Molecular interactions in binary solids: crystal structure of a cholesteryl ester solid solution.

The x-ray crystal structure analysis of a cholesteryl ester solid solution, cholesteryl undecanoate/cholesteryl laurate in a molar ratio 0.52/0.48, is described. The unit cell is monoclinic with a = 13.005(2) A, b = 9.005(1) A, c = 31.421(3) A, and beta = 90.82(1) degrees and the space group P2(1) with Z = 4 (two molecules per asymmetric unit). Thus, the d001 spacing is almost the value predicted by Vegard's law from the values for the pure compounds. The room-temperature crystal structure is very much like that of cholesteryl laurate monolayer I packing, in the form where the esterified fatty acid chains are fully extended, with no salient sign of conformational disorder seen in this binary solid. The final R factor for 6571 observed reflections is 0.097.