Effect of lithium on the properties of a liquid crystal formed by sodium dodecylsulphate and decanol in aqueous solution
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Date
2013
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AMER INST PHYSICS
Abstract
Understanding the molecular interactions that rule the physicochemical properties of molecular assemblies is of particular interest when trying to explain the behavior of much more complicated systems, such as the cell membranes. This work was devoted to study a discotic nematic lyotropic liquid crystal, formed by sodium dodecylsulphate (3% SDS-d(25)) and decanol (20% DeOH-alpha-d(2)), dissolved in aqueous solutions (0.1% D2O) of Na2SO4 or Li2SO4. The average size of the aggregates was estimated using fluorescence quenching experiments, and their dynamics were studied by measuring the H-2-NMR quadrupole splitting (Delta nu(Q)) and the longitudinal relaxation times (T-1) of the deuterated species. To provide an atomic insight into these assemblies, molecular dynamics simulations of the systems were carried out with atomic detail. As a previous step in this study, a reparameterization of the standard GROMOS 87 force field was required to perform the equilibrated simulations and to prevent instabilities emerging during the simulations. Finally, an excellent agreement between simulation and experimental data was obtained. In addition, variations in the long range electrostatic interactions at the aggregate/solution interface, the orientation and the re-orientational relaxation time of the water dipole, the translational diffusion coefficient of sodium ions, and the amphiphile-counterion coordination associated with the presence of Li+ in the solution were other key aspects investigated to explain the variation in the quadrupole splittings (Delta nu(Q)) in the presence of lithium in solution. (C) 2013 AIP Publishing LLC.
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Keywords
MOLECULAR-DYNAMICS SIMULATION, PARTICLE MESH EWALD, AGGREGATION NUMBER, MEMBRANE, MICELLE, WATER, PHASE, COUNTERION, SYSTEMS, STATE