Inevitable Nobel: In theory

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  • Published: Oct 15, 2013
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
thumbnail image: Inevitable Nobel: In theory

International model

Nobel Chemistry illustration by Johan Jarnestad/The Royal Swedish Academy of Sciences

The 2013 Nobel Prize for chemistry was awarded jointly to Martin Karplus of the University of Strasbourg, France and Harvard University, Cambridge, Massachusetts, Michael Levitt of Stanford University School of Medicine, Stanford and Arieh Warshel of the University of Southern California, Los Angeles, California, USA for the development of multiscale models for complex chemical systems.

Martin Karplus was born in Vienna, Austria in 1930, he received his PhD from the California Institute of Technology in 1953. Michael Levitt was born 1947 in Pretoria, South Africa and obtained a PhD in 1971 from the University of Cambridge. Arieh Warshel was born in 1940 in Kibbutz Sde-Nahum, Israel and got his PhD in 1969 from the Weizmann Institute of Science, in Rehovot, Israel.

Theoretical era

Most chemistry graduates of a certain age will be all too familiar with building molecular models from little plastic balls with arms and hollow, straw-like tubes to connect those "atoms" together. They are a powerful tactile and visual educational aid for showing how the atoms in a given structure relate to each other and can give some indication of proximity for atoms at different points in a molecule that would appear unrelated in a two-dimensional representation of the same structure, for instance. The 3D plastic model can hint at a much better explanation for NMR spectra of a sample of said compound. Unfortunately, such ball-and-stick models do not have much more to say about quantum mechanics.

Thankfully, theoretical chemists - Karplus, Levitt and Warshel working through the 1970s on the rapidly developing computers of the era laid the foundations for the powerful programs that chemists use today to help them predict the behaviour of molecules in chemical processes. Indeed, the computer models they created that mirror real-life chemistry have become essential tools to many of the biggest advances in chemistry. Chemical reactions usually occur far too quickly for chemists to get a detailed impression of the transfer of electrons, the shuffling of bonds, the relocation of atoms. The classical world of ball-and-stick or even space-filling 3D models has no chance of keeping up, mapping every possible process in even relatively simple chemical exchanges is not viable.

The ground-breaking work of Karplus, Levitt and Warshel allowed them to bridge the gap between the simplistic Newtonian classical physics of balls and sticks and to meld it with the fundamentally different realm of quantum mechanics. Their work then allowed chemists to roll back the veil and peer beneath the surface of a chemical process whether that was the activity of a catalyst adsorbing vehicle exhaust gases and expelling less noxious vapours or the processes involved in light absorption by green plants that converts carbon dioxide and water into sugars, photosynthesis.

Classical gas

Until their work, chemists had been able to use classical mechanics to imagine the behaviour and structure of even large molecules to a limited degree. The classical models were relatively simple, but their simplicity belied the true complexity of molecular behaviour and could not predict reaction mechanisms nor outcomes As such, quantum mechanics, which describes something closer to the true nature of interacting molecules, was essential to the Nobel-winning computer programs developed by this year's three recipients of the Prize.

This year's Nobel Laureates in chemistry took the best from both worlds and devised methods that use both classical and quantum physics. For instance, in simulations of how a drug couples to its target protein in the body, the computer performs quantum theoretical calculations on those atoms in the target protein that interact with the drug. The rest of the large protein is simulated using less demanding classical physics. The first step towards multiscale modelling occurred when Warshel visited Karplus at Harvard in the early 1970s. Warshel's background was in inter- and intra-molecular potentials, while Karplus was the QM expert. Together they constructed a computer program that could calculate the pi-electron spectra and the vibration spectra of a number of planar molecules with excellent results. This was the first time hybrid methods were used to describe complex chemical systems. In 1976, Warshel and Levitt showed that it was possible to construct a general scheme for a partitioning between electrons that are included in the classical modelling and electrons that are explicitly described by a QM model.

"The methodology has been used to study not only complex processes in organic chemistry and biochemistry, but also for heterogeneous catalysis and theoretical calculation of the spectrum of molecules dissolved in a liquid. But most importantly, it has opened up a fruitful cooperation between theory and experiment that has made many otherwise unsolvable problems solvable," the Nobel committee writes. Today, the computer is just as important a tool for chemists as the test tube. Simulations are so realistic that they predict the outcome of traditional experiments. For those graduate chemists of a certain age, perhaps they will have a fondness for the computer screen just as an earlier generation enjoyed the ball-and-stick.

Related Links

Nobel Chemistry 2013, PDF

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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