difference between pH_wp and pH_st may become much larger in certain cases. The difference (pH_wp–pH_st) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pH_st with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pH_wp scale, the apparent pK_a of phenol-red and 4-nitrophenol were determined in reverse micelles containing different buffers and different water content. The pK_a values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.     

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.     

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.     

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.     

脂肪醇和电解质对丙酸十二铵盐在四氯化碳中增溶水的影响

研究了己醇，辛醇、Ｋｕｉ醇和月桂醇对丙酸十二铵（ＤＡＰ）－四氯化碳反胶束溶液增溶水和氯化钠水溶液的影响，在ＤＡＰ浓度固定时，水增溶量对醇浓度的关系出现极大值，在醇浓度相同时，长碳链醇较短碳链醇有更大的增溶水能力，在固定ＤＡＰ浓度和增溶水量最大时，氯化钠的存在将导致水溶液增溶量的显著下降，乙酸十二铵（ＤＡＡ）、ＤＡＰ和丁酸十二铵（ＤＡＢ ）的四氯化碳溶液对氯化钠水溶液的增溶量随氯化钠浓度的升高而有不     

水杨酸-2′-乙基己基酯在胶束中的增溶位点

考察了阳离子、非离子和阴离子表面活性剂存在下水杨酸-2′-乙基己基酯(EHS)的吸收光谱和激发态分子内质子转移(ESIPT)荧光光谱.结果表明,EHS可增溶在胶束中,2′-乙基己基碳链朝向胶束内核,而水杨酸基朝向胶束-水界面;胶柬环境有利于EHS分子对紫外光的吸收和分子内氢键的形成,从而使ESIPT荧光显著增强,激发态分子以发射可见光和非辐射去活化方式衰减;并根据EHS和表面活性剂分子的结构和大小,解释了EHS分子在胶束中的结合位点,荧光猝灭和酯水解的光谱测量进一步为此结合位点提供了佐证.     

Effect of CO(2) and CHF(3) on the Solubilization of Protein in Reverse Micelles

The effect of dissolved CO(2) and CHF(3) on the precipitation of bovine serum albumin (BSA) from reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in 2,2,4-trimethylpentane (iso-octane) has been studied at 308.15 K. It was found that BSA can be precipitated completely by CO(2) while the AOT and water remain in the iso-octane continuous phase. This opens up a possibility for recovery of protein solids directly from reverse micellar solutions. CHF(3) is also an effective agent for precipitation of BSA in the reverse micelles when the expansion coefficient of CHF(3) exceeds 0.4. However, the condition required for complete removal of the BSA using CHF(3) results in some precipitation of AOT and water from the solution. Copyright 2000 Academic Press.     

水杨酸-2’-乙基己基酯在胶束中的增溶位点

考察了阳离子、非离子和阴离子表面活性剂存在下水杨酸-2’-乙基己基酯(EHS)的吸收光谱和激发态分子内质子转移(ESIPT)荧光光谱. 结果表明, EHS可增溶在胶束中, 2’-乙基己基碳链朝向胶束内核, 而水杨酸基朝向胶束-水界面; 胶束环境有利于EHS分子对紫外光的吸收和分子内氢键的形成, 从而使ESIPT 荧光显著增强, 激发态分子以发射可见光和非辐射去活化方式衰减; 并根据EHS和表面活性剂分子的结构和大小, 解释了EHS分子在胶束中的结合位点, 荧光猝灭和酯水解的光谱测量进一步为此结合位点提供了佐证.     

Supramolecular Micelles and Reverse Micelles Based on Cyclodextrin Polyrotaxanes

A new supramolecular self-assembly approach to construct micelles and reverse micelles was reported.Double-hydrophilic block copolymers poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAAm) was synthesized via atom transfer radical polymerization (ATRP) using PEO macroinitiator.Because of the lower critical solution temperature (LCST) phase behavior of PNIPAAm,PEO-b-PNIPAAm block copolymers self-assembled to form PNIPAAm-core micelles at 40 ℃.The PNIPAAm-core micelles were disassembled to unimers when the temperature was decreased to 25 ℃.But the addition of α-cyclodextrins (α-CDs) could induce the formation of PNIPAAm-shell micelles because of the "channel-type" crystallities induced by PEO/α-CDs polyrotaxanes.The assembly and disassembly procedure of micelles and reverse micelles were investigated by dynamic light scattering (DLS),X-ray diffraction (XRD),1H NMR and transmission electron microscopy (TEM).     

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.     

Location of Solubilization of 2′-ethylhexyl Salicylate in Micelles

Absorption and excited state intramolecular proton transfer (ESIPT) fluorescence of 2′-ethylhexyl salicylate (EHS) were examined in the presence of cationic, non-ionic, and anionic surfactants. It was found that linear EHS molecule was solubilized in micelles with its flexible and hydrophobic 2′-ethylhexyl chain toward the micellar core and with its rigid salicyl moiety toward the micelle-water interface. The UV absorption of EHS was improved and the intramolecular hydrogen bonding formation of EHS was favored, resulting in greatly enhanced ESIPT fluorescence. The excited EHS molecules decay via visible luminescence and non-radiative deactivation. The binding sites of EHS in micelles were explained at a molecular level in terms of molecular structures and sizes of EHS and surfactants. Dynamic fluorescence quenching and spectral measurements of ester hydrolysis of EHS provide further evidences for the binding sites of EHS in different micelles.     

Pluronic嵌段共聚物F127胶团对布洛芬的增溶(英文)

研究了PluronicF127胶团溶液对药物布洛芬(IBU)的增溶作用.通过芘探针荧光法测定了不同温度下F127在水溶液和0.01mo·lL-1pH7.4磷酸盐缓冲生理(PBS)溶液中的临界胶束浓度(cmc),采用高效液相色谱(HPLC)测定了F127溶液中布洛芬的溶解度,并依据公式计算了增溶参数(摩尔增溶量c和胶团-水分配系数K),考察了温度、溶剂和F68的加入对F127胶团化行为及其对布洛芬增溶作用的影响.结果表明:布洛芬的溶解度随F127质量分数的提高线性增加;随着温度升高,cmc急剧下降,胶团内核的疏水性增强,χ和K稍有增大;与水溶液相比,在PBS溶液中cmc减小,χ几乎不变,K显著降低;F68的加入对F127胶团的性质几乎无影响,对增溶的影响也不明显.对增溶参数的分析表明,K反映的是药物布洛芬的性质,χ则可反映嵌段共聚物F127的溶解效能,并证实了布洛芬是通过F127胶团的内核和栅栏层而实现增溶的.     

Solubilization of Polycyclic Aromatic Compounds into n-Decyltrimethylammonium Perfluorocarboxylate Micelles

Solubilization of polycyclic aromatic compounds in aqueous dilute solutions of three cationic amphiphiles was studied. The maximum additive concentrations (MACs) of the aromatic compounds were constant below their critical micelle concentrations (cmcs) and monotonically increased above the cmcs. The first stepwise association constants (K(1)) between a solubilizate monomer and a vacant micelle were evaluated from the MACs for the solubilizates using the mass action model for solubilization into micelles in the dilute solution. The standard Gibbs energy changes of solubilization (DeltaG degrees ) were calculated from K(1), and the enthalpy and entropy changes of solubilization were estimated from the temperature dependence. MACs of each surfactant at the same surfactant concentration above the cmc were different depending on the cmc, but there was little difference in the DeltaG degrees values. Some differences appeared in the enthalpy and entropy values in accordance with their micellar size or degrees of counterion binding to micelles. DeltaG degrees for solubilization decreased linearly with carbon number of aromatic solubilizate for each micellar solution. Copyright 2000 Academic Press.     

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。     

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。     

Molecular-Thermodynamic Model of Solubilization in Direct Spherical Micelles of Nonionic Surfactants

Colloid Journal - A thermodynamic model has been formulated for the formation work of a molecular aggregate consisting of molecules of a nonionic surfactant and a solubilisate in a...     

Measurement of Solubilization Location in Micelles Using Anchored Aggregation-Induced Emission Donors

Solubilization locations play a critical role in developing advanced surfactants and improving solubilization power in micelle-based applications. However, the current polarity-based techniques for measuring solubilization locations could come to conflicting conclusions. The key challenge is the unpredictable polarities in the micellar microenvironment. Now, an approach that is independent of micellar polarities is used to measure solubilization locations by covalently linking tetraphenylethylene (TPE) to the alkyl chain end of cationic surfactants. The solubilization locations of solubilized acceptors in the TPE-cored spherical micelles were accurately measured by calculating the Förster resonance energy transfer distance between anchored TPE donors and solubilized acceptors. Solubilization locations of solubilized substances in the micellar interior and at the micellar surface depend on their size and hydrophobicity, respectively.     

Enzymes Hosted in Reverse Micelles in Hydrocarbon Solution

Reverse micelles are spheroidal aggregates formed by certain surfactants in apolar media. In contrast to normal micelles in water, the polar head groups of the surfactant molecules are directed towards the interior of the aggregate and form a polar core which can solubilize water (the “water pool”); the lipophilic chains are exposed to the solvent. The water of the water pool exhibits properties that (depending on the mole ratio of water to surfactant) differ from those of bulk water. Surprisingly, these reverse micelles are able to solubilize in hydrocarbon solvents hydrophilic molecules, e.g., enzymes and even plasmids, that are much larger than the original water-pool diameter. These biopolymer-containing reverse micelles can be viewed as novel microreactors, whose physical properties can be controlled through the water content. Remarkable is the ability of enzyme-containing micelles to react with water-insoluble, hydrocarbon-soluble substrates, as in the example of lipoxygenase with linoleic acid.