Surface reactions on thin layers of silane coupling agents

The reactivity of immobilized functional groups in thin layers of (3-aminopropyl)triethoxysilane (APS), (3-mercaptopropyl)trimethoxysilane, (3-bromopropyl)trimethoxysilane, and (8-bromooctyl)trimethoxysilane on oxidized aluminum substrates was studied with reflection-adsorption infrared spectroscopy (RAIR), optical ellipsometry and contact-angle measurements. Mass changes on the surface associated with the surface-confined reactions were measured with the quartz crystal microbalance (QCM). Single layers of (3-aminopropyl)triethoxysilane on oxidized aluminum react with chlorodimethylsilane to give [(-O)[sub 3]Si(CH[sub 2])[sub 3]NH[sub 2][sup +]SiMe[sub 2]H]Cl[sup [minus]] and single layers of (3-mercaptopropyl)trimethoxysilane on oxidized aluminum react with phenylmercury hydroxide to give [(-O)[sub 3]Si(CH[sub 2])[sub 3]SHgPh], while no substitution reaction of (3-bromopropyl)trimethoxysilane and (8-bromooctyl)trimethoxysilane monolayers occurred with cyanide. Films of APS were further utilized to immobilize pepsin. It is discussed to which extent known reactions from solution can be transferred to interface reactions. 50 refs., 8 figs., 5 tabs.