Monitoring Local pH of Membranous Aggregates via Ratiometric Color Changing Response

A series of oxidized di(indolyl)arylmethanes (DIAM) with polyaromatic signaling moieties have been designed for monitoring local pH at the interfacial region of surfactant aggregates, such as micelles and vesicles. The oxidized DIAMs show changes in solution color from red to yellow when incorporated in cationic surfactants (at pH 7.4) and yellow to reddish pink when exposed to negatively-charged surfactants (at pH 5.0). The changes in surface charge can influence the interfacial pH (distinct from bulk pH of the medium) of the surfactant aggregates. The mechanistic studies indicate that the red-shifted absorption maxima observed in the presence of anionic amphiphiles (acidic local pH) originated from the protonated species. On the contrary, maxima in the blue region, triggered by positively charged amphiphiles (basic local pH), is attributed to the zwitterionic species. Such prototropic equilibrium affects charge transfer states of the molecules along with their self-assembly properties. Thus, it is evident that probes can predict as well as quantify the local pH change using the pseudophase ion exchange formalism. Also, the probes can detect the presence of anionic amphiphiles even when bound to phospholipid membranes.     

Internally catalyzed separation of adhered lipid membranes

When a giant vesicle composed of POPC (rendered anionic with 5 mol % POPG) touches a giant POPC vesicle (rendered cationic with 5 mol % of DDAB), the two vesicles adhere strongly. When, however, low levels (0.1-2 mol %) of a perylene-substituted lipid are incorporated in to the bilayer, the vesicles separate at a rate that depends on the additive concentration. The vesicles that drift apart lose charge, indicating that the anionic and cationic components of the vesicles have interchanged upon contact. Presumably, the large perylene disrupts bilayer packing to allow the intervesicular exchange, and subsequent charge neutralization, to occur with up to 104 rate increases. It is possible that adhered living cells release one another by, similarly, producing low levels of a membrane-bound lipid or protein that induces so-called "kiss-and-run" vesicle events by promoting the release of adhesive elements.     

Highly selective uptake and release of charged molecules by pH-responsive polydopamine microcapsules

A systematic study of the permeation of small molecules through Pdop microcapsules is reported. The zwitterionic Pdop microcapsules are prepared by oxidative polymerization of dopamine on polystyrene microspheres followed by core removal with THF. Rhodamine 6G, methyl orange and alizarin red are chosen as differently charged probing dyes. The loading amount is affected by pH and dye concentration. Highly selective and unidirectional uptake and release of charged molecules through Pdop microcapsules can be achieved by controlling pH value: at low pH, the Pdop particles incorporate cationic dye (rhodamine 6G); at high pH, they incorporate anionic dyes (methyl orange and alizarin red). In each case, the uptake is highly selective.     

Semi-quantitative determination of cationic surfactants in aqueous solutions using gold nanoparticles as reporter probes

Concentrations of cationic surfactants in aqueous solutions have been estimated on the basis of changes in the color of gold nanoparticles, used as reporter probes. We have shown that the colors of gold nanoparticles with anionic protective groups on their surfaces shift from red to indigo/purple and then back to red in a range of cationic surfactant solutions in which concentrations vary from very low to above the theoretical CMCs. The color changes occur near the theoretical CMCs, presumably because the presence of surfactant micelles in the solution prevents the gold nanoparticles from aggregating. We have used gold nanoparticles as reporter probes to determine the concentrations of cationic surfactants in products such as hair conditioners, which often contain large amounts of alkyltrimethylammonium halides. Although this approach can only provide an estimate, it can be performed simply by addition of a given amount of gold nanoparticles to a series of diluted solutions, without the need for instruments or labor-intensive procedures. Figure Photographs of a series of diluted hair conditioner solutions with added gold nanoparticles

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A new surfactant-fluorescence probe for detecting shape transitions in self-assembled systems

A new kind of fluorescence probe, a fluorophore-labeled anionic surfactant, sodium 12-(N-dansyl)amino-dodecanate (12-DAN-ADA), was designed and synthesized. The applications of 12-DAN-ADA as a fluorescence probe in molecular assemblies, especially in the transitions between micelles and vesicles, were investigated systematically. It was found that 12-DAN-ADA can efficiently differentiate the two different aggregate types (shapes) in mixed cationic and anionic surfactant systems and double-chain cationic surfactant systems. Experimental results showed that the fluorescence anisotropy of 12-DAN-ADA increased sharply, the emission maxima became blue-shifted, and the fluorescence lifetime rose notably when the aggregates transformed from micelles to vesicles in mixed cationic and anionic surfactant systems. The fluorescence anisotropy can also distinguish different aggregate types in single-component double-chain cationic surfactant systems. Further studies demonstrated that 12-DAN-ADA is a more useful probe of transitions between micelles and vesicles than commonly used fluorescence probes, such as pyrene and 1,6-diphenyl-1,3,5-hexatriene (DPH).     

Charge type and trans-membrane transport of fluorescent probes in surfactant vesicles

We describe the effects of charge type on the trans-membrane transport of anionic and cationic fluorescent probes in cationic, anionic, and zwitterionic surfactant vesicles.     

Characterization and Aggregation Behaviors of Mixed DDAB/SDS Solution With and Without Poly(4-styrenesulfonic Acid-Co-Maleic Acid) Sodium

Synthetic vesicles are formed by cationic and anionic surfactants, didodecyldimethylammonium bromide (DDAB), and sodium dodecylsulfate (SDS). The morphology, size, and aqueous properties of cationic/anionic mixtures are investigated at various molar ratios between cationic and anionic surfactants. The charged vesicular dispersions made of DDAB/SDS are contacted or mixed with negatively charged polyelectrolyte, poly(4-styrenesulfonic acid-co-maleic acid) sodium (PSSAMA), to form complexes. Depending on DDAB/SDS molar ratio or PSSAMA/vesicle charge ratio, complexes flocculation or precipitation occur. Characterization of the cationic/anionic vesicles or complexes formed by the catanionic vesicles and polyelectrolytes is performed by transmission electron microscope (TEM), dynamic light scattering (DLS), conductivity, turbidity, and zeta potential measurements. The size, stability, and the surface charge on the mixed cationic/anionic vesicles or complexes are determined.     

混合表面活性剂微乳状液的形成和相行为研究进展

讨论了单一表面活性剂,混合表面活性剂,助溶剂等对油／水微乳状液的形成和相行为的影响。对混合表面活性剂微乳状液的形成和相行为研究工作进行了归纳和总结,重点分析了正负离子表面活性剂微乳状液的相行为和表面活性剂微乳状液的相行为和表面活性剂效率,讨论了微乳状液形成的影响因素,并提出了这一研究领域可能的发展前景。     

Interaction of sodium N-lauroylsarcosinate with N-alkylpyridinium chloride surfactants: spontaneous formation of pH-responsive, stable vesicles in aqueous mixtures

The interaction of sodium N-lauroylsarcosinate (SLS) with N-cetylpyridinium chloride (CPC) and N-dodecylpyridinium chloride (DPC) was investigated in aqueous mixtures. A strong interaction between the anionic and cationic surfactants was observed. The interaction parameter, β was determined for a wide composition range and was found to be negative. The mixed systems were found to have much lower critical micelle concentration (cmc) and surface tension at cmc. The surfactant mixtures exhibit synergism in the range of molar fractions investigated. The self-assembly formation in the mixtures of different compositions and total concentrations were studied using a number of techniques, including surface tension, fluorescence spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), confocal fluorescence microscopy (CFM). Thermodynamically stable unilamellar vesicles were observed to form upon mixing of the anionic and cationic surfactants in a wide range of composition and concentrations in buffered aqueous media. TEM as well as DLS measurements were performed to obtain shape and size of the vesicular structures, respectively. These unilamellar vesicles are stable for periods as long as 3 months and appear to be the equilibrium form of aggregation. Effect of pH, and temperature on the stability was investigated. The vesicular structures were observed to be stable at pH as low as 2.0 and at biological temperature (37°C). In presence of 10 mol% of cholesterol the mixed surfactant vesicles exhibited leakage of the encapsulated calcein dye, showing potential application in pH-triggered drug release.     

Structural and spectroscopic investigation of ZnS nanoparticles grown in quaternary reverse micelles

ZnS nanoparticles were synthesized in four component "water in oil" microemulsions formed by a cationic surfactant (cetyltrimethylammonium bromide, CTAB), a cosurfactant (pentanol or butanol), n-hexane and water. The effect of various parameters (nature of cosurfactant, water/surfactant W(0), and alcohol/surfactant P(0)) on the formation and stability of ZnS nanoparticles was investigated thoroughly. UV-Vis spectroscopy was employed to directly follow the formation of ZnS systems in the microemulsions. Thus, particle size was estimated from the position of the first excitonic transition by employing an approximate finite-depth equation and an empirical correlation, giving average diameters in the ranges 2.3-2.5 and 3.0-3.5nm, respectively. Stable ZnS nanoparticles were obtained by employing low water and high cosurfactant amounts. This suggests that at high concentration the cosurfactant molecules act as capping agents on the surface of the inverse micelles, while low water amounts are needful to obtain water droplets with a radius close to that of the interfacial film spontaneous curvature. HRTEM analysis showed that the samples are formed by a few crystalline ZnS nanoparticles of spherical shape, embedded in and amorphous organic matrix, with a coherent scattering domain between 2 and 4nm.     

Electrochemical investigation of acid-base properties of ordered liquid systems

Acid-base properties of ordered media were investigated via potentiometry, polarography and electrochemical probes. Electrochemical probes have a pH-dependent reduction potential and their oxidized and reduced forms have a different affinity for aqueous and organic phases. Solutions of anionic, cationic and nonionic surfactants were investigated. One anionic and one cationic surfactant stabilized emulsion were studied. A water-dodecane-pentanol-anionic surfactant microemulsion and a water-heptane-butanol-cationic surfactant were also investigated for several compositions. In micellar solutions and emulsions, it was possible to standardize and use the classical glass electrode for pH values in the range 1-12. The hydrogen electrode was required in the microemulsion systems. The reduction of electrochemical probes was studied by polarography. It is shown that in the ordered media studied, the aqueous phase played the most important role in micellar solutions and in O/W emulsions, as far as acid-base properties were concerned. In microemulsions, the acid-base properties of the aqueous phase were very different to those of water. The alizarin probe could be reduced at a "local" pH of about 12 when the aqueous phase pH was only 6.     

The formation of polymer vesicles or "peptosomes" by polybutadiene-block-poly(L-glutamate)s in dilute aqueous solution

Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subsequent ring-opening polymerization of N-carboxyanhydrides and were characterized by NMR, IR, SEC, and circular dichroism. These polymers, when appropriately designed, form so-called "polymersomes" or "peptosomes", vesicles composed of modified protein units. The size and structure of the vesicles are determined by dynamic light scattering, small-angle neutron scattering, and freeze-fracture electron microscopy. It is also shown that the size of the peptosomes does not depend on the pH; that is, the solvating peptide units can perform a helix-coil transition without serious changes of the vesicle morphology.     

Digitonin as a Chemical Trigger for the Selective Transformation of Giant Vesicles

The rupture of cationic giant vesicles (see the picture) in the presence of anionic vesicles, or the reverse, on exposure to digitonin is dependent on the respective cholesterol levels (0–50 mol%). Thus a disparate giant vesicle population can be chemically induced to release the contents from only a portion of its members.     

木质素阳离子絮凝剂的合成及其絮凝性能研究

以酶解木质素、甲醛、二甲胺及阳离子化试剂为原料,制备了木质素基阳离子絮凝剂.改变阳离子化试剂的用量、缩合反应的温度和时间等因素,制备不同阳离子度的木质素阳离子絮凝剂;通过其对酸性黑10B的脱色效果研究,确定了最优的制备方案.利用最优条件制备的木质素阳离子絮凝剂对三种不同种类阴离子染料废水进行了絮凝脱色处理.结果表明,原...     

Architecture-controlled "SMART" Calix[6]arene self-assemblies in aqueous solution

Self-assemblies of a calix[6]arene (1) functionalized at the small rim by three imidazolyl arms and at the large rim by three hydrophilic sulfonato groups have been studied in water. Transmission electron microscopy, atomic force microscopy, and in situ dynamic light scattering showed that 1 forms multilamellar vesicles at a concentration equal to or higher than 10(-4) M. At pH 7.8 and 10(-4) M, the multilamellar vesicles present a relatively large polydispersity (50-250 nm in diameter). However, after sonication unilamellar vesicles of much lower polydispersity and smaller size are obtained. The impact of the pH and the presence of Ag+ ions have also been investigated. Whereas increasing the pH led to the formation of giant vesicles (450 nm), monodisperse vesicules of 50 nm were obtained at a pH (6.5) that is only slightly higher than the pKa of the tris(imidazole) core of 1. Most interestingly, in the presence of silver ions, micelles (2.5 nm large) were obtained instead of vesicles. These observations are attributable to the imidazole core in 1 that is not only sensitive to the presence of protons but also can bind a silver cation. The resulting geometrical change in the monomeric units triggers the collapse of the vesicles into micelles. This shows that the implementation of an acid-base functionality such as an imidazole group in the hydrophobic core of the amphiphilic calix[6]arene makes the aggregation architecture responsive to the pH and to metal ions.     

pH- and temperature-dependent release from cationic vesicles coexisting with copolymer of N-isopropylacrylamide and methacrylic acid

Vesicles containing rhodamine B were prepared by evaporation and hydration method using N-[3-(dimethylamino)propyl]-octadecanamide (DMAPODA) and stearic acid (SA). The vesicles were multi-lamellar on optical and electron micrographs. The mean size of vesicle was 807.9 nm and the values markedly increased by the addition of copolymers of N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) (P(NIPAM-co-MAA)), possibly due to electrostatic interactions between the cationic vesicle and the anionic copolymer. The release of rhodamine B from the vesicles for 20 h was 50–60% at neutral pHs and the values increased up to 93.1% when pH decreased to 3. The increased release is possibly because the salt bridge formed between DMAPODA and SA was broken down at the acidic pH, leading to the disintegration of the vesicles. On the other hand, the release was not as sensitive to temperature as it was to pH. The salt bridge seemed to be stable at the temperatures of the release experiments (23 °C, 33 °C and 43 °C). P(NIPAM-co-MAA) was added to the suspension of the vesicle and the release was investigated with varying pHs and temperatures. The copolymer was pH- and temperature-sensitive in terms of the turbidity change of its solution. Nevertheless, the copolymer was found to have little effect on the pH- and temperature-dependent release of the vesicles.     

Photophysical characterization of 1,8 naphthalimide in micelle-diblock copolymer nano-composite: a case of morphological transformation and vesicle formation

This paper reports a morphological transition of the spherical colloidal structures of the sodium dodecyl sulfate-polyethylene-b-polyethylene glycol (SDS-PE-b-PEG) complex and anionic micelle (SDS) to "rod-shaped" colloidal structures induced by a charge transfer dye, 1,8-naphthalimide (NAPMD) (forms anions in aqueous solution by intermolecular charge transfer). The distinct steady-state results of NAPMD in the above two media point toward the formation of a new microenvironment. SDS and SDS-PE-b-PEG form unilamellar (ULV) and multilamellar vesicles (MLV), respectively, along with the rod-shaped colloidal structures as observed from transmission electron microscopy (TEM) images. This dye causes a variation in the hydrophilic/hydrophobic ratio and forms a hydrogen bond with the copolymer in the SDS-PE-b-PEG complex and subjected to electrostatic interaction with the SDS micelle in aqueous solution, which causes this morphological transformation. These vesicles show complete encapsulation of a hydrophobic dye in its interior as evident from the TEM images. ULV get ruptured at low pH, pointing toward their lower stability over MLV at low pH value. The formation of these vesicles with complete idea of its mechanism, encapsulation of bioactive molecules and its rupture at lower pH raise hope as a potential nanoscale vehicle for biologically relevant compounds and their release at low pH medium.     

Dye-surfactant interactions: a review

The present state of knowledge of the mechanisms of dye-surfactant interactions for "normal" aqueous micelles is surveyed. The nature of the forces which lead to the binding of dye molecules in micelles, the influence of the cationic, anionic or non-ionic character of a surfactant on the absorption and/or fluorescence behaviour (below and above the critical micelle concentration), ion-association processes and the influence of additives on these processes are discussed. Some discussion along these lines on related systems (reverse micelles, vesicles, polyelectrolytes) is included.     

Facile synthesis of bioglass nanospheres for the adsorption of cationic and anionic dyes from aqueous solution

A novel adsorbent, bioglass nanospheres (BGN), has been prepared by a facile process. The BGN were spheres with an amorphous structure and a relatively high specific surface area, as indicated by SEM, transmission electron microscopy, BET, FTIR, and XRD. This paper was aimed at evaluating the adsorption behavior of this new material for the adsorptive removal of cationic (methylene blue, neutral red) and anionic (congo red) dyes from aqueous solution. The effects of the initial dye concentration, contact time, solution pH, and temperature were investigated. The adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The adsorption isotherm fit well to the Langmuir model. Thermodynamic analyses showed that the adsorption was physisorption, and it was also a spontaneous and endothermic process. The BGN exhibited a good reusability after five consecutive cycles for cationic dyes. In addition, the possible adsorption mechanism was also proposed based on the above experimental results.     

Swelling of Lamellar Gel from Catanionic Hydro- and Perfluoro-Carbon Surfactant Mixtures by Refractive-Index Matching

Bilayer swelling behavior of cationic and anionic surfactant mixtures in solution induced by adding glycerin was investigated. The measurements were performed a system, cationic tetradecyltrimetylammonium bromide (TTABr), and anionic sodium perfluorodecanoate (C₉F₁₉CO₂Na) surfactant mixtures with their stoichiometric mole ratio being exactly 1 in aqueous solution. The non-precipitated phase of cationic and anionic hydro- and perfluoro-carbon surfactant mixtures being the mole ratio of 1:1 could be identified to be lamellar gel phase, which was characterized by freeze-fracture transmission electron microscopy (FF-TEM) and x-ray diffraction (XRD) measurements. Deuterium nuclear magnetic resonance (²H NMR) and rheology were used to characterize the phase transition from the lamellar gel to smaller vesicles. Phase transition from lamellar gel to smaller vesicles can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by matching of refractive index between solvent and bilayers.