Films phospholipid monolayers

Stigter and Dill [98] studied phospholipid monolayers at the n-heptane-water interface and were able to treat the second and third virial coefficients (see Eq. XV-1) in terms of electrostatic, including dipole, interactions. At higher film pressures, Pethica and co-workers [99] observed quasi-first-order phase transitions, that is, a much flatter plateau region than shown in Fig. XV-6. 

The effect is more than just a matter of pH. As shown in Fig. XV-14, phospholipid monolayers can be expanded at low pH values by the presence of phosphotungstate ions [123], which disrupt the stmctival order in the lipid film [124]. Uranyl ions, by contrast, contract the low-pH expanded phase presumably because of a type of counterion condensation [123]. These effects caution against using these ions as stains in electron microscopy. Clearly the nature of the counterion is very important. It is dramatically so with fatty acids that form an insoluble salt with the ion here quite low concentrations (10 M) of divalent ions lead to the formation of the metal salt unless the pH is quite low. Such films are much more condensed than the fatty-acid monolayers themselves [125-127]. 

The popular applications of the adsorption potential measurements are those dealing with the surface potential changes at the water/air and water/hydrocarbon interface when a monolayer film is formed by an adsorbed substance. " " " Phospholipid monolayers, for instance, formed at such interfaces have been extensively used to study the surface properties of the monolayers. These are expected to represent, to some extent, the surface properties of bilayers and biological as well as various artificial membranes. An interest in a number of applications of ordered thin organic films (e.g., Langmuir and Blodgett layers) dominated research on the insoluble monolayer during the past decade. 

Monolayer Films at the A/W Interface. Previous studies of phospholipid monolayers at gas-liquid interfaces have shown that it is possible to follow the first order thermodynamic phase transition of these monolayer films using the infrared reflectance techniques described in this manuscript (see e.g. ref. 6 and references cited therein). For long chain hydrocarbon molecules, it has been demonstrated that the frequencies of the antisymmetric and symmetric CH2 stretching vibrations are conformation-sensitive, and may be empirically correlated with the order (i.e. the trans-gauche character) of the hydrocarbon chains (9-11). 

In a recent research, effect of hydrophobic surfactant proteins SP-B and SP-C on binary phospholipid monolayers was studied by IRRAS [65], The phospholipids examined were DPPC plus either DPPG or 1,2-dioleoyl-5 -glycero-3-phosphoglycerol (DOPG). IRRAS obtained at the air-water interface for a monolayer film of 7 1 DPPC-d62 DPPG plus 5 wt.% SP-B/C are shown in Fig. 5. Both C-H and C-D vibrational bands grow in intensity as the surface pressure increases and the surface density of the lipid molecules increases. As the average surface area per molecule is reduced, hydrophobic... 

A very suitable method for measurement of the lateral diffusion of molecules adsorbed at the foam film surfaces is Fluorescence Recovery after Photobleaching (FRAP) ([491-496], see also Chapter 2). Measurements of the lateral diffusion in phospholipid microscopic foam films, including black foam films, are of particular interest as they provide an alternative model system for the study of molecular mobility in biological membranes in addition to phospholipid monolayers at the air/water interface, BLMs, single unilamellar vesicles, and multilamellar vesicles. 

Fig. 9. CD spectra of the wild type E. coli LamB synthetic signal peptide in phospholipid monolayers. The experiment was carried out as described in Figs. 7 and 8. The solid line spectrum was obtained for films spread at pressures below the peptide s critical pressures of insertion, and the broken line spectrum for films spread above the peptide s critical pressure of insertion. Hence, the former represents inserted plus adsorbed peptide, and the latter is from adsorbed peptide only. Experimental details are reported in Briggs et al. (1986). Copyright 1986 by the American Association for the Advancement of Science.

Domain structures of phospholipid monolayer LB films were investigated by AFM. The domain structures of phospholipids (di-palmitoyl-phosphatidylcholine, DPPC) were studied as LB films. 

Although the first section of this chapter was concerned with structural and dynamic information on monolayers of lipopolymers, before investigating lipopolymer-phospholipid mixtures, it is reasonable to consider the structural information that exists concerning pure phospholipid monolayers at the air-water interface. Film balance experiments, X-ray and neutron reflectometry, and molecular dynamics simulations have provided insight into the structural properties of these biologically... 

Monolayers of distearoyl lecithin at hydrocarbon/water interfaces undergo temperature and fatty acid chain length dependent phase separation. In addition to these variables, it is shown here that the area and surface pressure at which phase separation begins also depend upon the structure of the hydrocarbon solvent of the hydrocarbon oil/aqueous solution interfacial system. Although the two-dimensional heats of transition for these phase separations depend little on the structure of the hydrocarbon solvent, the work of compression required to bring the monomolecular film to the state at which phase separation begins depends markedly upon the hydrocarbon solvent. Clearly any model for the behavior of phospholipid monolayers at hydrocarbon/water interfaces must account not only for the structure of the phospholipid but also for the influence of the medium in which the phospholipid hydrocarbon chains are immersed. 

Film pressure change An vs. time for a phospholipid monolayer, 1 - compression with lOcm/min, 2 - oscillation with f = 0.05 Hz, 3 - one oscillation in higher time resolution, 4 - phase lag tick, according to Kretzschmar (1988)... 

It has been mentioned previously that sterols were readily incorporated into lecithin or mixed phospholipid monolayers [194—196]. The area of sterol-containing films was smaller than that calculated for the separate components, indicating some kind of interaction between the two molecules [221,222]. Sterols have also been shown to reduce the phase transitions of pure lecithin dispersions [214]. It has been suggested that cholesterol modifies the fluidity of the hydrocarbon chains of the phospholipid molecules by disrupting the crystalline chain lattice of the gel phase and by inhibiting the flexing of the chains in the dispersed liquid-crystalline phase [221—226]. 

An extensive analysis of the polymorphism in phospholipid monolayers has been reported by Albrecht et al. (1978) who established a phase diagram of dipal-mitoyl-lecithin monolayers involving four phases. Two of these have the liquid-type of disordered chains (liquid-expanded films). It was proposed that one has disordered chains oriented perpendicular to the water surface and the other has disordered chains in a tilted arrangement. Furthermore two crystalline phases were described, one with tilted chains and the other with perpendicular chains. 

Pavinatto, F.J., et al. Cholesterol mediates chitosan activity on phospholipid monolayers and Langmuir- Blodgett films. Langmuir 25(17), 10051-10061 (2009)... 

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