New Triclinic Polymorph of Tristearin

Here we report on the discovery of a new triclinic crystal polymorphic form (beta(1)) of 1,2,3-stearoyl glycerol, or tristearin (SSS), CAS No. 555-43-1. This most stable polymorph of SSS has a melting point of 75.7 +/- 0.5 degrees C and an enthalpy of fusion of 243.9 +/- 10.5 J/g. The most stable polymorphic form for this well-known trisaturated monoacid triacylglycerol was obtained by static crystallization from a dilute solution of SSS in acetone at 4 degrees C over a period of 2 years. In contrast to the well-known beta(2) form of tristearin, which displays wide-angle X-ray scattering reflection positions (relative intensities) at 4.61 A (very strong), 3.86 A (medium), and 3.70 angstrom (medium), the new beta(1) tristearin displayed short-spacing positions (relative intensities) at 4.57 A (weak), 3.84 A (weak), and 3.68 A (very strong). The small-angle X-ray scattering long-spacings corresponding to the lamellar sizes from the (001) plane were 44.91 A, in contrast to 45.21 A for the beta(2) polymorph. This work clarifies controversies and uncertainties related to the number of triclinic polymorphs in trisaturated monoacid triaclyglycerols.

Automated summary

In this study, a new triclinic crystal polymorphic form (beta(1)) of tristearin was discovered with a melting point of 75.7 +/- 0.5 degrees C and an enthalpy of fusion of 243.9 +/- 10.5 J/g. This form was obtained through static crystallization from a dilute solution of tristearin in acetone at 4 degrees C over a period of 2 years. Compared to the well-known beta(2) form, the beta(1) tristearin exhibited different X-ray scattering reflection positions and intensities.