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Freezing and melting water in lamellar structures
J T Gleeson1, S Erramilli, S M Gruner
1Department of Physics, Joseph Henry Laboratories, Princeton University, New Jersey 08544.
Biophysical Journal
|August 1, 1994
Summary
Ice formation in lipid suspensions depends on water content. Below 9% water, ice doesn't form, allowing measurement of hydration forces between lipid bilayers.
Area of Science:
- Lipid bilayer behavior
- Physical chemistry of water
- Phase transitions in soft matter
Background:
- Lamellar lipid suspensions exhibit complex phase behavior with water.
- Understanding ice formation is crucial for cryobiology and materials science.
- Lipid headgroup interactions influence water structuring.
Purpose of the Study:
- To investigate the influence of water fraction on ice formation in lipid suspensions.
- To characterize the location and properties of ice within lamellar lipid systems.
- To quantify hydration forces between lipid bilayers using ice formation as a probe.
Main Methods:
- Differential scanning calorimetry to study freezing and melting transitions.
- Analysis of ice location within lipid bilayers via structural studies.
- Utilizing the chemical potential of ice to measure interbilayer forces.
Main Results:
- Ice formation and melting behavior are strongly dependent on water weight fraction.
- Below 9% water, ice does not form even at -40°C.
- Ice forms as crystalline pools in equilibrium with bound water, not between bilayers.
- Hydration repulsion between bilayers decays exponentially below 7 Å, with deviations at larger separations.
Conclusions:
- The water fraction critically dictates ice formation in lipid suspensions.
- Ice location within lipid systems is not interstitial but in separate pools.
- This phenomenon enables precise measurement of hydration forces between lipid bilayers.
- Hydration forces exhibit exponential decay at close contact, deviating at larger distances.