Internal structure of a model micelle via computer simulation

Abstract

The molecular dynamics method has been used in a preliminary computer simulation study of intramicellar structure. The simulation was performed on a simplified model of a spherical micelle composed of 40 13-member chains with head groups fixed on a spherical shell of 16 Á radius. Results are reported for the local density of CH2 and CH3 groups, for the distribution of gauche bonds, and for the average conformation of the chains.

Molecular Dynamics Simulation of a Phospholipid Micelle

“…2) show increasingly broad distributions for atoms nearer the end of the hydrophobic tail. This distribution, predicted by the interphase models of micelle structure (12,13), has been observed in previous micelle dynamics simulations of surfactants with shorter hydrocarbon chains (5)(6)(7)(8) and is consistent with experimental observations of micelles in solution (14). In general, such distributions have been taken as representing only trans-gauche conformational statistics of individual LPE hydrocarbon chains.…”

“…We have investigated this question by performing molecular dynamics simulations on a micelle model, constructed from LPE monomers known to form micelles in aqueous solution (2), that conforms to the commonly held notion of a radially symmetric structure. This model differs from previous simulations (5)(6)(7)(8) in that the LPE 636 monomers include zwitterionic head groups capable of forming a hydrogen-bonded surface network among themselves and with solvent molecules.The LPE monomer conformation was derived from the crystal structure (9) of dilaurylphosphatidylethanolamine (DLPE) by replacement of the fatty acid substituent at the central glycerol oxygen with a hydroxyl group. The model was assembled by aligning the extended hydrocarbon chains of the LPE molecules along radii of a sphere whose diameter was equal to the DLPE crystal bilayer thickness (48 A), and by including enough replicates (85 total) so that the surface area per phospholipid head group was similar to that of the DLPE crystal structure.…”

“…We have investigated this question by performing molecular dynamics simulations on a micelle model, constructed from LPE monomers known to form micelles in aqueous solution (2), that conforms to the commonly held notion of a radially symmetric structure. This model differs from previous simulations (5)(6)(7)(8) in that the LPE 636 monomers include zwitterionic head groups capable of forming a hydrogen-bonded surface network among themselves and with solvent molecules.…”

Hydrophile-lipophile balance of alkyl ethoxylated surfactants as a function of intermolecular energies

“…Since the rotation of external bonds does not appreciably change the molecular length, the percentage of molecules exhibiting marked differences from the most stable molecular length should be quite small, even at room temperature (~ e-~AzraT~). This might explain the fact that the molecular volumes, deduced from the experimental densities (see below), vary linearly with the molecular lengths estimated here, even though molecular dynamics studies [19] on liquid hydrocarbons have shown that between 25 and 30% of the bonds exhibit gauche [23], in which seven monomeric units turn twice per fiber period [24,25].…”

Simulation of surfactant solutions

“…O'Connell and co-workers [- [13][14][15] studied the structure of a micelle by confining the surfaetants in a sphere and connecting the heads with a force to the surface of this sphere. This force represents the interactions of the heads with the surrounding water.…”