Monolayer surface pressure

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. 

The spread mixed lipid monolayer studies provide information about the packing and orientation of such molecules at the water interface. These interfacial characteristics affect many other systems. For instance, mixed surfactants are used in froth flotation. The monolayer surface pressure of a pure surfactant is measured after the injection of the second surfactant. From the change in n, the interaction mechanism can be measured. The monolayer method has also been used as a model biological membrane system. In the latter BLM, lipids are found to be mixed with other lipidlike molecules (such as cholesterol). Hence, mixed monolayers of lipids + cholesterol have been found to provide much useful information on BLM. The most important BLM and temperature melting phenomena is the human body temperature regulation. Normal body temperature is 37°C (98°F), at which all BLM function efficiently. 

In some cases, particularly at high monolayer surface pressures, formation of rod-like PbSe particles was observed (Fig. 117) [648]. The thickness of the rods was typically 10 nm or less and the length was of the order of 100 nm. In addition to the rods, there were also many dot-like particles in the 10-nm size range (Fig. 117). Generation of rod-like semiconductor particles under monolayers provides a potential approach to nanofabricated quantum wires. 

The rate constant for the cis- trans photoisomerization can be calculated from the observed time dependence. The rate constants obtained at various monolayer surface pressures under identical conditions of illumination are plotted vs surface pressure in Figure 3. 

Experimental techniques for studying insoluble monolayers Surface pressure... 

In addition to describing the conformation of the hydrocarbon chains for amphiphilic molecules at the A/W interface, external reflectance infrared spectroscopy is also capable of describing the orientation of the acyl chains in these monolayers as a function of the monolayer surface pressure. The analysis of the orientation distribution for an infrared dipole moment at the A/W interface proceeds based on classical electromagnetic theory of stratified layers (2). In particular, when parallel polarized radiation interacts with the A/W interface, the resultant standing electric field has contributions from both the z component of the p-polarized radiation normal to the interface, as well as the x component of the p-polarized radiation in the plane of the interface. The E field distribution for these two... 

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 3.76. Stearic acid monolayers surface pressure (lower curves) and Volta potentials (upper curves). Influence of bivalent electrolytes. (Redrawn from E.D. Goddard, J.A. Ackilli, J. Colloid Set 18 (1963) 585.)...

The step height analysis of these two-dimensional cholesterol crystals gives 90 A, which corresponds to six layers of cholesterol (90 A/length of cholesterol molecule =15 A). This is different from what is seen for the collapsed films of Mg-(stearate)2, as is well known from monolayer surface pressure vs. area isotherms. ... 

The penetration of soluble proteins into spread, insoluble lipid monolayers was first studied by Schulman and Rideal. Their injection technique allows measurement of the surface pressure increase of the insoluble penetrated monolayer after the soluble species is coadsorbed. The interpretation of this result cannot lead to a quantitative interpretation of the penetration unless the degree of penetration is known. This value can be determined if the soluble species is radio-activly labeled. An experimental and theoretical study of the change in monolayer surface pressure and composition during penetration by a soluble component has shown that information on the mechanism of this process can be obtained. 

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.

A second example of the influence of the casting solvent on the morphology of EC film is given by the work of Rosilio et al. [153]. Monolayer surface pressure-area isotherms, wettability and permeability data clearly indicated that the EC films cast from various solvent systems differ not only in terms of their overall properties but also from one side to the other. 

Future studies in this area will require the radiolabelling of intrinsic membrane so that the amount of protein entering the monolayer can be accurately measured. More information should also be obtained on the dependence of the initial monolayer surface pressure on protein mediated fusion of vesicles with monolayers. The surface pressure at which the properties of a monolayer most closely mimic the properties of a bilayer is known to be relatively high. It is clear from our studies that protein extracts penetrate monolayers upto equilibrium surface pressures approaching the monolayer collapse pressure which suggests that data can be obtained from monolayer studies at surface pressures which are directly applicable to bilayers. 

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... 

In Fig. 8 it can be seen that the same data (DPPC monolayer surface pressure increments in the presence of various salt concentrations at 85 A per molecule) can be fitted equally well by the partitioning and the dispersion-force model, but not by the simple local binding model. 

Neumann has adapted the pendant drop experiment (see Section II-7) to measure the surface pressure of insoluble monolayers [70]. By varying the droplet volume with a motor-driven syringe, they measure the surface pressure as a function of area in both expansion and compression. In tests with octadecanol monolayers, they found excellent agreement between axisymmetric drop shape analysis and a conventional film balance. Unlike the Wilhelmy plate and film balance, the pendant drop experiment can be readily adapted to studies in a pressure cell [70]. In studies of the rate dependence of the molecular area at collapse, Neumann and co-workers found more consistent and reproducible results with the actual area at collapse rather than that determined by conventional extrapolation to zero surface pressure [71]. The collapse pressure and shape of the pressure-area isotherm change with the compression rate [72]. 

Fig. IV-21. Surface pressure versus area for monolayers of immiscible components a monolayer of pure cadmium arachidate (curve 1) and monolayers of mixed merocyanine dye, MC2, and cadmium arachidate of molar ratio r = 1 10 (curve 2) 1 5 (curve 3), 1 2 (curve 4), and pure MC2 (curve 5). The subphase is 2.5 x 0 M CdC, pH = 5.5 at 20°C. Curve 3a (O) was calculated from curves 1 and 5 using Eq. IV-44. (From Ref. [116].)...

Fig. XV-9. Fluorescence micrograph of the stripe patterns observed in a monolayer from a mixture of PA and SP-Bi-25 (20% by weight peptide) on a buffered saline subphase at 16 C and zero surface pressure. (From Ref. 55.)...

Fig. XV-14. Surface pressure-area isotherms at 298 K for a DPPC monolayer on phos-photungstic acid (10 Af) at the pH values shown with 10 A/ NaCl added. (From Ref. 123.)...

Langmuir-Blodgett was the first technique to provide a practical route for the constmction of ordered molecular assembhes. These monolayers, which provide design dexibiUty both at the individual molecular and at the material levels, are prepared at the water—air interface using a hiUy computerized trough (Fig. 1). Detailed discussions of troughs (4) and of surface pressure, 7T, and methods of surface pressure measurements are available (3,6). 

Fig. 1. A trough for deposition of monolayers on soHd substrates A, bath B, a moving barrier C, a motor D, a pressure-control device E, a surface pressure balance F, a motor with a gearbox that lowers and raises the substrate and G, a soHd substrate. The film material (S) has a hydrophobic tail and...

The monolayer resulting when amphiphilic molecules are introduced to the water—air interface was traditionally called a two-dimensional gas owing to what were the expected large distances between the molecules. However, it has become quite clear that amphiphiles self-organize at the air—water interface even at relatively low surface pressures (7—10). For example, x-ray diffraction data from a monolayer of heneicosanoic acid spread on a 0.5-mM CaCl2 solution at zero pressure (11) showed that once the barrier starts moving and compresses the molecules, the surface pressure, 7T, increases and the area per molecule, M, decreases. The surface pressure, ie, the force per unit length of the barrier (in N/m) is the difference between CJq, the surface tension of pure water, and O, that of the water covered with a monolayer. Where the total number of molecules and the total area that the monolayer occupies is known, the area per molecules can be calculated and a 7T-M isotherm constmcted. This isotherm (Fig. 2), which describes surface pressure as a function of the area per molecule (3,4), is rich in information on stabiUty of the monolayer at the water—air interface, the reorientation of molecules in the two-dimensional system, phase transitions, and conformational transformations. 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

Fig.4.53. Experimental and simulated PM (polarization modulated) IRRAS spectra of single monolayers of (A) PEG and (B) K(LK)7 at the air-water interface. The surface pressure was 20 mN m [4.281],...

The terminology of L-B films originates from the names of two scientists who invented the technique of film preparation, which transfers the monolayer or multilayers from the water-air interface onto a solid substrate. The key of the L-B technique is to use the amphiphih molecule insoluble in water, with one end hydrophilic and the other hydrophobic. When a drop of a dilute solution containing the amphiphilic molecules is spread on the water-air interface, the hydrophilic end of the amphiphile is preferentially immersed in the water and the hydrophobic end remains in the air. After the evaporation of solvent, the solution leaves a monolayer of amphiphilic molecules in the form of two-dimensional gas due to relatively large spacing between the molecules (see Fig. 15 (a)). At this stage, a barrier moves and compresses the molecules on the water-air interface, and as a result the intermolecular distance decreases and the surface pressure increases. As the compression from the barrier proceeds, two successive phase transitions of the monolayer can be observed. First a transition from the gas" to the liquid state. 

Traditional amphiphiles contain a hydrophilic head group and the hydrophobic hydrocarbon chain(s). The molecules are spread at molecular areas greater (-2-10 times) than that to which they will be compressed. The record of surface pressure (II) versus molecular area (A) at constant temperature as the barrier is moved forward to compress the monolayer is known as an isotherm, which is analogous to P-V isotherms for bulk substances. H-A isotherm data provide information on the molecular packing, the monolayer stability as de-... 

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