Water monomolecular films spread

Further, Mann and McGregor (12) suggested that the study of the ESR spectral characteristics of labeled molecules in monolayers could lead to an experimental determination of surface viscosity numbers for expanded monolayers, While we do not report surface viscosity numbers here, we do report the spectra obtained using two ellipsoidal molecules in monomolecular films spread on water. We also report the low surface pressure isotherms for these systems and comment on the extent to which isotherms in general reflect molecular motion in monolayers. 

Glazer and Dogan (4) studied BSA spread as a monomolecular film on water. In general, the surface titration curve resembled that of BSA in solution, with two inflections in the pH ranges 3.5 to 6.5 and 10.0 to... 

The trough itself measured 20 x 12 cm, was milled from a block of Teflon, and held approximately 750 ml of liquid. Monomolecular films were prepared on a subphase of (ultrapure) distilled water or on aqueous subsolutions containing varying concentrations of either NaF, HC1, NaOH, thiourea, or dimethyl sulfoxide (DMSO). Aliquots, between 50 and 250 pi, of the ethanol-solubilized microbubble-surfactant mixture were applied slowly to the surface of the subsolution from a Hamilton microsyringe. It was found unnecessary to allow the films to stand for more than 2 min after spreading before taking measurements. Furthermore, following compression or expansion, the surface pressure was observed to remain constant for periods of up to at least 10 min. All measurements were made at 20.0 0.5°C. 

Fatty acids spread spontaneously on water to form a monomolecular film. A benzene solution containing 0.10 mm3 of stearic acid is dropped into a tray full of water. The acid is insoluble in water, but spreads on the surface to form a continuous film covering an area of 400 cm2 after all of the benzene has evaporated. What is the average film thickness in (a) nanometers and (b) angstroms ... 

Monomolecular films of the membrane protein rhodopsin have been investigated in situ at the air-water interface by PM-IRRAS and X-ray reflectivity in order to find conditions that retain the protein secondary structure [104]. The spreading of rhodopsin at 0 or 5 mN/m followed by a 30 min incubation time at 21 °C resulted in the unfolding of rhodopsin. In contrast, when spreading is performed at 5 or 10 mN/m followed by an immediate compression at, respectively, 4 or 21 °C, the secondary structure of the protein is retained. 

A detailed account of the mechanism of spreading will be given in Chapter VI the final state of a monomolecular film with the excess collected locally in small drops seems always to be found with pure substances. Complex mixtures may, however, form much thicker films of considerable durability, e.g. kerosene on water. 

Solids spread on liquids to a monomolecular film, as has been described in Chapter II.4 Owing to the non-mobility of the particles of a solid, the molecules which are driven out next the water cannot drag a thick layer of the solid along with them, as happens when liquids spread. 

To test this model, the surface properties of the 22-kDa fragment at an air—water interface have been examined. The air—water interface system has been used extensively to model the interaction of apoli-poproteins with lipid (Phillips and Sparks, 1980 Shen and Scanu, 1980 Camejo and Munoz, 1981 Phillips and Krebs, 1986). When the 22-kDa fragment was spread as monomolecular film in a Langmuir trough, the surface pressure-molecular area isotherm was calculated to be —16 A /... 

When 1 cm of a solution containing 8.5 mg per 100 cm of stearic acid (mol. wt. = 284.3) dissolved in a volatile organic solvent is placed on the surface of water in a Langmuir trough, the solvent evaporates off, leaving the stearic acid spread over the surface as an insoluble monomolecular film. If the surface area occupied by the film is 400 cm, calculate the area occupied by each molecule of stearic acid in the film. 

A small quantity of a substance such as a fatty acid is added to the surface of a liquid such as water so that it spreads out to form a monomolecular film on the liquid, thereby lowering its surface tension. 

The measurement of surface pressure (jr) was accomplished using the Wilhelmy method in which a glass slide was partially immersed in the water subphase and the effective change in weight of the slide was recorded after a monomolecular film was spread and compressed at the air-water interface. The equation relating ir to change in weight of the slide is ... 

In the LB technique, a monolayer of amphiphilic molecules, prepared at the air-water interface, is transferred to a substrate, thus giving a monomolecular film. The molecules must be solvable in a volatile, water-insoluble (organic) solvent, but not, or to a very limited extent, in water. Thus, when the solution of the molecules in the organic solvent is spread over the surface of water, the solvent evaporates, leaving a monolayer of molecules at the air-water interface. This monolayer can be compressed and transferred to a substrate. When the molecules are replaced by colloidal, nanosized particles, monolayers of these particles on a substrate are obtained. Smectites are especially well suited for the LB technique. The elementary clay sheets are about 1 nm thick and a few tens to hundreds nm wide and long. In the alkali- or alkaline earth form, they are hydrophilic, but by ion exchange with suitable amphiphilic cations, they become hydrophobic. There are then two ways to prepare mono-layers of smectite clay particles by the LB technique. 

A monomolecular layer, or monolayer, can exist only at interfaces. Interfaces between two phases of the same compound (ice in water, water in contact with water vapour, etc.) are highly d)mamic and are continuously changing in molecular dimensions. A much less disturbed interface is that between a solid and liquid or between two liquids which are usually insoluble. However, most of the data available to date have been recorded either on unlmolecular films spread on liquid surfaces (liquid-air interfaces) or films transferred on to solid surfaces. 

The presence of both the non-polar hydrophobic hydrocarbon chain and the polar hydrophilic -COOH group is reflected in their physical characteristics. Thus fatty acids may be spread on the surface of water as monomolecular films or monolayers in which the molecules are orientated so that the polar -COOH group penetrates the surface and the hydrocarbon chain projects away from it. This property is even more pronounced in the case of the phospholipids. 

Langmuir Blodgett (LB) film preparation The LB films of regenerated cellulose were prepared in accordance with an earlier publication by Schaub et al. (21). Trimethylsilyl (TMS) cellulose (Jena Biosciences, Ltd.) was used as chloroform-soluble derivative that was spread on the water sur ce of an LB-trough (KSV 2000) as a monomolecular film (20). A hydrophobic glass slide with a gold coating on one side was used as the SPR-suitable substrate for LB-film depositioa... 

Under some circumstances, a material can spread out into a monatomic or mono-molecular layer or film. For example, solutions of stearic or oleic acid (both long-chain fatty acids) in a hydrocarbon solvent can be carefully dripped onto water when the solvent evaporates, the remaining fatty acids can arrange themselves into a monomolecular film on the water s surface. Such films have a definite surface coverage (that is, a definite area) depending on the number of fatty acid molecules present. 

There resulted an investigation of the extent to which water adsorbed on various silicate glass and related surfaces affects the spreading and the equilibrium contact angle of various pure organic liquids Of especial interest was the effect of the transition of the physically adsorbed water film from a polymolecular to a monomolecular film. 

The surface properties of the cyclic decapeptide antibiotics have been reported by Few and co-workers [78,79]. The surface tension at the air-water interface of ty rocidine A is greater than that of gramicidin SA, whilst polymyxin E causes only a slight decrease in the surface tension of the water [78]. The surface properties of the polymyxins A, B, Q D and when spread as monomolecular films have been related to their nephrotoxic action by Few and Schulman [79]. 

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