Preparation and Characterization of Dendrimer Monolayers and Dendrimer-Alkylthiol Mixed Monolayers Adsorbed to Gold
Technical rept. 1 Aug 97-28 Feb 98
TEXAS A AND M UNIV COLLEGE STATION DEPT OF CHEMISTRY
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Single-component monolayers of dendrimers and two-component monolayers consisting of dendrimers and n-alkylthiols immobilized on Au substrates are described. single-component monolayers are prepared by exposing an Au substrate to ethanolic solutions of amine- or hydroxy-terminated polyamidoamine PAMAM dendrimers. The resulting monolayers are highly stable and nearly close-packed for dendrimer generations ranging from 4 to 8 G4-G8, Electrochemical ac-impedance measurements indicate that the dendrimer surface is very porous towards the electroactive redox couple FeCN63-4-. Ferrocene-terminated dendrimer monolayers have also been investigated. Exposure of higher-generation dendrimer monolayers to ethanolic solutions of hexadecylthiol Cl6SH results in a dramatic compression of the dendrimers, and caused them to reorient on the surface from an oblate to prolate configuration. The dendrimers originally present on the surface do not desorb as a consequence of this configurational change. Comparison of the extent of adsorption of Cl6SH in different media vapor-phase N2, hexane, and ethanol shows that solvation of the dendrimer endgroups is the primary driving force for the structural change. Finally, the reactivity and stability of the dendrimer monolayers is investigated by on-surface functionalization of the dendrimer monolayer with 4-trifluoromethyl benzoyl chloride. The physical and chemical properties of the single- and two-component monolayers are evaluated using reflection infrared spectroscopy, ellipsometry, contact-angle measurements, ac-impedance spectroscopy, cyclic voltammetry, and surface acoustic wave SAW-based analyte-dosing experiments.
- Organic Chemistry
- Polymer Chemistry