Reporting in the Journal of the American Chemical Society, they use what they call 'proton grease' to make a molecular rotor spin faster – by a factor of ten million. The advance is a significant signpost on the road toward functional synthetic molecular machines, said Ken Shimizu, lead author and professor in the department of chemistry and biochemistry in the College of Arts and Sciences at USC.
The team constructed their rotor by combining quinoline and succinimide subunits. At first blush it might look like rotation in the resulting molecule would be essentially unrestricted, but the appearance is deceiving. The partial charge on the carbonyls has highly unfavorable overlap with the quinoline nitrogen when the molecule is in a planar transition state.
But when the nitrogen is protonated, the planar rotamer is stabilized – leading to a huge increase in the rotational rate.
"We designed it to have more favorable overlap after protonation, so we expected it to speed up," said Shimizu. "But we never anticipated the magnitude of the increase – we were surprised by how well it worked, which is a rare thing to say."
The barrier to rotation dropped from about 22 kcal/mol to 13 kcal/mol upon titration with acid. The increase in rotation speed was so dramatic, covering seven orders of magnitude, that the team had to cobble together two different measurement techniques – one for fast rotation, and another for slow.
And as they show in their research article, the speed-up is reversible: addition of base restored the barrier to rotation.
The field of molecular devices is in its infancy, but the possibilities are tantalizing. "We're kind of making cogs right now, but we're moving toward being able to make more complex devices," said Shimizu. "People are imagining all sorts of electronic and mechanical devices based on single molecules, and we're building up this toolbox to be able to create machines and devices on the molecular scale."
Despite coming up with the evocative term 'proton grease,' Shimizu recognizes the name carries potential baggage as well. "It makes it more accessible to use these analogies about brakes and grease and things like that – but it's a little bit dangerous too," he said.
"When people talk about in these molecular machines, they often assume that you can take an engine, for example, and just scale it down to a molecular size. And conceptually you can, but the actual physics behind that falls apart," said Shimizu. "We don't have friction at that scale, for example."
"But that's actually the most exciting part, too," he added. "When you start making things on that scale, the rules are completely different."
"By controlling motion on the molecular level, people imagine that you could make switches, memory, transformers – all sorts of electronic and mechanical devices as single molecules."
Steven Powell | Newswise Science News
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy