Nonionic Micellar Systems Research Articles

On-line preconcentration of fluorescein derivatives of essential amino acids using sweeping in a nonionic micellar system

A rapid and effective method of nonionic micellar electrokinetic chromatography with laser-induced fluorescence detection and sweeping as an online preconcentration method was developed for the simultaneous determination of free essential amino acids in supplement formulations. The analytes were derivatized using fluorescein isothiocyanate isomer I dissolved in dimethyl sulfoxide. Optimal separation conditions were achieved using an uncoated fused silica capillary (40.0 cm effective length, 50.2 cm total length, 50 µm internal diameter), 20 mM Na2B4O7, (pH 9.3), 50 mM Brij-35, and 15% (v v-1) methanol as running buffer. Complete separation of all analytes was achieved within 15 min. The optimized method exhibited good linearity (r2 > 0.997), acceptable precision (1.3 – 12.4%), and accuracy (88 – 112%) in concentration range 20 – 1000 ng mL−1. The limit of detection was 6 ng mL−1. The method successfully determined the quantity of free essential amino acids in a dietary supplement containing spirulina.

Comparative interaction of an anionic dye, ponceau 4R with triple viz., anionic, non-ionic and cationic micellar systems: Spectral and conductometric analysis

In this work, the interaction of ponceau 4R dye (P4R) with triple viz., anionic, nonionic and cationic micellar systems has been studied. The three surfactants employed were nonionic pluronic L-64 (PL-64), anionic sodium dodecyl sulphate (SDS) and cationic cetyl trimethyl ammonium bromide (CTAB). All the three dye - surfactants systems were investigated through UV - visible spectroscopy, conductivity, FT-IR, pH effect and SEM studies. There was short and strong bonding between the dye and all the three types of micelles as observed from FT-IR studies. The conductivity studies displayed greater interaction with CTAB than with SDS. The free energy of micellization, ∆G was observed to be -16.07 kJ mol−1 for P4R+ CTAB and -13.83 kJ mol−1 for P4R + SDS, demonstrating greater spontaneity and stability of the former combination. This can be explained due to strong electrostatic attraction between negatively charged P4R dye and positively charged micelle of CTAB. Overall, the anionic ponceau 4R dye has been successfully incorporated into the nonionic, anionic and cationic micellar systems. This is probably the first report of interaction of a similarly charged dye and surfactant system.

Oxacillin antibiotic removal from aqueous solution using nonionic micellar system or ionic liquid: a comparative study based upon experimental optimization and response surface methodology

Oxacillin antibiotic was removed from aqueous effluents using the biodegradable nonionic surfactant Triton X-114 (TX-114) and the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im]PF6). The experimental results of oxacillin extraction from aqueous solution according to the surfactant (Xt) or ionic liquid (XIL) concentration and temperature (T) were expressed by the following parameters: antibiotic extraction extent (E%), remaining antibiotic concentration (Xs,w), residual surfactant (Xt,w) or ionic liquid (XIL,w) concentration in aqueous phase after extraction, and volume fraction of coacervate at equilibrium (ϕc). High extraction yields were reached under optimal conditions: 99% for TX-114 and 89% using [C4C1im]PF6. The concentration of antibiotic in effluent was reduced by about 7-fold and 6-fold using TX-114 and [C4C1im]PF6, respectively. Sodium sulfate addition (3 wt%) increased E% from 20% to 88% at only 2 wt% of TX-114. Finally, solute stripping from the micellar phase using Winsor II microemulsion extraction was investigated. Thereby, 90% of the TX-114 in the micelle-rich phase was separated into the organic phase (Om).

Control Over Diffusion of Ionic Ferrocene Species in Aqueous Solution Using Surfactant Based Organized Media

The study of diffusion of chemical species is a fascinating domain of current research. In this work, diffusion of ionic ferrocene derivatives, ferrocenecarboxylic acid (FCA) and (ferrocenylmethyl)-trimethylammonium bromide (FMTAB) has been studied in the aqueous solution of a cationic surfactant, cetyltrimethylammonium bromide, an anionic surfactant, sodium dodecyl sulfate and a non-ionic surfactant, polyethyleneglycolp-(1,1,3,3-tetramethylbutyl)-phenylether by cyclic voltammetric measurements. The voltammetric peak currents of FCA and FMTAB have been used to determine the apparent diffusion coefficients (Dapp) in the supramolecular surfactant systems. The presence of surfactant slowed the diffusion of FCA and FMTAB. The Dapp is fairly dependent on the concentration and type of surfactants. The lowest Dapp of FCA is obtained in cationic micellar system, whereas, FMTAB demonstrated lowest Dapp in anionic micellar solution. Both FCA and FMTAB maintained a moderate value of Dapp in presence of nonionic micellar system. It has been observed that both hydrophobic and electrostatic interactions of ferrocene species with surfactant systems determine the relative binding affinity and incorporation, which eventually controls the diffusivity. Electrochemical parameters, current and potential as well as UV-visible spectroscopic results have been used to comprehend the influence of the surfactant system on the solvated state of ionic solutes.

Easy Removal of Methylparaben and Propylparaben from Aqueous Solution Using Nonionic Micellar System

AbstractThis study aimed to investigate the simultaneous removal of methylparaben (MePB) and propylparaben (PrPB) from effluents (each one at 16 mg/L) using a nonionic micellar system containing Triton X-114. Response surface methodology (RSM) has been carried out. Extraction results using nonionic surfactant two-phase system were considered as a function of surfactant concentration and temperature variation. Four responses were investigated: MePB and PrPB extraction yield (E), solute (Xs,w) and surfactant (Xsf,w) concentrations in the aqueous phase and the volume fraction of micellar phase (ϕC) at equilibrium. Very high extraction efficiencies (99 % for PrPB and 84 % for MePB) were achieved at optimal conditions. Thereby, the amounts of PrPB and MePB were reduced 80 and 5 times, respectively. The extraction improvement using sodium sulfate was also shown. Finally, the solute stripping from micellar phase by pH change was proved.

Effect of electrolytes as adjuvants in GFP and LPS partitioning on aqueous two-phase systems: 2. Nonionic micellar systems

Abstract Lipopolysaccharide endotoxins (LPS) are the most common contaminant pyrogenic compounds found in intracellular recombinant biomolecules purified from Gram-negative bacteria, such as Escherichia coli. Thus, the purification downstream processing should guarantee the effective removal of LPS from the final bioproduct, particularly, therapeutic biopharmaceuticals. Aqueous two-phase micellar systems (ATPMS) appear to be an excellent strategy to purify recombinant biopharmaceuticals from the cell lysate of E. coli, reducing high LPS concentrations. In order to demonstrate the effectiveness of ATPMS as a biopharmaceutical purification platform, the influence of inorganic salt electrolytes (NaCl, Li2SO4, KI, or KNO3) on the partitioning of green fluorescent protein (GFP) and LPS removal using ATPMS composed of n-decyl tetraethylene oxide (C10E4) was evaluated. The impact of different LPS concentrations on GFP partitioning was also studied. The addition of electrolytes (i.e., NaCl or Li2SO4) to the C10E4-based ATPMS have reduced the phase forming temperatures to very mild conditions (ca. 17.00 and 13.00 °C, for NaCl and Li2SO4, respectively). The selective partitioning ability of the proposed ATPMS was further demonstrated, where a complete removal of the LPS from the micelle-poor phase (REMLPS > 98%) and a preferential GFP recovery (RECGFP = 97%, KGFP > 7) to the micelle-poor phase was obtained. The GFP partitioning was even enhanced by increasing LPS loading (104–106 EU/mL), probably due to the formation of mixed micelles between LPS and C10E4. It is here demonstrated that a C10E4/buffer + salt-based ATPMS can be a useful and straightforward platform for the removal of endotoxin contaminants and the purification of recombinant biopharmaceuticals from E. coli cell lysates.

Quantitative analysis of micellar effect on the reaction rate of alkaline fading of phenolphthalein

Quantitative treatment of the kinetic data of the reaction between phenolphthalein dianion and hydroxide ion in aqueous solutions containing variable concentration of various surfactants is presented. Following surfactants are used: Brij-35 (nonionic), sodium n-dodecyl sulfate (anionic), cetyltrimethylammonium bromide (cationic) and 3-(dimethyl-n-dodecylammonio)-propansulfonate (zwitterionic). The quantitative treatment is carried out basing of Piszkiewicz’s, Berezin’s, and Pseudophase Ion-Exchange (PIE) models. It is revealed that the Berezin’s model is a more applicable one for describing the effect of nonionic, anionic, and zwitterionic micellar systems. The values of the corresponding kinetic parameters are discussed. The effect of cetyltrimethylammonium hydroxide on the reaction is also examined and quantitatively described by the PIE model. The research of systems based on a cationic surfactant shows previously unknown effect called by us as “diverting influence”.

Partitioning of nitroxides in dispersed systems investigated by ultrafiltration, EPR and NMR spectroscopy

HypothesisThe partitioning behavior of paramagnetic nitroxides in dispersed systems can be determined by deconvolution of electron paramagnetic resonance (EPR) spectra giving equivalent results with the validated methods of ultrafiltration techniques (UF) and pulsed-field gradient nuclear magnetic resonance spectroscopy (PFG-NMR). ExperimentsThe partitioning behavior of nitroxides with increasing lipophilicity was investigated in anionic, cationic and nonionic micellar systems and 10wt% o/w emulsions. Apart from EPR spectra deconvolution, the PFG-NMR was used in micellar solutions as a non-destructive approach, while UF based on separation of very small volume of the aqueous phase. FindingsAs a function of their substituent and lipophilicity, the proportions of nitroxides that were solubilized in the micellar or emulsion interface increased with increasing nitroxide lipophilicity for all emulsifier used. Comparing the different approaches, EPR deconvolution and UF revealed comparable nitroxide proportions that were solubilized in the interfaces. Those proportions were higher than found with PFG-NMR. For PFG-NMR self-diffusion experiments the reduced nitroxides were used revealing a high dynamic of hydroxylamines and emulsifiers. Deconvolution of EPR spectra turned out to be the preferred method for measuring the partitioning behavior of paramagnetic molecules as it enables distinguishing between several populations at their individual solubilization sites.

The pseudo-ternary phase diagrams and properties of anionic–nonionic mixed surfactant reverse micellar systems

Reverse micelles have drawn attention of many research workers. However, most of the early efforts were focused on the single-phase reverse micelles. In this study, rhamnolipid, a kind of biosurfactant, was firstly tested to form a mixed reversed micellar systems with tween 80. The pseudo-ternary phase diagrams and the properties of this formed reverse micellar systems were investigated, and the catalytic activity of lignin peroxidase was explored. The results show that the phase diagram was sensitive to some critical factors, such as pH and ionic concentration. The properties electrical conductivity of mixed reverse micelles indicated that electrical conductivity increased with the increase of water concentration, and viscosity varied as function of water content in a non-monotonic way giving two peaked plot. The highest activity of lignin peroxidase was up to 350% in the appropriate conditions. The findings further provide theoretical knowledge that the pseudo-ternary systems can increase the potential of lignin peroxidase as catalysts for various oxidations.

TBP induced double cloud point in aqueous EO13PO30EO13 solutions: investigating the evolution of associated micellar characteristics as a function of temperature

TBP solubilized Pluronic L64 solutions exhibit inter-micellar attraction driven micellar cluster formation upon cooling, which is unique in non-ionic micellar systems.

Influence of salts on the coexistence curve and protein partitioning in nonionic aqueous two-phase micellar systems

Aqueous two-phase micellar systems (ATPMS) can be exploited in separation science for the extraction/purification of desired biomolecules. Prior to phase separation the surfactant solution reaches a cloud point temperature, which is influenced by the presence of electrolytes. In this work, we provide an investigation on the cloud point behavior of the nonionic surfactant C10E4 in the presence of NaCl, Li2SO4 and KI. We also investigated the salts' influence on a model protein partitioning. NaCl and Li2SO4 promoted a depression of the cloud point. The order of salts and the concentration that decreased the cloud point was: Li2SO4 0.5 M > NaCl 0.5 M ≈ Li2SO4 0.2 M. On the other hand, 0.5 M KI dislocated the curve to higher cloud point values. For our model protein, glucose-6-phosphate dehydrogenase (G6PD), partitioning experiments with 0.5 M NaCl or 0.2 M Li2SO4 at 13.85 ºC showed similar results, with K G6PD ~ 0.46. The lowest partition coefficient was obtained in the presence of 0.5 M KI (K G6PD = 0.12), with major recovery of the enzyme in the micelle-dilute phase (%Recovery = 90%). Our results show that choosing the correct salt to add to ATPMS may be useful to attain the desired partitioning conditions at more extreme temperatures. Furthermore, this system can be effective to separate a target biomolecule from fermented broth contaminants.

Probing the amphiphile micellar to hexagonal phase transition using Positron Annihilation Lifetime Spectroscopy

Positron Annihilation Lifetime Spectroscopy (PALS) has been utilised only sparingly for structural characterisation in self assembled materials. Inconsistencies in approaches to experimental configuration and data analysis between studies has complicated comparisons between studies, meaning that the technique has not provided a cohesive data set across the study of different self assembled systems that advance the technique towards an important tool in soft matter research. In the current work a systematic study was conducted using ionic and non-ionic micellar systems with increasing surfactant concentration to probe positron behaviour on changes between micellar phase structures, and data analysed using contemporary approaches to fit four component spectra. A characteristic orthopositronium lifetime (in the organic regions) of 3.5±0.2ns was obtained for the hexagonal phase for surfactants with C12 alkyl chains. Chemical quenching of the positron species was also observed for systems with ionic amphiphiles. The application of PALS has also highlighted an inconsistency in the published phase diagram for the octa(ethylene oxide) monododecyl ether (C12EO8) system. These results provide new insight into how the physical properties of micellar systems can be related to PALS parameters and means that the PALS technique can be applied to other more complex self-assembled amphiphile systems.

Ultrafast torsional dynamics in nanoconfined water pool: Comparison between neutral and charged reverse micelles

Abstract Photophysical properties and the ultrafast excited state torsional dynamics of an amyloid fibril sensing dye, Thioflavin-T, have been investigated in Triton X-100 reverse micelle as a function of water content. This study has been undertaken to comprehend the effect of interfacial charge on the ultrafast torsional dynamics of Thioflavin-T in nanoconfined reverse micellar system. The emission intensity and the fluorescence lifetime of Thioflavin-T increases considerably in the nonionic reverse micellar system as compared to bulk water indicating a strong confinement effect on the photophysical behavior of the probe. The photophysical parameters of Thioflavin-T in Triton X-100 reverse micelle is found to be almost invariant with the increasing water content, which is in sharp contrast to its behavior in ionic reverse micelles (Journal of Physical Chemistry 113 (2009) 8532, Chemical Communication 47 (2011) 6912). This behavior has been rationalized on the basis of the differences in the localization sites of the probe in the nonionic and ionic reverse micelles. Photophysical properties of Thioflavin-T in triethyleneglycol monomethyl ether, which mimic the interior of the Triton X-100 reverse micelle, at different water content also confirms the site of localization of the probe in the nonionic reverse micelle. Present result in combination with that reported in ionic reverse micelles suggest that the reaction dynamics of the probe in the nanoconfined water pools of reverse micelle are strongly influenced by interfacial charge, which in fact control the location of the probe in the reverse micellar systems.

Determination of Ni(II) with picolinaldehyde-4-phenyl-3-thiosemicarbazone used as a chromogenic reagent in a nonionic micellar system

Spectrophotometric determination of Ni(II) was carried out using picolinaldehyde-4-phenyl-3-thiosemicarbazone (PAPT) as a complexing/chromogenic reagent. The possibility of using a micellar system was explored to enhance the degree of detection and allow a more sensitive spectrophotometric method for the determination of nickel ions. The anionic surfactant Triton X-100 greatly enhanced the molar absorptivity and limit of detection relative to that observed with bulk water or an organic solvent. The linear calibration graphs were obtained for 0.5-2.0 mg L^{-1} and 0.001-1.0 mg L^{-1} of Ni(II) in aqueous and surfactant media, respectively. Using this approach, the limit of detection for the PAPT-Ni(II) complex (based on 3 \sigma of blank absorbance/slope) was found to be 0.0008 mg L^{-1} with a micellar enhancement reagent. The interference from over 50 cations, anions, and complexing agents was studied at 0.50 mg L^{-1} of Ni(II); most metal ions can be tolerated in considerable amounts in aqueous micellar solutions.

His‐tagged protein purification by metal‐chelate affinity extraction with nickel‐chelate reverse micelles

Di(2-ethylhexyl) phosphoric acid (HDEHP) was used as a transition metal ion chelator and introduced to the nonionic reverse micellar system composed of equimolar Triton X-45 and Span 80 at a total concentration of 30 mmol/L. Ni(II) ions were chelated to the HDEHP dimers in the reverse micelles, forming a complex denoted as Ni(II)R(2). The Ni(II)-chelate reverse micelles were characterized for the purification of recombinant hexahistidine-tagged enhanced green fluorescent protein (EGFP) expressed in Escherichia coli. The affinity binding of EGFP to Ni(II)R(2) was proved by investigation of the forward and back extraction behaviors of purified EGFP. Then, EGFP was purified with the affinity reverse micelles. It was found that the impurities in the feedstock impeded EGFP transfer to the reverse micelles, though they were little solubilized in the organic phase. The high specificity of the chelated Ni(2+) ions toward the histidine tag led to the production of electrophoretically pure EGFP, which was similar to that purified by immobilized metal affinity chromatography. A two-stage purification by the metal-chelate affinity extraction gave rise to 87% recovery of EGFP. Fluorescence spectrum analysis suggests the preservation of native protein structure after the separation process, indicating the system was promising for protein purification.

A metal‐chelate affinity reverse micellar system for protein extraction

A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X-45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X-45 less than 0.6, thermodynamically stable reverse micelles of water content (W(0)) up to 30 are formed. Di(2-ethylhexyl) phosphoric acid (HDEHP; 1-2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine-rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper-chelate reverse micelles (Cu-RM) are characterized for their W(0), hydrodynamic radius (R(h)), and aggregation number (N(ag)). Similar with reverse micelles of bis-2-ethylhexyl sodium sulfosuccinate (AOT), R(h) of the Cu-RM is also linearly related to W(0). However, N(ag) is determined to be 30-90 at W(0) of 5-30, only quarter to half of the AOT reverse micelles. Then, selective metal-chelate extraction of histidine-rich protein (myoglobin) by the Cu-RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine-tagged proteins expressed as inclusion bodies.

Do ionic and hydrophobic probes sense similar microenvironment in Triton X-100 nonionic reverse micelles?

Rotational diffusion of two structurally similar ionic probes, rhodamine 110 and fluorescein, has been examined in nonionic reverse micellar system of Triton X-100/benzene-n-hexane/water as a function of mole ratio of the water to surfactant, W. This study has been undertaken to find out whether ionic and hydrophobic probes experience similar microenvironment in these reverse micelles. Experimental results indicate that, from W=0 to 3, the average reorientation time, which is a measure of the microviscosity experienced by the probe molecule, increases by 90% and 40% for rhodamine 110 and fluorescein, respectively, and from W=3 to 8, it decreases by 20% for both the probes. The increase in the average reorientation time with W has been rationalized on the basis of the flexible oxyethylene chains of the TX-100 surfactant being hydrogen bonded by the water molecules, which makes the core region less fluid. However, once the hydration of the oxyethylene chains is complete, further addition of water results in formation of water droplet; which renders the micelle-water interface in the core region less compact leading to a marginal decrease in the average reorientation time of the probe molecules. These explanations are consistent with the location of the probes and the structure of the Triton X-100/benzene-hexane/water reverse micelles. To compare how the microenvironment experienced by these ionic probes is different from the hydrophobic ones, results from our earlier work [J. Phys. Chem. B 108, 7944 (2004)] have been considered. Such a comparison revealed that both ionic and hydrophobic probes experience similar microenvironment in these reverse micelles until the hydration of the oxyethylene chains is complete. In case of hydrophobic probes, however, the onset of water droplet formation does not alter their microenvironment, which is due to their location in the reverse micellar cores.

A Partition Equilibrium Study of Sulfonephthalein Dyes in Nonionic Surfactant Systems at High pH

The acid base equilibria of two sulfonephthalein dyes, viz., bromothymol blue (BTB) and bromocresol green (BCG) in aqueous nonionic micellar solutions of Triton X100, Tween 20, Tween 40, Tween 60 and Tween 80 have been investigated spectroscopically using a partition equilibrium method. A red shift in the λ max of the visible absorption band corresponding to the base forms of the dyes with increase in surfactant concentration was observed at and above pH 9.0. For a particular dye-surfactant system the red shift increases with the increase in pH and was found to be greater for TX 100 than for the Tween surfactants. Red shift of the λ max of BTB was observed to be greater than that of BCG in all of the nonionic micellar systems investigated in buffered medium. The observed red shift has been attributed to stabilization of the base form of the dye by the polyoxyethylene (POE) head groups. The stabilization effect was found to decrease with increase in the number of carbon atom and unsaturation in the hydrophobic tail of the surfactant molecules. The equilibrium constant of the partition of the dyes between micellar and aqueous pseudophases (K ass ) was found to be greater for the more hydrophobic BTB than the less hydrophobic BCG. With the surfactants the K ass increases in the order Tween 80 < Tween 60 < Tween 40 < Tween 20 < TX 100. The pK a2 of the dyes were predicted using a partition equilibrium model and found to be in good agreement with the experimental values.

Bioseparations in Aqueous Micellar Systems Based on Excluded-Volume Interactions

Protein partitioning based on micellar-induced excluded-volume interactions is studied for different aqueous nonionic micellar systems. In particular, protein partitioning in the traditional aqueous micellar two-phase system is compared with a system where a gel phase is combined with a micellar phase and with a membrane system with micelles at the feed side of the membrane. A two-phase system is created using cylindricallyshaped n -decyl tetra(ethylene oxide) (C 10 E 4 ) micelles that are too large to diffuse into the gel-bead or across the membrane. Results are reported for the partition coefficient of single-component protein systems with myoglobin, ovalbumin, and BSA, and for binary protein mixtures. The individual protein partition coefficients in the mixtures follow the same protein concentration dependence as the partition coefficient obtained for the singlecomponent protein solutions.

Activity and Stability of Catalase in Nonionic Micellar and Reverse Micellar Systems

Catalase activity and stability in the presence of simple micelles of Brij 35 and entrapped in reverse micelles of Brij 30 have been studied. The enzyme retains full activity in aqueous micellar solution of Brij 35. Catalase exhibits "superactivity" in reverse micelles composed of 0.1 M Brij 30 in dodecane, n-heptane or isooctane, and significantly lowers the activity in decaline. The incorporation of catalase into Brij 30 reverse micelles enhances its stability at 50 degrees C. However, the stability of catalase incubated at 37 degrees C in micellar and reverse micellar solutions is lower than that in homogeneous aqueous solution.