SINGLE-CRYSTAL STRUCTURE OF A MIXED-CHAIN TRIACYLGLYCEROL - 1,2-DIPALMITOYL-3-ACETYL-SN-GLYCEROL

The mixed chain triacylglycerol 1,2-dipalmitoyl-3-acetyl-sn-glycerol was synthesized and its crystal structure was determined to a final reliability factor (R) of 0.11. Two molecules are present in the monoclinic unit cell: space group P2(1); a = 5.375(l), b = 8.286(2), c = 42.96(1) angstrom; beta = 93.30(2)-degrees, V = 1910 angstrom3, rho = 1.065 g/cm3, and mu = 5.7 cm-1. The structure is a trilayer: a bilayer of palmitate chains packed in the beta-mode (T//) and an interdigitated monolayer of acetates. The glycerol backbone and acetate extend roughly linearly from the sn-1 chain. The sn-2 chain bends around the C-2 carbon to lie next to the sn-1 chain. Analysis of the torsion angles indicate that the glycerol conformation of 1,2-dipalmitoyl-3-acetyl-sn-glycerol is markedly different from single acid triacylglycerols and from 1,2-diacyl-sn-glycerols but very similar to 1,2-dimyristoyl-sn-glycero-3-phosphocholine.