Synthesis and characterization of amine-terminated self-assembled monolayers containing diethylene glycol linkages

A new synthesis of amino di(ethylene glycol)-terminated alkylthiol 1 (AEG2) is described. This precursor, made via a Mitsunobu synthesis, is designed to form self-assembled monolayers (SAMs) on gold, which allow direct coupling of biomolecules. The AEG2 SAMs have been characterized by ellipsometry, X-ray photoelectron spectroscopy, and advancing water contact angle and by their interactions with proteins. Ellipsometry and X-ray photoelectron spectroscopy indicate that the AEG2 precursor forms well-ordered SAMs of the expected thickness and composition. Contact angle measurements indicate that the AEG2 SAMs are slightly more hydrophobic than SAMs of a di(ethylene glycol)-terminated alkylthiol (EG2). Interestingly, the AEG2 SAMs do not resist the nonspecific adsorption of fibrinogen, pyruvate kinase, or bovine serum albumin but do resist adsorption of streptavidin. Mixed SAMs of 20:80 mol % AEG2/EG2 composition resist the adsorption of pyruvate kinase and bovine serum albumin.