Abstract
Polymorphism, temperature of phase transition, enthalpy and entropy of trans-monounsaturated monoglycerols were investigated, and correlation between trans- and cis-monounsaturated monoglycerols was examined.
1) Trans-monounsaturated monoglycerols have β, α, and Sub-α type polymorphism, but Sub-α2 was not observed even in monobrassidoylglycerol. Consequently, the acyl groups of monoglycerols capable of forming Sub-α2 are restricted by the structure having saturated hydrocarbon longer than 18 carbon atoms. Trans-monounsaturated monoglycerols showed similar transition behavior to cis-monounsaturated monoglycerols, and easily transformed from metastable to stable state at room temperature.
2) Temperature of phase transition, enthalpy and entropy of trans-monounsaturated monoglycerols were listed in the Table. It was characteristic that enthalpy and entropy of monobrassidoylglycerol for Sub-α→α transition were larger than those of monoelaidoylglycerol.
3) Temperature of phase transition, enthalpy and entropy of trans-monounsaturated monoglycerols were larger than those of cis-monounsaturated monoglycerols at each phase. These differences between cis- and trans-monounsaturated monoglycerols were larger at metastable than stable state, and became larger in the monoglycerols having shorter acyl groups.
