Partition of Organophosphorus Pesticides into Lipid Bilayer Membranes

The partition of organophosphorus pesticides in the multi-lamellar vesicles of dipalmitoyl L-α-phosphatidylcholine increased with their hydrophobicity and a dramatic change occurred with the phase transition of membranes. Both the incorporation of a double bond into the acyl chains of lipid and their shortening enhanced the partition, while the addition of a charge at the membrane surface greatly reduced the partition. The similar profiles were obtained for the corresponding oxon derivatives but in a smaller extent. Fluorescence polarization studies using neutral (DPH) and positively charged (tma-DPH) probes have shown that the partitioning site of pesticides in membranes changed with their hydrophobicity. Both partition and fluorescence studies have strongly suggested that organophosphorus pesticides possessing the P=S moiety are partitioned in the hydrophobic core of the lipid bilayer, while the oxon derivatives are in the hydrophilic region near the glycerol backbone of lipid.