DODAB Concentration Research Articles

Cationic Biomimetic Particles of Polystyrene/Cationic Bilayer/Gramicidin for Optimal Bactericidal Activity.

Nanostructured particles of polystyrene sulfate (PSS) covered by a cationic lipid bilayer of dioctadecyldimethylammonium bromide (DODAB) incorporated gramicidin D (Gr) yielding optimal and broadened bactericidal activity against both Escherichia coli and Staphylococcus aureus. The adsorption of DODAB/Gr bilayer onto PSS nanoparticles (NPs) increased the zeta-average diameter by 8–10 nm, changed the zeta-potential of the NPs from negative to positive, and yielded a narrow size distributions for the PSS/DODAB/Gr NPs, which displayed broad and maximal microbicidal activity at very small concentrations of the antimicrobials, namely, 0.057 and 0.0057 mM DODAB and Gr, respectively. The results emphasized the advantages of highly-organized, nanostructured, and cationic particles to achieve hybrid combinations of antimicrobials with broad spectrum activity at considerably reduced DODAB and Gr concentrations.

Comparison between the interactions of the cationic surfactant DODAB with xanthan and galactomannan

The interactions of the cationic surfactant DODAB with anionic xanthan (XAN) and nonionic galactomannan (GMC) polysaccharides in solution were investigated using tensiometry, differential scanning microcalorimetry (μ-DSC), zeta potential and dynamic light scattering (DLS) techniques and by the calculated thermodynamic parameters of ΔGves0, ΔGads0, Γmax and amin. The surfactant formed large unilamellar vesicles (LUV) that aggregated with both the polymers in solution. Increasing DODAB concentrations resulted in greater and greater DODAB–XAN aggregates, high turbidity and even precipitation, while DODAB–GMC aggregates remained equal sized, clear solution and no precipitation observed. Further addition of DODAB to XAN solution was able to resuspend the precipitates. The interactions with both polysaccharides resulted in a more spontaneous adsorption of the DODAB–polymer aggregates at the air/solution interface with lower surfactant population.

Antimicrobial Particles from Cationic Lipid and Polyelectrolytes

Hybrid nanoparticles from cationic lipid and polymers were prepared and characterized regarding physical properties and antimicrobial activity. Carboxymethylcellulose (CMC) and polydiallyldimethylammonium chloride (PDDA) were sequentially added to cationic bilayer fragments (BF) prepared from ultrasonic dispersion in water of the synthetic and cationic lipid dioctadecyldimethylammonium bromide (DODAB). Particles thus obtained were characterized by dynamic light-scattering for determination of z-average diameter (Dz) and zeta-potential (zeta). Antimicrobial activity of the DODAB BF/CMC/PDDA particles against Pseudomonas aeruginosa or Staphylococcus aureus was determined by plating and CFU counting over a range of particle compositions. DODAB BF/CMC/PDDA particles exhibited sizes and zeta-potentials strictly dependent on DODAB, CMC, and PDDA concentrations. At 0.1 mM DODAB, 0.1 mg/mL CMC, and 0.1 mg/mL PDDA, small cationic particles with Dz = 100 nm and zeta = 30 mV were obtained. At 0.5 mM DODAB, 0.5 mg/mL CMC and 0.5 mg/mL PDDA, large cationic particles with Dz = 470 nm and zeta = 50 mV were obtained. Both particulates were highly reproducible regarding physical properties and yielded 0% of P. aeruginosa viability (10(7) CFU/mL) at 1 or 2 microg/mL PDDA dissolved in solution or in form of particles, respectively. 99% of S. aureus cells died at 10 microg/mL PDDA alone or in small or large DODAB BF/CMC/PDDA particles. The antimicrobial effect was dependent on the amount of positive charge on particles and independent of particle size. A high microbicide potency for PDDA over a range of nanomolar concentrations was disclosed. P. aeruginosa was more sensitive to all cationic assemblies than S. aureus.

Silica-based cationic bilayers as immunoadjuvants

BackgroundSilica particles cationized by dioctadecyldimethylammonium bromide (DODAB) bilayer were previously described. This work shows the efficiency of these particulates for antigen adsorption and presentation to the immune system and proves the concept that silica-based cationic bilayers exhibit better performance than alum regarding colloid stability and cellular immune responses for vaccine design.ResultsFirstly, the silica/DODAB assembly was characterized at 1 mM NaCl, pH 6.3 or 5 mM Tris.HCl, pH 7.4 and 0.1 mg/ml silica over a range of DODAB concentrations (0.001–1 mM) by means of dynamic light scattering for particle sizing and zeta-potential analysis. 0.05 mM DODAB is enough to produce cationic bilayer-covered particles with good colloid stability. Secondly, conditions for maximal adsorption of bovine serum albumin (BSA) or a recombinant, heat-shock protein from Mycobacterium leprae (18 kDa-hsp) onto DODAB-covered or onto bare silica were determined. At maximal antigen adsorption, cellular immune responses in vivo from delayed-type hypersensitivity reactions determined by foot-pad swelling tests (DTH) and cytokines analysis evidenced the superior performance of the silica/DODAB adjuvant as compared to alum or antigens alone whereas humoral response from IgG in serum was equal to the one elicited by alum as adjuvant.ConclusionCationized silica is a biocompatible, inexpensive, easily prepared and possibly general immunoadjuvant for antigen presentation which displays higher colloid stability than alum, better performance regarding cellular immune responses and employs very low, micromolar doses of cationic and toxic synthetic lipid.

IGC studies of binary cationic surfactant mixtures

Inverse gas chromatography (IGC) has been used to measure the interaction parameter between two twin-tailed cationic surfactants. Didodecyldimethylammonium (DDAB) and dioctadecyldimethylammonium (DODAB) bromides and their mixtures were used as stationary phases. IGC and DSC techniques have been used for the determination of the temperature zone of working. The activity coefficients at infinite dilution (on a mole fraction basis) were calculated for eleven probe solutes on each pure surfactant column. Values of interaction parameter between surfactants obtained at four weight fractions of the mixtures and at five temperatures are positive and suggested that the interactions is more unfavourable with the increment of DODAB concentration in the mixture. The results are interpreted on the basis of partial miscibility between DDAB and DODAB.

Biomimetic Particles

AbstractElectrostatically driven bilayer coverage from bilayer fragments onto oppositely charged latex produces a highly homodisperse particulate for biomolecules adsorption. Polystyrene sulfate (PSS) particles were covered with single cationic dioctadecyldimethylammonium bromide (DODAB) bilayers. Biomolecules adsorbed were DNA, bovine serum albumin (BSA), cholera toxin (CT) and a mixture of purified 18 kDa/14 kDa Taenia crassiceps proteins (18/14‐Tcra). Firstly, the DODAB/PSS assembly was characterized at 1 mM NaCl and 5 × 109 PSS particles/mL over a range of DODAB concentrations (0.001 ‐1 mM) by means of dynamic light scattering for particle sizing and zeta‐potential analysis. 0.01 mM DODAB was enough to produce perfectly homodisperse and cationic bilayer‐covered particles. Secondly, under these experimental conditions, BSA, CT, and 18/14‐Tcra adsorbed onto biomimetic bilayer‐covered particles yielding langmuirian isotherms with 1.23 × 1017, 0.82 × 1017, 3.37 × 1017 molecules per m2 at limiting adsorption and affinity constants (K) of 3.17 × 1010, 3.39 × 1010, and 1.75 × 1010 M−1, respectively. For DNA adsorption, isotherms did not attain an adsorption maximum up to 20 micrograms/mL DNA. PSS/DODAB/biomolecule assemblies were also characterized by means of dynamic light scattering and zeta‐potential analysis yielding highly monodisperse particles at and above maximal adsorption. In summary cationic bilayer‐covered particles are a novel, highly organized and, possibly, general support for biomolecules immobilization.

Colloid Stability of Lipid/Polyelectrolyte Decorated Latex

The colloid stability of supramolecular assemblies composed of the synthetic cationic lipid dioctadecyldimethylammonium bromide (DODAB) on carboxymethyl cellulose (CMC) supported on polystyrene amidine (PSA) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DODAB adsorption on CMC-covered particles. At 0.1 g L(-1) CMC and 2 x 10(11) PSA particles/mL, CMC did not induce significant particle flocculation, and a vast majority of CMC-covered single particles were present in the dispersion so that this was the condition chosen for determining DODAB concentration (C) effects on particle size and zeta potentials. At 0.35 mM DODAB, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DODAB/CMC/PSA assembly. At 0.1 g L(-1) CMC, isotherms of high affinity for DODAB adsorption on CMC-covered particles presented a plateau at a limiting adsorption of 700 x 10(17) DODAB molecules adsorbed per square meter PSA which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy (ca. 11-nm hydrodynamic thickness), and maximal adsorption of DODAB lipid onto this layer produced a compressed composite cationic film with 20 mV of zeta potential and about 10-nm mean thickness. The assembly of cationic lipid/CMC layer/polymeric particle was stable only well above charge neutralization of the polyelectrolyte by the cationic lipid, at relatively large lipid concentrations (at and above 1 mM DODAB) with charge neutralization leading to extensive particle aggregation.

Cationic Bilayer Fragments on Silica at Low Ionic Strength: Competitive Adsorption and Colloid Stability

The challenge of breaking open rigid bilayer vesicles upon contact with silica particles was circumvemted by using a dioctadecyldimethylammonium bromide (DODAB) dispersion consisting of open, nanosized bilayer fragments instead of vesicles. At low ionic strength and pH 6.5, DODAB adsorption from bilayer fragments on silica was quantified from adsorption isotherms at 0, 0.1, 0.5, 1.0, and 10.0 mM KCl. Adsorption increased as a function of KCl concentration and surface charge density on particles. The isotherm shapes were typical of competitive adsorption with a maximum possibly due to hydrophobic attraction between adsorbed and free bilayer fragments. Upon adsorption as flat patches on particles, the fragments did not apparently seal into a continuous and closed bilayer surrounding the particle, instead interacted via hydrophobic edges with free fragments in dispersion. At pH 6.5, over a range of DODAB (0−1.0 mM) and KCl concentrations (0.1−10.0 mM), from particle sizing, ζ-potential analysis, photographs of the mixtures, and particle sedimentation kinetics, the colloid stability of the particles in the mixtures was governed by the ratio R of the total surface areas for bilayers Ab and particles Ap, R = Ab/Ap. At R ∼ 0.5, the mean ζ-potential was zero, the mean particle diameter (Dz) was at maximum, sedimentation was rapid, and colloid stability was at minimum; at R > 1, ζ was positive, Dz was minimized, sedimentation was absent, and colloid stability was high. At low ionic strength ([KCl] < 10 mM), high colloid stability for particles in the presence of cationic bilayer fragments was achieved at or above R = 1, i.e., from the equivalence of total surface areas for bilayer fragments and particles.

Competitive Adsorption of Cationic Bilayers and Chitosan on Latex: Optimal Biocidal Action

The competitive adsorption of two biocides, the cationic polysaccharide (chitosan, CH) and some cationic bilayer fragments (composed of dioctadecyldimethylammonium bromide, DODAB), onto oppositely charged polystyrene sulfate (PSS) or poly(methyl methacrylate) (PMMA) particles is described. CH and/or DODAB effects on particle stabilization/flocculation are characterized from the following: (1) DODAB adsorption isotherms from bilayer dispersions onto PMMA particles in the presence or absence of CH or 10 mM NaCl; (2) effects of particle number density, DODAB or CH concentration on mean size, and ζ-potentials of PSS or PMMA particles; (3) visualization of positively stained cationic moieties on PMMA particles by transmission electron microscopy. Driving forces for DODAB bilayer adsorption were the electrostatic and the hydrophobic attraction between latex and bilayer, whereas, for CH, charge neutralization (overcompensation) led to particle flocculation (stabilization). Both cationic species seem to adsorb n...

Interactions between cationic liposomes and bacteria: the physical-chemistry of the bactericidal action

The bactericidal effect of dioctadecyldimethylammonium bromide (DODAB), a liposome forming synthetic amphiphile, is further evaluated for Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Staphylococcus aureus in order to establish susceptibilities of different bacteria species towards DODAB at a fixed viable bacteria concentration (2.5 × 107 viable bacteria/mL). For the four species, susceptibility towards DODAB increases from E. coli to S. aureus in the order above. Typically, cell viability decreases to 5% over 1 h of interaction time at DODAB concentrations equal to 50 and 5 μm for E. coli and S. aureus, respectively. At charge neutralization of the bacterial cell, bacteria flocculation by DODAB vesicles is shown to be a diffusion-controlled process. Bacteria flocculation does not yield underestimated counts of colony forming units possibly because dilution procedures done before plating cause deflocculation. The effect of vesicle size on cell viability demonstrates that large vesicles, due to their higher affinity constant for the bacteria (45.20 m-1) relative to the small vesicles (0.14 m-1), kill E. coli at smaller DODAB concentrations. For E. coli and S. aureus, simultaneous determination of cell viability and electrophoretic mobility as a function of DODAB concentration yields a very good correlation between cell surface charge and cell viability. Negatively charged cells are 100% viable whereas positively charged cells do not survive.▪The results show a clear correlation between simple adsorption of entire vesicles generating a positive charge on the cell surfaces and cell death.—Campanhã, M. T. N., E. M. Mamizuka, and A. M. Carmona-Ribeiro. Interactions between cationic liposomes and bacteria: the physical-chemistry of the bactericidal action. J. Lipid Res. 1999. 40: 1495–1500.

Interactions between Cationic Vesicles and Serum Proteins

Bovine serum albumin (BSA) and anti-bovine serum albumin (a-BSA) were separately incorporated in dioctadecyldimethylammonium bromide (DODAB) liposomes in water or in phosphate buffer saline (PBS). In water, 100% BSA or a-BSA incorporation in the liposomes contrasts with ca. 30% incorporation in PBS for both proteins, suggesting a major role for the electrostatic attraction between protein and liposome in determining the incorporation, though 30% incorporation can still be ascribed to the hydrophobic interaction. Neither of the two proteins, tested separately, can induce nonspecific liposome aggregation over an extensive range of combinations for DODAB and protein concentration as those possible in a microplate experiment. In water, electrophoretic mobility for the liposomes decreases slightly as a function of protein concentration but the liposome/protein complex remains positively charged even at the highest protein concentrations tested. Protein-induced rupture of liposomes containing [14C]sucrose was evaluated from dialysis of protein/liposome mixtures. In water or in PBS, protein-induced leakage of radioactive liposomal contents was not observed, suggesting that the hydrophobic interaction between serum proteins and the DODAB bilayer is superficial. Finally, the absence of molecular recognition between BSA and a-BSA separately incorporated in the liposomes in water is consistent with preservation of the liposomal positive charge at full protein coverage on the cationic liposomes. These results shed new light onto the mechanisms by which cationic liposomes can deliver proteins or other important macromolecules of biological origin in vivo: opsonization possibly preserves liposome charge and integrity.

Synthetic Bilayer Wetting on SiO2 Surfaces

Wetting on SiO2/Si wafers in the presence of dioctadecyldimethylammonium bromide (DODAB) bilayer vesicles is determined as a function of DODAB concentration and time of interaction between surface and vesicles. In 10 mM TRIS buffer at pH 7.4, the dynamic contact angle (θ) displays a maximum at an intermediate DODAB concentration (C) that corresponds to a minimum of contact angle hysteresis and is consistent with optimization of bilayer deposition. In pure water, θ is smaller than the contact angle for the bare surface consistently with adhesion of collapsed vesicles that carry water. In buffer, angles are larger than those for the bare surface, suggesting bilayer deposition under water and its conversion to a monolayer as the bilayer-bearing surface recedes into air. At a given C, θ against the interaction time (t) has an inverted-bell shape, indicating first vesicle adhesion, then bilayer deposition (at intermediate times), and finally further vesicle adhesion onto the deposited bilayer. Two major wettability parameters characterize bilayer deposition on the solid surface: minimization of contact angle hysteresis and maximization of the measured contact angle. Determination of dynamic contact angles is proposed as a quick and efficient technique to distinguish between vesicle adhesion and bilayer deposition on solid surfaces in general.

Cationic Vesicles as Bactericides

Dioctadecyldimethylammonium bromide (DODAB), a liposome-forming synthetic amphiphile, kills Escherichia coli, Salmonella thyphimurium, Pseudomonas aeruginosa, and Staphylococcus aureus in the micromolar range of DODAB concentrations. For the four species at cell concentrations higher than 107 bacteria/mL in the interaction mixtures, 5 μM DODAB, and 5 h of interaction time between bacteria and vesicles, 0% survival (no counts for viable cells) was obtained. The mechanism of cell death does not involve cell lysis or vesicle rupture as evaluated from measurements of cell leakage of phosphorylated compounds and from a vesicle disruption assay. The isolated external membrane of E. coli and DODAB cationic small vesicles do interact to yield an increase in the electrophoretic mobility of ghosts as a function of DODAB concentration. Surface charge for the ghosts becomes zero over the micromolar range of DODAB concentrations. Thus vesicle adhesion to the external membrane of the bacteria is certainly the first int...

Interactions between Cationic Vesicles and Cultured Mammalian Cells

The interaction of small cationic vesicles composed of dioctadecyldimethylammonium bromide (DODAB) with normal versus transformed mouse fibroblasts is described using cell microelectrophoresis, turbidimetry, and cell viability assays over a wide range of DODAB concentrations (10-7−10-3 M). Normal and transformed cells (104 cells/mL) attain a point of zero charge at, respectively, 18.0 and 1.6 μM DODAB. Further increasing DODAB concentration (C) generates positively charged cells. At 105 cells/mL and C ≥ 50 μM, DODAB induces cell−cell adhesion. For transformed and normal cells, peak adhesion occurs at 100 and 1000 μM DODAB, respectively. Upon 0.5 h interaction time with 100 μM DODAB, at 104 cells/mL, 20% of cell death is obtained for normal cells whereas transformed cells remain unaffected. Transformed cells have a higher affinity for DODAB vesicles than their normal counterparts but are more resistant to DODAB-induced cell death. The results indicate that DODAB vesicles interact with cells with very high ...

Bacteria Flocculation and Death by Cationic Vesicles

Dioctadecyldimethylammonium bromide (DODAB) vesicles kill Escherichia coli in the micromolar range of DODAB concentrations. At 1.2 x 10 6 bacteria/mL, the minimum bactericidal concentration is smaller than 0.5 μM DODAB for an interaction time of 24 h. DODAB effects on the cells are described using microelectrophoresis, viable counts and turbidimetry over a range of bacterial number densities, and DODAB concentrations. Electrophoretic mobility for the cells as a function of DODAB concentration establishes the DODAB amount required to attain charge neutralization on the cell surface and maximal flocculation rate and extent. From 10 8 bacteria/mL, there is rapid bacteria flocculation induced by DODAB. However, cell death is not related to aggregation taking place also for nonaggregated cells at much smaller bacteria number densities. The results may be of importance for improving water quality in contaminated reservoirs.