Two-component Langmuir Monolayers Research Articles

Influence of the Type of Biocompatible Polymer in the Shell of Magnetite Nanoparticles on Their Interaction with DPPC in Two-Component Langmuir Monolayers.

Magnetite nanoparticles (MNPs) are attractive nanomaterials for applications in magnetic resonance imaging, targeted drug delivery, and anticancer therapy due to their unique properties such as nontoxicity, wide chemical affinity, and intrinsic superparamagnetism. Their functionalization with polymers such as chitosan or poly(vinyl alcohol) (PVA) can not only improve their biocompatibility and biodegradability but it also plays an important role in their interactions with biological cells. In this work, the effect of the functionalization of MNPs with chitosan, PVA, and their blend on model cell membranes formed from 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) using a Langmuir technique was studied. The studies performed showed that the type of biocompatible polymer in the MNP shell plays a crucial role in the effectiveness of its adsorption process into the model cell membrane. Modification of MNPs with chitosan facilitates significantly more effective adsorption than coating them with PVA or with a chitosan and PVA blend. The presence of all the investigated MNPs in the DPPC monolayer at low concentrations does not affect its thermodynamic state, fluidity, or morphology, which is promising in terms of their biocompatibility. On the other hand, their high concentration (molar fraction above ≈0.05) exerts a disruptive effect on the model cell membrane and results in their aggregation, leading probably to the loss of their superparamagnetic properties essential for nanomedicine.

Lateral interaction of cholesterol with a semifluorinated amphiphile at the air–water interface

Lipid rafts consisting mainly of sphingomyelin and cholesterol (Ch) on biomembrane surfaces are deeply related to cellular processes such as protein trafficking and signal transduction. During the processes, the raft microdomains affect the fluidty of biological membranes, which is controlled to large extents by Ch. In this paper, we have investigated the interaction between Ch and a semiflurinated alcohol (F6H9OH) from the aspect of a fluidty control using surface chemistry. The two-component Langmuir monolayer at the air–water interface was characterized by the surface pressure (π)–molecular area (A) and surface potential (ΔV)−A isotherms. The compressibility modulus and excess Gibbs free energy of mixing were calculated from the π−A isotherms. And also the two-dimensional phase diagram was constructed on the basis of phase transition pressures and monolayer collapse pressures. Furthermore, the phase behavior of binary monolayers was visualized with fluorescence microscopy (in situ) and atomic force microscopy (ex situ). The result here indicates a possibility of fluidity control of Ch-related membranes by arranging the fluorination degree of the constituent lipids.

Two-Component Langmuir Monolayers and LB Films of DPPC with Partially Fluorinated Alcohol (F8H9OH)

The interaction of (perfluorooctyl)nonanol (F8H9OH) with dipalmitoylphosphatidylcholine (DPPC) was systematically studied in two-component monolayers at air-water interface. The thermodynamic property and phase morphology of the monolayers were investigated by isotherm measurements and several microscopic methods such as Brewster angle microscopy, fluorescence microscopy, and atomic force microscopy (AFM). The AFM topographies for Langmuir-Blodgett films of F8H9OH exhibit the formation of monodispersed surface micelles. In the two-component system, the incorporation of F8H9OH induces condensation (or solidification) of DPPC monolayers. The excess Gibbs free energy and interaction parameter (or energy) of the two components were calculated from the isotherm data. Both the phase transition pressure for the coexistence of ordered and disordered phases and collapse pressure of monolayers vary with the mole fraction of F8H9OH, indicating binary miscibility between F8H9OH and DPPC within a monolayer state. The miscibility is also confirmed visually by in situ and ex situ microscopy at micro- and nanometer scales.

Monolayer Compression Induces Fluidization in Binary System of Partially Fluorinated Alcohol (F4H11OH) with DPPC

A two-component Langmuir monolayer consisting of (perfluorobutyl)undecanol (F4H11OH) and dipalmitoylphosphatidylcholine (DPPC), a major component of pulmonary surfactants in mammals, has been investigated at the air-water interface. The binary monolayer has been systematically examined from both thermodynamic and morphological perspectives. The excess Gibbs free energy of mixing has been calculated from surface pressure (π)-molecular area (A) isotherms, and the results indicate that the miscibility of the two-component system shows a maximum in thermodynamical stability when the mole fraction (X(F4H11OH)) is 0.3. Results from a two-dimensional phase diagram (π vs. X(F4H11OH)) are consistent with these findings and depict the degree of miscibility resulting from the variation in the transition and collapse pressures relative to the concentration of X(F4H11OH). The miscibility is also supported by in situ Brewster angle microscopy and fluorescence microscopy, as well as ex situ atomic force microscopy for the system after transfer onto a mica substrate. Aside from temperature, a known driving force for the fluidization of DPPC monolayers is a change in surface composition caused by the addition of additive molecules. In the present study, however, the fluidization is driven by increasing surface pressures even at constant X(F4H11OH). Such a fluidization is a fascinating property when looked at in context of its potential implications for pulmonary replacement therapy, and hence, this study provides a fundamental insight into designing fluorinated materials for biomedical use.

Self-Assembly of Linactants: Micelles and Lyotropic Liquid Crystals in Two Dimensions

We report observations of phenomena within two-component Langmuir monolayers that are analogous to surfactant self-assembly in 3D solutions. A partially fluorinated fatty phosphonic acid played the role of 2D surfactant (linactant), and a perfluorinated fatty acid acted as the 2D solvent. Langmuir-Blodgett monolayers were prepared from mixtures of these compounds and examined using atomic force microscopy. Above a critical linactant mole fraction of approximately 0.013, distinctive monodisperse structural features were observed with a characteristic diameter of approximately 30 nm and a relative height of 1.4 nm. As the linactant concentration was further increased, the number density of these features increased linearly with concentration, whereas the size remained approximately the same. A quantitative analysis of these observations suggested that the features corresponded to self-limiting clusters composed of approximately 2000 linactant molecules and that the dispersed clusters represented a 2D micellar phase. Above a linactant mole fraction of 0.63, the clusters organized into a local hexagonal structure with short-range positional order indicative of a 2D "lyotropic" liquid crystalline phase; the correlation length increased systematically with increasing linactant concentration.

Effects of Fullerenes on Phospholipid Membranes: A Langmuir Monolayer Study

We investigate two-component Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC)/C(60) by recording surface pressure/area (pi/A) and surface potential/area (DeltaV/A) isotherms and by direct Brewster angle microscopy (BAM) imaging. Atomic force microscopy (AFM) is employed to study morphologies of the mixed monolayers transferred to a solid substrate by the Langmuir-Blodgett technique. C(60) is shown to have little influence on isotherms of the DPPC/C(60) monolayers even at a molar fraction as high as X(C60)=0.3. The elastic modulus (Cs(-1) versus pi curves of the DPPC/C(60) monolayers almost overlay each other, as well as that of pure DPPC, that is, the elasticities of pure DPPC monolayers and DPPC/C(60) monolayers are remarkably similar. AFM studies reveal that fullerene flocs form at low surface pressures (pi<or=15 mN m(-1)), are gradually disaggregated and dispersed in the DPPC monolayer with increasing surface pressure up to 35 mN m(-1), and are then progressively squeezed out to form protruded islands as the surface pressure increases up to 65 mN m(-1). Our work provides experimental support to the computational result that C(60) can dissolve in lipid bilayers without significantly compromising their mechanical properties, a finding which has important implications for the toxicity and development of drug vehicles from fullerene materials.

Two-Component Langmuir Monolayers of Single-Chain Partially Fluorinated Amphiphiles with Dipalmitoylphosphatidylcholine (DPPC)

The surface pressure (pi)-area (A) and surface potential (DeltaV)-A isotherms were measured for two-component monolayers made of dipalmitoylphosphatidylcholine (DPPC)/single-chain (perfluorooctyl)pentanol (F8C5OH) and DPPC/single-chain (perfluorooctyl)pentylphosphocholine (F8C5PC) on a substrate solution of 0.15 M NaCl at 293.2 K as a function of the composition of the two components. The Langmuir method and the ionizing electrode method were used. The data for these systems were analyzed using an additivity rule. Assuming a regular surface mixture, the Joos equation, which allows description of the collapse pressure of a monolayer made of two miscible components, was used to establish the miscibility within the monolayer. An interaction parameter and an interaction energy were calculated. The two-component DPPC/F8C5OH and DPPC/F8C5PC monolayers were miscible. Furthermore, the mean molecular area, surface potential, and phase diagrams enabled us to determine the molecular orientation of DPPC/F8C5OH and DPPC/F8C5PC in the monolayer. Two types of phase diagrams were obtained and classified into the positive azeotropic and negative azeotropic types. Fluorescence microscopy (FM) and Brewster angle microscopy (BAM) for the DPPC/F8C5OH and DPPC/F8C5PC systems show that both systems can dissolve the ordered micrometer-size solid DPPC domains. However, morphological analyses using atomic force microscopy (AFM) suggest partial miscibility or phase separation for DPPC and the partially fluorinated compounds on the nanometer scale. In particular, triskelion-shaped domains were evidenced for F8C5OH. These results indicate that the partially fluorinated amphiphiles investigated here fluidize the DPPC monolayer upon lateral compression and that these chemicals may be useful to develop their innovative applications in the biomedical field.

Mode of interaction of two fluorinated-hydrogenated hybrid amphiphiles with dipalmitoylphosphatidylcholine (DPPC) at the air–water interface

Two-component Langmuir monolayers formed on 0.02 M Tris buffer solution (pH 7.4) with 0.13 M NaCl at 298.2 K were investigated for two different fluorinated-hydrogenated hybrid amphiphiles (F6PH5PPhNa and F8PH5PPhNa or F6 and F8, respectively) with DPPC. Surface pressure ( π), surface potential (Δ V) and dipole moment ( μ ⊥) as a function of molecular surface area ( A) were measured by employing the Whilhelmy method and an ionizing electrode method. From the A– and Δ V– X F6 (or X F8) curves, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined as a function of surface mole fraction ( X F n ) at discrete surface pressures. Then, the behavior of occupied surface areas and surface potentials of the respective components could be made clearer. Compressibility ( C s), elasticity ( C s − 1 ) , and excess Gibbs energy (Δ G (ex)) as a function of X F6 (or X F8) were estimated at definite pressures. These physico-chemical parameters were found to reflect the mechanical strength of monolayer films formed. The regular solution theory being applied to Δ G (ex), the activity coefficients ( f) as well as the interaction parameter ( I p) between DPPC and two hybrid amphiphiles in the binary monolayers were evaluated. I p values thus obtained indicated that F8 molecules interact more strongly with DPPC molecules than F6. Moreover, in order to better understand the morphological monolayer state, Langmuir–Blodgett (LB) films made from DPPC and fluorinated-hydrogenated hybrid amphiphiles were examined by atomic force microscopy (AFM). The miscibility of the two components in the monolayer state is evidenced by these thermodynamic quantities and AFM observations. Furthermore, AFM images demonstrated that F8 could more effectively disperse the ordered domains of DPPC than F6.

Sum-Frequency Spectroscopy Analysis of Two-Component Langmuir Monolayers and the Associated Interfacial Water Structure

Sum-frequency spectroscopy (SFS) in the CH and OH stretching regions was employed to obtain structural information about Langmuir monolayers on the H(2)O subphase of the model lipid dioctadecyldimethylammonium bromide (DOMA) and of the neutral surfactant methyl stearate (SME) and their mixtures and about the interfacial water structure underneath the films. These results were compared with the sum-frequency spectra of the interface between Langmuir monolayers of stearic acid and stearic acid-DOMA monolayers and water to prove that the uncompensated headgroup charge of DOMA at the interface is the reason for structuring of interfacial water close to the studied monomolecular films. Sum-frequency spectra on D(2)O subphase were also studied to account for the interference between the CH and OH spectral signatures because of the coherent nature of the SFS signals. Interfacial water structure proved to be a determining factor in the behavior of the mixed lipid monolayers. A mixing induced amplification in the surface potential DeltaV observed in our previous work was explained with total increase of the dipole moment for the mixed films, bigger than the arithmetic average for DOMA and SME monolayers alone. The increase is due to the better packing of the molecules in the mixed films and to the decrease in the interfacial water dipole moment arising from a more disordered water structure underneath the mixed monolayers.

Cerebroside Langmuir monolayers originated from the echinoderms: II. Binary systems of cerebrosides and steroids

Two-component Langmuir monolayers formed on a subphase of 0.5 M sodium chloride solution were investigated for two different cerebrosides (LMC-1 and LMC-2) with steroids of cholesterol (Ch) and cholesteryl sodium sulfate (Ch-S); i.e. LMC-1/Ch, LMC-1/Ch-S, LMC-2/Ch, and LMC-2/Ch-S were examined in terms of surface pressure ( π), the surface potential (Δ V) and the dipole moment ( μ ⊥) as a function of surface area ( A) by employing the Langmuir method, the ionizing electrode method, and the fluorescence microscopy. Surface potentials (Δ V) of steroids were analyzed using the three-layer model proposed by Demchak and Fort [R.J. Demchak, T. Fort Jr., J. Colloid Interface Sci. 46 (1974) 191–202]. The miscibility of cerebrosides and steroids in the insoluble monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the steroid molar fraction ( X steroid) based upon the additivity rule. From the A– X steroid and Δ V m– X steroid plots, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined at the different surface pressures. The PMA and APSP with the mole fraction were discussed for the miscible system. Judging from the two-dimensional phase diagrams, they can be classified into two types. The first is a completely immiscible type; the combination of cerebrosides with cholesterol. The second is a negative azeotropic type, where cerebrosides and cholesteryl sodium sulfate are completely miscible both in the expanded state and in the condensed state. In addition, a regular surface mixture (the Joos equation for the analysis of the collapse pressure of two-component monolayers) allowed calculation of the interaction parameter ( ξ) and the interaction energy (−Δ ɛ) between the cerebrosides and Ch-S. The miscibility of cerebroside and steroid components in the monolayer state was also supported by fluorescence microscopy.

Properties of two-component Langmuir monolayer of single chain perfluorinated carboxylic acids with dipalmitoylphosphatidylcholine (DPPC)

The surface pressure ( π)– and the surface potential (Δ V)–area ( A) isotherms were obtained for two-component monolayers of four different perfluorocarboxylic acids (FC ns; perfluorododecanoic acid: FC12, perfluorotetradecanoic acid: FC14, perfluorohexadecanoic acid: FC16, perfluorooctadecanoic acid: FC18) with dipalmitoylphosphatidylcholine (DPPC) on substrate solution of 0.15 M NaCl (pH 2.0) at 298.2 K as a function of compositions in the mixtures by employing the Wilhelmy method, the ionizing electrode method, the fluorescence microscopy, and the atomic force microscopy. The data for the two-component monolayers on these systems were analyzed in terms of the additivity rule. Assuming a regular surface mixture, the Joos equation which allows one to describe the collapse pressure of a two-component monolayer with miscible components was used to declare the miscibility of the monolayer state, and an interaction parameter and an interaction energy were calculated. The new finding was that FC ns and DPPC are miscible or immiscible depending on chain length increment of fluorocarbon part. That is, FC12/DPPC monolayer was perfectly miscible, and FC14/DPPC, and FC16/DPPC (0 ≤ X FC16 ≤ 0.3) monolayers were partially miscible. While FC16/DPPC (0.3 < X FC16 < 1) and FC18/DPPC systems are immiscible in the monolayer state. Furthermore, the mean molecular area, the surface dipole moment, and the phase diagrams enabled us to estimate the molecular orientation of four different perfluorocarboxylic acids/DPPC in the two-component monolayer state. One type of phase diagrams was obtained and classified into the positive azeotropic type. The miscibility of FC ns and DPPC in the monolayer was also supported by fluorescence microscopy and atomic force microscopy. FC12/DPPC, FC14/DPPC and FC16/DPPC (0 ≤ X FC16 ≤ 0.3) two-component monolayers on 0.15 M NaCl (pH 2) showed that FC12, FC14 and FC16 (0 ≤ X FC16 ≤ 0.3) can dissolve or partially dissolve the ordered solid DPPC domains formed upon compression. This indicates that these fluorinated amphiphiles soften or harden the lipid depending on their chain length.

Nonequilibrium orientational patterns in two-component Langmuir monolayers.

A model of a phase-separating two-component Langmuir monolayer in the presence of a photoinduced reaction interconverting two components is formulated. An interplay between phase separation, orientational ordering, and reaction is found to lead to a variety of nonequilibrium self-organized patterns, both stationary and traveling. Examples of the patterns, observed in numerical simulations, include flowing droplets, traveling stripes, wave sources, and vortex defects.