A Critical Review of Surfactant-Mediated Phase Separations (Cloud-Point Extractions): Theory and Applications

Moment analysis method for determination of rate constants of solute permeation across interface of spherical molecular aggregates by means of high-performance liquid chromatography

A moment analysis method was developed for the study of solute permeation at the interface of spherical molecular aggregates. At first, new moment equations were developed for determining the partition equilibrium constant (Kp) and permeation rate constants (kin and kout) of solutes from the first absolute (μ1A) and second central (μ2C) moments of elution peaks measured by using high-performance liquid chromatography (HPLC). Then, the method was applied to the analysis of mass transfer phenomena of three solutes, i.e., hydroquinone, resorcinol, and catechol, at the interface of sodium dodecylsulfate (SDS) micelles. HPLC data were measured by using an ODS column and an aqueous phosphate buffer solution (pH = 7.0) as the mobile phase solvent. Pulse response experiments were conducted while changing SDS concentration (5 - 20 mmol dm-3) in the mobile phase under the conditions that the surface of ODS stationary phase was dynamically coated by SDS monomers. In order to demonstrate the effectiveness of the moment analysis method using HPLC, the values of Kp, kin, and kout were determined for the three solutes as 35 - 69, 2.4 × 10-8 - 1.4 × 10-6 m s-1, and 7.0 × 10-10 - 2.1 × 10-8 m s-1, respectively. Their values increase with an increase in the hydrophobicity of the solutes. The method has some advantages for the study of interfacial solute permeation of molecular aggregates. For example, neither immobilization nor chemical modification of both solute molecules and molecular aggregates is required when elution peaks are measured by using HPLC. Interfacial solute permeation takes place in the mobile phase without any chemical reaction or physical action on molecular aggregates. The values of Kp, kin, and kout were analytically determined from those of μ1A and μ2C by using the moment equations. The results of this study must contribute to the dissemination of an opportunity for studying the interfacial solute permeation of molecular aggregates to many researchers because of extremely high versatility of HPLC.

Molecular insights into the aggregation and solubilizing behavior of biocompatible amphiphiles Gelucire® 48/16 and Tetronics® 1304 in aqueous media

A comparative analysis of the micellar and solubilizing properties of two polyethylene glycol (PEG)-based amphiphilic biocompatible excipients: Gelucire® 48/16 (Ge 48/16) and Tetronics® 1304 (T1304), in the presence and absence of salt, was conducted. As there is a dearth of research in this area, the study aims to shed light on the behavior of these two nonionic surfactants and their potential as nanocarriers for solubilizing pharmaceuticals. Various techniques such as cloud point (CP), dynamic light scattering (DLS), small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FT-IR), UV spectrophotometry, and high-performance liquid chromatography (HPLC) were employed. The solubility of quercetin (QCT), a flavonoid with anti-inflammatory, antioxidant, and anti-cancer properties, was evaluated and the interaction between QCT and the micellar system was examined. The analysis revealed the occurrence of strong interactions between QCT and surfactant molecules, resulting in enhanced solubility. It was observed that the micellar size and solubilizing ability were significantly improved in the presence of salt, while the CP decreased. Ge 48/16 exhibited superior performance, with a remarkable increase in the solubility of QCT in the presence of salt, suggesting its potential as an effective nanocarrier for a range of pharmaceutics, and yielding better therapeutic outcomes.

Nanoparticulate pollutants in the environment: Analytical methods, formation, and transformation

The wide application of nanomaterials and plastic products generates a substantial number of nanoparticulate pollutants in the environment. Nanoparticulate pollutants are quite different from their bulk counterparts because of their unique physicochemical properties, which may pose a threat to environmental organisms and human beings. To accurately predict the environmental risks of nanoparticulate pollutants, great efforts have been devoted to developing reliable methods to define their occurrence and track their fate and transformation in the environment. Herein, we summarized representative studies on the preconcentration, separation, formation, and transformation of nanoparticulate pollutants in environmental samples. Finally, some perspectives on future research directions are proposed.

Innovative approaches in cloud-point extraction

Cloud-point extraction (CPE) is a pre-treatment technique for the extraction and preconcentration of different chemical compounds, such as metal ions, pesticides, drugs, phenols, vitamins etc., from various samples. CPE is based on the phenomenon of two phases (micellar and aqueous) forming after the heating of an aqueous isotropic solution of a non-ionic or zwitterionic surfactant above the cloud-point temperature. If analytes are added to the surfactant solution under suitable conditions, they should be extracted into the micellar phase, also called the surfactant-rich phase. Recently, the traditional CPE procedure is being increasingly replaced by improved CPE procedures. In this study, recent advances in CPE over the last three years (2020 - 2022), including the application of various innovative approaches, are reviewed. In addition to the basic principle of CPE, alternative extraction media in CPE, CPE supported by various auxiliary energies, a different modified CPE procedure and the use nanomaterials and solid-phase extraction in combination with CPE are presented and discussed. Finally, some future trends for improved CPE are presented.

Effect of Sulfate, Citrate, and Tartrate Anions on the Liquid-Liquid Equilibrium Behavior of Water + Surfactant

Cloud point extraction is a versatile method aimed at separating compounds from complex mixtures and arouses great technological interest, particularly among the biochemical industries. However, one must have deep knowledge of the liquid–liquid equilibrium behavior of systems to properly use the method. Thus, we used thermodynamic parameters to evaluate the effect of citrate, sulfate, and tartrate anions on the phase separation of water + Triton X-114® mixtures at 283.2 K, 293.2 K, and 303.2 K. In these systems, increasing the temperature and the anion molar fraction expanded the biphasic region in the following order: C6H5O73-> SO42- >  C4H4O62−. Unlike other studies based on the Hofmeister series, the Gibbs free energy of micellization correlated the anion effect on the biphasic region with the spontaneity of the micelle formation. The water molecules structured around these anions were evaluated according to the shell volume of the immobilized water by electrostriction, volume of water around the hydration shell, Gibbs free energy of hydration, and Gibbs free energy of electrostriction (ΔGel12). The citrate anion presented a higher ΔGel12 of −1781.49 kJ mol−1, due to the larger number of electrons around it. In addition, the partition coefficient of the surfactant in the two liquid phases revealed a linear dependence upon the anion mole fractions by following the previous anion sequence and temperature in the phase separation.

Physico-chemical parameters of phase separation of the mixture of BSA and triton X 100 in aqueous solutions of monohydroxy compounds

Clouding behavior and thermodynamic properties for the TX 100 + BSA mixture were investigated in aqueous and aq. alcoholic media. In an aqueous environment, the values of cloud point (CP), at which a clear solution becomes cloudy, for TX 100 decreases with augmentation of the concentration of BSA. The reverse result was obtained in the aq. alcoholic media. In this study, we have used ethanol (EtOH), 1-propanol (1-PrOH), and 2-butanol (2-BuOH) as alcohols. The changes of CP values in alcoholic media have been obtained in the following order: CP_H2O+EtOH > CP_H2O+2-BuOH > CP_H2O+1-PrOH. The standard free energy (∆G_c^o), standard enthalpy (∆H_c^o), and standard entropy (∆S_c^o) changes of clouding were derived at CP. The ΔG_c⁰ values of TX 100 + BSA decreases in the aqueous and alcoholic media with increasing the concentration of BSA and alcohol. This process becomes endothermic in the aq. alcoholic media. Different thermodynamic properties of transfer and entropy-enthalpy compensation parameters for the phase partitioning of the TX 100 + BSA mixture have been calculated and assessed properly.

Coarse-grained molecular dynamics simulations of immobilized micelle systems and their interactions with hydrophobic molecules

Micelles immobilized in polymer materials are of emerging interest in drug delivery, water treatment and other applications. Immobilization removes the need for membrane-based separation to eliminate micelles from the medium, enabling facile extraction and delivery in diverse industries. This work lays out a coarse-grained molecular dynamics simulations framework for the rapid identification of surfactants for use in immobilized micelle systems. Micelles are immobilized by constraining one end of the constituent surfactants in space, mimicking what would occur in a copolymer system. We demonstrate that constraints affect how the micelles interact with small hydrophobic molecules, making it important to account for their effects in various drug-micelle and pollutant-micelle simulations. Our results show that in several systems there is stronger interaction between hydrophobic small molecules and micelles in immobilized systems compared to unconstrained systems. These strengthened interactions can have important implications for the design of new micelle-based extraction and delivery processes.

A rapid room-temperature cloud point extraction for spectrophotometric determination of Copper (II) with 6,7-dihydroxy-2,4-diphenylbenzopyrylium chloride

The conditions for the surfactant rich phase of Triton X-100 formation and the extraction of Copper (II) as a complex with 6,7-dihydroxy-2,4-diphenylbenzopyrylium chloride at room temperature have been optimized. It was shown that the sodium salt of p-toluic acid can be used as a chemical initiator of cloud point extraction. The optimal conditions for room temperature cloud point extraction were found to be: pH 5.0; 1 v/v.% Triton X-100; 3.75·10^-2 M sodium salt of p-toluic acid and the addition of 0.5 M H₂SO₄ solution to pH 5.0. The formation of the surfactant rich phase begins instantly. The 2-propanol was proposed as a diluent for the surfactant rich phase. The calibration graph is linear in the range of Copper (II) concentrations of 6-870 μg/L, and the limit of detection and limit of determination are 1.8 and 6 μg/L, respectively. The proposed method was successfully applied for the spectrophotometric determination of Copper (II) in water samples with a relative standard deviation not exceeding 4.5%.

Microcystins can be extracted from Microcystis aeruginosa using amino acid-derived biosurfactants

Microcystin, a cyanotoxin produced by Microcystis aeruginosa growing in eutrophic waters, can promote liver tumors in people ingesting contaminated water. To date, water treatment systems have not been effective in removing or degrading these cyanotoxins. In this work, we investigated the inhibitory activity of surfactants on the growth of M. aeruginosa and their application to extract the intracellular produced cyanotoxins. The experiments involving growth inhibition and extraction of cyanotoxins were carried out using the non-biodegradable surfactant cetyl trimethyl ammonium bromide (CTAB) in addition to other biodegradable surfactants. These were Tween 80 and surfactants derived from amino acids and peptides, respectively, from arginine, SDA, and hydrolyzed peptone, SDP. We demonstrated that the tested surfactants could be used to inhibit the growth of M. aeruginosa. At this point, CTAB and SDA proved to be the most competent surfactants in reducing cyanobacterial growth. Moreover, microcystins have been successfully removed from the water employing a cloud point extraction protocol based on the use of these surfactants and ammonium sulfate.

A review on nanostructured silver as a basic ingredient in medicine: physicochemical parameters and characterization

Recent studies with silver nanoparticles (AgNPs) and the history of silver metal as a broad-spectrum bactericidal and virucidal agent, places silver as one of the future biocidal candidates in the field of nanomedicine to eliminate bacteria and viruses, especially multidrug resistant ones. In this review, we have described the various morphologies of AgNPs and correlated the enhanced bactericidal activity with their prominent {111} facets. In addition to prioritizing the characterization we have also discussed the importance of quantifying AgNPs and silver ion content (Ag+) and their different mechanisms at the chemical, biological, pharmacological, and toxicological levels. The mechanism of action of AgNPs against various bacteria and viruses including the SARS-CoV-2 was analyzed in order to understand its effectiveness as an antimicrobial agent with therapeutic efficacy and low toxicity. Further, there is the need to characterize AgNPs and quantify the content of free Ag+ for the implementation of new systematic studies of this promising agent in nanomedicine and in clinical practice.

Solvation of nonionic poly(ethylene oxide) surfactant Brij 35 in organic and aqueous-organic solvents

HYPOTHESIS

By combining the experimental small- and wide-angle x-ray scattering (SWAXS) method with molecular dynamics simulations and the theoretical 'complemented-system approach' it is possible to obtain detailed information about the intra- and inter-molecular structure and dynamics of the solvation and hydration of the surfactant in organic and mixed solvents, e.g., of the nonionic surfactant Brij 35 (C₁₂E₂₃) in alcohols and aqueous alcohol-rich ternary systems. This first application of the complemented-system approach to the surfactant system will promote the use of this powerful methodology that is based on experimental and calculated SWAXS data in studies of colloidal systems. By applying high-performance computing systems, such an approach is readily available for studies in the colloidal domain.

EXPERIMENTS

SWAXS experiments and MD simulations were performed for binary Brij 35/alcohol and ternary Brij 35/water/alcohol systems with ethanol, n-butanol and n-hexanol as the organic solvent component at 25 °C.

FINDINGS

We confirmed the presence of solvated Brij 35 monomers in the studied organic media, revealed their preferential hydration and discussed their structural and dynamic features at the intra- and inter-molecular levels. Anisotropic effective surfactant molecular conformations were found. The influence of the hydrophobicity of the organic solvent on the hydration phenomena of surfactant molecules was explained.

Pomegranate seed oil nanoemulsion enriched by α-tocopherol; the effect of environmental stresses and long-term storage on its physicochemical properties and oxidation stability

In this study, pomegranate seed oil (PSO) nanoemulsions loading different amounts of α-tocopherol (0-40%) were produced. The nanoemulsions were fabricated by ultra-sonication method and the influence of thermal treatment (20-90 °C), pH (2-8) and ionic strength (0-500 mM NaCl) were investigated on physicochemical properties of all treatments. Moreover, the oxidative stability and α-tocopherol degradation were also assessed on optimal enriched nanoemulsion formulation during 50-day storage. The droplet diameter, viscosity, antioxidant activity, encapsulation efficiency and loading capacity of optimal formulation were 37.5 nm, 514 cp, 92%, 3.45% and 92.5%, respectively. The peroxide value changed in the range of 4.5-5.3 and 6.7-10.5 meq O₂/kg in loaded and unloaded nanoemulsions, respectively. Transmission electron microscopy demonstrated spherical morphology of nanoemulsion droplets with diameter average of 40 nm. This study suggested that PSO nanoemulsion loading α-tocopherol could be introduced as delivery system with favorable features under severe environmental conditions.

Micelles of Oxyethylated Isononylphenols in Aqueous Solutions and Hydrophilic-Lipophilic Balance

We have measured the self-diffusion coefficients and calculated the effective hydrodynamic radii of micelles of ethoxylated isononylphenols in aqueous solutions in the presence of sodium chloride, as well as in their binary mutual mixtures, when approaching cloudy conditions. These cloudy conditions were created by an increase in temperature, a change in the concentration of an electrolyte in the solution, or a mutual ratio of neonols in their binary mixtures. The results are discussed within the concept of the hydrophilic-lipophilic balance.

Natural TiO2-Nanoparticles in Soils: A Review on Current and Potential Extraction Methods

The monitoring of anthropogenic TiO2-nanoparticles in soils is challenged by the knowledge gap on their characteristics of the large natural TiO2-nanoparticle pool. Currently, no efficient method is available for characterizing natural TiO2-nanoparticles in soils without an extraction procedure. Considering the reported diversity of extraction methods, the following article reviews and discusses their potential for TiO2 from soils, focusing on the selectivity and the applicability to complex samples. It is imperative to develop a preparative step reducing analytical interferences and producing a stable colloidal dispersion. It is suggested that an oxidative treatment, followed by alkaline conditioning and the application of dispersive agents, achieve such task. This enables the further separation and characterization through size or surface-based separation (i.e., hydrodynamic fractionation methods, filtration or sequential centrifugation). Meanwhile, cloud point extraction, gel electrophoresis, and electrophoretic deposition have been studied on various nanoparticles but not on TiO2-nanoparticles. Furthermore, industrially applied methods in, for example, kaolin processing (flotation and flocculation) are interesting but require further improvements on terms of selectivity and applicability to soil samples. Overall, none of the current extraction methods is sufficient toward TiO2; however, further optimization or combination of orthogonal techniques could help reaching a fair selectivity toward TiO2.

Hydration Shell Changes in Surfactant Aggregate Transitions Revealed by Raman-MCR Spectroscopy

Hydration states of many self-assemblies directly relate to their structures and functions. Here, we use Raman multivariate curve resolution (Raman-MCR) assisted by differential scanning calorimetry and nuclear magnetic resonance to explore the hydration properties of aggregates formed by three cationic ammonium surfactants, trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12(Br)₂), didodecyldimethylammonium bromide (DDAB), and dodecyltrimethylammonium bromide (DTAB). For 12-3-12(Br)₂, the transitions from spherical to rodlike and wormlike micelles lead to about 20% and 60% dehydration and gradually weaken water tetrahedral order and H-bond in hydration shells for both headgroup and hydrophobic chain. As to DDAB, unilamellar vesicles contain two kinds of hydration water species, but multicompartment vesicles exhibit decreased water order and weaker H-bond. DTAB only forms spherical micelles and its hydration structure is similar to that of the 12-3-12(Br)₂ spherical micelles. This work provides a basis to explore the hydration states of complex biological self-assemblies.

Adsorption onto MWCNTs Coupled with Cloud Point Extraction for Dye Removal from Aqueous Solutions: Optimization by Experimental Design

AIMS

The main aim of the study was to examine the feasibility and benefits of adsorption onto multi-walled carbon nanotubes (MWCNTs) coupled with cloud point extraction (CPE) for the removal of Rhodamine B (RB) from aqueous solutions.

BACKGROUND

MWCNTs offer the particular features of the ideal adsorbents for the organic dyes such as hollow tubular structure and specific surface area. Nevertheless, they suffer from the drawbacks of low dispersion in the aqueous solutions and separation inconvenience from the media. Cloud point extraction, combined with the adsorption onto MWCNTs can be a promising method to overcome the problems.

OBJECTIVE

In the study, adsorption onto MWCNTs coupled with CPE was applied for RB removal from aqueous solutions. The process was optimized by the response surface modeling method. Moreover, the applicability of the proposed method in the real sample analyses was investigated.

METHODS

MWCNTs were used as adsorbent and Triton X-100 (TX-100) as the nonionic surfactant for CPE process. The experiments were carried out based on a Box-Behnken design (BBD) with the input variables of MWCNTs dosage (0.6-1.2 mg), solution pH (3-9), clouding time (20-40 min) and TX-100 concentration (10-20 v/v%) using 5 mg L-1 RB solutions.

RESULT

Regression analyses resulted in a statistically significant quadratic model (R2=0.9718, F=24.96, p<0.0001) by which the optimum levels of the variables were predicted as: MWCNTs dosage of 0.7 mg, pH=3, clouding time of 39.9 minutes and TX-100 concentration of 19.91% (v/v). The predicted conditions were experimentally validated by achieving an RB removal of 94.24%.

CONCLUSION

Based on the results, the combination of the environmentally friendly technique of CPE with adsorption onto MWCNTs allows the efficient removal of RB from water samples and the method can be effectively optimized by the response surface modeling.

Twenty years of supramolecular solvents in sample preparation for chromatography: achievements and challenges ahead

Supramolecular solvents (SUPRAS) have progressively become a suitable alternative to organic solvents for sample preparation in chromatographic analysis. The inherent properties of these nanostructured solvents (e.g. different polarity microenvironments, multiple binding sites, possibility of tailoring their properties, etc.) offer multiple opportunities for the development of innovative sample treatment platforms not approachable by conventional solvents. In this review, major achievements attained in the combination SUPRAS-chromatography in the last 20 years as well as the challenges that should be addressed in the near future are critically discussed. Among achievements, particular attention is paid to the theoretical and practical knowledge gained that has helped make substantial progress in the area. In this respect, advances in the understanding of the mechanisms involved in SUPRAS formation and SUPRAS-solute interactions driving extractions are discussed, with a view to the setting up of knowledge-based extraction procedures. Likewise, the strategies followed to improve the compatibility of SUPRAS extracts with liquid and gas chromatography and adapt SUPRAS-based extractions to different formats are presented. Ongoing efforts to apply SUPRAS in multicomponent extractions and synthesize tailored SUPRAS for the development of innovative sample treatments are highlighted. Among challenges identified, discussion is focused on the automation of SUPRAS-based sample treatment and the elucidation of SUPRAS nanostructures, which are considered essential for their acceptance in routine labs and the design of tailored SUPRAS with programmed functions. Graphical abstract.

Mitigation of Rheumatic Arthritis in a Rat Model via Transdermal Delivery of Dapoxetine HCl Amalgamated as a Nanoplatform: In vitro and in vivo Assessment

Purpose

Dapoxetine HCl (DH), a selective serotonin reuptake inhibitor, may be useful for the treatment of rheumatic arthritis (RA). The purpose of this study was to investigate the therapeutic efficacy of transdermal delivery of DH in transethosome nanovesicles (TENVs). This novel delivery of DH may overcome the drawbacks associated with orally administered DH and improve patient compliance.

Methods

DH-TENV formulations were prepared using an injection- sonication method and optimized using a 3³ Box-Behnken-design with Design Expert^® software. The TENV formulations were assessed for entrapment efficiency (EE-%), vesicle size, zeta potential, in vitro DH release, and skin permeation. The tolerability of the optimized DH-TENV gel was investigated using a rat skin irritation test. A pharmacokinetic analysis of the optimized DH-TENV gel was also conducted in rats. Moreover, the anti-RA activity of the optimized DH-TENV gel was assessed based on the RA-specific marker anti-cyclic cirtullinated peptide antibody (anti-CCP), the cartilage destruction marker cartilage oligomeric matrix protein (COMP) and the inflammatory marker interleukin-6 (IL-6). Level of tissue receptor activator of nuclear factor kappa-Β ligand (RANKL) were also assessed.

Results

The optimized DH-TENV formulation involved spherical nanovesicles that had an appropriate EE- % and skin permeation characteristic. The DH-TENV gel was well tolerated by rats. The pharmacokinetics analysis showed that the optimized DH-TENV gel boosted the bioavailability of the DH by 2.42- and 4.16-fold compared to the oral DH solution and the control DH gel, respectively. Moreover, it significantly reduced the serum anti-CCP, COMP and IL-6 levels and decreased the RANKL levels. Furthermore, the DH-TENV gel attenuated histopathological changes by almost normalizing the articular surface and synovial fluid.

Conclusion

The results indicate that DH-TENVs can improve transdermal delivery of DH and thereby alleviate RA.

Use of the normalized hydrophilic-lipophilic-deviation (HLDN) equation for determining the equivalent alkane carbon number (EACN) of oils and the preferred alkane carbon number (PACN) of nonionic surfactants by the fish-tail method (FTM)

The standard HLD (Hydrophilic-Lipophilic-Deviation) equation expressing quantitatively the deviation from the "optimum formulation" of Surfactant/Oil/Water systems is normalized and simplified into a relation including only the three more meaningful formulation variables, namely (i) the "Preferred Alkane Carbon Number" PACN which expresses the amphiphilicity of the surfactant, (ii) the "Equivalent Alkane Carbon Number" EACN which accurately reflects the hydrophobicity of the oil and (iii) the temperature which has a strong influence on ethoxylated surfactants and is thus selected as an effective, continuous and reversible scanning variable. The PACN and EACN values, as well as the "temperature-sensitivity-coefficient"τ of surfactants are determined by reviewing available data in the literature for 17 nonionic n-alkyl polyglycol ether (C_iE_j) surfactants and 125 well-defined oils. The key information used is the so-called "fish-tail-temperature" T* which is a unique data point in true ternary C_iE_j/Oil/Water fish diagrams. The PACNs of C_iE_j surfactants are compared with other descriptors of their amphiphilicity, namely, the cloud point, the HLB number and the PIT-slope value. The EACNs of oils are rationalized by the Effective-Packing-Parameter concept and modelled thanks to the COSMO-RS theory.

Nitric Oxide and Hydrogen Peroxide Signaling in Extractive Shiraia Fermentation by Triton X-100 for Hypocrellin A Production

Shiraia mycelial culture is a promising biotechnological alternative for the production of hypocrellin A (HA), a new photosensitizer for anticancer photodynamic therapy (PDT). The extractive fermentation of intracellular HA in the nonionic surfactant Triton X-100 (TX100) aqueous solution was studied in the present work. The addition of 25 g/L TX100 at 36 h of the fermentation not only enhanced HA exudation to the broth by 15.6-fold, but stimulated HA content in mycelia by 5.1-fold, leading to the higher production 206.2 mg/L, a 5.4-fold of the control on day 9. After the induced cell membrane permeabilization by TX100 addition, a rapid generation of nitric oxide (NO) and hydrogen peroxide (H₂O₂) was observed. The increase of NO level was suppressed by the scavenger vitamin C (VC) of reactive oxygen species (ROS), whereas the induced H₂O₂ production could not be prevented by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), suggesting that NO production may occur downstream of ROS in the extractive fermentation. Both NO and H₂O₂ were proved to be involved in the expressions of HA biosynthetic genes (Mono, PKS and Omef) and HA production. NO was found to be able to up-regulate the expression of transporter genes (MFS and ABC) for HA exudation. Our results indicated the integrated role of NO and ROS in the extractive fermentation and provided a practical biotechnological process for HA production.

Study on the effect of the organic acid structure on the rheological behavior and aggregate transformation of a pH-responsive wormlike micelle system

A worm-like micelle (WLM) system can be obtained by mixing long-chain cationic surfactants and polybasic organic acids in an aqueous solution. However, the effect of different organic acid structures on the rheological behavior of WLM systems has not been researched. Herein, a novel pH-responsive wormlike micelle system (EATA) was constructed by the complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and benzene tricarboxylic acid (TA) at a molar ratio of 3 : 1. UC22AMPM/citric acid (EACA) was also prepared to perform a comparison. The rheological behavior, aggregate transformation and thickening mechanism of EATA solutions were investigated by using rheological measurements, cryo-TEM, DLS, surface tension and 1H NMR. The results show that, at low pH, spherical micelles were formed and the EATA solution exhibited a lower viscosity than the EACA system due to the strong hydrophobicity of the phenyl groups of TA molecules, but the viscosity reaches 106 mP s at pH 4.80. Because of the lower pKa value of TA than CA, the viscosity of the EATA system drops sharply with the appearance of precipitates caused by the isoelectric point when the pH is greater than 4.80. In addition, by circularly changing the pH value several times, the wormlike micelles could maintain their original viscoelasticity without being weakened in the slightest.

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

This 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.

Study on the Methods of Separation and Detection of Chelates

The separation and purification techniques of chelates can improve the accuracy of detecting results of the chelation rate. As a quantitative indicator of metal ion chelates, the chelation rate can not only reflect the completion of chelation but also determine the amount of metal ions in different forms. The determination of chelation rate can help to determine the suitable chelating reaction conditions, make theoretical basis for the fertilizer efficiency, analyze the stability of chelating fertilizers and study the action mechanism of trace elements. In our study, the methods of separation free metal ions from mixture were reviewed first, including gel filtration chromatography, organic solvent precipitation, ion exchange chromatography, membrane separation and high performance liquid chromatography. Then, the qualitative analysis methods of chelates were introduced briefly, including chemical identification, infrared spectroscopy, ultraviolet spectroscopy. A detailed overview of the quantitative determination methods of chelates were also shown, such as ethylenediaminetetraacetic acid titration, chemical titration, atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, spectrophotometric, chemical modified electrode. In addition, the merits and demerits of chelated rate determination methods of various determination methods were analyzed, and summarized the applicability of various methods, which provided a theoretical basis for optimizing chelating process, characterizing the structure of chelates and analyzing the mechanism of chelating fertilizer. The current methods of measuring chelation rate were also summarized and prospected.

Molecular Modeling of Surfactant Micellization Using Solvent-Accessible Surface Area

We report a new implicit solvent simulation model for studying the self-assembly of surfactants, where the hydrophobic interactions were captured by calculating the relative changes of the solvent-accessible surface area (SASA) of the hydrophobic domains. Using histogram-reweighting grand canonical Monte Carlo simulations, we demonstrate that this approach allows us to match both the experimental critical micelle concentrations (cmc) and micellar aggregation numbers simultaneously with a single phenomenological surface tension γ_SASA for the poly(oxyethylene) monoalkyl ether (C _mE _n) surfactants in aqueous solutions. Excellent transferability is observed: the same model can accurately predict the experimental cmc and aggregation numbers for the C _mE _n surfactants with the alkyl lengths m between 6 and 12 and the poly(oxyethylene) lengths n between 1 and 9. The SASA-based implicit solvent model put forward in this work is general and may be applied to study more complex amphiphilic systems such as surfactants with branched alkyl chains or surfactant-hydrocarbon mixtures.

Hexafluoroisopropanol/Brij-35 based supramolecular solvent for liquid-phase microextraction of parabens in different matrix samples

A novel supramolecular solvent (SUPRAS) based on hexafluoroisopropanol (HFIP)/Brij-35 was proposed for liquid-phase microextraction (LPME) of parabens in water samples, pharmaceuticals and personal care products. Brij-35 is a cost-effective and non-toxic non-ionic surfactant, but it has a high cloud point (>100 °C). HFIP, with the features of strong hydrogen-bond donor, high density and powerful hydrophobicity, was used as the cloud point-reducing agent and self-assembling and density-regulating solvent of Brij-35. Upon adding HFIP into the Brij-35 aqueous solution, the cloud point of Brij-35 was decreased to below room temperature, and the SUPRAS was formed in the bottom over a wide range of HFIP and Brij-35 concentrations at room temperature. The SUPRAS was composed of Brij-35, HFIP and water, having a density larger than water, and it showed a large spherical structure of positive micellar aggregates (2-8 μm). The HFIP/ Brij-35 SUPRAS-based LPME procedure was non-thermodependent and could be performed at room temperature with centrifugation using normal centrifuge tubes, being very simple. In the extraction of six parabens, the HFIP/ Brij-35 SUPRAS-based LPME method showed short extraction time (3.3 min), low solvent consumption (0.3 mL), and large enrichment factor (26-193). The method of HFIP/ Brij-35 SUPRAS-based LPME with HPLC-DAD gave good linearity for the quantification of parabens with correlation coefficients larger than 0.9990. The limits of detection based on a signal-to-noise ratio of 3 were from 0.042 to 0.167 μg L^-1. The recoveries for the spiked real samples were in the range of 90.2-112.4% with relative standard deviation less than 8.9%. Except for tap water, one or several paraben (s) were detected in all the other real samples.

Novel, energy efficient and green cloud point extraction: technology and applications in food processing

Recently, a novel technique for extraction of functional thermally sensitive bioactive components from food has been developed due to its green efficacy (no toxic chemicals) and cost effectiveness. Cloud point extraction (CPE) is one of the such best alternative techniques that can be used for extraction of wide range of organic and inorganic components using green surfactants. It is a simple, rapid and inexpensive extraction technique which involves clustering of non-ionic surfactant monomers to form a hydrophobic core (micelle), which then entraps the hydrophobic bioactive compounds within it. CPE can be applied for extraction of bioactives from food processing waste as well as separation and purification of proteins. Besides that, research has received special attention on sample preparation for analysis of food constituents in the last decade. The scope of CPE is very vast in these sectors because of the advantages of CPE over other methods. This review deals with significance of CPE method and their potential green applications in food processing.

Miniaturized sample preparation methods for saliva analysis

Saliva, as the first body fluid encountering with the exogenous materials, has good correlation with blood and plays an important role in bioanalysis. However, saliva has not been studied as much as the other biological fluids mainly due to restricted access to its large volumes. In recent years, there is a growing interest for saliva analysis owing to the emergence of miniaturized sample preparation methods. The purpose of this paper is to review all microextraction methods and their principles of operation. In the following, we examine the methods used to analyze saliva up to now and discuss the potential of the other microextraction methods for saliva analysis to encourage research groups for more focus on this important subject area.

Added-Value Surfactants

Surfactants are ubiquitous in cellular membranes, detergents or as emulsification agents. Due to their amphiphilic properties, they cannot only mediate between two domains of very different solvent compatibility like water and organic but also show fascinating self-assembly features resulting in micelles, vesicles, or lyotropic liquid crystals. The current review article highlights some approaches towards the next generation surfactants, for example, those with catalytically active heads. Furthermore, it is shown that amphiphilic properties can be obtained beyond the classical hydrophobic-hydrophilic interplay, for instance with surfactants containing one molecular block with a special shape. Whereas, classical surfactants are static, researchers have become more interested in species that are able to change their properties depending on external triggers. The article discusses examples for surfactants sensitive to chemical (e.g., pH value) or physical triggers (temperature, electric and magnetic fields).

Multicomponent Reactions Accelerated by Aqueous Micelles

Multicomponent reactions are powerful synthetic tools for the efficient creation of complex organic molecules in an one-pot one-step fashion. Moreover, the amount of solvents and energy needed for separation and purification of intermediates is significantly reduced what is beneficial from the green chemistry issues point of view. This review highlights the development of multicomponent reactions conducted using aqueous micelles systems during the last two decades.