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On the reversibility of the phase transitions in lipid-water systems

✍ Scribed by B. Tenchov

Publisher
Elsevier Science
Year
1991
Tongue
English
Weight
906 KB
Volume
57
Category
Article
ISSN
0009-3084

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✦ Synopsis

Heating and cooling phase sequences observed in phospholipid and glycolipid dispersions in excess water have been summarized. Differences between heating and cooling sequences and also with respect to a reference phase sequence "subgel--gel--lamellar liquid crystalline--cubic--inverted hexagonal" have been pointed out. Together with kinetic data obtained by alternating current (AC) calorimetry, these data have been used for a discussion on the reversibility of the lipid phase transitions. Several typical symptoms of irreversible behavior are (i) undercooling of stable phases; (ii) formation of phases which are metastable over the whole range of their existence; (iii) slow formation of the nascent phase requiring isothermal annealing out of the transition region; (iv) different nonconvergent transition pathways in heating and tooling. These phenomena are related to the appearance of slow rearrangement modes during the phase transitions with characteristic times longer than experimental time scales. Similarly slow relaxations supporting the existence of long-lived non-equilibrium lipid states in the biomembranes may have also certain physiological significance.

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