Structural Phase Transition due to a Release of Bound Water in Phospholipid Bilayers at Temperatures below 0°C

Abstract

Biophysical Chemistry / Liquid Crystals / Membranes / Phase TransitionsMeasurements of dielectric and calorimetric properties and of the lamellar repeat distance revealed a structural phase transition at temperatures below 0°C in hydrated phospholipid (DPPC) bilayers. The transition is marked 1. by a jump of the dielectric constant at microwave frequencies, 2. by a jump of the lamellar repeat distance, and 3. by an enthalpy of transition. These observations are interpretated by a change of the amount of bound water. Below the transition temperature only seven H,O molecules per lipid molecule are left bound as interlamellar water independent on the amount bound at higher temperatures. The observed loss of bound water at this subzero temperature phase transition may represent a physical process for irreversible freezing effects.Ber. Bunsenges. Phys. Chem. 88, 608-612 (1984) -0 Verlag Chemie GmbH, D-6940 Weinheim, 1984.

Subzero Temperature Behavior of Water in Microemulsions

“…153 clearly shows an endothermic peak below 0°C of bound water superimposed almost completely on the free water melting peak at about 0°C. On the other hand, the enlarged inset of thermogram 1a in Ref.…”

“…The values vary between 1 and 6 mol water/mol lipid [133]. Grünert et al [153] used dielectric spectroscopy, X-ray diffraction methods, and DSC runs to show that DPPC-water mixtures with more than seven H 2 O molecules per molecule of lipid undergo a phase transition at subzero temperatures. Bronshteyn and Steponkus [30] argue that overestimates of the unfrozen water content of DPPC liposomes are obtained owing to an erroneous determination of the baseline of DSC thermograms and to the dependence of the amount of water that freezes during cooling on the thermal history of the sample.…”

“…However, there is no sharp border between nonfreezable and bound water. The amount of bound water that exceeds these seven H 2 O molecules per lipid is thought to be squeezed out of the interbilayer regions together with the free water, which exists in samples with concentrations Ն15 H 2 O molecules/lipid [153]. Using an iterative procedure for a correct estimation of the baseline in the DSC thermograms and a three-step protocol of temperature change, they obtained hydration numbers of 4.7 and 5.6 mol water/mol DPPC for suspensions containing 30-70 and 16.2 Ϯ 0.2 wt% water, respectively.…”

“…Indeed, in the case of the DPPC-water system, Grünert et al [153] arguedrelying on X-ray diffraction data-that bound water is squeezed out of the interbilayer regions. Indeed, in the case of the DPPC-water system, Grünert et al [153] arguedrelying on X-ray diffraction data-that bound water is squeezed out of the interbilayer regions.…”

X-ray studies on polymorphism of lamellar lecithin/local anaesthetic/water mixtures

“…The chains are arranged in an orthogonal lattice within the bilayer. The distance between the lamellae is for 6.36 nm at 258 K. Grunert et al [5] discussed a value dL of 5.8 nm for the low temperature phase L, of the system dipalmitoyl lecithin/water. Since both dL values are of the same Structural parameters for the ternary system dipalmitoyl-lecithin/heptacaine/water with different compositions as a function of temperature.…”