On the average space shape of octadecadiene fatty acid chains with double bonds cis-cis, trans-trans-, cis-trans- and trans-cis-

The average shape characteristics (spans <g(1)>, <g(2)>, <g(3)> - in order of increasing magnitude) of unperturbed linear diene hydrocarbon chains of C-18:2 in the molecule-fixed coordinate system (with the axes along inertia tensor eigenvectors of each molecule conformation) were calculated by computer simulation. Analysis was made a) of the molecules with cis-cis or trans-trans-double bonds in the main chain between which 1 - 12 CH2 groups (n(m)) are located, and b) of the molecules with methylene-interrupted (n(m)=1) cis-trans- and trans-cis-double bonds. Monte Carlo method was used, with continuous variation of bond rotation angles within the (0,360 degrees) range considered, T = 298 K. It is shown that for n(m) =1,2,3, the transition of double bonds from both ends to the chain centre is accompanied by decreasing df max molecule spans <g(3)> and increasing of spans <g(2)>. For n(m) > 3 the abovelisted characteristics are non-monotonic functions. The molecules with methylene-interrupted cis-double bonds in the neighbourhood of the chain center (typical components of biomembrane lipids) are characterized by the greatest magnitude of <g(2)> and the least - <g(3)>.