Cholesterol Monolayers Research Articles

Electron micrographs of cholesterol monolayers

Electron micrographs of cholesterol monolayers

Mixed monolayers of cholesterol with fatty acids

The surface pressure versus mean area curves of the mixed monolayers of cholesterol with n-long chain fatty acids was obtained at various compositions and temperatures. It was observed that the area occupied by the expanded monolayer of fatty acid becomes somewhat smaller by addition of cholesterol. The surface pressure of the transition from expanded to condensed state varied with the composition and temperature, whereas the area occupied by the condensed monolayer composed of cholesterol and fatty acid satisfied the additivity rule. The two-dimensional phase diagram of the cholesterol-myristic acid system was constructed and the partial molar enthalpy of myristic acid was evaluated. It was concluded that cholesterol and fatty acid are miscible in the expanded state and immiscible in the condensed state and that the interaction between them is not specific but large enough to form the homogeneous expanded monolayer.

Interaction of morphine with cholesterol monolayers

Interaction of morphine with cholesterol monolayers

The Two-step Collapse of Mixed Monolayers of Cholesterol and Its Esters

Abstract Mixed monolayers of two insoluble components out of cholesterol and its acetate and propionate were spread on a dilute aqueous solution of disodium hexadecyl phosphate. The curves of the surface pressure against the molecular area were found to have two kink points, collapse points, although the curves of each component, and also that of the “concollapse” mixture, had only one collapse point. The diagram showing the relation between these two collapse pressures and the composition was entirely analogous to the phase diagrams of bulk mixtures which have an eutectic point. It has, therefore, been concluded that the mixed monolayer of two mutually immisible substances undergoes a two-step collapse. At the lower collapse point, one of the two components, i, starts separating from the monolayer. The lower collapse pressure, FCl′ varies with the mole fraction, Xi, according to FCl′=Fol′−(kT⁄Aol)lnXi. At the higher collapse point, the other component starts separating as well. Upon further compression, the surface pressure remains unchanged at the higher collapse pressure, which is equal to the equilibrium-spreading pressure and is independent of the composition.

Lateral diffusion of cholesterol in monolayers

The surface diffusion coefficient of cholesterol in cholesterol monolayers has been measured as a function of cholesterol surface concentration. Two different radio-chemical methods, one integral and the other differential, were developed which gave comparable results. In the integral method two cholesterol monolayers, one of which is radioactive, are isolated on inert hydrophilic supports and then brought into contact. After some time the supports are separated and the radioactivity of the supports is measured. The differential method is an autoradiographic experiment. Two cholesterol monolayers, one of which is radioactive, are separated by means of a thin barrier. Upon removal of the barrier and at later times, an autoradiographic plate is brought to within a fraction of a mm from the aqueous surface and exposed. The plates are developed and analyzed. The data show that the cholesterol surface diffusion coefficient in the dilute monolayers is approximately 10 −6 cm 2/s and is nearly independent of surface concentration up to a concentration corresponding to an area of 40 Å 2/molecule. As the monolayer becomes compressed beyond this surface concentration, the diffusion coefficient decreases abruptly with the deeply decreasing surface tension to about 10 −7 cm 2/s, when a fully condensed surface layer of 38 Å 2/molecule is reached. This diffusion coefficient is of the same order of magnitude as the diffusion coefficients measured in lipid bilayers and in membranes.

Drug‐Biomolecule Interactions: Mechanisms and Kinetics of Interactions of Biomolecules at Interfaces

At the air‐water interface, the area occupied by the molecules of each component of mixed monomolecular layers of cholesterol with hexadecyl alcohol, hexadecylic acid, or hexadecylamine was independent of the presence of the other component. The values of the free energy of mixing of these lipids were within the range of the entropic factor of the free energy even at high surface pressures. Mixed monolayers of cholesterol and bovine serum albumin showed a similar independence of the area per molecule and of the free energy of mixing values when the concentration of the protein was expressed in terms of amino acid residues per molecule of protein forming the mixed monolayer. Higher values of the free energy of mixing were obtained for mixed monolayers of cholesterol with dipalmitoyl lecithin and dipalmitoyl phosphatidylethanolamine than were expected from an entropic factor. The interaction between monomolecular layers of lipidic biomolecules with bulk subphase components, the energy of activation, interaction kinetics, and effects of added electrolytes were also studied. The implications of these data to a mechanism of action are discussed.

Letter: On the interaction of tetrodoxin with cholesterol monolayers.

Letter: On the interaction of tetrodoxin with cholesterol monolayers.

ChemInform Abstract: FORMATION AND COLLAPSE OF MIXED MONOLAYERS OF TRILAURIN WITH CHOLESTEROL AND WITH TRISTEARIN

The surface pressure-area curves of mixed monolayers and the equilibrium spreading pressure of solid mixtures were measured at 25 °C for cholesterol and trilaurin as well as tristearin and trilaurin. The phase diagrams of these mixtures were obtained by the measurement of the melting point. From two curves, one representing the relation between the collapse pressure (if the mixed monolayer was not overcompressed) and the composition of mixed monolayer, and the other representing the relation between the equilibrium spreading pressure and the composition of solid mixture, it was shown that the compositions of the mixed monolayer and the solid mixture coexisting in equilibrium were obtained. It was found that when the mixed monolayer of cholesterol and trilaurin was compressed, pure trilaurin began to collapse and deposit, and that the mixed monolayer of tristearin and trilaurin was apt to be overcompressed. It was concluded on the basis of phase rule and thermodynamics for plane interfaces that the equilib...

Reflection spectra from monolayers of amphotericin B and amphotericin B-cholesterol spread on water

Polarized specular reflection spectra have been obtained of the antibiotic polyene, amphotericin B, in its monolayers and in those of cholesterol in its expanded-liquid phase. An analysis of the reflectivity of the long wavelength member of the 3 band group observed in these spectra gives both its extinction coefficient and the orientation of its transition moment. In the case of the amphotericin B monolayers, an increase in surface pressure from 9.4 to 15.6 dynes/cm produces a decrease in the molar extinction coefficient from 1.20 · 10 5 to 0.65 · 10 5 and possibly a decrease in the angle which the heptaene transition moment makes with the surface. Accompanying these changes is red-shift of all three bands which shifts the long wavelength band from 4072 to 4150 Å. These changes in the molar extinction and wavelength with compression appear to be due to the formation of polyene-polyene complexes. The effect of an expanded-liquid monolayer of cholesterol on the surface interactions of amphotericin B is to increase the polyene orientation from 6° to 35° and shift the 4150 Å band to 4190 Å without further affecting the extinction coefficient of 0.65 · 10 5. The values of the wavelengths, extinction coefficients and orientations obtained from the reflection spectra of the two polyene monolayers were in agreement with those obtained from the transmission spectra of similar systems.

The equilibrium penetration of monolayers

The theory of monolayer permeation developed by Barnes, Quickenden, and Saylor has been modified to describe the equilibrium penetration of an insoluble monolayer by a surfactant in the subphase. The resultant equation has been tested against the experimental data of Pethica for the penetration of cholesterol monolayers by sodium dodecyl sulfate. These data give the required linear from when the adsorption is plotted against the reciprocal of the area per monolayer molecule. Values of the two parameters calculated from this plot are compared with the known properties of cholesterol monolayers and of sodium dodecyl sulfate. It is concluded that it is the size of the dodecyl sulfate ion that determines the extent of the penetration and that electrostatic effects arising from the ionic charge are not important.

Mixed monolayers of cholesterol and hexadecyl—trimethylammonium bromide

Cholesterol monolayers were spread over solutions of hexadecyl—trimethylammonium bromide (HDTAB) with extensive precautions to avoid contamination. The force-area curves for the cholesterol-HDTAB monolayers were not dependent upon the HDTAB concentration. The primary effects of the HDTAB were to make the cholesterol monolayers more gaseous, and to increase the area per cholesterol molecule from 40 Å 2 to 70 Å 2 at the collapse point. The stabilizing effect of HDTAB on cholesterol black lipid membranes is discussed. The kinetics of diffusion of HDTAB from monolayers to bulk was observed to obey first order approach toward equilibrium.

Formation and Collapse of Mixed Monolayers of Trilaurin with Cholesterol and with Tristearin

Abstract The surface pressure-area curves of mixed monolayers and the equilibrium spreading pressure of solid mixtures were measured at 25 °C for cholesterol and trilaurin as well as tristearin and trilaurin. The phase diagrams of these mixtures were obtained by the measurement of the melting point. From two curves, one representing the relation between the collapse pressure (if the mixed monolayer was not overcompressed) and the composition of mixed monolayer, and the other representing the relation between the equilibrium spreading pressure and the composition of solid mixture, it was shown that the compositions of the mixed monolayer and the solid mixture coexisting in equilibrium were obtained. It was found that when the mixed monolayer of cholesterol and trilaurin was compressed, pure trilaurin began to collapse and deposit, and that the mixed monolayer of tristearin and trilaurin was apt to be overcompressed. It was concluded on the basis of phase rule and thermodynamics for plane interfaces that the equilibrium spreading pressure is constant regardless of the composition of solid mixture if the solid mixture consists of two phases of mixed crystals, and that cholesterol and trilaurin form a regular solution in mixed monolayer.

Interaction of amphotericin B with monolayers of egg lecithin and cholesterol: polorized absorption spectra

Polarized absorption spectra have been obtained of the antibiotic polyene, amphotericin B, interacting with monolayers of egg lecithin, cholesterol and equimolar egg lecithin-cholesterol at low and high surface pressures. An expression is derived which enables the determination from the polarization data of the orientations of the transition moments of the polyene absorption bands at 4077 and 3645 Å. For some of the systems the 3645-Å band is replaced by a previously unreported band appearing between 3610 and 3632 Å. The orientation of the 4077-Å transition moment (parallel to the long molecular axis) is found to vary from an angle of 64 ° with the surface for the low-pressure monolayers of cholesterol to 21 ° for the high-pressure films of egg lecithin-cholesterol. For the band between 3610 Å and 3645 Å, the angle varies from 90 ° for cholesterol to 18 ° for the high-pressure mixed-lipid film. It is found that a large increase in surface pressure of the cholesterol and egg lecithin-cholesterol monolayers causes a decrease in the angle of the 4077-Å moment for both films and that of the higher energy moment for the mixed film. Increasing the content of cholesterol in these monolayers rotates the orientation of the transition moments for both bands toward the surface normal, the change being greatest for the low-pressure films. The effectiveness of amphotericin B in lowering the surface tension of these lipid monolayers is related to its binding, orientation and extent of penetration. For low-pressure cholesterol films where the surface interaction with the polyene is greatest, the binding and penetration are large and the polyene molecule is oriented with its long dimension nearly perpendicular to the surface.

The interaction of the “Folch-Lees” protein with lipids at the air-water interface

1. 1. The interaction of “Folch-Lees” apoprotein with different lipids has been studied at the air-water interface. Measurements of the change in surface pressure showed a high affinity of the Folch-Lees protein for a variety of myelin lipids such as cerebroside sulphate, phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine and cholesterol. Lipids such as sphingomyelin, cerebroside and lecithin show markedly less affinity for the Folch-Lees protein. 2. 2. The remarkable interaction of the Folch-Lees protein with cholesterol is dependent on the sterol structure. Epicholesterol, cholest-4-en-3-one, coprostanol, lanosterol and androstanol showed a reduced binding in this order. 3. 3. The two major proteins, the Folch Lees protein and the A 1 basic protein, show a different lipid affinity. The subsequent injection of A 1 basic protein and Folch-Lees protein underneath a cholesterol monolayer shows a preferential binding of Folch-Lees protein with cholesterol and a rejection of A 1 basic protein from the interface. The subsequent injection of A 1 basic protein and Folch-Lees protein underneath a cerebroside sulphate monolayer shows that both proteins can bind to cerebroside sulphate. The A 1 basic protein shows however the highest affinity for this typical myelin lipid.

The effects of DDT and its analogs upon lecithin and other monolayers

The effect of DDT, 11 analogs, dieldrin, and lindane was studied on the pressure-area curves obtained by compressing monolayers of lecithin. The minimum cross-sectional area of lecithin and the compounds was measured by photography of models. All compounds shifted the pressure area curves in a direction and to an amount that suggested they formed 1:1 complexes with lecithin, and the complex had the cross-sectional area of the compound. DDT did not complex with cholesterol monolayers. Both DDT and DDMU formed complexes with phospholipids from Torpedo electroplax which resembled those with lecithin. The lack of difference in effects on monolayers between physiologically active and inactive analogs indicated that the monolayer effects did not explain the physiological action of DDT.

Tetrodotoxin–cholesterol interactions at the air–water interface

A claimed, specific interaction of tetrodotoxin with cholesterol monolayers could not be repeated. An observed expansion of cholesterol monolayers on a subphase of the toxin in citrate and phosphate buffer was shown to be time dependent and probably due to a surfactant impurity of the phosphate salts.

Interaction of Cholesterol with Dibenzanthracenes at Air-Water Interface

A film balance approach using continuous compression was used to study the interaction of the carcinogen 1,2:5,6-dibenzanthracene and the noncarcinogen 1,2:3,4-dibenzanthracene with insoluble monolayers of cholesterol. Surface pressure and surface potential of mixed dibenzanthracene-cholesterol films spread on water and saline were studied. Results showed an association of 1,2:5,6-dibenzanthracene and no association of 1,2:3,4-dibenzanthracene with cholesterol. Surface potential data support the concept of carcinogen-cholesterol association. The data show a useful difference between a carcinogenic and a noncarcinogenic isomer at the air-water interface.

Influence of the polar group on interactions between phospholipids and sterols in monolayers. Rapid decomposition of phosphatidylethanolamines and cholesterol in monolayers at pH 11.9.

AbstractPressure‐area curves were obtained for monolayers of pure lipids or mixtures of lipids in order to investigate the effect of different polar groups upon interactions between molecules of various structures. Cholest‐4‐ene‐3‐one and cholestan‐3‐one were measured alone and in mixtures with di 16∶0‐lecithin, and 16∶0–18∶1‐lecithin, 16∶0–18∶3‐lecithin, and 16∶0–20∶4‐lecithin. All lecithin films were somewhat condensed by the ketones, but much less so than by cholesterol. Cholesterol was measured alone and with either di 16∶0 phosphatidylethanolamine (PE) or rat liver phosphatidylethanolamine at pH 2.0, 5.4 and 11.9. Cholesterol condensed the natural PE at pH 2.0 and 5.4, but not the di 16∶0 PE. At pH 11.9, both cholesterol and PE were chemically unstable in monolayers. The strong interaction of cholesterol with mixed phosphatidylethanolamines in monolayers suggests that cholesterol may also interact strongly with PE in membranes, of which PE are important components.

Ionic channels and nerve membrane constituents. Tetrodotoxin-like interaction of saxitoxin with cholesterol monolayers.

Saxitoxin (STX) and tetrodotoxin (TTX) have the same striking property of blocking the Na(+) channels in the axolemma. Experiments with nerve plasma membrane components of the squid Dosidicus gigas have shown that TTX interacts with cholesterol monolayers. Similar experiments were carried out with STX. The effect of STX on the surface pressure-area diagrams of lipid monolayers and on the fluorescence emission spectra of sonicated nerve membranes was studied. The results indicate a TTX-like interaction of STX with cholesterol monolayers. The expansion of the monolayers caused by 10(-6)M STX was 2.2 A(2)/cholesterol molecule at 25 degrees C. From surface pressure measurements at constant cholesterol area (39 A(2)/molecule) in media with various STX concentrations, it was calculated that the STX/cholesterol surface concentration ratio is 0.54. The apparent dissociation constant of the STX-cholesterol monolayer complex is 4.0 x 10(-7)M. The STX/cholesterol ratio and the apparent dissociation constant are similar to those determined for TTX. The presence of other lipids in the monolayers affects the STX-cholesterol association. The interactions of STX and TTX with cholesterol monolayers suggest (a) that cholesterol molecules may be part of the nerve membrane Na(+) channels, or (b) that the toxin receptor at the nerve membrane shares similar chemical features with the cholesterol monolayers.

Intermolecular Interaction and Dissolution Rate of the Mixed Monolayers of 1-Monoglycerides and Cholesterol

Intermolecular Interaction and Dissolution Rate of the Mixed Monolayers of 1-Monoglycerides and Cholesterol