INEQUIVALENCE OF SINGLE CHA AND CHB METHYLENE BONDS IN THE INTERIOR OF A DIUNSATURATED LIPID BILAYER FROM A MOLECULAR-DYNAMICS SIMULATION

Orientational order parameters for individual CHa and CHb bonds are lo cal measures for the alignment of the bonds in a membrane interior. Ex perimental values exist for some lipid systems but no results are avai lable from molecular dynamics (MD) simulations, although they are incr easingly used to study biomembranes. We present such detailed analysis of a one nanosecond MD simulation for a PLPC (16:0/18:2(Delta 9,12)) bilayer. The results show marked inequivalence for the CHa and CHb bon ds of the methylene segments in the beginning and in the double bond r egion of the diunsaturated sn-2 chain. They also suggest slight inequi valences in the saturated chain.