Mixed Self-Assembled Monolayers in Chemical Separations
Mary J. Wirth,
*
R. W. Peter Fairbank,
Hafeez O. Fatunmbi
Chemical separations of many biomolecules and pharmaceuticals are
limited by their electrostatic interaction with the surfaces of the
separation medium. Mixed self-assembled monolayers of octadecyl and
methyl chains organize into a dense, two-dimensionally cross-linked network over the chromatographic silica surface to reduce acid dissociation of the surface silanols. Molecular models predict that
two-dimensional cross-linking is sterically possible for pure
methylsiloxane monolayers, silicon-29 nuclear magnetic resonance measurements show that cross-linking predominates for mixed monolayers of primarily methylsiloxane, and chromatographic measurements confirm
that electrostatic interactions are reduced when the monolayer is
primarily methylsiloxane. Chromatographic separation of genetic variants of a highly charged protein, cytochrome c, demonstrates the
promise of self-assembled monolayers in separations of biomolecules.
M. J. Wirth and R. W. P. Fairbank are in the Department of
Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA. H. O. Fatunmbi is with Separation Methods Technologies, 2311 Ogletown Road, Newark, DE 19711, USA.
*
To whom correspondence should be addressed.
