Langmuir Monolayers Of Dipalmitoylphosphatidylcholine Research Articles

In situ nonlinear optical spectroscopic study of the structural chirality in DPPC Langmuir monolayers at the air/water interface.

We conduct a molecular study on the structural chirality in Langmuir monolayers composed of dipalmitoylphosphatidylcholine (DPPC) using in situ nonlinear optical spectroscopies, including second harmonic generation (SHG) and sum frequency generation (SFG). Chiral SHG response is observed from L-DPPC monolayers at moderate surface pressures and almost vanishes at a high surface pressure. SFG spectra of L-DPPC monolayers show chiral features that can be assigned to the terminal CH3 groups and the CH2 groups attached to the chiral center atom. This means that these achiral moieties form chiral superstructures at the interface. Along with increasing surface pressure, the structural chirality of CH3 groups shows a similar trend as that of chiral SHG, but CH2 chirality increases monotonically. Furthermore, in a racemic DPPC monolayer with a moderate surface pressure, both chiral SHG and chiral SFG of CH3 groups are absent, whereas chiral SFG of CH2 groups is clearly present, indicating that L- and D-DPPC are diastereomers at the air/water interface and interfacial CH2 prefers a certain orientation regardless of the molecular handedness. A molecular mechanism is proposed to explain the origin of the structural chirality in DPPC monolayers.

Investigation on the Interactions between Self-Assembled β-Sheet Peptide Nanofibers and Model Cell Membranes.

Self-assembled peptide nanofibers (NFs) obtained from β-sheet peptides conjugated with drugs, including antigenic peptides, have recently attracted significant attention. However, extensive studies on the interactions of β-sheet peptide NFs with model cell membranes have not been reported. In this study, we investigated the interactions between three types of NFs, composed of PEG-peptide conjugates with different ethylene glycol (EG) lengths (6-, 12- and 24-mer), and dipalmitoylphosphatidylcholine (DPPC) Langmuir membranes. When increasing the EG chain length, those interactions significantly decreased considering measurements in the presence of the NFs of: (i) changes in surface pressure of the DPPC Langmuir monolayers and (ii) surface pressure–area (π–A) compression isotherms of DPPC. Because the observed trend was similar to the EG length dependency with regard to cellular association and cytotoxicity of the NFs that was reported previously, the interaction of NFs with phospholipid membranes represented a crucial factor to determine the cellular association and toxicity of the NFs. In contrast to NFs, no changes were observed with varying EG chain length on the interaction of the building block peptide with the DPPC membrane. The results obtained herein can provide a design guideline on the formulation of β-sheet peptide NFs, which may broaden its potential.

Comparison with Crystallization of Calcium and Strontium Carbonates under DPPC Langmuir Monolayers

In this paper, using Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) as template, we have investigated the controlled crystallization of calcium and strontium carbonates to understand the biomineralization process at the inorganic-organic interface better. Although the calcite with a well-oriented (104) crystal plane has been obtained, as for the strontium carbonates, DPPC monolayers have resulted in the formation of the flower-like assemblies of strontianite needles; however, the oriented growth under the monolayers has not appeared. Using the lattice matching and electrostatic interaction at the inorganic-organic interface, we have discussed the possible mechanism of the phenomena.

Effects of γ-zein peptides on lipid membrane organization: Quartz crystal microbalance with dissipation and Langmuir monolayer studies

γ-zein peptides (VHLPPP)n present great potential as efficient molecule carriers across the cell membrane. To further understand the binding behavior of peptides with cell membrane, simplified models consisting of peptides and mono/bi-layer membranes (Langmuir monolayer and liposome) were used to studied the resulting response in the structure of peptide and cell membrane in the present work. The results showed that (VHLPPP)n=1,3 bound to dipalmitoylphosphatidylcholine (DPPC) liposomes and was induced to self-assemble into polyproline II (PP II) structure. The incorporation of (VHLPPP)n=1,3 in the DPPC Langmuir monolayers resulted in an increase in the surface pressure and a decrease in the collapse pressure, suggesting the increase of lipid monolayer fluidity. Fluorescence images further confirmed that the presence of (VHLPPP)n=1,3 promoted the formation of liquid-expanded (LE, dis-ordered) phases in lipid monolayers. Atomic force microscopy images found that (VHLPPP)n=1,3 preferred to penetrate in LE phase domains. In addition, (VHLPPP)3 possesses higher binding affinity with DPPC membrane models compared to (VHLPPP)1.

An Investigation into the Antibacterial Properties of Citrus and Plant Essential Oils

Langmuir Monolayers of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and E.coli lipid extract were used to investigate the antibacterial properties of essential oils, in particular sweet orange oil. DPPC served as the control membrane while DPPG served as the gram positive bacteria model and E.coli lipid extract was the gram negative bacteria model. The Langmuir Monolayer technique is useful for forming model cell membranes and allows for the analysis of the interactions between phospholipids and their molecular organization in the presence of another molecule. The main chemical in sweet orange oil, limonene, was found to disrupt phospholipid‐phospholipid interactions in all models except for DPPG simply because PG headgroups hydrogen bond with each other and there is no space for the hydrophobic limonene molecule. The largest disruption was observed for the E.coli extract lipids due to the unsaturated tails in these lipids resulting in less tight packing. Monolayers were seen in all three membrane systems to be destabilized as evidenced by the decrease in collapse pressure of the monolayer film but the E.coli lipid extract monolayer was the most affected in terms of fluidity as seen by the compression modulus. The antibacterial effects of orange oil on these systems is currently being compared to that of peppermint oil.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

DPPC monolayer response to non-spanning cobalt-cage metallosurfactants: Electrostatic complex formation

A novel series of amphiphilic cobalt-cage derivatives (ACCD), bearing a diaza-crown bridge and varying alkyl chains, facilitate ion transport across biomembrane models via self-aggregation. In this study, compression isotherm analyses and atomic force microscopy (AFM) were used to assess the interactions of these amphiphiles with Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) in order to elucidate electrostatic and steric contributions to ion transport. The stability and compressibility of DPPC monolayers are disrupted by ACCD molecules with short (C12) alkyl chains. These top-heavy amphiphiles (large cone angles) create voids at the interface of the hydrophobic/aqueous layer leading to monolayer expansion and packing efficiency of the aliphatic chains is disrupted. Long-tailed analogues (C16, C18) are cohesively integrated into DPPC monolayers due to their smaller cone angles at the interfacial region and increased hydrocarbon compatibility in the hydrophobic region. Thermodynamic data indicate the formation of electrostatic complexes between DPPC and longer-tailed amphiphiles consistent with AFM observations of aggregate structures at the corresponding concentrations.

Interaction of non-aqueous dispersions of silver nanoparticles with cellular membrane models

In this work, silver nanoparticles (AgNPs) dispersed in non-aqueous media and stabilized with polyether block polymers amide (PEBA) were incorporated in Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC), which served as a cell membrane model. The AgNPs presented surface activity, disturbing the viscoelastic properties of the floating film. They expanded the monolayers decreasing their surface elasticity as observed with surface pressure-area isotherms. Polarization modulation reflection-absorption spectroscopy showed that the permanence of AgNPs at the air-water interface is favored by PEBA, affecting both the hydrophilic and the hydrophobic groups of the phospholipid. Brewster angle microscopy showed that the AgNPs lead to the formation of aggregates at the air-water interface, establishing domains that shear with each other due to the low lateral viscosity of irregular and non-monomolecular domains. These data can be correlated to the possible toxicity and microbicide effect of AgNPs in lipidic surfaces such as in mammalian and microbial membranes.

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

The effect of highly concentrated salt solutions of marine-relevant cations (Na+, K+, Mg2+, and Ca2+) on Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), and infrared reflection-absorption spectroscopy (IRRAS). It was found that monovalent cations and Mg2+ have similar phase behavior, causing DPPC monolayers to expand, while Ca2+ induces condensation. All cations disrupted the surface morphology at high cation concentration, resulting in decreased reflectivity from the monolayer. Monolayer refractive index was calculated from BAM image intensity in the liquid condensed phase and decreased with increasing cation concentration, which suggests that orientation of the alkyl chains change. Monovalent ions increase ordering of the alkyl chains, more than divalents, yet have little interaction with the DPPC headgroup. Mg2+ induces gauche defects in the alkyl chain and increases headgroup hydration at low lipid coverage but increases chain ordering and dehydrates the headgroup at high lipid coverage. Ca2+ orders alkyl chains and dehydrates the phosphate moiety, independent of lipid phase. At the highest salt concentration investigated, significant narrowing of the asymmetric PO2− vibrational mode occurs and is attributed to considerable dehydration of the DPPC headgroup.

Membrane Cholesterol Modulates Superwarfarin Toxicity

Superwarfarins are modified analogs of warfarin with additional lipophilic aromatic rings, up to 100-fold greater potency, and longer biological half-lives. We hypothesized that increased hydrophobicity allowed interactions with amphiphilic membranes and modulation of biological responses. We find that superwarfarins brodifacoum and difenacoum increase lactate production and cell death in neuroblastoma cells. In contrast, neither causes changes in glioma cells that have higher cholesterol content. After choleterol depletion, lactate production was increased and cell viability was reduced. Drug-membrane interactions were examined by surface X-ray scattering using Langmuir monolayers of dipalmitoylphosphatidylcholine and/or cholesterol. Specular X-ray reflectivity data revealed that superwarfarins, but not warfarin, intercalate between dipalmitoylphosphatidylcholine molecules, whereas grazing incidence X-ray diffraction demonstrated changes in lateral crystalline order of the film. Neither agent showed significant interactions with monolayers containing >20% cholesterol. These findings demonstrate an affinity of superwarfarins to biomembranes and suggest that cellular responses to these agents are regulated by cholesterol content.

Complexation of phospholipids and cholesterol by triterpenic saponins in bulk and in monolayers

The interactions between three triterpene saponins: α-hederin, hederacoside C and ammonium glycyrrhizate with model lipids: cholesterol and dipalmitoylphosphatidylcholine (DPPC) are described. The oleanolic acid-type saponins (α-hederin and hederacoside C) were shown to form 1:1 complexes with lipids in bulk, characterized by stability constants in the range (4.0±0.2)·103–(5.0±0.4)·104M−1. The complexes with cholesterol are generally stronger than those with DPPC. On the contrary, ammonium glycyrrhizate does not form complexes with any of the lipids in solution. The saponin–lipid interactions were also studied in a confined environment of Langmuir monolayers of DPPC and DPPC/cholesterol with the saponins present in the subphase. A combined monolayer relaxation, surface dilational rheology, fluorescence microscopy and neutron reflectivity (NR) study showed that all three saponins are able to penetrate pure DPPC and mixed DPPC/cholesterol monolayers. Overall, the effect of the saponins on the model lipid monolayers does not fully correlate with the lipid–saponin complex formation in the homogeneous solution. The best correlation was found for α-hederin, for which even the preference for cholesterol over DPPC observed in bulk is well reflected in the monolayer studies and the literature data on its membranolytic activity. Similarly, the lack of interaction of ammonium glycyrrhizate with both lipids is evident equally in bulk and monolayer experiments, as well as in its weak membranolytic activity. The combined bulk and monolayer results are discussed in view of the role of confinement in modulating the saponin–lipid interactions and possible mechanism of membranolytic activity of saponins.

The negligible effects of the antifungal natamycin on cholesterol-dipalmitoyl phosphatidylcholine monolayers may explain its low oral and topical toxicity for mammals

Natamycin is an effective, broad spectrum antifungal with no reported resistance, in contrast to most antimicrobials. It also exhibits reduced (oral and topical) toxicity to humans, which is probably associated with the lack of effects on mammalian cell membranes. In this paper we employ Langmuir monolayers to mimic a cell membrane, whose properties are interrogated with various techniques. We found that natamycin has negligible effects on Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC), but it strongly affects cholesterol monolayers. Natamycin causes the surface pressure isotherm of a cholesterol monolayer to expand even at high surface pressures since it penetrates into the hydrophobic chains. It also reduces the compressibility modulus, probably because natamycin disturbs the organization of the cholesterol molecules, as inferred with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). In mixed cholesterol/DPPC monolayers, strong effects from natamycin were only observed when the cholesterol concentration was 50mol% or higher, well above its concentration in a mammalian cell membrane. For a sterol concentration that mimics a real cell membrane in mammals, i.e. with 25mol% of cholesterol, the effects were negligible, which may explain why natamycin has low toxicity when ingested and/or employed to treat superficial fungal infections.

Probing the interaction of oppositely charged gold nanoparticles with DPPG and DPPC Langmuir monolayers as cell membrane models

The growing use of nanoparticles in a variety of applications calls for detailed studies of their toxicology, which in turn require understanding the interactions between nanoparticles and living cells. Since simulating the interaction with real cell membranes is rather complex, Langmuir monolayers (LMs) have been used to mimic the first barrier encountered by a nanoparticle as it approaches a biological membrane to assess molecular-level interactions. In this study, we show how oppositely charged gold nanoparticles (Au-NPs) interact with monolayers of the zwitterionic dipalmitoylphosphatidyl choline (DPPC) and negatively charged dipalmitoylphosphatidyl glycerol (DPPG). The monolayers were spread on subphases containing two concentrations of either negatively charged Au-NPs coated with citrate anions or positively charged Au-NPs functionalized with the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH). For DPPG, electrostatic effects dominated which depended strongly on the NPs capping agent, being obviously larger for the positive nanoparticles. The in-plane elasticity for DPPG monolayers within the surface pressure range corresponding to real cell membranes increased with adsorption of positively charged NPs, but decreased with the negative ones. For the zwitterionic DPPC, on the other hand, significant effects only occurred for negatively charged NPs, including a decrease in elasticity. Therefore, it is concluded that the nature, namely the charge of the capping agents, is crucial for the interaction of charged NPs with the cell membrane.

Raft localization of Type I Fcε receptor and degranulation of RBL-2H3 cells exposed to decavanadate, a structural model for V2O5

Vanadium oxides (VOs) have been identified as low molecular weight sensitizing agents associated with occupational asthma and compromised pulmonary immunocompetence. Symptoms of adult onset asthma result, in part, from increased signal transduction by Type I Fcε receptors (FcεRI) leading to release of vasoactive compounds including histamine from mast cells. Exposure to (VOs) typically occurs in the form of particles which are insoluble. Upon contact with water or biological fluids, (VOs) form a series of soluble oxoanions, one of which is decavanadate, V10O28(6-) abbreviated V10, which is structurally related to a common vanadium oxide, that is vanadium pentoxide, V2O5. Here we investigate whether V10 may be initiating plasma membrane events associated with activation of FcεRI signal transduction. We show that exposure of RBL-2H3 cells to V10 causes a concentration-dependent increase in degranulation of RBL-2H3 and, in addition, an increase in plasma membrane lipid packing as measured by the fluorescent probe, di-4-ANEPPDHQ. V10 also increases FcεRI accumulation in low-density membrane fragments, i.e., lipid rafts, which may facilitate FcεRI signaling. To determine whether V10 effects on plasma membrane lipid packing were similarly observed in Langmuir monolayers formed from dipalmitoylphosphatidylcholine (DPPC), the extent of lipid packing in the presence and absence of V10 and vanadate was compared. V10 increased the surface area of DPPC Langmuir monolayers by 6% and vanadate decreased the surface area by 4%. These results are consistent with V10 interacting with this class of membrane lipids and altering DPPC packing.

Phospholipid Headgroup Charge Modifies Condensing Effect of Gangliosides on Lipid Films

In model membrane mixtures that mimic lipid raft compositions, the more ordered domains are enriched in the ganglioside, GM1, a glycolipid with a headgroup containing four neutral sugars and a negatively charged sialic acid. To understand the organization and partitioning of GM1 in cell membranes, the outer leaflet of the cell membrane was modeled using Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC), a phospholipid with a zwitterionic headgroup, and varying concentrations of GM1. At low biologically relevant concentrations, GM1 condenses the DPPC monolayer while at higher concentrations, it fluidizes, with a switch-over point between the two behaviors at a ratio of 3:1 DPPC:GM1.To examine the role of electrostatics, lipids with negatively charged phosphatidylglycerol (PG) and positively charged trimethylammonium-propane (TAP) headgroups were combined with various ratios of GM1. Fluidity of the monolayer was systematically altered by changing the hydrocarbon tail length. Additivity plots constructed for all mixtures show negative deviations from ideal mixing or condensation of the monolayer regardless of headgroup charge. For the zwitterionic and negatively charged lipids, the greatest condensation effect compared to the pure lipid was seen at low GM1 concentrations. In binary mixtures containing positively charged lipids, a similar magnitude of condensation occurred at all GM1 ratios. For less fluid lipid nears their triple point temperature, the addition of GM1 caused minimal condensation suggesting the effect is specific to lipids that can be easily ordered.

Liquid Expanded Monolayers of Lipids As Model Systems to Understand the Anionic Hofmeister Series: 1. A Tale of Models

In this work, we use Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC) as model systems to enhance the understanding of specific anion effects in physicochemical and biological systems. The 298 K isotherms (equation of state, EOS) of DPPC over solutions of a range of sodium salts depend strongly on the type and concentration of the salt in the subphase. We focus in particular on the liquid expanded phase region of the DPPC EOS and assume that the deviation of the isotherms over electrolyte solutions from that over pure water is due entirely to the charging of the lipid monolayer by the ions. We then examine the ability of a range of phenomenological continuum models to explain the pressure increase in the presence of electrolytes. The important finding is that insoluble lipid monolayers allow the discrimination between possible modes of ion-lipid interaction. Chemical binding models, simple or modified, cannot fit the range of data presented in this work. Both dispersion interaction and partitioning models fit most of the experimental isotherms and provide unique values for dispersion coefficients or ionic partitioning constants, respectively, even though the nature of these models is completely different (the former concentrates on the potential of mean force that acts on an ion in the double layer, while the latter concentrates on the treatment of interactions at the interface). Surprisingly, the respective fitting parameters are very highly correlated, reflecting, we believe, the effect of ion size on ionic properties and interactions. With sodium fluoride (NaF) as the subphase electrolyte, it is demonstrated that sodium exhibits a weak complexation-type interaction with the zwitterionic lipids. The simple dispersion and partitioning models cannot account for the NaF results, highlighting the need for more complex salt-lipid interaction models that account both for sodium binding and anion partitioning. This realization sets the stage for the companion paper.

The detrimental effect of serum albumin on the re-spreading of a dipalmitoyl phosphatidylcholine Langmuir monolayer is counteracted by a fluorocarbon gas

We have recently reported that fluorocarbon gases exhibit an effective fluidizing effect on Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC), preventing them from crystallizing up to surface pressures of ∼ 40 mN m − 1 , i.e. well above the DPPC's equilibrium surface pressure. We now report that gaseous perfluorooctyl bromide (gPFOB) promotes the re-spreading of DPPC Langmuir monolayers compressed on a bovine serum albumin (BSA)-containing sub-phase. The latter protein is known to maintain a concentration-dependent surface pressure that can exceed the re-spreading pressure of collapsed monolayers. This phenomenon was proposed to be responsible for lung surfactant inactivation. Compression/expansion isotherms and fluorescence microscopy experiments were carried out to assess the monolayers' physical state. We have found that, during expansion under gPFOB-containing air, the surface pressure of a DPPC monolayer on a BSA-containing sub-phase decreased to much lower values than when the DPPC monolayer was expanded in the presence of BSA under air (∼ 0 mN m − 1 vs. ∼ 7.5 mN m − 1 at 120 Å 2, respectively). Moreover, fluorescence images showed that, during expansion, the BSA-coupled DPPC monolayers, in contact with gPFOB, remained in the liquid-expanded state for surface pressures lower than 10 mN m − 1 , whereas they were in a liquid-condensed semi-crystalline state, even at large molecular areas (120 Å 2), when expanded under air. The re-incorporation of the PFOB molecules in the DPPC monolayer during expansion thus competes with the re-incorporation of BSA, thus preventing the latter from penetrating into the DPPC monolayer. We suggest that combinations of DPPC and a fluorocarbon gas may be useful in the treatment of lung conditions resulting from a deterioration of the native lung surfactant function due to plasma proteins, such as in the acute respiratory distress syndrome.

Study of penetration of amphotericin B into cholesterol or ergosterol containing dipalmitoyl phosphatidylcholine Langmuir monolayers

The interactions of amphotericin B (AmB) with sterols and phospholipids have been studied by adsorption of AmB from aqueous solutions into Langmuir monolayers from dipalmitoyl phosphatidylcholine (DPPC), ergosterol, cholesterol and their mixtures. The results show that AmB exhibits stronger interaction with cholesterol than ergosterol in one-component monolayers. However, for DPPC–sterol monolayers, the effectiveness of AmB penetration depends on the proportion of both film components in the mixed film as well as on the strength of interaction between DPPC and particular sterol.

Chiral interaction in enantiomeric and racemic dipalmitoyl phosphatidylcholine Langmuir monolayers

An Effective Pair Potential (EPP) theory is used to study relation between the molecular chiral structure of a phospholipid (Dipalmitoyl phosphatidyl choline; DPPC) and the shape of the mesoscopic domain composed of DPPC. It is experimentally known that the monolayers of DPPC in the condensed phase exhibit the formation of triskellion shaped domains. The curvature of the arms of the triskellions has specific handedness depending on the chirality of the constituent molecule. The study uses an equivalent description of the groups attached to the chiral center and calculates the mutual orientation of a pair of molecules (enantiomeric and racemic pairs). The pair potential is calculated using Lennard Jones potential. Also, the electrial interaction is computed using semi-empirical approach. Based on the minimum energy arrangement, the handedness of the aggregates and their pair potential are predicted. Theoretically obtained results are compared with the experimental results and also with the previously obtained coarse-grained description of the molecule. The study uses no adjustable parameter and uses the microscopic information obtained from X-ray diffraction data. It shows that the equivalent sphere description of the molecule can fairly describe the mesoscopic features of the domains such as the handedness based on the pair potential calculation.