Self-assembled monolayers on gold and their chemistry

Abstract

Introduction of various organic functional groups to organic thin films is a first step in their applications to sensors, catalysis, and nanotechnology in general. This dissertation reported on reactivity of vinyl-terminated self-assembled monolayers (SAMs) on gold toward olefin cross-metathesis (CM) and on a common intermediate method to present nitrilotriacetic acid (NTA) groups on gold surfaces for immobilizing His-tagged proteins onto the surfaces in the orientation-controlled way. Vinyl groups of undec-10-ene-1-thiol in SAMs were successfully converted into α, β-unsaturated carbonyl groups by the CM with acrylic acid, methyl acrylate, and acrylamide, and the CM was confirmed by FT-IR spectro scopy , X-ray photoelectron spectroscopy (XPS), and contact angle measurement. Ruthenium-catalyzed olefin CM has offered a versatile strategy for functionalization in solution chemistry with characteristics of a mild reaction condition and a high compatibility in functional groups. The study shows that various useful functional groups can be introduced to SAMs on gold by olefin CM, and suggests an alternative to synthesis of desired molecules in solution. Three different SAMs presenting carboxylic acids $[HS(CH_2)_{15}COOH (C15-COOH)$, $HS(CH_2)_{11}(OCH_2CH_2)_3OCH_2COOH$ (EG3-COOH), and $HS(CH_2)_{11}(OCH_2CH_2)_5OCH_2COOH$ (EG5-COOH)] were formed on Au(111) surfaces and the NTA group was then attached by coupling an NTA-containing primary amine with the COOH group on the surfaces, followed by a Ni(II) complexation for the orientation-controlled immobilization of His-tagged proteins onto surfaces. SAMs before and after the coupling reaction were characterized by contact angle goniometry, FT-IR spectroscopy, ellipsometry, XPS, and the coupling efficiency (“yield”) was estimated by XPS data. After the formation of surfaces presenting NTA and Ni(II) [NTA-Ni(II)], His-tagged proteins (green fluorescent protein and maltose-binding protein fused with S-tag) were bound ...