Chemistry Nobel honours trio who combined classical and quantum physics

Karplus, Levitt and Warshel have won the Nobel Prize for Chemistry

Karplus, Levitt and Warshel
The 2013 Nobel Prize for Chemistry has been awarded to Martin Karplus, Michael Levitt and Arieh Warshel for their development of computer models of complex chemical systems. All three researchers have close links to physics. Karplus, who is a US and Austrian citizen, originally studied physics and chemistry at Harvard University and is now based there and at the University of Strasbourg. Levitt, who has a physics degree from King’s College London, is a US and UK citizen working at Stanford University, while Warshel is a US and Israeli citizen based at the University of Southern California. The trio will share the SEK 8m (£775,000) and will receive their medals at a ceremony in Stockholm on 10 December.
Karplus, Levitt and Warshel won the prize for developing computational techniques that use both classical and quantum physics to describe complex chemical processes. Chemical models based on classical physics are relatively easy to compute and can therefore be used to simulate some aspects of the behaviour of large molecules such as proteins. The problem, however, is that these classical models cannot describe crucial aspects of chemistry such as how reactions proceed. To do so requires models based on quantum mechanics, which in turn need huge amounts of computing power. Quantum simulations can therefore only be applied to relatively small molecules.

Focusing on free electrons

In the late 1960s Karplus was developing quantum-based computer models that could simulate chemical reactions. Meanwhile, Levitt and Warshel were both working at the Weizmann Institute of Science in Israel where they developed a classical computer model that could simulate certain properties of large biological molecules. Warshel joined Karplus at Harvard in 1970 and the pair started to combine their classical and quantum approaches. They developed the first ever computer program to use quantum physics to model the behaviour of free electrons during a chemical reaction, while using classical physics to describe the rest of the atoms and electrons in a molecule.
Over the next few years, Levitt and Warshel worked together at the Weizmann Institute and the University of Cambridge with the aim of developing models of enzymes – long-chain molecules that play crucial roles in just about every biochemical process. This they achieved in 1976, but an important feature of the techniques developed by Karplus, Levitt and Warshel is that they can be applied to all types of chemistry. As a result, they are now not only being used to study molecules that are important for life, but also to develop new industrial processes, build better solar cells and synthesize new drugs.
The theoretical chemist Alán Aspuru-Guzik told “Karplus, Levitt and Warshel are true pioneers of modern computational chemistry.” Aspuru-Guzik, who is at Harvard, added “The quantum-mechanics/molecular-mechanics approach that they introduced is now a commonplace tool that helps scientists understand important problems related to life and, for example, understand how drug molecules work.”

Physics and chemistry

Karplus was born in Vienna in 1930 and immigrated to the US with his family in 1938. He studied physics and chemistry at Harvard before completing a PhD in chemistry at Caltech in 1953 working under Linus Pauling. After stints at the universities of Oxford and Illinois, he joined Harvard in 1966. In 1996 he took a second appointment at Strasbourg.
Levitt was born in 1947 in Pretoria, South Africa and obtained a bachelor’s degree in physics from King’s College London in 1967. After spending a year at the Weizmann Institute working on the theory of molecules he did a PhD on the conformational analysis of proteins at Cambridge. He then worked at the MRC Laboratory of Molecular Biology in Cambridge and the Weizmann Institute before arriving at the Stanford University School of Medicine in 1987. In a Tweet issued today by Stanford, Levitt is quoted as saying: “I never studied chemistry, actually; I’m a physicist. But that’s okay.”
Warshel, meanwhile, was born in 1940 at Kibbutz Sde-Nahum in Israel. He studied chemistry at Technion – Israel Institute of Technology before doing a Master’s and a PhD in chemical physics at the Weizmann Institute. After stints at Harvard and the Weizmann Institute, he joined the University of Southern California in 1976.
Found from the author Hamish Johnston, editor of

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