Monolayers condensed

Note, finally, that condensed monolayers could also modify the true standard rate j, which would account for the observed partial blocking of the ion transfer [8,15]. The present study, however, is restricted to the electrostatic effect. 

The effect of phospholipid monolayers on the rate of charge transfer has been the subject of several experimental studies, but still there is a need for additional experimental evidence. For large molecular areas, the effect on the rate of ion transfer seems to be negligible [5]. An increasing surface concentration of lipids leads to liquid expanded states where the electrostatic effects are noticeable. An enhanced rate of ion transfer across monolayers of pure phospholipids has then been observed both for the cases of tracer [11,12] and supporting electrolyte ion transfer [13,17]. Finally, the blocking effect is dominant in liquid condensed monolayers [15]. 

Comparison of the compression and expansion cycles for C-15 6,6 diacids linked with a carbonyl group (Fig. 41) and those linked with an amide group (Fig. 51A) show that the C-15 amide diacids, 6-(6-pentadecanoiccarbamoyl)-pentadecanoic acids (C-15 6,6 -A), also form much more highly condensed monolayers than do their keto counterparts. Addition of three methylene... 

The absorption characteristics of PS I were measured on the four kinds of subphase surfaces during compression. As an example, Figure 2 shows the absorption spectra of the PS I monolayers on the PBV subphase surface under different surface pressures. Two absorption bands at about 420-450 and 676 nm increase with the compression, indicating the accumulation of the PS I to form a condensed monolayer. Compared to the absorption spectrum of PS I in solution (Fig. 3), the band at around 436 nm splits into two peaks. The wave-shaped small band between 470 and 630 nm is due to a low single-to-noise ratio on the water surface. These spectral features together with the jt-A isotherms indicate that PS I remains at the interface, and that the loss of PS I, due to dissolving into the subphase, is not significant [2],... 

The equimolecular mixture of L-NaphAla-Ci a and L-Ala-Ci forms the stable condensed monolayer on the aqueous sub- phase of pH 8 and can be deposited onto solid plates at 30 mN/m and 10 °C as Y-type films by the vertical dipping... 

Zeelen found the extent of chiral discrimination to be dependent on the type of monomolecular phase that was formed. Thus, racemic and optically active samples displayed identical force-area curves (Fig. 14) when both formed liquid-expanded films, but owed considerably different curves (Fig. 15) under conditions where both samples formed a more highly condensed monolayer. 

Figure 18. Cyclic voltammograms of 1,4-benzoquinone (p-quinone) as permeability marker. Curve A in the absence of a cyclodextrin monolayer on a buffer solution containing no guest (p.1 M CH3C02Na-CH3C00H, pH 6.0). Curve B in the presence of the condensed monolayer of p-cyclodextrin derivative 41 on a buffer solution containing no guest. Curve C-E in the presence of the condensed monolayer of 41 on a buffer solution containing guest 59 at concentrations of 5.0 x 10", 1.0 x 10 , and 2.0 x 10 M, respectively (reprinted with permission from Anal. Chem. 1993, 65, 930. Copyright 1993 American Chemical Society).

Figure 19. Schematic representations of the permeation behaviors of electroactive markers through the condensed monolayer of p-cyclodextrin derivative 41 in the presence and absence of the guest, (a) Permeable markers, (b) Nonpermeable markers. ...

Table 6. Selectivity of Guest-Induced Permeability Decrease for a Channel Mimetic Sensing Membrane Composed of a Condensed Monolayer of P-Cyclodextrin Derivative (41) ...

Condensed monolayer films of pure 6 polymerized rapidly, as did mixed 6/DSPE films of up to 75% DSPE, provided the monolayers were in the condensed state [33], In the liquid-expanded state, polymerization did not occur. In the condensed state, lateral diffusion of individual lipids within the monolayer is severely restricted compared to the liquid-like state. This precludes initiation of polymerization by diffusive encounter between excited-state and ground-state diacetylene lipids. In order for polymerization to occur in the condensed state, the film must be separated into domains consisting of either pure 6 or pure DSPE. A demonstration that the rates of photopolymerization for pure 6 and mixed 6/DSPE monolayers are equal would be a more stringent test for separate domains of the lipids, but no kinetic data have been reported for this system. 

With a condensed monolayer, such as cholesterol, it may safely be assumed that each molecule occupies essentially the same area in both pure and mixed films (4). This value is approximately 38 sq. A. per cholesterol molecule. By making this assumption it is possible to obtain, by the method of intercepts (16), the partial molecular areas, (dA/dn)rr,T, at constant r and temperature, of the expanded component in a cholesterol-mixed film. An extrapolation (10) through MN (Type I, Figure 12), or MO if linear (Type II, Figure 12) to the Ai ordinate, yields the area per molecule of the expanded component in the mixed films, where the cholesterol content is either equal to or in excess of the compositions denoted by point N (Type I) or point O (Type II). Such... 

Concept of Intermolecular Cavities in Mixed Monolayers. In mixed monolayers a deviation in average area per molecule occurs if one component forms expanded and the other condensed monolayers. This reduction in average area per molecule has been attributed by previous workers to an interaction between components in the mixed monolayer. However, this need not be true in all cases where condensation occurs. In several instances the condensation can be explained on the basis of steric considerations in the mixed monolayers. Although the following discussion is based on lecithin-cholesterol monolayers, it is equally applicable to other mixed monolayers. 

The relationship between surface tension and temperature in emulsifiers was observed two decades ago by Lutton et al.43. They explained that this relationship is due to a transition from a liquid-expanded type of monolayer existing at high temperatures (above 40°C) to a solid condensed monolayer existing at a lower temperature (below 20°C). In solid condensed monolayers the molecular packing of the emulsifier molecules is much denser than in the liquid expanded monolayers, and these differences result in lower or higher surface tension, respectively. 

Surface Composition. The surface composition after spreading a known amount of PS as to obtain a condensed monolayer ( 0.36 fig/cm2) was obtained by measuring surface radioactivity of prothrombin or Ca++ injected to different concentrations underneath the lipid monolayer. The... 

Condensed monolayer with close-packed terminal CF3 groups 6... 

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