Monomolecular films at an air-water

Cohesive Forces in Monomolecular Films at an Air-Water Interface... 

N.L. Gershfeld, Cohesive forces in monomolecular films at an air-water interface, Advan. Chem. Ser. 84, 115 (1958). 

Figure 8.2 Association of phospholipid molecules, (a) As a monomolecular film at an air-water interface (b) as a bilayer in water (c) as a micelle in water (d) as a micelle in a non-polar solvent...

As can be seen from Fig. 6.3, it was found that the partially purified, microbubble-surfactant mixture does in fact form stable monomolecular films at an air/(distilled) water interface. During the first compression-expansion cycle a minor degree of hysteresis was observed, but this effect was essentially absent during recompression (Fig. 6.3) and is probably due to the presence of various contaminants in the microbubble-surfactant mixture (see Section 6.3). It was further found that these microbubble-surfactant monolayers remain quite insoluble (cf. Section 6.1.3) when highly compressed, i.e., up to measured surface pressures of 24 dyne/cm. 

A number of amphiphilic calixarenes have been shown to possess the ability to self-assemble in the form of insoluble monomolecular films at the air-water interface, which are called Langmuir monolayers. In order to exhibit the ability to form Langmuir monolayers, the amphiphilic derivative has to be designed so that it is not soluble in water. Indeed if the amphiphiles are partially water-soluble, they do not assemble at the air-water interface but (at least partially) in the water phase in the form of micelles [12, 30, 31]. Amphiphilic calixarenes, self-assembled as Langmuir monolayers at the air-water interface, typically float on the water surface with an orthogonal orientation with respect to the interface the aliphatic chains point into air while the polar functions are immerged into the subphase (Fig. 37.4). 

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 /... 

Membrane-active antimicrobial agents can react with monomolecular lipid films (or monolayers) orientated at an air-water interface. When such an agent is introduced beneath the monolayer, the orientation of the lipid molecules at the interface alters, producing measurable changes in surface pressure. 

At the air-water interface, water molecules are constantly evaporating and condensing in a closed container. In an open container, water molecules at the surface will desorb and diffuse into the gas phase. It is therefore important to determine the effect of a monomolecular film of amphiphiles at the interface. The measurement of the evaporation of water through monolayer films was found to be of considerable interest in the study of methods for controlling evaporation from great lakes. Many important atmospheric reactions involve interfacial interactions of gas molecules (oxygen and different pollutants) with aqueous droplets of clouds and fog as well as ocean surfaces. The presence of monolayer films would thus have an appreciable effect on such mass transfer reactions. 

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. 

Jarvis NL (1962) The effect of monomolecular films on surface temperature and convective motion at the air/water interface. J.Colloid Sci. 17 512-522 Kumar S, Gupta R, Baneijee S (1998) An experimental investigation of the characteristics of free surface turbulence in a channel flow. Physics of Fluids 10 437-456... 

Recently, a new and reproducible method to generate stable Upid membranes on SUMs has been described [141]. The membrane-spanning tetraether lipid MPL (main tetraether phospholipid of Thermoplasma acidophilum), and also mixtures of MPL with DPhPC at molar ratios of MPLiDPhPC =1 1 and 5 1, and pure DPhPC are spread at the air-water interface. The monomolec-ular films are subsequently transferred by one raising step (MPL and mixtures) or by a first lowering and subsequent raising step of the electrolyte (DPhPC) onto the SUM. SUM-supported MPL membranes show a lifetime of about 8 h but an additional monomolecular S-layer lattice recrystallized on the lipid-faced side increases the lifetime of the composite membrane significantly to about 21 h [141]. 

The most familiar transitions between surface phases in fluid interfaces are those in the so-called insoluble monomolecular films that some higher alcohols and fatty adds form at a water-air interface. Distinct surface phases and transitions between them are frequently observed also in monolayers of adsorbed gases on solid substrates, and are the subject of an exuberant modem literature. ... 

When an insoluble liquid a is placed at the liquid air interface of another liquid P, the first liquid can spread out as a thin film which becomes monomolecular if the area of liquid P is sufficiently large. Everyone has experienced the colors which are seen when oil is spread on water in a muddy puddle on the road. The colors result from the interference of the light rays reflected from the oil air interface with those reflected at the water oil interface. The interference occurs because the oil film is very thin. The properties of thin films are especially interesting when their thickness corresponds to one molecule. 

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