Effect of the fluorination degree of hydrophobic chains on the monolayer behavior of unsaturated diacylphosphatidylcholines bearing partially fluorinated 9-octadecynoyl (stearoloyl) groups at the air-water interface

The effect of the fluorination degree of hydrophobic chains on the monolayer behavior of unsaturated diacylphosphatidylcholines (PCs) was examined by employing a series of PCs bearing partially fluorinated 9-octadecynoyl (stearoloyl) groups (DF(n)StPCs, n: the number of fluorinated carbon atoms in a stearoloyl group; n = 1, 2, 4, 8), including their hydrophobic parts - partially fluorinated stearolic acids (F(n)StAs) - at the air-water interface. pi-A isotherm measurements and Brewster angle microscope observations revealed: (i) all DF(n)StPCs including F(n)StAs form monolayers of liquid character at 25 degrees C; (ii) they form more expanded monolayers than their non-fluorinated counterparts, distearoloyl-PC (DStPC) and stearolic acid, while the monolayer stability increases with n; (iii) compared with DStPC and DF(8)StPC, DF(n)StPCs (n=1, 2, 4) in the low-pi region tend to show a weakening in their self-aggregation property and an increase in the work required for monolayer compression; (iv) although DF(8)StPC forms the most expanded monolayer, the behavior of DF(8)StPC resembles that of DStPC rather than that of DF(n)StPCs (n = 1, 2, 4). The monolayer behavior of DF(n)StPCs (n=1, 2,4) is explained by postulating a flatly-lying conformation of hydrophobic chains, in which three polar parts (ester group, triple bond, CF2-CH2 linkage) in chains are immersed in the subphase at large areas. DStPC and DF(8)StPC lacking a CF2-CH2 linkage, however, do not likely adopt such a conformation. (C) 2014 Elsevier B.V. All rights reserved.