Lipids surface tension

It follows from Eqs. (73) and (74) that the only stabilizing force for a-modes at long X is the membrane tension, and critical voltage vanishes as cr 0. In experiments with black lipid membranes the surface tension a arises from the contact of the bilayer with the bulk phase contained in the surrounding rim and is typically < 0.002 N/m. Then choosing... 

FIGURE 3.3 Surface tension y plotted against the concentration c of lysine derivative 3.20. Critical aggregate concentration (O) cM=2430mg/L=2.43mM, yc =58mN/m. (Reprinted from Nalum Naess, S. et al., Chem. Phys. Lipids, 148, 63, 2007. With permission.)M... 

Figure 16 shows the experimental arrangement for the measurement of the surface pressure. The trough (200 mm long, 50 mm wide and 10 mm deep) was coated with Teflon. The subphase temperature was controlled within 0.1 C by means of a jacket connected to a thermostated water circulator, and the environmental air temperature was kept at 18 °C. The surface tension was measured with a Wilhelmy plate of platinum(24.5 x 10.0 x 0.15 mm). The surface pressure monitored by an electronic balance was successively stored in a micro- computer, and then Fourier transformed to a frequency domain. The surface area was changed successively in a sinusoidal manner, between 37.5 A2/molecule and 62.5 A2/molecule. We have chosen an unsaturated phospholipid(l,2-dioleoyl-3-sn-phosphatidyI-choline DOPC) as a curious sample to measure the dynamic surface tension with this novel instrument, as the unsaturated lipids play an important role in biomembranes and, moreover, such a "fluid" lipid was expected to exhibit marked dynamic, nonlinear characteristics. The spreading solution was 0.133 mM chloroform solution of DOPC. The chloroform was purified with three consecutive distillations. 

For lipid bilayers, equation (4) can be simplified. Above we have seen that the flat unsupported bilayer is without tension, i.e. y(0, 0) = 0, and therefore the first two terms must cancel y0 = — kcj. As argued above, JQ = 0, and thus also the third term drops out. The remaining two terms are proportional to the curvature to the power two. For a cylindrical geometry only, the term proportional to J2 is present. For spherical vesicles, the two combine into one ( kc + k)J2. The curvature energy of a homogeneously curved bilayer is found by integrating the surface tension over the available area ... 

Figure 20. (a) The (dimensionless) lateral compressibility (dilatational modulus, elastic area expansion modulus) (left ordinate) and the dimensionless area per molecule (right ordinate) as a function of the tail length (t) of the PC lipids in equilibrium bilayer membranes. The conversion to real compressibilities and areas per molecule is discussed in the text, (b) The (dimensionless) surface tension and the (dimensionless) lateral compressibility as a function of the relative expansion for the C PC lipid... 

The lateral compressibility, i.e. the relative area change upon an imposed membrane tension, decreases slightly more than linearly with the chain length. This means that it is more difficult to expand the membrane surface area of a long-chained lipid than a shorter one. In Figure 20 dimensionless units are used, which means that the surface tension is given in units kT/as. 

Lindahl, E. and Edholm, O. (2000). Spatial and energetic-entropic decomposition of surface tension in lipid bilayers from molecular dynamics simulations, J. Chem. Phys., 113, 3882-3893. 

Feller, S. E. and Pastor, R. W. (1999). Constant surface tension simulations of lipid bilayers the sensitivity of surface areas and compressibilities, J. Chem. Phys., Ill, 1281-1287. 

Chiu, S. W., Clark, M., Balaji, V., Subramaniam, S., Scott, H. L. and Jakobsson, E. (1995). Incorporation of surface tension into molecular dynamics simulation of an interface a fluid phase lipid bilayer membrane, Biophys. J., 69,1230-1245. 

If one places a very small amount of a lipid on the surface of water, it may affect surface tension in different ways. It may not show any effect (such as in the case of cholesterol), or it may show a drastic decrease in surface tension (such as in the case of stearic acid or tetra-decanol). An amphiphile molecule will adsorb at the... 

Any liquid surface, especially aqueous solutions, will exhibit asymmetric dipole or ions distribution at the surface as compared to the bulk phase. If SDS is present in the bulk solution, then we will expect that the surface will be covered with SD ions. This would impart a negative surface charge (as is also found from experiments). It is thus seen that the addition of SDS to water not only changes (reduces) surface tension but also imparts negative surface potential. Of course, the surface molecules of methane (in liquid state) will obviously exhibit symmetry in comparison to water molecules. This characteristic can also be associated to the force field resulting from induced dipoles of the adsorbed molecules or spread lipid films (Adamson and Gast, 1997 Birdi, 1989). 

Lung surfactant is a mixture of proteins and amphipathic lipids that acts like a detergent or soap to greatly decrease the surface tension forces at the alveolar fluid-air interface. 

Apparatus and Procedure. Surface Isotherms. The technique for determining the n-A and AV-A curves of the lipid films has been described (6). Briefly, the Wilhelmy plate method was used to measure surface tension, from which the surface pressure was calculated (n = 7h2o—yfiim) The surface potential was measured by means of a radioactive (226Ra) air electrode and a saturated calomel electrode connected to a high impedance model 610 B Keithley electrometer (Keithley Instruments, Cleveland, Ohio). 

Stearic acid (1.16 g) was dissolved in 100 ml of ethanol. A10 pi portion of the resulting solution was pipetted onto a dean surface of a dilute HC1 solution (in a shallow tray) where it spread to form a monolayer of stearic acid. Tire layer was compressed (by moving a Teflon barrier across the tray) until the surface pressure n started to rise sharply and reached 20 dyn / cm. Note that n = y0-y where y is the measured surface tension with the film present and yc is the higher surface tension of water alone. Tire compressed film occupied a 20 x 24 cm area. Calculate the cross-sectional area of an alkyl chain in stearic acid. [See J. B. Davenport, in Biochemistry and Methodology of Lipids (A. R. 

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