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Molecular Motors: Think Small and yet Smaller Again…

30.03.2017

Most of us immediately associate internal combustion engines with cars, however motors are active inside our body too. Biological motors, for example, use the energy stored in specific molecules to create muscle contraction or to activate internal pumps. There are numerous other examples of naturally occurring motors in humans, animals and microbes.

 

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A nanotech pioneer looks toward the future

These biological motors inspired the Nobel laureate Richard Feynman, who in 1959, first predicted nanotechnology during his famous lecture “There’s Plenty of Room at the Bottom”. Feynman was convinced that in the future it would become possible to create artificial structures and machines as small as a bacterial flagellum. In 1984, some 25 years after he first envisaged nanotechnology, Feynman was asked to give an updated version of his original presentation. This time, the talk was entitled “Tiny Machines” whereby he shared a more detailed vision of how he believed that molecular machines might be created at a nanometer scale. Speaking with great enthusiasm, Feynman’s aim was to inspire the audience to imagine the inconceivable.

Topological chemistry discovers a new type of chemical bond

Neither Feynman, however, nor anyone else attending his lecture, knew that the first steps towards developing molecular machines had already been undertaken. From the mid-20th century onwards, topological chemists from all around the world had tried to create new molecules in which molecular chains were mechanically linked. This was challenging because, at the time, only covalent bonds, in which atoms share electrons, were understood for their interlinking properties. 

Following successive failures, many research groups involved in the field gave up, leaving the science relatively unsupported. In 1983 however, a French working group led by chemist Jean-Pierre Sauvage made a breakthrough. Working with photochemistry, Sauvage developed a molecular complex which captured solar-energy and used it to produce chemical reactions. Recognition that the complex had the appearance of a molecular chain, in which two molecules were connected around a copper ion, led the research in a new direction. Using the complex as a model, his group then developed a method to bind a crescent-shaped molecule onto a ring-shaped one through use of a copper ion. In a second step, they then linked a third molecule to the crescent-shaped one, thereby creating a molecule in which two rings were interlinked through mechanical bonds for the first time. He called this new molecule type a catenane. Through his revolutionary method, Sauvage effectively revitalized topological chemistry.

Molecular machines on the horizon

Later on, Sauvage created different catenane knots, in addition to molecules in which the rings could rotate. Meanwhile, other scientists were also searching for moving molecules. In 1991 the Fraser Stoddart group designed molecules that attracted each other and created rotaxanes or ring-shaped molecules which were mechanically bound to an axle. In this way, since 1994, he and others constructed numerous molecular machines including a molecular shuttle, a lift and a rotaxane based computer chip. The first molecular motor which spun in a single direction was developed by Bernard Feringa in 1999. It was the blueprint for a four-wheel drive nanocar which he developed in 2011.

A well-deserved Nobel Prize

Jean-Pierre Sauvage, Fraser Stoddart and Bernard Feringa were awarded the latest Nobel Prize in Chemistry for the design and synthesis of molecular machines. Their groundbreaking research has resulted in a toolbox of chemical structures which allows researchers from around the globe to develop new and advanced nano-motors. It’s still not known how molecular machines might influence our lives in future, however, it’s clear that the potential is at least as great as it was for the electric motor nearly hundred years ago…