Change in volume magnetic susceptibility at the phase transition of dipalmitoylphosphatidylcholine.

We have observed a change at 41 degrees C in the relative volume magnetic susceptibility of an aqueous dispersion containing 13 wt% multilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles. The magnitude of the change is consistent with the known density change of the phospholipid bilayer and the assumption that the mass susceptibility of the system is constant through the transition. The superconducting susceptometer used in this study of the sharp transition of DPPC will be able to detect 1% changes in bilayer density for 10 wt% dispersions even when the transition temperature and transition width of phospholipid vesicle under various experimental conditions.