Gold oxide as a protecting group for regioselective surface chemistry

Abstract

Selective modification of electrode surfaces is a vital step in the development of many practical applications of self-assembled monolayers (SAMs). This paper describes a protection-deprotection strategy similar to that commonly utilized in organic synthesis, with gold oxide as a protecting layer, to direct self-assembly on one gold electrode in the presence of another.

Relative lability of gold-oxide thin films in contact with air, solvents, or electrolyte solutions

“…27 After the initial film thickness was measured, each sample was placed into a separate 20-mL scintillation vial containing air or a test liquid. 14,15 In this case, the oxide was completely removed within the first 30 min of immersion. After each measurement, the samples were placed back into their respective vials.…”

“…6 Nonetheless, oxide films on gold can be sufficiently inert under ordinary laboratory conditions to allow spectroscopic characterization and use in certain applications. 13,14 In addition to their use as masking films on gold electrodes to allow selective surface chemistry, 15 oxide films have also proven useful as model systems for the study of interfacial phenomena such as corrosion and catalysis. 13,14 In addition to their use as masking films on gold electrodes to allow selective surface chemistry, 15 oxide films have also proven useful as model systems for the study of interfacial phenomena such as corrosion and catalysis.…”

“…Temperature-programmed desorption (TPD) spectra, for example, indicated an activation energy for the desorption of O 2 from oxide monolayers on Au(111) of 30 kcal/mol (126 kJ/mol). 15 We also developed an analytical approach, combining x-ray photoelectron spectroscopy and spectroscopic ellipsometry to determine the complex refractive index of gold-oxide thin films. 21 In addition, recent examples of supported gold-oxide nanoparticles suggest that this inertness extends to the submicron size regime.…”

Spatially Selective Formation of Hydrocarbon, Fluorocarbon, and Hydroxyl-Terminated Monolayers on a Microelectrode Array

“…Like electrochemical oxidation, this process produces a thin oxide film on the gold, which can serve as a masking layer until removed. To reduce the oxide present on an individual track and make that track active to monolayer formation, a potential of −0.9 V (vs Ag/AgNO 3 ) was applied in a solution of 0.500 M H 2 SO 4 . − Monolayers were formed on the reduced track of interest by the application of forty stepped-potential pulses from 0.3 to −0.9 V, for 5 s at each potential, in a THF solution containing 1 mM of the dialkyl disulfide of interest and 0.1 M LiClO 4 as a supporting electrolyte. , After rinsing and drying, the next oxidized track to be used was reduced electrochemically, and the next SAM formed. Monolayers were formed on the three microelectrodes in the following order and with the following disulfides: track A , [CH 3 (CH 2 ) 15 S] 2 ; track C , [CF 3 (CF 2 ) 9 (CH 2 ) 2 S] 2 ; and track B , [HO(CH 2 ) 12 S] 2 (Scheme ).…”

“…Monolayers formed from hydroxyl-terminated alkyl thiosulfates, for example, contained large amounts of sulfate, resulting presumably from the reaction of SO 3 with the terminal hydroxyl groups . To address such problems with monolayer precursors bearing nucleophilic functional groups, we recently developed a protection–deprotection approach that uses gold oxide as a masking layer on particular electrodes to allow selective formation of SAMs from dialkyl disulfides on others . This method relies on the inability of dialkyl disulfides to reduce gold oxide, − and we used it successfully to form hydrocarbon and fluorocarbon SAMs on neighboring macroscopic (∼1 mm widths and ∼5 mm spacings) electrodes without cross-contamination.…”