Science, Vol.275, No.5296, 44-47, 1997
Mixed Self-Assembled Monolayers in Chemical Separations
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.
Keywords:PERFORMANCE LIQUID-CHROMATOGRAPHY;SILICA SURFACES;CAPILLARY ELECTROPHORESIS;HORIZONTAL POLYMERIZATION;ALKYLSILOXANE MONOLAYERS;TRIFUNCTIONAL SILANES;DERIVATIZED SILICA;STATIONARY PHASES;TEMPERATURE;ADSORPTION