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Polymorphic forms of 1,2-dipalmitoyl-sn-glycerol: a combined X-ray and electron diffraction study

1988; Elsevier BV; Volume: 48; Issue: 1-2 Linguagem: Inglês

10.1016/0009-3084(88)90130-2

1873-2941

Douglas L. Dorset, Walter Pangborn,

Enzyme Structure and Function

Quantitative crystallographic structure analyses are carried out for two polymorphic forms of 1,2-dipalmitoyl-sn-glycerol. A single crystal X-ray determination on the higher melting βL′-form reveals that the hairpin conformer structure is essentially identical to that of the dilauroyl homolog reported earlier (I. Pascher, S. Sundell and H. Hauser (1981) J. Mol. Biol. 153, 791–806) with inclined acyl chain packing in the O˔ methylene subcell. Lamellar electron diffraction intensity data from epitaxially crystallized samples were used to determine the structure of the lower melting αL-form. The chains pack in the hexagonal subcell and are perpendicular to the lamellar surface. An appropriately oriented molecular model based on the βL′-polymorphy does not lead to a satisfactory structure solutions but models based on the conformationally different 1,2-diglyceride moiety of several phospholipid structures does lead to a closer match to the observed diffraction data. In this proposed packing model for the αL-form, the hydroxyl oxygens are somewhat farther away from the unit cell origin than in the βL′-form crystal structure, and, in combination with the different molecular conformation, this might explain the observed stability of this crystal polmorph against acyl shifts.