REAL-TIME X-RAY-DIFFRACTION STUDY AT DIFFERENT SCAN RATES OF PHASE-TRANSITIONS FOR DIPALMITOYLPHOSPHATIDYLCHOLINE IN KSCN

Multibilayer arrays of dipalmitoylphosphatidylcholine (DPPC) in 1 M KSCN were characterized using real-time X-ray diffraction and differential scanning calorimetry. A phase transition sequence was observed as a function of increasing temperature which involved changes from the interdigitated subgel (L(c)(inter)) to interdigitated gel (L(beta)(inter)) to disordered (L(alpha)) bilayer states. The phase transition mechanisms were unambiguously determined by comparison of results from fast and slow scans. The L(c)(inter)-->L(beta)(inter) phase transition was shown to involve a continuous change in acyl chain spacing between the rectangular subgel acyl chain unit cell into an hexagonal gel acyl chain unit cell. The mechanism is similar to that for subgel to gel state transitions involving non-interdigitated DPPC bilayers.