Interaction studies of diacyl glycerol arginine-based surfactants with DPPC and DMPC monolayers, relation with antimicrobial activity

Antimicrobial agents have a major practical importance in food, pharmaceutical and cosmetic applications for preventing contamination. Our group has developed a novel class of cationic diacyl glycerol arginine-based surfactants denoted 1414RAc and 1212RAc. To assess the antimicrobial properties of these new surfactants we have studied how they interact with 1,2-dipalmitoyl-sn-glycero-3-phosphocoline (DPPC) and 1,2-dimiristoyl-sn-glycero-3-phosphocoline (DMPC) as model membranes, as well with living organisms endowed or not with external barriers, such as gram negative bacteria, the human protozoa Leishmania and mammalian cell line.

The structure and phase characteristics of mixed monolayers have been assessed through the analysis of static elasticity. The extent of component miscibility of surfactant and phospholipid in mixed monolayers has been studied using the additivity rule and the excess free energy of a mixture as a function of the phospholipid molar fraction for different surface pressure values. In all the mixtures studied, the mixed monolayer is thermodynamically favoured except for the 1212RAc/DMPC case that exhibits positive values of excess free energy.

The interaction with living cells has cytotoxic effects only in eukaryotic cells, by unspecific membrane permeabilization.     

Interaction of ionic surfactants with cornea-mimicking anionic liposomes

The interaction of surface-active molecules with lipid bilayers is ubiquitous both in biological systems and also in several technological applications. Here we explore the interaction of ionic surfactants with liposomes whose composition mimics the ocular epithelia. In this study, liposomes with a composition mimicking ocular epithelia are loaded with calcein dye above the self-quenching concentration. The liposomes are then exposed to surfactants, and the rate of dye leaked from the liposomes due to the interaction of surfactants is measured. Both cationic and anionic surfactants at various concentrations and ionic strengths are explored. Results show that the liposome bilayer permeability to the dye increases on exposure to the surfactants, leading to the release of the dye trapped in the core. However, the dye release stops after a finite time, suggesting a transient increase in permeability followed by healing. The leakage profiles exhibit two different timescales for the cationic surfactant but only one timescale for the anionic surfactant. The total dye leakage increases with surfactant concentration, and at a given concentration, the dye leakage is significantly higher for the cationic surfactants. The timescale for the healing decreases with increasing surfactant concentration, and increasing ionic strength increases the dye leakage for the anionic surfactant. These results show that the surfactant binding to the lipid bilayer increases the permeability while the bilayers heal likely because of the surfactant jump from the outer to the inner leaflet and/or rearrangement into tighter aggregates.     

Interaction of cationic liposomes with cell membrane models

The colloidal dispersion stability of nano-sized graphene sheets in supercritical fluid (SCF) media is very important for developing SCF-based exfoliation and dispersion technologies for stabilization and solubilization of graphenes. We carried out molecular dynamics simulations to elucidate the stability mechanism of graphene in supercritical CO(2) (scCO(2)). The potential of mean force (PMF) between two graphene nanosheets in scCO(2) was simulated, and the effect of scCO(2) density and temperature on the PMF behavior has been investigated. The simulation results demonstrate that there exists a free energy barrier between graphenes in the scCO(2) fluid, possibly obstructing the aggregation of graphenes. The single-layer confined CO(2) molecules between the graphene sheets can induce a dominating repulsion interaction between graphene sheets. At higher scCO(2) fluid density, there are more confined CO(2) molecules within the interplate regions, resulting in a stronger repulsive free energy barrier. The effect of temperature on the PMF is relatively minor. The scCO(2) solvent structure shows layered confined arrangement in the interfacial region near the graphene nanosheets, which is correlated well with the PMF profile curve.     

Interaction of cationic surfactants with carboxymethylcellulose in aqueous media

We have examined the polymer-surfactant interaction in mixed solutions of the cationic surfactants, i.e., dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltriphenylphosphonium bromide, and tetradecylpyridinium bromide and a semiflexible anionic polyelectrolyte carboxymethylcellulose in water and aqueous salt solutions by various techniques: tensiometry, viscosimetry or ion-selective electrode method, and dynamic light scattering. We have investigated the effect of varying surfactant chain length, head group size, counterion, and ionic strength on the critical aggregation concentration (CAC) of mixed polymer surfactant systems and the collapse of the polymer molecule under different solution conditions. The CAC decreases with increasing alkyl chain length. Above a certain surfactant concentration, mixed aggregates start growing until their macroscopic phase separation. The growth is more rapid with greater surfactant tail length and with increasing head group size. This is attributed in both cases to the increasing hydrophobic interaction between polymer and surfactant. Among surfactants with monovalent halide counterions, iodide induces the strongest binding, reflected by the onset of growth of the mixed aggregates at low surfactant concentration. This is perhaps related to the decreasing hydration of the counterion from chloride to iodide. The surfactant concentration at which the viscosity of the solution starts to decrease sharply is smaller than the CAC, and probably reflects polymer chain shrinkage due to noncooperative binding.     

Interaction of curcumin with lipid monolayers and liposomal bilayers

Curcumin shows huge potential as an anticancer and anti-inflammatory agent. However, to achieve a satisfactory bioavailability and stability of this compound, its liposomal form is preferable. Our detailed studies on the curcumin interaction with lipid membranes are aimed to obtain better understanding of the mechanism and eventually to improve the efficiency of curcumin delivery to cells. Egg yolk phosphatidylcholine (EYPC) one-component monolayers and bilayers, as well as mixed systems containing additionally dihexadecyl phosphate (DHP) and cholesterol, were studied. Curcumin binding constant to EYPC liposomes was determined based on two different methods: UV/Vis absorption and fluorescence measurements to be 4.26 × 10⁴ M⁻¹ and 3.79 × 10⁴ M⁻¹, respectively. The fluorescence quenching experiment revealed that curcumin locates in the hydrophobic region of EYPC liposomal bilayer. It was shown that curcumin impacts the size and stability of the liposomal carriers significantly. Loaded into the EYPC/DPH/cholesterol liposomal bilayer curcumin stabilizes the system proportionally to its content, while the EYPC/DPH system is destabilized upon drug loading. The three-component lipid composition of the liposome seems to be the most promising system for curcumin delivery. An interaction of free and liposomal curcumin with EYPC and mixed monolayers was also studied using Langmuir balance measurements. Monolayer systems were treated as a simple model of cell membrane. Condensing effect of curcumin on EYPC and EYPC/DHP monolayers and loosening influence on EYPC/DHP/chol ones were observed. It was also demonstrated that curcumin-loaded EYPC liposomes are more stable upon interaction with the model lipid membrane than the unloaded ones.     

Interaction of anionic dyes and cationic surfactants with ionic liquid character

The interactions of an imidazolium based ionic liquid (IL), namely 1-dodecyl-3-methylimidazolium chloride [C12 mim][Cl] with two sulfonated anionic dyes, azocarmine G and methyl orange, are studied spectrophotometrically in both acidic and basic media. ILs (with some surface active character) can interact with the above dyes and cause considerable shifts in their spectra. These interactions are then compared with some surfactant-dye interactions. Evolving factor analysis (EFA) and multivariate curve resolution-alternating least squares (MCR-ALS) are used for complete resolution of the measured spectrophotometric data. The concentration and spectral profiles of all species were calculated without any assumption of the chemical models. The spectral variation of dye solutions as a function of IL concentrations below and above the critical aggregation concentration (CAC) is analyzed using MCR-ALS as a soft-modeling technique. The ion pair formation constants between ILs and dyes were calculated using the obtained concentration profiles.     

Synthesis and surface and antimicrobial properties of novel cationic surfactants

A series of surfactants with tuned polarity were prepared, including a new class of compounds: gluco-pyridinium surfactants. Pure anomers were obtained by chromatographic separation. The conductivity and surface tension of surfactant solutions in water were measured, and provided interesting information regarding their aggregation behavior. Peculiarities were observed in the premicellar range. Tensidic parameters correlated with antimicrobial activity. A few parameters, mainly the hydrophobicity of the headgroup, may play a role in finding more efficient antimicrobial structures.     

Molecular interactions of cationic and anionic surfactants in mixed monolayers and aggregates

The properties of anionic-rich and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry and surface tension measurements and by determining the surfactant NMR self-diffusion coefficients. The critical aggregate concentration (CAC), surface tension reduction effectiveness(gamma(CAC)), surface excess(Gamma(max)), and mean molecular surface area (A(min)) were determined from plots of the surface tension (gamma) as a function of the total surfactant concentration. The compositions of the adsorbed films (Z) and aggregates (chi) were estimated by using regular solution theory, and then the interaction parameters in the aggregates (beta) and the adsorbed film phases (beta(sigma)) were calculated. The results showed that the synergism between the surfactants enhances the formation of mixed aggregates and reduces the surface tension. Further, the nature and strength of the interaction between the surfactants in the mixtures were obtained by calculating the values of the following parameters: the interaction parameter, beta, the size parameter, rho, and the nonrandom mixing parameter, P*. These results indicate that in ionic surfactant mixtures the optimized packing parameter has the highest value and that the size parameter can be used to account for deviations from the predictions of regular solution theory. It was concluded that, for planar air/aqueous interfaces and aggregation systems, this nonideality increases as the temperature increases. This trend is attributed to the increased dehydration of the surfactant head groups that results from increases in temperature. Further, our conductometry measurements show that the counterion binding number of mixed micelles formed in mixtures with a high CTAB content is different to those with a high SDS content. This difference is due to either their different aggregation sizes or the different interactions between the head groups and the counterions.     

Interaction of DNA oligomers with cationic lipidic monolayers: complexation and splitting

Interactions of native DNA with octadecylamine (ODA) and hexadecymdimethylammonium bromide (HTAB) monolayers at the air/water interface were studied by pi-A isotherms, ellipsometry, and X-ray reflectivity. We show that the microscopic structure of ODA-DNA complexes is definitely consistent with a single-stranded form for DNA. On the contrary, with HTAB, DNA complexes in its native form. The crucial difference in the behavior of these two fairly similar lipids is due to the presence of the amine group in ODA. These results should be relevant to applications such as DNA chips and sensors.     

Interaction between cationic surfactants and montmorillonites under nonequilibrium condition

Surfactant adsorption by two different montmorillonites was characterized by examining the time dependence of surfactant behavior on clay surfaces. Surfactants with different micelle concentrations were conducted in our experiment to observe a nonequilibrium activity of cationic surfactant on the clay over reaction periods ranging from 0.1 min to 11 days. Compared with Ca-montmorillonite (SAz), a more active intrusion of surfactant molecules into the interlayers was found in Na-montmorillonite (SWy). During a short "initiation" stage, the basal spacing of SWy montmorillonite increased rapidly with logarithmic time. For SAz montmorillonite, however, the abrupt basal spacing increase occurred at a later stage of the reaction. From the results, it is assumed that the difference in the adsorption behavior exhibited by the two montmorillonite types partly arises from their intrinsic nature; that is, inorganic cations originally existed on the clay surfaces. Additionally, the micelle concentration of the surfactants affects the development of organomontmorillonite, especially in the intercalant formation and stabilization under nonequilibrium.     

Interaction of sodium polyacrylate adsorbed on TiO2 with cationic and anionic surfactants

Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was used to identify the structures formed during the adsorption of sodium polyacrylate (NaPA) on charged TiO2 particles and to determine the subsequent interaction of the adsorbed polymer structure with cationic and anionic surfactants. The nature of the polymer structure was deduced from the adsorbed amount in tandem with the information obtained from monitoring the change in the relative intensity of the COO- and COOH infrared bands. In particular, it is found that the relative number of COO- and COOH groups on the polymer backbone for the adsorbed state differs from that of the same polymer in solution. This difference is due to a shift in the population of COO-/COOH groups on the polymer backbone that arises when the COO- groups bind to positively charged sites on the surface. A change in the number COO-/COOH groups on the polymer is thus related to a change in the bound fraction of polymer. It is shown that the initial NaPA approaching the bare surface adopts a flat conformation with high bound fraction. Once the bare sites on the surface are covered, the accommodation of additional polymer on the surface requires the existing adsorbed layer to adopt a conformation with a lower bound fraction. When the adsorbed NaPA is probed with a solution containing the anionic surfactant sodium dodecyl sulfate (SDS), the SDS competes for surface sites and displaces some of the bound NaPA segments from the surface, giving rise to an polymer layer adsorbed with an even lower bound fraction. In contrast, addition of a solution containing the cationic surfactant cetyltrimethylammonium bromide (CTAB) results in the binding of the surfactant directly to the free COO- sites on the adsorbed polymer backbone. Confirmation of a direct interaction of the CTAB headgroup with the free COO- groups of the polymer is provided by intensity changes in the headgroup IR bands of the CTAB.     

Solubilizing interactions of octylphenol surfactants with liposomes modeling the stratum corneum lipid composition

 The interaction of a series of polyethoxylated octylphenols (ethylene oxide units average 8.5–20.0) with liposomes modeling the stratum corneum (SC) lipid composition (40% ceramides, 25% cholesterol, 25% palmitic acid and 10% of cholesteryl sulfate) was investigated. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous-phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that free concentration for each surfactant tested was always similar to its critical micelle concentration (CMC) indi-cates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The Re and K para-meters for liposome saturation fell as the surfactant HLB increased. Thus, at this interaction step the higher the surfactant HLB, the higher the ability of these surfactants to saturate SC liposomes and the lower their degree of partitioning into liposomes. However, the maximum solubilizing ability was achieved at intermediate HLB values. Thus, the octylphenols with 20 and 12.5 ethylene oxide units showed, respectively, the highest power of saturation and solubilization of SC structures in terms of the total surfactant amounts needed to produce these effects. Different trends in the interaction of these surfactants with SC liposomes were observed when comparing the Re and K parameters with those reported for PC ones. Thus, whereas the SC liposomes were more resistant to the surfactant action, the affinity of these surfactants with these bilayer structures was higher in all cases. Received: 3 March 1997 Accepted: 22 May 1997     

The miscibility of dodecyltrihydroxyethylammonium bromide with cationic, nonionic and anionic surfactants in mixed monolayers and micelles

In this paper were analyzed the surface properties of surfactants and the miscibility and interactions between components of adsorbed monolayers and micelles formed from mixed systems. The investigated compounds differ in the structure of the polar head and represented cationic (dodecyltrihydroxyethylammonium bromide—DTEAB, dodecyltrimethylammonium bromide DTMAB), anionic (sodium dodecyl sulfate—SDS), and nonionic (dodecyl-β-d-glucoside—DG) surfactant. The experiments were based on the measurements of the surface tension of the aqueous solutions of the investigated compounds and their mixtures (cationic/nonionic—DTEAB/DG, cationic/cationic—DTEAB/DTMAB and cationic/anionic—DTEAB/SDS). The composition of the mixed films and micelles as well as the free energies of mixing values, which are a measure of the molecular interactions, was calculated basing on the equations resulting from the Motomura theory. The obtained results indicate that all the investigated systems mix nonideally both in the monolayers and micelles. The magnitude of the deviations from ideal behavior is strongly dependent on the type of the investigated mixture and increases in the following order: DTEAB/DTMAB < DTEAB/DG  DTEAB/SDS.     

Interaction of the cationic peptide bactenecin with mixed phospholipid monolayers at the air-water interface

The initial mechanism by which antimicrobial peptides target microbes occurs via electrostatic interactions; however, the mechanism is not well understood. We investigate the interaction of the antimicrobial peptide bactenecin with a 50:50 w:w% 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DMPG) phospholipid mixture at the air-water interface with different NaCl concentrations (0.01, 0.05, 0.1, 0.5 M) in the subphase. A larger shift of DPPC:DMPG isotherms was obtained for 0.1 M salt concentration at lower and higher pressures, demonstrating the influence of the negative charge of DMPG molecules and the screening of the electrostatic interaction by the salt concentration. Raman spectroscopy of monolayers demonstrated the presence of cysteine-cysteine bridges in bactenecin loops. The peptide adsorption in DPPC:DMPG monolayers observed by AFM images suggests a self-assembled aggregation process, starting with filament-like networks. Domains similar to carpets were formed and pore structures were obtained after a critical peptide concentration, according to the carpet model.     

Effect of cationic surfactants on enhancement of firefly bioluminescence in the presence of liposomes

Firefly bioluminescence (BL) was greatly affected by cationic surfactants coexisting with liposomes containing phosphatidylcholine and cholesterol. In this study, the effects of the type and concentration of cationic surfactants on BL were studied in the presence of the liposomes. Three types of cationic surfactant: benzalkonium chloride (BAC), n-dodecyltrimethylammonium bromide (DTAB), and benzethonium chloride (BZC), were used. As a common effect in these surfactants, BL intensity was increased and then drastically decreased with increasing surfactant concentration. This can be explained by the formation of cationic liposomes as BL enhancers at low concentration of the surfactant, and by the transformation into cationic (mixed) micelles as inhibitors at high concentration. The maximal BL intensity and the concentration for the maximal BL were dependent on the type of the surfactants. To explain the differences in these parameters in the enhanced BL, we determined the distribution coefficient, K, of the surfactants to the liposomal membrane. The result indicated that the surfactant with higher K value gives the maximal BL intensity at lower concentration.     

Interaction of poly(L-glutamic acid) with cationic surfactants carrying different head groups

Three cationic surfactants carrying a common hydrocarbon tail (dodecyl group) interact differently with fully ionized poly(L-glutamic acid)(PGA), depending on the type of their ionic head groups. Decrease of pH occurred in the order; dodecylammonium chloride (DAC) > dodecyldimethylammonium chloride (DDAC) > dodecyltrimethylammonium chloride (DTAC). The-helix of PGA was strongly induced by the addition of DAC and DDAC but weakly by DTAC. The induction was inhibited when NaCl concentration was greater than 0.05 M. In the solid state, proton transfer through hydrogen bonds from ionic heads of DDAC to carboxylate groups of the polypeptide was observed. Distortion of circular dichroism spectra occurred at high mixing ratios of surfactant to polymer, due to the aggregation of-helices, as confirmed by light scattering measurements and infrared absorption spectra.     

Functional polymeric monolayers and liposomes

Some lipid-like monomers were synthesized by acylation of synthetic and naturally occurring amine-containing lipids with acryloyl chloride. The surfactant properties and peculiarities of polymerization of lipid-like monomers in oriented systems were investigated. On the basis of such monomers, polymeric monolayers and liposomes were prepared that have the structural similarity to biomembranes and enhanced stability. The applicability of such systems for immobilization of membrane proteins was shown for the example of bacteriorhodopsin.     

Interaction between 14mer DNA oligonucleotide and cationic surfactants of various chain lengths

In the recent genomic era, a novel gene silencing approach has been introduced based on the use of small synthetic oligonucleotides, such as antisense RNAs, siRNAs, to inhibit the expression of a specific target gene. Successful implementation of this methodology calls for the development of efficient systems to deliver small oligonucleotides into the cells using various natural and synthetic cationic agents. While extensive studies have focused on the interaction of various natural and synthetic cationic surfactants with long DNA, less attention has been paid to surfactant interaction with small oligonucleotides. In this study, the interaction between 14mer double stranded DNA and alkyltrimethylammonium bromides of C16 (cetyl, CTAB), C14 (tetradecyl, TTAB), and C12 (dodecyl, DTAB) chain lengths was investigated at different charge ratios by gel electrophoresis, ethidium bromide exclusion, circular dichroism, and UV melting. Our gel studies at 1 microM oligonucleotide concentration showed that CTAB, TTAB, and DTAB neutralize the oligonucleotides at a charge ratio (Z+/-) of 1, 14, and 50, respectively. At lower charge ratios, CTAB and TTAB interact with oligonucleotides, and the complexes show electrophoretic mobility shifts in the gel, while such mobility shifts were completely absent in the case of DTAB. UV melting experiments revealed that interaction with all three surfactants increased the thermostability of the oligonucleotide. The extent of thermal stabilization was highest in the case of CTAB, moderate in the case of TTAB, and extremely low in the case of DTAB. Oligonucleotides within fully neutralized complexes denatured at further higher temperatures, and again, stabilization was the highest in the case of CTAB followed by TTAB and DTAB, hence revealing that the oligonucleotides interacted more strongly with CTAB than with the other two surfactants. Ethidium bromide exclusion studies also supported our UV melting studies, confirming that CTAB binds most strongly to the oligonucleotide. CD titrations of oligonucleotides with increasing amounts of surfactants revealed common spectral patterns consisting of the progressive loss of CD signals for native helical DNA conformations. Overall, our results demonstrate that interaction between oligonucleotides and cationic surfactants, although qualitatively similar to long double stranded DNA, shows subtle differences that need to be understood to improve small oligonucleotide delivery into the cells by using common delivery agents that have been used to deliver long pieces of DNA.