Changchun Hao

The behavior of the adsorption of cytochrome C on lipid monolayers: A study by the Langmuir-Blodgett technique and theoretical analysis.

Cytochrome c (Cyt c) is an essential component of the inner mitochondrial respiratory chain because of its function of transferring electrons. The feature is closely related to the interaction between Cyt c and membrane lipids. We used Langmuir-Blodgett monolayer technique combined with AFM to study the interaction of Cyt c with lipid monolayers at air-buffer interface. In our work, by comparing the mixed Cyt c-anionic (DPPS) and Cyt c-zwitterionic (DPPC/DPPE) monolayers, the adsorption capacity of Cyt c on lipid monolayers is DPPS>DPPE>DPPC, which is attributed to their different headgroup structures. π-A isothermal data show that Cyt c (v=2.5 μL) molecules are at maximum adsorption quantity on lipid monolayer. Moreover, Cyt c molecules would form aggregations and drag some lipids with them into subphase if the protein exceeds the maximum adsorption quantity. π-T curve indicates that it takes more time for Cyt c molecular conformation to rearrange on DPPE monolayer than on DPPC. The compressibility study reveals that the adsorption or intermolecular aggregation of Cyt c molecules on lipid monolayer will change the membrane fluidization. In order to quantitatively estimate Cyt c molecular adsorption properties on lipid monolayers, we fit the experimental isotherm with a simple surface state equation. A theoretical model is also introduced to analyze the liquid expanded (LE) to liquid condensed (LC) phase transition of DPPC monolayer. The results of theoretical analysis are in good agreement with the experiment.

Mixed monolayers of DOPC and palmitic acid at the liquid–air interface

The interactions between 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and palmitic acid (PA) in mixed monolayers were investigated through surface pressure measurements, fluorescence microscopy (FM) and atomic force microscopy (AFM). The miscibility of two components and the interactions between DOPC and PA in the mixed monolayers were accessed by analyzing surface pressure (π)-area (A) isotherms. It was found that there were both positive deviations for excess molecular area and excess Gibbs energy, which suggests the interaction is repulsive in all case and the strongest repulsive occurs at XPA=0.5 ratio. The FM and AFM images showed that there were discernible phase separations at selected surface pressures. The increase of surface pressure and the phenomenon that the PA-enriched domains have been connected to form much larger platforms are in agreement with the thermodynamic results.

A monolayer study on phase behavior and morphology of binary mixtures of sulfatides with DPPC and DPPE.

Sulfatides are important constituents of brain myelin membranes and it is thought to be involved in lateral domain formation in biological membranes. In this work, the interaction of mixed systems of sulfatide with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1, 2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), two of the major components in biological membranes, was investigated using the monolayer technique at the air-water interface. Based on the regular solution theory, the miscibility of the two binary systems in the mixed monolayer was evaluated in terms of mean surface area per molecule (A(m)), excess molecular area (DeltaA((ex))), surface excess Gibbs energy (DeltaG((ex))), interaction parameter (omega) as well as activity coefficients (f(1) and f(2)) of formed films. Thermodynamic analysis indicates in the two binary systems with negative deviations from the ideal behavior. Accordingly, the values of the Gibbs energy of mixing, sulfatide-DPPC form stable mixtures at X(sul)=0.4 (X(sul) is molar ratio of sulfatide in binary mixture) for all the selected pressures. As for sulfatide/DPPE system, at pi=5 and 30 mN m(-1), the minimum for the Gibbs energy of mixing was found at X(sul)=0.6 and 0.2 respectively. But the minimum appeared at X(sul)=0.4 for other surface pressures. The activity coefficients (f(1) and f(2)) of mixed monolayers were evaluated which show a marked dependence on the mole faction of sulfatide X(sul). AFM images could support the above findings as well as interpretation.

Thermodynamic and structural studies of DMPC and DSPC with DOTAP mixed monolayers at the air–water interface

According to the method of Langmuir-Blodgett the thermodynamic behavior and the miscibility of the two phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) with 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) in the mixed monolayer were evaluated in terms of the excess mean molecular area, excess Gibbs free energy and compressibility coefficient. DMPC and DOTAP were miscible and a repulsive interaction appeared between DMPC and DOTAP molecules at most of selected ratios and surface pressures. Meanwhile, the interaction between DSPC and DOTAP were attractive and the most stable monolayers were formed at the 3: 2 and 1: 4 stoichiometry. The morphology observations by fluorescence microscopy reveals that the size of the domains composed of DSPC were larger than DMPC.

A method for the preparation of curcumin by ultrasonic-assisted ammonium sulfate/ethanol aqueous two phase extraction

This study investigated a new and easy-to-industrialized extracting method for curcumin from Curcuma longa rhizomes using ultrasonic extraction technology combined with ammonium sulfate/ethanol aqueous two-phase system (ATPS), and the preparation of curcumin using the semi-preparative HPLC. The single-factor experiments and response surface methodology (RSM) were utilized to determine the optimal material-solvent ratio, ultrasonic intensity (UI) and ultrasonic time. The optimum extraction conditions were finally determined to be material-solvent rate of 3.29:100, ultrasonic intensity of 33.63W/cm2 and ultrasonic time of 17min. At these optimum conditions, the extraction yield could reach 46.91mg/g. And the extraction yields of curcumin remained stable in the case of amplification, which indicated that scale-up extraction was feasible and efficient. Afterwards, the semi-preparative HPLC experiment was carried out, in which optimal preparation conditions were elected according to the single factor experiment. The prepared curcumin was obtained and the purity could up to 85.58% by the semi-preparative HPLC.

Interfacial interactions and nanostructure changes in DPPG/HD monolayer at the air/water interface

Lung surfactant (LS) plays a crucial role in regulating surface tension during normal respiration cycles by decreasing the work associated with lung expansion and therefore decreases the metabolic energy consumed. Monolayer surfactant films composed of a mixture of phospholipids and spreading additives are of optional utility for applications in lung surfactant-based therapies. A simple, minimal model of such a lung surfactant system, composed of 1,2-dipalmitoyl-sn-glycero-3-[phosphor-rac-(1-gylcerol)] (DPPG) and hexadecanol (HD), was prepared, and the surface pressure-area (π-A) isotherms and nanostructure characteristics of the binary mixture were investigated at the air/water interface using a combination of Langmuir-Blodgett (LB) and atomic force microscopy (AFM) techniques. Based on the regular solution theory, the miscibility and stability of the two components in the monolayer were analyzed in terms of compression modulus (Cs-1), excess Gibbs free energy (Δexcπ), activity coefficients (γ), and interaction parameter (ξ). The results of this paper provide valuable insight into basic thermodynamics and nanostructure of mixed DPPG/HD monolayers; it is helpful to understand the thermodynamic behavior of HD as spreading additive in LS monolayer with a view toward characterizing potential improvements to LS performance brought about by addition of HD to lung phospholipids.

A Langmuir and AFM study on interfacial behavior of binary monolayer of hexadecanol/DPPE at the air-water interface

Hexadecanol is chemically stable and can be used as an effective addition in synthetic clinical lung surfactant preparations to improve their spreading properties. In this work, a detailed thermodynamic and structural characterization of a simple model system, which based on a hexadecanol-phospholipid mixture is reported. Langmuir monolayers of binary mixtures of hexadecanol/1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) have been studied with thermodynamic parameters and monolayer structure. The extent of the thermodynamic parameters has been evaluated by the direct related parameters, such as mean molecular area, percent of condensation, surface excess Gibbs free energies, isothermal compressibility, interaction energy parameter, activity coefficient and two-dimensional phase diagram. Monolayer film structure has been characterized by atomic force microscopy (AFM) technique. Combining thermodynamic and AFM data indicate that there exist repulsive and attractive interactions between the two film forming molecules and the binary films behave as non-ideal mixtures, which can be portrayed by the mole fraction of hexadecanol. At low mole fraction of hexadecanol, the monolayer is phase-separated and the interactions between hexadecanol and DPPE is more repulsive; while the content of hexadecanol up to 0.6, the monolayer becomes miscible and stable, the interaction between different molecules is more attractive. The addition of hexadecanol in the DPPE monolayer clearly affects the lateral organization of membranes and improves its surface tension kinetics. The results discussed in this context will be expected to be potential contribution for exogenous lung surfactant researches.

Interaction of Egg-Sphingomyelin with DOPC in Langmuir Monolayers

Lipid rafts are a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer miscibility behavior of mixed systems of Egg-Sphingomyelin (ESM) 1 with 2-dioleoyl-sn-glycero-3-phosphocholine was investigated in terms of mean surface area per molecule and excess molecular area ΔAex at certain surface pressure, surface pressure and excess surface pressure Δπex at certain mean molecular area. The stability and compressibility of the mixed monolayers was assessed by the parameters of surface excess Gibbs free energy ΔGex, excess Helmholtz energy ΔHex and elasticity. Thermodynamic analysis indicates ΔAex and Δπex in the binary systems with positive deviations from the ideal behavior, suggesting repulsive interaction. The maximum of ΔGex and ΔHex was at the molar fraction of ESM of 0.6, demonstrating the mixed monolayer was more unstable. The repul...

Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface*

The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure–area (π–A) isotherms and surface pressure–time (π–T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers.

Analysis of the induction of the myelin basic protein binding to the plasma membrane phospholipid monolayer

Myelin basic protein (MBP) is an essential structure involved in the generation of central nervous system (CNS) myelin. Myelin shape has been described as liquid crystal structure of biological membrane. The interactions of MBP with monolayers of different lipid compositions are responsible for the multi-lamellar structure and stability of myelin. In this paper, we have designed MBP-incorporated model lipid monolayers and studied the phase behavior of MBP adsorbed on the plasma membrane at the air/water interface by thermodynamic method and atomic force microscopy (AFM). By analyzing the pressure–area (π–A) and pressure–time (π–T) isotherms, univariate linear regression equation was obtained. In addition, the elastic modulus, surface pressure increase, maximal insertion pressure, and synergy factor of monolayers were detected. These parameters can be used to modulate the monolayers binding of protein, and the results show that MBP has the strongest affinity for 1,2-dipalmitoyl-sn-glycero-3- phosphoserine (DPPS) monolayer, followed by DPPC/DPPS mixed and 1,2-dipalmitoyl-sn-glycero-3-phospho-choline (DPPC) monolayers via electrostatic and hydrophobic interactions. AFM images of DPPS and DPPC/DPPS mixed monolayers in the presence of MBP (5 nM) show a phase separation texture at the surface pressure of 20 mN/m and the incorporation of MBP put into the DPPC monolayers has exerted a significant effect on the domain structure. MBP is not an integral membrane protein but, due to its positive charge, interacts with the lipid head groups and stabilizes the membranes. The interaction between MBP and phospholipid membrane to determine the nervous system of the disease has a good biophysical significance and medical value.