Molecular Dynamics Simulations of Alkylsilane Stationary Phase Order and Disorder. 1. Effects of Surface Coverage and Bonding Chemistry

Published

December 1, 2005

Author(s)

Katrice A. Lippa, Lane C. Sander, Raymond D. Mountain

Abstract

Shape-selective polymeric alkylsilane stationary phases are routinely employed over the more common monomeric phases in reversed-phase liquid chromatography (RPLC) to improve the separation of geometric isomers of shape-constrained solutes. We have investigated the molecular dynamics of chromatographic models that represent both monomeric and polymeric stationary phases with alkylsilane surface coverages and bonding chemistries typical of actual materials in an effort to elucidate the molecular-level structural features that control shape-selective separations. The structural characterization of these models are consistent with previous experimental observations of alkyl chain order and disorder: 1) alkyl chain order increases with increased surface coverage; and 2) monomeric and polymeric phases with similar surface coverages yield similar alkyl chain order (although subtle differences exist). In addition, a significant portion of the alkyl chain proximal to the silica surface is disordered (primarily gauche conformations) and the distal end is most ordered. Models that represent shape-selective RPLC phases possess a significant region of distal-end chain order with primarily trans dihedral angle conformations. This is consistent with the view that the alkyl chains comprising polymeric stationary phases contain a series of well-defined and rigid slots in which shape-constrained solutes can penetrate and hence be selectively retained.

Citation

Analytical Chemistry

Volume

77 No 24

Pub Type

Journals

Keywords

alkylsilanes, C18, molecular dynamic simulation, monometric, polymeric, reversed-phase liquid chromatography, RPLC, shape selectivity

Citation

Lippa, K. , Sander, L. and Mountain, R. (2005), Molecular Dynamics Simulations of Alkylsilane Stationary Phase Order and Disorder. 1. Effects of Surface Coverage and Bonding Chemistry, Analytical Chemistry (Accessed October 3, 2024)