or monounsat. analogues. The order of increasing probability of the sat. chains at 250 K is: NM < MMU < MMS, which indicates that the presence of CP rings unfavor the straightening of the sat. chains more than C=C double bonds and thereby suppress the close-packing of the lipids to form gel. However, the dihedral angles of the monounsat. chains are not much affected by the presence of CP rings or fully saturated chains.