Aqueous Solutions Of Amphiphiles Research Articles

Formation and survival of clay-mediated protocell membranes composed of single-chain amphiphiles in aqueous solutions

Protocell compartments composed of simple amphiphilic molecules could have survived on the clay mineral surfaces which can serve well as plausible sites for prebiotic chemistry on the early Earth. Herein we chose four common single-chain amphiphiles (SCAs), including the anionic surfactant sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS), the cationic surfactant dodecyltrimethylammonium bromide (DTAB) and the zwitterionic lauryl sulfobetaine (LSB)), as model constituents of early membranes to establish a tentative model for protocell compartment. Positively charged Mg2Al-/Mg2Fe-layered double hydroxides (LDHs) and FeS2 are viewed as models of clay minerals. We demonstrate by comprehensively experimental study that unconventional vesicles can be easily promoted in a SCA aqueous micellar solution in the presence of model particles. Morphology evolutions are traced by collecting samples from mixtures of LDHs and SCA aqueous solutions and then recording at different incubation times via negative-staining or cryo-transmission electron microscopy (NS-TEM or cryo-TEM) and dynamic light scattering (DLS). Additionally, the stability of SCA bilayer membranes under possible prebiotic environment are tentatively studied. This work not only offers a robust yet versatile approach for the fabrication of novel vesicles but also provides new insights into the origin of cellular life.

Self-assembly of DNA-organic hybrid amphiphiles by frame-guided assembly strategies

It has been reported that DNA-Organic hybrid amphiphiles in aqueous solution could self-assemble into various morphologies including micelles, fibers and vesicles, where the hydrophobic parts intend to aggregate to avoid touching with water and the hydrophilic DNA are exposed at the shell. The regulation of their self-assembling morphologies and sizes usually needs to change the molecular inner structure, or assembling conditions and methods. Hence, it is a huge challenging to obtain aggregate with single variable of morphology or size. Inspired by the diversity of cell membrane morphologies in living organisms, a novel Frame-Guided Assembly (FGA) strategy is firstly proposed. The amphiphiles are guided to assemble along the leading hydrophobic groups (LHGs) anchored on the frame and finally form morphologies with certain shape and uniform size in accordance with the predesigned frame. It has been successfully applied to direct self-assembly behaviors of amphiphiles, including DNA and Dendron hybrids, DNA and Polymer hybrids and small molecules lipids. This strategy breaks the limits of traditional assembly method, and makes it possible to prepare aggregates with programmed geometry and size, and lays foundation for the application in the life science and potentially solves the issues of nano assemblies and cellular uptake mechanism.

Supramolecular Hybrids from Cyanometallate Complexes and Diblock Copolypeptide Amphiphiles in Water.

The self-assembly of discrete cyanometallates has attracted significant interest due to the potential of these materials to undergo soft metallophilic interactions as well as their optical properties. Diblock copolypeptide amphiphiles have also been investigated concerning their capacity for self-assembly into morphologies such as nanostructures. The present work combined these two concepts by examining supramolecular hybrids comprising cyanometallates with diblock copolypeptide amphiphiles in aqueous solutions. Discrete cyanometallates such as [Au(CN)2]−, [Ag(CN)2]−, and [Pt(CN)4]2− dispersed at the molecular level in water cannot interact with each other at low concentrations. However, the results of this work demonstrate that the addition of diblock copolypeptide amphiphiles such as poly-(L-lysine)-block-(L-cysteine) (Lysm-b-Cysn) to solutions of these complexes induces the supramolecular assembly of the discrete cyanometallates, resulting in photoluminescence originating from multinuclear complexes with metal-metal interactions. Electron microscopy images confirmed the formation of nanostructures of several hundred nanometers in size that grew to form advanced nanoarchitectures, including those resembling the original nanostructures. This concept of combining diblock copolypeptide amphiphiles with discrete cyanometallates allows the design of flexible and functional supramolecular hybrid systems in water.

Liquid Crystal-Infused Porous Polymer Surfaces: A "Slippery" Soft Material Platform for the Naked-Eye Detection and Discrimination of Amphiphilic Species.

We report the design and characterization of liquid crystal (LC)-infused porous polymer membranes that can detect and report on the presence of natural and synthetic amphiphiles in aqueous solution. We demonstrate that thermotropic LCs can be infused into nanoporous polymer membranes to yield LC-infused surfaces that exhibit slippery behaviors in contact with a range of aqueous fluids. In contrast to conventional liquid-infused surfaces (LIS) or slippery liquid-infused porous surfaces (SLIPS) prepared using isotropic oils, aqueous solutions slide over the surfaces of these LC-infused materials at speeds that depend strongly upon the composition of the fluid, including the presence, concentration, or structure of a dissolved surfactant. In general, the sliding times of aqueous droplets on these LC-infused surfaces increase significantly (e.g., from times on the order of seconds to times on the order of minutes) with increasing amphiphile concentration, allowing sliding times to be used to estimate the concentration of the amphiphile. Additional experiments revealed other intrinsic and extrinsic variables or parameters that can be used to further manipulate droplet sliding times and discriminate among amphiphiles of similar structure. Our results are consistent with a physical picture that involves reversible changes in the interfacial orientation of anisotropic LCs mediated by the interfacial adsorption of amphiphiles. These materials thus permit facile "naked-eye" detection and discrimination of amphiphiles in aqueous samples using equipment no more sophisticated than a stopwatch. We demonstrate the potential utility of these LC-infused surfaces for the unaided, naked-eye detection and monitoring of amphiphilic biotoxins in small droplets of fluid extracted directly from cultures of two common bacterial pathogens (Pseudomonas aeruginosa and Staphylococcus aureus). The ability to translate molecular interactions at aqueous/LC interfaces into large and readily observed changes in the sliding times of small aqueous droplets on surfaces could open the door to new applications for antifouling, liquid-infused materials in the context of environmental sensing and other fundamental and applied areas.

A slip-spring framework to study relaxation dynamics of entangled wormlike micelles with kinetic Monte Carlo algorithm

HypothesisWormlike micelles (WLMs) formed due to the self-assembly of amphiphiles in aqueous solution have similar viscoelastic properties as polymers. Owing to this similarity, in this work, it is postulated that kinetic Monte Carlo (kMC) sampling of slip-springs dynamics, which is able to model the rheology of polymers, can also be extended to capture the relaxation dynamics of WLMs. TheoryThe proposed modeling framework considers the following relaxation mechanisms: reptation, union-scission, and constraint release. Specifically, each of these relaxation mechanisms is simulated as separate kMC events that capture the relaxation dynamics while considering the living nature of WLMs within the slip-spring framework. As a case study, the model is implemented to a system of sodium oleate and sodium chloride to predict the linear rheology and the characteristic relaxation times associated with the individual relaxation mechanisms at different pH and salt concentrations. FindingsLinear rheology predictions were found to be in good agreement with experimental data. Furthermore, the calculated relaxation times highlighted that reptation contributed to a continuous increase in viscosity while union-scission contributed to the decrease in viscosity of WLM solutions at a higher salinity and pH. This manifests the proposed model’s capability to provide insights into the key processes governing WLM’s rheology.

Multivesicular Vesicles: Preparation and Applications

AbstractMultivesicular vesicles, i. e. vesicles containing internal, non‐concentrically arranged smaller vesicles, are artificial, polymolecular compartment systems, which can be prepared from naturally occurring or fully synthetic bilayer‐forming amphiphiles in aqueous solution through various guided assembly procedures. The general concepts for the preparation of such “vesicles‐inside‐vesicles” systems (also called “vesosomes”) are summarized, and the different methods used are compared. Selected applications of multivesicular vesicles in the field of drug delivery, cell‐mimicking model systems, and as versatile compartments for the investigation of confined reactions are discussed.

Topological changes accompanying the phase transitions in AOT-water binary system in the presence of a strongly binding counter-ion

Self-assembly of amphiphiles in aqueous solution gives rise to diverse liquid crystalline phases with different structures and properties. These phases possess different symmetries and the transition between them is associated with strong topological changes. For example, it is intriguing how the 2-dimensional bilayer sheets transform into 1-dimensional rods (building blocks of hexagonal phase) via a complicated unit involving a node connecting three rods at a certain angle—the type-I Ia3d cubic phase. Using AOT–p-toluidine hydrochloride (PTHC)–water ternary system, we have gained insight into the transformation of the aforementioned building blocks of the different liquid crystalline phases from one symmetry to another during a phase transition. Small-angle X-ray diffractograms indicate that in addition to the Bragg peaks, diffuse scattering dominates the diffraction patterns both in the lamellar as well as the cubic phases present in the ternary system. The diffused scattering was attributed to the increase in the fluctuation which in turn is related to the change in topology associated with the phase transition from the inverse hexagonal to cubic to lamellar phases.

Laser diagnostics of self-organization of amphiphiles in aqueous solutions on the example of sodium octanoate

In this study, a method of non-contact laser diagnostics of self-organization processes of surfactants in aqueous solutions is proposed. The study of solutions of sodium octanoate using laser Raman and near-IR spectroscopy has shown that spectral bands of stretching vibrations of CC-, CH- and OH-groups (including second overtone of the OH-vibrations) of the surfactant molecules and water, as well as bands of intermolecular vibrations of hydrogen bonds O-H⋯O are sensitive to the change the conformation of the hydrocarbon radical of the surfactant and the dynamics of hydrogen bonds during self-organization of surfactants in solution. It was found that the dependence of the spectral characteristics of these bands on concentration of surfactants has peculiarities in the region of critical premicelle concentration (CPMC), first critical micelle concentration (CMC1) and second critical micelle concentration (CMC2). A method of determining the critical concentrations of surfactants in water based on the revealed peculiarities is proposed. A comparative analysis of the obtained CMC values using laser Raman and IR spectroscopy and those measured by independent contact methods – pH-metry, conductivity, surface tension measurement – has shown a good match of the determined parameters. Advantages of the method of laser diagnostics of surfactant self-organization in water were discussed.

Global small-angle scattering data analysis of inverted hexagonal phases.

A global analysis model has been developed for randomly oriented, fully hydrated, inverted hexagonal (HII) phases formed by many amphiphiles in aqueous solution, including membrane lipids. The model is based on a structure factor for hexagonally packed rods and a compositional model for the scattering length density, enabling also the analysis of positionally weakly correlated HII phases. Bayesian probability theory was used for optimization of the adjustable parameters, which allows parameter correlations to be retrieved in much more detail than standard analysis techniques and thereby enables a realistic error analysis. The model was applied to different phosphatidylethanolamines, including previously unreported HII data for diC14:0 and diC16:1 phosphatid-yl-ethanolamine. The extracted structural features include intrinsic lipid curvature, hydrocarbon chain length and area per lipid at the position of the neutral plane.

Kinetics of fluoride-catalysed synthesis of organosilica colloids in aqueous solutions of amphiphiles.

Reactions involving hydrophobic reactants in water can be much accelerated in organic solvent-free solutions containing amphiphiles at neutral pH and room temperature. Previously, we demonstrated that organosilica colloidal particles could be conveniently synthesized by a versatile salt-catalysis method in solutions modified with various amphiphilic molecules. The method precludes the use of any solvent, any added form of energy (thermal or mechanical), and any strong (or hazardous) acids/bases. Herein, the kinetic properties of the reaction were systematically investigated for fluoride-catalysed synthesis of colloidal organosilica from a thiol-functionalized organosilane precursor, (3-mercaptopropyl)trimethoxysilane. Continuous, real-time ATR-FTIR measurements allowed probing the time evolution of organosilica condensation in different reaction systems, containing one of the following: non-ionic surfactants (Tween 20, Tween 40, Tween 60, Tween 80, Triton X-100), anionic surfactant (sodium dodecyl sulphate; SDS), cationic surfactant (cetyltrimethylammonium bromide; CTAB), and amphiphilic polymers (polyvinyl alcohol and polyvinylpyrrolidone). Overall, while some amphiphile-specific properties were revealed, fluoride-catalysed synthesis was ultrafast with a universal two-phase kinetic scheme (e.g. transition within 5–10 min) for all amphiphiles studied.

The first representative of cationic amphiphiles bearing three unsaturated moieties: Self-assembly and interaction with polypeptide

Novel cationic amphiphile bearing three allyl fragments (hexadecyltriallylammonium bromide, TAS-16) in the headgroup has been synthesized. Using the set of physico-chemical methods its self-assembly properties and functional activity of aggregates have been studied. It has been established, that aggregation behavior of TAS-16 is similar to the well-known analogue of trimethylammoinium series – cetyltrimethylammonium bromide (CTAB). In particular, critical micelle concentration for both amphiphiles in aqueous solutions equals 1 mM, hydrodynamic diameters of aggregates of TAS-16 and CTAB are 2–4 nm and its charge characteristics (zeta potential values) are in the range of 70–80 mV. However, practically useful properties of TAS-16 are more significant in comparison with CTAB: solubilizing capacity toward hydrophobic azodye of novel amphiphile is 1.5-fold higher, and its binding capability with bovine serum albumin (BSA) is higher. It has been revealed, that complexation of TAS-16 with BSA is contributed by electrostatic interactions, and the favorable binding site of polypeptide macromolecule is tryptophane amino acid residue. It has been shown, that substitution of methyl groups by allyl fragment in the head group structure of amphiphile leads to significant increase of membranotropic properties of surfactant.

Polymer-Amphiphile Interactions: An Overview

Interactions between the polymers and amphiphiles in aqueous solutions have generated considerable interest among researchers because of the widespread applications, relatively complex behavior and improved physicochemical properties of the mixtures. Numerous studies on the surfactant-polymer systems have been carried out in recent years and the number of scientific reports has considerably increased. Various applications of polymers in different areas and many works concerning the amphiphiles are being published every year. Usually, the mixed systems containing polymers and amphiphiles show solution properties different from those of individual solutions due to interaction between the components. The present review article mainly focuses on the behaviour of polymers in aqueous solutions, in the absence or presence of amphiphiles, such as surfactants, drugs, etc. It also summarizes effect of the nature of amphiphiles on aggregation properties of polymers in aqueous solution, and interaction of conventional as well as gemini surfactants with polymers.

Effect of Hydrocarbon Chain and Amide Linkage on the Interfacial and Self-Assembly Properties of Nicotinic Acid Amphiphiles

Three nicotinic acid amphiphiles, sodium 6-octylnicotinate (SONA), sodium 6-decylnicotinate (SDNA), and sodium 6-decylnicotinic glycinate (SDNAG), have been synthesized, and the effect of hydrocarbon chain length as well as amide linkage on the self-assembly properties in aqueous solutions have been investigated using a number of techniques, including tensiometry, fluorometry, FT-IR spectroscopy, 1H NMR spectroscopy, UV–vis spectroscopy, dynamic light scattering, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Tensiometry measurements reveal the presence of two critical aggregation concentrations (CACs) for simple aliphatic chain amphiphiles, whereas a single CAC was obtained when glycine was introduced in the headgroup. Gel permeation chromatography studies indicate the presence of closed bilayer aggregates for all of the amphiphiles in aqueous solutions. XRD spectra indicate the presence of a non-interdigited bilayer structure. The presence of bilayer vesicles was confirmed by TEM m...

Effect of siloxane spacer length on organosilicon bi-quaternary ammonium amphiphiles

A series of organosilicon Bola-form bi-quaternary ammonium amphiphiles, [OH5C3(C2H5)2N+-(CH2)3-Si(CH2)3-O-(Si(CH3)2O)n-Si(CH2)3⋯(CH2)3-N+(C2H5)2C3H5O]Cl2− (SinN2Cl2, n=0, 4, 6, 8), with the same headgroups and different length of hydrophobic linkage has been synthesized. The critical micelle concentration (CMC) of each amphiphiles was determined by equilibrium surface tension. With the increased length of hydrophobic siloxane spacer, the CMC values follow the order of Si8N2Cl2<Si6N2Cl2<Si4N2Cl2<Si0N2Cl2. At the same time, thermodynamic parameters (ΔGm0, ΔHm0, ΔSm0) of micellization were calculated by Gibbs equation under the mass action model. It indicates that the micellization of the amphiphiles in aqueous solution is entropy-driven. Especially, the surface area (Amin) of Si4N2Cl2 is the largest attributing to the interaction of free-rotated siloxane spacer and its internal oxygen atom, which make the molecular stretch free. The antimicrobial property of Si4N2Cl2 is more effective than others below the concentration of CMC, while the antimicrobial property of Si8N2Cl2 is more effective above the concentration of CMC, which indicated that both the adsorbability in formation of micellar and the hydrophobicity arising from the different length of siloxane spacer are important to inhibit microbe. Moreover, their wetting ability has been characterized by contact angles on various material surfaces. It shows that the higher weight of lipophilic siloxane spacer leads to lower contact angels.

Correction: Conformational transition of a non-associative fluorinated amphiphile in aqueous solution

Correction for ‘Conformational transition of a non-associative fluorinated amphiphile in aqueous solution’ by Marc B. Taraban et al., RSC Adv., 2014, 4, 54565–54575.

Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers.

Position isomerism is ubiquitous in atmospheric oxidation reactions. Therefore, we have compared surface-active oxygenated amphiphilic isomers (1- and 3-pentanol) at the aqueous surface with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. The experimental data are complemented with molecular dynamics (MD) simulations. A concentration-dependent orientation and solvation of the amphiphiles at the aqueous surface is observed. At bulk concentrations as low as around 100 mM, a monolayer starts to form for both isomers, with the hydroxyl groups pointing towards the bulk water and the alkyl chains pointing towards the vacuum. The monolayer (ML) packing density of 3-pentanol is approx. 70% of the one observed for 1-pentanol, with a molar surface concentration that is approx. 90 times higher than the bulk concentration for both molecules. The molecular area at ML coverage (≈100 mM) was calculated to be around 32 ± 2 Å(2) per molecule for 1-pentanol and around 46 ± 2 Å(2) per molecule for 3-pentanol, which results in a higher surface concentration (molecules per cm(2)) for the linear isomer. In general we conclude therefore that isomers - with comparable surface activities - that have smaller molecular areas will be more abundant at the interface in comparison to isomers with larger molecular areas, which might be of crucial importance for the understanding of key properties of aerosols, such as evaporation and uptake capabilities as well as their reactivity.

Conformational transition of a non-associative fluorinated amphiphile in aqueous solution

A non-associative fluorinated amphiphile was synthesized. Instead of self-association at high concentrations, this amphiphile undergoes conformational transition in which the hydrophilic tails wrap around the fluorocarbon core to shield it from water, bearing certain similarity to protein folding in a crowded environment.

Perfluorinated Alcohols and Acids Induce Coacervation in Aqueous Solutions of Amphiphiles

We have discovered that water-miscible perfluorinated alcohols and acids (FA) can induce simple and complex coacervation in aqueous solutions of a wide range of amphiphilic molecules such as synthetic surfactants, phospholipids, and bile salts as well as polyelectrolytes. This unique phenomenon seems to be nearly ubiquitous, especially for complex coacervate systems composed of mixed catanionic amphiphiles. In addition, coacervation and aqueous phase separation were observed over a wide range of surfactants concentrations and for different mole fractions of the oppositely charged amphiphile.

Amphiphiles in aqueous solution: well beyond a soap bubble

Owing to their "dual" affinity, amphiphiles self-assemble in water to form different kinds of nanoscale multimolecular assemblies ranging from simple micelles and vesicles to highly organized fibers, helices and tubes. In this tutorial review the aggregates formed in water by head/tail amphiphiles are revisited and discussed from the point of view of supramolecular chemistry with a focus on their structure and recognition abilities. Their applications in materials chemistry, as soft templates for inorganic nanostructures, as well as in biological and medicinal chemistry are also illustrated. Special attention is paid to highlight intriguing aspects, for example the control of morphology and chirality, their modulation by experimental parameters and chiral symmetry breaking.

Palladium- or proton-induced submicro spherical aggregation of macrocyclic amphiphiles in aqueous solution

Synthetic amphiphiles have been found to self-assemble into a variety of structures such as micelles, vesicles, cylinders and lamellae in aqueous media over many length scales. We report herein cation-induced aggregation of hexaaza-cyclophanes in water. Pd(2+)- or proton-induced formation of submicro spherical aggregates was observed by several spectroscopic and microscopic methods.