Phase Transition Behavior of the Highly Asymmetric Chain Length N-lignoceroylsphingomyelin (C24:0-SM) Bilayer System

A study on phase transition behavior of sphingophospholipid-water system was performed for the highly asymmetric chain length N-lignoceroylsphingomyelin (C24:0-SM) with a differential scanning microcalorimetry (DSC). The C24:0-SM was partially synthesized by a deacylationreacylation process with naturally occurring sphingomyelin used as a starting material. The C24:0SM showed a low-temperature phase transition of the subgel-to-gel phase (TS), successively followed by the common phase transition of the gel-to-liquid crystal phase (TM). The TS transition enthalpy decreased with an increase in periods of thermal annealing performed at the TM transition temperature. This indicated that the TM transition accompanies a change in the packing mode which proceeds very slowly up to the annealing periods of 9h. In this accord, the electron micrographs of the subgel phase showed a drastic structural change of planer bilayer stacks into multilamellar vesicles and finally into small size unilamellar vesicles, which appear with increasing the periods of the annealing.