38 | New Scientist | 5 March 2022

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Niftier ways to manipulate molecules are bringing us advances on fronts

from sucking greenhouse gases from the air to inventing infinitely recyclable

materials and even creating artificial life. Katharine Sanderson reveals

seven of the most exciting innovations

Our insatiable appetite for energy has

got us into a mess, with the burning of

fossil fuels releasing greenhouse gases

that are heating the atmosphere. It is

enough to make you envious of plants,

which produce their own energy –

through photosynthesis – in a way that actually

uses up the greenhouse gas carbon dioxide.

If we could learn to mimic this trick on a grand

scale, it would enable us to effectively liquefy

sunlight to create a clean, green fuel.

Unfortunately, photosynthesis is a tough

chemical reaction to copy. It involves many

processes, including capturing sunlight,

splitting apart water molecules to yield

protons, and joining these protons with carbon

atoms from CO2 to ultimately produce fuel

in the form of sugars. In nature, these jobs are

performed by proteins that have had hundreds

of millions of years to evolve – and they still

only manage to turn energy from sunlight into

fuel with an efficiency of 1 per cent at best.

A decade ago, chemist Daniel Nocera at

Harvard University made a big stride forwards

when he developed catalysts based on nickel

and cobalt that could break apart water. That

is just one part of recreating photosynthesis,

however, and progress has since stuttered.

Then people started to realise that instead

of recreating photosynthesis from scratch,

we could combine the best bits of chemistry
and biology in a bionic leaf. Such leaves
typically employ materials that efficiently
absorb sunlight as well as natural proteins
that excel at stitching together fuel molecules.
A team led by Erwin Reisner at the University
of Cambridge recently used a material called
a perovskite to gather light and coupled it
with an enzyme called formate dehydrogenase.
The resulting bionic leaf converts light into
formate, a chemical that can be used in fuel
cells, with almost 1 per cent efficiency – on a
par with what nature can achieve.
Nocera has embraced a similar approach.
In 2016, he unveiled a system in which his
water-splitting catalysts produced protons
and electrons and fed these to bioengineered
bacteria. The set-up could use sunlight to turn
CO2 into fuel and biomass with an efficiency of
almost 11 per cent. “We did a complete artificial
photosynthesis that’s 10 to 100 times better
than nature,” says Nocera.
This is one great challenge that chemists
have more or less solved, then. “It’s not a
chemistry problem, necessarily, any more,”
says Nocera. “It’s not even a technology
problem.” For him, the reason we aren’t all
running our cars on fuel from bionic leaves
has more to do with a lack of will to build
GR the necessary infrastructure.

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During the industrial

revolution, simple

mechanisms like pistons

and ratchets were combined

to produce machines that

could do the work of many

people. The changes this brought

were both positive and negative, but

nobody denies how sweeping they were.

It might be wise to keep that in mind

today, as chemists develop molecular

machines – devices made not of iron,

but of atoms – which could be as

disruptive as any steam engine.

Simple molecular machines

have existed for about two decades.

Early examples include molecular

wheels that could move along an axle,

creating a piston-like mechanism.

Three pioneers of this work – Fraser

Stoddart at Northwestern University

in Illinois, Ben Feringa at the University

of Groningen in the Netherlands and

Jean-Pierre Sauvage at the University

of Strasbourg, France – were recognised

with a Nobel prize in 2016.

More useful machines are now being

made and tested. A few years ago, James

Tour at Rice University in Houston, Texas,

and his colleagues created a molecular >