Exploring the Properties of Unilamellar Vesicle Bilayers Formed by Ionic Liquid Surfactants for Future Applications in Nanomedicine.

Two ionic liquids (ILs) with amphiphilic properties composed of 1-butyl-3-methylimidazolium dioctylsulfosuccinate (bmim-AOT) and 1-hexyl-3-methylimidazolium dioctylsulfosuccinate (hmim-AOT) form unilamellar vesicles spontaneously simply by dissolving the IL-like surfactant in water. These novel vesicles were characterized using two different and highly sensitive fluorescent probes: 6-propionyl-2-(dimethylaminonaphthalene) (PRODAN) and trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (HC). These fluorescent probes provide information about the physicochemical properties of the bilayer, such as micropolarity, microviscosity, and electron-donor capacity. In addition, the biocompatibility of these vesicles with the blood medium was evaluated, and their toxicity was determined using Dictyostelium discoideum amoebas. First, using PRODAN and HC, it was found that the bilayer composition and the chemical structure of the ions at the interface produced differences between both amphiphiles, making the vesicles different. Thus, the bilayer of hmim-AOT vesicles is less polar, more rigid, and has a lower electron-donor capacity than those made by bmim-AOT. Finally, the results obtained from the hemolysis studies and the growth behavior of unicellular amoebas, particularly utilizing the D. discoideum assay, showed that both vesicular systems do not produce toxic effects up to a concentration of 0.02 mg/mL. This elegant assay, devoid of animal usage, highlights the potential of these newly organized systems for the delivery of drugs and bioactive molecules of different polarities.

Electrochemical Characterization of the Encapsulation and Release of 5-Fluorouracil in Nanocarriers Formed from Soy Lecithin Vesicles.

5-Fluorouracil (5-FU) is an antineoplastic agent known for its low bioavailability and limited cellular penetration, often resulting in adverse effects on healthy cells. Thus, finding vehicles that enhance bioavailability, enable controlled release, and mitigate adverse effects is crucial. The study focuses on encapsulating 5-FU within soy lecithin vesicles (SLVs) and assessing its impact on the carrier's properties and functionality. Results show that incorporating 5-FU does not affect SLVs' size or polydispersity, even postlyophilization. Liberation of 5-FU from SLVs requires system disruption rather than spontaneous release, with an encapsulation efficiency of approximately 43% determined using Square Wave Voltammetry. Cytotoxicity assays on colorectal cancer cells reveal SLV-based delivery's significant efficacy, surpassing free drug solution effects with 45% cell viability after 72 h vs 73% viability. The research addresses 5-FU's limited bioavailability by creating a biocompatible nanocarrier for efficient drug delivery, highlighting SLVs as promising for targeted cancer therapy due to sustained antiproliferative effects and improved cellular uptake. The study underscores the importance of tailored drug delivery systems in enhancing therapeutic outcomes and suggests SLV/5-FU formulations as a potential advancement in cancer treatment strategies.

Electrochemical and Spectroscopic Studies Performed for Indomethacin and 1-Naphthol Incorporated in 1-Butyl-3-methyl-imidazolium Bis(2-ethylhexyl) Sulfosuccinate Vesicles to Investigate Them as a Potentially pH-Sensitive Nanocarrier.

Characterization studies of 1-butyl-3-methyl-imidazolium bis(2-ethylhexyl) sulfosuccinate vesicles at different pH values have been carried out by using liquid surface tension, transmission electron microscopy, and dynamic light scattering. The results show that there are no vesicle changes in its size and negative Z potential at pH 3, 6, and 10. Furthermore, indomethacin and 1-naphthol, both pH-dependent, electroactive, and fluorescence probes, were used to further characterize the bilayer employing electrochemical and emission techniques. The partition of indomethacin and 1-naphthol between the water and bilayer pseudophases only occurs for the neutral species and does not happen for the anionic species because the highly negative Z bilayer potential prevents incorporation due to negative repulsion. For the neutral species, the partition constant values were evaluated by square wave voltammetry and emission spectroscopy. Finally, for the indomethacin incorporated into the vesicle bilayer at pH 3, the release profile was monitored over time at pH 6. It was found that a change in the pH values causes the complete release of indomethacin after 25 min, which led us to think that the vesicles presented in this work can be used as a pH-sensitive nanocarrier for neutral pH-sensitive drugs.

PRODAN Photophysics as a Tool to Determine the Bilayer Properties of Different Unilamellar Vesicles Composed of Phospholipids.

Vesicles formed by phospholipids are promising candidates for drug delivery. It is known that the lipid composition affects properties such as the rigidity-fluidity of the membrane and that it influences the bilayer permeability, but sometimes sophisticated techniques are selected to monitor them. In this work, we study the bilayer of different unilamellar vesicles composed of different lipids (1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC, and lecithin) and diverse techniques such as extruder and electrospun templates and using 6-propionyl-2-(N,N-dimethyl) aminonaphthalene (PRODAN) and its photophysics. Moreover, we were able to monitor the influence of cholesterol on the bilayers. We demonstrate that the bilayer properties can be evaluated using the emission feature of the molecular probe PRODAN. This fluorescent probe gives relevant information on the polarity and fluidity of the microenvironment for unilamellar vesicles formed by two different methods. The PRODAN emission at 434 nm suggests that the bilayer properties significantly change if DOPC or lecithin is used in the vesicle preparation especially in their fluidity. Moreover, cholesterol induces alterations in the bilayer's structural and microenvironmental properties to a greater or lesser degree in both vesicles. Thus, we propose an easy and elegant way to evaluate physicochemical properties, which is fundamental for manufacturing vesicles as a drug delivery system, simply by monitoring the molecular probe emission band centered at 434 nm, which corresponds to the PRODAN species deep inside the bilayer.

Green AOT reverse micelles as nanoreactors for alkaline phosphatase. The hydrogen bond "dances" between water and the enzyme, the reaction product, and the reverse micelles interface.

In this work, we present an investigation of the influence of water encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate/methyl laurate and 1,4-bis-2-ethylhexylsulfosuccinate/isopropyl myristate reverse micelles on the enzymatic hydrolysis of 1-naphthyl phosphate by alkaline phosphatase. Our results show that the enzyme is active in the biocompatible reverse micelles studied and that the Michaelis-Menten kinetic model is valid in all systems. We found that both micellar systems studied have a particular behavior toward pH and that the penetration of external solvents into the interfaces is crucial to understanding the effect. Methyl laurate does not disrupt the interface and is not necessary to control the pH value since alkaline phosphatase in the center of the micelles is always solvated similarly. In contrast, isopropyl myristate disrupts the interfaces so that the water and 1-naphthol molecules cannot form hydrogen bond interactions with the polar head of the surfactant. Then, when the water is at pH = 7, the 1-naphthol moves away to the interfaces inhibiting alkaline phosphatase which is not observable when the water is at pH = 10. Our study shows that the concept of pH cannot be used directly in a confined environment. In addition, our research is of great importance in the field of reactions that occur in reverse micelles, catalyzed by enzymes.

Amphiphilic Ionic Liquids Capable to Formulate Organized Systems in an Aqueous Solution, Designed by a Combination of Traditional Surfactants and Commercial Drugs.

The present review describes the state of the art in the conversion of pharmaceutically active ingredients (API) in amphiphilic Ionic Liquids (ILs) as alternative drug delivery systems. In particular, we focus our attention on the compounds generated by ionic exchange and without original counterions which generate different systems in comparison with the simple mixtures. In water, these new amphiphiles show similar or even better properties as surfactants in comparison with their precursors. Cations such as 1-alkyl-3-methyl-imidazolium and anions such as dioctyl sulfosuccinate or sodium dodecyl sulfate appear as the amphiphilic components most studied. In conclusion, this work shows interesting information on several promissory compounds and they appear as an interesting challenge to extend the application of ILs in the medical field.

A simple electrochemical immunosensor for sensitive detection of transgenic soybean protein CP4-EPSPS in seeds.

Soybean is the most produced crop in Argentina, and 99 % corresponds to genetically modified soybean. One of the main produced varieties is Roundup Ready® soybean (RR), which was modified to express the enzyme CP4 5-enolpyruvylshikimate 3-phosphate synthase (CP4 EPSPS), which confers resistance to glyphosate, the main herbicide worldwide used. The possible impact of genetically modified organisms (GMO) has generated public concerns, thus increasing interest in the development of GMOs detection devices. In this work, an electrochemical immunosensor for CP4 EPSPS detection in soybean seeds was obtained, by using a gold electrode modified with an anti-CP4 EPSPS polyclonal antibody produced in our laboratory. The presented immunosensor resulted in a simple, low-cost, fast, and reproducible device. Also, labeling and/or signal amplification system was not necessary, since the sensor showed high sensibility with a low detection limit (lower at 0,038 % RR soybean, 38 ng mL-1 CP4 EPSPS).

Deciphering Solvation Effects in Aqueous Binary Mixtures by Fluorescence Behavior of 4-Aminophthalimide: The Comparison Between Ionic Liquids and Alcohols as Cosolvents.

Ionic liquids (ILs) have received attention for many years due to them being very promising as green solvent substitutes, but they are not fully understood, especially their behavior dissolved in other solvents, for example, water. Thus, the goal of this contribution is to show insight into the different IL-water mixtures interaction. In this way, two protic ILs (PILs), ethylammonium nitrate (EAN) and 1-methylimidazolium acetate (MIA), mixed with water were investigated. To study the PILs-water interaction, the unique spectroscopical behavior in water of the molecular probe 4-aminophthalimide (4-AP) was used. 4-AP emission spectra show hypsochromic shifting by changing the excitation wavelength and, using time-resolved spectroscopy, can be detected by a blue shifting with time. Also, the water mixture of an aprotic IL, 1-methyl-3-butylimidazolium tetrafluoroborate (bmimBF4), and three alcohols, methanol (MeOH), 2-propanol (2-PrOH), and t-butanol (t-BOH), were investigated for comparison. Our results show that the water-ILs interaction is dominated by the size of the IL components, in particular, the cation size. Thus, in MIA-water and bmimBF4-water mixtures, 4-AP is mostly solvated by the IL, even at a low IL molar fraction, as in the t-BOH-water mixture. This finding is especially interesting when ILs-water mixtures are used as a solvent in an organic reaction, where it may call attention to water probably not being the solvent that is interacting with the reactants.

How the external solvent in biocompatible reverse micelles can improve the alkaline phosphatase behavior.

In the last decade, the nature of the nonpolar solvents that can be part of reverse micelles (RMs) has been the topic of several investigations to improve their applications. In this sense, the hydrolysis of 1-naphthyl phosphate catalyzed by the enzyme alkaline phosphatase (AP) was used as a probe to investigate the effect of the change of the external solvent on RMs formulated with the anionic surfactant sodium diethylhexyl sulfosuccinate (AOT). As external nonpolar solvents, two biocompatible lipophilic esters, isopropyl myristate and methyl laurate, and the traditional nonpolar solvents, n-heptane and benzene, were used. The results were compared among the RMs investigated and with the reaction in homogeneous media. Thus, the effect of the nanoconfinement as well as the impact of the replacement of a conventional external nonpolar solvent by biocompatible solvents were analyzed. The results indicate that the catalytic efficiency in the AOT RMs is larger than that in homogeneous media, denoting a different hydration level over the AP enzyme, which is directly related to the different degrees of nonpolar solvent penetration to the RM interface. Our findings demonstrated that toxic solvents such as n-heptane and benzene can be replaced by nontoxic ones (isopropyl myristate or methyl laurate) in AOT RMs without affecting the performance of micellar systems as nanoreactors, making them a green and promising alternative toward efficient and sustainable chemistry.

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems.

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Is it Necessary for the Use of Fluorinated Compounds to Formulate Reverse Micelles in a Supercritical Fluid? Searching the Best Cosurfactant to Create "Green" AOT Reverse Micelle Media.

Herein, we report the effect of employing two different alcohols, such as n-pentanol and 2,2,3,3,4,4,5,5-octafluoro pentanol (from now on F-pentanol), into 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs), to determine the interfacial activity and establish the best candidate to act as a cosurfactant in supercritical RMs. Dynamic light scattering (DLS), Fourier transform infrared (FT-IR), and fluorescence emission spectroscopy allowed us to determine and understand the behavior of alkanols in RMs. As a result, we found interesting displacements of alkanol molecules within the RMs, suggesting that the electrostatic interaction between SO3- and Na+ weakens because of new interactions of n-pentanol with SO3- through H-bonds, changing the curvature of the micellar interface. According to FT-IR and DLS studies, F-pentanol forms a RM polar core interacting through intermolecular H-bonds, suggesting no perturbations of the AOT RM interface. Hence, n-pentanol was selected as a cosurfactant to form supercritical RMs, which is confirmed by red edge excitation shift studies, using C343 as a molecular probe. Herein, we were able to create RMs under supercritical conditions without the presence of modified surfactants, fluorinated or multitailed compounds, which, to the best of our knowledge, was not shown before.

Influence of the AOT Counterion Chemical Structure on the Generation of Organized Systems.

The impact of the imidazolium counterion structure on the organized systems formed by the surfactant 1,4-bis-2-ethylhexylsulfosuccinate, AOT, both in aqueous solutions and in nonpolar solvents is investigated. With this in mind, we investigated if the ionic liquid-like (IL-like) surfactant 1-ethyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, emim-AOT, forms direct micelles or vesicles in water. Dynamic light scattering, zeta potential, conductivity, fluorescence spectroscopy, and UV-visible spectroscopy measurements were performed to characterize the organized systems in aqueous solutions. We also studied the self-aggregation of emim-AOT, 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, bmim-AOT, and of 1-hexyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, hmim-AOT, in nonpolar solvents. The results obtained showed that the IL-like surfactant emim-AOT forms direct micelles in water, as sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) does. However, emim-AOT aggregates are larger, have a lower surface charge, are more stable, and have a more polar and less fluid micellar interface than Na-AOT micelles. It was also observed that emim-AOT and hmim-AOT form reverse micelles in nonpolar solvents. The size of the imidazolium cations dramatically influences the size of the reverse micelles and their ability to solubilize water.

Water-soluble gold nanoparticles: recyclable catalysts for the reduction of aromatic nitro compounds in water.

A structure/catalytic activity study of water-soluble gold nanoparticles, stabilized by zwitterionic ligands derived from imidazolium salts, in the reduction of aromatic nitro compounds in pure water at different temperature, as well as their recyclability, was performed. Our studies indicate that the nanoparticles synthesized by an easy, fast and reproducible process, need a short characteristic induction time to restructure the surfaces and make them active. The differences observed in the catalytic activity of the nanoparticles, determined by using the typical Langmuir-Hinshelwood model, are strongly based on the degree of coverage and spatial arrangement of the imidazolium salts on them. Finally, we demonstrate that gold nanoparticles stabilized by non-traditional ligands can be an excellent choice for nitro compound degradation.

Catanionic nanocarriers as a potential vehicle for insulin delivery.

Diabetes is a disease that affects millions of people in the World, constituting a global problem. Patients are administered insulin subcutaneous injections, resulting in high costs and frequent infections in the injection site. A possible solution to this problem may be the use of nanotechnology. Nanotransporters can act as specific release systems able to overcome the current limitations to drug delivery. Liposomes and vesicles can deliver drugs directly and efficiently to the site of action, decreasing toxicity and adverse effects. In previous studies, we demonstrated the biocompatibility and safety of catanionic benzyl n-hexadecyldimethylammonium 1,4 -bis-2-ethylhexylsulfosuccinate (BHD-AOT) vesicles using both in vitro and in vivo tests. Thus, the aims of this work were to evaluate the ability of the BHD-AOT vesicles to encapsulate insulin; to analyze the structural properties and stability of the system, vesicle-Insulin (VIn), at different pH conditions; and to study the ability of VIn to decrease the glycemia in miceby different administration routes. Our results showed that 2 and 5 mg mL-1 of vesicles were able to encapsulate about 55 % and 73 % of insulin, respectively. The system VIn showed a significant increase in size from 120 to 350 nm, changes in the surface zeta potential value, and high stability to different pH conditions. A significant decrease of the glycemia after VIn administration was demonstrated in in vivo assays, including the oral route. Our results reveal that BHD-AOT vesicles may be an appropriate system to encapsulate and protect insulin, and may be a potential system to be administrated in different ways as an alternative strategy to conventional therapy.

Polyclonal antibody production anti Pc_312-324 peptide. Its potential use in electrochemical immunosensors for transgenic soybean detection.

A new polyclonal antibody that recognizes the CP4 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS), which provides resistance to glyphosate in soybean (Roundup Ready®, RR soybean), was produced. New Zealand rabbits were injected with a synthetic peptide (Pc_312-324, (PEP)) present in the soybean CP4-EPSPS protein. The anti-PEP antibodies production was evaluated by electrophoresis (SDS-PAGE) and an enzyme-linked immunosorbent assay (ELISA) was developed in order to study their specificity. The ELISA showed that the polyclonal antibody was specific to PEP. In addition, the anti- PEP was immobilized onto a gold disk electrode and the antigen-antibody interaction was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Moreover, the EIS showed that the electron transfer resistance of the modified electrode increased after incubation with solutions containing CP4-EPSPS protein from RR transgenic soybean, while no changes were detected after incubation with no-RR soybean proteins. These results suggest that the CP4-EPSPS was immobilized onto the electrode, due to the specific interaction with the anti-PEP. These results show that this antigen-antibody interaction can be detected by electrochemical techniques, suggesting that the anti-PEP produced can be used in electrochemical immunosensors development to quantify transgenic soybean.

Use of Ionic Liquids-like Surfactants for the Generation of Unilamellar Vesicles with Potential Applications in Biomedicine.

The goal of this work is to understand the influence of the counterion nature on the organized systems formed by 1,4-bis-2-ethylhexylsulfosuccinate surfactants in aqueous solutions and how these aggregates will influence the deoxyribonucleic acid (DNA)-surfactant interactions. With this in mind, two ionic liquid-like surfactants were investigated: 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) and 1-hexyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (hmim-AOT). Measurements of dynamic light scattering, ζ-potential, transmission electron microscopy, and fluorescence and UV-visible spectroscopy were performed to study the characteristics of the vesicles formed by bmim-AOT and hmim-AOT. Regarding the determination of the interaction of the surfactants with DNA, circular dichroism was used. The results obtained showed that bmim-AOT and hmim-AOT ionic liquid-like surfactants spontaneously form unilamellar vesicles in water at very low surfactant concentrations. The characteristics of these aggregates are dependent on the length of the tail of the counterions. The length of the hydrophobic chains of the counterions also influences the DNA-surfactant interactions through hydrophobic effects.

Interfacial Dynamics and Its Relations with ?Negative? Surface Viscosities Measured at Water?Air Interfaces Covered with a Cationic Surfactant.

We studied the dynamics of a cationic surfactant monolayer, Gemini 12-2-12, at the air?water interface for surfactant aqueous solutions at concentrations below the critical micelle concentration. We present surface rheology experiments performed in a Langmuir trough by the oscillatory barrier technique. From these, we found negative surface viscosities at certain frequencies. We demonstrate that this unphysical result is a consequence of an unconsidered surfactant dynamics within the interfacial region. By surface pressure relaxation experiments, after a sudden modification of the interfacial area and by dynamic surface tension and surface potential measurements, several relaxation phenomena and relaxation times were identified. We found that surfactant adsorption and desorption processes are asymmetric: the characteristic times and the number of processes involved in the mechanisms of adsorption and desorption are different. This asymmetry invalidates the usual data analysis procedure that leads to the negative viscosities. Similar mechanisms could be at the origin of the negative viscosities reported in other systems, a possibility that remains to be explored.

Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT.

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N',N'-tetramethylethylenediamine copper(ii)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.

Catanionic Reverse Micelles as an Optimal Microenvironment To Alter the Water Electron Donor Capacity in a SN2 Reaction.

The effect of interfacial water entrapped in two types of catanionic reverse micelles (RMs) on the kinetic parameters of the SN2 reaction between dimethyl-4-nitrophenylsulfonium trifluoromethanesulfonate (S+) and n-butylamine (BuNH2) was explored. Two catanionic surfactants, composed of a mixture of oppositely charged ionic surfactants without their original counterions, were used to create the RMs. Thus, benzyl- n-hexadecyldimethylammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (BHD-AOT) and cetyltrimethylammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (CTA-AOT) were formed. Also, the well-known anionic surfactant sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (Na-AOT) was employed as a comparison. Our results showed an important catalytic-like effect of all RMs investigated in comparison with a water-benzene mixture, and the rate constant values depend on the type of surfactant used. Faster reaction in BHD-AOT RMs than in CTA-AOT and Na-AOT RMs was observed. This behavior was attributed to the strong interaction (by hydrogen bonding with AOT anion and ion-dipole interaction with BHD+) between the entrapped water and the BHD-AOT interface, which reduces the solvation capacity of water on S+. In CTA-AOT (and Na-AOT) RMs, the water-interface interaction is weaker and the electron pairs of water can solvate S+ ions. In summary, the chemical structure of the counterion on the catanionic surfactant alters the interfacial region, allowing the progress of a reaction inside the RMs to be controlled.

Structural Characterization of Biocompatible Reverse Micelles Using Small-Angle X-ray Scattering, 31P Nuclear Magnetic Resonance, and Fluorescence Spectroscopy.

The most critical problem regarding the use of reverse micelles (RMs) in several fields is the toxicity of their partial components. In this sense, many efforts have been made to characterize nontoxic RM formulations on the basis of biological amphiphiles and/or different oils. In this contribution, the microstructure of biocompatible mixed RMs formulated by sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) and tri- n-octylphosphine oxide (TOPO) surfactants dispersed in the friendly solvent methyl laurate was studied by using SAXS and 31P NMR and by following the solvatochromic behavior of the molecular probe 4-aminophthalimide (4-AP). The results indicated the presence of RM aggregates upon TOPO incorporation with a droplet size reduction and an increase in the interfacial fluidity in comparison with pure AOT RMs. When confined inside the mixed systems, 4-AP showed a red-edge excitation shift and confirmed the increment of interfacial fluidity upon TOPO addition. Also, the partition between the external nonpolar solvent and the RM interface and an increase in both the local micropolarity and the capability to form a hydrogen bond interaction between 4-AP and a mixed interface were observed. The findings have been explained in terms of the nonionic surfactant structure and its complexing nature expressed at the interfacial level. Notably, we show how two different approaches, i.e., SAXS and the solvatochromism of the probe 4-AP, can be used in a complementary way to enhance our understanding of the interfacial fluidity of RMs, a parameter that is difficult to measure directly.