On the Structural and Dynamical Properties of DOPC Reverse Micelles

Abstract

The structure and dynamics of phospholipid reverse micelles are studied by molecular dynamics. We report all-atom unconstrained simulations of 1,2-dioleoyl-sn-phosphatidylcholine (DOPC) reverse micelles in benzene of increasing sizes, with water-to-surfactant number ratios ranging from W = 1 to 16. The aggregation number, i.e., the number of DOPC molecules per reverse micelle, is determined to fit experimental light-scattering measurements of the reverse micelle diameter. The simulated reverse micelles are found to be approximately spherical. Larger reverse micelles (W > 4) exhibit a layered structure with a water core and the hydration structure of DOPC phosphate head groups is similar to that found in phospholipid membranes. In contrast, the structure of smaller reverse micelles (W ≤ 4) cannot be described as a series of concentric layers successively containing water, surfactant head groups, and surfactant tails, and the head groups are only partly hydrated and frequently present in the core. The dynamics of water molecules within the phospholipid reverse micelles slow down as the reverse micelle size decreases, in agreement with prior studies on AOT and Igepal reverse micelles. However, the average water reorientation dynamics in DOPC reverse micelles is found to be much slower than in AOT and Igepal reverse micelles with the same W ratio. This is explained by the smaller water pool and by the stronger interactions between water and the charged head groups, as confirmed by the red-shift of the computed infrared line shape with decreasing W.

How Does Solvation Layer Mobility Affect Protein Structural Dynamics?

“…The model can be readily tested by comparing solvation shell dynamics at different locations, which can be achieved through a variety of spectroscopic techniques (e.g., ultrafast fluorescence, IR, NMR spectroscopies). Using simulations to predict changes in solvation shell dynamics is also viable, as calculated solvent dynamics have reasonably reproduced experimental measurements in recent studies (King et al, 2012 ; Dielmann-Gessner et al, 2014 ; Abel et al, 2016 ; George et al, 2016 ; Charkhesht et al, 2018 ).…”

Aggregation response of triglyceride hydrolysis products in cyclohexane and triolein

“…An overwhelming majority of computational studies of reverse micellar systems have focused on the anionic Aerosol OT surfactant (sodium bis-(2-ethylhexyl)sulfosuccinate) [37][38][39][40][41][42][43][44][45][46][47] . In re-cent years, however, there has been a surge of studies in which other surfactants and reverse micellar systems have been considered 21,[48][49][50][51][52][53][54][55][56][57][58][59][60] . Due to time-scale challenges, many of these studies have focused on preassembled aggregates, their structure, and the structure of confined water, while the self-assembly process and the resulting aggregate size distribution have been characterized only in a very few publications, see Refs.…”

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“…heptane (37). Abel et al have examined phospholipid reverse micelle structure and dynamics in benzene via similar methodology (41).…”