Protein binding onto surfactant-based synthetic vesicles

Synthetic vesicles were prepared by mixing anionic and cationic surfactants, aqueous sodium dodecylsulfate with didodecyltrimethylammonium or cetyltrimethylammonium bromide. The overall surfactant content and the (anionic/cationic) mole ratios allow one to obtain negatively charged vesicles. In the phase diagram, the vesicular region is located between a solution phase, a lamellar liquid crystalline dispersion, and a precipitate area. Characterization of the vesicles was performed by electrophoretic mobility, NMR, TEM, and DLS and we determined their uni-lamellar character, size, stability, and charge density. Negatively charged vesicular dispersions, made of sodium dodecylsulfate/didodecyltrimethylammonium bromide or sodium dodecylsulfate/cetyltrimethylammonium bromide, were mixed with lysozyme, to form lipoplexes. Depending on the protein/vesicle charge ratio, binding, surface saturation, and lipoplexes flocculation, or precipitation, occurs. The free protein in excess remains in solution, after binding saturation. The systems were investigated by thermodynamic (surface tension and solution calorimetry), DLS, CD, TEM, 1H NMR, transport properties, electrophoretic mobility, and dielectric relaxation. The latter two methods give information on the vesicle charge neutralization by adsorbed protein. Binding is concomitant to modifications in the double layer thickness of vesicles and in the surface charge density of the resulting lipoplexes. This is also confirmed by developing the electrophoretic mobility results in terms of a Langmuir-like adsorption isotherm. Charges in excess with respect to the amount required to neutralize the vesicle surface promote lipoplexes clustering and/or flocculation. Protein-vesicle interactions were observed by DLS, indicating changes in particle size (and in their distribution functions) upon addition of LYSO. According to CD, the bound protein retains its native conformation, at least in the SDS/CTAB vesicular system. In fact, changes in the alpha-helix and beta-sheet conformations are moderate, if any. Calorimetric methods indicate that the maximum heat effect for LYSO binding occurs at charge neutralization. They also indicate that enthalpic are by far the dominant contributions to the system stability. Accordingly, energy effects associated with charge neutralization and double-layer contributions are much higher than counterion exchange and dehydration terms.     

Interaction enthalpy of lysozyme with vesicles

Negatively charged vesicles made of non-stoichiometric amounts of sodium dodecylsulfate and cetyltrimethylammonium bromide were characterised by physico-chemical methods. Interactions with lysozyme were examined by calorimetry. A remarkable heat effect is observed upon diluting the protein with the vesicular pseudo-solvent. The maximum ΔH_bind value occurs at complete vesicle charge neutralisation by the protein.     

Dynamics of DNA adsorption on and release from SDS-DDAB cat-anionic vesicles: a multitechnique study

DNA adsorption and release from cat-anionic vesicles made of sodium dodecylsulfate-dodecyldimethylammonium bromide (SDS-DDAB) in nonstoichiometric amounts was investigated by different electrochemical, spectroscopic, and biomolecular strategies. The characterization of the vesicular system was performed by dynamic light scattering, which allowed estimating both its size and distribution function(s). The interaction dynamics was followed by dielectric spectroscopy and zeta-potential, as well as by agarose gel electrophoresis, AGE. Also, circular dichroism, CD, measurements were carried out, to ascertain possible structural rearrangements of DNA, consequent to the interactions with the cat-anionic vesicles. CD demonstrates that vesicle-bound DNA retains its native conformation. The results obtained by the aforementioned techniques are consistent and indicate that binding saturation is obtained at a [DNA/vesicles] charge ratio close to 0.8, considering only the excess surface charges on the vesicles. This result is apparently in contradiction with a purely electrostatic approach and is tentatively ascribed to the distance between charges on the biopolymer and the vesicle surface, respectively. A possible interpretation is discussed. The nucleic acid can be completely retrieved from the vesicles upon addition of adequate amounts of SDS, which is the defective surfactant in the vesicular system. Precipitation of the poorly soluble SD-DDA salt results in an almost complete release of DNA.     

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.     

An Assessment of the Aggregation and Adsorption Behavior of the Sodium Dodecylsulfate–Cetyltrimethylammonium Bromide Mixed Surfactant System in Aqueous Medium

Sodium dodecylsulfate and cetyltrimethylammonium bromide mixtures are important catanionic systems, as they have an inherent tendency to form vesicle structures. Despite extensive studies on the phase behavior and microstructures, there is dearth of basic information on the aggregation and adsorption behavior of this mixed system. In this work the critical micelle concentration, surface tension reduction effectiveness, surface excess, mixed micelle and monolayer compositions, activity coefficients, interaction parameters, counterion binding and Gibbs energy terms of this mixed system are determined by measuring its surface tension and conductance as a function of composition. The dependence of mixed micelle composition on surfactant concentration has been successfully demonstrated.     

Gelation of "catanionic" vesicles by hydrophobically modified polyelectrolytes

The gelation of mixed cationic/anionic surfactant vesicles of sodium dodecyl sulfate/didodecyldimethylammonium bromide and sodium dodecylbenzenesulfonate/cetyltrimethylammonium tosylate by hydrophobically modified sodium polyacrylate is studied rheologically. When the vesicles are cationically charged, mixtures with this anionic polyelectrolyte form precipitates. When the vesicles are anionically charged, however, these mixtures display a progression from a Maxwell fluid to a critical gel to a solidlike gel with increasing vesicle and/or polyelectrolyte concentration. Consideration of the viscous behavior with increasing vesicle and polymer volume fraction indicates that the gel network is formed by the bridging of the hydrophobically modified polymer between vesicles. The similarity between the gelation results for the two anionic systems suggests the results can be generalized to other similarly charged mixtures.     

Dynamic surface properties of polyelectrolyte/surfactant adsorption films at the air/water interface: poly(diallyldimethylammonium chloride) and sodium dodecylsulfate

The dynamic surface elasticity, dynamic surface tension, and ellipsometric angles of mixed aqueous poly(diallyldimethylammonium chloride)/sodium dodecylsulfate solutions (PDAC/SDS) have been measured as a function of time and surfactant concentration. This system represents a typical example of polyelectrolyte/surfactant complex formation and subsequent aggregation on the nanoscale. The oscillating barrier and oscillating drop methods sometimes led to different results. The surface viscoelasticity of mixed PDAC/SDS solutions are very close to those of mixed solutions of sodium polystyrenesulfonate and dodecyltrimethylammonium bromide but different from the results for some other polyelectrolyte/surfactant mixtures. The abrupt drop in surface elasticity when the surfactant molar concentration approaches the concentration of charged polyelectrolyte monomers is caused by the formation of microparticles in the adsorption layer. Aggregate formation in the solution bulk does not influence the surface properties significantly, except for a narrow concentration range where the aggregates form macroscopic flocks. The mechanism of the observed relaxation process is controlled by the mass exchange between the surface layer and the flocks attached to the liquid surface.     

Modulation of lysozyme charge influences interaction with phospholipid vesicles

Lysozyme is a globular protein which is known to bind to negatively charged phospholipid vesicles. In order to study the relationship between charge state of the protein and its interaction with negatively charged phospholipid membranes chemical modifications of the proteins were carried out. Succinylation and carbodiimide modification was used to shift the isoelectric point of lysozyme to lower and higher pH values, respectively. The binding of the modified lysozyme to phospholipid vesicles prepared from phosphatidic acid (PA) was determined using microelectrophoresis and ultracentrifugation. At acidic pH of the solution all lysozyme species reduced the surface charges of PA vesicles. Succinylated lysozyme (succ lysozyme) reduced the electrophoretic mobility (EPM) to nearly zero, whereas native lysozyme and carboxylated lysozyme (carbo lysozyme) changed the surface charge to positive values. At neutral pH, the reduction of surface charges was less for carbo lysozyme and unmodified lysozyme. Succ lysozyme did not change the EPM. Unmodified and carbo lysozyme decreased the magnitude of EPM, but the whole complex was still negatively charged. The bound fraction of all modified lysozyme to PA vesicles at high lysozyme/PA ratios was nearly constant at acidic pH. At low lysozyme/PA ratios the extent of bound lysozyme is changed in the order carbo>unmodified>succ lysozyme. Increasing the pH, the extent of bound lysozyme to PA large unilamellar vesicles (LUV) is reduced, at pH 9.0 only 35% of carbo lysozyme, 23% of unmodified lysozyme is bound, whereas succ lysozyme does not bind at pH 7.4 and 9.0. At low pH, addition of all lysozyme species resulted in a massive aggregation of PA liposomes, at neutral pH aggregation occurs at much higher lysozyme/PA ratios. Lysozyme binding to PA vesicles is accompanied by the penetration of lysozyme into the phospholipid membrane as measured by monolayer techniques. The penetration of lysozyme into the monolayer was modulated by pH and ionic strengths. The interaction of lysozyme with negatively charged vesicles leads to a decrease of the phospholipid vesicle surface hydration as measured by the shift of the maximum of the fluorescence signal of a headgroup labeled phospholipid. The binding of bis-ANS as an additional indicator for the change of surface hydrophobicity is increased at low pH after addition of lysozyme to the vesicles. More hydrophobic patches of the lysozyme-PA complex are exposed at low pH. At low pH the binding process of lysozyme to PA vesicles is followed by an extensive intermixing of phospholipids between the aggregated vesicles, accompanied by a massive leakage of the vesicle aqueous content. The extent of lysozyme interaction with PA LUV at neutral and acidic pH is in the order carbo lysozyme>lysozyme>succ lysozyme.     

Surface tension of lysozyme mixtures with dodecyltrimethylammonium bromide and sodium dodecylsulfate at water/air and water/octane interfaces

The effect of the concentration and composition of lysozyme-surfactant (cationic dodecyltrim-ethylammonium bromide and anionic sodium dodecylsulfate) mixtures on the surface tension at aqueous solution/air and aqueous solution/octane interphases is studied. It is established that the shape of surface tension isotherms for the mixed solutions depends on the character of interactions between the protein and surfactants.     

Examination of dodecylpyridinium chloride as a potentially selective fluorescence quenching agent for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons

Fluorescence behavior is reported for 13 alternant and 12 nonalternant polycyclic aromatic hydrocarbons (PAHs) dissolved in aqueous micellar cetyltrimethylammonium chloride (CTAC)+dodecylpyridinium chloride (DDPC) and sodium dodecylsulfate (SDS)+DDPC mixed surfactant solvent media. Experimental measurements indicate that the dodecylpyridinium cation selectively quenches fluorescence emission of alternant PAHs. Emission intensities of nonalternant PAHs, with a few noted exceptions, essentially remain constant, irrespective of both DDPC concentration and cosurfactant headgroup charge.     

Binding of solvent molecules by micelles of ionic surfactants

The distribution of molecules between the free (intermicellar) and the micelle-bound states is found from the results of selective measurements of their self-diffusion coefficients in micellar solutions of ionic surfactants, i.e., sodium dodecylsulfate and cetyltrimethylammonium bromide.     

Spectroscopic investigations in molecularly organized solvent media. Part 3. Examination of the nitromethane selective quenching rule in aqueous anionic + cationic and anionic + nonionic mixed surfactant solutions

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate (SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching selectivity was restored at concentration ratios of approximately 4?:?1 (anionic:cationic) or less.     

Effect of sodium dodecyl sulfate on dynamic surface properties of lysozyme solutions

The surface dilatation rheological properties of lysozyme/sodium dodecyl sulfate (SDS) mixed solutions are studied by the oscillating ring method. At the initial stage of adsorption, the rate of variations in the surface properties depends nonmonotonically on SDS concentration due to the reversal of the lysozyme/SDS complex charge with increasing degree of surfactant binding. The nonmonotonic kinetic dependences of the dynamic surface elasticity indicate the breakage of the secondary and tertiary structures of the protein in the surface layer. For lysozyme/SDS solutions, the denaturing effect of the interface appears to be stronger than for previously studied systems, namely, bovine serum albumin/dodecyltrimethylammonium bromide and β-lactoglobulin/dodecyltrimethylammonium bromide.     

CTAB/SDBS囊泡的自发形成与聚合

讨论了CTAB/SDBS复配比例、体系浓度对其囊泡自发形成的影响和不同制备方法与放置时间对囊泡尺寸的影响,同时用TEM考察了囊泡的结构与形态。通过TEM发现囊泡之间有相互聚集融合变大的趋势,粒径分析也发现随放置时间延长囊泡尺寸增大。所以这里采用聚合法来改善囊泡的稳定性。经粒径分析证实经聚合法处理的囊泡其尺寸明显比未处理的稳定。     

Fabrication of positively charged catanionic vesicles from ion pair amphiphile with double-chained cationic surfactant

In this study, a pseudodouble-chained ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), was prepared from a mixture of cationic surfactant, hexadecyltrimethylammonium bromide, and anionic surfactant, sodium dodecylsulfate. Positively charged catanionic vesicles were then successfully fabricated from HTMA-DS with the addition of cationic surfactants, dialkyldimethylammonium bromide (DXDAB), including ditetradecyldimethylammonium bromide (DTDAB), dihexadecyldimethylammonium bromide, and dioctadecyldimethylammonium bromide (DODAB), with a mechanical disruption approach. The control of charge characteristic and physical stability of the catanionic vesicles through the variations of DXDAB molar fraction and alkyl chain length was then explored by size, zeta potential, and Fourier transform infrared analyses. It was found that the molecular packing and/or molecular interaction of HTMA-DS with DXDAB rather than the electrostatic repulsion between the charged vesicles dominated the physical stability of the mixed HTMA-DS/DXDAB vesicles. The presence of DTDAB, which possesses short alkyl chains, could adjust the packing of the unmatched chains of HTMA⁺ and DS^? and promote the vesicle formation. However, the weak molecular interaction due to the short chains of DTDA⁺ could not maintain the vesicle structures in long-term storage. With increasing the alkyl chain length of DXDAB, it was possible to improve the vesicle physical stability through the enhanced molecular interaction in the vesicular bilayer. However, the long alkyl chains of DODAB unmatched with those of HTMA-DS, resulting in the vesicle disintegration in long-term storage. For the formation of stable charged catanionic vesicles of HTMA-DS/DXDAB, a good match in hydrophobic chains and strong molecular interaction were preferred for the vesicle-forming molecules.     

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.     

Electrochemical Behavior of Cationic‐Anionic Surfactant Solutions by Cyclic Voltammetry

The electrochemical behavior of cationic tetradecyltrimethylammonium bromide (TTABr), anionic sodium dodecylsulfate (SDS), cationic‐anionic (catanionic) mixed surfactant and self‐assembled solutions at Pt wire electrode has been studied by cyclic voltammetry (CV). On the basis of the cyclic voltammograms and determining the self‐assembled structures by using freeze‐fracture transmission electron microscopy (FF‐TEM), the mechanisms of the electrochemical reactions near the electrode for the two surfactant self‐assembled solutions, i.e., micelles and vesicles, are presented. When mixing TTABr and SDS, at the right mixing ratio of TTABr:SDS, vesicles are established spontaneously. The redox behavior of two vesicle‐phase solutions at a constant total concentration of 25 mmol·L^?1 with the ratios of TTABr:SDS 9.35:0.65 of positive charges of bilayer membranes and 1.25:8.75 of negative charges of bilayer membranes are investigated by cyclic voltammetry. These cyclic voltammograms of vesicles with different charges are compared with those of 100 mmol · L^?1 TTABr and 100 mmol · L^?1 SDS micelle solutions. This CV study on surfactant self‐assembled solutions should open up a new method of study in surfactant science.     

Dielectric Behavior of Middle Phase Microemulsion

l ntroductionMicroemulsiolls are transparent and nuid systems composed of water, oil andamphiphilic molecules. They form spontaneously with simple mixing. Microemulsionsmay be water- or oil- continuous and bicontinuous under some conditions of temperatureor composition. Middle phase microemulsions(MPME) is called the 'bicontinuousstate' which is considered to be a sponge-like random netWork. Owing to its ultralowinterfacial tellsiolls against the excess water and oil phase with which they ar…     

Imaging new transient nanostructures using a microfluidic chip integrated with a controlled environment vitrification system for cryogenic transmission electron microscopy

Nanostructures (vesicles, micelles, bilayers) are important in nanomedicine and biochemical processes. They are agents for encapsulation and eventual release of drugs, flavors, and fragrances. The structural transition from micelles to vesicles through disk-like intermediate states has been demonstrated previously. Here, we disclose a new route for the micelle-vesicle transition, where micelles aggregate to first form long tubules that become unstable, and break up into vesicles. A simple theory, based on energy principles, is presented to explain the tubule-vesicle transition. Observation of this new tubular intermediate state has been facilitated by the development of an integrated microfluidic chip/cryogenic transmission electron microscopy (cryo-TEM) unit. Although this transition has been observed in a specific amphiphilic system where micellar solutions of cetyltrimethylammonium bromide (CTAB) and dodecylbenzene sulfonic acid (HDBS) are mixed to form vesicles, this new tool can be applied broadly to study transient structures in nanoscale systems under the very controlled conditions provided by microfluidics.     

Spectroscopic investigations in molecularly organized solvent media. Part 3. Examination of the nitromethane selective quenching rule in aqueous anionic + cationic and anionic + nonionic mixed surfactant solutions

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate (SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching selectivity was restored at concentration ratios of approximately 4 : 1 (anionic:cationic) or less. Received: 22 May 1997 / Revised: 29 September 1997 / Accepted: 3 October 1997