Presentation Speech by Professor Sture Forsén of the Royal Swedish Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

The Nobel Prize in Chemistry for 1991 is being awarded for methodological developments in an important spectroscopic field – nuclear magnetic resonance spectroscopy. Scientists usually refer to this method by its acronym, “NMR,” and few would dispute that it is the single most important spectroscopic tool in modern chemistry. NMR spectroscopy allows detailed studies of the structure of small and large molecules in solution and provides unique information about the way molecules move and interact with each other.

The expression “methodological developments” – that is, the emergence of new theoretical or experimental tools or substantial improvements of old ones – merits further comments. A brief review of historical developments in chemistry, or for that matter in natural science as a whole, will convincingly show that methodological developments often have had an enormous and sometimes quite dramatic impact on the progress of science. Consider for example the invention of the microscope. The step from the primitive magnifying glass to devices in which two or more glass lenses were combined, made it possible to observe, in unprecedented detail, a whole new world of small dimensions. The detailed and astonishingly delicate anatomy of tiny insects was revealed. The compartmental, “cellular” structure of all living organisms was discovered. Eventually, microorganisms, yeast cells, bacteria, etc. were discovered – opening up a whole new branch of science, microbiology, and in the end providing a rational explanation for the causes of disease as well as how to treat or prevent them. This example alone will suffice to illustrate the importance of methodological developments in science.

One particular methodological development in which this year’s Laureate was a leading figure early in his scientific career was the introduction of Fourier transformation and pulse techniques in NMR spectroscopy, thereby improving the sensitivity of the technique tenfold or even hundredfold. Now I am sure that most of you will shake your head, Fourier transformation and pulse techniques; what is that? Let me try to illustrate it through an analogy. Remember first that spectroscopy is very much concerned with the detection of signals from a sample containing some compound. Assume that you are interested in finding out how well tuned a piano is. The traditional, “old-fashioned”, way of doing this would of course be to hit each key in succession and record the frequencies – the signals from our sample if you wish. Now a modern piano usually has 88 keys and it would take some time to go through them one by one, let us say 10 minutes, i.e. 600 seconds. Now there is a much faster way of getting the same results: stretch out both your arms and hit all keys at once, like this [sound effect]. You have now performed a pulse experiment. The result sounds awkward, but remember that all the tones are there in the response. But how could you possibly extract the individual tones from this cacaphony? That you can do by a mathematical analysis called – well you may have guessed it – Fourier transformation. A fast modern computer would perform this analysis in less than a second and the output from your computer would be the individual notes [new sound effect – a scale]. So the new way – the FT way – of checking the tuning of a piano would perhaps take six seconds instead of 600 seconds, a substantial improvement in time. This may sound senseless, why this hurry, even if this new method would allow you to tune 100 pianos in the time it took to tune one in the “old-fashioned” way? But, savings in time can be used in another way, to increase sensitivity. To continue our analogy, assume that you had encountered a piano with “signals” from the strings barely audible above the background noise in the room. Now you could improve the detection of these weak signals by hitting the keys of this same piano 100 times every sixth second and adding the result. This would improve the signal-to-noise ratio tenfold, in the jargon of scientists.

When Fourier transform NMR was introduced around 1970 it had a tremendous impact on the applicability of the NMR technique to chemistry. It now became feasible to study very weak signals from small amounts of material or from important elements with magnetic nuclei that are rare in nature, for example ¹³C and ¹⁵N. The Achilles heel of the NMR technique had hitherto been its poor sensitivity, but now this obstacle was largely removed.

A later revolutionary development in NMR, in which this year’s Chemistry Laureate played a leading role, was the introduction of more than one frequency dimension, 2, 3 or higher. In 2D NMR, the chemical “piano” is hit with pulses of varying lengths and intervals. This allows chemists to extract many parameters of interest from the NMR spectra with great ease. hopelessly muddled and hard-to-interpret spectra can be spread out and thereby simplify the analysis – much as a two-dimensional map of a landscape would be superior to a mere silhouette. 2D NMR makes it possible to find out which specific atoms in a molecule are closely linked by chemical bonds or which atoms are near each other in space, or which atoms take part in chemical exchange reactions, and much more. A whole new range of experiments have become possible and multidimensional NMR has substantially increased the range of applications to chemistry. The new method has been a prerequisite for the very important applications of NMR in structural biology that have taken place during the past decade.

Professor Ernst,

You have played a leading role in several of the most significant methodological developments that have taken place in the field of NMR spectroscopy over the past two decades; developments that have had a lasting impact on the way modern chemistry is conducted. You have, in an admirable way, combined excellent experimental know-how with extraordinary theoretical insight. In recognition of your services to chemistry, and to natural science as a whole, the Royal Swedish Academy of Sciences has decided to confer upon you this year’s Nobel Prize for Chemistry.

Professor Ernst, I have been granted the privilege of conveying to you the warmest congratulations of the Academy, and I now invite you to receive your Prize from the hands of His Majesty the King.