Conformational analysis and electronic structure calculations of S ‐1,2‐bis(2‐dibutenoyl)glycerol and S ‐1,2‐bis(2,4‐hexadienoyl)glycerol, two analogues of 1,2‐bis(2,4‐octadecadienoyl)‐ sn ‐glycero‐3‐phosphorylcholine

As a model for 1,2‐bis(2,4‐octadecadienoyl)‐ sn ‐glycero‐3‐phosphorylcholine, a doubly unsaturated membrane‐forming lipid molecule, force‐field (MMP2) calculations were performed on S ‐1,2‐bis(2‐dibutenoyl)glycerol, and CNDO/S‐calculations 2 CNDO: Complete neglect of differential overlap, a semi‐empirical quantum‐mechanical method. on the derived minimum‐energy conformations of S ‐1,2‐bis(2,4‐hexadienoyl)glycerol. The energy hypersurface especially with respect to the dihedral angles along the C(1)‐C(2) and the two CO ester bonds was explored and the rotational strength as a function of these angles was calculated. The two gauche ‐forms were found to be most stable, with a slight preference for the g − ‐form. The experimental circular dichroism data obtained for 1,2‐bis(2,4‐hexadienoyl)‐ sn ‐glycero‐3‐phosphorylcholine, the corresponding phosphorylcholine, indicate a dynamic equilibrium between two forms of opposite chirality possibly involving the g + ‐and the g − ‐forms.