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Query: UMLS:C0344329 (collapse)
 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The surface properties of fatty acid and fatty acid-alcohol mixtures were examined at 22-24 degrees C. At pH 12, sodium stearate forms a rigid surface film that generates an equilibrium spreading pressure of 16.5 dynes/cm. At pH 12, stearate-alkaline earth cation films collapse at the air-water interface and do not generate significant equilibrium spreading pressures. The rate of film collapse depends on the counterion decreasing in the sequence Ba2+ greater than Sr2+ greater than Ca2+. Stearate-stearyl alcohol mixtures form solid (condensed) films that are relatively stable and behave initially as homogeneous surfaces in their selectivities for counterions. Stearate-oleyl alcohol mixtures form fluid (expanded) films that are unstable. Lateral phase separations occur rapidly in fluid films and the stearate-alkaline earth cation phase collapses. The rate of film collapse in the fluid mixtures also depends on the counterion decreasing in the sequence Ba2+ greater than Ca2+. These surface properties suggest how a lipid anion may function as an ionophore in the translocation of alkaline earth cations.
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PMID:Surface phase separation and collapse of the stearate anion--alkaline earth cation complex. 83 1

Linolenic, linoleic, oleic, palmitic and stearic acids (FFA) collapse the electrical potential of pea stem mitochondria in the absence or in the presence of 0.5 mM Mg2+. Higher concentrations of this cation (5 mM) lower the rate of dissipation caused by linoleic, oleic and palmitic acids, while abolishing that induced by stearic acid. Carboxyatractyloside and ADP do not reverse the FFA-induced collapse both in the presence or absence of Mg2+. EDTA, EGTA or BHT do not influence the dissipation caused by FFA that, in addition, is not linked to lipid peroxidation evaluated as malondialdehyde or conjugated diene formation. Only linolenic acid sustains a peroxidation which, however, appears to be caused by its own oxidation catalysed by lipoxygenases rather than by membrane lipoperoxidation induced by this free fatty acid. These results suggest that neither the ATP/ADP exchanger nor lipid peroxidation appear to be involved in FFA-induced uncoupling in pea stem mitochondria.
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PMID:Electrical potential dissipation induced by free fatty acids in pea stem mitochondria. 164 82

Studies were performed to determine the mechanism by which stearic acid (18:0) selectively inhibits T-dependent immune responses in vitro. Incubation of mitogen-activated B and T cells with 18:0 resulted in dissimilar patterns of incorporation of the saturated fatty acid into their membranes. High-performance liquid chromatography (HPLC) analyses of T cells showed an accumulation of disaturated [corrected] 18:0-containing phosphatidylcholine (PC) that replaced normal cellular PC. Less significant quantities of the same PC species were seen to accumulate in B-cell membranes; rather, they increased their proportion of oleic acid (18:1)-containing PC. The different lipid compositions of the lymphocyte cell membranes after exposure to 18:0 were correlated with their plasma membrane potentials. In T cells, the accumulation of disaturated [corrected], 18:0-containing PC coincided with a rapid (within 8 hr) collapse of membrane integrity, as determined by flow cytometry. The collapse of membrane integrity was found to be time and dose dependent. No such depolarization was observed in B cells which, by virtue of their desaturating ability, were able to avoid incorporating large amounts of disaturated [corrected] 18:0-containing phospholipids into their membranes. It is proposed that a lack of stearoyl-CoA desaturase in T cells precludes them from desaturating exogenously derived 18:0, thus leading to increased proportions of 18:0-containing disaturated [corrected] PC in their cell membranes. The increased abundance of this PC species may enhance membrane rigidity to an extent that plasma membrane integrity is significantly impaired, leading to a loss of membrane potential and ultimately cell function and viability.
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PMID:Molecular basis for the immunosuppressive action of stearic acid on T cells. 237 42

Monolayer techniques were used to study the interactions of various lipids (cholesterol, lysophosphatidyl choline, phosphatidal ethanolamine, phosphatidyl choline, sphingomyelin, stearic acid, and lipids extracted from plasma high density lipoproteins and very low density lipoprotein) with the lipid-free protein subunit of rat plasma high density lipoprotein and with rat plasma albumin. The proteins were injected under the lipid monolayer at fixed area, and the increase in surface pressure (decrease in surface tension) was measured as a function of time. With all lipids, both the rate and magnitude of this increase were greater with the apolipoprotein than with albumin. The degree of film penetration of pure lipid films (at an initial film pressure of 15 dynes/cm) by the two proteins followed the same order: cholesterol > phosphatidal ethanolamine > phosphatidyl choline > stearic acid > sphingomyelin > lysophosphatidyl choline. Other variables studied were protein concentration, initial film pressure, and pH. Two distinctive properties of the apolipoprotein were the penetration of lipid films at pressures above the collapse pressure of the protein, and the formation of a film even at low salt concentration. High surface activity and strong interaction of HDL-protein with lipid monolayers may be associated with the flexibility of the protein molecule due to absence of disulfide bridges. The unusual surface activity of HDL-protein may be intimately related to the mechanism of formation of the lipoprotein.
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PMID:Lipid monolayers: interactions with the apoprotein of high density plasma lipoprotein. 572 15

The mechanism of interaction between chlorpromazine (CPZ) and artificial lipid membranes, negatively or positively charged liposomes was studied by an electron spin resonance (ESR) technique. Analysis by a 5-doxyl stearic acid (DS) spin probe indicated that regardless of the electric charge of liposomes, CPZ disordered the hydrophobic region near the surface of lipid membranes at CPZ/lipid > 1. In the same CPZ/lipid range, the lysis of liposomes was observed, and it was considered that the formation of the CPZ/lipid mixed micelles as a consequence of this collapse of liposomes would probably lead to the disordering of the 5-DS reporting region. As to the middle portion of the fatty acyl chains reported by the 12-DS spin probe, the membrane disordering action of CPZ was only detected with the negatively charged liposomes at a ratio of CPZ/lipid < 1, but no membrane alteration was observed with the positively charged liposomes, regardless of the concentration range of CPZ used. In comparing these two opposite results, it is conceivable that the disordering at the 12-DS reporting region was probably induced by the cationized CPZ which would enter into the hydrocarbon-polar interface, leading to an expansion of the space between the hydrocarbon chains at this area. Also, a strong influence of CPZ on the innermost portion of the lipid bilayers was observed with both the negatively and positively charged liposomes, as reported by the 16-DS probe. This perturbing action presumably occurred when undissociated CPZ molecules penetrated into the center of the bilayers (lipid core), which could have resulted in a reduction of hydrophobic interactions of the lipid molecules.
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PMID:ESR study of membrane perturbation and the lysis of liposomes induced by chlorpromazine. 812 59

The interaction of copper ions with a stearic acid Langmuir monolayer resulting in an extremely high level of copper binding to the monolayer in amounts much larger than the number of stearic acid molecules in the monolayer was studied. The shape of the pressure-area isotherm changed drastically upon pH changes from 4 to 6 in the presence of copper ions in the aqueous phase (at concentrations of 10(-5) to 10(-3)(M) or upon addition of copper ions to the aqueous phase under different monolayer compressions. The copper ion concentration changes in the bulk phase, caused by binding to the monolayer, were studied by EPR at the equilibrium after intensive mixing of the bulk phase and were found to depend on pH of the aqueous phase and the extent of monolayer compression. The highest level of binding (up to 100 copper ions per stearic acid molecule, pH 5.6, initial copper concentration 5.10(-4) M) was observed at a surface pressure of about 20 mN/m; further compression of the monolayer and the respective increase in surface pressure caused the reverse growth of aqueous phase copper ion concentration. At the collapse and destruction of the monolayer, the copper ion concentration in the bulk phase was similar to that in the absence of the monolayer. The EPR spectra and SAXS diffractograms of copper-containing stearic acid monolayers confirmed the high copper content in LB films obtained. An STM study of pure stearic acid and the copper-containing monolayer LB films, transferred to graphite wafers from the water subphase surface (pH 5.4) at various copper concentrations, discovered nanosized (about 5 nM) cluster formations on the monolayer surface. The data obtained indicate that the interaction of a charged Langmuir monolayer with copper ions and formation of copper-containing nanostructures depends on monolayer compression and is determined by the arrangement, order, mobility of the monolayer stearic acid molecules and by electrostatics at the interface.
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PMID:Interaction of copper ions with stearic acid Langmuir monolayers and formation of cluster structures in monolayers and Langmuir-Blodgett films. 923 65

The effect of strength of attraction and volume fraction on the mechanical properties of alumina particle networks were investigated. Alumina particle gels were formed reversibly and in situ in the rheometer by cooling alumina particle suspensions with adsorbed poly(12-hydroxy stearic acid) suspended in a marginal solvent, hexanol. The collapse of the polymer layer with decreasing solvency (temperature) induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. The gelation temperature depends on volume fraction. At the gel temperature, Tgel, the gel becomes predominantly elastic; at temperatures below Tgel, the elasticity increases with decreasing temperature. We find that the elastic modulus data, measured over a wide range of volume fraction (0.2 < &phi; < 0.425) and temperature (10-14 degreesC), follows: G = G0(&phi; - &phi;g)s. This scaling suggests the prefactor and exponent to be independent of temperature. We present some arguments for why subjecting a particle gel to a preshear procedure might result in an temperature-dependent prefactor. By invoking such an effect, we are able to rescale and collapse previously published moduli data on presheared suspensions according to the (&phi; - &phi;g) expression. Copyright 1999 Academic Press.
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PMID:Viscoelastic Properties of Particle Gels. 987 49

A Langmuir monolayer of stearic acid on pure water and in the presence of certain divalent metal ions such as Cd and Pb at pH approximately 6.5 of the subphase water collapses at constant area, while for other divalent ions such as Mg, Co, Zn, and Mn at the same subphase pH the monolayer collapses nearly at constant pressure. Films of stearic acid with Cd, Pb, Mn, and Co in the subphase (at pH approximately 6.5) have been transferred onto hydrophilic Si(001) using a horizontal deposition technique, just after and long after collapse. Electron density profiles obtained from X-ray reflectivity analysis show that a three-molecular-layer structure starts to form just after constant area collapse, where in the lowest molecular layer, in contact with the substrate, molecules are in asymmetric configuration, i.e., both hydrocarbon tails are on the same side of the metal-bearing headgroup that touches the substrate, while the molecules above the first layer are in symmetric conformation of the tails with respect to the headgroups. Further along collapse, when the surface pressure starts to rise again with a decrease in area, more layers with molecules in the symmetric configuration are added, but the coverage is poor. On the other hand, only bimolecular layers form after constant pressure collapse, with the lower and upper layers having molecules in asymmetric and symmetric configurations, respectively, and the upper molecular layer density increases with compression of the monolayer after collapse. A "Ries mechanism" for constant area collapse and a "folding and sliding mechanism" for constant pressure collapse have been proposed.
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PMID:Effect of metal ions on monolayer collapses. 1595 39

This paper reports the pi-A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). pi-A isotherm studies of mixed monolayer as well as the remarkable change in collapse pressure of the mixed monolayer isotherms definitely show that CA is incorporated into PMMA and SA matrices. However, CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates, as is evidenced from the scanning electron micrograph picture. The nature of these aggregated species in the mixed LB films has been revealed by UV-vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low-dimensional aggregates in the mixed LB films. Intensity distribution of different band systems is highly sensitive to the microenvironment of two different matrices as well as also on the film thickness.
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PMID:Role of microenvironment in the mixed Langmuir-Blodgett films. 1658 8

Langmuir monolayers of stearic acid on Co ions in the aqueous subphase have been deposited at different stages of constant pressure collapse, on hydrophilic Si(001) using a modified version of the inverse Langmuir-Schaefer method of horizontal deposition. The electron density profiles (EDPs) along the depth of the deposited films, extracted from the x-ray reflectivity data, show that a monolayer to bi-molecular layer transformation takes place after collapse. The molecules in the lower monolayer have asymmetric configurations with head groups touching water and tails in air, whereas molecules in the upper layer are in symmetric configurations with tails on both sides of the heads. Atomic force microscopy images of the deposited films after collapse, however, show nearly circular islands of height more than that of the bimolecular layer observed in the EDP. As pressure increases, ridges are seen to coexist with these islands. Although the coverage of such islands and ridges is low, they play an important role in determining the growth mode. The growth of the wetting and island layers, taken together, has a striking similarity with the Stranski-Krastanow mode, observed usually for heteroepitaxial growth.
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PMID:Growth of a collapsing Langmuir monolayer. 1680 47


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