Effect of water on lamellar structure of DPPC/sugar systems.

The ability of two monosaccharides, four disaccharides and one trisaccharide, to lower the transition temperature of L-alpha-dipalmitoyl phosphatidylcholine (DPPC) was investigated using differential scanning calorimetry (DSC) and the ability of these sugars to change the lateral packing of the acyl chains of DPPC was investigated using wide-angle X-ray diffraction. The sugars affected the gel-liquid crystal transition temperature (Tc) of DPPC when the water content of the DPPC/sugar systems was less than 20 wt.%. Specifically, Tc of the DPPC without sugar increased to approximately 106 degrees C, the Tc of the DPPC/monosaccharide system remained almost constant at 43 degrees C and of the DPPC/disaccharide or trisaccharide systems decreased to approximately 24 degrees C. In the dehydrated state, di- and trisaccharides caused looser packing of the DPPC hydrocarbon chains than the monosaccharides did, and the sugars affected the packing mode in different ways. The addition of water caused this difference in the sugars' effects on the packing mode to disappear and further addition of water caused the effect of sugar to almost disappear. Thus, the addition of water to a DPPC/sugar system weakens the interaction between the sugar and lipid and strengthens the DPPC chain packing.