Molecular dynamics analysis of the AOT/water/isooctane system: Effect of simulation time, initial configuration, and model salts

Gardner, Adam; Vásquez, Victor R.; Clifton, Andrew; Graeve, Olivia A.

doi:10.1016/j.fluid.2007.09.013

Cited by 31 publications

(45 citation statements)

References 45 publications

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“…We are aware that building preassembled reverse micelle does not constitute an ideal approach to simulate a RM system, even if it is a common practice in MD studies of micelles 36,[41][42][43][44][45][46][47] or reverse micellar structures 9,16,48,49,50 ,51 , compared to a random approach where the surfactant monomers are randomly placed in the simulation box [52][53][54][55][56] . But, as recently shown by 15 , the micellization process in AOT RM is long (close to 60 ns or more) and computationally expensive when the aggregates are small and/or when the micellar environment is simulated in great detail to reproduce experimental data.…”

Section: B Reverse Micelle Construction and Equilibrationmentioning

confidence: 99%

“…Recently, molecular dynamic simulations (MD) have been successfully used to gather additional information about AOT RM structure and dynamics at the atomic level [9][10][11][12][13][14][15][16] . These studies have underlined the effect of the charged, restricted microenvironment on the confined water structural 13,14,16 and dynamical properties 13,14,17 existing in RM.…”

Section: Introductionmentioning

confidence: 99%

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Molecular dynamics simulations of cytochrome c unfolding in AOT reverse micelles: The first steps

2010

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2This paper explores the reduced form of horse cytochrome c confined in reverse micelles (RM) of sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) in isooctane by molecular dynamics simulation. RMs of two sizes were constructed at a water content of W o = [H 2 O]/[AOT] = 5.5 and 9.1. Our results show that the protein secondary structure and the heme conformation both depend on micellar hydration. At low hydration, the protein structure and the heme moiety remain stable, whereas at high water content the protein becomes unstable and starts to unfold. At W o = 9.1, according to the X-ray structure, conformational changes are mainly localized on protein loops and around the heme moiety, where we observe a partial opening of the heme crevice. These findings suggest that within our time window (10 ns), the structural changes observed at the heme level are the first steps of the protein denaturation process, previously described experimentally in micellar solutions. In addition, a specific binding of AOT molecules to a few lysine residues of the protein was found only in the small-sized RM.3

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Section: B Reverse Micelle Construction and Equilibrationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of cytochrome c unfolding in AOT reverse micelles: The first steps

2010

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“…They also noted that there is less fluctuation in shape for the larger RMs ( w 0 > 10). 24 In a subsequent extensive and critical study of RM structure, they compared the results of their computational work to dynamic light scattering experiments on the same systems. They observed highly qualitative agreement between their simulations and experiment, and found nonspherical shapes for the reverse micelles.…”

Section: Introductionmentioning

confidence: 99%

Probing the Structure and Dynamics of Confined Water in AOT Reverse Micelles

et al. 2013

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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 non-polar bulk phase by a surfactant layer, poses significant challenges to empirical force fields due to the diversity of interactions between non-polar, 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 of 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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“…However, in terms of more detailed structural characterization, the composition regime where the viscosity maximum is observed has been mostly overlooked as previous small-angle X-ray and neutron scattering studies have focused primarily on micelles [21] and swollen systems at higher molar ratios [22][23][24]. More recent studies using self-diffusion NMR [25] and computer simulations [26] do give some cause for concern as according to them non-spherical droplet shapes seem to be the rule rather than the exception at low molar ratios. Moreover, microemulsions with cylindrical droplet structures are predicted from mean-field theory for systems with an actual radius of curvature different from the preferred one [27].…”

Section: Introductionmentioning

confidence: 99%

Variations in Structure Explain the Viscometric Behavior of AOT Microemulsions at Low Water/AOT Molar Ratios

Sharifi

Kudla

Oliveira

et al. 2011

Zeitschrift Für Physikalische Chemie

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The viscosity of AOT/water/decane water-in-oil microemulsions exhibits a well-known maximum as a function of water/AOT molar ratio, which is usually attributed to increased attractions among nearly spherical droplets. The maximum can be removed by adding salt or by changing the oil to CCl 4 . Systematic small-angle X-ray scattering (SAXS) measurements have been used to monitor the structure of the microemulsion droplets in the composition regime where the maximum appears. On increasing the droplet concentration, the scattering intensity is found to scale with the inverse of the wavevector, a behavior which is consistent with cylindrical structures. The inverse wavevector scaling is not observed when the molar ratio is changed, moving the system away from the value corresponding to the viscosity maximum. It is also not present in the scattering from systems containing enough added salt to essentially eliminate the viscosity maximum. An asymptotic analysis of the SAXS data, complemented by some quantitative modeling, is consistent with cylindrical growth of droplets as their concentration is increased. Such elongated structures are familiar from related AOT systems in which the sodium counterion has been exchanged for a divalent one. However, the results of this study suggest that the formation of non-spherical aggregates at low molar ratios is an intrinsic property of AOT.

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Molecular dynamics analysis of the AOT/water/isooctane system: Effect of simulation time, initial configuration, and model salts

Cited by 31 publications

References 45 publications

Molecular dynamics simulations of cytochrome c unfolding in AOT reverse micelles: The first steps

Molecular dynamics simulations of cytochrome c unfolding in AOT reverse micelles: The first steps

Probing the Structure and Dynamics of Confined Water in AOT Reverse Micelles

Variations in Structure Explain the Viscometric Behavior of AOT Microemulsions at Low Water/AOT Molar Ratios

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