Conformation of the oleate chains in crystals of cholesteryl oleate at 123 K.
1990; Elsevier BV; Volume: 27; Issue: 11 Linguagem: Inglês
10.1016/s0022-2275(20)38757-5
ISSN1539-7262
Autores Tópico(s)Analytical Chemistry and Chromatography
ResumoAt 123 K, crystals of cholesteryl cis-9-octadecenoate (cholesteryl oleate, C45H780P) are monoclinic, space group P21 with unit cell dimensions a = 12.356(2), b = 8.980(3), c = 18.382(2)A, @ = 85.49(2)', and have two molecules in the unit cell.The crystal structure including all H atoms has been determined from 38 12 independent X-ray reflections with sin O/A < 0.61 A-' and refined to give R, = 0.08.At 123 K, the crystal structure consists of an antiparallel efficient packing of cholesteryl ring systems to form layers that are very similar to those observed in the room temperature structure.The oleate chains that protrude from these layers have a somewhat different packing arrangement from the room temperature structure because they have undergone a conformational change.At 123 K, the oleate chains are well ordered and are almost fully extended except for a kink at the cis double bond.The oleate chains at 123 K are 1.7 8, longer than at 295 K due in part to an uncoiling whereby their helical character is lost.On cooling, there is a substantial change in the unit cell @-angle from obtuse (93.3') to acute (85.5') which involves a shearing motion of 2.5 A beof vibration (-0.2 A*) than the oleate carbon atoms 1214
Referência(s)