Counterion Effects and Dynamics of Parathion in Anionic Lyomesophases

Abstract

Ingestion of parathion produces catastrophic effects on mammals. Transformed into paraoxon, it inhibits acetylcholinesterase, producing acetylcholine accumulation. The distribution, orientation, and dynamics of parathion in different hydrophobic bilayer environments is interesting from both ecological and biological perspectives. A study of parathion-d4 dissolved in two nematic discotic lyotropic liquid crystals made of sodium and cesium decylsulfate (CsDS and NaDS)/decanol (10% 1,1-dideuterodecanol)/water (0.1% D2O)/M2SO4 (M=Na+, Cs+), is presented. Deuterium quadrupole splittings and relaxation times of all deuteriated species were measured. Parathion is strongly attached to both aggregates, increasing the alignment of CsDS and decreasing the alignment of NaDS. Molecular dynamics trajectories were calculated for both mesophases. CsDS appears more neutralized than NaDS. Despite the surface charge, parathion is associated to both aggregates, located near the interface, with the nitro group oriented to the headgroups and the ethoxy chains toward the hydrophobic core. When included in the CsDS interface, it stabilizes the system by shielding repulsive electrostatic interactions among headgroups. Included in NaDS, parathion induces an increase in the distance among counterions and sulfate headgroups, thus decreasing the degree of order.