title: The crystal structure of 1,2-dipalmitoyl-sn-glycerol at 123 K.
abstract: At 123 K, the crystal structure of 1,2-dipalmitoyl-sn-glycerol (C35H68O5, M(r) = 568.9) is monoclinic with space group P2(1), a = 5.480(1), b = 7.301(1), c = 43.145(7) A, beta = 92.91(1) degrees, V = 1724 A3, Dc = 1.0960 g cm-3 and Z = 2. Integrated X-ray intensities for 3574 independent reflections were measured with Ni-filtered Cu-K alpha radiation (lambda = 1.5418 A, mu = 0.56 mm-1), and these were all used in a full-matrix least-squares refinement which gave R(F2) = 0.142. Bond lengths and angles have e.s.d.s less than 0.01 A and 0.1 degrees for non-hydrogen atoms. Comparison with a previously reported study of the room temperature structure shows a very similar orthorhombic mode of chain packing but significant conformational differences in the polar headgroup. These changes may occur in conjunction with small changes in enthalpy (less than 1 kJ/mol) observed at 202, 193 and 136 K and with a discontinuity in the unit cell volume observed in the range 200-190 K. Analysis of the atomic mean square displacements at 123 K indicates the presence of internal torsional vibrations in the headgroup region that involve the carbonyl and hydroxyl O-atoms.
authors.affiliation: Department of Crystallography, University of Pittsburgh, PA 15260.
authors.forename: G W
authors.initials: GW
authors.lastname: Han
authors.forename: J R
authors.initials: JR
authors.lastname: Ruble
authors.forename: B M
authors.initials: BM
authors.lastname: Craven
mesh_terms: D003080:Cold Temperature; D018360:Crystallography, X-Ray; D004075:Diglycerides / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D013696:Temperature; D009626:Terminology as Topic; D013816:Thermodynamics
chemical_list: D004075:Diglycerides; C005071:dipalmitin