Palmitic acid, monolayers

Fig. 26 Hysteresis isotherms for the 1/5 palmitic acid/(A) racemic and (B) enantiomeric stearoylserine methyl ester (17% palmitic acid) monolayer system at 25°C. Arrows indicate direction of expansion and compression. Reprinted with permission from Arnett et al., 1989. Copyright 1989 American Chemical Society.

As on pure water substrates, the enantiomeric crystals of SSME did not spread on the enantiomeric SSME/palmitic acid monolayer-covered surfaces, while the spreading of the racemic crystals on the racemic film-covered water was actually enhanced. The palmitic acid crystals deposited on either racemic or enantiomeric film covered substrates spread to the same surface pressure, independent of stereochemistry. 

Conversely, the racemic film system appears to be solubilized by the achiral fatty acid component. At compositions of 10-33% palmitic acid, the ESP of the racemic system varies linearly with film composition, indicating that the monolayer in equilibrium with the racemic crystal is a homogeneous mixture of racemic SSME and palmitic acid. At compositions of less than 33% palmitic acid, the ESP is constant, indicating that three phases consisting of palmitic acid monolayer domains, racemic SSME monolayer domains, and racemic SSME crystals exist in equilibrium at the surface. 

Fig. 5. The Tsp dependences of log Ks(max). bright field electron micrographs and ED patterns of the palmitic acid monolayers.

Fig. 9. n-A isotherm, electron micrographs, and ED patterns of palmitic acid monolayer at Tsp of 283 K. 

Figure 4. Surface pressure vs. molecular area for palmitic acid monolayers spread on aqueous substrates of varying pH at 30°C. and 0.5N total cation concentration (KOH + KCl). Rapid compression...

Vickery, S.A., and R.C. Dunn. 2001. Direct observation of stmctural evolution in palmitic acid monolayers following Langmuir-Blodgett deposition. Langmuir 17 8204-8209. 

We calculated activity coefficients for palmitic acid with the A values extrapolated from kinetic data (see Figure 4). These coefficients are 0.063 cm/dyne at pH 10 and 0.088 cm/dyne at pH 11. Activity coefficients calculated from Ks data in a previous study (26) are 0.048 cm/dyne at pH 10 and 0.078 cm/dyne at pH 11. The similarities in the coefficients calculated by the two methods suggest that the desorbing palmitic acid monolayer was in a quasi—equilibrium and therefore,... 

Figure 8. Reciprocal plots (Equation 16) of Ki and [H+] data for palmitic acid monolayers spread on the designated buffers (see text) and maintained at the designated tt. Linear regression equations (solid lines) were calculated by least squares analyses of the data.

The initial observation of Sears and Schulman (3) that Na+ > K+ selectivity on strongly alkaline subphases reversed on a weakly alkaline subphase was confirmed in several studies. Desorption experiments (Figure 11) showed that palmitic acid monolayers with essentially complete ionization—strong fields—were condensed more by Na+ than by K+. At lower pH, the partially ionized monolayers—weaker fields—were condensed the same amount by Na+ and K+. 

Section six is devoted to Amphiphiles at Vapor-Liquid Interfaces. Zasadzinski and coworkers present a review of lung surfactant protein and the effects of such protein on altering phase structures in palmitic acid monolayers. They articulate some... 

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