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. 2013 Jun 20;117(24):7345-51.
doi: 10.1021/jp402270e. Epub 2013 Jun 6.

Probing the structure and dynamics of confined water in AOT reverse micelles

Anna Victoria Martinez  1 , Laura Dominguez, Edyta Małolepsza, Adam Moser, Zack Ziegler, John E Straub
Affiliations

Probing the structure and dynamics of confined water in AOT reverse micelles

Anna Victoria Martinez et al. J Phys Chem B. .

Abstract

Reverse micelles are attractive nanoscale systems used for the confinement of molecules in studies of structure and chemical reactions, including protein folding, and aggregation. The simulation of reverse micelles, in which a water "pool" is separated from a nonpolar bulk phase by a surfactant layer, poses significant challenges to empirical force fields due to the diversity of interactions between nonpolar, polar, and charged groups. We have explored the dependence of system density, reverse micelle structure, and water configurational relaxation times as a function of reverse micelle composition, including water:surfactant ratio, absolute number of water molecules, and force field using molecular dynamics simulations. The resulting structures and dynamics are found to depend more on the force field used than on varying interpretations of the water:surfactant ratio in terms of absolute size of the reverse micelle. Substantial deviations from spherical reverse micelle geometries are observed in all unrestrained simulations. Rotational anisotropy decay times and water residence times show a strong dependence on force field and water model used, but power-law relaxation in time is observed independent of the force field. Our results suggest the need for further experimental study of reverse micelles that can provide insight into the distribution and dynamics of shape fluctuations in these complex systems.

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Figures

Figure 1
Figure 1
Densities (kg/m3) for all simulated CHARMM RMs. The experimental values are in dark gray. The densities for the unrestrained RMs are to the left of the experimental values, and the densities for the restrained RMs are to the right. All calculated values for the CHARMM simulations are within 2% of the reported experimental densities.
Figure 2
Figure 2
Eccentricity parameter for the CHARMM unrestrained RMs for the last 15 ns of simulation. The eccentricity parameter is plotted versus time (left) with the normalized histogram of eccentricity values shown for the last 15 ns (right).
Figure 3
Figure 3
Structures of the unrestrained reverse micelles for the CHARMM force field. The images from left to right show the structures of the RMs at 0, 15, and 25 ns. The AOT sulfur head groups are represented by yellow sulfur atoms and red oxygen atoms. The AOT tails are in gray, and the water is in blue.
Figure 4
Figure 4
Rotational anisotropy decay auto-correlation functions for the unrestrained CHARMM reverse micelles. The inset plots show that the auto-correlation functions fit well to a tri-exponential function (top) or a stretched exponential function (bottom) up to approximately 10 or 20 ps. The large plots show that these fits fails to describe the correlation functions on longer time scales.
Figure 5
Figure 5
Rotational anisotropy decay auto-correlation functions for the unrestrained CHARMM reverse micelles on a log-log scale. The plot shows that the auto-correlation functions are described well with a power law decay from 1 to 100ps.
Figure 6
Figure 6
Distribution of water residence time for all AOTs head groups in the unrestrained RMs.
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References

    1. Hoar T, Schulman J. Transparent Water-in-Oil Dispersions: The Oleopathic Hydro-Micelle. Nature. 1943;152:102–103.
    1. Levinger NE. Water in Confinement. Science. 2002;298:1722–1723. - PubMed
    1. Thompson KF, Gierasch LM. Conformation of a Peptide Solubilizate in a Reversed Micelle Water Pool. J Am Chem Soc. 1984;106:3648–3652.
    1. Mukherjee S, Chowdhury P, Gai F. Tuning the Cooperativity of the Helix-Coil Transition by Aqueous Reverse Micelles. J Phys Chem B. 2006;110:11615–11619. - PubMed
    1. Mukherjee S, Chowdhury P, Gai F. Effect of Dehydration on the Aggregation Kinetics of Two Amyloid Peptides. J Phys Chem B. 2009;113:531–535. - PMC - PubMed

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