Membrane-contaminant interaction found by 3D force field calculations

Enthalpies of contaminant transfer from water to a 1,2-Dilauroyl-DL-phosphatidyl ethanolamine (DLPE) membrane were calculated in order to study the suitability of 3D force fields for the calculation of membrane-water partitioning constants (Kmw) and as potential descriptors for bio-concentration. A 3D DLPE membrane model was built in a MM+ force field using AM1 atomic charges. 3,5-Dichlorobiphenyl (PCB14), 4,4'-dichlorobiphenyl (PCB15), 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (PPDDT or p,p'-DDT) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were inserted into apolar and polar sites and their interaction energies with the membrane were calculated by geometrical optimization (GO). Energies of hydratation were subtracted from membrane-contaminant interactions of selected sites. The resulting values for the enthalpies of transfer from water to the membrane were 4.7, -2.3, 11.5 and -9.2 kcal/mol for PCB14, PCB15, PPDDT and atrazine, respectively. In contrast to PCB15, the value of PCB14 compared favorably with the experimental values of similar membranes. PCB14, PCB15 and PPDDT had their lowest energies in the apolar sites of the membrane, whereas atrazine tended to accumulate in the polar membrane-bulk water boundary site. Potential advantages and limitations of the approach were discussed.