Insertion of semifluorinated diblocks on DMPC and DPPC liposomes. Influence on the gel and liquid states of the bilayer.

Differential Scanning Calorimetry (DSC) was used to study the effect of the incorporation of a series of semifluorinated diblocks F(n)H(m) (F(6)H(10), F(6)H(16), F(8)H(14), F(8)H(16), F(8)H(18) and F(8)H(20)) on the gel and liquid states of the bilayer of large multilamellar DMPC and DPPC liposomes. The presence of the F(n)H(m) diblocks affects slightly the T(m) of the main gel-liquid transitions of DMPC and DPPC, but is accompanied by the appearance of a second transition in the calorimetric traces whose T(m) is mainly determined by the length of the F(n) segment. The DSC results are consistent with the previously established conclusion that the F(n) segments of the diblocks form a central layer in the core of the lipid bilayer, with the H(m) segments being interdigitated with the lipid chains. The DSC traces suggest that the structure of the fluorinated liposomes is a double bilayer at 3:4 and 1:2 and a trilayer at 2:1 lipid/F(n)H(m) molar ratios. At temperatures between the two phase transitions T(m)'s, the fluorinated liposomes are neither in a gel-like or a liquid-like state but rather possess both characteristics.