Fatty acids mixed monolayers with

Mixing fatty acids with fatty bases can dissolve films as the resulting complexes become water-soluble however, in some cases the mixed Langmuir film is stabilized [128]. The application of an electric field to a mixed lipid monolayer can drive phase separation [129]. 

The adsorbed layer at G—L or S—L surfaces ia practical surfactant systems may have a complex composition. The adsorbed molecules or ions may be close-packed forming almost a condensed film with solvent molecules virtually excluded from the surface, or widely spaced and behave somewhat like a two-dimensional gas. The adsorbed film may be multilayer rather than monolayer. Counterions are sometimes present with the surfactant ia the adsorbed layer. Mixed moaolayers are known that iavolve molecular complexes, eg, oae-to-oae complexes of fatty alcohol sulfates with fatty alcohols (10), as well as complexes betweea fatty acids and fatty acid soaps (11). Competitive or preferential adsorption between multiple solutes at G—L and L—L iaterfaces is an important effect ia foaming, foam stabiLizatioa, and defoaming (see Defoamers). 

It has been shown (Friberg, 2003 Birdi, 2002, 2008) that there exists a correlation between foam stability and the elasticity [E] of the film (i.e., the monolayer). In order for E to be large, surface excess must be large. Maximum foam stability has been reported in systems with fatty acid and alcohol concentrations well below the minimum in y. Similar conclusions have been observed with -C12H25S04Na [SDS] + -C12H25OH systems that give minimum in y versus concentration with maximum foam at the minimum point (Chattoraj and Birdi, 1984). Because of mixed mono-layer formation it has been found that SDS + C12H25OH (and some other additives) make liquid-crystalline structures at the surface. This leads to a stable foam (and liq-... 

Various inert compounds such as fatty acids, fatty alcohols, and lipids behave as two-dimensional diluents for Chi monolayers and lead to the formation of homogeneously mixed monolayers (20). These diluents have facilitated the study of Chl-Chl energy transfer within a two-dimensional plane as a function of the intermo-lecular Chi separation (26,27). In sufficiently dilute mixed monolayers, a majority of the Chi molecules are thought to exist in the monomeric state, with their mutual aggregations effectively suppressed within the geometrically controlled, ordered configuration. Multilayers (built-up monolayers) of Chi a have also been studied (23) and utilized for photovoltaic studies (see the next section). The molecular orientation in such Chi a multilayers has been ascertained from the observed dichroism in spectropolarization measurements with respect to absorption (23) and emission (28). 

Pyrene-labeled SA mixed monolayers were prepared by adsorption from solutions of the desired concentration of a particular fatty acid, along with a small fraction (1-5%) of the probe Py-C16. All solutions used were of total acid concentration of 5xl0 3M. 

Fluorescence Of Monolayers Containing Pyrene-Labeled Probes. A fluorescence probe method was also used as a complementary technique to study the thermodynamics of SA film formation. Mixed monolayers containing the fluorescence probe pyrene hexadecanoic acid, Py-C16, in host fatty acids of different lengths were prepared by adsoiption from solutions containing mostly the host fatty acid and a small fraction of Py-C16 (approximately 1 to 5 mol %). All monolayers were prepared under equilibrium adsoiption conditions. For fluorescence measurements only A1 substrate was used because when glass is used an impurity fluorescence from glass interferes with the pyrene fluorescence. 

The immisdbility of CF2- and CHi-chains was also utilized for the preparation of unsymmetric vesicle membranes. The hydrophobic parts of bolaamphiphile 5 with fatty acid and fluorocarbon sulfonate halves do not mix and all the fluorosulfonate halves were on the outer side of the monolayered vesicle membrane (Figure 4.7). The sulfonate head group was once more localized by the metachromatic effect, the hydrophobic parts with F- and H-substituted spin labels. 

In the small intestine, pancreozymin causes the gallbladder to contract, and bile, a micellar solution of bile acids, lecithin, and cholesterol, is secreted into the duodenum. Pancreozymin also causes discharge and continued synthesis of pancreatic lipase which adsorbs to the oil-water interface, liberating 2-monoglycerides and fatty acids (76). Whether bile acids adsorb to the interface and if so how they spatially orient with respect to lipolytic products and lipase is unknown. At concentrations below the CMC, bile acids will adsorb to monolayers of lipolytic products (77), but no information is available on the interaction of bile acid solutions above their CMC with monolayers of lipolytic products. Somehow, the lipolytic products are transferred to the bulk phase, where they form mixed micelles with bile acid molecules (Fig. 14). 

The composite subphase mentioned above is the key factor for the stable rare earth complex monolayers at air/liquid interface. During monolayer transfer process, it is found that the monolayers are too rigid to transfer onto solid substrates. The conventional film-forming molecule AA with a long aliphatic chain was mixed with them in the spreading solution in a molar ratio of 1 1. The obtained mixed LB films emitted homogeneous intense fluorescence. So the use of a fatty acid AA is the key factor for the monolayer transfer during LB film fabrication. 

Figure 8. Typical experimental setup with a fluorophore dispersed in the matrix of a mixed fatty acid monolayer.

Reichert, A., Ringsdorf, H. and Wagenknecht, A. (1992) Spontaneous domain formation of phospholipase A2 at interfaces fluorescence microscopy of the interaction of phospholipase A2 with mixed monolayers of lecithin, lysolecithin and fatty acid, Biochim. Biophys. Acta, submitted. 

The mixed layer strategy in which charge transfer complexes are dissolved in fatty-acid "solvents" to form stable monolayers was developed by Kuhn and Mobius(75). Palacin and coworkers (14 J5) have employed this general approach to produce LB films of water soluble phthalocyanine complexes with tricosenoic acid (24 carbons) by an ion-pair mechanism. Both in this case and with other ampMphilic Co (H) phthalocyanine complexes, the LB films formed (using fatty acid for mixed layers) result in homogeneous LB films with no evidence for domain structures. 

The different kinds of molecules can be incorporated in an LB multilayer. The resultant LB film has the structure of a organic superlattice if each kind of molecule is positioned within different molecular layers. It is also possible to incorporate different kinds of molecule within the same layer by forming mixed monolayers at the air-water interface (Figure 14.4). In the case of mixed monolayers, poorly surface active or even non-surface active molecules can be incorporated into films with the aid of highly surface active molecules such as long-chain fatty acids. 

Eujihira, M. Nishiyama, K. Hamaguchi, Y Tatsu, Y. Eluorescence microscopic study of change in pyrene cluster size in mixed monolayers of pyrene-substituted and normal fatty acids with chain-length matching. Chem. Lett. 1987, 253-256. 

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