Spontaneous formation of vesicles by sodium 2-dodecylnicotinate in water

Vesicle formation of single-tailed amphiphilic alkyltrimethylammonium bromides in water induced by dehydration-rehydration

We recently found that rough glass surfaces (RGSs) can in situ mediate the micelle-to-vesicle transition in single-component solutions of simple single-tailed amphiphiles (STAs), but only result in a relatively small number of vesicles coexisting with a large number of micelles. In the current work, a dehydration-rehydration (DHRH) method was used to induce the formation of vesicles in the single-component aqueous solutions of alkyltrimethylammonium bromides (C_nTABs, n = 12, 14, and 16), a kind of typical cationic STAs. That is, a C_nTAB micelle solution dropped on smooth glass surfaces (SGSs) was first dried, and the dried C_nTAB aggregates were then rehydrated in a monomer solution of C_nTAB. A large population of vesicles and even pure vesicle (or vesicle-dominated) systems were obtained, indicating that the DHRH process could more effectively induce the formation of STA vesicles than RGS in situ mediation. The so-obtained vesicles were characterized using DLS, FF-/cryo-TEM, AFM, SAXS, and fluorescence techniques, and their stability was determined. In addition, the effects of the conditions of DHRH and the chain length of C_nTABs on the vesicle formation were examined. It was demonstrated that the vesicles can be formed as long as the concentrations of C_nTABs in the rehydrated systems are higher than their critical micelle concentrations. The size and wall thickness of vesicles increase with an increase in chain length. A possible mechanism for the DHRH-induced vesicle formation is proposed: bilayer sheets are formed on SGSs during dehydration, and then detached from the SGSs to form vesicles during rehydration. A highly interdigitated structure of alkyl chains between two leaflets was identified in the bilayers, which probably is the origin of the formation and stability of STA vesicles.

Vesicle formation of single-chain amphiphilic 4-dodecylbenzene sulfonic acid in water and micelle-to-vesicle transition induced by wet-dry cycles

Simple single-chain amphiphiles (SCAs) can form vesicular structures in their single-component aqueous solutions, which has attracted great attention, but the understanding of their aggregation behavior is still limited. In this work, the aggregation behavior of 4-dodecylbenzene sulfonic acid (DBSA), a typical simple SCA, in water was investigated. The structure and properties of the aggregates formed were determined. In particular, the effect of wet-dry cycles on the structures of aggregates was examined. The mechanisms of aggregate formation and structural transition were discussed. It was found that the increase of DBSA concentration can drive the occurrence of a micelle-to-vesicle transition, showing a critical micelle concentration and critical vesicle concentration of ∼0.53 and 2.14 mM, respectively. The vesicles formed coexist with micelles in solution, with a unilamellar structure and ∼80 nm size, and exhibit size-selective permeability. In addition, the vesicles show remarkable stability upon long-term storage, exposure to high temperature, and freeze-thaw cycles. The H-bonding interaction between DBSA species and the interdigitated structure of alkyl chains in bilayers play a key role in the formation and stability of DBSA vesicles. Interestingly, it was found that the wet-dry cycle can induce a micelle-to-vesicle transition and an obvious increase in the size of the original vesicles, accompanied by the formation of some multilamellar vesicles. This work provides a better understanding of the aggregation behavior of simple SCAs in their single-component aqueous solutions.

Study on the Surface Properties and Aggregation Behavior of Quaternary Ammonium Surfactants with Amide Bonds

A number of techniques, including conductivity, surface tension, dynamic light scattering, transmission electron microscopy, and ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FT-IR), and ¹H-¹H 2D nuclear Overhauser effect spectroscopy (¹H-¹H 2D NOESY), have been used to investigate the effect of amide bonds on the interfacial and assembly properties of a cationic surfactant, N-anilinoformylmethyl-N-cetyl-N,N-dimethyl ammonium chloride (AMC-C ₁₆ ), in aqueous solutions. The adsorption of AMC-C ₁₆ has been found to be much better than that of the conventional cationic surfactant, benzyl cetyldimethylammonium chloride (BAC-16) at the air/water interface and in solution. The surface tension measurements show the presence of two critical aggregation concentrations (CAC₁ and CAC₂) for AMC-C ₁₆ . The presence of a strong intermolecular hydrogen bond of AMC-C ₁₆ was confirmed by ¹H NMR and FT-TR. The molecular interactions of AMC-C ₁₆ were detected by ¹H-¹H 2D NOESY. The results show that the rigid group (phenyl) of AMC-C ₁₆ was partially overlapped with its alkyl chain in aqueous solution, and the possible aggregation behavior for AMC-C ₁₆ was proposed. The effects of an inorganic salt (NaCl) and an organic salt (C₆H₅COONa) to the aggregates of AMC-C ₁₆ have been discussed.

Model of protocell compartments – dodecyl hydrogen sulfate vesicles

It is the first time to report simple single-alkyl sulfonic acid vesicles functioning as a model of protocell compartments.

Aggregation and Morphological Aptitude of Drug-Based Ionic Liquids in Aqueous Solution

Here, we present how replacing the usual inorganic counter ion with a pharmaceutically active aromatic one can greatly affect the interfacial as well as bulk properties of ionic liquids (ILs). We have synthesized a series of novel drug-based ILs, namely, 1-alkyl-3-methylimidazolium diclofenate ([C _n mim][DF]; n = 6, 8, 10, 12, and 14) abbreviated as DF-ILs, wherein DF^- is a well-recognized analgesic and nonsteroidal anti-inflammatory drug. We show strong synergistic interactions between C _n mim⁺ and aromatic DF^- attributed to reduced electrostatic repulsions and increased hydrophobicity from their incorporation, reflecting a 300-fold smaller critical aggregation concentration than that of their Cl^- analogue [C _n mim][Cl]. Interfacial properties for such strongly associating systems are discussed and clearly established to have remarkably improved properties than those of their Cl^- analogues. The decreasing polarity of the cybotactic region of pyrene with increase in the chain length "n" indicates an increased extent of packing of cationic head groups in the Stern layer. DF^- ion seems to play a vital role in the formation of the resulting aggregates, as probed by small angle neutron scattering and transmission electron microscopy. The thermodynamical insights of the aggregation process have been studied using isothermal titration calorimetry and temperature-dependent conductivity experiments. Unilamellar vesicles are formed at extremely low concentration, and also it is the first report that puts into picture the formation of vesicles for [C₆mim][DF] with such a short chain.

Microviscosity, encapsulation, and permeability of 2-ketooctanoic acid vesicle membranes

In the current work, the microviscosity, encapsulation, and permeability of 2-ketooctanoic acid (KOCOOH) vesicle membranes were investigated by steady-state and time-resolved fluorescence techniques, using 1,6-diphenyl-1,3,5-hexatriene (DPH), riboflavin, and calcein as fluorescence probes. Our results show that the microviscosity of KOCOOH membranes is similar to that of common bilayer aggregates, the KOCOOH vesicles have the ability to encapsulate hydrophilic guests, and the KOCOOH membranes are permeable to ions. The permeation of OH^- across KOCOOH membranes can be well described using a first-order kinetic model. The KOCOOH vesicles may be a good alternative protocell model that possesses some functional properties necessary for early cell membranes. To the best of our knowledge, this is the first report on the characteristics of vesicle membranes of single-tailed keto-acid amphiphiles.

Vesicles of 2-ketooctanoic acid in water

We report the spontaneous formation of vesicles from 2-ketooctanoic acid (KOCOOH), a single-tailed weakly acidic surfactant, in water. The vesicles were characterized using negative-staining, cryogenic transmission electron microscopy, conductivity, and atomic force microscopy. The pH effect on the vesicle formation and the stability of the vesicular structures were determined. The vesicles form at a very low concentration (ca. 1.4 mM) and within a wide pH range (ca. 2-10). Uni- and multilamellar vesicle structures are observed, which coexist in the KOCOOH solution. The hydrogen bonding between KOCOOH molecules probably plays an important role in the formation of the vesicles. Importantly, the vesicles exhibit remarkable stability upon long-term storage, and in artificial seawater. KOCOOH vesicles are a good alternative model system for protocell-like vesicles, as they are easily formed under plausible prebiotic conditions. In addition, they may have the same potential applications, such as in medicine, chemical engineering, and biotechnology, as conventional vesicles. To the best of our knowledge, this is the first report on the vesicles of single-tailed keto-acid amphiphiles.

Spontaneous Vesiculation and pH-Induced Disassembly of a Lysosomotropic Detergent: Impacts on Lysosomotropism and Lysosomal Delivery

Lysosomotropic detergents (LDs) selectively rupture lysosomal membranes through mechanisms that have yet to be characterized. A consensus view, currently, holds that LDs, which are weakly basic, diffuse across cellular membranes as monomers in an uncharged state, and via protonation in the acidic lysosomal compartment, they become trapped, accumulate, and subsequently solubilize the membrane and induce lysosomal membrane permeabilization. Here we demonstrate that the lysosomotropic detergent O-methyl-serine dodecylamide hydrochloride (MSDH) spontaneously assembles into vesicles at, and above, cytosolic pH, and that the vesicles disassemble as the pH reaches 6.4 or lower. The aggregation commences at concentrations below the range of those used in cell studies. Assembly and disassembly of the vesicles was studied via dynamic light scattering, zeta potential measurements, cryo-TEM, and fluorescence correlation spectroscopy and was found to be reversible via control of the pH. Aggregation of MSDH into closed vesicles under cytosolic conditions is at variance with the commonly held view of LD behavior, and we propose that endocytotic pathways should be considered as possible routes of LD entry into lysosomes. We further demonstrate that MSDH vesicles can be loaded with fluorophores via a solution transition from low to high pH, for subsequent release when the pH is lowered again. The ability to encapsulate molecular cargo into MSDH vesicles together with its ability to disaggregate at low pH and to permeabilize the lysosomal membrane presents an intriguing possibility to use MSDH as a delivery system.

A Nonconventional Model of Protocell-like Vesicles: Anionic Clay Surface-Mediated Formation from a Single-Tailed Amphiphile

We report a novel model system of precursor cellular membranes, self-assembled from micellar solution of a common anionic single-tailed amphiphile (STA), including sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). The self-assembly process was mediated with solid surfaces of Mg2Al-CO3 hydrotalcite-like compound (HTlc), an anionic clay, in the absence of cosurfactants or any additives. The resultant STA vesicles were characterized using negative-staining and cryogenic transmission electron microscopies, as well as dynamic light scattering and steady state fluorescence techniques. Interestingly, the obtained STA vesicles displayed good stability even after the removal of the anionic clay surface (ACS), and a self-reproduction phenomenon was observed for the "preformed" STA vesicles when mixing with corresponding STA micellar solutions. More importantly, the micelle-to-vesicle transition for SDS could be still arisen in high-salinity artificial seawater under the ACS mediation. Instead of conventional fatty acid scenario, our finding provides another novel possible model for protocell-like vesicles, which are easily formed under the plausible prebiotic conditions.

Structural rearrangement in the aqueous solution of surface active ionic liquid 1-butyl-3-methylimidazolium bis(2-ethylhexyl) sulfosuccinate

The aggregation behaviors of surface active ionic liquid 1-butyl-3-methylimidazolium bis(2-ethylhexyl) sulfosuccinate in aqueous solutions were investigated by conductometry, densimetry, fluorimetry, (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM), which confirmed two distinguished critical concentrations. The first critical concentration was believed to be the critical aggregation concentration (CAC), where two different types of aggregates were formed, namely, micelles with the size of 10 nm and vesicles with the size of 100 nm. The second critical concentration at two-fold CAC was suggested to be resulting from the insertion of the imidazolium cations into aggregates.

An easy approach for constructing vesicles by using aromatic molecules with β-cyclodextrin

Vesicles were formed in aqueous solution using β-cyclodextrin (β-CD) complexes with a series of ultra-small aromatic molecules. The vesicles are easy to prepare without a complicated synthesis procedure and their structure was identified and characterized using various techniques, including transmission electron microscopy, atomic force microscopy and dynamic laser light scattering. Using the β-CD/l-phenylalanine system as a representative example, the structural factors that caused the self-assembly were revealed using proton nuclear magnetic resonance, Fourier transform infrared spectroscopy and X-ray diffraction. In addition, the vesicular architecture could be endowed with a diverse range of stimuli-responses, as a consequence of the selective addition of various guest molecules. It is anticipated that this novel assembly strategy could be further extended, and that it presents new opportunities for the development of nanocarriers and soft materials.

Vesicles composed of one simple single-tailed surfactant

Vesicles formed spontaneously from only one simple single-tailed surfactant (DTAB) mediated by a rough glass surface.

Effect of pH and oxygen atom of the hydrophobic chain on the self-assembly property and morphology of the pyridyl boronic acid based amphiphiles

The surface activity and aggregation behavior of two synthesized boronic acid based anionic surfactants, sodium salt of 2-dodecyl pyridine-5-boronic acid (SDDPB) and sodium salt of 2-oxydodecyl pyridine-5-boronic acid (SODDPB), were studied in buffer solution at pH 9 and 13 containing carbohydrates. The self-assembly formation was investigated by use of a number of techniques including surface tension, conductivity, fluorescence spectroscopy, dynamic light scattering, X-ray diffraction, and transmission electron microscopy (TEM). Both of the amphiphiles exhibit a single break in the surface tension vs log(concentration) plots, indicating existence of one critical aggregation concentration. Steady state fluorescence spectroscopy was used to determine the polarity indexes using pyrene and the rigidity of the microenvironments of the aggregates using 1,6-diphenyl-1,3,5-hexatriene (DPH) as fluorescence probe molecules. The pKa's of both amphiphiles were determined in buffer solutions of different pH's. XRD studies were performed to shed light on the morphology of the self-assemblies. TEM micrographs revealed the existence of vesicles for both the amphiphiles in buffer solution of pH 9, but at pH 13, TEM pictures indicate the existence of closed vesicles in SDDPB solution and at concentrated solution the vesicles are fused to form sponge-like micelles. After aging the vesicular solution of pH 13 of SDDPB, the closed vesicles are destroyed. In contrast, for SODDPB at pH 13, TEM pictures suggest the existence of spherical and complex micelles in solution which were further transformed into crystal-like structure upon aging. The average hydrodynamic radii were determined by dynamic light scattering measurement. Therefore, for the first time, we have successfully synthesized two new surfactants containing pyridyl-boronic acid as a headgroup which shows remarkable tuning of morphology in two different pH's and in the presence of two different carbohydrates.

Functionalized vesicles based on amphiphilic boronic acids: a system for recognizing biologically important polyols

We report on a new approach for creating water-soluble functionalized vesicles employing N-alkyl-3-boronopyridinium triflates (alkyl = Me, C12H25, C16H33) as sensors for monosaccharides. The nanoaggregate properties were studied by means of DLS, TEM, high-resolution (1)H NMR, and the solvatochromic dyes Reichardt's betaine and Methyl Orange. The vesicles were shown to have 30-200 nm diameters depending on the amphiphile chain length. Diol binding to the vesicles was studied by steady-state fluorescence and UV-vis using Alizarin Red S as a probe in the solution at pH 7.4 in the presence and in the absence of D-glucose and D-fructose. Strong sensing ability of boronic acid functional moieties in the order D-fructose > D-glucose was demonstrated, and apparent binding constants were estimated.