[Conformation of hydrocarbon chains in a lipid bilayer]

Based on the linear relationship between the entropy change deltaS during the phase transition and the length of he hydrocarbon chains of some lipids, the dependence of the probability of the trans--(pt) and gauche--(pg) conformation of the "averaged" methylene group of the chain on the increment deltas is deduced. Values of the probabilities for liquid n-alkanes, tri-glycerines and fatty acids are pt approximately equal to 0.6 and pg+ approximately equal to pg- approximately equal to 0.2, for liquid crystalline lecithin bilayers pt approximately equal to 0.8 and pg+ = pg- approximately equal to 0.1. From these data the average number of gaucheisomers per a plamitin chain in the dipalmitoylphosphatidylcholine molecule is estimated to be approximately 2.8-3.