In situ synchrotron radiation X-ray diffraction study of crystallization kinetics of polymorphs of 1,3-dioleoyl-2-palmitoyl glycerol (OPO)

Abstract

We examined the influence of kinetics on the polymorphic behavior of 1,3-dioleoyl-2-palmitoyl glycerol (OPO), a triacylglycerol (TAG) present in natural oils such as olive oil and human breast milk. Pure OPO was heated at 15 °C min⁻¹ in all cases. The polymorphic crystallization of OPO was studied at different cooling rates (15, 2, 1, and 0.5 °C min⁻¹), and the dynamic polymorphic transformations were characterized on heating by simultaneously using Differential Scanning Calorimetry (DSC) and Synchrotron Radiation X-Ray Diffraction (SR-XRD) with small-angle X-ray diffraction (SAXD) and wide-angle X-ray diffraction (WAXD). Thermo-Optical Microscopy (TOM) was also used in order to observe the polymorphic transitions. Polymorphic forms of OPO were identified and characterized. As the cooling rate decreased, more stable forms crystallized, not following the Ostwald step rule, although in most cases concurrent crystallization occurred and the whole process was highly complex.