Mixed vesicle formation on a ternary surfactant system: didodecyldimethylammonium bromide/dodecylethyldimethylammonium bromide/water

Aqueous dispersions of nanostructures formed through the self-assembly of iminolipids with exchangeable hydrophobic termini

The addition of amines to an aldehyde surfactant, which was designed to be analogous to didodecyldimethylammonium bromide, gave exchangeable "iminolipids" that self-assembled to give stable aqueous dispersions of nano-sized vesicles. For example, sonication of suspensions of the n-hexylamine-derived iminolipid gave vesicles 50 to 200 nm in diameter that could encapsulate a water-soluble dye. The iminolipids could undergo dynamic exchange with added amines, and the resulting equilibrium constants (K_rel) were quantified by ¹H NMR spectroscopy. In the absence of lipid self-assembly, in CDCl₃, the assayed primary amines gave very similar K_rel values. However in D₂O the value of K_rel generally increased with increasing amine hydrophobicity, consistent with partitioning into a self-assembled bilayer. Amines with aromatic groups showed significantly higher values of K_rel in D₂O compared to similarly hydrophobic alkylamines, suggesting that π-π interactions favor lipid self-assembly. Given this synergistic relationship, π-rich pyrenyliminolipids were created and used to exfoliate graphite, leading to aqueous dispersions of graphene flakes that were stable over several months.

Temperature-induced vesicle to micelle transition in cationic/cationic mixed surfactant systems

Temperature-induced vesicle to micelle transition (VMT), which has rarely been reported in cationic/cationic mixed surfactant systems, was systemically studied in a didodecyldimethylammonium bromide (DDAB)/dodecyltrimethylammonium chloride (DTAC) aqueous solution. We investigated the effect of temperature on DDAB/DTAC aqueous solutions by means of turbidity, conductivity, cryo-TEM, a UV-vis spectrophotometer, and a steady-state fluorescence spectrometer. It was found that increasing temperature could induce the transformation from the vesicle to the micelle in this cationic/cationic mixed surfactant system. The degree of transformation can be easily controlled by the operation temperature. Additionally, by adjusting the proportion of the mixed cationic/cationic systems and employing cationic surfactants with different chain-lengths, we were able to conclude that the hydrophobic tail length of the surfactant affects the aggregation behavior of cationic/cationic mixed surfactant systems as a function of temperature. It is universal to induce the transformation from the vesicle to the micelle by temperature in cationic/cationic mixed surfactant systems. A possible mechanism for the temperature-induced VMT was proposed based on the experimental results.

Assessment of DNA complexation onto polyelectrolyte-coated magnetic silica nanoparticles

The polyelectrolyte-DNA complexation method to form magnetoplexes using silica-coated iron oxide magnetic nanoparticles as inorganic substrates is an attractive and promising process in view of the potential applications including magnetofection, DNA extraction and purification, and directed assembly of nanostructures. Herein, we present a systematic physico-chemical study that provides clear evidence of the type of interactions established, reflects the importance of the DNA length, the nanoparticle size and the ionic strength, and permits the identification of the parameters controlling both the stability and the type of magnetoplexes formed. This information can be used to develop targeted systems with properties optimized for the various proposed applications of magnetoplexes.

Multicomponent folate-targeted magnetoliposomes: design, characterization, and cellular uptake

Folate-targeted cationic magnetoliposomes (FTMLs) have been prepared with coencapsulated doxorubicin (DOX) and anionic superparamagnetic iron oxide (SPIO) nanoparticles (NPs) with 5 nm γ-Fe(2)O(3) cores and 16 nm hydrodynamic diameters. NP encapsulation (89%) was confirmed by cryogenic transmission electron microscopy (TEM), and the presence of the oppositely charged NPs did not cause liposome aggregation. The FTMLs had an average diameter of 174 ± 53 nm and existed as unilamellar and cup-shaped liposomes, which was attributed to dissimilar lipid packing parameters and the presence of PEG-lipids. A 3-fold increase in DOX release was achieved over 2 hours when the encapsulated SPIO NPs were heated by an alternating current electromagnetic field operating at radio frequencies (RF). Results with human cervical cancer cells (HeLa), which have been shown to exhibit high folate receptor (FR) expression, confirmed FTML surface binding and cellular uptake. In contrast, no uptake was observed for lower FR-expressing human breast carcinoma cells (ZR-75-1).

FROM THE CLINICAL EDITOR

This study discusses the design and cellular uptake of multifunctional folate-targeted cationic magnetoliposomes enabling doxorubicin delivery and SPIO labeling.

A theoretical and experimental approach to the compaction process of DNA by dioctadecyldimethylammonium bromide/zwitterionic mixed liposomes

The compaction of DNA by cationic liposomes constituted by a mixture of a cationic lipid, dioctadecyldimethylammonium bromide (DODAB), and a zwitterionic lipid, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), has been evaluated by means of experimental studies (electrophoretic mobility, conductometry, cryogenic electron transmission microscopy or cryo-TEM, and fluorescence spectroscopy) as well as theoretical calculations. This information reveals that DODAB/DOPE and DODAB/DLPC liposomes are mostly spherical and unilamellar, with a mean diameter of around 70 and 61 nm, respectively, a bilayer thickness of 4.5 nm, and gel-to-fluid transition temperatures, T(m), of around 19 and 28 degrees C, respectively. Their positively charged surfaces efficiently compact the negatively charged DNA by means of a strong entropically driven surface interaction that yields DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes as confirmed by zeta potential and ethidium bromide fluorescence intercalation assays. These experiments have permitted as well the evaluation of the different microenvironments of varying polarity of the DNA helix, liposomes, and/or lipoplexes. DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes have been characterized by isoneutrality ratios (L/D)(phi) of around 4.7 and 4.8, respectively, a more fluid membrane than that of the parent liposomes, and T(m) around 24 and 28 degrees C, respectively, as revealed by fluorescence anisotropy. Cryo-TEM micrographs reveal a rich scenario of nanostructures and morphologies, from unilamellar DNA-coated liposomes to multilamellar lipoplexes passing through cluster-like structures. Phase diagrams (aggregation and re-entrant condensation phenomena), calculated by means of a phenomenological theory, have confirmed the experimental concentration domains and the isoneutrality conditions. The influence of helper lipid in the compaction process, as well as the optimum choice among those herein chosen, has been analyzed.

Electrochemical and spectroscopic study of octadecyltrimethylammonium bromide/DNA surfoplexes

The use of cationic micelles consisting of octadecyltrimethylammonium bromide (C18TAB) to compact calf thymus DNA has been investigated in aqueous buffered solution at 310.15 K by means of conductometry, electrophoretic mobility, and several fluorescence spectroscopy methods. The results indicate that C18TAB micelles, consisting of 44 monomers on average, may compact DNA molecule by an electrostatic interaction that takes place at the cationic spherical micelle surface. The surfoplexes thus formed show a surface density charge that goes from negative to positive values at a Lmic/D mass ratio of around 1.0 (where Lmic and D are the masses of micellized cationic surfactant and DNA), called the isoneutrality ratio (Lmic/D)phi. Values of this characteristic parameter, determined in this work not only from the electrochemical experimental data but also from spectroscopic measurements, are in very good agreement with those ones calculated from molecular parameters and some other properties also obtained in this work. The electrostatic character of the DNA-micelle interaction has been confirmed by analyzing the decrease in fluorescence emission of the fluorophore ethidium bromide, EtBr, initially intercalated between DNA base pairs, as long as the surfoplexes are formed. Fluorescence anisotropy experiments have revealed that micelle packing becomes more rigid in the presence of DNA, but once the surfoplex is formed, the fluidity increases with the Lmic/D mass ratio, attaining its maximum when the isoneutrality ratio is exceeded. This fact, together with the net positive charge of the surfoplexes with the Lmic/D mass ratio over the isoneutrality ratio, makes this regimen of lipid and DNA content the optimum for efficiency in the transfection process.

Spontaneous formation of nanovesicles in mixtures of nonionic and dialkyl chain cationic surfactants studied by surface tension and SANS

Surface tension and small-angle neutron scattering have been used to characterize the surface properties and the structure of the aggregates formed in the dilute part of the ternary system didodecyldimethyl ammonium bromide, DDAB/tetraethylene glycol monododecyl ether, C12E4/D2O. For surfactant molar ratios, Rn, between 0.3 and 1 (pure DDAB), the surface tension measurements show the existence of two break points at concentrations of around 10(-5) and 10(-3) mol/L, respectively. The SANS measurements have shown that the first break point corresponds to a critical micellar concentration (cmc) and the second one corresponds to a critical vesicle concentration (cvc). In the intermediate composition range, Rn = 0.3-0.8, very small unilamellar vesicles (nanovesicles) are formed with the inner radius varying between 28 and 85 A and a bilayer thickness of approximately 23 A. At Rn = 0.8, we observed a transition from small vesicles (V) to large bilamellar or multilamellar vesicles (BLV, MLV) with a relatively large lamellar periodicity of around 1000 A. In the nonionic-rich region below Rn = 0.3, more classical surface tension behavior was observed, with only one break point corresponding to the onset of formation of small globular micelles.

Self-assembly in mixed dialkyl chain cationic-nonionic surfactant mixtures: dihexadecyldimethyl ammonium bromide-monododecyl hexaethylene glycol (monododecyl dodecaethylene glycol) mixtures

The self-assembly of dialkyl chain cationic surfactant dihexadecyldimethyl ammonium bromide, DHDAB, and nonionic surfactants monododecyl hexaethylene glycol, C(12)E(6), and monododecyl dodecaethylene glycol, C(12)E(12), mixtures has been studied using predominantly small-angle neutron scattering, SANS. The scattering data have been used to produce a detailed phase diagram for the two surfactant mixtures and to quantify the microstructure in the different regions of the phase diagram. For cationic-surfactant-rich compositions, the microstructure is in the form of bilamellar, blv, or multilamellar, mlv, vesicles at low surfactant concentrations and is in an L(beta) lamellar phase at higher surfactant concentrations. For nonionic-rich compositions, the microstructure is predominantly in the form of relatively small globular mixed surfactant micelles, L(1). At intermediate compositions, there is an extensive mixed (blv/mlv) L(beta)/L(1) region. Although broadly similar, in detail there are significant differences in the phase behavior of DHDAB/C(12)E(6) and DHDAB/C(12)E(12) as a result of the increasing curvature associated with C(12)E(12) aggregates compared to that of C 12E 6 aggregates. For the DHDAB/C(12)E(12) mixture, the mixed (blv/mlv) L(beta)/L(1) phase region is more extensive. Furthermore, C(12)E(12) has a greater impact upon the rigidity of the bilayer in the blv, mlv, and L(beta) regions than is the case for C(12)E(6). The general features of the phase behavior are also reminiscent of that observed in phospholipid/surfactant mixtures and other related systems.

Spectrofluorimetric characterization of mixed nanoaggregates comprising a double-chain cationic surfactant and a cationic or non-ionic single-chain surfactant

A series of mixed vesicle and pre-vesicle nanoaggregates, comprising a cationic double-chain surfactant (di-decyldimethylammonium bromide, di-C(10)DMAB, or di-dodecyldimethylammonium bromide, di-C(12)DMAB), and a cationic (dodecylethyldimethylammonium bromide, C(12)EDMAB) or non-ionic (octyl-beta-D-glucopyranoside, OBG) single-chain surfactant have been characterized by means of steady-state fluorescence spectroscopy. For that purpose, the fluorescent emission of two probes, one anionic (TNS) and the other non-ionic (PRODAN), which is known to be sensitive to the polarity, rigidity, and/or microviscosity of the environment within which the probes are housed, has been measured in the presence of the above-mentioned mixed aggregates. The results of this analysis yield interesting information about the characteristics of the vesicle surface and bilayer, as well as about the existence of clusters and/or nanoaggregates prior to the formation of vesicles.

Cationic Prevesicle and Vesicle Nanoaggregates: An Experimental and Theoretical Study

The formation of spontaneous mixed prevesicles and vesicles consisting of a cationic double-chain surfactant, didecyldimethylammonium bromide (di-C(10)DMAB), and a cationic single-chain alkyltrimethylammonium bromide with 10 and/or 14 carbon atoms (decyltrimethylammonium bromide, C(10)TAB, and/or tetradecyltrimethylammonium bromide, C(14)TAB) has been investigated by means of a series of (i) highly precise experimental techniques, such as conductometry, transmission electronic microscopies (TEM and cryo-TEM), laser Doppler electrophoresis (LDE), and steady-state fluorescence spectroscopy and (ii) theoretical models, such as the DLVO theory and two of its main further modifications, Inoues's and Sogami's models. Two new potentials, based on the combination of DLVO or Inoue potentials with that of Sogami, have been proposed and checked. This theoretical analysis has been carried out not only for the aggregates studied in this work but also for other di-C(m)DMAB + C(n)TAB (m = 10, 12 and n = 10, 12, 14) systems previously reported by us. In respect to the experimental study, special emphasis has been devoted to the prevesicle domain. We have confirmed the existence of two critical aggregation concentrations in the very diluted concentration domain, where the conductivity plot shows a zigzag pattern: the so-called mixed critical aggregate concentration, CAC* and the mixed critical vesicle concentration, CVC*. Contrarily, only CVC* is detected. The pre-CAC* nanoaggregates, with a variety of sizes and shapes, do not show a clear aggregation pattern, but even at such low concentrations a small number of nanoaggregates with a clear and ordered aggregation pattern has been visualized. In the postvesicle domain, the aggregates (vesicles) are unilamellar and spherical with a medium polidispersity and a net averaged surface density charge of around 14 x 10(-3) (pure vesicles) and 24 x 10(-3) C m(-2) (mixed vesicles). The hydrophobicities of the lipidic bilayer and the surface of the vesicles resemble those of media with dielectric constants of around 30 and 75, respectively. Finally, theoretical predictions confirm the stability of the pure and mixed vesicles studied in this work and in other works previously reported.

Electrochemical, microscopic, and spectroscopic characterization of prevesicle nanostructures and vesicles on mixed cationic surfactant systems

Several experimental techniques (conductivity, zeta potential, transmission electronic microscopy, and steady-state fluorescence spectroscopy) have been used to study the formation of mixed colloidal aggregates consisting of a cationic double-chain surfactant, di-dodecyldimethylammonium bromide (di-C12DMAB), and a single-chain alkyltrimethylammonium bromide with 10 and/or 14 carbon atoms (decyltrimethylammonium bromide, C10TAB, and/or tetradecyltrimethylammonium bromide, C14TAB). Special interest has been devoted to the prevesicle domain, within which the formation of aggregated nanostructures was first reported in our laboratory. For that purpose, studies have been carried out on the very dilute region by means of conductivity experiments, confirming the existence of two critical aggregation concentrations in that concentration domain: the so-called mixed critical aggregate concentration, CAC, and the mixed critical vesicle concentration, CVC. By carrying out TEM experiments on negatively stained samples, we were surprised to find a number of aggregates without a clear aggregation pattern and with a variety of sizes and shapes at concentrations below CAC, where only monomers were expected. However, the nanoaggregates found at concentrations between CAC and CVC, also by TEM microscopy, show a clear and ordered "fingerprint"-like aggregation pattern similar to the liquid-crystalline phases reported for DNA-liposome complexes and/or DNA packed with viral capsids. Finally, at total surfactant concentrations above CVC, the aggregates were confirmed, by means of cryo-TEM micrographs and zeta potential measurements, to be essentially unilamellar spherical vesicles with a medium polydispersity and a net-averaged surface density charge of around 12 x 10(-3) C m(-2). The fluorescence emission of two probes, TNS (anionic) and PRODAN (nonionic), allows for the analysis of the micropolarity and microviscosity of the different microenvironments present in aqueous surfactant solutions where the above-mentioned vesicle and prevesicle aggregates are present.

Aggregation behavior in mixed system of double-chained anionic surfactant with single-chained nonionic surfactant in aqueous solution

The aggregation behavior of mixed systems of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) or sodium bis(4-phenylbutyl) sulfosuccinate (SBPBS) with nonionic surfactant pentaethylene glycol mono-n-dodecyl ether (C12E5) have been studied by means of steady-state fluorescence, electrical conductivity, dynamic light scattering, transmission electron microscopy, electrophoretic light scattering and pyrene solubilization measurements. The critical concentrations for aggregation, micropolarity, mobility, solubilization capacity and morphology of aggregates are characterized. Two critical concentrations for aggregation are observed in the mixed surfactants, which may correspond to the formation of different kinds of aggregates. Moreover, it is more favorable for AOT-C12E5 to form mixed vesicles compared to SBPBS-C12E5 at higher mole fraction of C12E5. In addition, it is revealed that SBPBS-C12E5 mixture has larger solubilization capacity for pyrene than AOT-C12E5 system.

New insights into self-organization of a model lipid mixture and quantification of its adsorption on spherical polymer particles

The adsorption of lipids onto spherical polymer colloids led to original assemblies presenting structural characteristics adjustable with the lipid formulation. The model system selected for this work involved sulfate-charged poly(styrene) submicrometer particles and zwitterionic/cationic lipid mixtures composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP). According to the theoretical packing parameter calculations and whatever the DPPC/DPTAP ratio, the two lipids self-assembled in aqueous media to spontaneously form vesicles. A phase transition investigation of these DPPC/DPTAP vesicles using differential scanning calorimetry revealed particular thermotropic behaviors, especially for the equimolar formulation where very strong interactions occurred between DPPC and DPTAP. Furthermore, the coating of the lipids around particles was monitored versus DPPC/DPTAP ratio by means of numerous appropriate techniques. First, a thermogravimetric analysis, providing decomposition profiles of lipid/polymer particle assemblies with temperature, was atypically carried out for such nanostructures. Then, 1H NMR spectroscopy enabled the exact DPPC/DPTAP molar ratios adsorbed on particles to be determined by differentiating both lipids. Subsequently, it also pointed out the major role of electrostatic interactions as driving forces in the assembly elaboration process. In addition to these findings, quantitative information has been collected and correlated with chemical lipid assays and permitted the statement of a lipid bilayer coverage for the assemblies prepared in water, in agreement with quasi-elastic light scattering data.

Self-organization of the ternary didecyldimethylammonium bromide/octyl-beta-D-glucopyranoside/water system

The spontaneous and thermodynamically stable mixed vesicles constituted by a double-chain cationic surfactant with 10 carbon atoms hydrophobic tail, didecyldimethylammonium bromide (di-C(10)DMAB), and a nonionic single-chain surfactant, octyl-beta-d-glucopyranoside (OBG), have been characterized in aqueous media by means of a series of experimental techniques, as well as a theoretical approach. Conductivity data allow for the determination of the concentrations at which the monomer-to-vesicle (CVC) and/or vesicle-to-micelle (CMC) transitions occur. Electrophoretic mobilities, obtained from laser-doppler-electrophoresis experiments, permit the determination of zeta-potentials and, from them, the surface charge density of the vesicle aggregates. Cryogenic transmission electron microscopy (cryo-TEM) provides pictures of the vesicles, their size and shape being, thus, determined. Finally, the sensitivity of the emission spectra of some fluorescent probes, such as the cationic TNS and the nonionic PRODAN, to the polarity of the environment, allow for a complete study of different pre- and post-vesicle microdomains, of variable rigidity and micropolarity. This, in turn, yield interesting information about the vesicle surface and bilayer, as well as, about the existence of clusters and/or nanoaggregates prior to the formation of vesicles, as was proposed by us in a previous paper.

Aggregation phenomena on the ternary ionic-nonionic surfactant system: didodecyldimethylammonium bromide/octyl-beta-D-glucopyranoside/water. Mixed microaggregates, vesicles, and micelles

The formation of a variety of mixed colloidal aggregates has been investigated on a ternary ionic-nonionic system constituted by (i) a double-chain cationic surfactant with a 12-carbon atom hydrophobic tail, didodecyldimethylammonium bromide (di-C(12)DMAB), (ii) a nonionic single-chain surfactant, octyl-beta-D-glucopyranoside (OBG), and (iii) water. The study has been carried out by means of conductivity, zeta-potential, transmission electron microscopy (TEM), and cryogenic transmission electron microscopy (cryo-TEM) experiments on the highly diluted, very diluted, and moderately diluted regions. The formation of mixed microaggregates, prior to the appearance of mixed vesicles, has been undoubtly confirmed by conductivity, TEM, and zeta-potential results. The concentrations at which these mixed colloidal aggregates form, i.e., the mixed critical microaggregate concentration (CAC), the mixed critical vesicle concentration (CVC), and the mixed critical micelle concentration (CMC), have been determined from conductivity data, while the zeta-potential experiments allow for the characterization of the aggregate/solution interface. The shape and size of the microaggregates and vesicles have been evaluated from TEM and cryo-TEM micrographs, respectively. All of the experimental evidence has been also analyzed in terms of the theoretical packing parameter, P.