Surface Pressure Isotherms Research Articles

Precise and instrumental measurement of thermodynamics and kinetics of froth flotation by langmuir-blodgett technique

Froth flotation is most common means in mineral separation, and the in-situ measurement of flotation is of significance. However there were no instrumental means of measuring kinetics and thermodynamics for this process up to date. Herein, for the first time a facile method was developed by using Langmuir-Blodgett (LB) technique to get precise recording of kinetics and thermodynamics for adsorption process of Langmuir hybrid layer at the air/water interface. The formation of hybrid Langmuir monolayer was assumed to simulate the adsorption of mineral particles by frother/collector bubbles in the micro-flotation although this was a semi-static adsorption process. The kinetic parameters including time constant (τ1/e, 32.0∼139.0 s) and adsorption rate constant (k, 0.0315∼0.00718 s−1) were precisely determined according to surface pressure vs. time (π-t) plots of Langmuir monolayer which consisted of floated minerals particles and collector molecules. The thermodynamic data such as partition coefficient (Kd, 0.221−0.339), Gibbs free energy of adsorption ΔG (2.68∼3.74 kJ mol−1), and minimum dosages of collector molecules (potassium butylxanthate) were derived from the surface pressure vs. molecular area (π-A) isotherms. Taking the major mineral of pyrite with minor of dolomite and quartz as a froth flotation model, the recovery yield of concentrate pyrite obtained from LB technique was found in good agreement with the common tests used micro-flotation, suggesting the consistency of the new-developed LB method in predicting kinetics and thermodynamics for froth flotation.

Studies of Langmuir and Langmuir-Schaefer Films of Poly(3-Hexylthiophene) and Poly(Vinylidene Fluoride).

The synergistic use of blends of regioregular poly(3-hexylthiophene) (P3HT) and poly(vinylidene fluoride) (PVDF) or poly((vinylidene fluoride)-block-(methyl methacrylate)) (PVDF-PMMA) to form Langmuir and Langmuir-Schaefer (LS) films is reported. P3HT has wide applications in sensor devices because of its properties such as conductivity, luminescence, and chromism; however, the stiffness of the films and the difficulty in organizing the molecules may pose a problem in these applications. In this context, polymers based on PVDF can be used in the formation of thin P3HT films and present an alternative to improve the organization of P3HT molecules. In addition, PVDF acts as a plasticizer, making the film less rigid. The films were obtained from the blends of P3HT/PVDF and P3HT/PVDF-PMMA in a solution containing chloroform and DMAc (N,N-dimethylacetamide). Surface pressure isotherms, in situ ultraviolet-visible (UV-vis) spectroscopy, polarization-modulation infrared reflection-absorption spectroscopy, and Brewster angle microscopy techniques were used to analyze Langmuir films. The surface morphology of LS films was characterized by atomic force microscopy and UV-vis spectroscopy, and their degradation was analyzed by UV-vis spectroscopy after exposure to natural light under atmospheric conditions. The Langmuir films containing PVDF indicate a direct formation of the ferroelectric β phase, with dipoles parallel to the water surface. The Langmuir films formed by P3HT presented dipoles of side chains parallel and aromatic groups perpendicular to the water surface. P3HT and PVDF or PVDF-PMMA films show high molecular organization compared with pure P3HT films. The results suggest that these films could be used to improve the properties of P3HT in several device applications, such as in optical and electrical sensors.

Chain Cleavage of Bioinspired Bacterial Membranes Photoinduced by Eosin Decyl Ester.

Photodynamic therapy (PDT) is promising for bacterial inactivation since cellular internalization of photosensitizers (PS) is not crucial for the treatment effectiveness. Photoinduced damage in the lipid envelope may already induce microbial inactivation, which requires PS capable of easily penetrating into the membrane. Herein, we report on the insertion of the PS eosin decyl ester (EosDec) into Langmuir films of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG), and cardiolipin (CLP) used as mimetic systems of bacterial membranes. Surface pressure isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) indicated that the hydrophobic nature of EosDec favored deeper penetration in all the phospholipid monolayers. The incorporation of EosDec led to monolayer expansion, especially in the anionic DOPG and CLP owing to repulsive electrostatic interactions, and induced disorder in the lipid chains. Light irradiation of DOPE, DOPG, and CLP monolayers containing EosDec increased the rate of material loss to the subphase, which is attributed to cleavage of lipid chains triggered by contact-dependent reactions between excited states of EosDec and lipid unsaturations. The latter is key for membrane permeabilization and efficiency in microbial inactivation.

Antioxidant in a model biomembrane – astaxanthin and its esters mixed with DPPC in Langmuir films

Amphiphilic properties of astaxanthin molecule and its esters make it possible to include it in self-organized structures based on lipid membrane components. Astaxanthin and its mono- and diesters were isolated from the extract of the microalgae Haematococcus Pluvialis, purified by column chromatography, and identified by thin-layer chromatography. The absence of impurities in astaxanthin and its esters was confirmed by means of high performance liquid chromatography method with detection in the ultraviolet-visible region and mass spectrometric detection. The model systems of the cell membrane lipid bilayer — Langmuir films of mixtures of DPPC with astaxanthin and its mono- and diesters, were formed at the air-water interface and studied by a complex of methods. It was found that an increase in the amount of astaxanthin, as well as the addition of its esters to the Langmuir films of DPPC, leads to an increase of values of area per molecule at the surface pressure isotherm uprise and decrease of Langmuir film collapse pressure. The addition of astaxanthin mono- and diesters prevents the phase transition in the DPPC monolayer more strongly than unesterified astaxanthin.

Self-Propelled Motion of a Camphor Disk on a Nervonic Acid Molecular Layer and Its Dependence on Phase Transition.

We studied the self-propelled motion of a camphor disk placed on water developed with a nervonic acid molecular layer to investigate the dependence of types of motion on the properties of amphiphilic compounds. The surface pressure (Π) versus area (A) isotherm exhibited a transition point corresponding to a phase transition between the fluid (F) and fluid/condensed (F/C) phases of nervonic acid. The type of motion was determined by not only the surface pressure of the nervonic acid molecular layer but also the phase, either F or F/C. When the temperature of water was varied through the phase transition temperature Tp40 (∼23 °C), with an area of 40 Å2 per nervonic acid molecule in the molecular layer, no motion and oscillatory motion were observed reversibly above and below Tp40, respectively. Our results suggest that the features of camphor motion depend on not only the surface pressure but also the nature of the phase in the nervonic acid molecular layer.

The impact of blue light in monolayers representing tumorigenic and nontumorigenic cell membranes containing epigallocatechin-3-gallate

Natural products such as epigallocatechin-3-gallate (EGCG) have been suggested for complementary treatments of cancer, since they lower toxic side effects of anticancer drugs, and possess anti-inflammatory and antioxidant properties that inhibit carcinogenesis. Their effects on cancer cells depend on interactions with the membrane, which is the motivation to investigate Langmuir monolayers as simplified membrane models. In this study, EGCG was incorporated in zwitterionic dipalmitoyl phosphatidyl choline (DPPC) and anionic dipalmitoyl phosphatidyl serine (DPPS) Langmuir monolayers to simulate healthy and cancer cells membranes, respectively. EGCG induces condensation in surface pressure isotherms for both DPPC and DPPS monolayers, interacting mainly via electrostatic forces and hydrogen bonding with the choline and phosphate groups of the phospholipids, according to data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Both monolayers become more compressible upon interaction with EGCG, which may be correlated to the synergy between EGCG and anticancer drugs reported in the literature. The interaction with EGCG is stronger for DPPC, leading to stronger morphological changes in Brewster angle microscopy (BAM) images and higher degree of condensation in the surface pressure isotherms. The changes induced by blue irradiation on DPPC and DPPS monolayers were largely precluded when EGCG was incorporated, thus confirming its antioxidant capacity for both types of membrane.

Correlating mono- and bilayers of lipids to investigate the pronounced effects of steroid hormone 17α-ethynylestradiol on membrane models of DPPC/cholesterol

Risks to human health have been reported owing to prolonged exposure to hormones, whose action depends on their molecular-level interaction with cell membranes. In this study, we investigate the interaction of the synthetic hormone 17 α-ethynylestradiol (EE2) in two different membrane models, Langmuir monolayers and giant unilamellar vesicles (GUVs) made with a binary mixture of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and cholesterol (Chol) in order to mimic the plasma membrane of mammalian cells. EE2 was found to expand the Langmuir monolayers, with shifts to larger areas per molecule in the surface pressure isotherm. In all of these observations, stronger effects were noted for the DPPC/Chol monolayers with XChol = 0.3, which mimics the proportion of phospholipid/sterol in the plasma membrane. At high surface pressures, EE2 is believed to weaken the attractive interactions between DPPC and Chol, in addition to affecting the ordering of the lipid chains as indicated in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. In GUVs obtained with XChol = 0.3 mixtures, EE2 induced a phase contrast loss as a result of increased permeability of the lipid bilayer. The results with Langmuir monolayers and GUV combined point to EE2 action on representative cell membranes, which can be correlated with physiological effects caused by indirect intake of EE2.

Isothermal measurements of a Langmuir monolayer of a non-polar fluorocarbon chain molecule

Traditionally Langmuir monolayers and lipids bilayers (including cell membranes) on water interfaces are made of amphiphilic molecules with both polar hydrophilic and non-polar hydrophobic parts. It has been discovered that non-polar fluorocarbon chain molecules without the polar hydrophilic part, F(CF2)20F, can also form Langmuir monolayers on water. Here we report the surface pressure vs. area isotherm measurements of a F(CF2)20F film on water, which show the film’s maximum compression modulus (greatest resistance to lateral compression) at about 30 Å2/molecule, independent of the compression speed, like the Langmuir monolayers of long chain saturated fatty acids do. The cross-section area of the fluorocarbon chain is 28.1 Å2 in 3-D crystalline F(CF2)20F. Our measurements confirm the formation of a Langmuir monolayer by F(CF2)20F, a non-polar fluorocarbon chain molecule. We observed a general trend that greater the lateral compression speed, lower the maximum compression modulus, lower the resistance to lateral compression. Nicholas Sheetz and Clayton Smith are grateful to financial support from the National Science Foundation through the SOARS Research Fellowship at Shepherd University.

Isothermal measurements of a Langmuir monolayer of a non-polar fluorocarbon chain molecule.

Traditionally Langmuir monolayers and lipids bilayers (including cell membranes) on water interfaces are made of amphiphilic molecules with both polar hydrophilic and non-polar hydrophobic parts. It has been discovered that non-polar fluorocarbon chain molecules without the polar hydrophilic part, F(CF2)20F, can also form Langmuir monolayers on water. Here we report the surface pressure vs. area isotherm measurements of a F(CF2)20F film on water, which show the film’s maximum compression modulus (greatest resistance to lateral compression) at about 30 Å2/molecule, independent of the compression speed, like the Langmuir monolayers of long chain saturated fatty acids do. The cross-section area of the fluorocarbon chain is 28.1 Å2 in 3-D crystalline F(CF2)20F. Our measurements confirm the formation of a Langmuir monolayer by F(CF2)20F, a non-polar fluorocarbon chain molecule. We observed a general trend that greater the lateral compression speed, lower the maximum compression modulus, lower the resistance to lateral compression.Nicholas Sheetz and Clayton Smith are grateful to financial support from the National Science Foundation through the SOARS Research Fellowship at Shepherd University.

Establishment of a Synthetic In Vitro Lung Surfactant Model for Particle Interaction Studies on a Langmuir Film Balance.

With the intention to provide a robust and economical model that can be used for predicting particle interactions with the pulmonary surfactant, this study was aimed to find an artificial surfactant model that perfectly mimics the properties of the natural pulmonary surfactant. A surfactant model should be reproducible, robust, and able to predict interactions between the pulmonary surfactant and exogenous influences from air and the aqueous site. We compared three synthetic models with the natural bovine surfactant Alveofact. The lung conditions were simulated by spreading the surfactants at the air/aqueous interface on a Langmuir trough with movable barriers. All three artificial surfactant models showed properties very similar to that of Alveofact. Visualization of the monolayers by atomic force microscopy revealed very similar structures with domain formation. The Tanaka lipid mixture has already shown good results in vitro and in vivo in previous studies. The 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) model has large conformations in the surface pressure isotherms and showed a biomimetic exclusion plateau, indicative of an effective lung surfactant formulation. Also, the equilibrium spreading pressure was similar. DPPC-1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-1'-rac-glycerol (POPG) had the greatest similarities with Alveofact in the hysteresis areas. The kinetic constants of the relaxation experiments during desorption showed that the PCPG model (at 30 mN/m) had almost identical diffusion and dissolution values as Alveofact. As a proof of concept, the interaction of the models with PLGA nanoparticles showed promising results in all experiments for all the three surfactant models. The results show that the choice of components in a model play a crucial role in obtaining reproducible results. The selected models can be used for further studies as synthetic in vitro lung models.

Crystallization of poly(ε-caprolactone) at the air-water interface studied by IRRAS and GI-WAXS

Poly (ε-caprolactone) (PCL) dissolved in chloroform was spread on the water surface of a Langmuir trough and after solvent evaporation, the surface pressure vs area (π-A) Langmuir isotherm was recorded. An extended plateau region indicates a 1st order phase transition related to PCL crystallization as also confirmed by Brewster angle microscopy (BAM). Infrared reflection absorption spectroscopy (IRRAS) and grazing incidence wide angle X-ray scattering (GI-WAXS) reveal details of the PCL crystallization process on a molecular level. The IRRAS and GI-WAXS experiments confirm that crystallization occurs at the plateau region of the π-A Langmuir isotherm. GI-WAXS also confirms that the polymer chains in the crystals are tilted by ≈ 21° with respect to the water surface normal direction. This value is consistent with IRRAS data at a maximum compression state of ≈ 2 Å2.

Collapse of Langmuir monolayer formed by the mixture of short- and long-tailed fatty acid molecules

Surface pressure versus molecular area (π-A) isotherms of stearic acid (SA), behenic acid (BA) and their mixtures are studied at high subphase pH (≈ 9.5) in presence of Ba2+ ions. It is found that the collapse pressure (πC) and dip pressure (πD) points of binary fatty acid monolayer varies depending on the relative amount of the two components and nearly follow the Langmuir growth model. Out-of-plane structures obtained from the X-ray reflectivity and atomic force microscopy analysis imply that SA shows multi-layered structure that gradually decreases with the decrease in SA proportion in the mixed film. The transition from constant pressure to constant area collapse is observed when the weightage of BA becomes ≥66% for the mixed film. The change in the collapse behaviour and collapsed structure is explained using the two-dimensional percolated networks formed by the tail-tail hydrophobic interactions of relatively more hydrophobic long-chained BA molecules.

Real-time monitoring of the effect of carbon nanoparticles on the surface behavior of DPPC/DPPG Langmuir monolayer

Air pollution has become increasingly serious. Fine particulate matter (PM2.5) is the most well-known air pollutant, which leads to some common respiratory diseases when inhaled into the lungs to certain concentration. However, there is a lack of research on the process of dynamically monitoring the real-time effect of nanoparticles on the pulmonary surfactant monolayer. In this study, the DPPC/DPPG monolayer is prepared by the Langmuir method to simulate the lung surfactant monolayer during respiration and the carbon nanoparticles are introduced to the monolayer under different surface pressures to simulate the real dynamic process of inhaling nanoparticles during breathing. The effect of carbon nanoparticles on the surface behavior of DPPC/DPPG monolayer in real-time was examined in details by a combination of surface pressure (π)-area (A) isotherms, compressibility modulus (Cs-1)-surface pressure (π) isotherms and the Brewster angle microscopy (BAM). The results have shown that the introduction of carbon nanoparticles under different surface pressures affects the properties of lipid monolayers. The added carbon nanoparticles under lower surface pressure are easy to penetrate the lipid molecules to inhibit monolayer phase transition. When the carbon nanoparticles are introduced to the monolayer under higher surface pressure, they tend to self-aggregate to reduce the monolayer stability rather than interact with lipid tail chains. This work not only confirms the exotic hydrophobic carbon nanoparticles retain in the DPPC/DPPG monolayer irreversibly and affect the surface behavior of monolayer during respiration, but also opens a new idea for real-time monitoring of the effects of PM2.5 on lung health.

Impact of Engineered Carbon Nanodiamonds on the Collapse Mechanism of Model Lung Surfactant Monolayers at the Air-Water Interface.

Understanding interactions between inhaled nanoparticles and lung surfactants (LS) present at the air-water interface in the lung, is critical to assessing the toxicity of these nanoparticles. Specifically, in this work, we assess the impact of engineered carbon nanoparticles (ECN) on the ability of healthy LS to undergo reversible collapse, which is essential for proper functioning of LS. Using a Langmuir trough, multiple compression-expansion cycles are performed to assess changes in the surface pressure vs. area isotherms with time and continuous cyclic compression-expansion. Further, theoretical analysis of the isotherms is used to calculate the ability of these lipid systems to retain material during monolayer collapse, due to interactions with ECNs. These results are complemented with fluorescence images of alterations in collapse mechanisms in these monolayer films. Four different model phospholipid systems, that mimic the major compositions of LS, are used in this study. Together, our results show that the ECN does not impact the mechanism of collapse. However, the ability to retain material at the interface during monolayer collapse, as well as re-incorporation of material after a compression-expansion cycle is altered to varying extent by ECNs and depends on the composition of the lipid mixtures.

Thermodynamic and Morphological Properties of Trastuzumab Regulated by the Lipid Composition of Cell Membrane Models at the Air-Water Interface

Trastuzumab (Tmab) is an antibody with anti-cancer properties, whose action occurs when the tumor is associated to the overexpression of the human epidermal growth factor receptor. This drug binds to the receptor, blocking downstream signaling pathways, which controls the cancer progression. Tmab also interacts with glycosaminoglycans and proteoglycans of the cell surface and extracellular matrix so that this interaction helps control cellular events in tumorigenic endothelial cells. In this sense, it is interesting, to study the action of this drug in cellular membrane models to understand its action in cellular membranes and in other lipid surfaces with pharmaceutical interest. In this work, Tmab was incorporated in lipid monolayers at the air-water interface and their thermodynamic, morphological and structural effects were investigated with tensiometry, Brewster angle microscopy (BAM) and polarization-modulation reflection-absorption infrared spectroscopy (PM-IRRAS), respectively. For that, we employed the phospholipids dipalmitoylphosphatidylcholine (DPPC), and dipalmitoylphosphoethanolamine (DPPE), and their mixtures with cholesterol. Tmab expanded all lipid films and affected the compressional and structural properties as observed by surface pressure isotherms, in-plane elasticity, and PM-IRRAS, respectively. BAM showed distinctive morphological patterns for the monolayers and infrared spectroscopy showed an increased number of gauche conformers related to the CH2 stretching mode, indicating film molecular disorder. Also, the antibody kept the beta-sheet structure of the polypeptide backbone adsorbed at the lipid monolayers though the secondary conformation changed according to the monolayer composition. The results then suggest that the membrane lipid profile affects the adsorption of Tmab at lipid monolayers, which can be associated to the fact that antibody-receptor interactions at the lipid membrane environment can possibly be tuned by changing the lipid composition at the receptor vicinity.

Role of Toluidine Blue-O Binding Mechanism for Photooxidation in Bioinspired Bacterial Membranes.

The alarming increase in bacterial resistance to antibiotics has demanded new strategies for microbial inactivation, which include photodynamic therapy whose activity relies on the photoreaction damage to the microorganism membrane. Herein, the binding mechanisms of the photosensitizer toluidine blue-O (TBO) on simplified models of bacterial membrane with Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) were correlated to the effects of the photoinduced lipid oxidation. Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were also used as a reference of mammalian membranes. The surface pressure isotherms combined with polarization-modulated infrared reflection absorption spectroscopy revealed that TBO expands DOPC, DOPE, and DOPG monolayers owing to electrostatic interactions with the negatively charged groups in the phospholipids, with a stronger adsorption on DOPG, which has a net surface charge. Light irradiation made the TBO-containing DOPC and DOPE monolayers less unstable as a result of the singlet oxygen (1O2) reaction with the chain unsaturation and hydroperoxide formation. In contrast, the decreased stability of the irradiated TBO-containing DOPG monolayer suggests the cleavage of carbon chains. The anionic nature of DOPG allowed a deeper penetration of TBO into the chain region, favoring contact-dependent reactions between the excited triplet state of TBO and lipid unsaturations or/and hydroperoxide groups, which is the key for the cleavage reactions and further membrane permeabilization.

Pyrene-based amphiphile regulated C60 aggregation in monolayers and Langmuir–Blodgett films

The advantage of using Langmuir–Blodgett (LB) method in assembling thin films is mainly the effective controlling the orientation of the molecules and deposition of mono- and multilayer films with an organized and ordered layer structure. In this paper, we have studied the interactions between C60 and a kind of pyrene-based amphiphile, N, N’-bis(octadecyl)-L-(1-pyrenebutyric acid)-glutamic diamide (abbreviated as LPG) in monolayers and in LB films by surface-pressure isotherms, CD spectroscopy, fluorescence spectroscopy, and atomic force microscopy (AFM). It has been found that the existing state of C60 was closely related to the mixing ratio of C60 to LPG. Miscibility and AFM image investigation revealed that C60 molecules were embedded into the LPG monolayer as monomers when the mole fraction of C60 was below 0.33 (molar ration of LPG to C60 is 2:1). Meanwhile, the inserting of C60 disturbed the packing of LPG. As a result, the magnitude of supramolecular chirality, which was derived from the self-assembly of LPG, decreased with the addition of C60. When more C60 molecules were mixed with LPG, they have to form three dimensional aggregates due to high adhesive energy. The donor-acceptor interaction between pyrene moieties and C60 was supposed to be the driving force to disperse C60 in LPG monolayer. A reasonable mechanism of the transition from C60 monomers to aggregates in LPG monolayer was also proposed.

Lung surfactant monolayer – A good natural barrier against dibenzo-p-dioxins

The present study deals with interaction of two air pollutants: dibenzodioxin, DD, and its’ monochlorinated derivative, 2-chlorodibenzodioxin, 2CLDD, with models of the lung surfactant (LS) system. A monolayer composed of DPPC and POPC in 1:1 molar ratio was used as a model of LS. One component monolayers of DPPC and POPC were also examined, to model the interiors of LC and LE domains in LS, respectively. Molecular dynamics simulations and measurements of surface pressure isotherms, as well as polarization modulation-infrared reflection-absorption spectra were employed to study the influence of dioxins on the monolayers. We demonstrate, that both dioxins adsorb and accumulate in the hydrophobic parts of all three monolayers. DD molecules prefer flat orientation on the surface at large areas. Upon compression, they lift and orient perpendicularly to the monolayer. Flat orientation of DD molecules leads to their large surface area. In consequence they preferentially locate in vicinity of unsaturated chains of POPC – they are small enough to fill void spaces created by kinks in unsaturated chains. 2CLDD orient along monolayer normal already at the largest areas and preference for POPC was not observed for them. In laterally relaxed states, a condensing effect, connected with reduction of surface area available to the lipids was observed for both dioxins. In the case of 2CLDD, additional locally ordering influence of dioxin molecules was detected. In compressed states, the presence of dioxin molecules hinders alignment and uniform ordering of lipid chains.

Investigation of Drug for Pulmonary Administration-Model Pulmonary Surfactant Monolayer Interactions Using Langmuir-Blodgett Monolayer and Molecular Dynamics Simulation: A Case Study of Ketoprofen.

Pulmonary administration is widely used for the treatment of lung diseases. The interaction between drug molecules and pulmonary surfactants affects the efficacy of the drug directly. The location and distribution of drug molecules in a model pulmonary surfactant monolayer under different surface pressures can provide vivid information on the interaction between drug molecules and pulmonary surfactants during the pulmonary administration. Ketoprofen is a nonsteroidal anti-inflammatory drug for pulmonary administration. The effect of ketoprofen molecules on the lipid monolayer containing 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-glycerol (DPPG) is studied by surface pressure (π)-area (A) isotherms and compressibility modulus (Cs-1)-surface pressure (π) isotherms. The location and distribution of ketoprofen molecules in a lipid monolayer under different surface pressures are explored by surface tension, density profile, radial distribution function (RDF), and the potential of mean force (PMF) simulated by molecular dynamics (MD) simulation. The introduction of ketoprofen molecules affects the properties of DPPC/DPPG monolayers and the location and distribution of ketoprofen molecules in monolayers with various surface pressures. The existence of ketoprofen molecules hinders the formation of liquid-condensed (LC) films and decreases the compressibility of DPPC/DPPG monolayers. The location and distribution of ketoprofen molecules in the lipid monolayer are affected by cation-π interaction between the choline group of lipids and the benzene ring of ketoprofen, the steric hindrance of the lipid head groups, and the hydrophobicity of ketoprofen molecule itself, comprehensively. The contact state of lipid head group with water is determined by surface pressure, which affects the interaction between drug molecules and lipids and further dominates the location and distribution of ketoprofen in the lipid monolayer. This work confirms that ketoprofen molecules can affect the property and the inner structure of DPPC/DPPG monolayers during breathing. Furthermore, the results obtained using a mixed monolayer containing two major pulmonary surfactants DPPC/DPPG and ketoprofen molecules will be helpful for the in-depth understanding of the mechanism of inhaled administration therapy.

Influence of temperature on dynamic surface properties of spread DPPC monolayers in a broad range of surface pressures

This work is focused on the study of the dynamic surface properties of spread monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), which is the main component of the pulmonary surfactant (PS), in the region of high surface pressures and at different temperatures. The increase of temperature from 25 to 35 °C led to a decrease of surface elasticity in the high surface pressure range corresponding to physiological conditions inside alveoli during breathing. Furthermore, the obtained results evidenced that the relaxation processes in spread DPPC monolayer were accelerated with the increase of temperature, which resulted in two different effects. On one hand, it led to the increase of hysteresis of surface pressure isotherms, which was an important condition for maximizing air penetration into alveoli; whereas on the other hand, it prevented reaching extremely high surface pressure, which could result in a premature alveolar collapse.