Vesicle formation in oleyldimethylamine oxide/sodium oleate mixtures

Vesicle formation in a mixture of oleyldimethylamine oxide (OleylDMAO) and sodium oleate (NaOl) was investigated by viscoelastic measurements and cryoscopic transmission electron micrograph (cryo-TEM) observations. The viscoelastic properties changed with increasing mole fraction of NaOl (X _NaOl) from the Maxwell behavior of OleylDMAO solutions (X _NaOl=0) suggesting a transient network of long flexible chains. For X _NaOl=0.2 and 0.4 mixtures, both the shear storage modulus G and the shear loss modulus G showed weak dependences on angular frequency with a relation G>G. From cryo-TEM observations, vesicles coexisted with threadlike micelles in mixtures of X _NaOl=0.2 and 0.3. As X _NaOl increased further (X _NaOl=0.5 and 0.6), threadlike micelles disappeared and the coexistence of vesicles and globular micelles was observed. At X _NaOl=0.5, the viscosity decreased remarkably, which was consistent with the disappearance of threadlike micelles. The results indicated that vesicles were formed by the addition of NaOl to OleylDMAO solutions, contrary to the expectation of a decrease of the packing parameter with the introduction of electric charges.     

In Situ Amperometric Detection of Vesicles and Microgel Phases in an Aggregating System: Calcium Alginate

In situ amperometric characterization of an aggregating system in terms of molecular adsorption and single microparticle interactions at the electrode interface is demonstrated using a model system: alginate/Ca(II) in an aqueous electrolyte solution. Recording of chronoamperometric curves of oxygen reduction at the dropping mercury electrode is designed for detection of dip‐shaped signals of individual gel microparticles. By addition of Ca(II) decrease of alginate adsorption is accompanied by appearance of signals indicating vesicle type association of alginate molecules and microparticles of gel phase. AFM imaging provided evidence of initial stage in calcium alginate gel formation.     

Thermosensitive polymeric vesicles self-assembled by PNIPAAm-b-PPG-b-PNIPAAm triblock copolymers

PNIPAAm-b-PPG-b-PNIPAAm triblock copolymers were prepared by redox polymerization. The self-assembly behavior and thermosensitive property of the copolymers in water were studied using ¹H-NMR, TEM and a UV spectrophotometer. The results showed that the LCST of the copolymers was 32 °C, which was consistent with that of pure PNIPAAm. The copolymers could form a vesicular structure in an aqueous solution by self-assembly. The hollow structure of the PNIPAAm-b-PPG-b-PNIPAAm vesicles combined with the temperature-sensitive property may enable many potential applications of the vesicles.     

Cationic vesicles as chiral selector for enantioseparations of nonsteroidal antiinflammatory drugs by micellar electrokinetic chromatography

A vesicle-forming chiral cationic surfactant (1R,2S)-(-)-N-dodecyl-N-methyl-ephedrinium bromide was evaluated as a pseudo-stationary phase in micellar electrokinetic chromatography (MEKC) for enantioseparation of eight non-steroidal anti-inflammatory drugs e.g., carprofen, flurbiprofen, fenoprofen, ibuprofen, indoprofen, ketoprofen, naproxen and suprofen by capillary electrophoresis. The effects of varying experimental conditions such as pH and concentration of surfactant in the running buffer on the enantiomer separation of the drugs are reported. A mixture of five of the above drugs was separated and each enantiomeric pair was also separated simultaneously in a single run by use of the surfactant. The strong electrostatic interactions between the analytes and the vesicles seemed to have a major role in the enantiomeric separation of the profens.     

Preparation of dehydrated powder of hemoglobin vesicles

The carbonyl hemoglobin (CO-Hb), which was used to prevent denaturation (metHb) during the preparation of samples, was encapsulated into lipid vesicles constituted from unsaturated phospholipid, cholesterol and unsaturated fatty acid. Unsaturated components were polymerized by γ-irradiation to enhance the stability of bilayer membrane. An aqueous dispersion of resulting Hb vesicles was freeze-dried in the presence of saccharides (50–200 mM) to obtain a dehydrated powder of Hb vesicles. Change in the vesicle size, the leakage of encapsulated Hb and the oxidation of Hb to metHb were not observed. Therefore, the long-term storage of Hb vesicles can be realized as a dry powder.     

A multifrequency EPR study of poly(PADPA) synthesized with Trametes versicolor laccase from the aniline dimer p-aminodiphenylamine (PADPA) in the presence of anionic vesicles

Poly(PADPA) synthesized with the enzyme Trametes versicolor laccase (TvL) at pH = 3.5 in aqueous solution from the aniline dimer p-aminodiphenylamine (PADPA) was studied by EPR spectrometry at X-band and W-band frequencies. For the synthesis of poly(PADPA), vesicles formed from AOT (sodium bis-(2-ethylhexyl)sulfosuccinate) were used as structure-directing templates, and TvL/O₂ as catalyst and oxidant. The isolated product is abbreviated as “poly(PADPA)-TvL-AOT” to distinguish it from poly(PADPA) obtained by other means. The EPR spectrum of poly(PADPA)-TvL-AOT recorded at room temperature is complex. It can be decomposed into two separate Dyson–type spectral components. Furthermore, the spectra measured at high frequency exhibit a line broadening behavior in comparison to the spectra recorded at low frequency where there is no line broadening. This behavior was used to estimate the effective inter-chain spin exchange interaction for each monitored spectral component. The obtained effective distances between the polymer (or oligomer) chains in both identified components of poly(PADPA)-TvL-AOT can be explained by considering slightly different interactions between the chains and the AOT molecules present in the sample. Additionally, due to different average g tensor values, g_av, of these components, it seems that each spectral component originates from one of two different molecular subunits (or local structural motifs) within the polymer (or oligomer) chains.     

Analytical applications of organized assemblies for on-line spectrometric determinations: present and future

An amphiphile (surfactant) spread on water can lead to the formation of different aggregates: vesicles, miscelles, emulsions or microemulsions; depending on its concentration; its molecular structure and/or the experimental conditions. Such aggregates, (a) may concentrate products, reactants or analytes and so improve the analytical sensitivity and (b) may solubilize such substances and so favorably change the analytical selectivity. Bilayer membrane vesicles for instance, apart from their wide applications in cosmetic and pharmaceutical industries, have a great analytical potential due to their ability to (i) reversibly sequester metal ions avoiding matrix interference and (ii) improve cold vapor (Hg and Cd) and hydride (As, Se, Pb) chemical generation. Micellar solutions have also found wide applications in different areas of analytical chemistry, showing their capacity to concentrate and separate a significant variety of analytes. Among the numerous micelle-based separation techniques, cloud point extraction offers an excellent enrichment factor for metal ions, allowing their quantification at microgram/litre levels. Also agitating a mixture of water, oil and one or more surfactants under controlled experimental conditions, a cloudy mixture (emulsion) or a transparent solution (microemulsion) can be formed. Adequate formulation is necessary in order to obtain a stable organized media. To fulfill this requirement, a major effort is necessary in order to shorten the gap between the current knowledge on this topic and the promising field of applications that await development. Recent publications show that self-assembly structures from highly viscous samples can be accomplished on-line with the advantages of drastically reducing the time of analysis and assuring the absolute control over the stability of the aggregate. Flow systems allow effective mixing of samples with added surfactant and provide continuous pumping of the resulting mixture to sensitive detectors for the on-line determination of different analytes in complex samples.     

Synthesis of unsymmetrical saturated or diacetylenic cationic bolaamphiphiles

This work presents the synthesis of novel unsymmetrical bolaamphiphiles bearing a sugar residue and a cationic glycine betaine moiety connected to both ends of a C₂₂ or C₃₂ oligomethylene bridging chain possessing or not a diacetylenic unit. Preliminary transmission electron microscopy (TEM) studies revealed the polymorphism of these bola lipids with regard to their self-assembled morphologies in water depending on the presence or not of the diacetylenic functionality and on alkyl chain length.     

Hydrodynamic lift of vesicles and red blood cells in flow — from Fåhræus & Lindqvist to microfluidic cell sorting

Hydrodynamic lift forces acting on cells and particles in fluid flow receive ongoing attention from medicine, mathematics, physics and engineering. The early findings of Fåhræus & Lindqvist on the viscosity change of blood with the diameter of capillaries motivated extensive studies both experimentally and theoretically to illuminate the underlying physics. We review this historical development that led to the discovery of the inertial and non-inertial lift forces and elucidate the origins of these forces that are still not entirely clear. Exploiting microfluidic techniques induced a tremendous amount of new insights especially into the more complex interactions between the flow field and deformable objects like vesicles or red blood cells. We trace the way from the investigation of single cell dynamics to the recent developments of microfluidic techniques for particle and cell sorting using hydrodynamic forces. Such continuous and label-free on-chip cell sorting devices promise to revolutionize medical analyses for personalized point-of-care diagnosis. We present the state-of-the-art of different hydrodynamic lift-based techniques and discuss their advantages and limitations.     

Routes to Functional Vesicle Membranes without Proteins

Fixation of reaction partners at appropriate distances from one another is a structural prerequisite for vectorial reactions and reaction sequences. In biological systems (e.g. the photosynthetically active thylakoid membrane or membrane receptors) the positions of the reaction centers are fixed by membrane-protein complexes, but little is known about the structure of these complexes. Ordered reactive systems in synthetic vesicle membranes were first obtained by employing amphiphiles with reactive head groups as building units, by regioselective incorporation of foreign molecules into the membrane, by alignment of bolaamphiphiles with two head groups of differing solubility or size, and by the formation of domains. Chiral superstructures have also been observed in membranes, and the first stereoselective reactions have been performed in vesicle membranes. The report concludes with a brief discussion of membranes constructed from non-amphiphilic building blocks and problems which still have to be solved.