Solubilization of glucose and related sugars by lecithin.

The solubilization of glucose and several related sugars in benzene solutions of rigorously purified phosphatidylcholine has been studied; the equilibrium degree of solubilization has been found to depend on the size of the sugar molecule relative to that of the lecithin micelle, and on the number and the acidity of its free hydroxyl groups. The uptake of glucose increased as the lecithin concentration decreased, achieving a 1: 1 molar ratio at a concentration below the critical micelle concentration at which small micelles of lecithin aggregate into larger ones. Osmometric evidence indicated that, at higher concentrations, the glucose was carried within the lecithin micelle. Enthalpy and entropy of solubilization have been evaluated, and are consistent with a mechanism involving hydrogen bonding via the glucose hydroxyl groups. Cholesterol, when present as cosolute, competed for hydrogen bonding sites on the lecithin and thus lowered the degree of solubilization, but in benzene solutions lecithin exhibited a 5: 1 preference for glucose hydroxyl over cholesterol hydroxyl.