Calorimetric investigation of the complex phase behavior of glucocerebroside dispersions

Abstract

The thermotropic behavior of aqueous dispersions of glucocerebroside from [human] Gaucher''s spleen was investigated by differential scanning calorimetry. Glucocerebroside apparently undergoes 2 distinct phase transitions centered at 47 and 83.degree. C, respectively. The high-temperature transition is associated with the main gel-liquid crystalline transition and has an enthalpy change of 13.6 kcal/mol of lipid; this transition is not rapidly reversible and the liquid crystalline phase supercools to a metastable gel phase. The low-temperature transition is exothermic with an enthalpy change of -6.3 kcal/mol and involves a transformation of the metastable gel phase to a more highly ordered gel conformation, without involving changes in the conformational state of the hydrocarbon chains. The behavior of these transitions as a function of the amount of water suggests that the origin of the metastability is related to a hydration-dehydration process of the cerebroside molecule. Experiments with synthetic D-erythro-N-palmitoylglucocerebroside revealed the same thermotropic behavior. These glucocerebroside transitions are irreversible and together define a unidirectional cycle in which each state of the molecule can only be reached by completing the entire cycle.