ScienceJanuary 24, 2017

‘It looks like magic’ – David Leigh on the gobsmacking potential of molecular motors


Smaller than a pinhead, the machines in Professor David A Leigh’s lab are created by chemistry that manipulates the properties of tiny elements to create motion. Leigh, who is coming to NZ for February’s AMN8 conference, talks to Charles Anderson

Think of David Leigh as a caveman chief at the beginnings of civilisation.

Think of him marvelling at a stone wheel as it rolls downhill with little effort. Think of asking him then to envision the combustion engine. To envision the motor car, Henry Ford and the automobile industry. Roads, buses and mass transport. The poor caveman chief simply could not have any idea about what the future might hold for his humble stone cylinder.

It is a comparison Leigh makes with the field he works in. He also works with machines. But these are not robots in factories, electronic calculators, hydraulic presses or mechanical engines. Leigh works at a much smaller level.

“All of our advances since technology began have been driven by ever increasing miniaturisation,” Leigh says from his lab at the University of Manchester. “In the 1950s computers were the size of a room with little computing power. Now they are millions of times more powerful, all in the size of a pinhead.”

Professor David A Leigh. Photo: University of Manchester
‘It sounds like Harry Potter stuff’: Professor David A Leigh. Photo: University of Manchester

Go even smaller than the pinhead. The ultimate end of this spectrum is to go the molecular level. Leigh’s machines are created by chemistry that manipulates the properties of some of the smallest elements known. These machines then create functions that can be visible to the human eye.

Everything in life relies on these sorts of machines, Leigh says. They are the essence of biology. Nature uses controlled molecular motion for everything from photosynthesis and energy storage to the way that muscles move and the way that cells communicate.

“In contrast, mankind, at the beginning of the 21st century, uses controlled molecular motion for nothing,” Leigh says.

But what if we could control these processes? What if you could use the processes that allow life to occur to do … more?

Leigh says if we can learn to do that then it will completely change how we think about and design materials.

However, in envisioning such a future Leigh says you cannot merely use your ideas of what a machine is in the macro world and shrink it down. Matter behaves differently at different sizes.

For example, you could not build a scale combustion engine in the molecular world. Heat dissipates instantaneously over such tiny distances and at that level such a creation could not work.

“So you have to come up with different ideas of how to move things,” Leigh says. “You can’t use your intuitive ideas from the big world.”

It was 20 years ago that Leigh was working in his lab when a chance discovery led him to witnessing a process where materials “self assembled”.

Unlike many processes where there is a line of things that need to be checked off before a finished product is created, these materials would create themselves in an instant.

Once he saw these molecular creations, known as catenanes, he spent the next two decades trying to figure out ways to control their movement.

Leigh’s work followed on from another scientist, Jean-Pierre Sauvage, who had started to use similar structures as the building blocks for molecular machines.

Normally molecules are joined by a bond in which atoms share electrons but here they are linked mechanically.

Sauvage shared the Nobel Prize of chemistry last year for his work on molecular machines.

“In terms of development, the molecular motor is at the same stage as the electric motor was in the 1830s when scientists displayed various spinning cranks and wheels unaware they would lead to washing machines, fans and food processors,” the Nobel award citation reads. “Molecular machines will most be used in the development of things such as new materials, sensors and energy storage systems.”

Leigh takes the idea of possibilities further. Perhaps instead of pharmaceutical factories where drugs are created by macro world robots, they could be created by molecular machines. Perhaps you might require a workspace that needs to have two different qualities — sticky and smooth. If you shine a light on it it could become smooth in an instant. Perhaps you need something transported to you over a different surface. Shine a light on it and that thing will indeed move.

“It sounds like Harry Potter stuff,” Leigh admits.

But it’s not. Leigh has already been part of successful experiments where liquid droplets have been moved uphill by such a molecular machine.

In this case the machine is a surface, one molecule thick. Then by applying energy, in this case light, the tension between the droplet and the surface changes. This means the droplet’s shape changes. But what Leigh didn’t know when he did this experiment was that the shape of the droplet would change so radically that it would be propelled forward.

“The most important thing about that is that everyone can see it and it looks like magic,” he says.

“That’s exactly the sort of thing it’s important to show, that these things will be able to do things that can’t presently be done. If we can move a droplet maybe we can next move a coffee cup or another object and maybe eventually vehicles along a surface without needing to bother with wheels.”

Leigh says 20 years ago he could not foresee how far this science would come. He says they all know where they would like to go with the technology but the route to get there is not obvious.

“It’s a bit like mining. You can start off and hit a small vein of gold but don’t know where to go or how much gold is there. Then maybe gold leads on to oil.”

This is part of a series of articles for the Spinoff about and from AMN8, The Eighth International Conference on Advanced Materials and Nanotechnology, in Queenstown from February 12-16 2017. For details on public events in Christchurch, Wanaka, Queenstown and Nelson, click here. This content series is sponsored by the conference’s hosts, The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.

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