The Effect of Self Interdigitating Phospholipids on Bilayer Membranes
Christiaan van Gorkum
Project Advisor: Phoebe Dea

     Differential scanning calorimetry (DSC) and fluorescence spectroscopy were used to investigate the phase behavior of hydrated dipalmitoylphosphatidylcholine (DPPC), a 16 carbon chain phospholipid, upon mixing with a self interdigitating phospholipid (SIP). Interdigitation is a special phase of bilayer membranes in which the phospholipids acyl chains interpenetrate, halving membrane thickness.
     Mixtures of DPPC and SIP showed increasing main transition temperatures (T_m’s) with rising SIP percentage. Consecutive heating and cooling scans had shifting T_m’s, shoulder peaks appeared or disappeared and an increasing trend in hysteresis between heating and cooling T_m was discovered in presence of 30-50% SIP.
     For the fluorescence studies, 2-(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (β-DPH HPC), a phospholipid bound probe, was added in low concentration to the DPPC - SIP mixtures to determine the percentage SIP which causes bilayers to interdigitate. Decreasing fluorescence intensity is directly correlated to exposure of β-DPH HPC to aqueous environment, as occurs with interdigitation. This appeared to be at 30% SIP.
     The trend in hysteresis and decrease in fluorescence indicate that a ~40% ratio of SIP : DPPC can induce interdigitation of bilayer membranes.

Support provided by: Chemistry Alumni Fund Fellowship