Modulation of the Polymorphism of the Palmitic Acid/Cholesterol System by the pH

Abstract

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Influence of cholesterol on the structure of stratum corneum lipid model membrane

“…A similar phase separation probably occurs in the state ␣ of our systems. The repeat distance of the L-phase agrees with D-values obtained for a palmitic acid/CHOL system at high pH as described by Quimet et al [45]. These authors even showed that with increasing CHOL concentration in the palmitic acid/CHOL system, the lamellar repeat distance slightly increases.…”

12-Hydroxystearic acid lipid tubes under various experimental conditions

“…Moreover, there is still a strong debate dealing with the deprotonation state of the fatty acid in such mixtures. This has been noted in catanionic systems [20] but also in mixtures with alcohols [13,21,22]. In the stock solution of our microtubes, the pH is around 9.8 but we expect that both carboxylate and carboxylic groups coexist, although the concentration of COO À is probably higher since the pH is basic.…”

“…However, the ratio [COO À ]/[COOH] is difficult to estimate since the pK a of a fatty acid varies with experimental conditions. Indeed, the pK a of fatty acids are expected to be below 7 but it was shown to be close to 8 for cholesterol-palmitic acid systems [21,23].…”

Impact of interfacial cholesterol-anchored polyethylene glycol on sterol-rich non-phospholipid liposomes

“…reports. 27,41 The widths of these spectra were found to be very similar to those observed at pH 8.4 The measured diffusion coefficient in these conditions was 2.0 × 10 -11 m 2 /s, a value corresponding to that reported for PEG2000-PE micelles. 42 When PEG-Chol proportion in a mix with PA and cholesterol was between 1 and 20%, PEG diffusion coefficients were relatively constant and corresponded to about 2.4 × 10 -12 m 2 /s.…”

“…41 The protonation state of the carboxylic group dictates the bilayer stability through its modulation of the lipid mixing properties and the bilayer interface hydration. At lower pH, PA head group is protonated, favoring phase separation from cholesterol and reducing the hydration of the bilayer interface; as a consequence, the destabilization of the fluid lamellar phase is observed.…”