Abstract
Polymorphism of 1, 3-diacylglycerols (on the carbon number of each acyl group, 4 kinds are even and 2 kinds are odd) was examined by differential scanning calorimetry (DSC) and IR spectrometry.
1) Polymorphism of 1, 3-diacylglycerols by DSC indicates endothermic and exothermic peaks during transition from β-a to β-b type. Heat of this transition is extremely small. As the length of the molecularchain becomes shorter, transition to β-b type occurs during elevation of temperature in DSC. Consequently, transition from β-a to β-b can be observed more sharply, the faster the elevation of temperature during DSC measurement.
2) Transition temperatures were measured and data are given in the accompanying table. Fusion temperature of β-b type is the same as that reported, but the transition temperatures from β-a to β-b type as measured by DSC are lower by 12.2°C (C18) to 17.3°C (C14) than those reported.
3) Time required for transition of 1, 3-diacylglycerols of which each aryl group has odd number of carbon atoms was shorter than that of 1, 3-diacylglycerols of which each acyl group has neighboring even number of carbon atoms. Relationship between the time required for transition and molecular chain length shows alternation.
4) 1-Mono- and 1, 3-di- and tristearoylglycerols with the same acyl group were heat treated at 50°C and the time required for transition was compared. The time required for transition of 1, 3-distearoylglycerol was 10h and equal to that of tristearoylglycerol and markedly shorter than that (80h) of 1-monostearoylglycerol.
