USE OF SELF-ASSEMBLED MONOLAYERS TO COVALENTLY TETHER PROTEIN MONOLAYERS TO THE SURFACE OF SOLID SUBSTRATES

We have employed X-ray diffraction to study the sequential formation of single monolayers of the protein yeast cytochrome c and its bimolecular complex with the photosynthetic reaction center covalently bound to self-assembled monolayers of 11-siloxyundecanethiol on inorganic multilayer substrates. Optical absorption spectroscopy and dissociation experiments indicate that the cytochrome c monolayer is covalently attached to the self-assembled monolayer via a disulfide bond; since only one such binding site is available on this protein's surface, this attachment should produce a vectorially-oriented protein monolayer, as was the case with previously published work using a Langmuir-Blodgett monolayer. These measurements are consistent with the cytochrome c and its bimolecular reaction center complex forming a close-packed monolayer on the surface of the solid substrate. By utilizing the interference between the meridional X-ray diffraction from the inorganic multilayer substrate and that from the organic overlayers, one can ascertain the sequential fabrication of these bioorganic monolayers via their electron density profiles, derived uniquely to approximately 13-angstrom resolution.