Size,Charge, and Stability of Fully Serine‐Based Catanionic Vesicles: Towards Versatile Biocompatible Nanocarriers

Vesicles based on mixed cationic and anionic surfactants (catanionic vesicles) offer a number of advantageous colloidal features over conventional lipid‐based vesicles, namely spontaneity in formation, long‐term stability, and easy modulation of size and charge. If biocompatibility is added through rational design of the chemical components, the potential for biorelated applications further emerges. Here, we report for the first time on two catanionic vesicle systems in which both ionic amphiphiles are derivatized from the same amino acid—serine—with the goal of enhancing aggregate biocompatibility. Phase behavior maps for a mixture with chain length symmetry, 12Ser/12‐12Ser, and another with asymmetry, 16Ser/8‐8Ser, are presented, for which regions of vesicles, micelles, and coexisting aggregates are identified. For the asymmetric mixture, detailed phase behavior and microstructure characterization have been carried out based on surface tension, light microscopy, cryo‐SEM, cryo‐TEM, and dynamic light scattering analysis. Vesicles are found with tunable mean size, pH, and zeta potential. Changes in aggregate shape with varying composition and the effect of preparation methods and aging on vesicle features and stability have been investigated in detail. The results are discussed in the light of self‐assembly models and related catanionic systems reported before. A versatile system of robust vesicles is thus presented for potential applications.     

Adsorption, association and precipitation in hexadecyltrimethylammonium bromide/sodium dodecyl sulfate mixtures

The phase equilibria of surfactant aqueous mixtures, hexadecyltrimethylammonium bromide and sodium dodecyl sulfate, have been studied by polarizing microscopy, quasielastic light scattering, conductivity, potentiometric, electrophoretic, and surface tension measurements. Adsorption at the air/solution interface, association and precipitation in bulk solution strongly depended on the molar ratio and the concentration of surfactants. Catanionic vesicles coexisted with crystalline catanionic salts in a broad concentration range. The relative proportions of crystallites and vesicles varied according to the concentration and the molar ratio of the surfactants. The solid crystalline phase was progressively converted to catanionic vesicles with increasing surfactant molar ratio. At the highest excess of one of the surfactants transition from catanionic vesicles to mixed micelles occurred. The formation and stability of different phases are discussed in terms of surfactant molecular packing constraints and electrostatic interactions in the headgroup region. Surfactant tail-length asymmetry and the change of electrostatic interactions in the headgroup region from attractive to repulsive are governing factors for the transition from planar to curved bilayers. Received: 9 June 1998 Accepted: 18 August 1998     

Effect of hydrophilic groups of Ca surfactants and hydrophobic chains of C(n)DMAO on coordinated vesicle formation

The effects of hydrophilic headgroups of Ca surfactants, calcium dodecylsulfate (Ca(DS)(2)), calcium dodecylsulfonate (Ca(DSA)(2)), and calcium laurate (CaL(2)) and hydrophobic chains of alkyldimethylamine oxide (C(n)DMAO, n = 12, 14, 16) on the formation of Ca(2+)-ligand coordinated vesicles was investigated in detail. On the basis of phase behavior studies, rheological properties and freeze-fracture transmission electron microscope (FF-TEM) images were measured. Quite different phase behaviors were observed in different surfactant systems. For a Ca surfactant with a highly polar group, Ca(DS)(2), vesicles were observed in all Ca(DS)(2)/C(n)DMAO (n = 12, 14, and 16) systems, whereas for Ca surfactant with lower polar group, Ca(DSA)(2), vesicles can form in Ca(DSA)(2)/C(n)DMAO systems of n = 14 and 16 but not for n = 12. For CaL(2), the surfactant with the least polar group, vesicles form only in the CaL(2)/C(16)DMAO system. The results demonstrate that in the systems formed by Ca surfactants and C(n)DMAO, the formation of vesicles is driven not only by interaction between Ca(2+) and the N → O groups of C(n)DMAO but also by electrostatic and hydrophobic interactions. Vesicles prefer to form in Ca surfactants with highly polar headgroups and C(n)DMAO with long chain length.     

Two routes to vesicle formation: metal-ligand complexation and ionic interactions

Two routes to vesicle formation were designed to prepare uni- and multilamellar vesicles in salt-free aqueous solutions of surfactants. The formation of a surfactant complex between a double-chain anionic surfactant with a divalent-metal ion as the counterion and a single-chain zwitterionic surfactant with the polar group of amine-oxide group is described for the first time as a powerful driving force for vesicle-phases constructed from salt-free mixtures of aqueous surfactant solutions. As a typical example, a Zn(2+)-induced charged complex fluid, vesicle-phase has been studied in aqueous mixtures of tetradecyldimethylamine oxide (C(14)DMAO) and zinc 2,2-dihydroperfluorooctanoate [Zn(OOCCH(2)C(6)F(13))(2)]. This ionically charged vesicle-phase formed due to surfactant complexation has interesting rheological properties and is not shielded by excess salts because there are no counterions in the solution. Such a vesicle-phase of surfactant complex is important for many applications; for example, the vesicle-phase was further used to produce in situ the vesicle-phase of the salt-free cationic/anionic (catanionic) surfactants, C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13). The salt-free catanionic vesicle-phase could be produced through injecting H(2)S gas into the C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) vesicle-phase, because the zwitterionic surfactant C(14)DMAO can be charged by the H(+) released from H(2)S to become a cationic surfactant and Zn(2+) was precipitated as ZnS. After the ZnS precipitates were removed from C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) solutions, the final mixed solution does not contain excess salts as do other cationic/anionic surfactant systems. Both the C(14)DMAO-Zn(OOCCH(2)C(6)F(13))(2) complex and the resulting catanionic C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13) solution are birefringent Lalpha-phase solutions that consist of uni- and multilamellar vesicles. Ring-shaped semiconductor ZnS materials with encapsulated ZnS precipitates and regular spherical ZnS particles were prepared, which resulted in a transition from vesicles composed of metal-ligand complexes to vesicles held together by ionic interactions in the salt-free aqueous systems. This strategy should provide a new method to prepare inorganic materials. The present routes to form vesicles solve a problem: how to prepare nanomaterials using surfactant self-assembly, with structure controlled not by the growing material, but by the phase behavior of the surfactants.     

Lamellar phase formation in catanionic mixtures of hydrogenated and fluorinated surfactants: a comparative study

The properties and phase behaviors of the catanionic mixtures consisting of tetradecyltrimetylammonium bromide (TTABr) and different anionic surfactants (i.e., sodium docanoate, C₁₀HOONa; sodium laurate, C₁₂HOONa; sodium perfluorodecanoate, C₁₀FOONa) were examined, in particular when the molar mixing ratio in the aqueous solution was exactly 1:1. Although the three inspected systems have identical head groups and counterions, they exhibited very different lamellar (L_α) phases. When using the hydrogenated surfactants, the C₁₀HOONa–TTABr system formed domain-like L_α/L₁ two phases and the C₁₂HOONa–TTABr system formed cream-like L_α/L₁ two phases, respectively. In the case of the perfluorinated surfactant, the C₁₀FOONa–TTABr system formed interdigitated and tilted L_α gel. The microstructures of the three L_α phases were characterized by polarized microscope, freeze-fracture transmission electron microscope, small angle X-ray scattering, and X-ray diffraction. The phase transition of the lamellar gel at different temperature was studied by differential scanning calorimetry and rheological measurements. The results elucidated the formation of the L_α phase in catanionic mixtures containing hydrogenated or fluorinated anionic surfactants with molar mixing ratio of 1:1.     

The formation of vesicles by N-dodecyl-N-methylpyrrolidinium bromide ionic liquid/copper dodecyl sulfate and application in the synthesis of leaflike CuO nanosheets

The phase behavior of the mixed catanionic surfactants in aqueous solution, composed of the long-chain ionic liquid (IL) N-dodecyl-N-methylpyrrolidinium (C₁₂MPB) and a divalent metal surfactant copper dodecyl sulfate (Cu(DS)₂·4H₂O), was investigated. The phase diagram of the catanionic system was mapped through visual observation and electrical conductivity measurement. The formation of vesicles was confirmed in the lamellar phase (L_α) through transmission electron microscopy (TEM). Rheological measurements were used to study the macroscopic properties of the birefringent L_α phase. Electrostatic and hydrophobic interactions are regarded as the main driving forces for the formation of vesicles. Furthermore, the vesicles were successfully used as the templates to prepare the leaflike CuO nanomaterials.     

Vesicle-micelle transition in mixtures of dioctadecyldimethylammonium chloride and bromide with nonionic and zwitterionic surfactants

We have investigated the effect of mixing spontaneously formed dispersions of the cationic vesicle-forming dioctadecyldimethylammonium chloride and bromide (DODAX, with X being anions Cl- (C) or Br- (B)) with solutions of the micelle-forming nonionic ethylene oxide surfactants penta-, hepta-, and octaethyleneglycol mono-n-dodecyl ether, C12E(n) (n = 5, 7, and 8), and the zwitterionic 3-(N-hexadecyl-N,N-dimethylammonio)propane sulfonate (HPS). We used for this purpose differential scanning calorimetry (DSC), turbidity, and steady-state fluorescence spectroscopy to investigate the vesicle-micelle (V-M) transition yielded by adding C12E(n) and HPS to 1.0 mM vesicle dispersions of DODAC and DODAB. The addition of these surfactants lowers the gel-to-liquid crystalline phase transition temperature (T(m)) of DODAC and DODAB, and the transition becomes less cooperative, that is, the thermogram transition peak shifts to lower temperature and broadens to disappear when the V-M transition is complete, the vesicle bilayer becomes less organized, and the T(m) decreases, in agreement with measurements of the fluorescence quantum yield of trans-diphenylpolyene (t-DPO) fluorescence molecules incorporated in the vesicle bilayer. Turbidity data indicate that the V-M transition comes about in three stages: first surfactants are solubilized into the vesicle bilayer; after saturation, the vesicles are ruptured, and, finally, the vesicles are completely solubilized and only mixed micelles are formed. The critical points of bilayer saturation and vesicle solubilization were obtained from the turbidity and fluorescence curves, and are reported in this communication. The solubility of DODAX is stronger for C12E(n) than it is for HPS, meaning that C12E(n) solubilizes DODAX more efficiently than does HPS. The surfactant solubilization depends slightly on the counterion, and varies according to the sequence C12E5 > C12E7 > C12E8 > HPS.     

Self-assembly in a catanionic mixture with an aminoacid-derived surfactant: from mixed micelles to spontaneous vesicles

The aqueous self-assembly of a novel lysine-derived surfactant with a gemini-like architecture, designated here as 12-Lys-12, has been experimentally investigated for the amphiphile alone in water and in a mixture with dodecyltrimethylammonium bromide (DTAB). The neat surfactant forms interesting micrometer-sized rigid tubules in the dilute region, resulting in very viscous solutions. For the catanionic mixture with DTAB, various single and multiphase regions were identified (up to a total surfactant concentration of 1.5 wt %) by means of combined polarizing light microscopy, cryo-TEM, and NMR. In the DTAB-rich side, for a mixing molar ratio in the range 2 < DTAB/12-Lys-12 < 4, a region of stable, unilamellar vesicles can be found. Furthermore, it was found that upon addition of 12-Lys-12 to pure DTAB solutions, the mixed micelles grow and beyond a given mixing ratio, vesicles assemble and coexist with small micelles. The transition is not continuous, since there is a narrow mixing range where phase separation occurs. Self-diffusion measurements and cryo-TEM imaging show that the average vesicle radius is on the order of 30-40 nm.     

Stabilization of catanionic vesicles via polymerization

Polymerizable cationic surfactant methacryloyloxyoctyl trimethylammonium bromide (MOTB) and anionic surfactant sodium 4-(omega-methacryloyloxyoctyl)oxy benzene sulfonate (MOBS) were synthesized. Stable catanionic vesicles can spontaneously form upon mixing the two oppositely charged surfactants in aqueous solution, which was further permanently fixed by polymerization. Surface tensiometry, nuclear magnetic resonance (NMR), static and dynamic laser light scattering (LLS), and cryogenic transmission electron microscopy (cryo-TEM) were used in combination to characterize the catanionic vesicles before and after polymerization. The kinetics of formation and breakdown of unpolymerized catanionic vesicles were studied in detail employing stopped-flow light scattering. In contrast to unpolymerized vesicles, the polymerized ones exhibit permanent stability under external perturbations such as dilution or adding excess MOTB. A tentative explanation is proposed about why free radical polymerization can successfully fix the catanionic vesicles, the structure of which is well-known to be in dynamic equilibrium exchange with unimers.     

Interactions in Aqueous Mixtures of Alkylammonium Chlorides and Sodium Cholate

The interactions of alkylammonium chlorides (the number of carbon atom per chain was either 12, 14, or 16) with sodium cholate have been investigated by a combination of techniques including light and electron microscopy, surface tension, conductivity, light scattering, and microelectrophoretic measurements. The phase behavior has strongly depended on the molar ratio and actual concentration of oppositely charged surfactants. The change in the composition of the aggregates leads to a shape transformation from globular to elongated micelles to open and/or closed bilayers (vesicles) and precipitation. The length of micelles has been found to decrease dramatically with the concentration shift to the micellar regions of either surfactant. Upon a moderate excess of one surfactant, the mean hydrodynamic diameter of aggregates increases and wormlike micelles and/or open and closed bilayers are formed. Microscopic observations of alkylammonium cholates (novel catanionic surfactants precipitated in and/or close to equimolar region) have shown the presence of a variety of morphologies including twisted ribbons, tubules and bundles of tubules.     

Spontaneous Formation of Biocompatible Vesicles in Aqueous Mixtures of Amino Acid‐Based Cationic Surfactants and SDS/SDBS

The spontaneous formation of vesicles by six amino acid‐based cationic surfactants and two anionic surfactants (sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS)) is reported. The head‐group structure of the cationic surfactants is minutely altered to understand their effect on vesicle formation. To establish the regulatory role of the aromatic group in self‐aggregation, both aliphatic and aromatic side‐chain‐substituted amino acid‐based cationic surfactants are used. The presence of aromaticity in any one of the constituents favors the formation of vesicles by cationic/anionic surfactant mixtures. The formation of vesicles is primarily dependent on the balance between the hydrophobicity and hydrophilicity of both cationic and anionic surfactants. Vesicle formation is characterized by surface tension, fluorescence anisotropy, transmission electron microscopy, dynamic light scattering, and phase diagrams. These vesicles are thermally stable up to 65 °C, determined by temperature‐dependent fluorescence anisotropy. According to the MTT assay, these catanionic vesicles are nontoxic to NIH3T3 cells, thus indicating their wider applicability as delivery vehicles to cells. Among the six cationic surfactants examined, tryptophan‐ and tyrosine‐based surfactants have the ability to reduce HAuCl₄ to gold nanoparticles (GNPs), which is utilized to obtain in‐situ‐synthesized GNPs entrapped in vesicles without the need for any external reducing agent.     

Micellization of dissymmetric cationic gemini surfactants and their interaction with dimyristoylphosphatidylcholine vesicles

The micellization process of a series of dissymmetric cationic gemini surfactants [CmH2m+1(CH3)2N(CH2)6N(CH3)2C6H13]Br2 (designated as m-6-6 with m = 12, 14, and 16) and their interaction with dimyristoylphosphatidylcholine (DMPC) vesicles have been investigated. In the micellization process of these gemini surfactants themselves, critical micelle concentration (cmc), micelle ionization degree, and enthalpies of micellization (DeltaHmic) were determined, from which Gibbs free energies of micellization (DeltaGmic) and entropy of micellization (DeltaSmic) were derived. These properties were found to be influenced significantly by the dissymmetry in the surfactant structures. The phase diagrams for the solubilization of DMPC vesicles by the gemini surfactants were constructed from calorimetric results combining with the results of turbidity and dynamic light scattering. The effective surfactant to lipid ratios in the mixed aggregates at saturation (Resat) and solubilization (Resol) were derived. For the solubilization of DMPC vesicles, symmetric 12-6-12 is more effective than corresponding single-chain surfactant DTAB, whereas the dissymmetric m-6-6 series are more effective than symmetric 12-6-12, and 16-6-6 is the most effective. The chain length mismatch between DMPC and the gemini surfactants may be responsible for the different Re values. The transfer enthalpy per mole of surfactant within the coexistence range may be associated with the total hydrophobicity of the alkyl chains of gemini surfactants. The transfer enthalpies of surfactant from micelles to bilayers are always endothermic due to the dehydration of headgroups and the disordering of lipid acyl chain packing during the vesicle solubilization.     

Phase behavior in mixtures of cationic and anionic surfactants in aqueous solutions

Phase behavior of cationic/anionic surfactant mixtures of the same chain length (n=10, 12 or 14) strongly depends on the molar ratio and actual concentration of the surfactants. Precipitation of catanionic surfactant and mixed micelles formation are observed over the concentration range investigated. Coacervate and liquid crystals are found to coexist in the transition region from crystalline catanionic surfactant to mixed micelles.The addition of oppositely charged surfactant diminishes the surface charge density at the mixed micelle/solution interface and enhances the apparent degree of counterion dissociation from mixed micelles. Cationic surfactants have a greater tendency to be incorporated in mixed micelles than anionic ones.     

Formation of monodisperse charged vesicles in mixtures of cationic gemini surfactants and anionic SDS

The aggregation behavior of catanionics formed by the mixture of cationic geminis derived from dodecyltrimethylammonium chloride (DTAC) and anionic sodium dodecylsulfate (SDS) was studied by means of phase studies and comprehensive small-angle neutron scattering (SANS) experiments at 25 °C and 50 mM overall concentration. The results are compared to those for the previously studied SDS + DTAC system. Various gemini spacers of different natures and geometries were used, but all of them had similar lengths: an ethoxy bridge, a double bond, and an aromatic ring binding the two DTACs in three different substitutions (ortho, meta, and para). SANS and SAXS data analysis indicates that the spacer has no large effect on the spheroidal micelles of pure surfactants formed at low concentration in water; however, specific effects appear with the addition of electrolytes. Microstructures formed in the catanionic mixtures are rather strongly dependent on the nature of the spacer. The most important finding is that for the hydrophilic, flexible ethoxy bridge, monodisperse vesicles with a fixed anionic/cationic charge ratio (depending only on the surfactant in excess) are formed. Furthermore, the composition of these vesicles shows that strongly charged aggregates are formed. This study therefore provides new opportunities for developing tailor-made gemini surfactants that allow for the fine tuning of catanionic structures.     

Investigations into the bending constant and edge energy of bilayers of salt-free catanionic vesicles

Using molecular dynamics simulation, we performed theoretical calculations on the curvature constant and edge energy of bilayers of salt-free, zero-charged, cationic and anionic (catanionic) surfactant vesicles composed of alkylammonium cations (C(m)(+)) and fatty acid anions (C(n)(-)). Both the minimum size and edge energy of vesicles were calculated to examine the relation between the length of the surfactant molecules and the mechanical properties of the catanionic bilayers. Our simulation results clearly demonstrate that, when the chain lengths of the cationic and anionic surfactants are equal, both the edge energy and the rigidity of the catanionic bilayers increase dramatically, changing from around 0.36 to 2.77 kBT·nm(-1) and around 0.86 to 6.51 kBT·nm(-1), respectively. For the smallest catanionic vesicles, the curvature is not uniform and the surfactant molecules adopt a multicurvature arrangement in the vesicle bilayers. We suspect that the multicurvature bending of bilayers of catanionic vesicles is a common phenomenon in rigid bilayer systems, which could aid understanding of ion transport through bilayer membranes.     

Adsorption and micellar properties of a mixed system of nonionic-nonionic surfactants

We study the surface adsorption and bulk micellization of a mixed system of two nonionic surfactants, namely, ethylene glycol mono-n-dodecyl ether (C12E1) and tetraethylene glycol mono-n-tetradecyl ether (C14E4), at different mixing ratios at 15 degrees C. The pure C14E4 monolayer cannot show any indicative features of phase transition because of both hydration-induced and dipolar repulsive interactions between the bulky head groups. On the other hand, the monolayers of pure C12E1 and its mixture with C14E4 undergo a first-order phase transition, showing a variety of surface patterns in the coexistence region between the liquid expanded (LE) and liquid condensed (LC) phases under the same experimental conditions. For pure C12E1, the domains are of a fingering pattern while those for the C12E1/C14E4 mixed system are found to be compact circular and small irregular structures at 2:1 and 1:1 molar ratios, respectively. The critical micelle concentration (cmc) values of both the pure and the mixed systems were measured to understand the micellar behavior of the surfactants in the mixture. The cmc values of the mixed system were also calculated assuming ideal behavior of the surfactants in the mixture. The experimental and calculated values are found to be very close to each other, suggesting an almost ideal nature of mixing. The interaction parameters for mixed monolayer and micelle formation were calculated to understand the mutual behavior of the surfactants in the mixture. It is observed that the interaction parameters for mixed monolayer formation are more negative than those of micelle formation, indicating a stronger interaction between the surfactants during monolayer formation. It is concluded that since both the surfactants bear EO units in their head groups, structural parity and hydrogen bonding between the surfactants allow them to be closely packed during monolayer and micelle formation.     

正负离子表面活性剂在短链脂肪醇/水中沉淀-囊泡转化和双水相的形成

首次报道在短链脂肪醇/水溶剂中十二烷基硫酸钠和辛基三甲基溴化铵混合体系由沉淀转化为囊泡，并出现表面活性剂双水相的新现象，以期探索正负离子表面活性剂混合体系研究的新途径。     

环境因素对正负表面活性剂体系相行为的影响

在1:1正负离子表面活性剂混合体系(十二烷基硫酸钠/辛基三甲基溴化铵 SDS-C8NM3Br; 十二烷基硫酸钠/十二烷基三甲基溴化铵,SDS-C12NM3Br)中加入短链脂肪醇 (乙醇,正丙醇,正丁醇),正负离子表面活性剂沉淀溶解,出现表面活性剂双水相.上相有液晶存在,下相有囊泡自发形成.折光率数据和电镜结果表明:上相为表面活性剂富集相,下相表面活性剂浓度较低.混合体系中,出现表面活性剂双水相所需短链脂肪醇的体积百分数,随短链脂肪醇的链长增加而降低.温度升高,出现表面活性剂双水相所需短链脂肪醇的体积百分数降低.对SDS/C8NM3Br/H2O体系的研究结果表明:超声处理,可使混合体系中沉淀向囊泡转化,与短链脂肪醇的加入后的作用类似.     

Cosolvent effects on the spontaneous formation of vesicles from 1:1 anionic and cationic surfactant mixtures

This paper aims to provide a practical catanionic vesicle-boosting method by means of cosolvent addition in water and to propose a theoretical explanation which can delineate the general trend of cosolvent effects and elucidate the possible role of cosolvent in the formation of catanionic vesicles. Effects of four homologous cosolvents (methanol, ethanol, 1-propanol, and 1-butanol) on the spontaneous formation of vesicles from eight 1:1 anionic-cationic mixed surfactant systems, sodium alkyl sulfates-alkyltrimethylammonium bromides (C(n)SO4Na-C(m)N(CH3)3Br; n = 12, 14; m = 8, 10, 12, 14), at a total surfactant concentration of 10 mM were systematically studied. The experimental results revealed that varied changes in vesicle formability of different mixed surfactant systems may result from various kinds and amounts of cosolvent. Four types of cosolvent effects, however, can be classified. Among them, cosolvent effects type 2 and type 3 would serve the purpose and were exemplified by C12SO4Na-C10N(CH3)3Br, C14SO4Na-C10N(CH3)3Br, and C12SO4Na-C12N(CH3)3Br mixed surfactants. Furthermore, the effectiveness of vesicle boosting increases in the order 1-butanol > 1-propanol > ethanol > methanol. An explanation of cosolvent effects based on the medium dielectric constant was then proposed.     

pH-dependent phase behavior of carbohydrate-based gemini surfactants. Effect of the length of the hydrophobic spacer

The phase behavior of a series of carbohydrate-based gemini surfactants with varying spacer lengths was studied using static and dynamic light scattering between pH 2 and 12. Cryo-electron microscopy pictures provide evidence for the different morphologies present in solution. The spacer length of the gemini surfactants was varied from two to 12 methylene units. At near neutral pH, spherical vesicles were obtained for gemini surfactants with a spacer shorter than 10 methylene units, whereas nonspherical vesicles were obtained for spacer lengths of 10 and 12. Upon decreasing the pH, the vesicles underwent transitions toward worm-like micelles and spherical micelles for a spacer length of six and larger, whereas for shorter spacers, these transitions are not observed. For the shortest spacer at low pH, perforated vesicles are observed, and vesicles built from the gemini surfactant with a spacer of four methylene units only underwent a transition toward worm-like micelles. Upon increasing the pH to slightly basic values, flocculation followed by redispersion upon charge reversal was observed up to a spacer length of eight methylene units. The redispersal is explained by hydroxide-ion binding to the uncharged vesicular surface. By contrast, vesicles formed from the gemini surfactants with 10 and 12 methylene units only undergo a transition toward inverted phases. The observations can be understood in terms of the packing parameter.