Mixed azide-terminated monolayers: a platform for modifying electrode surfaces.
We have prepared and characterized mixed self-assembled monolayers (SAM) on gold electrodes from azido alkane thiols and various omega-functionalized alkane thiols. In the presence of copper(I) catalysts, these azide-modified surfaces are shown to react rapidly and quantitatively with terminal acetylenes forming 1,2,3-triazoles, via "click" chemistry. The initial azide substituents can be identified and monitored using both grazing-angle infrared (IR) and X-ray photoelectron spectrosopies. Acetylenes possessing redox-active ferrocene substituents react with the azide-terminated mixed SAMs and electrochemical measurements of the ferrocene-modified SAM electrodes have been used to quantify the redox centers attached to these platforms. Time-resolved electrochemical measurements have enabled us to follow the formation of these ferrocene centers and thus to measure the rate of the surface "click" reaction. Under optimal conditions this well-behaved second-order reaction takes place with a rate constant of 1 x 10(3) M(-)(1) s(-)(1). Typical reaction times of several minutes were realized using micromolar concentrations of acetylene. These techniques have been used to construct well-characterized, covalently modified monolayers that can be employed as functional electrode surfaces.
Collman
James P
JP
Department of Chemistry, Stanford University, Stanford, California 94305, USA. jpc@stanford.edu
Devaraj
Neal K
NK
Eberspacher
Todd P A
TP
Chidsey
Christopher E D
CE
D001386:Azides / Q000737:chemistry*; D004563:Electrochemistry / Q000295:instrumentation; D004566:Electrodes; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties
D001386:Azides