Crystal-structure determination of b-C₁₅C₁₇C₁₇ from high-resolution powder diffraction

Jan B. van Mechelen, Dirk J.A. De Ridder, René Peschar, Henk Schenk

University of Amsterdam, Laboratory for Crystallography, IMC, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands

The crystal structure of the b polymorph of the pure triacylglycerol C₁₅C₁₇C₁₇ (2,3-diheptadecanoyl-1-pentadecanoylglycerol), has been determined using high resolution synchrotron powder diffraction. The simulated annealing approach, as implemented in the program FOX [1], was used to obtain the initial model. The model was refined with the Rietveld refinement program GSAS [2]. Bond- angle- and plane group restraints have been applied.

The crystal structure model shows that the b polymorph of C₁₅C₁₇C₁₇ crystallizes in the tuning-fork conformation. The zig-zag planes of the acyl chains are parallel packed. The methyl end groups of two adjacent layers form a plane but the hydrocarbon chain ends are not in line.

[1] Favre-Nicolin V. and Cerny R. (2002). J. Appl. Cryst. 35, 734-743.

[2] A.C. Larson and R.B. Von Dreele, "General Structure Analysis System (GSAS)", Los Alamos National Laboratory Report LAUR 86-748 (1994).