Influence of calcium on phosphatidylglycerol. Two separate lamellar structures.

The influence of calcium on the structure of rac-1,2-ditetradecylglycerol-3-phosphoglycerol is investigated by differential scanning calorimetry and by X-ray diffraction. It is shown that 1 M CaCl2 (pH 4.6) induces two separate lamellar phases in the same sample at 20 degrees C. These two phases can be clearly distinguished by their X-ray diffraction patterns. The type of phase observed depends on the pretreatment of the sample. At high temperature (90 degrees C), when the hydrocarbon chains are in the disordered state, the small angle reflections are in the ratio 1:1/square root 3:1/2 and thus indicate the presence of a hexagonal phase.