Modification of dry 1,2-dipalmitoylphosphatidylcholine phase behavior with synthetic membrane-bound stabilizing carbohydrates.

Carbohydrates, particularly disaccharides, have been shown to accumulate in organisms as protective solutes during periods of stress such as freezing and desiccation. Cholesterol and lipid derivatives containing the protective carbohydrates galactose or maltose, O-11-(1-beta-D-galactosyloxy)-3,6,9-trioxaundecanyl]ol (TEC-GAL), O-11-(1-beta-D-maltosyloxy)-3,6,9-trioxaundecanyl]ol (TEC-MAL), and 14-(galactosyloxy)-N,N-dimethyl-O-(dipalmitoylphosphatidyl)- 6,9,12-trioxa-3- azoniatetradecanol (DP-GAL), have been synthesized to investigate the interaction of a protective carbohydrate moiety tethered to the 1,2-dipalmitoylphosphatidylcholine (DPPC) bilayer surface. Toward this goal, we have investigated the calorimetric and infrared spectroscopic behavior of mixtures of DPPC codried with these glycolipids. The synthetic glycolipids are shown to decrease significantly the main transition temperature (max Cp) of dry DPPC with a concomitant reduction in the cooperativity of the transition, as evidenced by a decrease in the enthalpy with increasing glycolipid. The decrease in transition temperature is shown to be related to chain melting monitored by the CH2 symmetric stretch frequency through the transition using FTIR. We also present evidence that the glycolipids interact with the interfacial region of DPPC, as shown by the decrease in the phosphate symmetric stretch intensity with increasing concentration of glycolipid. These observed effects are similar to the action of bulk protective sugars with DPPC; however, the concentration of glycolipid and the associated carbohydrate concentration needed to effect the observed changes are reduced compared to the quantity of bulk carbohydrate previously shown to give similar results with DPPC.