DNA conformational dynamics in the presence of catanionic mixtures

Preparation and Characterization of Cationic Vesicles from a New Type of Ion Pair Amphiphile Carbethopendecinium-Dodecylsulfate

The aim of this work was to prepare and characterize a yet undescribed type of catanionic vesicle based on a new ion pair amphiphile, which were formed from carbethopendecinium bromide (also called Septonex) and sodium dodecylsulfate. The vesicles were prepared by mixing an amphiphilic pair together with dioctadecyldimethylammonium chloride and cholesterol at a concentration of 0, 5, 10, 15, 20, 30, 40, and 60 mol %. Final size, polydispersity and stability was studied by dynamic and electrophoretic light scattering. Fluorescence anisotropy, generalized polarization and high-resolution ultrasound spectroscopy were used to determine membrane order and hydration their outer part. The vesicles appeared to be stable in the short term independently of the cholesterol content. From a long-term (28 days) perspective, it was possible to detect a threshold of 15 mol % above which the vesicles were stable. The same cholesterol content threshold also applied to stability at elevated temperatures. Fluorescence measurements showed that the phase transition temperature was located at significantly lower temperatures compared to a similar system composed of hexadecyl-trimethylammonium-dodecyl sulfate. Using differential scanning calorimetry, it was found that this temperature was slightly affected by the cholesterol content and was around 15 °C. The results from ultrasonic spectroscopy together with generalized polarization and anisotropy showed a threshold of 20 mol % cholesterol content, above which the properties of the vesicular membrane, such as its stiffness and hydration, began to change significantly.

Bile acid derivative-based catanionic mixtures: versatile tools for superficial charge modulation of supramolecular lamellae and nanotubes

Self-assembled structures formed by mixtures of cationic and anionic surfactants are interesting tools for applications requiring interactions with charged particles and molecules. Nevertheless, they present instability close to the equimolar composition and poor morphological versatility, which is generally restricted to vesicles and micelles. Against this general trend, we report on bile salt derivative based catanionic mixtures assembling in tubules and lamellae depending on the mixture composition. Electrophoretic mobility measurements prove that the composition also dictates their superficial charge, which can be tuned from negative to positive by increasing the positively charged surfactant fraction in the mixtures. The study of the catanionic aggregates was conducted by means of microscopy and spectroscopy techniques and compared to the self-assembly behaviors of the individual building blocks. This study broadens the so far small array of bile salt derivative catanionic systems, confirming their distinctive behavior in the spectrum of catanionic mixtures.

The effect of temperature, composition and alcohols on the microstructures of catanionic mixtures of sodium dodecylsulfate and cetyltrimethylammonium bromide in water

The influence of mixing protocol, composition, temperature, ageing and added alcohols on the characteristics of the microstructures of sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB) mixtures has been investigated in this paper. In this catanionic mixture (1 weight% total surfactant content) temperature induced microstructural transition occurs, which is (i) a micelle-to-vesicle transition (MVT) if α_SDS (mole fraction of SDS) = 0.7, 0.8 or 0.9 and (ii) a vesicle-to-micelle transition (VMT) if α_SDS = 0.1, 0.2 or 0.3. In the mixture of α_SDS = 0.7, specific conductivity and dynamic light scattering measurements also support the occurrence of MVT. Transition electron microscopy and small angle neutron scattering measurements were also made to assess the characteristics of the microstructures. Alcohols added to the mixture of α_SDS = 0.7 reduced the size of the vesicle, while only monohydric alcohols suppressed the temperature induced transition indicating that the number and location of -OH groups of the alcohols have a dramatic modulating influence on the structural transition occurring in catanionic mixtures. The influence of the alcohols is explained in terms of changes produced in the dielectric constant and hydrophobicity of the medium.

From surfactant to cellulose and DNA self-assembly. A 50-year journey

Surfactants have been the basis for applications in several industrial sectors for a long time. However, fundamental research was 50 years ago still limited to a small number of academic groups and even basic aspects were controversial. The field has since undergone an enormous expansion and the improved understanding has laid the basis of numerous new products as well as been the basis of important parts of nano-science and -technology.The present author has during 50 years in academia devoted most of his research to amphiphilic compounds, including both surfactants and polymers. Hereby, I had the privilege of following a very exciting development. In 2015, I had the honour to receive the Life-time Achievement Award of IACIS, the International Association of Colloid and Interface Scientists. IACIS organizes since the 1970s a tri-annual symposium, typically the best attended in the field. For the first time since 2000, it was in 2015 organized in Europe, namely Mainz, Germany. This treatise is based on my award lecture in Mainz, which covered developments from my first research as a new Ph D student in Stockholm to current work as an emeritus and visiting professor. Interestingly, discoveries in my very early work contributed to solving problems in now on-going research. Håkan Wennerström kindly wrote a quite comprehensive paper about my achievements a few years ago (Adv Colloid Interf Sci 205:1-8, [1]). In writing the present paper, I have strived at covering mainly topics not treated in detail by Håkan. In fact, I will emphasize very much our early studies as well as our studies of surfactant self-assembly by NMR and in particular look at the developments of our research and connections between different research topics.

DNA association-enhanced physical stability of catanionic vesicles composed of ion pair amphiphile with double-chain cationic surfactant

Physical stability control of vesicle/DNA complexes is a key issue for the development of catanionic vesicles composed of ion pair amphiphile (IPA) as DNA carriers. In this work, physical stability characteristics of the complexes of DNA with positively charged catanionic vesicles composed of an IPA and a double-chain cationic surfactant, dihexadecyldimethylammonium bromide (DHDAB), were explored. It was found that in water, the mixed IPA/DHDAB catanionic vesicles became stable when the mole fraction of DHDAB (xDHDAB) was increased up to 0.5. The improved physical stability of the vesicles with a high xDHDAB could be related to the enhanced electrostatic interaction between the vesicles. When the catanionic vesicles interacted with DNA, excellent physical stability was detected for the vesicle/DNA complexes especially with a high xDHDAB. However, this could not be fully explained by the electrostatic interaction effect, and the role of molecular packing within the vesicular bilayers was apparently important. The corresponding Langmuir monolayer study demonstrated that the molecular packing of mixed IPA/DHDAB layers became ordered with DNA association due to inhibited desorption of the positively charged moiety of the IPA. Moreover, the DNA association-induced improvement in the molecular packing of the mixed IPA/DHDAB layers became pronounced with increased xDHDAB. The results imply that one can fabricate catanionic vesicle/DNA complexes with excellent physical stability through the improved molecular packing in the IPA vesicular bilayers with DHDAB addition and DNA association.

Confining ss-DNA/carbon nanotube complexes in ordered droplets

In 1/1 mass ratio mixtures made of single strand DNA and single-walled carbon nanotubes lyotropic nematic phases are formed. The process is assisted by segregative phase separation procedures. The liquid crystalline order occurring therein was confirmed by optical polarizing microscopy and zero-shear rheology. The resulting nematic droplets were dispersed in protein or cationic surfactant solutions, under appropriate pH and/or ionic strength conditions. The components of the hosting fluid(s) rapidly adsorb onto the droplets, form a permanent peel on their surface, and confine them. The peel resists osmotic gradients and has significant stability. The distribution of the species in the droplet and in the peel was determined by SEM. Data indicate that the peel contains protein or surfactant, depending on the titrant, when the core is rich in DNA and nanotubes. According to electron microscopy, nematic order in the droplets is partly retained.

Interaction between DNA and trimethyl-ammonium bromides with different alkyl chain lengths

The interaction between λ--DNA and cationic surfactants with varying alkyl chain lengths was investigated. By dynamic light scattering method, the trimethyl-ammonium bromides-DNA complex formation was shown to be dependent on the length of the surfactant's alkyl chain. For surfactants with sufficient long alkyl chain (CTAB, TTAB, DTAB), the compacted particles exist with a size of ~60-110 nm at low surfactant concentrations. In contrast, high concentration of surfactants leads to aggregates with increased sizes. Atomic force microscope scanning also supports the above observation. Zeta potential measurements show that the potential of the particles decreases with the increase of surfactant concentration (CTAB, TTAB, DTAB), which contributes much to the coagulation of the particles. For OTAB, the surfactant with the shortest chain in this study, it cannot fully neutralize the charges of DNA molecules; consequently, the complex is looser than other surfactant-DNA structures.

Catanionic gels based on cholic acid derivatives

In this paper, the preparation and characterization of an anionic and a cationic surfactant obtained by chemical modifications of a natural bile acid (cholic acid) are reported. The bile acid was modified by introducing a diamine or a dicarboxylic aromatic residue on the lateral chain. The pure cationic surfactant self-assembles in a network of fibers with a cross-section gyration radius of about 15.1 Å, providing hydrogels with a pH-dependent compactness. On the other hand, the anionic molecule gives rise to prolate ellipsoid micelles. Homogeneous catanionic mixtures have also been obtained, with molar fraction of each surfactant ranging from 0.125 to 0.875. At total surfactant concentration of 0.05% (w/v), the mixtures form gels of fibrils partially arranged in secondary twisted superstructures. Comparison of this concentration with the minimum gelation concentration of the pure cationic derivative (0.16% w/v) suggests that, in the mixtures, the presence of the electrostatic component in self-assembly of the molecules allows the formation of gels starting from more dilute samples. In view of these achievements, this work suggests that catanionic mixtures can be exploited to enhance the efficiency of gelators.

Evidence for the role of hydrophobic forces on the interactions of nucleotide-monophosphates with cationic liposomes

In this work, the interaction of nucleotide-monophosphates (NMPs) with unilamellar liposomes made of 1,2-Dioleoyl-3-Trimethylammonium-Propane (DOTAP) and 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine (DOPE) was investigated. Here, we demonstrate how adsorption is affected by the type of nucleotide-monophosphate. Dynamic light scattering (DLS) results revealed, for each NMP, that a distinguishable concentration exists at which a significant growth of the aggregates occurs. Adenosine 5'-monophosphate (AMP) and guanosine 5'-monophosphate (GMP) have shown a higher propensity to induce liposome aggregation process and in particular GMP appears to be the most effective. From ζ-potential experiments we found that liposomes loaded with purine based nucleotides (AMP and GMP) are able to decrease the ζ-potential values to a greater extent in comparison with the pyrimidine based nucleotides thimydine 5'-monophosphate (TMP) and uridine 5'-monophosphate (UMP). Moreover, a careful analysis of nucleotide-liposome interactions revealed that nucleotides have different capacity to induce the formation of nucleotide-liposome complexes, and purine based nucleotides have higher affinities with lipid membranes. On the whole, the data emphasize that the mechanisms driving the interactions between liposomes and NMPs are also influenced by the existence of hydrophobic forces.

Delivery of RNA and its intracellular translation into protein mediated by SDS-CTAB vesicles: potential use in nanobiotechnology

Catanionic vesicles are supramolecular aggregates spontaneously forming in water by electrostatic attraction between two surfactants mixed in nonstoichiometric ratios. The outer surface charges allow adsorption to the biomembrane by electrostatic interactions. The lipoplex thus obtained penetrates the cell by endocytosis or membrane fusion. We examined the possible cytotoxic effects and evaluated the transfection efficiency of one vesicle type as compared to known commercial carriers. We show that the individual components of two different vesicles types, CTAB (cetyltrimethylammonium bromide) and DDAB (didodecyldimethylammonium bromide) are detrimental for cell survival. We also assayed the cytotoxicity of SDS-DDAB vesicles and showed dose and time dependency, with the DDAB component being per se extremely cytotoxic. The transfection efficiency of exogenous RNA mediated by SDS-CTAB increases if vesicles assemble in the presence of the reporter RNA; finally, freezing abrogates the transfection ability. The results of our experimental strategy suggest that catanionic vesicles may be adopted in gene therapy and control of antiproliferative diseases.

Phase behavior and molecular thermodynamics of coacervation in oppositely charged polyelectrolyte/surfactant systems: a cationic polymer JR 400 and anionic surfactant SDS mixture

Coacervation in mixtures of polyelectrolytes and surfactants with opposite charge is common in nature and is also technologically important to consumer health care products. To understand the complexation behavior of these systems better, we combine multiple experimental techniques to systematically study the polymer/surfactant binding interactions and the phase behavior of anionic sodium dodecyl sulfate (SDS) surfactant in cationic JR 400 polymer aqueous solutions. The phase-behavior study resolves a discrepancy in the literature by identifying a metastable phase between the differing redissolution phase boundaries reported in the literature for the surfactant-rich regime. Isothermal titration calorimetry analyzed within the framework of the simple Satake-Yang model identifies binding parameters for the surfactant-lean phase, whereas a calculation for polymer-bound micelles coexisting with free micelles is analyzed in the surfactant-rich redissolution regime. This analysis provides a preliminary understanding of the interactions governing the observed phase behavior. The resulting thermodynamic properties, including binding constants and the molar Gibbs free energies, enthalpies, and entropies, identify the relative importance of both hydrophobic and electrostatic interactions and provide a first approximation for the corresponding microstructures in the different phases. Our study also addresses the stability and metastability of oppositely charged polyelectrolytes and surfactant mixtures.

DNA condensation at freestanding cationic lipid bilayers

We describe a previously unreported coil-globule transition of DNA electrostatically bound to a freestanding fluid cationic lipid membrane. The collapse of a DNA coil into a compact globule takes place after the DNA molecule attaches in an extended conformation to the membrane. DNA condensation is favored at a higher cationic lipid content, while at lower membrane charge densities coexistence of DNA random coils, partially collapsed conformations, and globules is observed.

Biological activity of SDS-CTAB cat-anionic vesicles in cultured cells and assessment of their cytotoxicity ending in apoptosis

SDS-CTAB cat-anionic vesicles are supramolecular aggregates forming complexes with biopolymers and enter the cells via membrane fusion or endocytosis. Different applicative areas exist: gene therapy, drug delivery and nanotechnology. We previously examined the absorption/release of biopolymers from vesicles in solution. Here we evaluate their cytotoxicity in cultured cells; to this end we characterized the vesicles and analyzed their biological effects at cellular and molecular level. At low concentration these vesicles have scarce consequences on normal cell growth; at higher dosage they activate apoptotic death processes, due to membrane damage. In conclusion, the use of these particles in nano-biotechnology represents an actual possibility.

Pharmaceutical applications for catanionic mixtures

Mixtures of oppositely charged surfactants, so called catanionic mixtures, are a growing area of research. These mixtures have been shown to form several different types of surfactant aggregates, such as micelles of various forms and sizes, and lamellar structures, such as vesicles. In this review, a short introduction to the field of catanionic mixtures is presented and the pharmaceutical possibilities offered by such mixtures are reviewed. There are several interesting ideas on how to apply catanionic mixtures to improve the delivery of, for example, drug compounds and DNA, or for HIV treatment.

Photo-assisted gene delivery using light-responsive catanionic vesicles

Photoresponsive catanionic vesicles have been developed as a novel gene delivery vector combining enhanced cellular uptake with phototriggered release of vesicle payload following entry into cells. Vesicles with diameters ranging from 50 to 200 nm [measured using cryo-transmission electron microscopy (TEM) and light-scattering techniques] form spontaneously, following mixing of positively charged azobenzene-containing surfactant and negatively charged alkyl surfactant species. Fluorescent probe measurements showed that the catanionic vesicles at a cation/anion ratio of 7:3 formed at surfactant concentrations as low as 10 microM of the azobenzene surfactant under visible light (with the azobenzene surfactant species principally in the trans configuration), while 50-60 microM of the azobenzene surfactant is required to form vesicles under UV illumination (with the azobenzene surfactant species principally in the cis configuration). At intermediate surfactant concentrations (ca. 15-45 microM) under visible light conditions, transport of DNA-vesicle complexes occurred past the cell membrane of murine fibroblast NIH 3T3 cells through endocytosis. Subsequent UV illumination induced rupture of the vesicles and release of uncomplexed DNA into the cell interiors, where it was capable of passing through the nuclear membrane and thereby contributing to enhanced expression. Single-molecule fluorescent images of T4-DNA demonstrated that the formation of vesicles with a net positive charge led to compaction of DNA molecules via complex formation within a few seconds, while UV-induced disruption of the vesicle-DNA complexes led to DNA re-expansion to the elongated-coil state, also within a few seconds. Transfection experiments with eGFP DNA revealed that photoresponsive catanionic vesicles are more effectively taken up by cells compared to otherwise identical alkyl (i.e., nonazobenzene-containing and thus nonlight-responsive) catanionic vesicles, presumably because of pi-pi stacking interactions that enhance bilayer rigidity in the photoresponsive vesicles. Subsequent UV illumination following endocytosis leads to further dramatic enhancements in the transfection efficiencies, demonstrating that vector unpacking and release of DNA from the carrier complex can be the limiting step in the overall process of gene delivery.

Polymersome carriers: from self-assembly to siRNA and protein therapeutics

Polymersomes are polymer-based vesicular shells that form upon hydration of amphiphilic block copolymers. These high molecular weight amphiphiles impart physicochemical properties that allow polymersomes to stably encapsulate or integrate a broad range of active molecules. This robustness together with recently described mechanisms for controlled breakdown of degradable polymersomes as well as escape from endolysosomes suggests that polymersomes might be usefully viewed as having structure/property/function relationships somewhere between lipid vesicles and viral capsids. Here we summarize the assembly and development of controlled release polymersomes to encapsulate therapeutics ranging from small molecule anti-cancer drugs to siRNA and therapeutic proteins.

Polymer-vesicle association

Mixed polymer-surfactant systems have been intensively investigated in the last two decades, with the main focus on surfactant micelles as the surfactant aggregate in interaction. The main types of phase behavior, driving forces and structural/rheological effects at stake are now fairly well understood. Polymer-vesicle systems, on the other hand, have received comparatively less attention from a physico-chemical perspective. In this review, our main goal has been to bridge this gap, taking a broad approach to cover a field that is in clear expansion, in view of its multiple implications for colloid and biological sciences and in applied areas. We start by a general background on amphiphile self-assembly and phase separation phenomena in mixed polymer-surfactant solutions. We then address vesicle formation, properties and stability not only in classic lipids, but also in various other surfactant systems, among which catanionic vesicles are highlighted. Traditionally, lipid and surfactant vesicles have been studied separately, with little cross-information and comparison, giving duplication of physico-chemical interpretations. This situation has changed in more recent times. We then proceed to cover more in-depth the work done on different aspects of the associative behavior between vesicles (of different composition and type of stability) and different types of polymers, including polysaccharides, proteins and DNA. Thus, phase behavior features, effects of vesicle structure and stability, and the forces/mechanisms of vesicle-macromolecule interaction are addressed. Such association may generate gels with interesting rheological properties and high potential for applications. Finally, special focus is also given to DNA, a high charge polymer, and its interactions with surfactants, and vesicles, in particular, in the context of gene transfection studies.

Aggregation of single-chained cationic surfactant molecules into vesicles induced by oligonucleotide

Vesicles have many important applications in many different fields. In the present paper, we report for the first time that oligonucleotide can induce single-chained cationic surfactant molecules to aggregate into vesicles by determining turbidity with a Uv-vis spectrophotometer, observing images with a transmission electron microscope and/or fluorescence microscope, and dynamic light scattering. This study may increase the efficiency and applicability for a DNA/amphiphile system.

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.

Nucleotides and nucleolipids derivatives interaction effects during multi-lamellar vesicles formation

In this paper a micellar interface, constituted by the cationic surfactant CTAB, in presence of 1,2-epoxydodecane and nucleotides was used for catanionic multi-lamellar vesicles (MLVs) formation. The micellar solution of CTAB is able to disperse the 1,2 epoxydodecane in the micellar core promoting the reaction of this reagent with the nucleotide attracted by the positive surface charge of the micellar aggregates. The alkylation of AMP and UMP nucleotides leads to the synthesis of nucleolipids. The behaviour of the supramolecular structures formed depends on the starting reagents (AMP, UMP and AMP+UMP) and on the assembly capabilities of the products. In particular nucleotides and nucleotides derivatives interaction effects are evaluated during the multi-lamellar vesicles formation. NMR spectroscopy and UV-vis measurements performed on MLVs showed strong aryl interactions. Interestingly, NMR spectra revealed prevailing stacking interactions between complementary nucleolipids. The assembly of complementary nucleotides affects the course of the reaction during the MLVs formation. Moreover the MLVs supramolecular stability has been tested by means of turbidity and UV-vis measurements. In particular, an enhanced stability has been found in systems prepared with complementary nucleotides confirming that in these systems the self-assembly process is influenced by nucleolipids interactions. Furthermore by following the hypocromic effect during the micellar catalysis, we showed that even in the earlier stages of the reaction significant differences are detectable.

PVA-DNA cryogel membranes: characterization, swelling, and transport studies

Double-stranded (ds) DNA from salmon testes has been incorporated into PVA hydrogels obtained by a technique of repeated freezing and thawing. The cryogels obtained are free of potential toxic species like chemical cross-linkers, and consequently, they can be used in pharmaceutical or medical applications. These cryogels show a good mechanical resistance and a white and opaque appearance caused by a heterogeneous porous structure. Encapsulated DNA molecules can be in a compacted or an extended conformation in the PVA matrix and can be controlled by tailoring the degree of crystallinity of the PVA network; this is supported by fluorescence microscopy and UV and FTIR spectroscopic studies. The two forms of encapsulated DNA were observed for different types of matrixes: an extended one in a more crystalline network and a globular one in a more amorphous one. Different associations of base pairs have also been observed. PVA cryogel crystallinity could be tailored by the cryogel contact with different salt solutions. Cryogel surface (scanning electron microscopy) and bulk morphology (porosimetry), swelling, DNA retention, and delivery kinetics have also been studied. All these investigations clearly show strong interactions between PVA and DNA.

DNA encapsulation by biocompatible catanionic vesicles

The encapsulation of DNA by catanionic vesicles has been investigated; the vesicles are composed of one cationic surfactant, in excess, and one anionic. Since cationic systems are often toxic, we introduced a novel divalent cationic amino-acid-based amphiphile, which may enhance transfection and appears to be nontoxic, in our catanionic vesicle mixtures. The cationic amphiphile is arginine-N-lauroyl amide dihydrochloride (ALA), while the anionic one is sodium cetylsulfate (SCS). Vesicles formed spontaneously in aqueous mixtures of the two surfactants and were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM); the vesicles are markedly polydisperse. The results are compared with a study of an analogous system based on a short-chained anionic surfactant, sodium octylsulfate (SOS). Addition of DNA to catanionic vesicles resulted in associative phase separation at very low DNA concentrations; there is a separation into a precipitate and a supernatant solution; the latter is first bluish but becomes clearer as more DNA is added. From studies using cryo-TEM and small angle X-ray scattering (SAXS) it is demonstrated that there is a lamellar structure with DNA arranged between the amphiphile bilayers. Comparing the SOS containing DNA-vesicle complexes with the SCS ones, an increase in the repeat distance is perceived for SCS. Regarding the phase-separating DNA-amphiphile particles, cryo-TEM demonstrates a large and nonmonotonic variation of particle size as the DNA-amphiphile ratio is varied, with the largest particles obtained in the vicinity of overall charge neutrality. No major differences in phase behavior were noticed for the systems here presented as compared with those based on classical cationic surfactants. However, the prospect of using these systems in real biological applications offers a great advantage.

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.

Visualization of Different Pathways of DNA Release from Interpolyelectrolyte Complex

The release of double-stranded DNA from its interpolyelectrolyte complex with positively charged poly(allylamine hydrochloride) via exchange reaction with added polyanion, poly(sodium styrenesulfonate), is directly observed by fluorescence microscopy. It is shown that the pathways of DNA release depend essentially on the amount of added low-molecular-weight salt. At low salt content, the DNA release proceeds via the formation of an intermediate "beads-on-string" structure, whereas at high salt content the release goes directly from globule to coil states without any intermediate structures. The reasons for different character of DNA release are discussed.

Dynamics of adsorption of an oppositely charged polymer-surfactant mixture at the air-water interface: poly(dimethyldiallylammonium chloride) and sodium dodecyl sulfate

The dynamic adsorption behavior of mixtures of the cationic polymer poly(dimethyldiallylammonium chloride) [poly(dmdaac)] and the anionic surfactant sodium dodecyl sulfate (SDS) has been studied at the expanding liquid surface of an overflowing cylinder. A combination of ellipsometry and external reflection Fourier transform infrared spectroscopy was used to measure the adsorbed amounts of poly(dmdaac) and SDS as a function of the bulk surfactant concentration for various polymer concentrations in the range 0-0.2 g dm-3. Laser Doppler velocimetry was used to determine the surface age, which was approximately 1 s for solutions where the polymer adsorbed. The interfacial behavior is rationalized in terms of competition between surface activity and mass transport to the expanding surface. At low surfactant concentrations, adsorption of both poly(dmdaac) and SDS is enhanced as a result of the formation in solution of polymer-surfactant complexes that are more surface active than either component alone. The rate of adsorption of these complexes is diffusion-controlled, and their interfacial composition remains constant at three dmdaac units per SDS molecule over a 5-fold change in the surfactant concentration. For the higher polymer concentrations studied, the complexes saturate the air-water interface: the adsorbed amount is independent of the polymer concentration and remains constant also over a factor of 5 in the surfactant concentration. Once the number of bound surfactant molecules per dmdaac monomer exceeds 0.3, the complexes begin to form large aggregates, which are not surface active due to their slower mass transport. The adsorbed amount decreases rapidly on approach to the equivalence point (one SDS molecule per dmdaac monomer), and when it is reached, only a very small amount of material remains at the interface. At still higher surfactant concentrations, the free SDS adsorbs but there is no adsorbed poly(dmdaac). The dynamic adsorption data are compared with equilibrium measurements of the same system by Staples et al. (Langmuir 2002, 18, 5147), which show very different surface compositions and no significant change in surface coverage at the equivalence point.

Coil-globule coexistence and compaction of DNA chains

In this work we discuss different factors governing coil-globule coexistence in the compaction process of DNA. We initially analyse the role played by fluctuations in the degree of binding of an external compacting agent in the conformational behavior of the chain backbone. The analysis relies both on Monte Carlo simulation results and simple statistical approaches. Compacting agents of various binding characteristics are taken into consideration and the degree of charge neutralization upon the chain is related to conformational indicators. Selected model systems comprising stiff chains in the presence of multivalent ions are employed to assess intrinsic single-chain conformational fluctuation, in the presence of external agents but not resulting from differences in binding. It is shown that trends found for a variety of compacting agents, including the extension of the coil-globule coexistence regions, can be rationalised on the basis of this analysis.

Lysozyme binding onto cat-anionic vesicles

Mixing aqueous sodium dodecylsulfate with cetyltrimethylammonium bromide solutions in mole ratios close to (1.7/1.0) allows the formation of cat-anionic vesicles with an excess of negative charges on the outer surface. The vesicular dispersions are mixed with lysozyme, and interact electrostatically with the positive charges on the protein, forming lipo-plexes. Dielectric relaxation, zeta-potential, and light scattering indicate the occurrence of interactions between vesicles and the protein. According to CD, the vesicle-adsorbed protein retains its native conformation. Binding and surface saturation, inferred by dielectric relaxation and zeta-potential, fulfil a charge neutralisation stoichiometry. Adsorbed lysozyme promotes the vesicle clustering and is concomitant with the lipo-plexes flocculation. Above the charge neutralisation threshold, lysozyme in excess remains dispersed in molecular form. Attempts were made to determine in what conditions protein release from the vesicles occurs. Accordingly, the full neutralisation of sodium dodecylsulfate in excess by cetyltrimethylammonium bromide ensures the lipo-plexes break-up, the precipitation of the mixed surfactants and the protein release in native form.

Polymer-surfactant and protein-surfactant interactions

The phase behavior and some physicochemical properties of homopolymers (HP) and hydrophobically modified (HMP) polymers, as well as of polyelectrolytes (PE) and proteins (PR), in the presence of aqueous surfactants, or their mixtures, are discussed. Mixing the above components gives rise to the formation of organized phases, whose properties are controlled by polymer and/or surfactant content, temperature, pH, and ionic strength. Depending on the nature, concentration, and net charge of both solutes, molecular solutions, polymer-surfactant complexes, adsorption onto micelles and vesicles, gels, liquid crystalline phases, and precipitates are observed. Such rich polymorphic behavior is the result of a complex balance between electrostatic, excluded volume, van der Waals, and other contributions to overall system stability. It is also modulated by the molecular details and architecture of both the polymer and the surfactant. Different experimental methods allow investigation of the above systems and getting information on the nature of polymer-surfactant interactions (PSI). Surface adsorption and thermodynamic methods, together with investigation of the phase diagrams, give information on the forces controlling PSI and on the existence of different phases. Conductivity, QELS and viscosity allow estimating the size and shape of polymer-surfactant (protein-surfactant) complexes. Optical microscopy, cryo-TEM, AFM, NMR, fluorescence, and relaxation methods give more information on the above systems. Use of the above mixtures in controlling gelation, surface covering, preparing dielectric layers, and drug release is suggested.