Counterion Effects and Dynamics of Parathion in Anionic Lyomesophases

Victor Bahamonde; Hernán Ahumada; Ramiro Araya-Maturana; Boris E. Weiss-López

doi:10.1071/CH09423

RESEARCH ARTICLE

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Counterion Effects and Dynamics of Parathion in Anionic Lyomesophases

Victor Bahamonde ^A , Hernán Ahumada ^B , Ramiro Araya-Maturana ^C and Boris E. Weiss-López ^A ^D

+ Author Affiliations

- Author Affiliations

^A Universidad de Chile, Facultad de Ciencias, Departamento de Química, Casilla 653, Santiago, Chile.

^B Universidad de Santiago de Chile, Facultad de Química y Biología, Departamento Química de los Materiales Av. Lib. B. O’Higgins 3363, Santiago, Chile.

^C Universidad de Chile, Facultad de Ciencias Químicas y Farmacéuticas, Departamento de Química Orgánica y Fisicoquímica, Casilla 233, Santiago 1, Chile.

^D Corresponding author. Email: bweiss@uchile.cl

Australian Journal of Chemistry 63(1) 68-74 https://doi.org/10.1071/CH09423
Submitted: 1 August 2009 Accepted: 16 September 2009 Published: 8 January 2010

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.

Acknowledgements

The authors acknowledge financial assistance from Fondecyt, Grant 1095175, and Facultad de Ciencias de la Universidad de Chile. Victor Bahamonde acknowledges a Doctoral Fellowship from Conicyt. We acknowledge Dr. Rodrigo Montecinos for the estimation of the aggregation numbers.

References

Counterion Effects and Dynamics of Parathion in Anionic Lyomesophases

Abstract

Acknowledgements

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