NMR characterization of dilauroyl phosphatidylcholine in adsorbed monolayers at fluid interfaces studied by multiscale computations

Structural characteristics of model monolayers of dilauroyl phosphatidylcholine (1,2-dilauroyl-sn-glycerol-3-phosphatidylcholine [DLPC]) adsorbed at the water/vapors and water/octane interfaces were studied by means of computational chemistry methods. Coarse-grained, followed by all-atom molecular dynamics simulations were used to obtain the monolayers equilibrium structures at room temperature at both fluid interfaces. The analysis of the polar head orientation, polar region thickness, tail lengths, and NMR order parameter revealed that the different interface composition affects only the tail lengths and their orientation with respect to the interface. At the octane/water boundary the DLPC tails are less extended than the tails at the water/vacuum interface and are rather significantly tilted or multiply folded. Very similar structuring of the polar DLPC region at both studied boundaries was established. Dynamic C-13 NMR chemical shift values, (C-13) computed with density functional theory allowed to identify the interface effect on the DLPC molecular structure and the intramolecular motions in the adsorbed monolayer at the room temperature equilibrium. Detailed analysis of these dynamic (C-13) values compared with available experimental data and static (C-13) estimates of one DLPC low-energy conformer are presented and discussed.