Polymorphism and Mixing Phase Behavior in Ternary Mixture Systems of SOS–SSO–OSO: Formation of Molecular Compound Crystals

Abstract

This paper reports the phase behavior of ternary mixtures of saturated and cis-monounsaturated mixed-acid triacylglycerols (TAG) of SOS (1,3-distearoyl-2-oleoyl-glycerol), SSO (1,2-distearoyl-3-oleoyl-rac-glycerol), and OSO (1,3-dioleoyl-2-stearoyl-glycerol) examined with X-ray diffractometry and a differential scanning calorimeter. The ternary mixtures were crystallized by cooling from melt (60 C) to 5 C, and the crystals were then stabilized by storing the mixture samples at 28 C for 10 days. The following results were obtained. (1) Molecular compound (MC) crystals of stable β polymorph having a double-chain-length structure (β-2) were formed in mixtures of SOS/SSO/OSO in which the concentration of SOS was 50% with varying concentrations of SSO/OSO. This is in contrast to the fact that the stable polymorphic forms of the component TAG are β-3 for SOS and OSO and β 0 -3 for SSO. (2) When the concentration of SOS deviated from 50%, immiscible mixtures of β-2 MC made of SOS/SSO/OSO and the component TAG (β-3 of SOS and OSO and β 0 -3 of SSO) were formed. Therefore, ternary mixtures of SOS/(SSO + OSO) = 50/50 with different concentrations of SSO and OSO are miscible mixtures of β-2 of SOS/SSO and SOS/OSO. Keywords Ternary phase behavior Á Molecular compound Á Polymorphism Á Triacylglycerol J Am Oil Chem Soc (2018) 95: 447-460.

Mixing Phase Behavior of Tripalmitin and Oleic-Rich Molecular Compound-Forming Triacylglycerols

“…The stable diagram of OPO/OOP showed to be eutectic at the 50/50 composition, whereas the higher difference in melting temperature between TAGs due to an additional palmitic acid moiety caused the shifting of the eutectic point to a composition at 70–80% OOP in POP/OOP mixtures and above 90% OPO in the PPO/OPO system. − Interestingly, a simple change in the palmitic acid sn -position in POP/OPO mixtures resulted in the formation of a molecular compound (MC) at a 1:1 concentration ratio with its own unique structural and thermodynamic properties . Equivalent mixing behavior was observed in POP/PPO mixtures, as well as in their stearic acid-based counterparts, as a result of the specific stabilizing interactions occurring between mixed-acid TAGs with a particular molecular symmetry. ,, Moreover, the ability of molecular compound-forming binary systems to form stable β-2L (MC) ternary solid solutions has been recently reported for SOS/SSO/OSO mixtures …”

Tripalmitin‐Driven Crystallization of Palm Oil: The Role of Shear and Dispersed Particles

“…Instead, excess POP may have complexed with PPO and PPP to form MC POP:PPO:PPP in addition to MC POP:PPP already present. A precedent for the intersolubility between three TAG forming one MC has been observed in mixtures of 1,3-distearoyl-2-oleoyl-sn-glycerol, 1,2-distearoyl-3-oleoylrac-glycerol, and 1,3-dioleoyl-2-stearoyl-sn-glycerol (Watanabe et al, 2018). POO simply acted as a diluent in this mixture as indicated by the lower signal-to-noise ratio in WAXD, SAXD, and DSC (Fig.…”

An Insight into the Solid-State Miscibility of Triacylglycerol Crystals

“…After 10 days of thermodynamic stabilization at 28 °C, mixtures with a 50SOS/50(SSO/OSO) composition showed to be exclusively formed by molecular compound and, more specifically, by a miscible β-2L phase of MC SOS/SSO and MC SOS/OSO . By contrast, eutectic mixtures of MC SOS/SSO/OSO and either β’-3L (SSO) or β-3L (OSO) crystals were formed when the mentioned concentration ratio was not present in the mixtures [ 66 ]. According to the SR-XRD data gathered during the cooling and subsequent heating of the mixtures at 2 °C·min −1 , MC SOS/SSO/OSO was not readily obtained from the melt, and α (MC SOS/SSO ) and β (MC SOS/OSO ) crystallized instead.…”

“…Lastly, strong interactions between TAGs that exhibit specific molecular composition and symmetry may lead to the formation of a molecular compound, whose unique structural and thermodynamic properties strongly differ from those of the individual TAGs [ 57 , 64 , 65 , 66 ]. Contrary to solid solutions, this kind of association presents a stoichiometric nature, which eventually results in phase diagrams with juxtaposed eutectic mixtures of the molecular compound and each component TAG bounded by the mixture at equimolecular composition.…”