Structures and Binary Mixing Characteristics of Enantiomers of 1-Oleoyl-2,3-dipalmitoyl-sn-glycerol (S-OPP) and 1,2-Dipalmitoyl-3-oleoyl-sn-glycerol (R-PPO)

• Published in: Journal of the American Oil Chemists' Society 2013-12, Vol.90 (12), p.1809-1817
• Main Authors: Mizobe, Hoyo, Tanaka, Tomoyuki, Hatakeyama, Naoko, Nagai, Toshiharu, Ichioka, Kenji, Hondoh, Hironori, Ueno, Satoru, Sato, Kiyotaka
• Format: Article
• Language: English
• Subjects: Agriculture; Biomaterials; Biotechnology; Calorimetry; Chemistry; Chemistry and Materials Science; cooling; Crystallization; differential scanning calorimetry; Enantiomer; enantiomers; Food Science; glycerol; Industrial Chemistry/Chemical Engineering; Melting point; mixing; Oils & fats; Original Paper; palmitic acid; Polymorphism; PPO; Racemic structure; Triacylglycerols; X-ray diffraction
• ISSN: 0003-021X; 1558-9331
• DOI: 10.1007/s11746-013-2339-4

We performed differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffraction (SR-XRD) experiments of polymorphic structures and binary mixing characteristics of the enantiomers of 1-oleoyl-2,3-dipalmitoyl-sn-glycerol (S-OPP) and 1,2-dipalmitoyl-3-oleoyl-sn-glycerol (R-PPO). In the two enantiomers, oleic and palmitic acid moieties are asymmetrically connected at the sn-1 and sn-3 positions of the glycerol groups, with palmitic acid moiety at the sn-2 position. Pure enantiomer samples (>99 %) were synthesized and employed throughout this study. The following results were obtained. (1) A basic feature of the mixture systems of S-OPP and R-PPO is of a eutectic nature due to different polymorphic structures of two enantiomers and the racemic compound of PPO (rac-PPO). (2) Polymorphic behavior of S-OPP and R-PPO was quite similar, both having α-2 and β′-3, whereas rac-PPO contained α ᵣₐc-3, β′ᵣₐc-2, and β′ᵣₐc-3. The DSC measurements showed that the melting points of β′-3 (S-OPP = 35.3 °C and R-PPO = 34.9 °C) were higher than that of β′ᵣₐc-3 (31.0 °C). β was not crystallized in the pure enantiomers, and rac-PPO. (3) αᵣₐc-3 was crystallized at low cooling rates (~2 °C/min), whereas α-2 of the two enantiomers was crystallized only with very rapid cooling (~10 °C/min). (4) Triple-chain-length structures were formed in αᵣₐc-3, β′S-3 (=β′R-3), and β′ᵣₐc-3; α-2 with a double-chain-length structure was formed in both enantiomers. These results indicate the importance of the relationship between subcell packing and glycerol conformation in the polymorphism and mixing characteristics of asymmetric unsaturated–saturated-saturated mixed-acid triacylglycerols.