Surface pressure-molecular area isotherm

Figure 1. The surface pressure-molecular area isotherm of the DPPC monolayer at 22 °C (Figure 1A, top) with the infrared frequencies of the CH, antisymmetric stretching vibration, plotted against molecular area for the DPPC monolayer (Figure IB, bottom).

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 /... 

Fig. 3 Langmuir film balance schematic, a - monolayer of lipid in a quasi gas state, b -state of maximal compaction indicative of molecular area, c - monolayer collapse point reflecting monolayer rigidity. Tested monolayer was palmitic acid over H2O to produce a typical surface pressure/molecular area isotherm.

This chapter is basically divided in two parts, namely, the study of surface pressure-molecular area (jr — A) isotherms of phospholipids at ITIES and their effect on ion transfer. In the first part, the emphasis is put on topics which have been left out from Ref [5], i.e., Langmuir film techniques and theoretical modeling of jr — isotherms, as well as on the latest progress in the field, especially on experiments that combine Langmuir techni-... 

Prior to LB transfer, the surface pressure - molecular area (n-A) isotherms of dialkylsilane under various pH and temperature conditions were investigated. The pH condition of the subphase (water phase under the monolayer) is a crucial factor for the monolayer state. The condensed phase was formed directly without formation... 

Figure 17. Experimental system for the measurement of surface pressure-molecular area (n-A) isotherms and the horizontal touch cyclic voltammetry/ and schematic representations for the control of permeabilities through oriented monolayers formed at low and high applied surface pressures.

The monolayer of amphiphile spread on water is then compressed into a well-packed state. The profile of monolayer compression is recorded as surface pressure-molecular area (n-A) isotherm. Typical examples of n-A isotherms are shown in Fig. 4.33. The transverse axis of the isotherm represents the molecular area, which can be obtained by dividing the total surface area by the number of amphiphile molecules. The surface pressure is derived by subtracting the surface tension of the monolayer-covered water surface from that of pure water. This has dimensions corresponding to two-dimensional pressure. Surface pressure cannot be regarded as a normal three-dimensional pressure. For convenience, when discussing the phase of two-dimensional monolayer here, the surface pressure is treated as a two-dimensional pressure. 

FIG. 23 Surface pressure vs. area/molecule isotherms at 300 K from molecular dynamics simulations of Karaborni et al. (Refs. 362-365). All are for hydrocarbon chains with carboxylate-like head groups, (a) (filled squares) A 20-carbon chain, (b) (filled circles) A 16-carbon chain with a square simulation box the curve is shifted 5 A to the right, (c) (open squares) A 16-carbon chain with a nonsquare box with dimensions in the ratio xly = (3/4) to fit a hexagonal lattice the curve is shifted 5 A to the right. (Reproduced with permission from Ref. 365. Copyright 1993 American Chemical Society.)... 

This way it has been possible to observe the anticipated conformational transition by experiment. Cylindrical brushes of polybutylacrylate-graft polymethacrylate were adsorbed on the surface of water from a CHCI3 solution on a Langmuir trough and studied by recording the tt-A (surface pressure vs molecular area) isotherm. At different stages of compression, the monolayer was... 

Figure 3.79. Surface pressure jt) versus molecular area isotherm of pentadecanoic (C15) acid L monolayer on pure water at alxrut 30°C. Various features of isotherm can be identified with different structural phases. Adapted, by permission, from D. K. Schwartz, Surf. Sci. Reports 27, 241 (1997), p. 248, Fig. 1. Copyright 1997 Elsevier Science B.V.

While the barrier confines the amphiphiles to a smaller area, the force exerted by the monolayer is continuously measured and a surface pressure (I7)-area (A) isotherm can be drawn at a constant temperature. This curve plots the surface pressure (force per unit length) versus the mean molecular area occupied by the amphiphiles at the air/water interface. Usually, a U-A isotherm shows four interesting regions [21]. An initial horizontal region where the mean molecular area is large and the interaction between molecules is small so the surface pressure is approximately constant. The first linear region deviates from the... 

Fig. 3 Surface pressure-mean molecular area isotherm from an eimphiphilic triblock copolymer. Nomenclature of polymer phases is shown. Reprinted from [66] with permission. Copyright 2006 American Chemical Society...

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. 1.9 S urface pressure ( r)-area (A) isotherms obtained for a lipid mixture (DPPC POPG PA, 68 22 9 (by weight)), alone and with 10% (w/w) of either SP-C peptide or SP-C peptoid added. Results indicate that the addition of the SP-C mimics engenders biomimetic surface activity, as indicated by lift-off at a higher molecular area and the introduction of a plateau...

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-... 

In a study of mixed monolayers of C60 and p-iert-butylcalix[8]arene, different isotherm behavior was obtained [256]. The surface pressure was observed to rise at a lower molecular area (1.00 nm molecule vs. 2.30 mn molecule in the prior study). Similar isotherms were observed whether a 1 1 mixture or a solution prepared by dissolving the preformed 1 1 complex was spread. The UV spectra of the transferred LB films appeared different than that of bulk C60. It was concluded that a stable 1 1 complex could be formed by spreading the solution either of the mixture or of the complex. This was confirmed in a later study by the same group that included separate spreading of the calixarene and the C60... 

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