title: Probing molecular dynamics in chromatographic systems using high-resolution 1H magic-angle-spinning NMR spectroscopy: interaction between p-Xylene and C18-bonded silica.
abstract: The exact nature of the interaction between small molecules and chromatographic solid phases has been the subject of much research, but detailed understanding of the molecular dynamics in such systems remains elusive. High-resolution (1)H magic-angle-spinning (MAS) NMR spectroscopy has been applied to the investigation of C18-bonded silica material as used in chromatographic separation techniques together with an adsorbed model analyte, p-xylene. Two distinct p-xylene and water environments were identified within the C18-bonded silica through the measurement of (1)H NMR chemical shifts, T(1) and T(2) relaxation times and diffusion coefficients, including their temperature dependence. The results have been analyzed in terms of two environments, p-xylene within the C18 chains, in slow exchange on the NMR time scale with p-xylene in a more mobile state adsorbed as a layer in close proximity to the C18 particles, but which is distinct from free liquid p-xylene. The techniques used here could have more general applications, including the study of drug molecules bound into phospholipid membranes in micelles or vesicles.
authors.affiliation: Biological Chemistry, Biomedical Sciences Division, Faculty of Medicine, Imperial College London, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ UK.
authors.forename: Muireann
authors.initials: M
authors.lastname: Coen
authors.forename: Ian D
authors.initials: ID
authors.lastname: Wilson
authors.forename: Jeremy K
authors.initials: JK
authors.lastname: Nicholson
authors.forename: Huiru
authors.initials: H
authors.lastname: Tang
authors.forename: John C
authors.initials: JC
authors.lastname: Lindon