Fifteen phase diagrams were prepared using data from differential scanning calorimetry analysis of binary blends of representative diacid 1,3-DAG. The behavior observed in binary phase diagrams is related to the difference in T m (DT m ) between system components-eutectic for DT m \ 26°C and monotectic for DT m [ 30°C. Binary blends were prepared using six diacid 1,3-DAG: 1and 1,3-palmitoyl-oleoyl-rac-glycerol. Diacid 1,3-DAG were synthesized using representative FA: hexanoic (6:0)-shortchain FA; lauric (12:0)-medium-chain FA; palmitic (16:0)-long-chain FA; and oleic (18:1)-mono-unsaturated FA. In addition to the aforementioned phase diagrams, the physical chemistry of 1,3-hexanoyl-lauroyl-rac-glycerol, 1,3-hexanoyl-oleoyl-rac-glycerol and 1,3-lauroyl-oleoylrac-glycerol is reported.

A complete methodology (including synthesis, purification and analysis) for the preparation of 1,3-DAG is described. For a successful synthesis project, the strengths and weaknesses of each particular process should be taken into account and measures taken to offset or balance potential weaknesses. To this end, we describe some of the challenges associated with: chemically and enzymatically catalyzed acylglycerol syntheses; recrystallization and flash chromatography for purification of partial acylglycerols; and thin-layer chromatography (TLC) separation of DAG. For this work, 1-MAG intermediates and subsequent diacid 1,3-DAG were prepared using non-enzymatic methods, whereas, monoacid 1,3-DAG were prepared by enzymatic methods. It was not always possible to obtain pure samples of target compounds-in recrystallizations this is due to solid solution formation and co-crystallization and in chromatographic separations it is due to co-elution of components with similar R f . Furthermore, TLC R f of DAG is determined by two main factors: acyl chain length and positional isomerism. Interestingly, while the role of positional isomerism is well-known, the role of acyl chain length in these separations has only recently come to light.

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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-2position), 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.

Crystallization and melting behavior, smallangle X-ray scattering, X-ray powder diffraction and infra-red absorbance were measured for nine 1,3-acyl-palmitoyl-racglycerols (1,3-acetoyl-, -butyroyl-, -hexanoyl-, -octanoyl-, -decanoyl-, -lauroyl, -myristoyl-and -oleoyl-palmitoyl-racglycerol and 1,3-dipalmitoyl-glycerol). All but one of the prepared 1,3-diacylglycerols (1,3-DAG) were b-stable with 1,3-acetoyl-palmitoyl-rac-glycerol being the exception (b 0 -stable). Small-angle X-ray scattering indicates that molecules in b-tending diacid 1,3-DAG adopt a herringbonetype configuration similar to monoacid 1,3-DAG. In this configuration acyl chains of the same length associate and regular chain-end matching between terminal methyl groups delineate lamellae. In contrast, molecules in crystalline 1,3-acetoyl-palmitoyl-rac-glycerol are oriented similar to those of 1(3)-monoacylglycerol. Interestingly, DSC curves indicate five of the nine diacid compounds have meta-stable forms-suggesting these forms are quite common for diacid 1,3-DAG. Meta-stable forms are observed in the melting curve when the difference in length between acyl chains is large (1,3-acetoyl-, -butyroyl-and -hexanoyl-palmitoylrac-glycerol), and in the crystallization curve when the difference is moderate (1,3-decanoyl-and -lauroyl-palmitoylrac-glycerol).