Synthesis and monolayer properties of double-chained phosphatidylcholines containing perfluoroalkyl groups of different length

A series of double-chained phosphatidylcholines (PCs), 1,2-dioctadec-9′-ynoyl-sn-glycero-3-phosphocholine analogs containing perfluoroalkyl moieties (CF₃, C₂F₅, n-C₄F₉ or n-C₈F₁₇) as the terminal segment in two hydrophobic chains, 1a-d, were synthesized. Equilibrium spreading pressures of these fluorinated PCs at the air-water interface were measured as an indication of monolayer stability, in order to obtain the minimal fluorine content in PC molecule efficient to exhibit monolayer stabilizing effect. The monolayer stability sigmoidally increased with the fluorine content in PC molecule and subsequently leveled off above a certain fluorine content, i.e., n-C₄F₉ moiety, at 25 °C. Under this condition, the replacement of at least five hydrogen atoms at the terminal hydrophobic segment in double-chained PC molecule by fluorine atoms, i.e., CF₃CF₂ moiety, is required to exhibit the monolayer stabilizing effect, whereas further fluorination of double-chained PC (F(CF₂)_n; n > 4) has a minor effect on the monolayer stability.