Structure and pseudosymmetry of cholesterol at 310 K.

The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form [Hsu & Nordman (1983). Science, 220, 604-606], has been fully refined using augmented X-ray data. The crystals are triclinic, space group P1, with (reassigned) cell parameters a = 27.565 (10), b = 38.624 (16), c = 10.748 (4) A, alpha = 93.49 (3), beta = 90.90 (3), gamma = 117.15 (3) degrees, and V = 10151 (7) A(3). The unit cell contains Z = 16 molecules, of which eight are related to the other eight by unusual twofold rotational pseudosymmetry. The structure is related to the room-temperature phase, with Z = 8, by a rearrangement of some of the molecules, and by a doubling of the a axis.