Dynamics and Orientation of Parathion Dissolved in a Discotic Nematic Lyomesophase

Abstract

Parathion, an organophosphorous pesticide, presents serious hazards to the environment and health. It inhibits acetylcholinesterase, an enzyme incorporated in the cell membrane. A study on the behaviour of parathion in a lipid environment is interesting from environmental cleaning and biological perspectives. 2H NMR quadrupole splittings (ΔνQ) and longitudinal relaxation times (T1) of parathion-d4, dissolved in a nematic discotic lyomesophase made of tetradecyltrimethylammonium chloride/decanol (10% 1,1-dideuterodecanol)/water (0.1% D2O)/NaCl, have been measured. ΔνQ and T1 from DHO and 1,1-dideuterodecanol were also obtained. For a detailed understanding of the experimental results, a 19 ns molecular dynamics (MD) simulation of a bilayer fragment including three parathion molecules was calculated. Parathion is strongly attached to the aggregate and the solubilization increases the alignment of the interface components. Calculated densities show that parathion is located in the hydrophobic core, near the interface, and experiences an electrostatic interaction with the ammonium headgroups. On average, the molecule orients with the ring plane containing the bilayer normal.