Poly(ethylene glycol) (PEG) enhances dynamic surface activity of a bovine lipid extract surfactant (BLES)

Shortage or malfunction of pulmonary surfactant in alveolar space leads to a critical condition termed respiratory distress syndrome (RDS). Surfactant replacement therapy, the major method to treat RDS, is an expensive treatment. In this paper, the effect of poly(ethylene glycol) (PEG) to improve dynamic surface activity of a bovine lipid extract surfactant (BLES) was studied by axisymmetric drop shape analysis (ADSA) and a captive bubble method. The activity of BLES+PEG mixtures was compared to that of a natural surfactant containing surfactant proteins A and D. When PEG was added into BLES mixtures, the surface tension hysteresis of BLES films was minimized when the films were compressed by more than 50%. PEG also helps to quickly restore surfactant films after film collapse. Thus, as far as surface tension effects go, the findings suggest that PEG might be used as a substitute for surfactant-associated protein SP-A in therapeutic surfactant products, and might also be used to reduce the amount of BLES required in clinical applications.     

Interfacial organizations of gel phospholipid and cholesterol in bovine lung surfactant films

Pulmonary surfactants stabilize the lung by way of reducing surface tension at the air-lung interface of the alveolus. 31P NMR, thin-layer chromatography, and electrospray ionization mass spectroscopy of bovine lipid extract surfactant (BLES) confirmed dipalmitoylphosphatidylcholine (DPPC) to be the major phospholipid species, with significant amounts of palmitoyl-oleoylphosphatidylcholine, palmitoyl-myristoylphosphatidylcholine, and palmitoyl-oleoylphosphatidylglycerol. BLES and DPPC spread at the air-water interface were studied through surface pressure area, fluorescence, and Brewster angle microscopy measurements. Langmuir-Blodgett films of monomolecular films, deposited on mica, were characterized by atomic force microscopy. BLES films displayed shape, size, and vertical height profiles distinct from those of DPPC alone. Calcium ions in the subphase altered BLES film domain structure. The addition of cholesterol (4 mol %) resulted in the destabilization of compressed BLES films at higher surface pressures (>40 mN m-1) and the formation of multilayered structures, apparently consisting of stacked monolayers. The studies suggested potential roles for individual surfactant lipid components in supramolecular arrangements, which could be the contributing factors in pulmonary surfactant to attain low surface tension at the air-water interface.     

Effect of surfactant concentration on the critical thicknesses of liquid films

Summary It is shown that an increase in surfactant concentration at first causes the critical thicknesses of rupture on microscopic films to decrease but gradually a nearly constant value is reached. With films of aqueous solutions of fatty acids (valeric, caproic, caprylic and capric acids), this dependence correlates well with the effect of the surfactant concentration on the damping of capillary waves. With surfactants of the detergent type (OPE-7, OPE-20) in addition to the change of the critical thickness, the transition from rupture to formation of black spots is described, as the surfactant concentration exceedsC _bl. The remarkable fact in the latter case is the independence of the critical thickness of the final state, be it rupture or formation of first or second black films.On the basis of the experimental data the assumption is put forward that the critical thickness of rupture or the critical thickness of formation of black spots is substantially affected by macroscopic non-uniformities in the film thickness. Thus the conclusion is reached that the critical thickness of an ideally plane parallel film which is the object of the theory, must be obtained by extrapolation of the measured value toward extremely small radii.

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Zusammenfassung Es wird gezeigt, daß die kritischen Zerreißdicken mikroskopischer Schaumfilme, die mit der Zunahme der Tensidkonzentration zunächst abnehmen, dann aber ungefähr konstante Werte erreichen. Diese Abhängigkeit ist in guter Übereinstimmungmitdem Einfluß des Tensides auf die Kapillarwellendämpfung in wäßrigen Lösungen von vier Fettsäuren. Bei Tensiden, die gute Schäumer sind (OPE-7, OPE-2) zerreißt der Film mit der Zunahme der Konzentration überC _bl nicht, sondern es bilden sich schwarze Flecke. Es ist sehr interessant, daß die kritische Dicke unabhängig von dem Endzustand (Zerreißen oder Bildung schwarzer Flecke) ist.Aufgrund dieser Experimente wird angenommen, daß die kritische Dicke bei dem Zerreißen oder bei der schwarzen Fleckebildung mikroskopischer Schaumfilme wesentlich von den makroskopischen Ungleichheiten der Filmdicke beeinflußt wird. Daraus wird gefolgert, daß die kritische Dicke eines idealen planparallelen Films durcheine Extrapolation der Meßwerte aufeinen unendlich dünnen Film ermittelt werden kann.

     

Thermodynamic studies of bovine lung surfactant extract mixing with cholesterol and its palmitate derivative

Langmuir film behavior of bovine lipid extract surfactant (BLES), mixed with cholesterol (CHOL) and cholesterol palmitate (CHOLP), has been studied by surface pressure (pi)-area (A) measurements. Associative interactions, observed for both systems, were less favored at lower BLES content. The presence of unsaturated phospholipids and surfactant proteins in BLES favored the association. Miscibility of BLES was better with CHOLP than with CHOL at all compositions, indicating more compact packing of the BLES-CHOLP than of the BLES-CHOL system. The most stable mixtures were found at 30-40 mol% CHOL and at low pi and at 20-25 mol% CHOLP but at higher pi. These results suggest that BLES-CHOL miscibility is better at low pi and low CHOL concentrations, while BLES-CHOLP miscibility is better at high pi and high CHOLP concentrations.     

Effect of mycolic acid on surface activity of binary surfactant lipid monolayers

In pulmonary tuberculosis, Mycobacterium tuberculosis lies in close physical proximity to alveolar surfactant. Cell walls of the mycobacteria contain loosely bound, detachable surface-active lipids. In this study, the effect of mycolic acid (MA), the most abundant mycobacterial cell wall lipid, on the surface activity of phospholipid mixtures from lung surfactant was investigated using Langmuir monolayers and atomic force microscopy (AFM). In the presence of mycolic acid, all the surfactant lipid mixtures attained high minimum surface tensions (between 20 and 40 mN/m) and decreased surface compressibility moduli <50 mN/m. AFM images showed that the smooth surface topography of surfactant lipid monolayers was altered with addition of MA. Aggregates with diverse heights of at least two layer thicknesses were found in the presence of mycolic acid. Mycolic acids could aggregate within surfactant lipid monolayers and result in disturbed monolayer surface activity. The extent of the effect of mycolic acid depended on the initial state of the monolayer, with fluid films of DPPC-POPC and DPPC-CHOL being least affected. The results imply inhibitory effects of mycolic acid toward lung surfactant lipids and could be a mechanism of lung surfactant dysfunction in pulmonary tuberculosis.     

Effect of bovine serum albumin on the surface properties of ionic liquid-type Gemini surfactant

The effect of bovine serum albumin on the surface properties of IL-type gemini surfactant ([C₁₀-4-C₁₀im]Br₂), have been investigated by surface tension method. The critical micelle concentration (CMC) as a function of BSA concentrations at various temperatures was investigated. The CMC of [C₁₀-4-C₁₀im]Br₂ increases with increasing the concentration of BSA as well as the temperature of the system. The interfacial parameters viz; maximum surface excess concentration (Γ_max), the minimum area per molecule (A_min), and surface pressure at CMC (Π_cmc) were calculated. In addition, thermodynamic parameters of adsorption and micellization were evaluated by using surface tension data. The results indicated that the binding of [C₁₀-4-C₁₀im]Br₂ to BSA is spontaneous and exothermic in nature. The process is entropy driven and hydrophobic interactions are the major driving forces.     

Effect of polymer-plasticizer interactions on the oxygen permeability of starch-sorbitol-water films

This study evaluated the oxygen permeability (O.P.) of starch-sorbitol-water films produced by casting. With a sorbitol content <20%, O.P. (0.15 10⁻¹⁶ cm²/s.Pa for 8.8% sorbitol) was lower than for other polymers classically used as oxygen barriers. With a sorbitol content >20%, O.P. (1.6 10⁻¹⁶ cm²/s.Pa for 24.9% sorbitol) was higher than for starch films without a plasticizer. These results were correlated with molecular mobility as determined by time-domain NMR. Low and high O.P. corresponded respectively to a decrease and an increase of molecular mobility relative to sorbitol content.     

Drop impact on surfactant films and solutions

Drops impacting on horizontal aqueous surfactant films have been analyzed using a high-speed camera. Drops of either water or aqueous surfactant solutions had a diameter of 2.4?±?0.4 mm and impacted with a velocity of 0.1 to 1.3 m/s. As surfactants, anionic sodium dodecyl sulfate and cationic cetyltrimethyl ammonium bromide were used. Pure water drops impacting on freestanding surfactant films showed coalescence, bouncing, partial bouncing, passing, and partial passing. For bouncing, the concentration of surfactant in the surfactant film must exceed the critical micelle concentration. When surfactant was added to the drop, coalescence and partial passing were suppressed. We attribute the different behavior to different hydrodynamic boundary conditions at the surface of pure water and surfactant solution, leading to different repulsive hydrodynamic forces arising when the air has to flow out of the closing gap between the two liquid surfaces. The boundary condition changes as a function of surfactant concentration from a slip to no-slip, leading to stronger hydrodynamic repulsion. In addition, estimates of the characteristic velocities show that diffusion of air into the water is slow and can only account for the very last thinning of the air gap before coalescence.     

Black foam films stabilized with the mixtures of bovine serum albumin and nonionic surfactant Tween 80

Stable black films are prepared for the first time from aqueous solutions of Tween 80-bovine serum albumin mixtures. Conditions for their formation and stabilization factors are studied in a Scheludko-Exerowa cell by microinterferometry. It is found that such films are formed when saturated surface layers consist of surfactant-protein 1: 1 complexes, Tween 80 molecules, or their mixtures. A possible mechanism for the thinning of liquid layers and the stabilization of black films is discussed.     

Effect of vegetable oils on obtaining lipid nanocarriers for sea buckthorn extract encapsulation

The principal aim of the present study was to develop new safe and highly antioxidant nanostructured lipid carriers loaded with sea buckthorn extract. Three vegetable oils — grape seed oil, sea buckthorn oil and St. John's wort oil (Hypericum perforatum oil) — were used as matrix components and the modified high shear homogenization technique has been employed for the synthesis of nanostructured materials. The effect of these oils on the antioxidant and antimicrobial activities of loaded sea buckthorn extract — nanostructured lipid carriers — has also been studied. For this purpose, a combination of two solid lipids: cetyl palmitate with glyceryl stearate and lecithin/block copolymer has been used. The obtained nanostructured lipid carriers have been characterized for the particle size and zeta potential by means of dynamic light scattering measurements. The nano-dimension morphology of loaded nanostructured lipid carriers was confirmed by transmission electron microscopy. Their crystallinity measured by differential scanning calorimetry has revealed a high disordered lipid matrix. The properties of sea-buckthorn-extract-loaded nanoparticles have been evaluated by an appropriate in vitro analysis (chemiluminescence method). The presence of the three vegetable oils influences extensively the antioxidant properties of the developed nano-formulations, as has been demonstrated using the chemiluminescence technique. The antimicrobial activity of the studied nanostructured lipid carriers, analyzed by the diffusion disc method, shows in most of the samples a high efficiency against Escherichia coli bacteria.     

Effect of oxygen on the electronic structure of highly crystalline picene films

The electronic structure of highly crystalline picene films with a standing-up orientation grown epitaxially on the Ag(110) surface was investigated. Upon exposure to oxgen gas, O(2) molecules incorporate at the interstitial sites within the a-b plane of the film. Features related to the highest three occupied molecular orbitals shift toward a lower binding energy which results in the inactivation of traps and the reduction of the charge injection barrier by about 1 eV. It is suggested that the highest two picene orbitals are inverted due to the strong interactions between the singly occupied oxygen π orbital and the highest occupied orbital of picene.     

Effects of hydrostatic pressure on lipid and surfactant phases

In the last years a number of advances have been made in our understanding of the high pressure phase behaviour of lipid and surfactant systems, in particular of phospholipid bilayers which can serve as model biomembrane systems. Hydrostatic pressure has been used as a physical parameter for studying the stability and energetics of lyotropic lipid mesophases, but also because high pressure is an important feature of certain natural membrane environments (e.g. of marine biotopes) and because the high pressure phase behaviour of biomolecules is of biotechnological interest (e.g. for high pressure food processing). It has been demonstrated that temperature and pressure have non-congruent effects on the structural and phase behaviour of these systems. By using the pressure–jump relaxation technique in combination with time-resolved synchrotron X-ray diffraction, the kinetics of different mesophase transformations was also investigated.     

Effect of oxygen vacancies in anodic titanium oxide films on the kinetics of the oxygen electrode reaction

The effect of oxygen vacancies in the anodic oxide film on passive titanium on the kinetics of the oxygen electrode reaction has been studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Oxide films of different donor density were prepared galvanostatically at various current densities until a potential of 20.0 V_SHE was achieved. The semiconductive properties of the oxide films were characterized using EIS and Mott-Schottky analysis, and the thickness was measured using ellipsometry. The film thickness was found to be almost constant at ∼44.7 ± 2.0 nm, but Mott-Schottky analysis of the measured high frequency interracial capacitance showed that the donor (oxygen vacancy) density in the n-type passive film decreased sharply with increasing oxide film formation rate (current density). Passive titanium surfaces covering a wide range of donor density were used as substrates for ascertaining relationships between the rates of oxygen reduction/evolution and the donor density. These studies show that the rates of both reactions are higher for passive films having higher donor densities. Possible explanations include enhancement of the conductivity of the film due to the vacancies facilitating charge transfer and the surface oxygen vacancies acting as catalytic sites for the reactions. The possible involvement of surface oxygen vacancies in the oxygen electrode reaction was explored by determining the kinetic order of the OER with respect to the donor concentration. The kinetic orders were found to be greater than zero, indicating that oxygen vacancies are involved as electrocatalytic reaction centers in both the oxygen evolution and reduction reactions. This paper was submitted in honor of the many contributions to electrochemistry that have been made by Professor Boris Grafov. The article is published in the original.     

Effect of β-sheet crystalline content on mass transfer in silk films

The material properties of silk are favorable for drug delivery due to the ability to control material structure and morphology under ambient, aqueous processing conditions. Mass transport of compounds with varying physical-chemical characteristics was studied in silk fibroin films with control of β-sheet crystalline content. Two compounds, vitamin B12 and fluorescein isothiocynate (FITC) labeled lysozyme were studied in a diffusion apparatus to determine transport through silk films. The films exhibited size exclusion phenomenon with permeability coefficients with contrasting trends with increases in β-sheet crystallinity. The size exclusion phenomenon observed with the two model compounds was characterized by contrasting trends in permeability coefficients of the films as a function of β-sheet crystallinity. The diffusivity of the compounds was examined in the context of free volume theory. Apart from the β-sheet crystallinity, size of the compound and its interactions with silk influenced mass transfer. Diffusivity of vitamin B12 was modeled to define a power law relationship with β-sheet crystallinity. The results of the study demonstrate that diffusion of therapeutic agents though silk fibroin films can be directed to match a desired rate by modulating secondary structure of the silk proteins.     

Physico-chemical properties of surfactant and protein films

Major recent advancesThe study of the physico-chemical properties of protein and surfactant films continues to be a growing field of research, which is multidisciplinary in nature. Recent advances include further evidence of the compatibility of protein and surfactants at fluid interfaces, the application of new surface-sensitive techniques combined with traditional surface pressure instruments, the development of computer simulation of the displacement of proteins by emulsifiers, and the analysis of mixed films on the basis of quantitative theoretical models.     

Kinetics of oxygen adsorption on silver films

Kinetics of oxygen adsorption on silver films prepared by metal vacuum evaporation and condensation technique has been studied. The adsorption proceeds in accordance with the kinetic law of Zeldovich-Roginskii. Oxygen dissolution in the silver subsurface layers result in a decrease of the initial adsorption rate and an enhanced exponential decrease of the adsorption rate as a function of surface coverage.     

Effect of the counterion on the rate of electron transfer in dendrimer films

The electrochemical behavior of a film composed of a redox-active dendrimer was studied as a function of the type of counterion available during its reduction and reoxidation. The rate of permeation/migration of counterions into the film appeared to be the bottleneck to electron transfer through the film. Because the dendrimer is rather hydrophobic, increasing the hydrophobicity of the counterion increased the rate and extent of electron hopping within the films.     

Effect of electrolyte cations on the charge transfer in films of prussian blue

Charge transfer in films of Prussian blue is studied by cyclic voltammetry and chronoamperometry at potentials of first (PB/PW) and second (PB/PY) redox processes in solutions of potassium, cesium, and ammonium nitrates (pH 4.0). The current relaxation following a film perturbation by a small-amplitude voltage pulse is analyzed with theoretical relationships obtained earlier for the charge transfer in redox polymers. Parameters, characterizing the charge transfer rate (formal diffusion coefficient, instantaneous current), are calculated and analyzed as a function of the film oxidation state and the supporting-electrolyte nature     

Dewetting behavior of aqueous cationic surfactant solutions on liquid films

Previous experimental work has shown that the spreading of a drop of aqueous anionic surfactant solution on a liquid film supported by a negatively charged solid substrate may give rise to a fingering instability (Afsar-Siddiqui, A. B.; Luckham P, F.; Matar, O. K. Langmuir 2003, 19, 703-708). However, upon deposition of a cationic surfactant on a similarly charged support, the surfactant will adsorb onto the solid-liquid interface rendering it hydrophobic. Water is then expelled from the hydrophobic regions, causing film rupture and dewetting. In this paper, experimental results are presented showing how the surfactant concentration and film thickness affect the dewetting behavior of aqueous dodecyltrimethylammonium bromide solutions. At low surfactant concentrations and large film thicknesses, the film ruptures at a point from which dewetting proceeds. At higher concentrations and smaller film thicknesses, the ruptured region is annular in shape and fluid moves away from this region. At still higher concentrations and smaller film thicknesses, the deposited surfactant forms a cap at the point of deposition that neither spreads nor retracts. This variation in dewetting mode is explained by considering the relative Marangoni and bulk diffusion time scales as well as the mode of assembly of the surfactant adsorbed on the solid surface.     

Effect of film thickness on the electro-reduction of molecular oxygen on electropolymerized cobalt tetra-aminophthalocyanine films

We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O₂) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O₂ reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O₂ to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy.