Molecular Dynamics Simulation of Monoalkyl Glycoside Micelles in Aqueous Solution:  Influence of Carbohydrate Headgroup Stereochemistry

Abstract

Comparative molecular dynamics simulations of n-octyl-beta-D-galactopyranoside (beta-C8Gal) and n-octyl-beta-D-glucopyranoside (beta-C8Glc) micelles in aqueous solution have been performed to explore the influence of carbohydrate stereochemistry on glycolipid properties at the atomic level. In particular, we explore the hypothesis that differences in T(m) and T(c) for beta-C8Gal and beta-C8Glc in lyotropic systems arise from a more extensive hydrogen bonding network between beta-C8Gal headgroups relative to beta-C8Glc, due to the axial 4-OH group in beta-C8Gal. Good agreement of the 13 ns micelle-water simulations with available experimental information is found. The micelles exhibit a similar shape, size, and degree of exposed alkyl chain surface area. We find net inter- and intra-headgroup hydrogen bonding is also similar for beta-C8Gal and beta-C8Glc, although n-octyl-beta-D-galactopyranoside micelles do exhibit a slightly greater degree of inter- and intra-headgroup hydrogen bonding. However, the main distinction in the calculated microscopic behavior of beta-C8Glc and beta-C8Gal micelles lies in solvent interactions, where beta-d-glucosyl headgroups are considerably more solvated (mainly at the equatorial O4 oxygen). These results agree with preceding theoretical and experimental studies of monosaccharides in aqueous solution. A number of long water residence times are found for solvent surrounding both micelle types, the largest of which are associated with surface protrusions involving headgroup clusters. Our simulations, therefore, predict differences in hydrogen bonding for the two headgroup stereochemistries, including a small difference in inter-headgroup interactions, which may contribute to the higher T(m) and T(c) values of beta-C8Gal surfactants relative to beta-C8Glc in lyotropic systems.

Molecular Simulations of Dodecyl-β-maltoside Micelles in Water: Influence of the Headgroup Conformation and Force Field Parameters

“…The lower 〈 f tail 〉 values of GLYCAM06 indicate that for those micelles the surfactant alkyl chains of the micelle are more protected from the solvent than those obtained in the simulations with the CHARMM force fields. In comparison, the 〈 f tail 〉 values reported in this work are lower than those found by Stephenson et al 51 for a micelle with 45 β-C 12 G 2 (∼17.0 %), and also lower than for micelles with 27 octyl-β-galactose47 (∼30%) and 92 octyl-β-glucose monomers (20%) 46. The latter is probably due to the smaller size of the headgroup in those micelles, which shields less the micelle hydrophobic core from water.…”

“…This finding has been observed in the various MD simulations performed in this study, regardless of the force field. Finally, in contrast with previous simulations 46,47 of octyl-β-glucoside micelles, the integrity of the micelles studied with the GLYCAM and CHARMM force fields is maintained all along our simulation time window (14 ns), and no surfactant molecules escaped from the micelle. This is consistent with previous experimental results obtained for alkyl-maltoside micelles where it was found that monomer exchange between micelle and the solvent is in the order of 0.1 to 1.2 μs 89…”

“…, refs 27,28,29,30,31,32,33,34,35, 36,37,38,39,40). MD with alkyl-glycosides (such as alkyl- β - O -glucoside (C 8 Glc 1 ) or alkyl-β- O -galactoside (C 8 Gal)) have been also performed in the past, involving bilayers,41, 42, 43 micelles 44,45, 46, 47 or interacting with a plant protein 48. In the studies of Bogusz et al 44 and Chong et al 47, the influence of the surfactant headgroup conformation on the micelle structure and hydration has been thoroughly examined.…”

“…solvent accessible surface area, headgroup cluster structure, number of isolated water at the micelle surface) are significantly modified by the stereochemistry of the carbohydrate head 44,47. It was also noted that the sugar counterpart is responsible for strong perturbations of the water structure at the micelle surface and it affects the formation of a large hydrogen bond (HB) network at the micelle surface between water and the headgroups, and within the headgroups themselves (inter- and intra- HBs, respectively) 41,47,49. This HB network may also explain the good thermal stability of the surfactants49 and cryoprotective effects 36,50…”

Energetics of clouding and size effects in non-ionic surfactant mixtures: The influence of alkyl chain length and NaCl addition

“…Similar results have been observed for alkylmonoglucoside surfactants (i.e. C 10 G 1 and C 8 G 1 ), suggesting that this network could explain the thermal stability and cryoprotective effects of these surfactants [31,32].…”