Monolayer Surface Tension Research Articles

Finite size effects and optimization of the calculation of the surface tension in surfactant mixtures at liquid/vapour interfaces

The surface tension of monolayers with mixtures of anionic and nonionic surfactant at the liquid/vapour interface is studied. Previous works have observed that calculations of the surface tension of simple fluids show artificial oscillations for small interfacial areas, indicating that the surface tension data fluctuate due to the finite size effects and periodic boundary conditions. In the case of simulations of monolayers composed of surfactant mixtures, the surface tension not only oscillates for small areas but can also give non-physical data, such as negative values. Analysis of the monolayers with different surfactant mixtures, ionic (DTAB, CTAB, SDS) and nonionic (SB3-12), was done for density profiles, parameters of order and pair correlation functions for small and large box areas and all of them present similar behaviour. The fluctuations and the non-physical values of the surface tension are corrected when boxes with large interfacial areas are considered. The results indicate that in order to obtain reliable values of the surface tension, in computer simulations, it is important to choose not only the correct force field but also the appropriate size of the simulation box.

Lipid-Coated Nanobubbles in Plants.

One of the more surprising occurrences of bulk nanobubbles is in the sap inside the vascular transport system of flowering plants, the xylem. In plants, nanobubbles are subjected to negative pressure in the water and to large pressure fluctuations, sometimes encompassing pressure changes of several MPa over the course of a single day, as well as wide temperature fluctuations. Here, we review the evidence for nanobubbles in plants and for polar lipids that coat them, allowing nanobubbles to persist in this dynamic environment. The review addresses how the dynamic surface tension of polar lipid monolayers allows nanobubbles to avoid dissolution or unstable expansion under negative liquid pressure. In addition, we discuss theoretical considerations about the formation of lipid-coated nanobubbles in plants from gas-filled spaces in the xylem and the role of mesoporous fibrous pit membranes between xylem conduits in creating the bubbles, driven by the pressure gradient between the gas and liquid phase. We discuss the role of surface charges in preventing nanobubble coalescence, and conclude by addressing a number of open questions about nanobubbles in plants.

Molecular basis of transport of surface functionalised gold nanoparticles to pulmonary surfactant.

Ligands like alkanethiol (e.g. dodecanethiol, hexadecanethiol, etc.) and polymers (e.g. poly(vinyl pyrrolidone), polyethylene glycol-thiol) capped to the gold nanoparticles (AuNPs) are widely used in biomedical field as drug carriers and as promising materials for probing and manipulating cellular processes. Ligand functionalised AuNPs are known to interact with the pulmonary surfactant (PS) monolayer once reaching the alveolar region. Therefore, it is crucial to understand the interaction between AuNPs and PS monolayers. Using coarse-grained molecular dynamics simulations, the effect of ligand density, and ligand length have been studied for two classes of ligands on a PS model monolayer consisting of DPPC, POPG, cholesterol and SP-B (mini-peptide). The ligands considered in this study are alkanethiol and polyethylene glycol (PEG) thiol as examples of hydrophobic and hydrophilic ligands, respectively. It was observed that the interaction between AuNPs and PS changes the biophysical properties of PS monolayer in compressed and expanded states. The AuNPs with hydrophilic ligand, can penetrate through the monolayer more easily, while the AuNPs with hydrophobic ligand are embedded in the monolayer and participated in deforming the monolayer structure particularly the monolayer in the compressed state. The bare AuNPs hinder to lower the monolayer surface tension value at the interface, however introducing ligand to the bare AuNPs or increasing the ligand length and density have an impact of lowering of monolayer surface tension to a minor extent. The simulation results guide the design of ligand protected NPs as drug carriers and can identify the nanoparticles' potential side effects on lung surfactant.

The pore-forming activity of sticholysin I is enhanced by the presence of a phospholipid hydroperoxide in membrane

Sticholysin I (StI) is a pore-forming toxin (PFT) belonging to the actinoporin protein family characterized by high permeabilizing activity in membranes. StI readily associates with sphingomyelin (SM)-containing membranes originating pores that can lead to cell death. Binding and pore-formation are critically dependent on the physicochemical properties of membrane. 1-palmitoyl-2-oleoylphosphatidylcholine hydroperoxide (POPC–OOH) is an oxidized phospholipid (OxPL) containing an –OOH moiety in the unsaturated hydrocarbon chain which orientates towards the bilayer interface. This orientation causes an increase in the lipid molecular area, lateral expansion and decrease in bilayer thickness, elastic and bending modulus, as well as modification of lipid packing. Taking advantage of membrane structural changes promoted by POPC-OOH, we investigated its influence on the permeabilizing ability of StI. Here we report the action of StI on Giant Unilamellar Vesicles (GUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and SM containing increasing amount of POPC-OOH to assess vesicle permeability changes when compared to OxPL-lacking membranes. Inclusion of POPC-OOH in membranes did not promote spontaneous vesicle leaking but resulted in increased membrane permeability due to StI action. StI activity did not modify the fluid-gel phase coexistence boundaries neither in POPC:SM or POPC-OOH:SM membranes. However, the StI insertion mechanism in membrane seems to differ between POPC:SM and POPC-OOH:SM mixtures as suggested by changes in the time course of monolayer surface tension measurements, even though a preferable binding of the toxin to OxPL-containing systems could not be here demonstrated. In summary, modifications in the membrane imposed by lipid hydroperoxidation favor StI permeabilizing activity.

Interfacial interaction between benzo[a]pyrene and pulmonary surfactant: Adverse effects on lung health

Inhaled polycyclic aromatic hydrocarbons (PAHs) can directly interact with the lung surfactant (PS) lining of alveoli, thereby affecting the normal physiological functions of PS, which is a serious threat to lung health. In spite of the extensive study of benzo[a]pyrene (BaP, a representative of PAHs), its potential biophysical influence on the natural PS is still largely unknown. In this study, the interfacial interaction between PS (extracted from porcine lungs) and BaP is investigated in vitro. The results showed that the surface tension, phase behavior, and interfacial structure of the PS monolayers were obviously altered in the presence of BaP. A solubilization test manifested that PS and its major components (dipalmitoyl phosphatidylcholine, DPPC; bovine serum albumin, BSA) could in turn accelerate the dissolution of BaP, which followed the order: PS > DPPC > BSA, and mixed phospholipids were significantly responsible for the solubilization of BaP by PS. In addition, solubilization of BaP also enhanced the consumption of hydroxyl radicals (·OH) in the simulated lung fluid, which could disturb the balance between oxidation and antioxidation.

Molecular insights on the interference of simplified lung surfactant models by gold nanoparticle pollutants

Inhaled nanoparticles (NPs) are experienced by the first biological barrier inside the alveolus known as lung surfactant (LS), a surface tension reducing agent, consisting of phospholipids and proteins in the form of the monolayer at the air-water interface. The monolayer surface tension is continuously regulated by the alveolus compression and expansion and protects the alveoli from collapsing. Inhaled NPs can reach deep into the lungs and interfere with the biophysical properties of the lung components. The interaction mechanisms of bare gold nanoparticles (AuNPs) with the LS monolayer and the consequences of the interactions on lung function are not well understood. Coarse-grained molecular dynamics simulations were carried out to elucidate the interactions of AuNPs with simplified LS monolayers at the nanoscale. It was observed that the interactions of AuNPs and LS components deform the monolayer structure, change the biophysical properties of LS and create pores in the monolayer, which all interfere with the normal lungs function. The results also indicate that AuNP concentrations >0.1 mol% (of AuNPs/lipids) hinder the lowering of the LS surface tension, a prerequisite of the normal breathing process. Overall, these findings could help to identify the possible consequences of airborne NPs inhalation and their contribution to the potential development of various lung diseases.

Equilibrium of phosphatidylcholine-ergosterol in monolayers at the air-water interface

The purpose of this study was to investigate the interaction between phosphatidylcholine (PC) and ergosterol (ERG) in monolayers at the air–water interface. We measured the surface tension of pure and mixed lipid monolayers at 22 °C using the Langmuir method with a Teflon trough and Nima 9002 tensiometer. Surface tension values were used to calculate π-A isotherms and determine molecular surface areas.Interactions between PC and ERG caused significant deviation from the additivity rule. The theory described in this paper was used to determine a stability constant reflecting the area occupied by one molecule of the PC–ERG complex and the complex formation energy (Gibbs energy).

Complex formation equilibria between cholesterol and diosgenin analogues in monolayers determined by the Langmuir method.

The purpose of this study was to investigate the interaction between diosgenin analogues [DioA: diosgenin acetate (DAc) and (25R)-5α,6β-dihydroxyspirostan-3β-ol acetate (DSol)] and cholesterol (Ch) monolayers at the air/water interface. The surface tension of pure and mixed lipid monolayers at 22 °C was measured by using the Langmuir method with a Teflon trough and a Nima 9002 tensiometer. The surface tension values were used to calculate the π-A isotherms and to determine the molecular surface areas. The interactions between Ch and each DioA resulted in significant deviations from the additivity rule. The theory described in this work was used to determine the stability constants, the areas occupied by one molecule of Ch-DAc or Ch-DSol, and the complex formation energy (Gibbs free energy) values.

Measuring bilayer surface energy and curvature in asymmetric droplet interface bilayers.

For the past decade, droplet interface bilayers (DIBs) have had an increased prevalence in biomolecular and biophysical literature. However, much of the underlying physics of these platforms is poorly characterized. To further our understanding of these structures, lipid membrane tension on DIB membranes is measured by analysing the equilibrium shape of asymmetric DIBs. To this end, the morphology of DIBs is explored for the first time using confocal laser scanning fluorescence microscopy. The experimental results confirm that, in accordance with theory, the bilayer interface of a volume-asymmetric DIB is curved towards the smaller droplet and a lipid-asymmetric DIB is curved towards the droplet with the higher monolayer surface tension. Moreover, the DIB shape can be exploited to measure complex bilayer surface energies. In this study, the bilayer surface energy of DIBs composed of lipid mixtures of phosphatidylgylcerol (PG) and phosphatidylcholine are shown to increase linearly with PG concentrations up to 25%. The assumption that DIB bilayer area can be geometrically approximated as a spherical cap base is also tested, and it is discovered that the bilayer curvature is negligible for most practical symmetric or asymmetric DIB systems with respect to bilayer area.

Ballistic Penetration of Highly Charged Nanoaerosol Particles through a Lipid Monolayer.

To be used as a drug, inhaled nanoaerosol particles (NAPs) must first penetrate the lipid layer on top of the lung fluid before they will be able to reach the lung epithelium. We investigated how the penetration of NAPs through a model lipid monolayer (LM) depends upon their charging level and size. It was shown that deposition of NAPs 20-200 nm in diameter and charged to the Rayleigh limit gradually increased the surface tension of a dipalmitoylphosphatidylcholine monolayer (DPPC), indicating a loss of lipid molecules from the monolayer. This phenomenon was reproduced with a variety of NAPs produced from glucose, proteins, and polymers. Transfer of the lipid material into the subphase was documented by direct visualization of lipid nanoparticles in the subphase with atomic force microscopy after deposition of glucose NAPs on a DPPC monolayer, followed by collection of the lipid nanoparticles on a mica surface. Partial restoration of tension upon storage indicates that some of the lipid may return to the monolayer. Experiments with the deposition of highly charged calibrated polystyrene nanoparticles showed that the amount of lipid removed from the surface was roughly proportional to the overall surface area of the deposited NAPs. When the number of charges on the NAPs was reduced from their Rayleigh level of 103-104 units to 1-10 units, no notable changes in monolayer surface tension were observed even with prolonged deposition of such NAPs. It was therefore concluded that only highly charged NAPs of a certain size acquire sufficient speed from their attraction by mirror charges to enable ballistic penetration through a lipid monolayer.

The Gating Mechanism of Mechanosensitive Channels in Droplet Interface Bilayers

ABSTRACTMscL, a large-conductance mechanosensitive channel, is a ubiquitous osmolyte release valve that aids bacteria in surviving abrupt hypo-osmotic shocks. The large scale of its tension-driven opening transition makes it a strong candidate to serve as a transducer in novel stimuli-responsive biomolecular materials. In the previous work, a low-threshold gain-of-function V23T mutant of MscL produced a reliable activation behavior in a droplet interface bilayer (DIB) with applied axial droplet compression. Near the maximal compression, the aqueous droplets deform and the resulting increase in surface area leads to an increase in tension in the water-lipid-oil interface. This increase in tension is the product of the relative change in the droplet surface area and the elastic modulus of the DPhPC lipid monolayer (∼120 mN/m). This paper, presents a study of the physical processes that cause MscL gating in the DIB. Analysis of video during compression and relaxation of the droplets is utilized to estimate the change in the surface area of the droplet and the variation on monolayer surface tension. The monolayer surface tension is proportional to the area change of the droplet normalized to the original surface area. The results demonstrate that the area change in the droplet is negligible at frequencies above 1 Hz, but is approximately 2% at frequencies in the range of 100 mHz. In addition, at low frequencies (∼0.2 Hz) bilayer thinning occurs at maximum compression, proving an increase in bilayer tension. However, this study also shows that gating at frequencies higher than 0.2 Hz could be achieved through the application of high duty cycle oscillation (∼75%). The relative change in monolayer area increases significantly at higher duty cycle oscillations where the compression stroke is much faster than the relaxation stroke.

Molecular structure and stability of the sorbitan monostearate (Span60) monolayers film at the water–air interface: A molecular dynamics simulation study

A sorbitan monostearate (Span60) monolayer film at the water–air interface is presented in the first study using molecular dynamics simulation to investigate this system. The models of the Span60 monolayers in a condensed phase were investigated for all temperatures of the film formation ranging from 22°C to 42°C. Monolayer structure and dynamical properties of the Langmuir film were presented and compared with the experimental data. This study provides insight into the molecular level properties of the surfactant assembly including the monolayer structure, surface tension, lateral diffusion and hydrogen bond dynamics which these results are in good agreement with in experimental data. In addition, this study reveals that the hydrogen bond plays an important role to enhance the film stability. The number and lifetime of hydrogen bonds for the Span60/water are reduced with increasing temperature due to higher mobility of water molecules near the interface. Conversely, the strong interaction among the Span60 molecules themselves and slight decrease in the number of the Span60/water hydrogen bonds with increasing temperature. As a result, the Span60 monolayer film remains stable over these temperature ranges.

Investigation of transmembrane protein fused in lipid bilayer membranes supported on porous silicon

This article investigates a device made from a porous silicon structure supporting a lipid bilayer membrane (LBM)fused with Epithelial Sodium Channel protein. The electrochemically-fabricated porous silicon template had pore diameters in the range 0.2~2 µm. Membranes were composed of two synthetic phospholipids: 1,2-diphytanoyl-sn-glycero-3-phosphoserine and 1,2-diphytanoyl-sn-glycero-3-phosphoethanolamine. The LBMwas formed by means of the Langmuir-Blodgett and Langmuir-Schaefer techniques, at a monolayer surface tension of 26 m Nm−1 in room temperature and on a deionized water subphase, which resulted in an average molecular area of 0.68–0.73 nm2. Fusion of transmembrane protein was investigated using Atomic Force Microscopy. Initial atomic force microscopy results demonstrate the ability to support lipid bilayers fused with transmembrane proteins across a porous silicon substrate. However, more control of the membrane’s surface tension using traditional membrane fusion techniques is required to optimize protein incorporation.

Effects of Perfluorocarbon Gases on the Size and Stability Characteristics of Phospholipid-Coated Microbubbles: Osmotic Effect versus Interfacial Film Stabilization

Micrometer-sized bubbles coated with phospholipids are used as contrast agents for ultrasound imaging and have potential for oxygen, drug, and gene delivery and as therapeutic devices. An internal perfluorocarbon (FC) gas is generally used to stabilize them osmotically. We report here on the effects of three relatively heavy FCs, perfluorohexane (F-hexane), perfluorodiglyme (F-diglyme ), and perfluorotriglyme (F-triglyme), on the size and stability characteristics of microbubbles coated with a soft shell of dimyristoylphosphatidylcholine (DMPC) and on the surface tension and compressibility of DMPC monolayers. Monomodal populations of small bubbles (~1.3 ± 0.2 μm in radius, polydispersivity index ~8%) were prepared by sonication, followed by centrifugal fractionation. The mean microbubble size, size distribution, and stability were determined by acoustical attenuation measurements, static light scattering, and optical microscopy. The half-lives of F-hexane- and F-diglyme-stabilized bubbles (149 ± 8 and 134 ± 3 min, respectively) were about 2 times longer than with the heavier F-triglyme (76 ± 7 min) and 4-5 times longer than with air (34 ± 3 min). Remarkably, the bubbles are smaller than the minimal size values calculated assuming that the bubbles are stabilized osmotically by the insoluble FC gases. Particularly striking is that bubbles 2 orders of magnitude smaller than the calculated collapse radius can be prepared with F-triglyme, while its very low vapor pressure prohibits any osmotic effect. The interface between an aqueous DMPC dispersion and air, or air (or N(2)) saturated with the FCs, was investigated by tensiometry and by Langmuir monolayer compressions. Remarkably, after 3 h, the tensions at the interface between an aqueous DMPC dispersion (0.5 mmol L(-1)) and air were lowered from ~50 ± 1 to ~37 ± 1 mN m(-1) when F-hexane and F-diglyme were present and to ~40 ± 1 mN m(-1) for F-triglyme. Also noteworthy, the adsorption kinetics of DMPC at the interface, as obtained by dynamic tensiometry, were accelerated up to 3-fold when the FC gases were present. The compression isotherms show that all these FC gases significantly increase the surface pressure (from ~0 to ~10 mN m(-1)) at large molecular areas (70 Å(2)), implying their incorporation into the DMPC monolayer. All three FC gases increase the monolayer's collapse pressures significantly (~61 ± 2 mN m(-1)) as compared to air (~54 ± 2 mN m(-1)), providing for interfacial tensions as low as ~11 mN m(-1) (vs ~18 mN m(-1) in their absence). The FC gases increase the compressibility of the DMPC monolayer by 20-50%. These results establish that, besides their osmotic effect, FC gases contribute to bubble stabilization by decreasing the DMPC interfacial tension, hence reducing the Laplace pressure. This contribution, although significant, still does not suffice to explain the large discrepancy observed between calculated and experimental bubble half-lives. The case of F-triglyme, which has no osmotic effect, indicates that its effects on the DMPC shell (increased collapse pressure, decreased interfacial tension, and increased compressibility) contribute to bubble stabilization. F-hexane and F-diglyme provided both the smallest mean bubble sizes and the longest bubble half-lives.

Comparative study of the interaction of synthetic methionine-enkephalin and its amidated derivate with monolayers of zwitterionic and negatively charged phospholipids

Using Langmuir's monolayer technique, the surface behavior and the interaction of the synthetic neuropeptide methionine-enkephalin (Met-enk) and its amidated derivate (Met-enk-NH(2)) with monolayers of the zwitterionic dimyristoylphosphatidylcholine (DMPC) and the negatively charged dimyristoylphosphatidylglycerol (DMPG) were studied. The surface tension (γ, mN/m) of DMPG and DMPC monolayers as a function of time (after injection of the peptide under the interface) was detected. The decrease in γ values showed that there was a strong penetration effect of both types of Met-enk molecules into the monolayers, being significantly stronger for the amidated derivate, Met-enk-NH(2). We suggest that the interaction between the neuropeptides and DMPC was predominantly determined by peptides amphiphilicity, while the electrostatic forces play significant role for the insertion of the cationic Met-enk-NH(2) in DMPG monolayers, especially at high packing densities. Our results demonstrate the potential of lipid monolayers formed in Langmuir's trough to be successfully used as an elegant and simple membrane models to study lipid-peptide interactions at the air/water interface.

Membrane penetration of the FYVE domain is modulated by pH

The FYVE domain (Fab1, YOTB, Vac1, EEA1) binds phosphatidylinositol 3‐phosphate [PtdIns(3)P] in membranes of early endosomes and penetrates bilayers. Here, we investigate the membrane anchoring mechanism by NMR, liposome binding, monolayer surface tension, mutagenesis, and in‐vivo localization experiment. Our results show that the extent of the FYVE domain insertion into PtdIns(3)P‐enriched membranes is substantially enhanced by acidic conditions and contacts with anionic lipids. The EEA1 FYVE domain associates with POPC/POPE/PtdIns(3)P vesicles with a Kd of 49 nM at pH 6.0, however binding is ~~24 fold weaker at pH 8.0. The decrease of the binding affinity is primarily due to much faster dissociation of the FYVE domain from membranes in basic media. The membrane penetration is modulated by the tandem His residues in the RRHHCRXCG signature motif, mutations of which abolish the pH‐sensitivity. The increased membrane association in vitro and in vivo by the Hrs, RUFY1, Vps27p and WDFY1 FYVE domains in a low pH environment demonstrates that pH‐dependency is a general function of the FYVE protein family.Supported by NIH grants GM071424 and CA113472 (TGK).

On The Properties Of Surfactant Monolayers At Low Surface Tensions

The properties of surfactant monolayers at the air/water interface depend strongly on the monolayer surface density. As the density increases, the monolayers undergo transitions from gas to liquid and condensed phases, and transform from 2D to 3D geometry as their stability limit is reached. For a given surfactant, the higher the surface density, the smaller is the monolayer area, and lower is the resulting surface tension at the interface. We found that for selected lipid mixtures and lung surfactant extracts, the monolayer surface tension - area isotherms deviate from the expected dependence. For these mixtures, the captive bubble surfactometer measurements show that at low surface tensions (< 20 mN/m) the reduction of surface tension is accompanied by an increase rather than a decrease of monolayer area. We used a combination of experimental techniques, theoretical models and computer simulations to investigate the properties of monolayers of varying composition at low surface tensions. We hypothesize that the observed effect originates from monolayer 2D-3D transformations. Monolayer wrinkling in particular leads to a decrease of monolayer apparent area and lowers the total surface tension.

Effects of Cholesterol—Sphingomyelin Interactions on Penetration of Neuropeptides to their Monolayers

ABSTRACTIn the present study, the surface behavior and interactions between the synthetic analogue of the endogenous neuropeptide Methionine-enkephalin (Met-enk) and monolayers composed of cholesterol (Chol), sphingomyelin (SM) and their mixtures are studied. The measurements are made by using Langmuir's monolayer technique simultaneously with Wilhelmy method for determination of monolayer (on subphase of 0,14 M NaCl) surface tension as a function of time and lipid molecular area. After the injection of the Met-enk into the subphase, a decrease in surface tension is detected in all experiments. The data obtained show that the peptide penetrates the monolayers of both lipid types as well as of their mixtures. It is proved that, regarding the Met-enk penetration, there is a synergetic effect in the mixed monolayers of Chol and SM. Most probably, this is due to the ability of cholesterol to regulate the fluidity of lipid monolayers. Thus, we suggest that Chol facilitates the penetration of the neuropeptide in SM monolayer films.

Inhibitory effects of mycobacterial cell wall lipids on bovine lung surfactant extract: An in vitro study at the air–aqueous interface

Lung surfactant is a lipoprotein mixture synthesized by the type II alveolar cells in the lungs and lines the air–aqueous interface. It is essential for stabilizing the pulmonary alveoli. Deficiency or dysfunction of the surfactant due to chemicals or toxins results in alveolar collapse and if untreated leads to respiratory distress. In pulmonary tuberculosis, Mycobacterium tuberculosis bacteria reside in the alveoli, in close physical proximity with the alveolar surfactant. The surface active mycobacterial cell wall lipids may easily detach from bacterial cell wall and interact with surfactant components altering their surface activity. In this study, effects of mycolic acid and cord factor (the abundant surface lipids of mycobacterial cell wall) on the surface activity of modified bovine surfactant extract (Survanta™) were characterized in vitro using the Wilhelmy surface balance at physiological temperature (37 °C) and pH 7.4. Inhibitory effects of mycobacterial cell wall lipids on the terminal airway surfactant were evaluated using a capillary surfactometer. Addition of graded amounts of mycolic acid and cord factor significantly increased the minimum surface tension of Survanta™ monolayer from <1 mN/m to ∼11–20 mN/m. Presence of mycobacterial cell wall lipids decreased the rate and magnitude of Survanta™ adsorption and fluidized the surfactant monolayer. Capillary surfactometer study exhibited 100% capillary closure on addition of mycobacterial cell wall lipids to the modified bovine surfactant extract. AFM imaging revealed alteration of surface topography and presence of aggregates on addition of mycobacterial cell wall lipids to Survanta™ monolayer. This study suggests a biophysical inhibition of lung surfactant which may play a role in the pathogenesis of pulmonary tuberculosis.

Dibucaine effects on structural and elastic properties of lipid bilayers

In this work we report the interaction effects of the local anesthetic dibucaine (DBC) with lipid patches in model membranes by Atomic Force Microscopy (AFM). Supported lipid bilayers (egg phosphatidylcholine, EPC and dimyristoylphosphatidylcholine, DMPC) were prepared by fusion of unilamellar vesicles on mica and imaged in aqueous media. The AFM images show irregularly distributed and sized EPC patches on mica. On the other hand DMPC formation presents extensive bilayer regions on top of which multibilayer patches are formed. In the presence of DBC we observed a progressive disruption of these patches, but for DMPC bilayers this process occurred more slowly than for EPC. In both cases, phase images show the formation of small structures on the bilayer surface suggesting an effect on the elastic properties of the bilayers when DBC is present. Dynamic surface tension and dilatational surface elasticity measurements of EPC and DMPC monolayers in the presence of DBC by the pendant drop technique were also performed, in order to elucidate these results. The curve of lipid monolayer elasticity versus DBC concentration, for both EPC and DMPC cases, shows a maximum for the surface elasticity modulus at the same concentration where we observed the disruption of the bilayer by AFM. Our results suggest that changes in the local curvature of the bilayer induced by DBC could explain the anesthetic action in membranes.