Coexisting aggregates in mixed aerosol OT and cholesterol microemulsions

Bursting the bubble: A molecular understanding of surfactant-water interfaces

Surfactant science has historically emphasized bulk, thermodynamic measurements to understand the microemulsion properties of greatest industrial significance, such as interfacial tensions, phase behavior, and thermal stability. Recently, interest in the molecular properties of surfactants has grown among the physical chemistry community. This has led to the application of cutting-edge spectroscopic methods and advanced simulations to understand the specific interactions that give rise to the previously studied bulk characteristics. In this Perspective, we catalog key findings that describe the surfactant-oil and surfactant-water interfaces in molecular detail. We emphasize the role of ultrafast spectroscopic methods, including two-dimensional infrared spectroscopy and sum-frequency-generation spectroscopy, in conjunction with molecular dynamics simulations, and the role these techniques have played in advancing our understanding of interfacial properties in surfactant microemulsions.

Rehydration of dried mushroom specimens with Aerosol® OT for scanning electron microscopy

Morphological, anatomical and ultrastructural characteristics are important for taxonomical and phylogenetic studies of fungi. For scanning electron microscopy (SEM), usually only dry voucher specimens are available. For dried plant material, Aerosol® OT (AOT) has been shown to be a suitable rehydration agent for SEM preparation. For swelling and stabilization of fungal cells, however, this simple method does not yield satisfactory results. Here, we show that a combination of AOT with ultrasonic bath and rehydration in a vacuum desiccator is a good method to distend fungal cells like basidiospores and pleuro- and cheilocystidia for SEM analysis. Tissues of several species of Agaricomycetes with diverse morphological structures were exposed to the treatment. Diverse concentrations of AOT as well as treatments in an ultrasonic bath and a vacuum desiccator were tested to optimize the surface reconstruction and to reduce preparation artefacts. The evaluated rehydration method is a cheap, quick and nontoxic method to prepare dried specimens of fungal cells for SEM analysis.

Molecular Dynamics Simulation Insight into Interfacial Stability and Fluidity Properties of Microemulsions

Although the interfacial properties of microemulsions have been extensively studied in both experimental and simulation research studies, the molecular mechanisms of stability and fluidity about microemulsion are still poorly understood. Herein, we report a molecular dynamics simulation study to elaborate the motion of an emulsion droplet involving dichain surfactant Aerosol OT (AOT) and its dynamics evolution at the oil-water interface. By varying the concentrations of AOT, we show that the interfacial thickness and emulsification rate display a piecewise change as the interfacial coverage increases and the W/O emulsion is more stable than the O/W one while O/W emulsion presents better fluidity. In addition, the dispersed system combined with water/AOT/n-heptane tends to form a W/O microemulsion instead of an O/W microemulsion due to the structural collapse of the latter. This work provides a molecular understanding of microemulsion interfacial stability and fluidity.

A Synthetic Isoprenoid Lipoquinone, Menaquinone-2, Adopts a Folded Conformation in Solution and at a Model Membrane Interface

Menaquinones (naphthoquinones, MK) are isoprenoids that play key roles in the respiratory electron transport system of some prokaryotes by shuttling electrons between membrane-bound protein complexes acting as electron acceptors and donors. Menaquinone-2 (MK-2), a truncated MK, was synthesized, and the studies presented herein characterize the conformational and chemical properties of the hydrophobic MK-2 molecule. Using 2D NMR spectroscopy, we established for the first time that MK-2 has a folded conformation defined by the isoprenyl side-chain folding back over the napthoquinone in a U-shape, which depends on the specific environmental conditions found in different solvents. We used molecular mechanics to illustrate conformations found by the NMR experiments. The measured redox potentials of MK-2 differed in three organic solvents, where MK-2 was most easily reduced in DMSO, which may suggest a combination of solvent effect (presumably in part because of differences in dielectric constants) and/or conformational differences of MK-2 in different organic solvents. Furthermore, MK-2 was found to associate with the interface of model membranes represented by Langmuir phospholipid monolayers and Aerosol-OT (AOT) reverse micelles. MK-2 adopts a slightly different U-shaped conformation within reverse micelles compared to within solution, which is in sharp contrast to the extended conformations illustrated in literature for MKs.

Unique catanionic vesicles as a potential “Nano-Taxi” for drug delivery systems. In vitro and in vivo biocompatibility evaluation

We evaluatein vitroandin vivotoxicity and stability in an acidic environment of new vesicles formed by the catanionic surfactant AOT-BHD in order to investigate their potential application as an oral drug delivery system.

Effect of Confinement on the Properties of Sequestered Mixed Polar Solvents: Enzymatic Catalysis in Nonaqueous 1,4-Bis-2-ethylhexylsulfosuccinate Reverse Micelles

The influence of different glycerol, N,N-dimethylformamide (DMF) and water mixtures encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane reverse micelles (RMs) on the enzymatic hydrolysis of 2-naphthyl acetate by α-chymotrypsin is demonstrated. In the case of the mixtures with DMF and protic solvents it has been previously shown, using absorption, emission and dynamic light-scattering techniques, that solvents are segregated inside the polar core of the RMs. Protic solvents anchor to the AOT, whereas DMF locates to the polar core of the aggregate. Thus, DMF not only helps to solubilize the hydrophobic substrate, increasing its effective concentrations but surprisingly, it does not affect the enzyme activity. The importance of ensuring the presence of RMs, encapsulation of the polar solvents and the corrections by substrate partitioning in order to obtain reliable conclusions is highlighted. Moreover, the effect of a constrained environment on solvent-solvent interactions in homogenous media and its impact on the use of RMs as nanoreactors is stressed.

How the cation 1-butyl-3-methylimidazolium impacts the interaction between the entrapped water and the reverse micelle interface created with an ionic liquid-like surfactant

The behavior of the interfacial water entrapped in reverse micelles (RMs) formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) dissolved in benzene (or chlorobenzene) was investigated using noninvasive techniques such as dynamic light scattering (DLS), static light scattering (SLS), FT-IR and (1)H NMR. The DLS and SLS results reveal the formation of discrete spherical and non-interacting water droplets stabilized by the bmim-AOT surfactant. Moreover, since the droplet size increases as the W0 (W0 = [water]/[surfactant]) value increases, water interacts with the RM interface. From FT-IR and (1)H NMR data, a weaker water-surfactant interaction in bmim-AOT RMs in comparison with the RMs created by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) is detected. Consequently, there are less water molecules interacting with the interface in bmim-AOT RMs, and their hydrogen bond network is not completely disrupted as they are in Na-AOT RMs. The results show how the nature of the new cation impacts the interaction between the entrapped water and the RM interface, modifying the interfacial water structure in comparison with the results known for Na-AOT.

Size and shape trump charge in interactions of oxovanadates with self-assembled interfaces: application of continuous shape measure analysis to the decavanadate anion

Using ⁵¹V NMR spectroscopy, dynamic light scattering and continuous shape analysis to characterize two polyoxometalate-encapsulation in reverse micelles.

The strikingly different miscibility of n-octanol in highly-confined and quasi-confined water

n-Octanol, a water-immiscible alcohol, is found to be significantly miscible with highly-confined water, but immiscible with quasi-confined water.

On the characterization of NaDEHP/n-heptane nonaqueous reverse micelles: the effect of the polar solvent

Schematic representation of different interfaces in the novel nonaqueous NaDEHP/n-heptane reverse micelle.

Effect of the cationic surfactant moiety on the structure of water entrapped in two catanionic reverse micelles created from ionic liquid-like surfactants

The behavior of water entrapped in reverse micelles (RMs) formed by two catanionic ionic liquid-like surfactants, benzyl-n-hexadecyldimethylammonium 1,4-bis-2-ethylhexylsulfosuccinate (AOT-BHD) and cetyltrimethylammonium 1,4-bis-2-ethylhexylsulfosuccinate (AOT-CTA), was investigated by using dynamic (DLS) and static (SLS) light scattering, FTIR, and (1)H NMR spectroscopy techniques. To the best of our knowledge, this is the first report in which AOT-CTA has been used to create RMs and encapsulate water. DLS and SLS results revealed the formation of RMs in benzene and the interaction of water with the RM interface. From FTIR and (1)H NMR spectroscopy data, a difference in the magnitude of the water-catanionic surfactant interaction at the interface is observed. For the AOT-BHD RMs, a strong water-surfactant interaction can be invoked whereas for AOT-CTA this interaction seems to be weaker. Consequently, more water molecules interact with the interface in AOT-BHD RMs with a completely disrupted hydrogen-bond network, than in AOT-CTA RMs in which the water structure is partially preserved. We suggest that the benzyl group present in the BHD(+) moiety in AOT-BHD is responsible for the behavior of the catanionic interface in comparison with the interface created in AOT-CTA. These results show that a simple change in the cationic component in the catanionic surfactant promotes remarkable changes in the RMs interface with interesting consequences, in particular when using the systems as nanoreactors.

Supramolecular assemblies obtained by mixing different cyclodextrins and AOT or BHDC reverse micelles

In this contribution we show the effect of the surfactant polar head and the external solvent on the incorporation of different cyclodextrins (CDs) {α-CD, β-CD, γ-CD, decenylsuccinyl-β-CD (Mod-β-CD), and hydroxypropyl-β-CD (hp-β-CD)} in different reverse micelles (RMs) {benzene/sodium 1,4-bis(2-ethylhexyl) sulfosuccinate(AOT)/water, and benzene/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/water} and compare them with previous results obtained in n-heptane/AOT/water RMs. To investigate the different systems, we have used UV-vis spectrophotometry, induced circular dichroism spectroscopy (ICD), and the achiral molecular probe methyl orange (MO). The results show dramatic differences changing the external solvent and the surfactant, which are explained by considering the differences in the RMs interface composition, the water-surfactant interaction, and the CDs' location in the different media investigated. None of the CDs were incorporated into the benzene/AOT/water RMs at any [H2O]/[surfactant] ratio studied (W0) whereas it was previously shown that Mod-β-CD and hp-β-CD could be included in n-heptane/AOT/water RMs. However, all of the CDs are incorporated in benzene/BHDC/water RMs at W0 > 10 and hp-β-CD is dissolved even at W0 = 0. Different from what was found in n-heptane/AOT RMs, in BHDC RMs MO showed ICD signals with two different CDs: Mod-β-CD and hp-β-CD. The results are explained by considering the known difference in the interfacial water structure for AOT and BHDC RMs and the electron-rich region on the secondary hydroxyl (wider side of the CDs), which helps to solubilize all CDs in BHDC. This study shows that chiral cyclodextrin could be available for a guest in an organic medium such as the RMs. Therefore we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin.

Correlation of insulin-enhancing properties of vanadium-dipicolinate complexes in model membrane systems: phospholipid langmuir monolayers and AOT reverse micelles

We explore the interactions of V(III) -, V(IV) -, and V(V) -2,6-pyridinedicarboxylic acid (dipic) complexes with model membrane systems and whether these interactions correlate with the blood-glucose-lowering effects of these compounds on STZ-induced diabetic rats. Two model systems, dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers and AOT (sodium bis(2-ethylhexyl)sulfosuccinate) reverse micelles present controlled environments for the systematic study of these vanadium complexes interacting with self-assembled lipids. Results from the Langmuir monolayer studies show that vanadium complexes in all three oxidation states interact with the DPPC monolayer; the V(III) -phospholipid interactions result in a slight decrease in DPPC molecular area, whereas V(IV) and V(V) -phospholipid interactions appear to increase the DPPC molecular area, an observation consistent with penetration into the interface of this complex. Investigations also examined the interactions of V(III) - and V(IV) -dipic complexes with polar interfaces in AOT reverse micelles. Electron paramagnetic resonance spectroscopic studies of V(IV) complexes in reverse micelles indicate that the neutral and smaller 1:1 V(IV) -dipic complex penetrates the interface, whereas the larger 1:2 V(IV) complex does not. UV/Vis spectroscopy studies of the anionic V(III) -dipic complex show only minor interactions. These results are in contrast to behavior of the V(V) -dipic complex, [VO2 (dipic)](-) , which penetrates the AOT/isooctane reverse micellar interface. These model membrane studies indicate that V(III) -, V(IV) -, and V(V) -dipic complexes interact with and penetrate the lipid interfaces differently, an effect that agrees with the compounds' efficacy at lowering elevated blood glucose levels in diabetic rats.

How TOPO affects the interface of the novel mixed water/AOT:TOPO/n-heptane reverse micelles: dynamic light scattering and Fourier transform infrared spectroscopy studies

The proportion of TOPO in water/AOT:TOPO/n-heptane reverse micelles produces dramatic changes in the water structure, droplet size and composition of the interface.

Enzymatic hydrolysis of N-benzoyl-L-tyrosine p-nitroanilide by α-chymotrypsin in DMSO-water/AOT/n-heptane reverse micelles. A unique interfacial effect on the enzymatic activity

The reverse micelle (RM) media are very good as nanoreactors because they can create a unique microenvironment for carrying out a variety of chemical and biochemical reactions. The aim of the present work is to determine the influence of different water-dimethyl sulfoxide (DMSO) mixtures encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane RMs on the enzymatic hydrolysis of N-benzoyl-L-tyrosine p-nitroanilide (Bz-Try-pNA) by α-chymotrypsin (α-CT). The reaction was first studied in homogeneous media at different DMSO-water mixture compositions and in DMSO-water/AOT/n-heptane RMs. The hydrolysis rates of Bz-Try-pNA catalyzed by α-CT were determined by UV-vis spectroscopy. The reaction follows the Michaelis-Menten mechanism and the kinetic parameters: kcat, KM, and kcat/KM were evaluated under different conditions. In this homogeneous media, DMSO plays an important role in the solubilization process of the peptide which is almost insoluble in water, but it has a tremendous impact on the inactivation of α-CT. It is shown that the enzyme dissolved in a 20% molar ratio of the DMSO-water mixture does not present enzymatic activity. Dynamic light scattering has been used to assess the formation of DMSO-water/AOT/heptane RMs at different DMSO compositions. The results also show that there is preferential solvation of the AOT RM interface by water molecules. To test the use of these RMs as nanoreactors, the kinetic parameters for the enzymatic reaction in these systems have been evaluated. The parameters were determined at fixed W(S) {W(S) = ([water] + [DMSO])/[AOT] = 20} at different DMSO-water compositions. The results show that the Michaelis-Menten mechanism is valid for α-CT in all the RM systems studied and that the reaction takes place at the RM interface. Surprisingly, it was observed that the enzyme encapsulated by the RMs show catalytic effects with similar kcat/KM values at any DMSO composition investigated, which evidence that DMSO molecules are localized far from the RM interface.

Gel formulation containing mixed surfactant and lipids associating with carboplatin

The interaction of amphiphilic molecules such as lipids and surfactants with the hydrophilic drug carboplatin was investigated to identify suitable self-assembling components for a potential gel-based delivery formulation. (1) H-NMR Studies in sodium bis(2-ethylhexyl) sulfosuccinate (aerosol-OT, AOT)-based reverse micelles show that carboplatin associates and at least partially penetrates the surfactant interface. Langmuir monolayers formed by dipalmitoyl(phosphatidyl)choline are penetrated by carboplatin. Carboplatin was found to also penetrate the more rigid monolayers containing cholesterol. A combined mixed surfactant gel formulation containing carboplatin and cholesterol for lymphatic tissue targeting was investigated for the intracavitary treatment of cancer. This formulation consists of a blend of the surfactants lecithin and AOT (1 : 3 ratio), an oil phase of isopropyl myristate, and an aqueous component. The phases of the system were defined within a pseudo-ternary phase diagram. At low oil content, this formulation produces a gel-like system over a wide range of H(2) O content. The carboplatin release from the formulation displays a prolonged discharge with a rate three to five times slower than that of the control. Rheological properties of the formulation exhibit pseudoplastic behavior. Microemulsion and Langmuir monolayer studies support the interactions between carboplatin and amphiphilic components used in this formulation. To target delivery of carboplatin, two formulations containing cholesterol were characterized. These two formulations with cholesterol showed that, although cholesterol does little to alter the phases in the pseudo-ternary system or to increase the initial release of the drug, it contributes significantly to the structure of the formulation under physiological temperature, as well as increases the rate of steady-state discharge of carboplatin.

Nanocarrier possibilities for functional targeting of bioactive peptides and proteins: state-of-the-art

This review attempts to provide an updated compilation of studies reported in the literature pertaining to production of nanocarriers encasing peptides and/or proteins, in a way that helps the reader direct a bibliographic search and develop an integrated perspective of the subject. Highlights are given to bioactive proteins and peptides, with a special focus on those from dairy sources (including physicochemical characteristics and properties, and biopharmaceutical application possibilities of e.g. lactoferrin and glycomacropeptide), as well as to nanocarrier functional targeting. Features associated with micro- and (multiple) nanoemulsions, micellar systems, liposomes and solid lipid nanoparticles, together with biopharmaceutical considerations, are presented in the text in a systematic fashion.