The interaction between DNA and cationic lipid films at the air-water interface

The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air-aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the Pi-A isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded-liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson-Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer.     

Brewster angle microscopy of calcium oxalate monohydrate precipitation at phospholipid monolayer phase boundaries

The precipitation of calcium oxalate monohydrate (COM) at phospholipid monolayers confined to the air/water interface is observed in situ with the aid of Brewster angle microscopy. COM crystals appear as bright objects that are easily identified and quantified to assess the effects of different conditions on crystallization. Crystal precipitation was monitored at monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in liquid condensed (LC) and liquid expanded (LE) phases. Within the LC phase, higher pressures reduce the incidence of crystallization at the interface, implying that within this phase precipitation is enhanced by higher compressibility or fluidity of the monolayer. Precipitation at biphasic LC/LE and LE/gas (G) monolayers was also studied. COM appears preferentially at phase boundaries of the DPPC LC/LE and LE/G monolayers. However, when an LC/LE phase boundary is created by two different phospholipids that are phase segregated, such as DPPC and 1,2-dimyristoyl-sn-glycero-3-phosphocholine, crystal formation occurs away from the interface within the DPPC LC phase. It is suggested that COM growth at phase boundaries is preferred only when there is molecular exchange between the phases.     

The magnitude of condensation induced by cholesterol on the mixtures of sphingomyelin with phosphatidylcholines-Study on ternary and quaternary systems

The studies on the condensing and ordering effect of cholesterol by application of the Langmuir monolayer technique are usually performed on binary lipid/cholesterol systems. The results concerning a quantitative analysis of these effects in multicomponent monolayers are very limited. In this work the condensing and ordering effect of cholesterol in ternary (SM/DSPC/Chol and SM/DOPC/Chol) and quaternary (SM/DSPC/DOPC/Chol) films was investigated. It was evidenced that the systems containing saturated PC (both SM/DSPC and SM/DSPC/Chol) are always more condensed and chain-ordered than the systems containing unsaturated PC (SM/DOPC and SM/DSPC/DOPC and their mixtures with cholesterol). However, the magnitude of condensation provoked by cholesterol at higher surface pressures is stronger on the monolayers containing unsaturated PC. The addition of cholesterol into SM/PC films induces the increase of chain-ordering however, the effectiveness of cholesterol as an ordering agent is determined by the presence/absence of unsaturated phospholipid. The magnitude of the effect of cholesterol on the investigated mixed monolayer was analyzed in the context of the influence of sterol on lipid chains (ordering, straightening and reorientation of chains) as well as the reorientation of polar heads.     

RNA and DNA association to zwitterionic and charged monolayers at the air-liquid interface

The objective of this work is to establish under which conditions short RNA molecules (similar to miRNA) associate with zwitterionic phospholipids and how this differs from the association with cationic surfactants. We study how the base pairing (i.e., single stranded versus double stranded nucleic acids) and the length of the nucleic acid and the charge of the lipid/surfactant monolayer affect the association behavior. For this purpose, we study the adsorption of nucleic acids to monolayers composed of dipalmitoyl phosphatidylcholine (DPPC) or dioctadecyl-dimethyl-ammoniumbromide (DODAB) using the surface film balance, neutron reflectometry, and fluorescence microscopy. The monolayer studies with the surface film balance suggested that short single-stranded ssRNA associates with liquid expanded zwitterionic phospholipid monolayers, whereas less or no association is detected for double-stranded dsRNA and dsDNA. In order to quantify the interaction and to determine the location of the nucleic acid in the lipid/surfactant monolayer we performed neutron reflectometry measurements. It was shown that ssRNA adsorbs to and penetrates the liquid expanded monolayers, whereas there is no penetration of nucleic acids into the liquid condensed monolayer. No adsorption was detected for dsDNA to zwitterionic monolayers. On the basis of these results, we propose that the association is driven by the hydrophobic interactions between the exposed hydrophobic bases of the ssRNA and the hydrocarbon chains of the phospholipids. The addition of ssRNA also influences domain formation in the DPPC monolayer, leading to fractal-like interconnected domains. The experimental results are discussed in terms of the implication for biological processes and new leads for applications in medicine and biotechnology.     

Reorganization and caging of DPPC, DPPE, DPPG, and DPPS monolayers caused by dimethylsulfoxide observed using Brewster angle microscopy

The interaction between dimethylsulfoxide (DMSO) and phospholipid monolayers with different polar headgroups was studied using "in situ" Brewster angle microscopy (BAM) coupled to a Langmuir trough. For a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer, DMSO was shown to significantly impact the structure of the liquid expanded (LE) and gaseous phases. The domains reorganized to much larger domain structures. Domains in the liquid condensed (LC) phase were formed on the DMSO-containing subphase at the mean molecular area where only gaseous and LE phases were previously observed on the pure water subphase. These results clearly demonstrate the condensing and caging effect of DMSO molecules on the DPPC monolayer. Similar effects were found on dipalmitoyl phosphatidyl ethanolamine, glycerol, and serine phospholipids, indicating that the condensing and caging effect is not dependent upon the phospholipid headgroup structure. The DMSO-induced condensing and caging effect is the molecular mechanism that may account for the enhanced permeability of membranes upon exposure to DMSO.     

Langmuir balance investigation of superoxide dismutase interactions with mixed-lipid monolayers

Higher than theoretical encapsulation efficiencies in liposomes of the cytoplasmic protein, superoxide dismutase (SOD), were previously observed. The high encapsulation of SOD led to the consideration of lipid-protein interactions and the embedding of SOD in the lipid bilayer. Difficulty in other methods such as dynamic scanning calorimetry due to cholesterol obscuring the measurements brought about the interest for a modified Langmuir monolayer relaxation study. A novel method was devised to distinguish between different lipid compositions that formed either a favorable or an unfavorable environment for SOD. Normalized monolayer relaxations with SOD were compared between mixed-lipid compositions containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), and cholesterol (Chol). Lipid-monolayer relaxation with and without SOD in the subphase was plotted over 30 min to determine if the protein was altering the lipid-monolayer relaxation. The monolayer relaxation with SOD was normalized to the monolayer relaxation without SOD over the 30 min period. The results indicated that lipid length and mole percent of cholesterol were important parameters that must be adjusted in order to support a favorable environment for SOD interaction with the lipid. It was determined that hydrophobic interactions were dominant over electrostatic forces; thus, SOD was embedding into the lipid monolayer. Additionally, this study was correlated to a previous liposome study and proved that lipid-protein interactions were the reason for the higher encapsulation efficiencies. The significance of this method is that it (1) provides a connection between lipid-protein interactions observed in monolayers and bilayers and (2) establishes a simple and effective manner to test lipid compositions for lipid-protein interaction that will aid in optimization of liposome encapsulation efficiency.     

Memory effects on the interfacial characteristics of dioctadecyldimethylammonium bromide monolayers at the air-water interface

The structural and dynamic characteristics of dioctadecyldimethylammonium bromide (DODAB) monolayers on a pure water subphase were investigated by surface film balance, Brewster angle microscopy, and relaxation in area and surface pressure at constant surface pressure and area, respectively. The first compression-expansion cycle of the monolayer is not reversible and the second pi-A compression isotherm deviates to larger molecular areas relative to the first one. At a microscopic level this hysteresis may be assigned to an irreversible hydration of the ammonium groups of DODAB. The morphology and reflectivity of DODAB monolayers during compression and expansion on the monolayer depend on the monolayer history. Bright domains randomly dispersed were observed during compression before collapse. Surprisingly, this random distribution of domains changes into a fractal-like structure during the monolayer expansion in a narrow range of surface pressures. This morphology does not form when the monolayer is previously compressed above the collapse surface pressure. 2D foam-like structure is often observed when the film is expanded at maximum area. Relaxation phenomena in DODAB monolayers are attributed to monolayer reorganization and nucleation of liquid-condensed domains from the liquid-expanded phase. These time-dependent processes are irreversible.     

Effects of lipid chain unsaturation and headgroup type on molecular interactions between paclitaxel and phospholipid within model biomembrane

Molecular interactions between paclitaxel, an anticancer drug, and phospholipids of various chain unsaturations and headgroup types were investigated in the present study by Langmuir film balance and differential scanning calorimetry. Both the lipid monolayer at the air-water interface and the lipid bilayer vesicles (liposomes) were employed as model cell membranes. It was found that, regardless of the difference in molecular structure of the lipid chains and headgroup, the drug can form nonideal, miscible systems with the lipids at the air-water interface over a wide range of paclitaxel mole fractions. The interaction between paclitaxel and phospholipid within the monolayer was dependent on the molecular area of the lipids at the interface and can be explained by intermolecular forces or geometric accommodation. Paclitaxel is more likely to form thermodynamically stable systems with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1,2-dielaidoyl-sn-glycero-3-phosphocholine (DEPC) than with 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). Investigation of the drug penetration into the lipid monolayer showed that DPPC and DEPC have higher incorporation abilities for the drug than DPPE and DSPC. A similar trend was also evidenced by DSC investigation with liposomes. While little change of DSC profiles was observed for the DPPE/paclitaxel and DSPC/paclitaxel liposomes, paclitaxel caused noticeable changes in the thermographs of DPPC and DEPC liposomes. Paclitaxel was found to cause broadening of the main phase transition without significant change in the peak melting temperature of the DPPC bilayers, which demonstrates that paclitaxel was localized in the outer hydrophobic cooperative zone of the bilayer, i.e., in the region of the C1-C8 carbon atoms of the acyl chain or binding at the polar headgroup site of the lipids. However, it may penetrate into the deeper hydrophobic zone of the DEPC bilayers. These findings provide useful information for liposomal formulation of anticancer drugs as well as for understanding drug-cell membrane interactions.     

Sensitivity of cationic surfactant templates to specific anions in liquid interface crystallization

We investigated the specific effects of potassium salts of various anions upon the interfacially templated crystal nucleation of K(2)SO(4). Previously, we have shown that the presence of several salts at low concentrations could induce changes in important crystallization characteristics templated by 1-octadecylamine at the liquid-liquid interface, and that these changes depended greatly on the specific identity of the salt. In this work we extend our surfactant monolayers to include dimethyldioctadecylammonium bromide (DODAB) and hexadecyltrimethylammonium bromide (CTAB). Addition of 10 mM of various potassium salts results in a diminution in efficiency of the templating capability of CTAB monolayer, as evidenced by higher C(onset) values and polycrystalline habit. The ability of the anions to perturb these values varied in a manner consistent with a Hofmeister series. However, DODAB maintained its templating effectiveness regardless of the nature of the salt or concentration. DODAB and CTAB are likely to be undergoing different reordering effects in the monolayer upon binding with chaotropic anions: a combined reduction in surface charge with different monolayer ordering results in a differing template ability. These studies have provided significant insights into the understanding of the interaction of ordered surfactant arrays with salts, and provide exciting possibilities for crystal engineering and materials design.     

Halofantrine-phospholipid interactions: monolayer studies.

The antimalarial agent halofantrine penetrates dipalmitolylphosphatidylcholine (DPPC) monolayers resulting in an increase in surface pressure and an expansion in area occupied by the lipid components of the monolayer. This phenomenon is observed at concentrations (0.05-0.2 microm) of halofantrine that have no surface activity. Penetration increases with drug concentration and is greatest at low initial surface pressures of the monolayer. A critical surface pressure of the DPPC monolayer has been determined from constant area and constant pressure conditions. The magnitude of these values support the hypothesis that halofantrine readily penetrates the DPPC monolayers. The presence of cholesterol in the DPPC monolayer hampers penetration and a lower critical surface pressure is obtained under such conditions. Even then, a slower rate of penetration is observed only in monolayers maintained at high initial surface pressures (10, 15 mN/m), corresponding to the liquid condensed phase of the monolayer, and not at low surface pressures (2.5, 5.0 mN/m). These results help to give a better understanding of the dynamics of the halofantrine-phospholipid interaction as well as the pharmacodynamic character of the drug.     

磷脂单分子膜普适状态方程研究

从现有的磷脂单分子膜状态方程入手, 以磷脂临界相变面积(A_c)和相变温度(T_c)为参比, 引入对比面积(A_r), 对比温度(T_r), 并通过分析磷脂分子间作用力和底液分子与磷脂分子间作用力的影响, 提出了第三参数——相对铺展因子的概念, 导出了磷脂单分子膜普适状态方程. 运用1,2-二豆蔻酰基-sn-丙三基-3-磷脂酸, 1,2-二豆蔻酰基-sn-丙三基-3-磷脂酰胆碱, 1,2-二棕榈酰基-sn-丙三基-3-磷脂酰胆碱等磷脂单分子膜的实验数据进行一致性校验的结果表明, 该模型在扩展膜(LE)直至凝聚膜(LC)的整个区域均能较好地描述磷脂单分子膜的π-A曲线. 所获得的各磷脂的相对铺展因子绝对值直接表明了该物质的成膜特性.     

Combined scanning electrochemical microscopy–Langmuir trough technique for investigating phase transfer kinetics across liquid/liquid interfaces modified by a molecular monolayer

The first combination of scanning electrochemical microscopy (SECM) with a Langmuir trough for liquid/liquid interfaces is described. The technique has been examined and demonstrated through investigations of the effect of monolayers of l-α-phosphatidylcholine, distearoyl (DSPC) on the kinetics of oxygen transfer from decane to water. The stability of monolayers, formed in this way, on the timescale of SECM measurements has been identified as a function of compression speed and subphase composition. Monolayers were stable over a wide range of pressures and molecular areas, but at high compression a decrease in surface pressure with time was observed. This effect was attributed to desorption of the lipid from the interface. In this situation, it was possible to perform SECM measurements (tip-interface approach curves) rapidly under surface pressure control, without causing significant disturbance to the monolayer. DSPC had no detectable effect on the oxygen transfer kinetics when the monolayer was in the liquid-expanded phase, but in the liquid-condensed phase a significant decrease in the rate of oxygen transfer was observed.     

Molecular interactions of cord factor with dipalmitoylphosphatidylcholine monolayers: implications for lung surfactant dysfunction in pulmonary tuberculosis

Molecular interactions between mycobacterial cell wall lipid, cord factor (CF) and the abundant surfactant lipid, dipalmitoylphosphatidylcholine (DPPC) were investigated using Langmuir monolayers at physiological temperatures (37 degrees C). Surface topography of the films was visualized by atomic force microscopy (AFM). Thermodynamic behavior of the mixed monolayers was evaluated by investigating the molecular area excess, excess Gibbs free energy of mixing and maximum compressibility modulus (SCM(max)). Cord factor formed immiscible and thermodynamically unstable monolayers with DPPC. Monolayer presence of cord factor altered the physical state of DPPC monolayers from liquid condensed to liquid expanded with the lowering of SCM(max) from 160 to 40 mN/m, respectively. AFM imaging exhibited smooth homogenous surface topography of DPPC films which in the presence of cord factor was markedly altered with the appearance of aggregates and increased surface roughness. The results highlight the capacity of cord factor to disturb DPPC monolayer organization and structure. Interfacial presence of cord factor results in DPPC monolayer fluidization. Lung surfactant function is attributed to its ability to form well packed low compressibility films. Such molecular interactions suggest a dysfunction of lung surfactant in pulmonary tuberculosis due to surfactant monolayer fluidization.     

Interaction of self-assembled squalenoyl gemcitabine nanoparticles with phospholipid-cholesterol monolayers mimicking a biomembrane

Gemcitabine (dFdC or Gem) is a water-soluble cytotoxic drug, with poor cellular uptake in the absence of a nucleoside transporter. To improve its diffusion through membranes, it was modified by grafting of a squalenoyl moiety. In water, this derivative is able to form stable and monodispersed nanoparticles made of inverse hexagonal phases. The formation and interfacial properties of the squalenoyl gemcitabine (SQ-Gem) nanoparticles, and their ability to interact with phospholipid and cholesterol monolayers modeling a biomembrane, was assessed from surface tension measurements and Brewster angle microscopy. To get a better insight into the mechanisms of SQ-Gem interaction with the various lipids, the interfacial behavior of SQ-Gem and squalene was also studied by surface pressure and surface potential measurements, in the absence and in the presence of phospholipids and cholesterol. The results showed that SQ-Gem nanoparticles adsorbed at the free air/water interface and disrupted to form a monolayer. SQ-Gem molecules released from the adsorbed nanoparticles were also able to penetrate into condensed phospholipid-cholesterol mixed monolayers. The kinetics of this penetration was apparently controlled by intermolecular interactions between the drug and the adsorbed lipids. Whereas distearoylphosphatidylcholine (DSPC) hindered SQ-Gem penetration, cholesterol favored it, which could have important implications in the therapeutic field since cholesterol targeting could alter lipid raft composition and cancer cell survival.     

Fatty-acid monolayers at the nematic/water interface: phases and liquid-crystal alignment

The two-dimensional (2D) phases of fatty-acid monolayers (hexadecanoic, octadecanoic, eicosanoic, and docosanoic acids) have been studied at the interface of a nematic liquid crystal (LC) and water. When observed between crossed polarizers, the LC responds to monolayer structure owing to mesoscopic alignment of the LC by the adsorbed molecules. Similar to Langmuir monolayers at the air/water interface, the adsorbed monolayer at the nematic/water interface displays distinct thermodynamic phases. Observed are a 2D gas, isotropic liquid, and two condensed mesophases, each with a characteristic anchoring of the LC zenithal tilt and azimuth. By varying the monolayer temperature and surface concentration we observe reversible first-order phase transitions from vapor to liquid and from liquid to condensed. A temperature-dependent transition between two condensed phases appears to be a reversible swiveling transition in the tilt azimuth of the monolayer. Similar to monolayers at the air/water interface, the temperature of the gas/liquid/condensed triple-point temperature increased by about 10 degrees C for a two methylene group increase in chain length. However, the absolute value of the triple-point temperatures are depressed by about 40 degrees C compared to those of analogous monolayers at the air/water interface. We also observe a direct influence by the LC layer on the mesoscopic and macroscopic structure of the monolayer by analyzing the shapes and internal textures of gas domains in coexistence with a 2D liquid. An effective anisotropic line tension arises from elastic forces owing to deformation of the nematic director across phase boundaries. This results in the deformation of the domain from circular to elongated, with a distinct singularity. The LC elastic energy also gives rise to transition zones displaying mesoscopic realignment of the director tilt or azimuth between adjacent regions with a sudden change in anchoring.     

Atomic force microscopy studies of ganglioside GM1alpha in dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine mixed monolayers and hybrid bilayers

The membrane states of the alpha-series ganglioside GM1alpha in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed monolayers and hybrid bilayers were investigated using atomic force microscopy (AFM). The AFM image for the GM1alpha/DOPC/DPPC ternary monolayers showed the formation of GM1alpha-raft in the DOPC matrix. As increase of the surface pressure, GM1alpha are condensed in DPPC-rich domains; long and slender GM1alpha-rafts are separated from the DPPC-rich domains into the DOPC matrix. The GM1alpha/DOPC/DPPC ternary monolayers were deposited on mica coated with the first layer (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine: DPPE) using the Langmuir-Schaeffer technique. The AFM image for the hybrid bilayers showed that same molecules were heterogeneously concentrated according to increase of the surface pressure to form GM1alpha-raft, DPPC-rich domain and DOPC matrix, being in agreement with the observation on the monolayer experiment. The found phenomenon implies that a binding of lectin to GM1alpha causes the increase of the surface pressure, the localization of GM1alpha and the succeeding formation of the raft as a first step of a specific signal transduction.     

Fluorescence microscopy observation of self-organized microstructure formed by a rare earth compound

The morphologies of monolayers containing Eu(TTA)3Phen (TTA=thenoyltrifluoroace-tone, Phen = 1, 10-phenanthroline) were studied at the air/liquid interface on different subphases by fluorescence microscopy (FM). The composite subphase was the basic premise for the stable existence of the rare earth compound at air/liquid interface. The process that rare earth compound phase changes from liquid expanded state to liquid condensed state corresponded to a plateau in the π-A isotherm. In the pure Eu(TTA)3Phen monolayer, rod domains of Eu(TTA)3Phen formed and packed with no order. In the mixed monolayers with stearic acid (SA), phase transition of SA occurred first and formed domains with an electric gradient field, which induced the rare earth compound to form luminescent ring domains. Influence of intermolecular interaction on the self-organized microstructure was revealed.     

Study of pH-sensitive copolymer/phospholipid complexes using the langmuir balance technique: effect of anchoring sequence and copolymer molecular weight

The behavior of three copolymers of N-isopropylacrylamide (NIPAM), methacrylic acid (MAA), and hydrophobic moiety was studied at phospholipid monolayer/subphase interfaces. The hydrophobic moieties, N-terminal dioctadecylamine (DODA) and random octadecylacrylate (ODA), were used as anchoring groups. The interactions between a 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC) monolayer and the copolymers were studied using the Langmuir balance technique. The effect of subphase pH, distribution of anchors along the copolymer chain, and copolymer molecular weight on the nature of the interactions between the copolymer chains and the DSPC monolayer were investigated. A first-order kinetics model was used to analyze the copolymers adsorption at the DSPC monolayer/subphase interface and allowed the interaction area between the copolymer chains and the DSPC monolayer, A(x), to be determined. The interaction area appears to depend on the subphase pH and the copolymer molecular weight. On decreasing pH, the interaction area of high molecular weight copolymers increases significantly; this is consistent with the copolymer chain phase transition from an extended coil to a collapsed globule while pH is lowered. In the latter conformation, strong hydrophobic attractive interactions between the copolymer chains and the hydrophobic part of the DSPC monolayer favor the copolymer intercalation, which could eventually provoke the phospholipidic layer destabilization or rupture.     

Effects of lipid chain length on molecular interactions between paclitaxel and phospholipid within model biomembranes

Molecular interactions between an anticancer drug, paclitaxel, and phosphatidylcholine (PC) of various chain lengths were investigated in the present work by the Langmuir film balance technique and differential scanning calorimetry (DSC). Both the lipid monolayer at the air-water interface and lipid bilayer vesicles (liposomes) were employed as model biological cell membranes. Measurement and analysis of the surface pressure versus molecular area curves of the mixed monolayers of phospholipids and paclitaxel under various molar ratio showed that phospholipids and paclitaxel formed a nonideal miscible system at the interface. Paclitaxel exerted an area-condensing effect on the lipid monolayer at small molecular surface areas and an area-expanding effect at large molecular areas, which could be explained by the intermolecular forces and geometric accommodation between the two components. Paclitaxel and phospholipids could form thermodynamically stable monolayer systems: the stability increased with the chain length in the order DMPC (C14:0)>DPPC (C16:0)>DSPC (C18:0). Investigation of paclitaxel penetration into the pure lipid monolayer showed that DMPC had a higher ability to incorporate paclitaxel and the critical surface pressure for paclitaxel penetration also increased with the chain length in the order DMPC>DPPC>DSPC. A similar trend was testified by DSC studies on vesicles of the mixed paclitaxel/phospholipids bilayer. Paclitaxel showed the greatest interaction with DMPC while little interaction could be measured in the paclitaxel/DSPC liposomes. Paclitaxel caused broadening of the main phase transition without significant change at the peak melting temperature of the phospholipid bilayers, which demonstrated that paclitaxel was localized in the outer hydrophobic cooperative zone of the bilayer. The interaction between paclitaxel and phospholipid was nonspecific and the dominant factor in this interaction was the van der Waals force or hydrophobic force. As the result of the lower net van der Waals interaction between hydrocarbon chains for the shorter acyl chains, paclitaxel interacted more readily with phospholipids of shorter chain length, which also increased the bilayer intermolecular spacing.     

Interaction between polymer capsules with hydrophobic cores and a model cellular membrane at an air–water interface

Submicrocapsules have been prepared from diethylaminoethyl dextran and xanthan gum on oil cores by ultrasonic treatment. These capsules have been modified with poly-L-lysine via electrostatic adsorption. The behavior of the capsules has been investigated at an air–water interface after their introduction into the aqueous subphase. The interaction of the capsules with a 1,2-dimyristoyl-sn-glycero-3-phosphocholine monolayer formed on the water surface (model cellular membrane) has been studied both upon their introduction under the condensed monolayer and with the use of a dilute colloidal solution of the capsules as a subphase.