Mixed layers of DPPC and a linear poly(ethylene glycol)-b-hyperbranched poly(glycerol) block copolymer having a cholesteryl end group

Interactions of the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) with the amphiphilic diblock copolymer Ch-lPEG₃₀-b-hbPG₂₄ (ChP) are studied at the air–water interface by surface pressure–mean molecular area (π–mmA) measurements of mixed Langmuir films and adsorption measurements of ChP to the air–water interface covered with DPPC monolayers at different initial surface pressure values π ₀. ChP is composed of a single hydrophobic cholesteryl (Ch) moiety covalently bound to a diblock copolymer consisting of a hydrophilic linear poly(ethylene glycol) (lPEG) block and a hydrophilic hyperbranched poly(glycerol) (hbPG) block. Langmuir isotherms and compression moduli of the mixed Langmuir films of different molar ratios reveal distinct interactions between DPPC and ChP during compression. It is demonstrated that the behavior of the DPPC/ChP mixtures is dominated by DPPC up to a molar ratio of 10:1, whereas the behavior is predominantly governed by ChP in mixtures with lower DPPC content (molar ratios of 5:1, 2:1, and 1:1). In adsorption measurements, a strong affinity of ChP to DPPC is observed after injection into the water subphase. The surface pressure value π _in up to which ChP is able to penetrate into DPPC monolayers is determined to the remarkably high value of 48.2 mN/m which attests the favorable interactions between DPPC and the Ch moiety of ChP. Atomic force microscopy on LB films of DPPC/ChP mixtures of different molar ratios transferred onto hydrophilic substrates confirms the presence of two different phases, a DPPC-rich phase and a ChP-rich phase.     

Sum frequency generation spectroscopic study of the condensation effect of cholesterol on a lipid monolayer

Sum frequency generation (SFG) spectra and surface pressure–molecular area (π–A) isotherms have been obtained for mixed cholesterol–DPPC monolayers with cholesterol mole fractions, x(chol.), from 0 to 1.0, at the air–water interface, under same conditions, at 22 °C. Analysis of the spectra indicated that incorporation of cholesterol into the monolayers at 3 mN m⁻¹ greatly increases the conformational and orientational order of the alkyl chains of DPPC, maximizing these properties at x(chol.)=0.4. Analysis also indicated that order in the mixed monolayers at 15 and 35 mN m⁻¹ is not affected by incorporation of cholesterol. The π–A isotherms measured at 3 mN m⁻¹ for the mixed monolayer with x(chol.)=0.4 have the largest negative deviation of the molecular area relative to those of ideal mixtures (the so-called “condensation effect” of cholesterol), indicating the most thermodynamically stable state. Comparison of results from SFG spectra and π–A isotherms explicitly proved that the condensation effect can be interpreted in terms of conformational and orientational ordering of the alkyl chains of DPPC.     

Influence of N,O-carboxymethyl chitosan on the properties of octadecanoic acid/octadecylamine monolayers and the fractal structure of calcium carbonate

The properties of octadecanoic acid-otctadecylamine monolayers and growth of calcium carbonate (CaCO₃) induced by the monolayers on the surface of supersaturated CaCO₃ solution with N,O-carboxymethyl chitosan (CMC) are studied. The results suggest that CMC is either adsorbed on or inserted into the monolayers, as is confirmed by π-A, dπ/dA-A, and π-t isotherms. The adsorption of CMC changes the properties of the monolayers, a process that results in the transformation of the shape of CaCO₃ particles from crystal-like into the fractal pattern beneath the monolayers. Different fractal morphologies, such as butterfly and wicker branches consisting of hollow ellipsoidal, solid ellipsoidal, and spherical particles, correspondingly, are observed; these morphologies depend on the CMC concentration in the subphase. The dimensions of fractal patterns are determined. The mechanisms of the formation of CaCO₃ crystals and fractal structures are discussed. The text was submitted by the authors in English.     

Bile salt structural effect on the thermodynamic properties of a catanionic mixed adsorbed monolayer

The interfacial effects of two bile salts (sodium deoxycholate (NaDC) and sodium dehydrocholate (NaDHC)) in a catanionic mixed adsorbed monolayer have been investigated at 25 °C. The surfactant interfacial composition, the interfacial orientation of the molecules and the energy changes are analysed to show a thermodynamic evidence of the hydrophobic BSs effect during its intercalation into interfacial adsorbed didodecyldimethyl ammonium bromide (DDAB) molecules. Both mixed systems (NaDC–DDAB and NaDHC–DDAB) have analogous adsorption efficiencies, which are similar from a pure DDAB monolayer and superior to that obtained for both bile salts molecules. Nevertheless, their adsorption effectiveness is different: NaDC causes an increment of Γ while NaDHC produces the opposite effect. The adsorption efficiency in surface tension reduction is due to the existence of interfacial synergistic interactions (confirmed by the analysis of β ^γ and ΔG _ad ⁰ values). Maximum synergistic interaction is seen for α _BSs = 0.4. The hydrophobic steroid backbone of NaDHC molecule presents a deep interfacial penetration than NaDC. This fact causes a great disturbance of DDAB hydrocarbon tails and conduces to a large separation of molecules (high A _m values) which explains the reduction of adsorption effectiveness (low Γ _m values).     

Thermodynamic behavior of D-sphingosine/cholesterol monolayers and the topography observed by AFM

Lipid rafts are of 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 behavior of mixed systems of D-sphingosine with choles-terol was investigated in terms of the mean surface area per molecule(Am),excess molecular area(Aex),surface excess Gibbs energy(Gex),interaction parameter(ω),activity coefficients(1 and 2) as well as elasticity(C...     

Synergistic behavior of sodiumdodecylsulfate and 1,2-diheptanoyl-sn- glycero-3-phosphocholine in an aqueous medium: interfacial and bulk behavior

The synergistic behavior of sodiumdodecylsulfate (SDS) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) binary mixtures has been studied with interfacial and pyrene fluorescence(I ₁/ I ₃) intensity measurements. From the interfacial data, the interfacial parameters; the maximum surface excess (Γ_max), or the minimum area per molecule (A _min), and the surface pressure at the critical micellar concentration (π_cmc) have been evaluated. The cmc value has been used for evaluating the free energies of micellization (ΔG ^o _m). The mixed micelle formation was evaluated with the help of the Clint equation. The SDS plus DHPC mixed micelles showed negative departure from ideality indicating synergistic interactions between the unlike components. The quantitative analysis of mixed micelle, mixed monolayer and the composition of the mixed micelle was carried out with the help of regular solution approximation. The interaction parameters, β and β^σ, in the mixed micelle as well as in the mixed monolayer, respectively showed negative values indicating synergistic behavior of SDS and DHPC molecules.     

Synthesis and monolayer film of a series of new twin-tailed gemini cationic surfactants at the air/water interface

A series of new dimeric surfactants, twin-tailed gemini surfactants, 2(12)-s-2(12), were successfully prepared and characterized, and their monolayer films investigated by the measurement of surface pressure-area (π-A) and surface pressure-time (π-t) isotherms at the air/water interface by a Langmuir film balance. Compared to their monomeric counterparts, their collapse pressure (γ_collapse) is smaller, whilst all the molecular area parameters are larger. The limited area (A_limited) and the initial area (A_initial) of these twin-tailed gemini surfactants change with increasing spacer length s, and the surface pressure decreases with increasing time. It was also found that the higher the initial surface pressure, the larger the attenuation.      

Lipolysis of didecanoyl-lecithin/triolein mixed monolayers by phospholipaseA 2

A study of enzyme lipolysis by pancreatic phospholipaseA ₂ and by vipera berus phospholipaseA ₂ on monomolecular mixed films of didecanoyl-lecithin and triolein on an aqueous subphase of pH 8 has been carried out. The influence of the composition of the mixed film, the surface pressure of the film and the amount and type of the injected enzyme on the lipolysis rate were studied.In order to relate the lipolytic activity with the monolayer state, the compression isotherms of the didecanoyl-lecithin/triolein mixed monolayers have also been obtained.The resuls are compared to observations on lipolytic activity of phospholipaseA ₂ on the didecanoyl-lecithin/cholesterol mixed monolayers. Triolein improves the kinetic conditions of the lipolysis of lecithin films in a higher degree than cholesterol. Probably it increases the enzyme penetration by the fluidifying effect exerted on the lecithin monolayers.     

Preparation and Characterization of 6-<Emphasis Type="Italic">O</Emphasis>-(4-stearyloxytrityl)Cellulose acetate Langmuir–Blodgett Films

Multilayer films of 2,3-di-O-acetyl-6-O-(4-stearyloxytrityl)cellulose (ASTC) were prepared and investigated. The fairly high surface pressure (π)–area (A) isotherms (36– 47 mN/m) suggest that the balky and hydrophobic trityl group contribute to form a condensed monolayer. The cellulose derivative formed a homogeneous monolayer at 10 mN/m. The monolayer on the water surface was transferred successfully at 10 mN/m onto various substrates by modifying the preparation methods, to form Z-type multilayer films. The ultraviolet–visible (UV–Vis) absorbance was independent of the number of layers, indicating that each layer is made of definite number of anhydroglucose unit (AGU). The monolayer thickness determined from atomic force microscope (AFM) and ellipsometry was calculated to be about 1.9 nm, suggesting that the long alkyl chain in the film has a so-called hairy-rod type structure. This is the first paper about the Z-type LB film prepared from cellulose derivatives having long mono-alkyl chain only at 6-O-position.     

Properties of Spreaded Collagen I Monolayers on the Surface of Aqueous tert-Butanol and n-Hexanol Solutions

Properties of the monolayers of collagen isolated from the sclera of pig's eye are studied at the air–water interface with increasing tert-butanol or n-hexanol concentrations in a subphase. In the case of aqueous n-hexanol solutions, its adsorption on the subphase surface results in the formation of mixed monolayer whose properties depend on n-hexanol concentration in the subphase and the ratio between the number of alcohol and collagen molecules in the monolayer. At higher n-hexanol surface concentration, the phase separation of the monolayer into the domains of the condensed phase of alcohol and fibrous collagen occurs. A decrease in water activity in the presence of tert-butanol leads to a drastic reduction of collagen surface activity. This effect can be explained by both the constrained collagen spreading on the surface of tert-BuOH solutions and adsorption of alcohol molecules on collagen resulting in macromolecule hydrophilization. Alcohol critical concentrations are disclosed above which collagen monolayers are not formed.     

Validity of the Kelvin equation in estimation of small pore size by nitrogen adsorption

 We have investigated a practical lower limit of a pore-size estimation by the nitrogen desorption isotherms at 77 K using the Kelvin equation. Changes in pore size of porous silica glasses before and after the monolayer preadsorption of n-propylalcohol were estimated by measuring the nitrogen adsorption and desorption isotherms. These changes should correspond to the thickness of monolayer of adsorbed n-propylalcohol. The thickness of monolayers obtained for the samples whose pore sizes are below ca. 2 nm were underestimated, when the Kelvin equation was applied to the nitrogen desorption isotherms using the values of surface tension and molar volume of bulk liquid nitrogen at 77 K. Below ca. 2 nm pore radius a careful application of the Kelvin equation is required to estimate a pore size. These results suggest that a change in the physical properties of liquid nitrogen in such a small pore occurs. It is supposed that the interaction between the solid surface and adsorbate molecules causes the changes in the surface tension and density of liquid nitrogen in such a narrow pore. Received: 21 March 1997 Accepted: 18 July 1997     

Fabrication of anodic photocurrent generation systems by use of 6-O-dihydrophytylcellulose as a matrix or a scaffold of porphyrins

Langmuir-Blodgett (LB) films containing porphyrin molecules were fabricated by use of 6-O-dihydrophytylcellulose (DHPC) toward anodic photocurrent generation systems. To suppress the porphyrin aggregation, two different approaches were applied: (1) mixing a low-molecular-weight porphyrin having a diterpenoid carbon skeleton (DPor) with DHPC as a matrix (matrix fabrication) and (2) bonding porphyrin molecules to the hydroxyl groups of DHPC covalently, converting into 6-O-dihydrophytyl-2,3-di-O-[p-(10,15,20-triphenyl-5-porphyrinyl)-benzoyl]cellulose as a scaffold (scaffold fabrication). The structure and film properties of the monolayers and the LB films were investigated by the surface pressure (π)–area (A) isotherm measurements, atomic force microscopy, UV–Vis spectroscopy, and absorption dichroism measurements. The porphyrin aggregation in the LB film could be well suppressed only by the scaffold fabrication, leading to the improvement of the photocurrent quantum yields. The efficient photocurrent performance can be demonstrated by the isolation and the parallel orientation of porphyrin moieties due to the cellulose rigid scaffold. This paper was the subject of the Best Poster Award of the 235th edition of the ACS National Meeting, Cellulose and Renewable Materials.     

Adsorption of TX100 and TX165 at the aqueous solution–air interface: free enthalpy of adsorption and equation of state

Surface tension measurements of aqueous solutions of TX100 and TX165 were made at different temperatures. The thermodynamic parameters of the adsorption calculated from the surface tension measurements, using several methods, have given slightly different values. The equation of state for the TX100 and TX165 monolayers at the solution–air interface was analysed. There is excellent agreement between the modified Volmer equation of state and the experimental π–A isotherms. Received: 13 July 1999/Accepted in revised form: 20 October 1999     

Dynamic Behaviors and Morphology Change of Anionic Phospholipid DPPG Monolayer Caused by Bovine Serum Albumin at Air-Water Interface

The interaction between bovine serum albumin (BSA) and the anionic 1.2-dipalmitoyl-snglycero- 3-(phospho-rac-(1-glycerol)) (sodium salt) (DPPG) phospholipid at different subphase pH values was investigated at air-water interface through surface pressure measurements and atomic force microscopy (AFM) observation. By analyzing surface pressure-mean molecular area (π-A) isotherms, the limiting molecular area in the closed packing state-the concentration of BSA (A_lim-[BSA]) curves, the compressibility coefficient-surface pressure (C_S^-1-π) curves and the difference value of mean molecular area-the concentration of BSA (ΔA-[BSA]) curves, we obtained that the mean molecular area of DPPG monolayer became much larger when the concentration of BSA in the subphase increased at pH=3 and 5. But the isotherms had no significant change at different amount of BSA at pH=10. In addition, the amount of BSA molecules adsorbed onto the lipid monolayer reached a threshold value when [BSA]>5×10^-8 mol/L for all pHs. From the surface pressure-time (π-t) data, we obtained that desorption and adsorption processes occurred at pH=3, however, there was only desorption process occurring at pH=5 and 10. These results showed that the interaction mechanism between DPPG and BSA molecules was affected by the pH of subphase. BSA molecules were adsorbed onto the DPPG monolayers mainly through the hydrophobic interaction at pH=3 and 5, and the strength of hydrophobic interaction at pH=3 was stronger than the case of pH=5. At pH=10, a weaker hydrophobic interaction and a stronger electrostatic repulsion existed between DPPG and BSA molecules. AFM images revealed that the pH of subphase and [BSA] could affect the morphology features of the monolayers, which was consistent with these curves. The study provides an important experimental basis and theoretical support to understand the interaction between lipid and BSA at the air-water interface.     

Effects of Calcium Ions on Thermodynamic Properties of Mixed Bilirubin/Cholesterol Monolayers

The mixed monolayer behavior of bilirubin/cholesterol was studied through surface pressure-area (?-A) isotherms on aqueous solutions containing various concentrations of calcium ions. Based on the data of ?-A isotherms, the mean area per molecule, collapse pressure, surface compressibility modulus, excess molecular areas, free energy of mixing, and excess free energy of mixing of the monolayers on different subphases were calculated. The results show an expansion in the structure of the mixed monolayer with Ca2+ in subphase, and non-ideal mixing of the components at the air/water interface is observed with positive deviation from the additivity rule in the excess molecular areas. The miscibility between the components is weakened with the increase of concentration of Ca2+ in subphase. The facts indicate the presence of coordination between Ca2+ and the two components. The mixed monolayer, in which the molar ratio of bilirubin to cholesterol is 3:2, is more stable from a thermodynamic point of view on pure water. But the stable 3:2 stoichiometry complex is destroyed with the increase of the concentration of Ca2+ in subphase. Otherwise, the mixed monolayers have more thermodynamic stability at lower surface pressure on Ca2+ subphase.     

Structure of surface films of malonate mono- and dinitroxyl methanofullerenes

An effect of aqueous subphases composition on the character of change of the bilayer structure of malonate mono- and dinitroxyl methanofullerenes surface films has been established. Their transformation to monolayers takes place in the presence of hydroxy-containing compounds (quercetin, dihydroquercetin, 4-methylphenol, ascorbic acid, as well as in a buffer mixture with pH 10). A loosening of mixed films on the basis of nitroxyl methanofullerenes in the presence of compounds affecting radical processes (2,4,6-tri(tert-butyl)phenol, 2-methyl-3-nitrosopropane, and TEMPO) has been demonstrated. The character of compression isotherms π = f(A ₀) (π is a surface pressure, A ₀ is an effective molecular area of methanofullerene) of the mixed films on water depends on the nature of component incorporated and the reaction time in solution: in all the cases, A ₀ increased almost 2-fold, to 1.05 nm² molecule⁻¹, whereas a compressibility parameter β decreased 2–3-fold, to (1–2)·10¹⁷ N m⁻³. Visualization of the thin film surfaces (atomic force spectroscopy) showed that a decrease of parameter β in the Langmuir layers corresponds to the particle aggregation and structurization of the films. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1920–1931, September, 2008.     

Interaction of Egg-Sphingomyelin with DOPC in Langmuir Monolayers

Lipid rafts are a dynamic microdomain structure found in recent years, enriched in sphin-golipids, 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) with 1, 2-dioleoyl-sn-glycero-3-phosphocholine was in-vestigated in terms of mean surface area per molecule and excess molecular area ΔA_ex at certain surface pressure, surface pressure and excess surface pressure Δπ_ex at certain mean molecular area. The stability and compressibility of the mixed monolayers was assessed by the parameters of surface excess Gibbs free energy ΔG_ex, excess Helmholtz energy ΔH_ex and elasticity. Thermodynamic analysis indicates ΔA_ex and Δπe_ex in the binary systems with positive deviations from the ideal behavior, suggesting repulsive interaction. The max-imum of ΔG_ex and ΔH_ex was at the molar fraction of ESM of 0.6, demonstrating the mixed monolayer was more unstable. The repulsive interaction induced phase separation in the monolayer     

Study of the interaction and activation of lipase from Pseudomonas fluorescens in surfactant monolayers and precipitates

The activation of lipase from Pseudomonas fluorescens (PFL) upon its immobilization in surfactant coprecipitates (hexadecane-1,2-diol (HDD), cetyl alcohol (CetOH), N-cetylacetamide (CetAA), and cetylamine (CetNH₂)) organized in monolayers at the interface were studied by the Langmuir—Blodgett monolayer technique. Incorporation of the enzyme into surfactant monolayers at the surface pressure = 10 mN m^–1 results in an apparent increase in the area per molecule. In the series of noncharged surfactants CetOH—HDD—CetAA, this effect increases in proportion to the amount of the enzyme incorporated in the monolayer. The catalytic activity of the lipase—surfactant coprecipitates in an organic solvent as regards esterification increases in the same sequence, indicating similarity of the interaction of lipase with surfactant monolayers and coprecipitates. For = 10 mN m^–1, the CetNH₂ monolayer with liquid-expanded state incorporates the largest amount of the enzyme (PFL : CetNH₂ = 1 : 290); the CetOH monolayer, which exists in the condensed state under the same conditions, incorporates the smallest amount (PFL : CetOH = 1 : 1700). The hydrolytic activity of PFL in mixed monolayers with surfactants increases 1.5—11-fold; the esterification activity in surfactant coprecipitates, 1.6—9-fold. The lipase activation effects are explained by facilitated transport of substrates into mixed monolayers and surfactant—enzyme precipitates in aqueous and organic media, respectively.     

Influence of temperature on the composition of mixed monolayer formed at the methyl alcohol/acetic acid aqueous solutio–air interface

The influence of temperature on the composition of mixed monolayer formed at the methyl alcohol/acetic acid aqueous solution was examined by surface tension measurements. Surface tension of various two-component solutions was obtained at 10, 20 and 28 °C temperatures in the 0–0.5 M range of bulk concentration of alcohol and acid, respectively. Three independent methods, i.e., the Gibbs adsorption equation (GAE), regular solution approximation (RSA) and Butler adsorption isotherm (BAI) were applied to calculate surface composition of the methyl alcohol/ acetic acid mixed monolayer. It was shown that in the temperature range of 10–28 °C the surface molar fraction of the solutes remained constant for the fixed bulk concentration of alcohol and acid. Additionally, based on the RSA and BAI methods, we showed there were no interactions between solute molecules in the mixed monolayer in the studied range of concentrations. Received: 18 December 1997 Accepted: 8 May 1998     

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.