Monolayer surface pressure effect

S. G., McLaughlin, S., Effect of monolayer surface pressure on the activities of phosphoinositide-specific phospholipase C-beta 1, -gamma 1, and -delta 1, Biochemistry 1994, 33, 3032-3037. 

It is very well known that different macromolecular arrangements may be induced either by changing the nature of the subphase [44, 68, 69] or by changing the spreading solvent [70], However, only a few studies describing these effects on polymer monolayer surface pressure behavior have been reported [71-73]. 

Figure 6. Effect of CTA+ ions on the surface pressure of the lecithin monolayers. Surface pressure increase, AII2 vs. surface pressure, Ii2, of the pure lecithin monolayers.

Boguslavsky V, Bebecchi M, Morris AJ, Jhon DY, Rhee SG, McLaughlin S (1994) Effect of monolayer surface pressure on the activities of phosphoinositide-spedfic phospholipase C-p.l, -y.l, and 81. Biochemistry 33 3032-3037... 

Therefore, the following method was suggested and realized (the scheme is shown in Fig. 17). A 1.5 M solution of KCl or NaCl (the effect of preventing BR solubility of these salts is practically the same) was used as a subphase. A platinum electrode was placed in the subphase. A flat metal electrode, with an area of about 70% of the open barriered area, was placed about 1.5-2 mm above the subphase surface. A positive potential of +50 -60 V was applied to this electrode with respect to the platinum one. Then BR solution was injected with a syringe into the water subphase in dark conditions. The system was left in the same conditions for electric field-induced self-assembly of the membrane fragments for 1 hour. After this, the monolayer was compressed to 25 mN/m surface pressure and transferred onto the substrate (porous membrane). The residual salt was washed with water. The water was removed with a nitrogen jet. 

The importance of lipophilicity to bitterness has been well established, both directly and indirectly. The importance of partitioning effects in bitterness perception has been stressed by Rubin and coworkers, and Gardner demonstrated that the threshold concentration of bitter amino acids and peptides correlates very well with molecular connectivity (which is generally regarded as a steric parameter, but is correlated with the octanol-water partition coefficient ). Studies on the surface pressure in monolayers of lipids from bovine, circumvallate papillae also indicated that there is a very good correlation between the concentration of a bitter compound that is necessary in order to give an increase in the surface pressure with the taste threshold in humans. These results and the observations of others suggested that the ability of bitter compounds to penetrate cell membranes is an important factor in bitterness perception. 

Ruckenstein and Li proposed a relatively simple surface pressure-area equation of state for phospholipid monolayers at a water-oil interface [39]. The equation accounted for the clustering of the surfactant molecules, and led to second-order phase transitions. The monolayer was described as a 2D regular solution with three components singly dispersed phospholipid molecules, clusters of these molecules, and sites occupied by water and oil molecules. The effect of clusterng on the theoretical surface pressure-area isotherm was found to be crucial for the prediction of phase transitions. The model calculations fitted surprisingly well to the data of Taylor et al. [19] in the whole range of surface areas and the temperatures (Fig. 3). The number of molecules in a cluster was taken to be 150 due to an excellent agreement with an isotherm of DSPC when this... 

Phospholipid monolayers at liquid-liquid interfaces influence the charge transfer processes in two ways. On the one hand, the phospholipids constitute a barrier that blocks the process by impeding the transferring species to reach the interface [1,15,48]. On the other hand, the phospholipids modify the electrical potential difference governing the process [60]. While the first influence invariably leads to a decreased rate, the second one might result in either a decreased or an increased rate of charge transfer. The net effect of the phospholipids on the charge transfer process depends on the state of the monolayer, and therefore studies with simultaneous electrochemical and surface pressure control are preferable [10,41,45]. 

The dynamic surface tension of a monolayer may be defined as the response of a film in an initial state of static quasi-equilibrium to a sudden change in surface area. If the area of the film-covered interface is altered at a rapid rate, the monolayer may not readjust to its original conformation quickly enough to maintain the quasi-equilibrium surface pressure. It is for this reason that properly reported II/A isotherms for most monolayers are repeated at several compression/expansion rates. The reasons for this lag in equilibration time are complex combinations of shear and dilational viscosities, elasticity, and isothermal compressibility (Manheimer and Schechter, 1970 Margoni, 1871 Lucassen-Reynders et al., 1974). Furthermore, consideration of dynamic surface tension in insoluble monolayers assumes that the monolayer is indeed insoluble and stable throughout the perturbation if not, a myriad of contributions from monolayer collapse to monomer dissolution may complicate the situation further. Although theoretical models of dynamic surface tension effects have been presented, there have been very few attempts at experimental investigation of these time-dependent phenomena in spread monolayer films. 

Enantiomeric recognition was clearly displayed in films spread from solution and films in equilibrium with their crystals, and was sharply dependent on the acidity of the subphase. Protonation of the amide group appeared to be necessary for spreading to stable monolayers. For example, the crystals of the racemate deposited on a 10n H2S04 solution at 25°C spread quickly to yield a film with an ESP of 7.7 dyn cm"1, while the single enantiomers spread only to a surface pressure of 3.9 dyn cm-1 (Table 1). Similar effects are observed at 15 and 35°C. The effect of stereochemistry on equilibrium spreading is even more pronounced at lower subphase acidities. On 6n sulfuric acid, the racemate spread to an equilibrium surface pressure of 4.9 dyn cm-1, while the enantiomeric systems spread to less than 1 dyn cm-1. 

When spread from dilute hexane solution, acid-dependent enantiomeric discrimination was observed in the 11/A compression isotherms of the monolayer at 25°C (Fig. 12). It is interesting to note that at higher subphase acidities, both racemic and enantiomeric film systems become more highly expanded, and the surface pressures where enantiomeric discrimination commences occur at high (85-90 A2/molecule) average molecular areas. This may be taken as direct evidence of headgroup ionization effects. The surface... 

Figure 6 Effect of alkyl-chain length of aliphatic acid cadmium salts monolayers, [CH3(CH2) .2COO-]2 Cd, on the amount of incorporated water (W2) and the evaporation speed of the water (v). The broken line is calculated from eq. (3). (surface pressure 30 mN m-i, dipping speed 100 mm min-1, 20 °C, at the 5th dipping cycle).

The effect of protein and other monolayers on mass-transfer rates depends quantitatively 50) on the surface compressional modulus, Cr this is defined as the reciprocal of the compressibility of the contaminating surface film, i.e., Cr = —A dU/dA. For films at the oil-water interface Cr is often close to II, the surface pressure, which is equal to the lowering of the interfacial tension by the film. 

The quantity Cr correlates the effects of monolayers, both spread and adsorbed, on K, as in Fig. 11. As one may show quantitatively with talc particles, the eddy velocity at the interface is greatly reduced by the mono-layer. The latter restrains fresh liquid from being swept along the surface, i.e., there is less clearing of the old surface. If now All is the surface pressure resisting the eddy due to its partly clearing an area (Fig. 12) in... 

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