Range Of Surface Pressures Research Articles

Cholesterol-induced interfacial area condensations of galactosylceramides and sphingomyelins with identical acyl chains.

The interfacial interactions occurring between cholesterol and either galactosylceramides (GalCers) or sphingomyelins (SMs) with identical acyl chains have been investigated using Langmuir film balance techniques. Included among the synthesized GalCers and SMs were species containing palmitoyl (16:0), stearoyl (18:0), oleoyl [18:1 delta 9(c)], nervonoyl [24:1 delta 15(c)], or linoleoyl [18:2 delta 9,12(c)] acyl residues. The cholesterol-induced condensations in the average molecular areas of the monolayers were determined by classic mean molecular area vs composition plots as well as by expressing the changes in terms of sphingolipid cross-sectional area reduction over the surface pressure range from 1 to 40 mN/m (at 1 mN/m intervals). The results show that, at surface pressures approximating bilayer conditions (30 mN/m), acyl heterogeneity in naturally occurring SMs (bovine of egg SM) enhanced the area condensation induced by cholesterol compared with their predominant molecular species (e.g. 18:0 SM in bovine SM; 16:0 SM in egg SM). Nonetheless, cholesterol always had a greater condensing effect on SM compared to GalCer when these sphingolipids were acyl chain matched and in similar phase states (prior to mixing with cholesterol). Also, the cholesterol-induced area changes for a given sphingolipid type (e.g. SM or GalCer) were similar whether the acyl chains were saturated, cis-delta 9-monounsaturated, or cis-delta 9,12-diunsaturated if the sphingolipids were in similar phase states (prior to mixing with cholesterol) and compared at equivalent surface pressures. These results indicate that, under conditions were hydrocarbon structure is matched, the sphingolipid head group plays a dominant role in determining the extent to which cholesterol reduces sphingolipid cross-sectional area. Despite the larger cholesterol-induced area condensations observed in SMs compared to those in GalCers, the molecular-packing densities showed that equimolar GalCer-cholesterol films were generally packed as tight as or slightly tighter than those of the SM-cholesterol films. The results are discussed in terms of a molecular model for sphingolipid-cholesterol interactions. Our findings also do only raise questions as to whether cholesterol-induced condensation data provide a reliable measure of the affinity, i.e. interaction strength, between cholesterol and different lipids but also provide insight regarding the stability of sterol/sphingolipid 1-1 rich microdomains thought to exist in caveolae and other cell membrane regions.

Organization of Spread Monolayers of Poly(Lauryl methacrylate) at the Air-Water Interface from Neutron Reflectometry on Partially Labeled Isomers

Surface pressure isotherms of poly(lauryl methacrylate) (PLMA) spread monolayers at the air-water interface show that the thermodynamic state of the polymer is poorer than Θ conditions. Neutron reflectivity has been used to determine the organization of the polymer at the interface. To obtain maximum information, four variations of PLMA were synthesized, each with different isotopic labeling, and these were spread on two different aqueous subphases, D 2 O and air contrast matched water. Reflectivities were recorded at two different surface pressures of 5 and 9 mN m -1 . Interpretation of these reflectivity profiles using the optical matrix calculation methods suggested a two-layer structure with the methacrylate backbone immersed in the subphase and the lauryl substituent protruding into the air phase but being penetrated to some extent by water. Direct analysis of the reflectivity data using partial structure factors allowed the dimensions, separations, and compositions of each of the layers to be determined. The backbone and substituent layers were describable by Gaussian distributions with standard deviations of 6 and 16 A, respectively, at the highest surface pressure investigated. Over the same surface pressure range, the near surface water layer had a hyperbolic tangential organization. Separations between layers obtained from cross partial structure factors remained relatively unchanged as the surface pressure increased. The methacrylate backbone-rich and near surface water layers were separated by 2 A, and the lauryl substituent-rich and water layer separation was ca. 6 A. Methacrylate backbone and side chain distributions were separated by ca. 3 A at 9 mN m -1 . These values were interpreted as indicative of complete immersion of the backbone and partial immersion of the lauryl substituents.

Modeling success and failure of Langmuir-Blodgett transfer of phospholipid bilayers to silicon dioxide

Formation of planar phospholipid bilayers on solid and porous substrates by Langmuir-Blodgett transfer of monolayers from the air-water interface could be of much greater utility if the process were not irreproducible and poorly understood. To that end the energetics of transferring two phospholipid monolayers to a hydrophilic surface has been examined. An approximate mathematical relationship is formulated that relates the surface pressure of the precursor monolayers to the tension within the bilayer created. Data are presented that demonstrate that bilayer transfer can be carried out reproducibly even with refractory phospholipids such as phosphatidylcholine, but only over a very narrow range of precursor monolayer surface pressures. This range is related to the lysis tension of the bilayer. The morphology of films formed within and below the successful range of surface pressures are examined by fluorescence microscopy, and the observed features are discussed in terms of the relationship above. These results provide practical guidelines for successful formation of lipid bilayers on hydrophilic surfaces; these guidelines should prove useful for research into the properties of biomembranes and for development of bilayer-based biosensors.

Transitions in a Spread Film of a Side-Chain Liquid Crystal Polymer

Abstract A series of side-chain liquid crystal polymers have been screened for successhl deposition using the Langmuir Blodgett method. It was found that the best materials had glass transitions below room temperature. The behaviour of the spread film of one material was studied in detail using surface isotherms, surface potential, X-ray and neutron reflection techniques. It was found to undergo a phase transition from a thin, low density film to a thicker, more dense one as the surface pressure was increased. This corresponds to a reorientation of the mesogenic units so that about half of them point upwards. At higher pressure a transition to a multilayer occurs on the water surface. In the surface pressure range where deposition is possible, neutron reflection shows that the spread film has a stratum of close packed mesogenic units outermost and the total thickness (38 A) agrees very well with the smectic layer spacing in the bulk. This similarity in structure could explain the ease of deposition.

High-sensitivity biosensor based on LB technology and on nanogravimetry

Quartz-resonator nanobalances are utilized here as effective transducers capable of determining with high sensitivity the mass changes due to specific protein-protein, antigen-antibody and ligand-receptor binding or self-assembly of functional complexes. The resulting highly sensitive biosensor is based on two quartz resonators (one active and the second used as a reference) and on Langmuir-Blodgett (LB) protein monolayers. The electronics are composed of two separate blocks, one designed to acquire by a personal computer the data coming from the other card, a 24-bit digital counter directly connected to the two oscillators. In the case of immunosensor application, the active and reference oscillators are covered respectively by antibodies specific to a given antigen and by antibodies non-specific to the antigen, in order to disciminate the physical adsorption effects. Deposition of antibody monolayers is performed by the LB technique in a surface pressure range of 20–35 mN m −1 onto gluteraldehyde pre-treated quartz resonators. A thermal treatment of the antibody layer up to 150 °C results in the reorganization of the film, and significantly improves the sensitivity and the properties of the immunosensor.

Infrared external reflection spectroscopic studies of phase transitions in Langmuir monolayers of stearyl alcohol

There is a steadily growing body of evidence that much of the information available concerning the properties of Langmuir monolayers concerns systems which are not in a state of equilibrium. What are now known to be unrelaxed monolayers of stearyl alcohol exhibit a high surface pressure phase transition whose signature in the isotherm changes from a ‘‘kink’’ (0–8 °C), to a small nearly flat region (8–15 °C), and finally to another kink (at higher temperatures). We have carried out external reflection infrared spectroscopic studies of relaxed monolayers of stearyl alcohol along a representative isotherm from each of the mentioned temperature regions. The results of our studies indicate that in each region the surfactant hydrocarbon chain becomes more ordered (i.e., has fewer gauche conformations) as the surface pressure is increased. We find that (i) at 5 °C, throughout the surface pressure range where the change in intramolecular chain order occurs, the collective tilt of the hydrocarbon chains remains nearly constant. For this isotherm the kink signals the point at which the hydrocarbon chains have achieved a very high degree of intramolecular order, perhaps the all-trans limit. (ii) In the 11 °C monolayer, in the phase often referred to as ‘‘superfluid’’, the intramolecular disorder in the hydrocarbon chains is measurably greater than in the equivalent phases in the higher and lower temperature regions. We also show that in the relaxed monolayer the nearly flat portion of the isotherm observed in the unrelaxed monolayer is almost totally absent, leaving only a kink very similar to those observed at higher and lower temperatures. (iii) At 25 °C, although the hydrocarbon chains in the relaxed monolayer attain a relatively high degree of intramolecular order, the high surface pressure phase transition is not observed. Instead, the surface pressure levels off at a value below that at which the transition is expected, and below the equilibrium spreading pressure. We suggest that the leveling off at the surface pressure signals that molecules from the monolayer are forced into solution. (iv) At low surface pressure the spectroscopic data imply that the monolayer consists of a heterogeneous array of ordered islands.

Displacement currents generated during compression of fatty acid and phospholipid monolayers at the water-air interface

Displacement currents generated during the compression of monolayers of stearic acid and phospholipids (DSPC and DPPE) on the surface of water were investigated. Current peaks were observed not only in the surface pressure range larger than zero but also in the zero surface pressure range. Changes in the current in the zero pressure range were larger than those in the higher pressure range. The results suggested that the state of existence of molecules on the water surface changes remarkably, even in the zero surface pressure range, and that two processes contributed to the generation of the currents: one involving the movement and aggregation of molecules and the other concerning the movement of the aggregates. The effective dipole moments of the molecules on the water surface were determined to be 172 mD, 626 mD and 247 mD at 20 °C for stearic acid, DSPC and DPPE respectively.

A very simple and easily manufactured collimated anamorphotic system with two cylindrical mirrors in spectrograph AApS[formula omitted] (1992) 288–292

Pluto’s tenuous atmosphere exhibits remarkable seasonal change as a result of the planet’s substantial obliquity and highly eccentric orbit. Over the past two decades, occultations have revealed that the atmospheric pressure on Pluto has increased substantially, perhaps by a factor as large as 2 to 4, as the planet has moved from equinox towards solstice conditions. These data have also shown variations in the strength of the dynamical activity in the atmosphere, as revealed by the varying abundance and amplitude of spikes in the occultation light curves resulting from refractive focussing by atmospheric waves. Toigo et al. (Toigo et al. [2010]. Icarus, 208, 402–411) explored the possibility that these waves are caused by solar-induced sublimation and diurnal deposition from N2 frost patches, driven by weak vertical winds resulting from the rising and sinking gas as it is released from or deposited onto the surface. Here, we extend this model to account explicitly for seasonal variations in average insolation and for the significant damping of vertical wave propagation by kinematic viscosity and thermal diffusivity (Hubbard et al. [2009]. Icarus, 204, 284–289). Damping is extremely effective in suppressing vertical propagation of waves with vertical wavelengths of a few kilometers or less, and the dominant surviving tidal modes have characteristic vertical wavelengths λ∼10–13km. We estimate the expected strength and regional characteristics of atmospheric tides over the course of Pluto’s orbit for a variety of assumed spatial distributions of surface frost and atmospheric surface pressure. We compute the predicted strength of tide-induced wave activity based on the actual frost distribution observed on Pluto from Hubble Space Telescope (HST) observations (Stern et al. [1997]. Astron. J., 113, 827; Buie et al. [2010]. Astron. J., 139, 1128–1143), and compare the results to calculations for volatile transport models of Young (Young [2013]. Astrophys. J., 766, L22) and Hansen et al. (Hansen et al. [2015]. Icarus, 246, 183–191). We develop simple scaling rules to estimate the variation of the strength of tidal activity with surface pressure PS and solar declination δ⊙, and show that the maximum expected temperature perturbation at an atmospheric pressure of P=0.1Pa scales as dTmax∝cosδ⊙/PS. Wave activity is strongest in the near-equatorial region (latitude|ϕ|≲30°), being only weakly dependent on the detailed frost distribution. Using a 3-D time-dependent geometric optics ray-tracing code, we compute model light curves for the geometric circumstances of three high-SNR occultations (2002 August 21, 2006 June 12, and 2012 July 18), taking into account the detailed three-dimensional characteristics of the tides as different regions of the atmosphere are probed over the course of each occultation chord. We compare the strength and abundance of the scintillations in the models with those seen in the data, using both the HST frost maps and the volatile transport model predictions. The striking asymmetries in the strengths of spikes between ingress and egress seen in some events are reproduced in the tidal model simulations, due primarily to the latitudes probed during the occultation: occultations at high northern or southern latitudes uniformly have much weaker wave activity than more equatorial events. A surface pressure range of PS=1–2Pa provides the best match between models and observations. With the impending arrival of the New Horizons spacecraft at Pluto in 2015, we predict that wave activity in the upper atmosphere will be strongest at equatorial regions, and controlled in amplitude primarily by the surface pressure and damping effects, rather than by the detailed frost distribution. If Pluto’s atmosphere begins to collapse in the coming decades, we expect that future stellar occultations will provide evidence for greatly enhanced atmospheric wave activity.

Study of the Dynamic Behavior of Stearic Acid Monolayers at the Air-Water Interface in the Range of Low Surface Pressures by a Current-Measuring Technique

We have studied the dynamic behavior of stearic acid monolayers on the surfaces of pure water and of salt solutions in the range of immeasurably low surface pressures during the course of monolayer compression, by using a current-measuring technique. For monolayers formed on the surfaces of pure water and of deionized water containing cadmium ions, displacement current was generated when the area per molecule was smaller than about 60 Å2, whereas the current was negligibly small in the range of area per molecule greater than about 60 Å2. For monolayers formed on the surface of distilled water containing aluminum ions, displacement current was generated in the entire range during the course of monolayer compression. Finally, the mechanism on the current generation observed in the present current measurement was theoretically analyzed.

Surface free energy variations in Langmuir-Blodgett Multilayers: Contact angle measurements

Static contact angles have been measured during deposition of 22-tricosenoic acid on to hydrophobically treated silicon and the angles of immersion and emersion have been found to be identical under certain conditions. The difference between the two angles measured on one up- and downcycle was observed to decrease with increasing film thickness for the first 16 layers. The difference between the angles measured in bulk films was also observed to decrease with increasing deposition pressure until the angles measured on immersion and emersion were identical after sufficient layers had been deposited at or above 35 mN m −1. A new model for the transfer of molecules from the water surface to the substrate, which incorporates two different types of molecular reorganization, is proposed to explain these observations. The differences in surface free energies of successive bilayers are calculated for a range of surface pressures. It is found that these differences may be either positive or negative without violating the energy criteria for deposition.

Measurement of fluorescence depolarization for chlorophyll-a and chlorophyll-b in spread monolayers at the nitrogen-water interface

Fluorescence polarization has been measured for chlorophyll-a (Chl-a) and chlorophyll-b (Chl-b) in spread monolayers of dioleoylphosphatidylcholine as functions of monolayer compression in the surface pressure range 2–30 dyn cm −1. Concentrations of chlorophyll from a mole fraction of 0.0025 to pure chlorophyll were used. Polarization in Chl-b was found to be 3–4 times greater than in Chl-a under similar conditions and to exhibit a marked dependence on surface pressure. The polarization of Chl-a was only marginally affected by surface pressure.

Physical and surface properties of insect apolipophorin III.

Apolipophorin III (apoLp-III) from Manduca sexta has a molecular weight of 18,100. Based on its hydrodynamic properties (sedimentation and diffusion coefficients, frictional ratio, intrinsic viscosity) and its behavior during gel permeation chromatography, we concluded that apoLp-III is a prolate ellipsoid with an axial ratio of about 3. The circular dichroic spectrum of apoLp-III suggests that the protein contains approximately 50% alpha-helix. At the air-water interface, apoLp-III forms a monolayer which is gaseous at surface pressures less than or equal to 1 dyne/cm. The isotherm of this phase yields an excluded molecular area of 3800 A2/molecule (23 A2/amino acid). At a surface pressure of 22.1 dynes/cm, the monolayer undergoes a phase transition reminiscent of a first-order phase transition of pure lipids. The monolayer can be compressed in this surface pressure range to an area per molecule of 480 A2 (2.9 A2/amino acid). Since a globular protein of molecular weight 18,100 could occupy an area of only about 2000 A2 when bound to a surface, it is suggested that in the expanded state, apoLp-III must unfold on the surface, whereas in the compressed state, the molecule is oriented with its minor axis parallel to the water surface. ApoLp-III binds with high affinity (Kd = 1.9 X 10(-7)M) to both phosphatidylcholine- and diacylglycerol-coated polystyrene beads. All of these results are consistent with the proposal that apoLp-III plays a key role in increasing the capacity of the insect lipoprotein, lipophorin, to transport diacylglycerol by stabilizing the increment of lipid-water interface that results from diacylglycerol uptake.

Studies of Acylamino Acid Monolayers by π-A curves. I. Acylamino Acids with Alkyl Side Chain

Abstract In order to obtain some information regarding the behavior of amino acids at interfaces, the monolayers of N-acyl l-α-amino acids with alkyl side chains on water have been investigated by measuring the surface pressure vs. area curves at various temperatures. It has been found that N-octadecanoylglycine and N-octadecanoylalanine form the condensed monolayers over the whole surface pressure range measured, N-octadecanoylvaline forms the expanded monolayer at a lower surface pressure, and N-octadecanoylleucine and N-octadecanoylisoleucine collapse at high surface pressures. From the experimental results, it has been concluded that the amino acid residue with a long side chain occupies a large area at the air/water interface and interferes with the condensation of acylamino acid monolayer. It has also been found that the methyl esterification of amino acid residue makes the monolayer state unstable although it produces less significant effect than the increase in the alkyl chain length of amino acid residue.

Effect of surface pressure on mixed dipalmitoyl-lecithin—serum albumin monolayer composition

The lipoprotein surface film which covers the lung alveoli determines their stability and the observed lung pressure—volume hysteresis [1,2]. Serum albumin (SA) and dipalmitoyllecithin (DPL) mixed monolayers may serve as models for this alveolar surface film [3]. The change of surface pressure II of the mixed monolayers was measured during the cyclic alteration of the film area in the range 0–45 dyn cm −1 or 0–70 dyn cm −1. The initial monolayer composition changes, following the increase in surface pressure, as a result of three processes: 1. Conformational changes of SA molecules and reversible expulsion of protein residues. 2. Desorption (irreversible) of the biopolymer from the highly compressed mixed monolayers [7]. 3. Collapse of dipalmitoyllecithin. Various approaches were used for the evaluation of compositional changes of mixed monolayers during monolayer compression. In the range of surface pressures between 13 and 45 dyn cm −1 processes (1) and (2) above involve the displacement of practically all SA residues from the surface plane. At II > 70 dyn cm −1 the monolayers were found to collapse irreversibly and DPL molecules were found to leave the surface. We conclude that the effect of surface pressure on mixed monolayer composition in the range of surface pressures 0–45 dyn cm −1 is due to processes (1) and (2). In the range 0–70 dyn cm −1, processes (1), (2) and (3) occur.

The interaction of glycophorin with dipalmitoylphosphatidylcholine at the air—water interface

The interaction between glycophorin, the major sialoglycoprotein of the human erythrocyte membrane, and dipalmitoylphosphatidylcholine (DPPC) has been investigated in mixed monolayers at the air—water interface. Surface pressure—area isotherms have been measured for monolayers covering a range of glycophorin—DPPC molar ratios from 1:1765 to 1:44 at 20°C. The phase transition from the liquid-expanded to liquid-condensed monolayer states characteristic of pure DPPC monolayers is no longer observable in mixed monolayers at glycophorin to DPPC molar ratios in the range 1:355 to 1:44 and the isotherms at low areas per lipid molecule have a lower surface pressure than that calculated for an ideal mixture of the pure components. Analysis of the results indicates that in the range of surface pressure from 15–30 mNm −1, glycophorin withdraws between approximately 1300 to 200 DPPC molecules from participation in chain-melting in the monolayer.

Kinetics of N 2O decomposition on polycrystalline platinum

The kinetics of N 2O decomposition on polycrystalline Pt is studied over a wide range of surface temperatures (400 < T < 1200 °C) and pressures (0.01 < P N 2O < 0.50 Torr) in a steady-state flow system with conversions less than 6% so that differential rates are obtained. It is found that a single Langmuir-Hinshelwood (LH) rate expression correlates all rate data within ± 10% at all temperatures and pressures to give a reaction activation energy of 34.9 kcal/mole and a heat of adsorption of N 2O of 21.3 kcal/mole. A simple reaction mechanism which can give this rate expression is also proposed.

Thermodynamic characteristics of anionic—cationic adsorption films based on a butler-type equation, II

It was stated that the simplified form of an integral adsorption isotherm based on the Butler's equation and derived previously (D. Góralczyk and B. Waligóra J. Colloid Interface Sci. 82, 1 (1981)), describes satisfactorily the surface behavior of the solutions containing equimolar amounts of anionic and cationic surfactants with various surface ativity only within the range of great surface pressures. On the other hand, in the case of a small degree of surface coverage, deviation appear due to the presence of excess of ions with longer alkyl chain in the mixed adsorption film. The values of Δ G of adsorption for anionic—cationic surfactants are within the limits of experimental error equal to the sum of the values characteristic for single ionic substances being components of the mixture. The presence of adsorption film influences on the water structure in the surface layer which causes nonzero values of Δ G H2 O .

A possible orientation change of cardiotoxin molecule during its interaction with phospholipid monolayer

The monomolecular film technique was used in order to study the specific interactions of 4 cardiotoxins from Elapidae snake venom Naja mossambica mossambica with different phospholipids. The interaction, at pH 7.5, of cardiotoxin (10 -7M) with both neutral and negatively charged phospholipids occurs up to a very high critical surface pressure ( π = 45 dynes/cm with the latest). The apparent molecular area of cardiotoxin molecule, during its insertion into a negatively charged phospholipid film, presents only two characteristic values : 1400 Å 2 for π < 20 dynes/cm and 420 Å 2 for π > 30 dynes/cm , the transition occuring in a very narow range of surface pressure ( 25 ± 5 dynes/cm ). Thus, according to the surface pressure, the cardiotoxin may present two different orientations : “flat” or “edgewise” and the transition between both could account for lytic activity of cardiotoxin.

Regulation of phospholipase A2 activity by the lipid-water interface: a monolayer approach.

Interfacial regulation of phospholipase A2 activity on lecithin monolayers was investigated by using radioactively labeled enzyme. Labeling of the protein with 125I did not produce a change of the enzyme and protein properties as compared to the 3H fully amidinated phospholipase A2. The induction time observed during pre-steady-state kinetics reflects the rate-limiting step of the penetration of the enzyme in the interface. This penetration is reversible. However, in the surface pressure range where the enzyme is able to hydrolyze the lecithin films, the desorption of the protein from the film is slow as compared to the adsorption. Below a surface pressure of 10 dyn/cm nonspecific adsorption occurs. Using lecithins with fatty acids of different chain lengths, we have shown that the kinetics of the penetration process is governed by the packing density of the substrate molecules independent of the surface pressure. However, the steady-state surface concentration of the enzyme increases with the fatty acyl chain length of the lecithin, indicating that hydrophobic interaction occurs between phospholipase A2 and the lipid molecules at the interface. From the lecithins used pancreatic phospholipase A2 preferentially splits substrate molecules with nine carbon atoms in the acyl chain.

The contact angle of phospholipid monolayer on a wilhelmy plate

Contact angles of phospholipid monolayers with polished glass plate were measured by a Wilhelmy method. On monolayers of dipalmitoyl phosphatidyl choline and sphingomyelin with choline residue, we obtained finite contact angles which increased with the increase of surface pressure. On the other hand, on monolayers of dipalmitoyl phosphatidyl ethanolamine without choline residue and fatty acids, such as myristic acid and stearic acid, we had nearly zero contact angles in the surface pressure range of 0–40 dyn cm −1.