Effect of perfluoroalkyl chain length on monolayer behavior of partially fluorinated oleic acid molecules at the air-water interface

A series of oleic acid (OA) analogs containing terminal perfluoroalkyl groups (CF3, C2F3, n-C3F7, n-C4F9 or n-C8F57) was synthesized to clarify how the fluorinated chain length affects the stability and molecular packing of liquid-expanded OA monolayers at the air-water interface. Although the substitution of terminal CF3 group for CH3 in OA had no effect on monolayer stability, further fluorination led to a gradual increase in monolayer stability at 25 degrees C. Surface pressure-area isotherm revealed that partially fluorinated OA analogs form more expanded monolayers than OA at low surface pressures, and that the monolayer behavior of OA analogs with the even-carbon numbered fluorinated chain is almost the same as that of OA upon monolayer compression, whereas the behavior of OA analogs with the odd-carbon numbered fluorinated chain significantly differs from that of OA. These results indicate; (i) the terminal short part (at least C-2 residue) in OA predominantly determines the liquid-expanded monolayer stability; (ii) the molecular packing state of OA may be perturbed by the substitution of a short odd-carbon numbered fluorinated chain; (iii) hence, OA analogs with even-carbon numbered chain are considered to be preferable as hydrophobic building blocks for the synthesis of fluorinated phospholipids. (c) 2013 Elsevier Ireland Ltd. All rights reserved.