Effect of hydroxyl group position and system parameters on the features of hydroxystearic Acid monolayers.

The characteristic features of hydroxystearic acid monolayers OH-substituted in the mid position of the alkyl chain deviate considerably from those of the usual nonsubstituted stearic acid. The phase behavior, domain morphology, and two-dimensional lattice structure of 9-, 11-, and 12-hydroxystearic acids are studied, using pi-A isotherms, Brewster angle microscopy (BAM), and grazing incidence X-ray diffraction (GIXD), to obtain detailed information on the effect of the exact position of the OH-substitution. The pi-A isotherms of all three hydroxyoctadecanoic acids have an extended flat plateau region, the extension of which only slightly decreases with the increase of temperature.

Model membrane/substrate interactions: ethanol and procaine interactions.

The ability of ethanol to lower the surface tension of water plays a major role in its ability to affect membrane lipids. Typical lipids will show little expansion on exposure to ethanol substrates and may even show condensations. At the same time, the overall stability of the lipid phase is significantly reduced.

Surface Reactivity of Iron Oxide Pigmentary Powders toward Atmospheric Components: XPS, FESEM, and Gravimetry of CO and CO2 Adsorption.

The adsorption of carbon monoxide and carbon dioxide (CO and CO2) on a number of specially prepared alpha-Fe2O3 samples was measured gravimetrically at 25°C. The samples were prepared from a steel-pickling waste (97 wt% FeSO4·7H2O) by roasting the original material at 700°C for 5 h in air, oxygen, and nitrogen. Estimated surface coverages by the adsorbed CO and CO2 were made on the basis of nitrogen-adsorption-based surface areas, while the nature of the sample surfaces was investigated by both X-ray photoelectron spectroscopy (XPS) and field emission SEM (FESEM) techniques.

Surface Reactivity of Iron Oxide Pigmentary Powders toward Atmospheric Components: XPS and Gravimetry of Oxygen and Water Vapor Adsorption.

The adsorption of oxygen and water vapor on a number of specially prepared alpha-Fe2O3 samples was measured gravimetrically at 25°C. The samples themselves were prepared from a steel-pickling chemical waste (97 wt% FeSO4·7H2O) by roasting the original material at 700°C for 5 h in air, oxygen, and nitrogen. Estimated surface coverages by the adsorbed oxygen and water vapor were made on the basis of nitrogen-adsorption-based surface areas, while the nature of the sample surfaces was investigated by both X-ray photoelectron spectroscopy (XPS) and field emission SEM (FESEM) techniques.

A comparative monomolecular film study of 1,2-di-O-palmitoyl-3-O-(alpha- and beta-D-glucopyranosyl)-sn-glycerols.

The polar headgroup contribution to monolayer behavior of dipalmitoylglucosylglycerol has been examined through studies of 1,2-di-O-palmitoyl-3-O-(alpha-D-glucopyranosyl)-sn-glycerol (di-16:0-alpha GlcDG) and 1,2-di-O-palmitoyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol (di-16:0-beta GlcDG) in which the sugar headgroup is linked via an alpha or beta linkage to the diacylglycerol moiety. The results indicate that the limiting areas per molecule of the resultant condensed states are smaller than those of the corresponding phosphatidylcholine (DPPC) but larger than those of dipalmitoylphosphatidylethanolmine (DPPE). In the expanded state, while the areas per molecule are similar to those of DPPC at low pressures, both glycolipids occupy smaller areas at higher pressures.

Electrostatically induced growth of spiral lipid domains in the presence of cholesterol.

The formation of crystalline domains of the phospholipid L-alpha-dimyristoyl-phosphatidic acid containing 1 mol% cholesterol, was studied as a function of head group charge by fluorescence microscopy with monolayers at the air/water interface. It is shown that the usual dendritic growth occurs at low pH (8), whereas spiral domains are formed at high pH (11), where the head group contains two negative charges. The findings are ascribed to an electrostatically induced chain tilt that, in conjunction with an in-plane dipole moment, causes a ferroelectric state.

Mixed monolayers of straight-chain/branched-chain phospholipids. I. Mixed monolayers of distearoyl phosphatidylcholine and diisoeicosanoyl phosphatidylcholine.

The temperature dependence of the force/area isotherms of monolayer of distearoyl phosphatidylcholine (DSPC), diisoeicosanoyl phosphatidylcholine (DIEPC) and a complete mixed compositional range of these two lecithins are reported. The isotherms for DSPC closely resemble those previously reported for dipalmitoyl phosphatidylcholine but are shifted to higher temperatures by 16 degrees C. The isotherms of DIEPC, an iso-branched lecithin, show differences from these obtained for similar straight-chain lecithins in that the full condensed isotherms are more expanded, the fully expanded isotherms are more condensed and therefore the liquid expanded (LE)/liquid condensed (LC) intermediate region is significantly reduced.

Molecular packing in steroid-lecithin monolayers. IV. Mixed films of epicoprostanol with dipalmitoyl phosphatidylcholine.

Studies of the two-component monomolecular film system, dipalmitoyl phosphatidylcholine (DPPC) - epicoprostanol have been carried out at 21 degrees C utilizing a wide compositional range of films. The results obtained indicate that on initial mixing of the two components, epicoprostanol condensed expanded DPPC films to a greatly reduced degree and expanded condensed DPPC films to a significantly greater degree compared with cholesterol. It is thought that, even on an initial compressional procedure, partial microscopic segregation of epicoprostanol takes place.

Fluorescent probes in model membranes. II. Monolayer studies of 2,2'-(vinylenedi-p-phenylene)bisbenzoxazole, d-3-aminodesoxyequilenin and N-octadecylnaphthyl-2-amino-6-sulfonic acid with host-lipid tetradecanoic acid.

Film studies at the air-water interface have been carried out for pure films of 2,2'-(vinylenedi-p-phenylene)bisbenzoxazole (VPBO), d-3-aminodesoxyequilenin (EQ) and N-octadecylnapthyl-2-amino-6-sulfonic acid (ONS), and for mixed films with tetradecanoic acid for the first two fluorescent probes. Pure film isotherms indicate highly rigid non-monomolecular films for both VPBO and EQ, revealing the presence of strong intermolecular forces. In mixed films with tetradecanoic acid VPBO rapidly segregates with resultant film loss over a wide concentration range.

Fluorescent probes in model membranes I: anthroyl fatty acid derivatives in monolayers and liposomes of dipalmitoylphosphatidylcholine.

A study of three fluorescent anthroyl probes has been carried out using pure and mixed monomolecular films with dipalmitoylphosphatidylcholine. In addition, fluorescence depolarization and differential scanning calorimetry data were obtained from dipalmitoylphosphatidylcholine vesicles with incorporated anthroyl probes. The three probes used were 2-(9-anthroyl)palmitic acid.

Model membrane studies of spin-label probes. Part 1. Mixed monolayers of 12-nitroxide stearic acid and myristic acid.

Pure and mixed monomolecular films of a cell membrane spin label probe, 12-nitroxide stearic acid have been studied where myristic acid was selected as the host lipid. The behavior of 12-nitroxide stearic acid at the air water interface is understood in terms of two molecular configurations: erect (with only the carboxyl group in the interface) and bent (with both the carboxyl group and the oxazolidine ring in the interface). In mixed films both of these conformations play a role at high surface pressures.

A comparison of a spin-label and a fluorescent cell membrane probe using pure and mixed monomolecular films.

Monocular films studies of 12-nitroxide stearic acid and 12-(9-anthroyl) stearic acid reveal that deviations from the behavior of the parent molecule (stearic acid) are as much dictated by the polar, or nonpolar, nature of the probe group as by its size. In mixed films under membrane-like conditions, the spin label probe, 12-nitroxide stearic acid, exhibits positive deviations from ideality and should read too high a fluidity. The picture is, however, complicated by a tendency of this probe molecule to adopt a bent conformation, a tendency apparently enhanced by specific interactions with the lecithin zwitterion.

Water vapor from a lunar breccia: implications for evolving planetary atmospheres.

The exposure of a typical complex lunar breccia to hydrogen after a thorough outgassing produces a fully reduced surface state. Subsequent outgassing over a wide temperature range results in the production of water vapor formed from the chemisorbed hydrogen and oxygen from the lunar sample; the proposed mechanism has been confirmed in terms of the chemisorption of deuterium and the release of heavy water. Since the conditions of the experiments are consistent with those on the lunar surface, it is postulated that water vapor will be produced on the moon through the interaction of the solar wind with lunar soil.