Aqueous Micellar Systems Research Articles

Micelle-Assisted C(sp2)-H Functionalization for C-Se and C-X Bond Formation in the Aqueous Medium.

An environmentally sustainable, versatile, and cost-effective approach for C-Se and C-X (X = I, Br, and Cl) bond formation through C-H functionalization assisted by micellar catalysis in water is developed. The reaction utilizes a minimum amount of diorganyl diselenides and potassium halides for the respective functionalizations. The present protocol was suitable for scale-up synthesis, which directly provided the desired selenylated products without the need for chromatographic purification, in sufficient purity. The aqueous micellar catalysis system was reusable for up to 5 reaction cycles without compromising the reaction yield.

Investigating aqueous micellar systems enhancement tools for a sensitive spectrofluorimetric determination of anti-TB: Rifampicin.

Rifampicin is a frontline antibiotic in the management of tuberculosis. Since no spectrofluorimetric methods are reported for this drug, this approach was challenged to craft a sensitive, reliable, valid, fast, and green methodology. In recent years, fluorescence spectroscopy has received a lot of interest. Its benefits include ecological greenness and analytical performance. The pharmaceutical industries greatly like this approach because of its low energy and decreased solvent usage, which make it both economical and environmentally friendly. This methodology was based on utilizing the enhanced native fluorescence of the rifampicin at 341 nm after excitation at 241 nm in a beta-cyclodextrin micellar system. Modern developments in analytical chemistry have been applied to reduce risks to the workplace and environment by using distilled water as a dilution solvent for method application and optimization. The method was found excellent green with 97 eco-scale and 0.86 AGREE scores besides an 89.6 overall whiteness score. The range of linearity for rifampicin raw material was 0.2-1.5μg·mL-1, and the average recoveries for raw material and spiked plasma were 100.15% and 99.64%, respectively. The suggested technique worked well for the commercial oral syrup of Rimactane® and did not conflict with any common additives.

Biotransformation of t-butyl phenols by micellar nanoreactors of peroxidase/ionic surfactants at mild conditions: nanobiocatalyst performance and kinetic analysis

Recently, some bulk reaction media were substituted by micellar systems. Micellar media can be created by different types of surfactants which generate micellar nanoreactors for diverse reactions. Ionic surfactants can be used as aqueous micellar systems, providing mild conditions for the specified reactions. Ionic surfactants: sodium dodecyl sulfate, sodium decyl sulfate (SDeS), sodium octyl sulfate (SOS), n-dodecyl trimethyl ammonium bromide, and cetyltrimethylammonium bromide were used to prepare aqueous micellar and entrapped peroxidase nanoreactors as biocatalysts. Oxidative coupling reactions were investigated for a series of phenolic hydrogen donors including 2-tert-butyl phenol, 4-tert-butyl phenol, and 2,4-tert-butyl phenol catalyzed by micellar nanoreactors of horseradish peroxidase (HRP) with hydrogen peroxide and/or tert-butyl peroxide as oxidants. Higher oxidation reaction rates were obtained for 2-tert-butylphenol and 4-tert-butylphenol with hydrogen peroxide in 90 mM SDeS (SDeS90) and 150 mM SOS (SOS150) nanoreactors, respectively. Among the micellar nanoreactors studied, the SDeS90 nanoreactor showed excellent protection of the enzyme against the peroxide inactivation effect. The long-term activity of the HRP/SDeS90 nanobiocatalyst was related to the gradual diffusion of peroxide into the nanoreactor. The biocatalytic kinetic parameters: V max, k cat, catalytic efficiency, and suicide-peroxide inactivation rate constants were determined for HRP/SDeS90. Reactions were carried out successfully under mild conditions in the micellar nanoreactors. Results confirmed that substituted functional groups on the benzene ring affect the oxidative reaction routes and products. Excellent protection of the enzyme, enhanced biocatalytic parameters, higher selectivity, and yield, in the peroxidative coupling of alkylphenols, reveal the high potential of such micellar nanoreactors for diverse organic synthesis and biotransformation.

Dynamic Phosphorus: Thiolate Exchange Cascades with Higher Phosphorothioates

AbstractIn this study, we introduce phosphorus, a pnictogen, as an exchange center for dynamic covalent chemistry. Cascade exchange of neutral phosphorotri‐ and ‐tetrathioates with thiolates is demonstrated in organic solvents, aqueous micellar systems, and in living cells. Exchange rates increase with the pH value, electrophilicity of the exchange center, and nucleophilicity of the exchangers. Molecular walking of the dynamic phosphorus center along Hammett gradients is simulated by the sequential addition of thiolate exchangers. Compared to phosphorotrithioates, tetrathioates are better electrophiles with higher exchange rates. Dynamic phosphorotri‐ and ‐tetrathioates are non‐toxic to HeLa Kyoto cells and participate in the dynamic networks that account for thiol‐mediated uptake into living cells.

Dynamic Phosphorus: Thiolate Exchange Cascades with Higher Phosphorothioates.

In this study, we introduce phosphorus, a pnictogen, as an exchange center for dynamic covalent chemistry. Cascade exchange of neutral phosphorotri- and -tetrathioates with thiolates is demonstrated in organic solvents, aqueous micellar systems, and in living cells. Exchange rates increase with the pH value, electrophilicity of the exchange center, and nucleophilicity of the exchangers. Molecular walking of the dynamic phosphorus center along Hammett gradients is simulated by the sequential addition of thiolate exchangers. Compared to phosphorotrithioates, tetrathioates are better electrophiles with higher exchange rates. Dynamic phosphorotri- and -tetrathioates are non-toxic to HeLa Kyoto cells and participate in the dynamic networks that account for thiol-mediated uptake into living cells.

Origin of steady state stress fluctuations in a shear-thinning worm-like micellar system

Large, irregular stress fluctuations under a constant applied shear rate are observed during the flow of dilute worm-like micellar solutions even at low Reynolds numbers. Statistical properties of such fluctuations showing signatures of chaos and elastic turbulence have been studied extensively. Although the mechanisms like boundary slippage, dynamics of shear band interface, time-dependent secondary flows, and inertio-elastic effects are conceived as the possible factors for such striking flow properties, their contributions in different non-linear flow regimes remain poorly understood. Here, we study the Taylor–Couette flow of a well-characterized aqueous worm-like micellar system formed by 2 wt. % cetyltrimethylammonium tosylate and 100 mM sodium chloride (2 wt. % CTAT + 100 mM NaCl). For a fixed applied shear-rate just beyond the onset of shear-thinning, high-speed optical imaging in the flow-gradient plane reveals spatiotemporally varying velocity gradients in the system. In this regime, the magnitude of stress fluctuations remains insignificant. However, the fluctuation becomes substantial beyond a critical shear rate deep inside the non-linear regime of the flow curve when significant free-surface undulations, sustained stick-slip, and elastic recoil events are observed. Imaging in the flow-vorticity and the gradient-vorticity plane indicates that such dynamics are primarily driven by the elasticity-induced turbulent flows in the system. Furthermore, in this regime, we find that the characteristic persistent time of stress fluctuations matches well with the time scales of the stick-slip events, as well as the micellar breaking time, indicating a possible connection between the striking stress dynamics and the micellar kinetics.

Ferric heme b in aqueous micellar and vesicular systems: state-of-the-art and challenges.

Ferric heme b (= ferric protoporphyrin IX = hemin) is an important prosthetic group of different types of enzymes, including the intensively investigated and widely applied horseradish peroxidase (HRP). In HRP, hemin is present in monomeric form in a hydrophobic pocket containing among other amino acid side chains the two imidazoyl groups of His170 and His42. Both amino acids are important for the peroxidase activity of HRP as an axial ligand of hemin (proximal His170) and as an acid/base catalyst (distal His42). A key feature of the peroxidase mechanism of HRP is the initial formation of compound I under heterolytic cleavage of added hydrogen peroxide as a terminal oxidant. Investigations of free hemin dispersed in aqueous solution showed that different types of hemin dimers can form, depending on the experimental conditions, possibly resulting in hemin crystallization. Although it has been recognized already in the 1970s that hemin aggregation can be prevented in aqueous solution by using micelle-forming amphiphiles, it remains a challenge to prepare hemin-containing micellar and vesicular systems with peroxidase-like activities. Such systems are of interest as cheap HRP-mimicking catalysts for analytical and synthetic applications. Some of the key concepts on which research in this fascinating and interdisciplinary field is based are summarized, along with major accomplishments and possible directions for further improvement. A systematic analysis of the physico-chemical properties of hemin in aqueous micellar solutions and vesicular dispersions must be combined with a reliable evaluation of its catalytic activity. Future studies should show how well the molecular complexity around hemin in HRP can be mimicked by using micelles or vesicles. Because of the importance of heme b in virtually all biological systems and the fact that porphyrins and hemes can be obtained under potentially prebiotic conditions, ideas exist about the possible role of heme-containing micellar and vesicular systems in prebiotic times.

Production of soy protein concentrate with the recovery of bioactive compounds: From destruction to valorization

This work aimed to develop a novel methodology based on aqueous micellar systems (AMS), for producing soy protein concentrates (SPC) from soybean flour and recovering high-valuable bioactive compounds as by-products. Ethoxylated aliphatic alcohols Tergitol 15-S-7 and Tergitol 15-S-9, non-toxic and biodegradable surfactants, were selected to form the AMS. The methodology consisted of an extractive stage of soybean flour with AMS, which rendered both a pellet, i.e., the SPC, and a supernatant containing the extracted bioactive compounds. The latter was further heated above the cloud point temperature, thus resulting in a biphasic system formed by a micelle-rich phase (MP) and an aqueous phase (AP). Obtained SPC showed a noticeable loss (∼90%) of trypsin inhibitor activity, a total protein content close to 60%, soluble protein amounts varying from 19% to 34%, and remarkable released (by simulated digestion) antioxidant and antihypertensive activities. Those indicators are similar to or even better than those corresponding to SPC from the classical acid-extraction method. The AMS also exhibited an enhanced efficiency for extracting antinutrients such as non-digestible oligosaccharides, trypsin inhibitors, and lectins mostly recovered at the AP and separated from isoflavones, which were concentrated and isolated at the MP. The recovery of all the mentioned bioactive compounds, whether beneficial or undesirable, broadens their uses in research, food, and pharmacological fields.This successful performance, simplicity, scalability, and sustainability make the proposed AMS-based extraction a powerful tool for processing plant derivatives and valorizing their by-products.

Recovery of acid proteases from fishery discards with aqueous micellar two-phase systems and their use for X-ray film recycling

The continuous expansion of fish production results in increasing amounts of discards, i.e. viscera, skin and frame, whose inappropriate disposal causes environmental damage. Conversion of this waste into value-added products is one of the best alternatives to reduce the pollution problem. The feasibility of using aqueous micellar two-phase systems (AMTPS), formed by biodegradable Genapol X-080 (GX-080) and sodium citrate, to recover valued acid proteases from surubí (Pseudoplatystoma sp) fishery discards was evaluated for the first time. The effects of biomass load, pH and surfactant concentration on the extraction were analyzed using a two-level full factorial design. GX-080 concentration and biomass load were the most significant factors (p < 0.05). AMTPS formed by GX-080 4% w/w showed a successful performance for the recovering of 69% of AP from the crude extract in the surfactant-rich phase with a purification factor of 1.83. Regard to the storage stability, this extract conserved at least 89% of its proteolytic activity for 76 days at 0 °C. It also showed a notable hydrolyzing activity of the gelatin-silver coating of used X-ray films, thus opening new perspectives on the use of acid proteases for recycling purposes.

Cloud point extraction based on non-ionic surfactants: An ecofriendly tool for recovering papain from papaya latex

The potential use of cloud point extraction with aqueous micellar two-phase systems (AMTPS), formed by the non-ionic biodegradable surfactants Triton X-114 (TX-114) and Genapol X-080 (GX-080), to recover papain (PAP) from fresh papaya latex was evaluated. Binodal curves obtained for both surfactants, in absence and presence of PAP, showed cloud points below 40 °C, the PAP presence slightly favoring the phase separation phenomenon. Partitioning experiments showed that PAP migrated toward the micelle-poor phase independently of the surfactant and the working temperature assayed, this behavior being consistent with this enzyme hydrophilic character. PAP recoveries of over 60% in the poor-micelle phase were obtained when partitioned fresh papaya latex in both surfactant-based AMTPS. TX-114 systems (4.00% w/w, 33 °C) allowed recovering 66% of PAP with a purification factor of 4.6. On GX-080 systems (4.00% w/w, 42 °C) a yield of 78% PAP and a purification factor of 3.7 were achieved. This AMTPS also allowed the separation of PAP from reducing sugars present in papaya latex. These results show that TX-114 and GX-080-based AMTPS could be potentially used as simple and economical tools at recovering PAP from papaya latex.

A novel method based on saponification coupled to micelle-extraction for recovering valuable bioactive compounds from soybean oil deodorizer distillate

The feasibility of using saponification coupled to extraction with mixed micellar systems to recover bioactive compounds from soybean oil deodorizer distillate, was evaluated for the first time. Under the selected conditions, saponification with KOH 0.6 M and aqueous micellar system prepared with Tergitol 15-S-7 9% w/w, rhamnolipids 0.25 %w/w and sodium citrate 100 mM pH 5.00, at 65 °C, allow the recovery of almost 100% of α- and δ- tocopherols, and 90% of γ-tocopherols. LC-MS measurements demonstrated that the final extract also contained phytosterols and squalene. Additionally, the obtained extract preserved about 100% of the total antioxidant activity. This result was attributable to the fact that 93% of the tocopherols recovered in the micellar phases resulted to be associated with surfactant micelles, environment that is known to improve their antioxidant capacity. These results open perspectives to the use of this methodology to extract these valuable compounds from complex oily sources.

Purification of immunoglobulin Y from egg yolk using thermoresponsive aqueous micellar two-phase systems comprising ionic liquids

Immunoglobulin Y (IgY) represents an important class of antibodies, being present in egg yolk, with relevant medical applications and involving non-invasive methods of extraction. However, due to the complexity of egg yolk, the purification levels required for use in most medical applications demands the application of multi-step and cost-intensive techniques. Therefore, it is of upmost importance to develop a biocompatible and cost-effective downstream process to purify IgY from egg yolk. In this work, IgY was purified from the egg yolk water-soluble protein fraction (WSPF) by the application of thermoresponsive aqueous micellar two-phase systems (AMTPS) composed of the non-ionic surfactant Triton X-114 and surface-active ionic liquids (SAILs) as co-surfactants. The best thermoresponsive systems allowed, in a single step, to recover IgY in the surfactant-poor phase with a purity level of 69%, and up to 73% if consecutive extraction cycles are performed, while maintaining the structural integrity of the antibodies. Considering these results, a downstream process was designed and proposed, consisting of four main steps: (i) recovery of the WSPF; (ii) purification of IgY by applying AMTPS; (iii) isolation of the IgY from the main solvents using an ultrafiltration step; (iv) recycling of the AMTPS phase-forming components by precipitating the contaminant proteins.

Polyether‐Based Diblock Terpolymer Micelles with Pendant Anthracene Units—Light‐Induced Crosslinking and Limitations Regarding Reversibility

Front Cover: Article number 2100485 by Felix H. Schacher and co-workers describes the preparation of polyether-based, amphiphilic diblock terpolymers with pendant anthracene units. The crosslinking of these units via light-induced [4+4]-cycloaddition is studied using UV-vis and NMR spectroscopy. The article further explains the limited reversibility of the reaction if applied in aqueous micellar systems.

Unusual Growth and Hydration Characteristics of Oil Solubilized Micelles in Aqueous Pluronic Systems.

Lipophile induced modulations of self-assembly characteristics in aqueous Pluronic systems merit attention because of wide-ranging uses of Pluronics as solubilizing agents of lipophilic substances. In this paper, we report unusual evolutions of structural and hydration properties in lavender essential oil (LO) solubilized Pluronic P85 aqueous micellar systems as a function of micellar volume fraction and temperature. Our DLS, SANS, and viscometry studies show that the spherical-to-wormlike micellar structural transition observed in 1% P85 solutions upon solubilization of LO quite unexpectedly gets suppressed with increased P85 concentration to ≥5%. Detailed SANS studies reveal that the core sizes of the oil solubilized micelles cannot attain the threshold value required for the onset of structural transition at higher copolymer concentrations due to their progressive shrinking with an increase in P85 concentration. Oil solubilized P85 solutions show two cloud points and very interestingly exhibit micellar growth upon cooling to their lower cloud points. Steady state fluorescence studies explain this based on increasing dehydration of micellar corona with a decrease in temperature, very much opposite to what is observed in pure aqueous Pluronic systems. The results give new insight into viscous flow properties and low temperature storage possibilities of oil solubilized aqueous Pluronic systems.

Chromogenic chemodosimeter based on a silylated azo compound detects cyanide in water and cassava

A novel silylated azo compound was synthesized and fully characterized. This compound was used in a chromogenic chemodosimeter approach for the highly selective detection of cyanide (CN–) in acetonitrile/water and in an aqueous micellar system. The anion breaks the Si–O bond, delivering a dye and causing a change in the color of the solution (from yellow to blue). The chemodosimeter was employed for the naked–eye and quantitative detection of CN– in tap water and cassava roots.

Effect of dicationic ionic liquids on cloud points of tergitol surfactant and the formation of aqueous micellar two-phase systems

A cloud point evaluation was performed for the nonionic surfactant Tergitol 15-S-7 in aqueous solutions of McIlvaine buffer (pH 7.0). Cloud point temperatures of the selected nonionic surfactant were studied in relation to the effect that the addition of dicationic ionic liquids (ILs) had on the systems. The dicationic ILs with different alkyl spacer lengths were derived from 1, n-bis(3-methylimidazolium-1-yl)alkane bromide ([BisAlk(MIM)2][2Br]) — in which Alk = But, Hex, Oct, and Dec. The dicationic ILs with longer alkyl spacer chains (Alk ≥ 6) led to an increase in the Tergitol’s cloud point values, due to their ability to fold their structures in solution, which increase the interactions of ILs with tergitol in the mixed micelles. This increase was even more pronounced when the concentration of the dicationic ILs was increased. Furthermore, the addition of dicationic ILs increased the micelles size; however, the hydrodynamic diameter of mixed micelles did not depend on the length of the ILs’ alkyl spacer chains. The Tergitol/IL systems with lower critical micellar concentration values will result in higher cloud point values, due to the greater colloidal dispersion stability.

Using coarse-grained molecular dynamics to understand the effect of ionic liquids on the aggregation of Pluronic copolymer solutions.

This study is aimed to enhance the understanding of the interaction between ionic liquids (ILs) and non-ionic Pluronic triblock copolymers in aqueous two-phase micellar systems (ATPMS) used for the selective separation/purification of hydrophobic biomolecules. The ILs allow a precise control of the cloud point phase separation temperature (CPT), particularly important when the stability of the molecule is highly dependent on temperature. The effect of choline-based ILs, with two different counter-anions, chloride and hexanoate, was evaluated using molecular dynamics simulations (MD) for F-68 and L-35 Pluronic aqueous solutions. The simulations revealed the role played by the anions during the Pluronic self-assembly, with choline chloride hindering Pluronic aggregation and the choline hexanoate favouring micelle formation and coalescence, in agreement with the experimental data. A detailed study of the accessible surface area of Pluronic showed a progressive dehydration of the Pluronic hydrophilic micelle corona in choline hexanoate mixtures promoting inter-micelle interactions and, consequently, micelle coalescence. With the addition of choline hexanoate, it was observed that the hydrophilic segments, which form the micelle corona, twisted towards the Pluronic micelle core. The electrostatic interaction is also shown to play a key role in this IL-Pluronic aqueous solution, as the hexanoate anions are accommodated in the Pluronic micelle core, while the choline cations are hosted by the Pluronic micelle corona, with the ions interacting with each other during the self-assembly process. In addition, a comparison study of F-68 and L-35 aqueous solutions shows that the IL impact depends on the length of the Pluronic hydrophilic segment. This work provides a realistic microscopic scenario of the complex interactions between Pluronic copolymers and ILs.

Feasibility of packed columns for continuous cloud point extraction with subsequent product recovery

In this work the feasibility of continuous cloud point extraction in packed columns was evaluated. Therefore, extraction of phenylacetic acid with aqueous micellar two-phase systems containing the nonionic surfactant Triton X-114 was chosen as a model system. Raschig rings and structured packing CY from Sulzer were evaluated in terms of HETP, extraction efficiency and enrichment factor. Additionally, the product recovery from the micellar phase was addressed. Back-extraction via pH-shift and adsorption were evaluated to remove phenylacetic acid from the micellar phase, whereas the successful continuous back-extraction in a Kühni column was demonstrated. Finally, several process concepts to recycle the micellar phase and to further purify phenylacetic acid after back-extraction are suggested.

Development of a Microfluidic Platform for R-Phycoerythrin Purification Using an Aqueous Micellar Two-Phase System.

Temperature-dependent aqueous micellar two-phase systems (AMTPSs) have recently been gaining attention in the isolation of high-added-value biomolecules from their natural sources. Despite their sustainability, aqueous two-phase systems, and particularly AMTPSs, have not been extensively applied in the industry, which might be changed by applying process integration and continuous manufacturing. Here, we report for the first time on an integrated microfluidic platform for fast and low-material-consuming development of continuous protein purification using an AMTPS. A system comprised of a microchannel incubated at high temperature, enabling instantaneous triggering of a two-phase system formation, and a microsettler, allowing complete phase separation at the outlets, is reported here. The separation of phycobiliproteins and particularly the purification of R-phycoerythrin from the contaminant proteins present in the aqueous crude extract obtained from fresh cells of Gracilaria gracilis were thereby achieved. The results from the developed microfluidic system revealed that the fractionation performance was maintained while reducing the processing time more than 20-fold when compared with the conventional lab-scale batch process. Furthermore, the integration of a miniaturized ultrafiltration module resulted in the complete removal of the surfactant from the bottom phase containing R-phycoerythrin, as well as in nearly twofold target protein concentration. The process setup successfully exploits the benefits of process intensification along with the integration of various downstream processes. Further transfer to a meso-scale integrated system would make such a system appropriate for the separation and purification of biomolecules with high commercial interest.

Amphiphilic copolymer aqueous solutions with cholinium ionic liquids as adjuvants: New insights into determination of binodal curves and phase-separation mechanisms

Aqueous two-phase micellar systems (ATPMS) are more than simple amphiphilic copolymer or surfactant aqueous solutions since due to the formation of biphasic regimes, at certain temperatures, these can be successfully used for the separation, encapsulation, and formulation of several bio-based compounds. The recent use of ionic liquids (ILs) as adjuvants in the formation of ATPMS have enlarged its “working window”, but the measurement of respective binodal curves is still very empiric and dependent of operator accuracy through the visual determination of cloud-point temperature. In this work, the range of ATPMS using ILs as adjuvants was extended, providing more insights about their phase formation mechanisms, as well as into determination of cloud-point values of the lower critical solution temperature (LCST)-type demixing transition by using the new temperature modulated optical refractometry approach. The binodal curves of ATPMS composed of Pluronic® L35/PBS buffer at pH 7.4 + cholinium ILs were determined, by using two different methods, i.e.: cloud-point temperature (TCP) visual determination versus temperature modulated optical refractometry (TMOR). TMOR method was more sensitive to the determination of biphasic transition, particularly, in highly diluted solutions (< 3.0 wt% of Pluronic L35). The results also established that the addition of cholinium ILs decreased significantly the phase separation temperatures of Pluronic L35/PBS, with an increase of biphasic region (viz. lower of TCP values) as a function of the relative hydrophobicity of the IL anion, i.e.: [Hex]− > [But]− > [Pro]− > [Ac]− > Cl−. The use of cholinium ILs as adjuvants is particularly important to provide mild conditions for ATPMS-based separation and encapsulation strategies, while TMOR-based methods allow an improvement of phase separation determination accuracy.