Physicochemical Properties of Phosphatidylcholine (PC) Monolayers with Different Alkyl Chains, at the Air/Water Interface

Abstract

Physicochemical properties of a series of PC monolayers with different alkyl chains (C24, C20, C16, and C8), at the air/water interface were investigated. The surface pressure is influenced mainly by the hydrophobicity of the PCs, which is confirmed by the curve shape and the onset value of π-A isotherms at the air/water interface by increasing the number of alkyl chain. The onset values of surface pressure were 125 Å 2 /molecule for DOPC(C8), 87 Å 2 /molecule for DPPC(C16), 75 Å 2 /molecule for DAPC(C20), and 55 Å 2 /molecule for DLPC(C24), respectively. The orientations of alkyl chains at the air/water interface are closely connected with the rigidity of the monolayers, and it was confirmed by the tendency of monolayer thickness in ellipsometry data. The temperature dependence of a series of PCs shows that the surface pressure decreases by increasing temperature, because the longer the alkyl chain length, the larger the hydrophobic interaction in surface pressure. The temperature effects and the conformational changes of unsaturated and saturated PCs were confirmed by the computer simulation study of the cis-trans transition with POPC and DPPC(C16). The cistrans conformational energy difference of POPC is 62.06 kcal/mol and that of DPPC(C16) is 6.75 kcal/mol. Due to the high conformational energy barrier of POPC, phase transition of POPC is limited in comparison with DPPC(C16).

Interactions of Alkylphosphocholines with Model Membranes—The Langmuir Monolayer Study

“…Regarding the isotherms for pure membrane lipids, their characteristics are very well known and our results are in a good agreement with the data already published (see, e.g., Cadena-Nava et al 2006 for cholesterol; for DPPC Klopfer and Vanderlick 1996; Duncan and Larson 2008; Crane et al 1999; and for POPC Yun et al 2003). Cholesterol forms very condensed monolayers and collapses at a surface pressure of about 44 mN/m, while DPPC exhibits a characteristic transition region (at ca.…”

Affinity of Alkylphosphocholines to Biological Membrane of Prostate Cancer: Studies in Natural and Model Systems

“…The π / A isotherms for cholesterol and POPC are in agreement with those reported in literature (see for example Miñones et al 2009; or Cadena-Nava et al 2006 for cholesterol and Yun et al 2003 for POPC). The isotherm for model membrane is of a very similar shape to that for pure POPC, however, it is shifted towards smaller areas.…”

An AFM study of solid-phase bilayers of unsaturated PC lipids and the lateral distribution of the transmembrane model peptide WALP23 in these bilayers

“…This looser packing is confirmed by the larger area per lipid [~45–50 Å 2 for saturated di-16:0-PC and ~55–60 Å 2 for (16:0,18:1)-PC (Yun et al 2003)] and larger average chain ordering S of ~0.75, which is closer to that of a saturated palmitoyl chain in the fluid phase ( S  = 0.65) than in the gel phase ( S  = 0.9) (Binder and Gawrisch 2001). In fact, enhanced solubility and reduced lateral ordering of WALP were also found in fluid di-16:0-PC bilayers (Sparr et al 2005).…”

“…The asymmetry between the oleoyl and palmitoyl chain for POPC makes parallel alignment of the chains more difficult than for two symmetrical, unsaturated chains (Yun et al 2003). Computer simulations show that at low temperatures the saturated sn -1 16:0 hydrocarbon chain is fully extended and packs with a tilt angle with respect to the bilayer normal in a gel L β ′ phase, whereas the unsaturated sn -2 18:1 chain can pack only partially parallel to the sn -1 chain (Lee et al 1995; Leekumjorn and Sum 2007).…”