SDS/CTAB/H2O的双水相性质及萃取作用

正负离子表面活性混合物;牛血清蛋白质;色氨酸;SDS/CTAB/H2O的双水相性质及萃取作用     

外加盐作用形成的正负离子表面活性剂双水相

癸基三乙基溴化铵-癸基磺酸钠（C10NE-C10SO3）等摩尔混合均相体系（即使在表面活性剂总浓度高达0.2 mol•L－1时仍然可形成稳定的均相溶液）在外加盐NaF、Na2SO4和Na3PO4的作用下可自发分离成两个水相（双水相）.研究了该类双水相体系的形成、相行为及其对牛血清蛋白（BSA）的分配，并与普通的正负离子表面活性剂混合双水相体系进行了比较.结果表明，该类双水相体系克服了普通的正负离子表面活性剂混合双水相体系的一些不足，具有一些独特的优点.该类双水相体系的相行为可以通过外加盐进行调控,通过外加盐的种类来调控和优化BSA的分配行为.图1表2参8     

Effect of 1-hexanol on the phase behavior of SDS/CTAB/NaBr/H2O system

Abstract

The influence of 1-hexanol on the phase behavior of sodium dodecyl sulfate (SDS)/cetyltrimethyl ammonium bromide (CTAB)/NaBr/H₂O system has been systematically investigated in this paper. The results showed 1-hexanol effectively dissolved the precipitate formed by the CTAB and SDS surfactants, while liquid crystal (LC) and aqueous two phase system (ATPS) were formed in a wider range. When the molar ratio of 1-hexanol to surfactant is higher than 1, the precipitation in the system disappeared completely and was transformed into ATPS and LC, indicating that alcohol inserted at least evenly between every two surfactant molecules and hence effectively weakened the electrostatic interaction between the anionic and cationic surfactants and limited the formation of precipitation. Polarizing microscope (POM) with crossed polarizers was employed to investigate the textures of liquid crystals. It was shown that the existence of lamellar LC was confirmed by “Maltese crosses” textures. Additionally, we showed that the thermal stability of LC was promising. The ATPS and LC regions remained stable and changed slightly when the temperature was increased from 40 to 70?°C. The results indicated that ATPS and LC of the system were quiet resistant to temperature with the addition of 1-hexanol.     

The significant effects of linear medium chain fatty alcohols on phase behavior of aqueous solution of mixed cationic–anionic surfactant

The effect of 1-hexanol on the phase behavior of aqueous solutions of sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) has been systematically studied. The phase ranges of vesicle and liquid crystal (LC) can be greatly extended with the addition of 1-hexanol. These specific structures distributed symmetrically on the two sides of the SDS/CTAB equimolar line in the pseudo ternary phase diagram. The aqueous two phase system (ATPS) contained vesicles that would transform into lamellar LC with the change of ratio of SDS/CTAB. The phase behaviors of SDS/CTAB system with addition of different alcohols (C₅OH–C₈OH) showed similar trends in structural transition except for phase span, demonstrating that the obstruction of electrostatic interaction between surfactant polar heads was affected by the insertion depth of the added alcohols.     

盐对正负离子表面活性剂双水相性质的影响

主要研究了盐对SDS/CTAB/H₂O混合系统双水相相行为的影响, 并对双水相上相的液晶性质进行了初步的探索. 结果表明: 盐能促使阴离子双水相区和阳离子双水相区分别向SDS和CTAB方向移动, 并使双水相区加宽. 反离子扩散双电层中盐的离子半径越大, 其对ATPS区的位置及相区宽度的影响程度越大. 盐的浓度达到一定值时, 它对双水相的影响可以达到饱和状态. ATPS_a区的饱和盐浓度值大于ATPS_c区的饱和盐浓度值. 异号盐离子对反离子层的限制作用与其离子半径有关.     

pH及有机小分子物质对SDS/CTAB/H2O系统双水相性质的影响

正离子表面活性剂与负离子表面活性剂混合物能产生比单一表面活性剂更高的表面活性[1 ] 。在适当条件下 ,正负离子表面活性剂的水溶液能产生两个互不相溶的水相 ,即表面活性剂双水相系统[2 ] (ＡｑｕｅｏｕｓＴｗｏ -ＰｈａｓｅＳｙｓｔｅｍ -ＡＴＰＳ)。作者曾指出双水相上相为液晶 (ＬｉｑｕｉｄＣｒｙｓｔａｌ -ＬＣ)结构 ,下相为各向同性溶液 ,盐离子通过改变双水相中表面活性剂有序组合体的反离子层的状态而对双水相的组成、结构等产生重要的影响[3,4] 。本文进一步研究ｐＨ及有机小分子物质在十二烷基硫酸钠 /十六烷基三甲基溴化铵 /…     

Properties and Extraction for [Ni(NH3)6]2+ of ATPS-a Formed by Aqueous Cationic–Anionic Surfactant Mixtures

The properties and extraction for [Ni(NH₃)₆]²⁺ of anionic aqueous two-phase systems (ATPS-a) that formed in mixtures of cetyltrimethylammonium bromide (CTAB) and excess sodium dodecyl sulfate (SDS) aqueous solutions were investigated. The results showed that the properties and extraction effects were strongly affected by the surfactant concentration, the temperature of system, and the mole fraction of surfactants. The increase of temperature induces narrower phase region and larger phase volume ratio. In addition, [Ni(NH₃)₆]²⁺ was extracted into the surfactant-rich phase with higher distribution coefficient when the liquid crystal had the birefringent properties. Moreover, the distribution coefficient can be improved through reducing the concentration of surfactant from 0.15 to 0.05 mol · L^?1 or increasing mole fraction of CTAB from 21.9% to 23.1%. The results showed that ATPS of cationic–anionic surfactants was efficient for [Ni(NH₃)₆]²⁺ extraction with distribution coefficients of 13.5 when the total surfactant concentration was 0.05 mol · L^?1, mole fraction of CTAB was 21%, and temperature was 34°C.     

Rheology and microstructure studies of SDS/CTAB/H2O system

Phase behavior of mixed sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) aqueous solution was studied. The rheological properties and microstructure were investigated using a rheostat and freeze-fracture technique and are shown to be closely related to the phase behavior. Experimental investigations reveal two symmetrical aqueous two-phase systems (ATPS) in the ternary phase diagram of SDS/CTAB/H₂O system. In the surfactant rich phase of ATPS or in the adjacent stoichiometric state of ATPS, the system has high viscosity because of its long range ordered structure. Lamellar phase was found in the high viscosity samples in which the cationic and anionic surfactant are in 1: 3 or 3: 1 stoichiometry. In addition, the viscosity has a tendency to increase when salt was added to the solution. The viscosity increase is due to the salt can screen the repulsion between different charged headgroups and thus reduces the effective size of surfactants and facilitates the spherical or rod likes micelles to be transformed to worm-like micelles which can form hexagonal or liquid crystal phases. Large-size salt ions like sodium sulfate (especially organic salt ions) have more significant effect on the surfactant solution viscosity. The text was submitted by the authors in English.     

The Influence of Sodium Phosphate on Extraction Phenomena of Aqueous Two‐Phase Cationic/Anionic Surfactant Systems

The phase behavior of dodecyltrimethylammonium bromide (DTAB)/sodium dodecyl sulfonate (AS)/H₂O system in the presence and in the absence of sodium phosphate has been studied. Two kinds of aqueous two‐phase systems (ATPSs) were formed, one is ATPS‐A in which anionic surfactant is in excess, the other is ATPS‐C in which cationic surfactant is in excess. For the CTAB/AS/H₂O system, the addition of sodium phosphate changes the extraction phenomena of both ATPS‐A and ATPS‐C. For the DTAB/AS/H₂O system, the addition of sodium phosphate changes the extraction phenomena of ATPS‐C. For ATPS‐C, the addition of trivalent PO₄ ^3? results in a strong extraction effect of ATPS‐C to cationic water‐soluble dye methylene blue.     

Distribution of emulsified monomers with different water solubility

The location and distribution of acrylic acid and styrene in emulsions made with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), or an anionic surfactant, sodium dodecylsulfate (SDS), were determined with ultra-violet spectroscopy, conductivity, and potentiometry. In these systems, the acrylic acid remains in the aqueous phase near the micelle surface, whereas the styrene is located in the micelles or in emulsified droplets. In the absence of acrylic acid, some of the styrene is solubilized in the micelle interior and some is adsorbed at the micelle inner surface. Upon addition of acrylic acid, all the styrene is displaced to the center of the micelles. The interaction between acrylic acid and CTAB micelles is stronger than that between acrylic acid and SDS micelles. With CTAB, acrylic acid is adsorbed at the micelle surface, whereas with SDS, acrylic acid remains in the intermicellar solution. These differences can account for the differences reported in the emulsion copolymerization of acrylic acid and styrene using CTAB or SDS.     

Salt Effects on Aqueous Cationic/Anionic Surfactant Two‐Phase Regions

The influence of added salts (KCl, NaF, NaCl, NaBr, Na₂SO₄, Na₃PO₄) on aqueous cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfonate (AS) two‐phase regions were studied. For KCl, the concentration dependence of salt effect on aqueous two‐phase regions was investigated. When brine substitutes pure water as a solvent, the positions of aqueous two‐phase regions in the phase diagram change. The results indicate that for aqueous two‐phase systems with excess anionic surfactant (ATPS‐A), the salt effect was mainly dependent on the cationic inorganic counterions, whereas for aqueous two‐phase systems with excess cationic surfactant (ATPS‐C), the salt effect was mainly dependent on the anionic inorganic counterions. The shift of aqueous two‐phase region is strengthened following the Hofmeister series. All the experiments were performed at 318.15 K.     

蛋白质在表面活性剂与高分子共组双水相体系中 的分配

高分子和正负离子表面活性剂混合物可形成一种新型双水相体系。研究蛋白质在溴化十二烷基三乙铵/十二烷基硫酸钠与聚氧乙烯(EO)-聚氧丙烯(PO)嵌段共聚物(EO~2~0PO~8~0)共组双水相体系中的分配。通过在高分子接上亲和配基,研究蛋白质在带有亲和配基高分子的双水相体系中的分配。将表面活性剂富集相稀释或加热高分子富集相,又可形成新的双水相体系,由此可进行蛋白质的多步分配。在蛋白质的分配完成之后,通过将表面活性剂富集相进一步稀释或将高分子富集相加热至高分子浊点以上可将表面活性剂和高分子与目标蛋白质分离。正负离子表面活性剂和高分子还可以循环使用。     

Investigation of the chiral surfactant N-dodecoxycarbonylvaline in electrokinetic chromatography: improvements in elution range and pH stability via mixed micelles and vesicles, and the hydrophobicity determination of basic pharmaceutical drugs

The chiral surfactant dodecoxycarbonylvaline (DDCV) has proven to be an effective pseudostationary phase for the separation of many enantiomeric pharmaceutical compounds. In this study the elution range and the prediction of octanol-water partitioning for the DDCV micellar system was examined. Through incorporation of DDCV in mixed micelles and unilamellar vesicles, enhancement of the elution range was observed. The mixed micelles contained a second anionic surfactant, sodium dodecyl sulfate (SDS), while the vesicles were composed of DDCV and the cationic surfactant cetyltrimethylammonium bromide (CTAB). Enantioselectivity, as well as other chromatographic and electrophoretic parameters, were compared between the mixed micelles, vesicles, and DDCV micelles. The hydrophobicity of the DDCV system was also evaluated as a predictor of n-octanol-water partition coefficients for 15 beta amino alcohols. The correlation between the logarithm of the retention factor (log k) and log P(ow) for seven hydrophobic beta-blockers and eight beta-agonists were r2 = 0.964 and r2 = 0.814, respectively.     

Phase equilibrium and insulin partitioning in aqueous two-phase systems containing block copolymers and potassium phosphate

In this work, phase diagrams of aqueous two-phase systems (ATPS) containing PEO–PPO–PEO block copolymers and potassium phosphate as well as the partitioning behavior of insulin in these systems are presented. Experiments aimed at the identification of the effects of copolymer structure (by varying the number of EO units per polymer molecule), temperature (283.15 and 298.15 K) and pH (5.0 and 7.0) on the phase behavior of these systems were carried out. The results indicated the enlargement of the two-phase region upon increasing the temperature, pH and copolymer hydrophobicity (expressed as the PO/EO ratio in the copolymer molecule). Experimental measurements of the partitioning of human insulin in these ATPS also indicated the dependency of the partition coefficients on temperature, pH, and copolymer hydrophobicity, with the latter being the most influential factor. Finally, experimental data on the phase behavior and insulin partitioning were correlated using an excess Gibbs energy virial-type model modified in order to account for coulombic interactions and ionization equilibrium between the various forms of the phosphate ion.     

Effect of ionic micellar medium on kinetics and mechanism of oxidation of bovine serum albumin: A pulse radiolysis study

Effect of protein–micelle interaction on bovine serum albumin (BSA) oxidation by trichloromethyl peroxyl radical (CCl₃O₂^·) in anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethyl ammonium bromide (CTAB) micellar media has been studied using nanosecond pulse radiolysis technique. Viscosity measurement and light scattering studies have suggested that SDS and CTAB micelles produce BSA–micelle aggregates of different sizes and polydispersity. Oxidation kinetics and transients have been affected both by anionic SDS and cationic CTAB micelles but in a different manner. Tryptophanyl-CCl₃O₂^· adduct radical to tyrosyl radical transformation in BSA has been observed in anionic SDS micelles but not in cationic CTAB micelles. Similar studies have also been done with tryptophan and tyrosine amino acids, which undergo oxidation in BSA. The study suggests that Coulombic and hydrophobic interactions between micelles and protein affect the structure of the protein to shield its functional amino acids, like tryptophan and tyrosine, to neutral oxidizing radical.     

A new model to study the phase transition from microstructures to nanostructures in ionic/ionic surfactants mixture

The phase behavior and aggregate structures of mixtures of the oppositely charged surfactants cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) are explored at high dilution by pulsed field gradient stimulated echo (PFG-STE) NMR. The aggregation numbers and hydrodynamic radii of vesicles and mixed micelles were determined by a combination of viscosity and self-diffusion coefficient measurements. The average size of the mixed micelles was larger than that of micelles containing uniformly charged head groups. Analysis of the variations of the self-diffusion coefficient and viscosity with changing concentration of CTAB or SDS in the cationic-rich and anionic-rich regions revealed a phase transition from vesicles to mixed micelles. Differences in the lengths of the CTAB and SDS hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phase), and vesicles form spontaneously over a wide range of compositions in both cationic-rich and anionic-rich solutions. The results obtained from conductometry measurements confirmed this transition. Finally, according to the capacitor model, a new model was developed for estimating the surface potentials and electrostatic free energy (g(elec)). Then we investigated the variations of electrostatic and transfer free energy in phase transition between mixed micelle and vesicle.     

Microstructures of Aqueous Two‐Phase Systems Formed by Mixture of Polymer and Cationic‐Anionic Surfactants

Microstructure and phase behavior of decyltriethylammonium bromide (C₁₀NE)/sodium decylsulfonate (C₁₀SO₃)/poly(ethylene oxide) (PEO)/water quaternary systems were studied by freeze‐fracture transmission electron microscopy, small angle X‐ray diffraction, and dynamic light scattering methods. Aqueous two‐phase systems (ATPS) could be prepared by properly mixing the aqueous solution of PEO and equimolar mixed C₁₀NE and C₁₀SO₃. It was shown that the top phase of the ATPS was surfactant‐enriched and mainly composed of multi‐lamellar structure, while the bottom phase of the ATPS was polymer‐enriched in which some vesicles were observed.     

Characterization of surfactant and phospholipid vesicles for use as pseudostationary phases in electrokinetic chromatography

The physical, electrophoretic and chromatographic properties (mean diameter, electroosmotic flow, electrophoretic mobility, elution range, efficiency, retention, and hydrophobic, shape, and chemical selectivity) of three surfactant vesicles and one phospholipid vesicle were investigated and compared to a conventional micellar pseudostationary phase comprised of sodium dodecyl sulfate (SDS). Chemical selectivity (solute-pseudostationary phase interactions) was discussed from the perspective of linear solvation energy relationship (LSER) analysis. Two of the surfactant vesicles were formulated from nonstoichiometric aqueous mixtures of oppositely charged, single-tailed surfactants, either cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) in a 3:7 mole ratio or octyltrimethylammonium bromide (OTAB) and SDS in a 7:3 mole ratio. The remaining surfactant vesicle was comprised solely of bis(2-ethylhexyl)sodium sulfosuccinate (AOT) in 10% v/v methanol, and the phospholipid vesicle consisted of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and phosphatidyl serine (PS) in 8:2 mole ratio. The mean diameters of the vesicles were 76.3 nm (AOT), 86.9 nm (CTAB/SOS), 90.1 nm (OTAB/SDS), and 108 nm (POPC/PS). Whereas the coefficient of electroosmotic flow (10(-4) cm2 V(-1) s(-1)) varied considerably (1.72 (OTAB/SDS), 3.77 (CTAB/SOS), 4.05 (AOT), 5.26 (POPC/PS), 5.31 (SDS)), the electrophoretic mobility was fairly consistent (-3.33 to -3.87 x 10(-4) cm2 V(-1) s(-1)), except for the OTAB/SDS vesicles (-1.68). This resulted in elution ranges that were slightly to significantly larger than that observed for SDS (3.12): 3.85 (POPC/PS), 8.6 (CTAB/SOS), 10.1 (AOT), 15.2 (OTAB/SDS). Significant differences were also noted in the efficiency (using propiophenone) and hydrophobic selectivity; the plate counts were lower with the OTAB/SDS and POPC/PS vesicles than the other pseudostationary phases (< or = 75,000/m vs. > 105,000/m), and the methylene selectivity was considerably higher with the CTAB/SOS and OTAB/SDS vesicles compared to the others (ca. 3.10 vs. < or = 2.6). In terms of shape selectivity, only the CTAB/SOS vesicles were able to separate all three positional isomers of nitrotoluene with near-baseline resolution. Finally, through LSER analysis, it was determined that the cohesiveness and hydrogen bond acidity of these pseudostationary phases have the greatest effect on solute retention and selectivity.     

Protein partitioning in thermoseparating systems of a charged hydrophobically modified ethylene oxide polymer

The phase behavior of a thermoseparating cationic hydrophobically modified ethylene oxide polymer (HM-EO) containing tertiary amines has been investigated at different pH, salt and sodium dodecyl sulfate (SDS) concentrations, in order to find a water/HM-EO two-phase system suitable for protein partitioning. The used polymer forms micellar aggregates that can be charged. By changing pH and SDS concentrations the netcharge of the SDS/HM-EO aggregate can be shifted from positive to negative. Bovine serum albumin (BSA) and lysozyme were partitioned in the thermoseparated two-phase systems of the cationic polymer at different pH, salt and SDS concentrations. The dominant attractive interactions between the polymer aggregates and the studied proteins were shown to be of electrostatic (Coulomb) nature rather than hydrophobic interaction. At low ionic strength the positively charged polymeric aggregates attracted negatively charged BSA and repelled positively charged lysozyme. Upon addition of SDS the negatively charged aggregates attracted lysozyme and repelled BSA. Thus, it was possible to direct proteins with different charges to the polymeric phase and redirect them to a polymer-depleted phase by changing the netcharge of the polymeric aggregates. The effect of different salts on the partitioning of BSA in a system of slightly positively charged HM-EO was studied. NaCl and KBr have a significant effect on driving the BSA to the polymer-depleted phase, whereas KF and K2SO4 have a smaller effect on the partitioning. The cloud point temperature of the charged polymer decreased upon addition of SDS near the isoelectric molar ratio of SDS to polymer and also upon salt addition. In the latter case the decrease was smaller than expected from model calculations based on Flory-Huggins theory, which were performed for a charged thermoseparating polymer at different charges and salt concentrations.     

Aqueous two-phase systems for protein separation: a perspective

Aqueous two-phase systems (ATPS) that are formed by mixing a polymer (usually polyethylene glycol, PEG) and a salt (e.g. phosphate, sulphate or citrate) or two polymers and water can be effectively used for the separation and purification of proteins. The partitioning between both phases is dependent on the surface properties of the proteins and on the properties of the two phase system. The mechanism of partitioning is complex and not very easy to predict but, as this review paper shows, some very clear trends can be established. Hydrophobicity is the main determinant in the partitioning of proteins and can be measured in many different ways. The two methods that are more attractive, depending on the ATPS used (PEG/salt, PEG/polymer), are those that consider the 3-D structure and the hydrophobicity of AA on the surface and the one based on precipitation with ammonium sulphate (parameter 1/m*). The effect of charge has a relatively small effect on the partitioning of proteins in PEG/salt systems but is more important in PEG/dextran systems. Protein concentration has an important effect on the partitioning of proteins in ATPS. This depends on the higher levels of solubility of the protein in each of the phases and hence the partitioning observed at low protein concentrations can be very different to that observed at high concentrations. In virtually all cases the partition coefficient is constant at low protein concentration (true partitioning) and changes to a different constant value at a high overall protein concentration. Furthermore, true partitioning behavior, which is independent of the protein concentration, only occurs at relatively low protein concentration. As the concentration of a protein exceeds relatively low values, precipitation at the interface and in suspension can be observed. This protein precipitate is in equilibrium with the protein solubilized in each of the phases. Regarding the effect of protein molecular weight, no clear trend of the effect on partitioning has been found, apart from PEG/dextran systems where proteins with higher molecular weights partitioned more readily to the bottom phase. Bioaffinity has been shown in many cases to have an important effect on the partitioning of proteins. The practical application of ATPS has been demonstrated in many cases including a number of industrial applications with excellent levels of purity and yield. This separation and purification has also been successfully used for the separation of virus and virus-like particles.