In 1991 the organic chemist Sir Fraser Stoddart, who has died aged 82, synthesised artificial molecular machines for the first time. They mimic the way that some biological materials are able to move in a quasi-mechanical, interlocking way.
Stoddart had previously noted that natural occurring organic molecules such as the protein myosin, which drives the contraction of muscles, or motor enzymes that help maintain DNA, acted like tiny machines. He realised that the molecular components of these machines could, like the cogs, pistons and switches of macroscale machines, move relative to each other and, more importantly, can bond together mechanically and become entangled. By building their synthetic equivalents, powered by electrical energy, chemical reactions or light, he created an entirely new field in organic chemistry.
The first machine, which he named a rotaxane, consisted of a ring-shaped molecule threaded on to a longer molecule that functioned like an axle. More complex molecular machines would follow, created both by Stoddart and other chemists following his lead, including successfully synthesising catenanes – two interlocked molecular rings. His work bridged the gap between chemistry and the engineering challenges of operating at the very small scale of nanoelectrical systems, and he expanded the field of supramolecular chemistry – the branch of chemistry beyond the molecule.
Molecular machines are built using specialised equipment, with techniques such as scanning tunnelling microscopy and X-ray crystallography employed to validate the structures, function and efficiency of the artificial molecular machines that they are synthesising.
These machines expanded the potential applications of nanotechnology. Innovations such as molecular lifts (nanoscale devices that move molecules across cell membranes) and computer memory chips smaller than a white blood cell but with a memory storage capacity of 160,000 bits, all benefited from Stoddart’s initial work, as did the emerging medical nanobot technology.
For his initial discoveries and subsequent research in the field, Stoddart was awarded the 2016 Nobel prize in chemistry, sharing it with the Dutch organic chemist Ben Feringa and French coordination chemist Jean-Pierre Sauvage.
Born in Edinburgh, Fraser was the only child of Jean (nee Jane Fortune) and Thomas Stoddart, who were farmers. He was raised at Edgelaw Farm, Midlothian, a tiny community a dozen miles south of the Scottish capital that, for the first 18 years of his life, had no electricity. At the local primary school in Carrington his teachers encouraged his love of building toys from Meccano, to which he attributed his later professional interest.
He won a scholarship to Melville college, one of Scotland’s foremost independent schools, and in 1960 went to the University of Edinburgh, where he studied chemistry, physics and mathematics. After gaining a BSc (1964) in chemistry, he stayed at Edinburgh, researching natural gums in acacia trees for his doctorate (1966).
Following postings at Queens University in Ontario, Canada, and the University of Sheffield, in 1978 he started work at the laboratory belonging to the chemicals conglomerate ICI in Runcorn, Cheshire, where he began researching mechanically interlocked chemicals, a passion that would come to define his academic career.
Among a string of academic appointments, the most significant were his posts as reader (1982-90)and then professor of organic chemistry at Birmingham (1990-97), where his groundbreaking work on molecular machines began; at the University of California, Los Angeles (1997-2007); and his directorship of the Center for the Chemistry of Integrated Systems at Northwestern University in Illinois (2008-23).
His academic papers were notable for their cartoon-like form of presentation, eschewing a more common formal written manner for standardised, colour-coded diagrammatic representations of molecular properties. The style has been adopted by other researchers in the field.
Stoddart was a strong believer in the importance of eliminating all barriers in the face of free movement of students and researchers. He frequently stated that “science is global; science knows no boundaries”. He also believed that global warming was the biggest threat to humanity, adding that: “The Nobel prize was humbling but it doesn’t mean anything if what you are doing isn’t benefiting society.”
Subsequently, after realising hydrogen’s potential as a clean and efficient combustible fuel, in 2021 he co-founded, with Samer Taha and Omar Yaghi, a California-based startup called H2MOF, dedicated to solving the challenges associated with hydrogen storage and transportation. A few months before his death, Stoddart reported, in the journal Nature Chemistry, nanomaterial with record high hydrogen storage density, pointing to the possibility of significant progress in this field.
Often outspoken and no respecter of the bureaucratic processes of many of the institutions for whom he worked, Stoddart expressed opinions that often brought him into conflict with their academic rigidity and administrative requirements. However, he was intent on sharing his knowledge, and over the last 35 years of his life trained more than 500 PhD students in his laboratories.
Knighted in 2006, he received the Albert Einstein world award of science (2007) and the Royal Society of Chemistry’s centenary prize (2014). He was elected a fellow of the Royal Societies of London and Edinburgh, winning the former’s Davy medal in 2008 and the latter’s Royal medal in 2010. He was also a member of the US National Academy of Sciences.
In 1968 he married Norma Scholan, a biochemist. She died in 2004, and he is survived by their daughters, Fiona and Alison, and five grandchildren.
• James Fraser Stoddart, chemist, born 24 May 1942; died 30 December 2024
