Crystallization, Polymorphism, and Binary Phase Behavior of Model Enantiopure and Racemic Triacylglycerols

• Published in: Crystal growth & design Vol. 11; no. 5; pp. 1723 - 1732
• Main Authors: Craven, R. John, Lencki, Robert W
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 04.05.2011
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase diagrams of metals and alloys; Physics; Solid-solid transitions; Specific phase transitions; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Racemates; Infrared spectroscopy; Phase diagrams; Unit cell; Enantiomer; Metastable states; Crystallization; XRD; Polymorphism; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg101654c

Triacylglycerols (TAG) are the main component in fats and oils and a major component in many food and consumer products. These compounds are always asymmetric (about the sn-2 position), while many diacid and all triacid TAG are chiral. To understand what effect this has on their crystallization behavior, model enantiopure (1,2-bisdecanoyl-3-palmitoyl-sn-glycerol) and racemic (bisdecanoyl-1(3)-palmitoyl-rac-glycerol) TAG were prepared and characterized. In addition, a binary phase diagram was prepared to investigate their phase behavior and the racemate’s crystalline tendency. For the subject compounds, infrared spectroscopy and X-ray powder diffraction data indicate the enantiopure TAG is β′-stable, whereas the racemic mixture is β-stable. In addition, based on the phase diagram, the high-melting form of the racemic mixture is a racemic compound (with a unit cell containing equal quantities of both enantiomers). Racemic (and near-racemic) mixtures also crystallize in a lower-melting metastable conglomerate β′ form. Thus, there are critical differences between the crystallization behavior of enantiopure and racemic TAG, and future investigations of these compounds should reflect these findings.