Scanning calorimetric evidence for a third phase transition in phosphatidylcholine bilayers.

Abstract
A 3rd phase transition, centered at about 18.degree. C, was observed by differential scanning calorimetry in a multilamellar suspension of dipalmitoyl phosphatidylcholine that was held at 0.degree. C for several days. This transition is less cooperative than the other 2 transitions which are well-known for this system and it is accompanied by an enthalpy increase about 3 times as large as that of the so-called pretransition at 35.degree. C and about half that of the main gel to liquid crystal transition at 41.degree. C. The reversal of this transition on colling is extremely slow.