A semi-empirical conformation analysis of the interaction of n-alkanols with dipalmitoyphosphatidylcholine

The interaction of a homologous series of saturated aliphatic n-alkanois ( containing 1-13 carbon atoms) with dipalmitoylphosphatidylcholine was studied by a semi-empirical conformational analysis. The minimal conformational energy of the isolated molecule at the hydrocarbon-water interface was calculated as the sum of the contributions resulting from the Van der Waals, torsional, electrostatic and transfer energies. From the conformers of minimal energies were calculated the hydrophilic-hydrophobic balance, the distance between hydrophilic and hydrophobic centres and the energies of interaction between homologous alkanols and between alkanols and lipids. Using these parameters, different modes of conformation, orientation and interaction of n-alkanols and dipalmitoylphosphatidylcholine were described. For methanol, ethanol and n-propanol, the gauche conformers were the most probable interacting only with the lipid polar heads. Only all-trans conformers were obtained for alkanols with longer acyl chains. n-Butanol to n-octanoi form clusters in the lipid matrix. Longer n-alkanols are randomly distributed in the lipid layer. However, due to the increase in hydrocarbon chain-length, n-nonanol and higher alkanols have an interaction energy identical or superior to that found in a pure lipid monolayer, leading to a more orederde alkanol-lipid organization.