Adsorption of DNA onto anionic lipid surfaces

Currently self-assembled DNA delivery systems composed of DNA multivalent cations and anionic lipids are considered to be promising tools for gene therapy. These systems become an alternative to traditional cationic lipid–DNA complexes because of their low cytotoxicity lipids. However, currently these nonviral gene delivery methods exhibit low transfection efficiencies. This feature is in large part due to the poorly understood DNA complexation mechanisms at the molecular level. It is well-known that the adsorption of DNA onto like charged lipid surfaces requires the presence of multivalent cations that act as bridges between DNA and anionic lipids. Unfortunately, the molecular mechanisms behind such adsorption phenomenon still remain unclear. Accordingly a historical background of experimental evidence related to adsorption and complexation of DNA onto anionic lipid surfaces mediated by different multivalent cations is firstly reviewed. Next, recent experiments aimed to characterise the interfacial adsorption of DNA onto a model anionic phospholipid monolayer mediated by Ca^2 + (including AFM images) are discussed. Afterwards, modelling studies of DNA adsorption onto charged surfaces are summarised before presenting preliminary results obtained from both CG and all-atomic MD computer simulations. Our results allow us to establish the optimal conditions for cation-mediated adsorption of DNA onto negatively charged surfaces. Moreover, atomistic simulations provide an excellent framework to understand the interaction between DNA and anionic lipids in the presence of divalent cations. Accordingly,our simulation results in conjunction go beyond the macroscopic picture in which DNA is stuck to anionic membranes by using multivalent cations that form glue layers between them. Structural aspects of the DNA adsorption and molecular binding between the different charged groups from DNA and lipids in the presenceof divalent cations are reported in the last part of the study. Although this research work is far from biomedical applications, we truly believe that scientific advances in this line will assist, at least in part, in the rationaldesign and development of optimal carrier systems for genes and applicable to other drugs.     

Adsorption of polymer/solvent complexes on silica surfaces

In this work local chain conformation, polymer/solvent interactions and particle size of different PMMA/solvent or PMMA/surfactant/solvent systems were investigated by dynamic light scattering, infrared spectroscopy and capillary viscosimetry. Aggregation can be forced, in the chlorinated solvents, through mixing with a small amount of PEG non‐ionic surfactants. Nano‐gel particles can also be formed by stereocomplexation of i‐ and s‐PMMA in certain solvents. The adsorption of stereoregular PMMA on silica was investigated by ¹H NMR. The strong relative lowering of the peak ascribed to isotactic sequences has provided evidence of a stereospecific adsorption of the isotactic segments. The conformation and the secondary structure induced by the PMMA stereoregularity may, therefore, be considered as a significant factor in the adsorption process. According to the miscibility of the components, PMMA/PEG mixtures are shown to increase the amount of polymer adsorbed and also to modify the stereoselectivity of the adsorption. Aggregative adsorption is assumed to deeply influence the organisation of the polymer at the silica/solvent interface. Finally, adsorption of aggregates of stereocomplexes can be used to pattern surfaces in thin films.     

Adsorption of polyelectrolyte multilayers and complexes on silica and cellulose surfaces studied by QCM-D

The adsorption of polyelectrolyte (PE) multilayers and complexes, obtained from both high- and low-charge polyelectrolytes, was studied on silica and on cellulose model surfaces by quartz crystal microbalance with dissipation (QCM-D). The film properties acquired with the different strategies were compared. When polyelectrolytes were added on an oppositely charged surface in sequence to form multilayers both the change in frequency and dissipation increased. The changes in frequency and dissipation were clearly higher if low-charge PEs were used in the multilayer formation. The substrate, silica or cellulose, did not affect the adsorption behaviour of low-charge PEs and only minor differences were seen in the adsorbed amounts and changes in dissipation of high-charge PEs between SiO₂ and cellulose. The complexes formed by low-charge PEs had higher changes in frequency and dissipation at low ionic strength on both surfaces, while the complexes formed from high-charge polyelectrolytes adsorbed more at high salt concentration. The complexes of low-charge polyelectrolytes adsorbed more on silica, while the complexes formed by high-charge PEs formed thicker layers on cellulose. The charge ratio had a significant effect on the adsorption and the highest changes in frequency and dissipation were obtained in the anionic/cationic charge ratio of 0.5–0.6. Generally, the multilayers and complexes formed by low-charge polyacrylamides adsorbed highly and formed rather thick layers on both surfaces, unlike the high-charge PEs which formed thin layers using either one of the addition techniques.     

Adsorption of a cationic surfactant onto cellulosic fibers I. Surface charge effects

The adsorption of four cationic surfactants with different alkyl chain lengths on cellulose substrates was investigated. Cellulose fibers were used as model substrates, and primary alcohol groups of cellulose glycosyl units were oxidized into carboxylic groups to obtain substrates with different surface charges. The amount of surfactant adsorbed on the fiber surface, the fiber zeta-potential, and the amount of surfactant counterions (Cl(-)) released into solution were measured as a function of the surfactant bulk concentration, its molecular structure, the substrate surface charge, and the ionic strength. The contribution of each of these parameters to the shape of the adsorption isotherms was used to verify if surfactant adsorption and self-assembly models usually used to describe the behavior of surfactant/oxide systems can be applied, and with which limitations, to describe cationic surfactant adsorption onto oppositely charged cellulose substrates.     

Adsorption of phenol and benzyl alcohol onto surfactant modified silica

The adsorption of the surfactant, dodecyltrimethylammonium bromide, DTAB, and the co-adsorption of the additives phenol and benzyl alcohol, onto silica from aqueous solutions are investigated. The adsorption of DTAB is found to increase with increasing alcohol concentration in solutions where the DTAB concentration is below the cmc. Moreover, the corresponding adsorption of DTAB decreases when the DTAB concentration is above the cmc. The co-adsorption of the alcohol is found to increase with increasing alcohol concentration, and benzyl alcohol co-adsorbs more strongly than phenol. The surfactant modified silica shows a very high ability to incorporate phenol and benzyl alcohol. The results are discussed in relation to solubilization site and surfactant aggregate shape.     

Adsorption of cationic polymers on the surfaces of anionic glass microspheres

The adsorption of cationic copolymers prepared by the quaternization of poly(4-vinylpyridine) with bromoacetic acid and/or ethyl bromide on the surface of anionic glass microspheres and the stability of the as-prepared complexes against dissociation in water-salt solutions are studied. Experiments are performed with the use of two types of copolymers: copolymers carrying cationic and hydrophobic units and copolymers carrying cationic and zwitterionic (electroneutral) units in main chains. For hydrophobic copolymers, the limiting adsorption decreases as the molar fraction of cationic groups in the copolymer, α, increases. In the case of hydrophilic copolymers, the dependence of limiting adsorption on α has a bellshaped pattern with a maximum at α = 0.15 and a horizontal segment at α > 0.4. Hydrophobic copolymers feature irreversible binding with microspheres at α > 0.24; hydrophilic copolymers, at α ≥ 0.15. The obtained data may be used for creation of biocidal polymer coatings and sorption layers that reversibly desorb from the surface with a change in the salt concentration in the surrounding aqueous solution.     

Surface properties of mixed anionic/cationic surfactant solutions

Summary Published experimental surface pressures for mixtures of anionic and cationic surfactants are compared to what can be predicted from the surface behaviour of the separate constituents. Simple theory correctly predicts, for soluble surfactants, a large increase of surface pressure upon mixing an anionic and a cationic solution having the same surface pressure, and, for insoluble surfactants, a decrease of surface pressure upon mixing at a given area per long chain ion. These effects are due to the different adsorption characteristics of the four electroneutral combinations involved, and will occur even in the absence of specific surface interactions.

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Zusammenfassung Es wurden bekannte Oberflächendrucke für Mischfilme von Aniontensiden und Kationtensiden mit theoretischen Voraussagen, begründet auf dem Grenzflächenverhalten der einzelnen Komponenten, verglichen. Die einfache Theorie sagt richtig voraus, daß die Mischung zweier wäßriger Lösungen von Aniontensid bzw. Kationtensid mit gleichem Oberflächendruck, eine starke Erhöhung des Oberflächendruckes zur Folge haben muß, während die Mischung zweier unlöslicher Filme bei gegebener Tensidadsorption den Oberflächendruck herabsetzt. Dieses Verhalten wird aufgrund der verschiedenen Adsorptionseigenschaften der vier betreffenden Salze gedeutet, und ist von spezifischen Oberflächenwechselwirkungen unabhängig.

     

Sodium polyacrylate adsorption onto anionic and cationic silica in the presence of salts

Sodium polyacrylate is well known for its application as a scale inhibitor in common household products, and the effects of both monovalent and divalent metal cations on its structure have been covered by a range of previous publications. In the present article, we extend this work by using solvent relaxation NMR to look at the adsorption of the polyelectrolyte onto both positively and negatively charged silica and how this is altered by calcium chloride. In the anionic case, we found that polyacrylate adsorption was predictably very weak, and interestingly, perhaps counterintuitively, it was further reduced by calcium ions. This is probably linked to NaPA-Ca2+ binding, which changes the conformation and charge of the polyelectrolyte. In contrast, NaPA adsorbs very strongly on cationic silica, to the point that precipitation often occurs, particularly on addition of salt.     

Organo-modified cationic silica nanoparticles/anionic polymer as flocculants

The synthesis of quaternized silica nanoparticles and its application to fine clay flocculation were investigated. N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was used as a cationic reagent to introduce quaternary amine groups onto the surfaces of silica nanoparticles via the formation of covalent bonds between the methoxy groups of the cationic reagents and the silanol groups in the silica surface. The zeta potential, zeta, and charge density of the silica particles modified under various reaction conditions were determined. Dynamic clay flocculation experiments using a photometric dispersion analyzer (PDA) showed that the cationic silica alone contributed little to the flocculation. However, the cationic silica, in conjunction with an anionic polymer of high M(w) and low charge density, led to a significant improvement in the flocculation of fine clay particles. The mechanism of flocculation was explored by a systematic investigation of interaction between cationic silica and anionic polymers as well as of their adsorption behavior on clay surfaces. The influence of factors such as pH and electrolyte concentration on clay flocculation was also investigated.     

Characteristics of proflavine solubilized in complexes of anionic polymers with a cationic surfactant

Absorption and emission spectra of 3,6-diaminoacridine (proflavine) are reported in mixed solutions of dodecyltrimethylammonium bromide (DTAB) with various polyelectrolytes including the sodium salts of poly(acrylic acid) (PAA). poly(methacrylic acid) (PMA), poly(styrenesulfonic acid) (PSS), poly(garacturonic acid) (pectate), and the alternating copolymers of maleic acid with ethylene (PMA-E) and styrene (PMA-S). The spectral change indicates the association of the dye (blue-shift) on these polyions except on PSS, the easy dissociation of the aggregated form into the monomeric form and the solubilization into the hydrophobic PMA-S/DTAB complex (red-shift), the little dissociation in the PAA/DTAB, PMA/DTAB and PMA-E/DTAB complexes, and the liberation of the bound dye in the case of pectate/DTAB complexes. In the PSS system, the strong interaction of the dye with the styrene groups induces the completely different spectral behavior. These results are discussed with the cooperative binding of the dye and the surfactant ion.     

Adsorption of mixtures of nonionic sugar-based surfactants with other surfactants at solid/liquid interfaces II. Adsorption of n-dodecyl-beta-D-maltoside with a cationic surfactant and a nonionic ethoxylated surfactant on solids

Synergy and antagonism between sugar-based surfactants, a group of environmentally benign surfactants, and cationic surfactants and nonionic ethoxylated surfactants have been investigated in this study with solids which adsorbs only one or other when presented alone. Sugar-based n-dodecyl-beta-D-maltoside (DM) does not adsorb on silica by itself. However, in mixtures with cationic dodecyltrimethylammonium bromide (DTAB) and nonionic nonylphenol ethoxylated decyl ether (NP-10), DM adsorbs on silica through hydrophobic interactions. In contrast, although DM does adsorb on alumina, the presence of NP-10 reduces the adsorption of DM as well as that of the total surfactant adsorption. Such synergistic/antagonistic effects of sugar-based n-dodecyl-beta-D-maltoside (DM) in mixtures with other surfactants at solid/liquid interfaces were systematically investigated and some general rules on synergy/antagonism in mixed surfactant systems are identified. These results have implications for designing surfactant combinations for controlled adsorption or prevention of adsorption.     

Adsorption of cationic surfactants and subsequent adsolubilization of organic compounds onto cellulose fibers

Cationic surfactants with different hydrophobic chain length were adsorbed onto cellulose fibers in an aqueous medium. The adsorption isotherms exhibited three characteristic regions which were interpreted in terms of the mode of aggregation of the surfactant molecules at the solid–liquid interface. The hydrophobic layers were used as a reservoir to trap various slightly water soluble organic molecules. A quantitative study of these phenomena suggested typical partition behavior of the organic solutes between the aqueous phase and the surfactant layer. The surfactant chain length (from C12 to C18) was shown to play an important role in terms of the capacity to retain the organic solute and the capacity increased with the number of carbon atoms.     

Interfacial tension in phase-separated aqueous cationic/anionic surfactant mixtures

Interfacial tensions in two aqueous phase-separated cationic/anionic surfactant mixtures, CTAB/AS and 12-3-12/AS, without and with NaBr added were determined by the spinning drop method at 318.15 K. CTAB, 12-3-12 and AS are the abbreviations for cetyltrimethylammonium bromide, 1,3-propanediyl-bis(dodecyldimethylammonium bromide) and sodium dodecyl sulfonate, respectively. The interfacial tension sigma was found to be in the range of 0.06-21 microNm(-1). Toward a better understanding of the influence of the concentration difference between the separated phases in aqueous two-phase systems (ATPS) to interfacial tension, compositions of equilibrium phases were determined by elemental analysis coupled with material balance and electroneutrality. The investigation indicates that the concentration differences of surfactant ions between the separated phases and the adsorption of surfactant ions at the interface are the decisive factors determining the magnitude of interfacial tension.     

Immobilization of cationic polymer particles having active ester groups onto solid surfaces

Monodispersed cationic polymer particles with sulfonium groups and active ester groups at their surfaces were prepared by emulsifier-free emulsion copolymerization of styrene (ST) with a water-soluble active ester monomer, methacryloyloxyphenyldimethylsulfonium methylsulfate (MAPDS). The cationic polymer particle monolayers were fabricated on unmodified and aminated glass plates by electrostatic interactions and chemical reactions, respectively. The polymer particles were immobilized onto unmodified glass plates at relatively regular intervals in the absence of electrolytes, and the morphology of particle monolayers on the glass plates was changed with solid content of latex, electrolyte and cationic surfactant concentration. The polymer particles were immobilized onto aminated glass plate as aggregates by controlling the pH of latex and electrolyte concentration. Remaining active ester groups of the particle monolayers were confirmed to react easily with primary amino compounds.     

Deposition of spherical particles onto cylindrical solid surfaces. II. Experimental studies

This paper presents experimental studies of the deposition of silicone oil drops onto two different solid surfaces in an aqueous solution. A series of deposition tests were conducted to measure the dimensionless mass transfer rate (Sherwood number). The effects of three kinds of aqueous solutions and two solid surfaces on the deposition process were studied and compared with the numerical predictions based on the well-known DLVO theory. More specifically, both the experimentally measured and the numerically predicted Sherwood numbers monotonically decrease as the pH value of the aqueous solution increases. It was also found that two ionic surfactant solutions have similar influences while the electrolyte solutions have opposite effects on the deposition rate on different solid surfaces. Finally, comparison of all the experimental results for the bare glass surface with the numerical simulations shows that the deposition process of the silicone oil drops onto the hydrophilic solid surface can be satisfactorily described by the classical DLVO theory. However, the deposition data for the FC725 precoated surface are significantly larger than the numerical predictions. This fact suggests that the so-called non-DLVO attractive interaction is involved in the deposition process with the hydrophobic solid surface. This additional non-DLVO attractive interaction, which is generally called the hydrophobic interaction, still remains to be incorporated into the existing DLVO theory, if this is possible.     

Adsorption of cationic copolymer nanoparticles onto bamboo fiber surfaces measured by conductometric titration

Monosized nanoparticles of 57.3 nm were prepared by cationic emulsion polymerization using a polymerizable emulsifier DMHB. The adsorption of nanoparticles onto bamboo fibers was measured by conductometric titration. The results indicated that the adsorption capacity increased with increasing contact time until 120 min. The equilibrium data for nanoparticles adsorption onto bamboo fibers were well fitted to the Langmuir equation. Moreover, the monolayer adsorption capacity of nanoparticles in the concentration range (from 0.03 g/L to 0.6 g/L) studied, as calculated from Langmuir isotherm model at 25℃, was found to be 38.61 mg/g of fibers. The SEM images showed that the nanoparticles form a uniform monolayer on bamboo fiber surfaces.     

Interaction of water-soluble cationic porphyrin with anionic surfactant

The interaction of a cationic water-soluble porphyrin, 5,10,15,20-tetrakis [4-(3-pyridiniumpropoxy)phenyl]porphyrin tetrakisbromide (TPPOC3Py), with anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solution has been studied by means of UV-vis, (1)H NMR, fluorescence, circular dichroism (CD) spectra and dynamic laser light scattering (DLLS), and it reveals that TPPOC3Py forms porphyrin-surfactant complexes (aggregates), including ordered structures J- and H-aggregates, induced by association with surfactant monomers below the SDS critical micelle concentration (cmc), and forms micellized monomer upon the cmc, respectively. The position of TPPOC3Py in the micelle is determined, which is not in the micelle core instead of intercalated among the SDS chains, most likely with the pyridinium group extending into the polar headgroup region of the micelle.     

Salt-induced phase inversion in aqueous cationic/anionic surfactant two-phase systems

Phase inversion of aqueous two-phase systems with excess cationic surfactant (abbreviated as ATPS-C) formed by aqueous mixtures of 1,3-propanediyl bis(dodecyl dimethylammonium bromide) (abbreviated as 12-3-12) and sodium dodecyl sulfonate (abbreviated as AS) at 318.15 K was investigated. The experimental results indicate that addition of NaF, NaCl, NaHCO 3, or NaNO 3 can result in phase inversion of ATPS-C formed by 12-3-12/AS systems; however, addition of NaBr cannot lead to phase inversion. TEM micrographic experiments illustrate that there is no direct relationship between the microstructures of the concentrated phase in ATPS-C and phase inversion. To interpret the phase-inversion phenomena of ATPS-C, the phase composition, phase density, and phase volume ratio between the dilute phase and the concentrated phase in ATPS-C were investigated. Phase composition analysis results illustrate that for the ATPS-C formed by 0.10 mol.kg (-1) 12-3-12/AS mixed system, the concentration of Br (-) counterions in the dilute phase of ATPS-C increases with addition of NaF, NaCl, NaHCO 3, or NaNO 3. At the same time, the molar ratio between the F (-) (Cl (-), HCO 3 (-), or NO 3 (-)) counterions and Br (-) counterions in the concentrated phase of ATPS-C increases also. It illustrates that part of the bromide counterions which are the natural counterions of the surfactant 12-3-12 in excess are exchanged by other anionic counterions when an additional salt is added to the system. The investigation indicates that the common ground of the added F (-), Cl (-), HCO 3 (-), or NO 3 (-) counterions is that they all make a smaller density contribution than that of Br (-) counterions, although they have a weaker or stronger counterion binding ability with the mixed positively charged aggregates in ATPS-C than that of Br (-) counterion. Density experiments illustrate that the density increase of the dilute phase is larger than that of the concentrated phase in the ATPS-C with addition of NaF, NaCl, NaHCO 3, or NaNO 3; thus, phase inversion occurs. The densities of the added inorganic sodium salt aqueous solution and the order of the Hofmeister series for the added inorganic anions with respect to the chaotropic headgroup of 12-3-12 play important roles in the phase inversion of ATPS-C.     

DNA and cationic surfactant complexes at hydrophilic surfaces. An ellipsometry and surface force study

The adsorption and formation of DNA and cationic surfactant complexes at the silica-aqueous interface have been studied by ellipsometry. The interaction between the DNA-surfactant complexes at the mica-aqueous interface has been determined by the interferometric surface force apparatus. Adsorption was as expected not observed on negatively charged hydrophilic surfaces for DNA and when DNA-cationic surfactant complexes were negatively charged. However, adsorption was observed when there is an excess of cationic surfactant, just below the point of phase separation. The adsorption process requires hours to reach steady state. The adsorbed layer thickness is large at low surface coverage but becomes more compact and thinner at high coverage. A long-range repulsive force was observed between adsorbed layers of DNA-cationic surfactant complexes, which was suggested to be of both electrostatic and steric origin. The forces were found to be dependent on the equilibration time and the experimental pathway.