New Scientist reports a single hydrogen atom has been snipped off a molecule and then added back on again, marking the first time a single chemical bond has been broken and reforged in a controlled, reversible way.
Update: The work was done at 4.7 degrees kelvin
Update 2: some points from Robert Freitas This is good research but it was not mechanical so not mechanosynthesis. The donation step was site specific but not positionally controlled.
The team first used their STM to locate a methylaminocarbyne (CNHCH3) molecule that was fixed to a platinum surface.
Then they turned up the voltage, increasing the flow of electrons. That was enough to break one bond – between the molecule’s nitrogen and hydrogen atom – but not to disturb any of the other bonds, leaving a molecule of methylisocyanide (CNCH3).
To reverse the process, the group simply bathed the sample in hydrogen gas. The platinum surface catalysed the splitting of the hydrogen molecules into their hydrogen atoms, which reacted with nitrogen in the methylisocyanide molecule to re-form methylaminocarbyne.
This kind of reversible alteration could be used in molecular electronics, says Yousoo Kim at the Surface Chemistry Laboratory in Wako, Japan, who carried out the experiment with colleagues.
Abstract of the original paper which describes the work
Reversible Control of Hydrogenation of a Single Molecule
Satoshi Katano,1 Yousoo Kim,1* Masafumi Hori,1,2 Michael Trenary,3 Maki Kawai1,2*
Low-temperature scanning tunneling microscopy was used to selectively break the N-H bond of a methylaminocarbyne (CNHCH3) molecule on a Pt(111) surface at 4.7 kelvin, leaving the C-H bonds intact, to form an adsorbed methylisocyanide molecule (CNCH3). The methylisocyanide product was identified through comparison of its vibrational spectrum with that of directly adsorbed methylisocyanide as measured with inelastic electron tunneling spectroscopy. The CNHCH3 could be regenerated in situ by exposure to hydrogen at room temperature. The combination of tip-induced dehydrogenation with thermodynamically driven hydrogenation allows a completely reversible chemical cycle to be established at the single-molecule level in this system. By tailoring the pulse conditions, irreversible dissociation entailing cleavage of both the C-H and N-H bonds can also be demonstrated.
1 Surface Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
2 Department of Advanced Materials, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8651, Japan.
3 Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607–7061, USA.