MIXED SELF-ASSEMBLED MONOLAYERS IN CHEMICAL SEPARATIONS

Chemical separations of many biomolecules and pharmaceuticals are limi ted by their electrostatic interaction with the surfaces of the separa tion medium. Mixed self-assembled monolayers of octadecyl and methyl c hains organize into a dense, two-dimensionally cross-linked network ov er the chromatographic silica surface to reduce acid dissociation of t he surface silanols, Molecular models predict that two-dimensional cro ss-linking is sterically possible for pure methylsiloxane monolayers, silicon-29 nuclear magnetic resonance measurements show that cross-lin king predominates for mixed monolayers of primarily methylsiloxane, an d chromatographic measurements confirm that electrostatic interactions are reduced when the monolayer is primarily methylsiloxane. Chromatog raphic separation of genetic variants of a highly charged protein, cyt ochrome c, demonstrates the promise of self-assembled monolayers in se parations of biomolecules.