Influence of Surface Coverage on the Conformation and Mobility of C18 Modified Silica Gels

Published

October 12, 2021

Author(s)

G Srinivasan, Lane C. Sander, K Muller

Abstract

C18 modified silica gels with surface coverages of 2 mol/m2 to 8.2 mol/m2, were prepared by different synthetic pathways and characterized by Fourier Transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR) spectroscopy and chromatographic measurements. The influence of temperature and bonding density on the conformational order of C18 modified silica gels has been studied in detail by FTIR spectroscopy. The silane functionality and degree of cross-linking of silane ligands on the silica surface are evaluated by 29Si cross polarization magic angle spinning (CP/MAS) NMR while the structural order and mobility of the alkyl chains are investigated by 13C CP/MAS NMR spectroscopy. CH2 symmetric and anti-symmetric stretching bands as well as CH2 wagging bands are used as IR probes for monitoring the conformational order and flexibility of the alkyl chains in the C18 phases. Qualitative information about the conformational order is achieved via frequency shifts of the CH2 symmetric and anti-symmetric stretching bands. The relative amounts of kink/gauche-trans-gauche, double-gauche and end-gauche conformers in the alkyl chains are determined from analysis of CH2 wagging bands. These results indicate that surface coverage plays a dominant role in the conformational order of C18 modified silica gels. The FTIR and NMR data are discussed in the context of the chromatographic shape selectivity differences.

Citation

Analytical and Bioanalytical Chemistry

Pub Type

Journals

Keywords

C18 alkyl modified silica gels, conformational order, FTIR, mobility NMR, shape selectivity, surface coverage

Citation

Srinivasan, G. , Sander, L. and Muller, K. (2021), Influence of Surface Coverage on the Conformation and Mobility of C₁₈ Modified Silica Gels, Analytical and Bioanalytical Chemistry (Accessed April 25, 2024)