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A Golden Glimpse of Thorny Thiol Tunneling

Press/Media: ResearchAcademic

31/08/2020
Thiol–metal bonding is a tempting tool for studying how electrons move through molecules. It creates self-assembled monolayer films (SAMs) useful in chemistry, physics, biology, and materials science. One method, exposing gold to solutions containing alkanethiols, relies on the sulfides reorganizing themselves and depositing alkanes of interest on the metal surface. But they remain mysterious, because on larger scales, useful for molecular electronics, they form multiple types of bonds, each with their own properties, including different tunneling charge-transport.
One research group, for example, reported that sulfur outcompeted disulfides to create a homogeneous, covalent-bonded layer on a gold surface. A more recent study found instead non-covalent gold–disulfide–gold bonds co-existing alongside covalent sulfur–gold bonds.
Now, Petra Rudolf, Ryan Chiechi, and co-workers have mapped the journey of disulfides as they convert into covalent bonds through free thiols, which might resolve the contradiction in the previous studies (DOI: 10.1021/jacs.0c06508). The team observed a well-known thiol and a variant of it with X-ray photoelectron spectroscopy as the thiols bonded with gold under different growing conditions. They conclude from the progression of energy peaks in the spectra that free thiols can, over time, help reduce heterogeneous disulfides to create a homogeneous, high-quality SAM.

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